Natural Laminar Flow Flight Experiment
NASA Technical Reports Server (NTRS)
Steers, L. L.
1981-01-01
A supercritical airfoil section was designed with favorable pressure gradients on both the upper and lower surfaces. Wind tunnel tests were conducted in the Langley 8 Foot Transonic Pressure Tunnel. The outer wing panels of the F-111 TACT airplane were modified to incorporate partial span test gloves having the natural laminar, flow profile. Instrumentation was installed to provide surface pressure data as well as to determine transition location and boundary layer characteristics. The flight experiment encompassed 19 flights conducted with and without transition fixed at several locations for wing leading edge sweep angles which varied from 10 to 26 at Mach numbers from 0.80 to 0.85 and altitudes of 7620 meters and 9144 meters. Preliminary results indicate that a large portion of the test chord experienced laminar flow.
Research in Natural Laminar Flow and Laminar-Flow Control, part 3
NASA Technical Reports Server (NTRS)
Hefner, Jerry N. (Compiler); Sabo, Frances E. (Compiler)
1987-01-01
Part 3 of the Symposium proceedings contains papers addressing advanced airfoil development, flight research experiments, and supersonic transition/laminar flow control research. Specific topics include the design and testing of natural laminar flow (NLF) airfoils, NLF wing gloves, and NLF nacelles; laminar boundary-layer stability over fuselage forebodies; the design of low noise supersonic/hypersonic wind tunnels; and boundary layer instability mechanisms on swept leading edges at supersonic speeds.
Progress in natural laminar flow research
NASA Technical Reports Server (NTRS)
Holmes, B. J.
1984-01-01
For decades, since the earliest attempts to obtain natural laminar flow (NLF) on airplanes, three classical objections to its practicality have been held in the aeronautical community. These objectives concerned first, the capability to manufacture practical airframe surfaces smooth enough for NLF; second, the apparent inherent instability and sensitivity of NLF; and third, the accumulation of contamination such as insect debris in flight. This paper explains recent progress in our understanding of the achieveability and maintainability of NLF on modern airframe surfaces. This discussion explains why previous attempts to use NLF failed and what has changed regarding the three classical objections to NLF practicality. Future NASA research plans are described concerning exploring the limits of NLF usefulness, production tolerances, operational considerations, transition behavior and measurement methods, and NLF design applications.
Research in Natural Laminar Flow and Laminar-Flow Control, part 1
NASA Technical Reports Server (NTRS)
Hefner, Jerry N. (Compiler); Sabo, Frances E. (Compiler)
1987-01-01
Since the mid 1970's, NASA, industry, and universities have worked together to conduct important research focused at developing laminar flow technology that could reduce fuel consumption for general aviation, commuter, and transport aircraft by as much as 40 to 50 percent. The symposium was planned in view of the recent accomplishments within the areas of laminar flow control and natural laminar flow, and the potential benefits of laminar flow technology to the civil and military aircraft communities in the United States. Included were technical sessions on advanced theory and design tool development; wind tunnel and flight research; transition measurement and detection techniques; low and high Reynolds number research; and subsonic and supersonic research.
Natural laminar flow airfoil analysis and trade studies
NASA Technical Reports Server (NTRS)
1979-01-01
An analysis of an airfoil for a large commercial transport cruising at Mach 0.8 and the use of advanced computer techniques to perform the analysis are described. Incorporation of the airfoil into a natural laminar flow transport configuration is addressed and a comparison of fuel requirements and operating costs between the natural laminar flow transport and an equivalent turbulent flow transport is addressed.
F-111 TACT natural laminar flow glove flight results
NASA Technical Reports Server (NTRS)
Montoya, L. C.; Steers, L. L.; Trujillo, B.
1981-01-01
Improvements in cruise efficiency on the order of 15 to 40% are obtained by increasing the extent of laminar flow over lifting surfaces. Two methods of achieving laminar flow are being considered, natural laminar flow and laminar flow control. Natural laminar flow (NLF) relies primarily on airfoil shape while laminar flow control involves boundary layer suction or blowing with mechanical devices. The extent of natural laminar flow that could be achieved with consistency in a real flight environment at chord Reynolds numbers in the range of 30 x 10(6) power was evaluated. Nineteen flights were conducted on the F-111 TACT airplane having a NLF airfoil glove section. The section consists of a supercritical airfoil providing favorable pressure gradients over extensive portions of the upper and lower surfaces of the wing. Boundary layer measurements were obtained over a range of wing leading edge sweep angles at Mach numbers from 0.80 to 0.85. Data were obtained for natural transition and for a range of forced transition locations over the test airfoil.
Design of fuselage shapes for natural laminar flow
NASA Technical Reports Server (NTRS)
Dodbele, S. S.; Vandam, C. P.; Vijgen, P. M. H. W.
1986-01-01
Recent technological advances in airplane construction techniques and materials allow for the production of aerodynamic surfaces without significant waviness and roughness, permitting long runs of natural laminar flow (NLF). The present research effort seeks to refine and validate computational design tools for use in the design of axisymmetric and nonaxisymmetric natural-laminar-flow bodies. The principal task of the investigation involves fuselage body shaping using a computational design procedure. Analytical methods were refined and exploratory calculations conducted to predict laminar boundary-layer on selected body shapes. Using a low-order surface-singularity aerodynamic analysis program, pressure distribution, boundary-layer development, transition location and drag coefficient have been obtained for a number of body shapes including a representative business-aircraft fuselage. Extensive runs of laminar flow were predicted in regions of favorable pressure gradient on smooth body surfaces. A computational design procedure was developed to obtain a body shape with minimum drag having large extent of NLF.
Design of fuselage shapes for natural laminar flow
NASA Astrophysics Data System (ADS)
Dodbele, S. S.; Vandam, C. P.; Vijgen, P. M. H. W.
1986-03-01
Recent technological advances in airplane construction techniques and materials allow for the production of aerodynamic surfaces without significant waviness and roughness, permitting long runs of natural laminar flow (NLF). The present research effort seeks to refine and validate computational design tools for use in the design of axisymmetric and nonaxisymmetric natural-laminar-flow bodies. The principal task of the investigation involves fuselage body shaping using a computational design procedure. Analytical methods were refined and exploratory calculations conducted to predict laminar boundary-layer on selected body shapes. Using a low-order surface-singularity aerodynamic analysis program, pressure distribution, boundary-layer development, transition location and drag coefficient have been obtained for a number of body shapes including a representative business-aircraft fuselage. Extensive runs of laminar flow were predicted in regions of favorable pressure gradient on smooth body surfaces. A computational design procedure was developed to obtain a body shape with minimum drag having large extent of NLF.
Natural Laminar Flow Design for Wings with Moderate Sweep
NASA Technical Reports Server (NTRS)
Campbell, Richard L.; Lynde, Michelle N.
2016-01-01
A new method for the aerodynamic design of wings with natural laminar flow is under development at the NASA Langley Research Center. The approach involves the addition of new flow constraints to an existing knowledge-based design module for use with advanced flow solvers. The uniqueness of the new approach lies in the tailoring of target pressure distributions to achieve laminar flow on transonic wings with leading-edge sweeps and Reynolds numbers typical of current transports. The method is demonstrated on the Common Research Model configuration at critical N-factor levels representative of both flight and high-Reynolds number wind tunnel turbulence levels. The design results for the flight conditions matched the target extent of laminar flow very well. The design at wind tunnel conditions raised some design issues that prompted further improvements in the method, but overall has given promising results.
Flight tests of a supersonic natural laminar flow airfoil
NASA Astrophysics Data System (ADS)
Frederick, M. A.; Banks, D. W.; Garzon, G. A.; Matisheck, J. R.
2015-06-01
A flight test campaign of a supersonic natural laminar flow airfoil has been recently completed. The test surface was an 80 inch (203 cm) chord and 40 inch (102 cm) span article mounted on the centerline store location of an F-15B airplane. The test article was designed with a leading edge sweep of effectively 0° to minimize boundary layer crossflow. The test article surface was coated with an insulating material to avoid significant heat transfer to and from the test article structure to maintain a quasi-adiabatic wall. An aircraft-mounted infrared camera system was used to determine boundary layer transition and the extent of laminar flow. The tests were flown up to Mach 2.0 and chord Reynolds numbers in excess of 30 million. The objectives of the tests were to determine the extent of laminar flow at high Reynolds numbers and to determine the sensitivity of the flow to disturbances. Both discrete (trip dots) and 2D disturbances (forward-facing steps) were tested. A series of oblique shocks, of yet unknown origin, appeared on the surface, which generated sufficient crossflow to affect transition. Despite the unwanted crossflow, the airfoil performed well. The results indicate that the sensitivity of the flow to the disturbances, which can translate into manufacturing tolerances, was similar to that of subsonic natural laminar flow wings.
Computational Optimization of a Natural Laminar Flow Experimental Wing Glove
NASA Technical Reports Server (NTRS)
Hartshom, Fletcher
2012-01-01
Computational optimization of a natural laminar flow experimental wing glove that is mounted on a business jet is presented and discussed. The process of designing a laminar flow wing glove starts with creating a two-dimensional optimized airfoil and then lofting it into a three-dimensional wing glove section. The airfoil design process does not consider the three dimensional flow effects such as cross flow due wing sweep as well as engine and body interference. Therefore, once an initial glove geometry is created from the airfoil, the three dimensional wing glove has to be optimized to ensure that the desired extent of laminar flow is maintained over the entire glove. TRANAIR, a non-linear full potential solver with a coupled boundary layer code was used as the main tool in the design and optimization process of the three-dimensional glove shape. The optimization process uses the Class-Shape-Transformation method to perturb the geometry with geometric constraints that allow for a 2-in clearance from the main wing. The three-dimensional glove shape was optimized with the objective of having a spanwise uniform pressure distribution that matches the optimized two-dimensional pressure distribution as closely as possible. Results show that with the appropriate inputs, the optimizer is able to match the two dimensional pressure distributions practically across the entire span of the wing glove. This allows for the experiment to have a much higher probability of having a large extent of natural laminar flow in flight.
Flight Tests of a Supersonic Natural Laminar Flow Airfoil
NASA Technical Reports Server (NTRS)
Frederick, M. A.; Banks, D. W.; Garzon, G. A.; Matisheck, J. R.
2014-01-01
A flight test campaign of a supersonic natural laminar flow airfoil has been recently completed. The test surface was an 80-inch (203 cm) chord and 40-inch (102 cm) span article mounted on the centerline store location of an F-15B airplane. The wing was designed with a leading edge sweep of effectively 0 deg to minimize boundary layer crossflow. The test article surface was coated with an insulating material to avoid significant heat transfer to and from the test article structure to maintain a quasi-adiabatic wall. An aircraft-mounted infrared camera system was used to determine boundary layer transition and the extent of laminar flow. The tests were flown up to Mach 2.0 and chord Reynolds numbers in excess of 30 million. The objectives of the tests were to determine the extent of laminar flow at high Reynolds numbers and to determine the sensitivity of the flow to disturbances. Both discrete (trip dots) and 2-D disturbances (forward-facing steps) were tested. A series of oblique shocks, of yet unknown origin, appeared on the surface, which generated sufficient crossflow to affect transition. Despite the unwanted crossflow, the airfoil performed well. The results indicate the sensitivity of the flow to the disturbances, which can translate into manufacturing tolerances, were similar to that of subsonic natural laminar flow wings.
Flight Tests of a Supersonic Natural Laminar Flow Airfoil
NASA Technical Reports Server (NTRS)
Frederick, Michael A.; Banks, Daniel W.; Garzon, G. A.; Matisheck, J. R.
2015-01-01
A flight-test campaign of a supersonic natural laminar flow airfoil has been recently completed. The test surface was an 80-inch (203 cm) chord and 40-inch (102 cm) span article mounted on the centerline store location of an F-15B airplane (McDonnell Douglas Corporation, now The Boeing Company, Chicago, Illinois). The test article was designed with a leading edge sweep of effectively 0 deg to minimize boundary layer crossflow. The test article surface was coated with an insulating material to avoid significant heat transfer to and from the test article structure to maintain a quasi-adiabatic wall. An aircraft-mounted infrared camera system was used to determine boundary layer transition and the extent of laminar flow. The tests were flown up to Mach 2.0 and chord Reynolds numbers in excess of 30 million. The objectives of the tests were to determine the extent of laminar flow at high Reynolds numbers and to determine the sensitivity of the flow to disturbances. Both discrete (trip dots) and 2-D disturbances (forward-facing steps) were tested. A series of oblique shocks, of yet unknown origin, appeared on the surface, which generated sufficient crossflow to affect transition. Despite the unwanted crossflow, the airfoil performed well. The results indicate the sensitivity of the flow to the disturbances, which can translate into manufacturing tolerances, were similar to that of subsonic natural laminar flow wings.
Research in Natural Laminar Flow and Laminar-Flow Control, part 2
NASA Technical Reports Server (NTRS)
Hefner, Jerry N. (Compiler); Sabo, Frances E. (Compiler)
1987-01-01
Part 2 of the Symposium proceedings includes papers addressing various topics in basic wind tunnel research/techniques and computational transitional research. Specific topics include: advanced measurement techniques; laminar flow control; Tollmien-Schlichting wave characteristics; boundary layer transition; flow visualization; wind tunnel tests; flight tests; boundary layer equations; swept wings; and skin friction.
Natural laminar flow experiments on modern airplane surfaces
NASA Technical Reports Server (NTRS)
Holmes, B. J.; Obara, C. J.; Yip, L. P.
1984-01-01
Flight and wind-tunnel natural laminar flow experiments have been conducted on various lifting and nonlifting surfaces of several airplanes at unit Reynolds numbers between 0.63 x 10 to the 6th power/ft and 3.08 x 10 to the 6th power/ft, at Mach numbers from 0.1 to 0.7, and at lifting surface leading-edge sweep angles from 0 deg to 63 deg. The airplanes tested were selected to provide relatively stiff skin conditions, free from significant roughness and waviness, on smooth modern production-type airframes. The observed transition locations typically occurred downstream of the measured or calculated pressure peak locations for the test conditions involved. No discernible effects on transition due to surface waviness were observed on any of the surfaces tested. None of the measured heights of surface waviness exceeded the empirically predicted allowable surface waviness. Experimental results consistent with spanwise contamination criteria were observed. Large changes in flight-measured performance and stability and control resulted from loss of laminar flow by forced transition. Rain effects on the laminar boundary layer caused stick-fixed nose-down pitch-trim changes in two of the airplanes tested. No effect on transition was observed for flight through low-altitude liquid-phase clouds. These observations indicate the importance of fixed-transition tests as a standard flight testing procedure for modern smooth airframes.
High-flaps for natural laminar flow airfoils
NASA Technical Reports Server (NTRS)
Morgan, Harry L.
1986-01-01
A review of the NACA and NASA low-drag airfoil research is presented with particular emphasis given to the development of mechanical high-lift flap systems and their application to general aviation aircraft. These flap systems include split, plain, single-slotted, and double-slotted trailing-edge flaps plus slat and Krueger leading-edge devices. The recently developed continuous variable-camber high-lift mechanism is also described. The state-of-the-art of theoretical methods for the design and analysis of multi-component airfoils in two-dimensional subsonic flow is discussed, and a detailed description of the Langley MCARF (Multi-Component Airfoil Analysis Program) computer code is presented. The results of a recent effort to design a single- and double-slotted flap system for the NASA high speed natural laminar flow (HSNLF) (1)-0213 airfoil using the MCARF code are presented to demonstrate the capabilities and limitations of the code.
Flight Tests of a Supersonic Natural Laminar Flow Airfoil
NASA Technical Reports Server (NTRS)
Frederick, Mike; Banks, Dan; Garzon, Andres; Matisheck, Jason
2014-01-01
IR thermography was used to characterize the transition front on a S-NLF test article at chord Reynolds numbers in excess of 30 million Changes in transition due to Mach number, Reynolds number, and surface roughness were investigated - Regions of laminar flow in excess of 80% chord at chord Reynolds numbers greater than 14 million IR thermography clearly showed the transition front and other flow features such as shock waves impinging upon the surface A series of parallel oblique shocks, of yet unknown origin, were found to cause premature transition at higher Reynolds numbers. NASA has a current goal to eliminate barriers to the development of practical supersonic transport aircraft Drag reduction through the use of supersonic natural laminar flow (S-NLF) is currently being explored as a means of increasing aerodynamic efficiency - Tradeoffs work best for business jet class at M<2 Conventional high-speed designs minimize inviscid drag at the expense of viscous drag - Existence of strong spanwise pressure gradient leads to crossflow (CF) while adverse chordwise pressure gradients amplifies and Tollmien-Schlichting (TS) instabilities Aerion Corporation has patented a S-NLF wing design (US Patent No. 5322242) - Low sweep to control CF - dp/dx < 0 on both wing surfaces to stabilize TS - Thin wing with sharp leading edge to minimize wave drag increase due to reduction in sweep NASA and Aerion have partnered to study S-NLF since 1999 Series of S-NLF experiments flown on the NASA F-15B research test bed airplane Infrared (IR) thermography used to characterize transition - Non-intrusive, global, good spatial resolution - Captures significant flow features well
NASA Technical Reports Server (NTRS)
Somers, Dan M. (Inventor)
2005-01-01
An airfoil having a fore airfoil element, an aft airfoil element, and a slot region in between them. These elements induce laminar flow over substantially all of the fore airfoil element and also provide for laminar flow in at least a portion of the slot region. The method of the invention is one for inducing natural laminar flow over an airfoil. In the method, a fore airfoil element, having a leading and trailing edge, and an aft airfoil element define a slot region. Natural laminar flow is induced over substantially all of the fore airfoil element, by inducing the pressures on both surfaces of the fore airfoil element to decrease to a location proximate the trailing edge of the fore airfoil element using pressures created by the aft airfoil element.
Expanding the Natural Laminar Flow Boundary for Supersonic Transports
NASA Technical Reports Server (NTRS)
Lynde, Michelle N.; Campbell, Richard L.
2016-01-01
A computational design and analysis methodology is being developed to design a vehicle that can support significant regions of natural laminar flow (NLF) at supersonic flight conditions. The methodology is built in the CDISC design module to be used in this paper with the flow solvers Cart3D and USM3D, and the transition prediction modules BLSTA3D and LASTRAC. The NLF design technique prescribes a target pressure distribution for an existing geometry based on relationships between modal instability wave growth and pressure gradients. The modal instability wave growths (both on- and off-axes crossflow and Tollmien-Schlichting) are balanced to produce a pressure distribution that will have a theoretical maximum NLF region for a given streamwise wing station. An example application is presented showing the methodology on a generic supersonic transport wingbody configuration. The configuration has been successfully redesigned to support significant regions of NLF (approximately 40% of the wing upper surface by surface area). Computational analysis predicts NLF with transition Reynolds numbers (ReT) as high as 36 million with 72 degrees of leading-edge sweep (?LE), significantly expanding the current boundary of ReT - ?LE combinations for NLF. This NLF geometry provides a total drag savings of 4.3 counts compared to the baseline wing-body configuration (approximately 5% of total drag). Off-design evaluations at near-cruise and low-speed, high-lift conditions are discussed, as well as attachment line contamination/transition concerns. This computational NLF design effort is a part of an ongoing cooperative agreement between NASA and JAXA researchers.
NASA Technical Reports Server (NTRS)
Carmichael, B. H.
1979-01-01
The potential of natural laminar flow for significant drag reduction and improved efficiency for aircraft is assessed. Past experience with natural laminar flow as reported in published and unpublished data and personal observations of various researchers is summarized. Aspects discussed include surface contour, waviness, and smoothness requirements; noise and vibration effects on boundary layer transition, boundary layer stability criteria; flight experience with natural laminar flow and suction stabilized boundary layers; and propeller slipstream, rain, frost, ice and insect contamination effects on boundary layer transition. The resilient leading edge appears to be a very promising method to prevent leading edge insect contamination.
A theoretical investigation of forebody shapes designed for natural laminar boundary-layer flow
NASA Technical Reports Server (NTRS)
Barger, R. L.
1979-01-01
The design of forebody shapes for natural laminar flow is discussed. For subsonic flow, computed results for three shapes of different fineness ratios indicate that laminar flow can be attained under conditions that approximate those on the forebody of a cruise missile flying at a low altitude at a high subsonic Mach number. For supersonic (Mach 2.00) design, a one-parameter family of hyperbolic arcs was used to generate forebody shapes having a favorable pressure gradient over the forebody length. Computed results for these shapes indicated laminar and transitional flow over the range of Reynolds numbers considered.
Laminar Flow Aircraft Certification
NASA Technical Reports Server (NTRS)
Williams, Louis J. (Compiler)
1986-01-01
Various topics telative to laminar flow aircraft certification are discussed. Boundary layer stability, flaps for laminar flow airfoils, computational wing design studies, manufacturing requirements, windtunnel tests, and flow visualization are among the topics covered.
An Approach to the Constrained Design of Natural Laminar Flow Airfoils
NASA Technical Reports Server (NTRS)
Green, Bradford E.
1997-01-01
A design method has been developed by which an airfoil with a substantial amount of natural laminar flow can be designed, while maintaining other aerodynamic and geometric constraints. After obtaining the initial airfoil's pressure distribution at the design lift coefficient using an Euler solver coupled with an integral turbulent boundary layer method, the calculations from a laminar boundary layer solver are used by a stability analysis code to obtain estimates of the transition location (using N-Factors) for the starting airfoil. A new design method then calculates a target pressure distribution that will increase the laminar flow toward the desired amount. An airfoil design method is then iteratively used to design an airfoil that possesses that target pressure distribution. The new airfoil's boundary layer stability characteristics are determined, and this iterative process continues until an airfoil is designed that meets the laminar flow requirement and as many of the other constraints as possible.
Discrete-Roughness-Element-Enhanced Swept-Wing Natural Laminar Flow at High Reynolds Numbers
NASA Technical Reports Server (NTRS)
Malik, Mujeeb; Liao, Wei; Li, Fei; Choudhari, Meelan
2015-01-01
Nonlinear parabolized stability equations and secondary-instability analyses are used to provide a computational assessment of the potential use of the discrete-roughness-element technology for extending swept-wing natural laminar flow at chord Reynolds numbers relevant to transport aircraft. Computations performed for the boundary layer on a natural-laminar-flow airfoil with a leading-edge sweep angle of 34.6 deg, freestream Mach number of 0.75, and chord Reynolds numbers of 17 × 10(exp 6), 24 × 10(exp 6), and 30 × 10(exp 6) suggest that discrete roughness elements could delay laminar-turbulent transition by about 20% when transition is caused by stationary crossflow disturbances. Computations show that the introduction of small-wavelength stationary crossflow disturbances (i.e., discrete roughness element) also suppresses the growth of most amplified traveling crossflow disturbances.
DRE-Enhanced Swept-Wing Natural Laminar Flow at High Reynolds Numbers
NASA Technical Reports Server (NTRS)
Malik, Mujeeb; Liao, Wei; Li, Fe; Choudhari, Meelan
2013-01-01
Nonlinear parabolized stability equations and secondary instability analyses are used to provide a computational assessment of the potential use of the discrete roughness elements (DRE) technology for extending swept-wing natural laminar flow at chord Reynolds numbers relevant to transport aircraft. Computations performed for the boundary layer on a natural laminar flow airfoil with a leading-edge sweep angle of 34.6deg, free-stream Mach number of 0.75 and chord Reynolds numbers of 17 x 10(exp 6), 24 x 10(exp 6) and 30 x 10(exp 6) suggest that DRE could delay laminar-turbulent transition by about 20% when transition is caused by stationary crossflow disturbances. Computations show that the introduction of small wavelength stationary crossflow disturbances (i.e., DRE) also suppresses the growth of most amplified traveling crossflow disturbances.
An approach to the constrained design of natural laminar flow airfoils
NASA Technical Reports Server (NTRS)
Green, Bradford Earl
1995-01-01
A design method has been developed by which an airfoil with a substantial amount of natural laminar flow can be designed, while maintaining other aerodynamic and geometric constraints. After obtaining the initial airfoil's pressure distribution at the design lift coefficient using an Euler solver coupled with an integml turbulent boundary layer method, the calculations from a laminar boundary layer solver are used by a stability analysis code to obtain estimates of the transition location (using N-Factors) for the starting airfoil. A new design method then calculates a target pressure distribution that will increase the larninar flow toward the desired amounl An airfoil design method is then iteratively used to design an airfoil that possesses that target pressure distribution. The new airfoil's boundary layer stability characteristics are determined, and this iterative process continues until an airfoil is designed that meets the laminar flow requirement and as many of the other constraints as possible.
Boundary layer stability analysis of a natural laminar flow glove on the F-111 TACT airplane
NASA Technical Reports Server (NTRS)
Runyan, L. J.; Steers, L. L.
1980-01-01
A natural laminar flow airfoil has been developed as a part of the aircraft energy efficiency program. A NASA flight program incorporating this airfoil into partial wing gloves on the F-111 TACT airplane was scheduled to start in May, 1980. In support of this research effort, an extensive boundary layer stability analysis of the partial glove has been conducted. The results of that analysis show the expected effects of wing leading-edge sweep angle, Reynolds number, and compressibility on boundary layer stability and transition. These results indicate that it should be possible to attain on the order of 60% laminar flow on the upper surface and 50% laminar flow on the lower surface for sweep angles of at least 20 deg, chord Reynolds numbers of 25 x 10 to the 6th and Mach numbers from 0.81 to 0.85.
Flight investigation of natural laminar flow on the Bellanca Skyrocket II
NASA Technical Reports Server (NTRS)
Holmes, B. J.; Obara, C. J.; Gregorek, G. M.; Hoffman, M. J.; Freuhler, R. J.
1983-01-01
Two major concerns have inhibited the use of natural laminar flow (NLF) for viscous drag reduction on production aircraft. These are the concerns of achieveability of NLF on practical airframe surfaces, and maintainability in operating environments. Previous research in this area left a mixture of positive and negative conclusions regarding these concerns. While early (pre-1950) airframe construction methods could not achieve NLF criteria for waviness, several modern construction methods (composites for example) can achieve the required smoothness. This paper presents flight experiment data on the achieveability and maintainability of NLF on a high-performance, single-propeller, composite airplane, the Bellanca Skyrocket II. The significant contribution of laminar flow to the performance of this airplane was measured. Observations of laminar flow in the propeller slipstream are discussed, as are the effects of insect contamination on the wing. These observations have resulted in a new appreciation of the operational feasibility for achieving and maintaining NLF on modern airframe surfaces.
Design of a Slotted, Natural-Laminar-Flow Airfoil for Business-Jet Applications
NASA Technical Reports Server (NTRS)
Somers, Dan M.
2012-01-01
A 14-percent-thick, slotted, natural-laminar-flow airfoil, the S204, for light business-jet applications has been designed and analyzed theoretically. The two primary objectives of high maximum lift, relatively insensitive to roughness, and low profile drag have been achieved. The drag-divergence Mach number is predicted to be greater than 0.70.
Nacelle/pylon/wing integration on a transport model with a natural laminar flow nacelle
NASA Technical Reports Server (NTRS)
Lamb, M.; Aabeyounis, W. K.; Patterson, J. C., Jr.
1985-01-01
Tests were conducted in the Langley 16-Foot Transonic Tunnel at free-stream Mach numbers from 0.70 to 0.82 and angles of attack from -2.5 deg to 4.0 deg to determine if nacelle/pylon/wing integration affects the achievement of natural laminar flow on a long-duct flow-through nacelle for a high-wing transonic transport configuration. In order to fully assess the integration effect on a nacelle designed to achieve laminar flow, the effects of fixed and free nacelle transitions as well as nacelle longitudinal position and pylon contouring were obtained. The results indicate that the ability to achieve laminar flow on the nacelle is not significantly altered by nacelle/pylon/wing integration. The increment in installed drag between free and fixed transition for the nacelles on symmetrical pylons is essentially the calculated differences between turbulent and laminar flow on the nacelles. The installed drag of the contoured pylon is less than that of the symmetrical pylon. The installed drag for the nacelles in a rearward position is greater than that for the nacelles in a forward position.
Overview of Laminar Flow Control
NASA Technical Reports Server (NTRS)
Joslin, Ronald D.
1998-01-01
The history of Laminar Flow Control (LFC) from the 1930s through the 1990s is reviewed and the current status of the technology is assessed. Early studies related to the natural laminar boundary-layer flow physics, manufacturing tolerances for laminar flow, and insect-contamination avoidance are discussed. Although most of this publication is about slot-, porous-, and perforated-suction LFC concept studies in wind tunnel and flight experiments, some mention is made of thermal LFC. Theoretical and computational tools to describe the LFC aerodynamics are included for completeness.
A Method for the Constrained Design of Natural Laminar Flow Airfoils
NASA Technical Reports Server (NTRS)
Green, Bradford E.; Whitesides, John L.; Campbell, Richard L.; Mineck, Raymond E.
1996-01-01
A fully automated iterative design method has been developed by which an airfoil with a substantial amount of natural laminar flow can be designed, while maintaining other aerodynamic and geometric constraints. Drag reductions have been realized using the design method over a range of Mach numbers, Reynolds numbers and airfoil thicknesses. The thrusts of the method are its ability to calculate a target N-Factor distribution that forces the flow to undergo transition at the desired location; the target-pressure-N-Factor relationship that is used to reduce the N-Factors in order to prolong transition; and its ability to design airfoils to meet lift, pitching moment, thickness and leading-edge radius constraints while also being able to meet the natural laminar flow constraint. The method uses several existing CFD codes and can design a new airfoil in only a few days using a Silicon Graphics IRIS workstation.
NASA Technical Reports Server (NTRS)
Joslin, Ronald D.
1998-01-01
Aircraft laminar flow control (LFC) from the 1930's through the 1990's is reviewed and the current status of the technology is assessed. Examples are provided to demonstrate the benefits of LFC for subsonic and supersonic aircraft. Early studies related to the laminar boundary-layer flow physics, manufacturing tolerances for laminar flow, and insect-contamination avoidance are discussed. LFC concept studies in wind-tunnel and flight experiments are the major focus of the paper. LFC design tools are briefly outlined for completeness.
Experimental Results for a Flapped Natural-laminar-flow Airfoil with High Lift/drag Ratio
NASA Technical Reports Server (NTRS)
Mcghee, R. J.; Viken, J. K.; Pfenninger, W.; Beasley, W. D.; Harvey, W. D.
1984-01-01
Experimental results have been obtained for a flapped natural-laminar-flow airfoil, NLF(1)-0414F, in the Langley Low-Turbulence Pressure Tunnel. The tests were conducted over a Mach number range from 0.05 to 0.40 and a chord Reynolds number range from about 3.0 x 10(6) to 22.0 x 10(6). The airfoil was designed for 0.70 chord laminar flow on both surfaces at a lift coefficient of 0.40, a Reynolds number of 10.0 x 10(6), and a Mach number of 0.40. A 0.125 chord simple flap was incorporated in the design to increase the low-drag, lift-coefficient range. Results were also obtained for a 0.20 chord split-flap deflected 60 deg.
Operational considerations for laminar flow aircraft
NASA Technical Reports Server (NTRS)
Maddalon, Dal V.; Wagner, Richard D.
1986-01-01
Considerable progress has been made in the development of laminar flow technology for commercial transports during the NASA Aircraft Energy Efficiency (ACEE) laminar flow program. Practical, operational laminar flow control (LFC) systems have been designed, fabricated, and are undergoing flight testing. New materials, fabrication methods, analysis techniques, and design concepts were developed and show much promise. The laminar flow control systems now being flight tested on the NASA Jetstar aircraft are complemented by natural laminar flow flight tests to be accomplished with the F-14 variable-sweep transition flight experiment. An overview of some operational aspects of this exciting program is given.
F-111 natural laminar flow glove flight test data analysis and boundary layer stability analysis
NASA Technical Reports Server (NTRS)
Runyan, L. J.; Navran, B. H.; Rozendaal, R. A.
1984-01-01
An analysis of 34 selected flight test data cases from a NASA flight program incorporating a natural laminar flow airfoil into partial wing gloves on the F-111 TACT airplane is given. This analysis determined the measured location of transition from laminar to turbulent flow. The report also contains the results of a boundary layer stability analysis of 25 of the selected cases in which the crossflow (C-F) and Tollmien-Schlichting (T-S) disturbance amplification factors are correlated with the measured transition location. The chord Reynolds numbers for these cases ranges from about 23 million to 29 million, the Mach numbers ranged from 0.80 to 0.85, and the glove leading-edge sweep angles ranged from 9 deg to 25 deg. Results indicate that the maximum extent of laminar flow varies from 56% chord to 9-deg sweep on the upper surface, and from 51% chord at 16-deg sweep to 6% chord at 25-deg sweep on the lower. The results of the boundary layer stability analysis indicate that when both C-F and T-S disturbances are amplified, an interaction takes place which reduces the maximum amplification factor of either type of disturbance that can be tolerated without causing transition.
Mimicking Natural Laminar to Turbulent Flow Transition: A Systematic CFD Study Using PAB3D
NASA Technical Reports Server (NTRS)
Pao, S. Paul; Abdol-Hamid, Khaled S.
2005-01-01
For applied aerodynamic computations using a general purpose Navier-Stokes code, the common practice of treating laminar to turbulent flow transition over a non-slip surface is somewhat arbitrary by either treating the entire flow as turbulent or forcing the flow to undergo transition at given trip locations in the computational domain. In this study, the possibility of using the PAB3D code, standard k-epsilon turbulence model, and the Girimaji explicit algebraic stresses model to mimic natural laminar to turbulent flow transition was explored. The sensitivity of flow transition with respect to two limiters in the standard k-epsilon turbulence model was examined using a flat plate and a 6:1 aspect ratio prolate spheroid for our computations. For the flat plate, a systematic dependence of transition Reynolds number on background turbulence intensity was found. For the prolate spheroid, the transition patterns in the three-dimensional boundary layer at different flow conditions were sensitive to the free stream turbulence viscosity limit, the reference Reynolds number and the angle of attack, but not to background turbulence intensity below a certain threshold value. The computed results showed encouraging agreements with the experimental measurements at the corresponding geometry and flow conditions.
Laminar and Turbulent Flow in Water
ERIC Educational Resources Information Center
Riveros, H. G.; Riveros-Rosas, D.
2010-01-01
There are many ways to visualize flow, either for laminar or turbulent flows. A very convincing way to show laminar and turbulent flows is by the perturbations on the surface of a beam of water coming out of a cylindrical tube. Photographs, taken with a flash, show the nature of the flow of water in pipes. They clearly show the difference between…
Natural laminar flow data from full-scale flight and wind-tunnel experiments
NASA Technical Reports Server (NTRS)
Holmes, B. J.; Coy, P. F.; Yip, L. P.; Brown, P. W.; Obara, C. J.
1981-01-01
Experimental results obtained at NASA Langley during studies of natural laminar flow (NLF) over commercially produced aircraft surfaces are reported. The general aviation aircraft examined were light aircraft, yet displayed NLF extents close to the maximum available and equivalent to high performance business aircraft flying envelopes. Sublimating chemicals and acoustic detection techniques were employed to measure the boundary layer transition. Theoretical predictions of boundary layer stability were found to match well with the experimental data, with consideration given to both swept wings and the amplitudes of allowable waves on the airfoil surfaces. The presence of the NLF on the airfoil surfaces confirmed the benefits available from use of composite materials for airfoil surfaces.
An Exploratory Investigation of a Slotted, Natural-Laminar-Flow Airfoil
NASA Technical Reports Server (NTRS)
Somers, Dan M.
2012-01-01
A 15-percent-thick, slotted, natural-laminar-flow (SNLF) airfoil, the S103, for general aviation applications has been designed and analyzed theoretically and verified experimentally in the Langley Low-Turbulence Pressure Tunnel. The two primary objectives of high maximum lift and low profile drag have been achieved. The constraints on the pitching moment and the airfoil thickness have been satisfied. The airfoil exhibits a rapid stall, which does not meet the design goal. Comparisons of the theoretical and experimental results show good agreement. Comparison with the baseline, NASA NLF(1)-0215F airfoil confirms the achievement of the objectives.
Natural laminar flow airfoil design considerations for winglets on low-speed airplanes
NASA Technical Reports Server (NTRS)
Vandam, C. P.
1984-01-01
Winglet airfoil section characteristics which significantly influence cruise performance and handling qualities of an airplane are discussed. A good winglet design requires an airfoil section with a low cruise drag coefficient, a high maximum lift coefficient, and a gradual and steady movement of the boundary layer transition location with angle of attack. The first design requirement provides a low crossover lift coefficient of airplane drag polars with winglets off and on. The other requirements prevent nonlinear changes in airplane lateral/directional stability and control characteristics. These requirements are considered in the design of a natural laminar flow airfoil section for winglet applications and chord Reynolds number of 1 to 4 million.
On the Spectrum of Natural Oscillations of Two-Dimensional Laminar Flows
NASA Technical Reports Server (NTRS)
Grohne, D.
1957-01-01
In the investigation of stability of a two-dimensional laminar flow with respect to small disturbances, a disturbance of the stream function moving downstream (in the direction of the x-axis) by the "partial wave formula" is described.
Supersonic laminar flow control research
NASA Technical Reports Server (NTRS)
Lo, Ching F.
1994-01-01
The objective of the research is to understand supersonic laminar flow stability, transition, and active control. Some prediction techniques will be developed or modified to analyze laminar flow stability. The effects of supersonic laminar flow with distributed heating and cooling on active control will be studied. The primary tasks of the research applying to the NASA/Ames Proof of Concept (POC) Supersonic Wind Tunnel and Laminar Flow Supersonic Wind Tunnel (LFSWT) nozzle design with laminar flow control are as follows: (1) predictions of supersonic laminar boundary layer stability and transition, (2) effects of wall heating and cooling for supersonic laminar flow control, and (3) performance evaluation of POC and LFSWT nozzles design with wall heating and cooling effects applying at different locations and various length.
Supersonic Laminar Flow Control Research
NASA Technical Reports Server (NTRS)
Lo, Ching F.; Wiberg, Clark G.
1996-01-01
The objective of this research is to understand supersonic laminar flow stability, transition and active control. Some prediction techniques will be developed or modified to analyze laminar flow stability. The effects of distributed heating and cooling as an active boundary layer control technique will be studied. The primary tasks of the research apply to the NASA/Ames PoC and LFSWT's nozzle design with laminar flow control and are listed as follows: Predictions of supersonic laminar boundary layer stability and transition; Effects of wall heating and cooling on supersonic laminar flow control on a flat plate; Performance evaluation of the PoC and LFSWT nozzle designs with wall heating and cooling applied at different locations and various lengths; Effects of a conducted-vs-pulse wall temperature distribution for the LFSWT; and Application of wall heating and/or cooling to laminar boundary layer and flow separation control of airfoils and investigation of related active control techniques.
NASA Technical Reports Server (NTRS)
Irani, E.; Snyder, M. H.
1988-01-01
An averaging total pressure wake rake used by the Cessna Aircraft Company in flight tests of a modified 210 airplane with a laminar flow wing was calibrated in wind tunnel tests against a five-tube pressure probe. The model generating the wake was a full-scale model of the Cessna airplane wing. Indications of drag trends were the same for both instruments.
NASA Technical Reports Server (NTRS)
Rozendaal, R. A.
1986-01-01
The linear boundary layer stability analyses and their correlation with data of 18 cases from a natural laminar flow (NLF) flight test program using a Cessna Citation 3 business jet are described. The transition point varied from 5% to 35% chord for these conditions, and both upper and lower wing surfaces were included. Altitude varied from 10,000 to 43,000 ft and Mach number from 0.3 to 0.8. Four cases were at nonzero sideslip. Although there was much scatter in the results, the analyses of boundary layer stability at the 18 conditions led to the conclusion that crossflow instability was the primary cause of transition. However, the sideslip cases did show some interaction of crossflow and Tollmien-Schlichting disturbances. The lower surface showed much lower Tollmien-Schlichting amplification at transition than the upper surface, but similar crossflow amplifications. No relationship between Mach number and disturbance amplification at transition could be found. The quality of these results is open to question from questionable wing surface quality, inadequate density of transition sensors on the wing upper surface, and an unresolved pressure shift in the wing pressure data. The results of this study show the need for careful preparation for transition experiments. Preparation should include flow analyses of the test surface, boundary layer disturbance amplification analyses, and assurance of adequate surface quality in the test area. The placement of necessary instruments and usefulness of the resulting data could largely be determined during the pretest phase.
Laminar-flow wind tunnel experiments
NASA Technical Reports Server (NTRS)
Harvey, William D.; Harris, Charles D.; Sewall, William G.; Stack, John P.
1989-01-01
Although most of the laminar flow airfoils recently developed at the NASA Langley Research Center were intended for general aviation applications, low-drag airfoils were designed for transonic speeds and wind tunnel performance tested. The objective was to extend the technology of laminar flow to higher Mach and Reynolds numbers and to swept leading edge wings representative of transport aircraft to achieve lower drag and significantly improved operation costs. This research involves stabilizing the laminar boundary layer through geometric shaping (Natural Laminar Flow, NLF) and active control involving the removal of a portion of the laminar boundary layer (Laminar-Flow Control, LFC), either through discrete slots or perforated surface. Results show that extensive regions of laminar flow with large reductions in skin friction drag can be maintained through the application of passive NLF boundary-layer control technologies to unswept transonic wings. At even greater extent of laminar flow and reduction in the total drag level can be obtained on a swept supercritical airfoil with active boundary layer-control.
Supersonic laminar flow control research
NASA Technical Reports Server (NTRS)
Lo, Ching F.; Wiberg, Clark G.
1995-01-01
The objective of this research is to understand supersonic laminar flow stability, transition and active control. Some prediction techniques will be developed or modified to analyze laminar flow stability. The effects of distributed heating and cooling as an active boundary layer control technique will be studied. The primary tasks of the research apply to the NASA/Ames PoC and LFSWT's nozzle design with laminar flow control and are listed as follows: (1) predictions of supersonic laminar boundary layer stability and transition; (2) effects of wall heating and cooling on supersonic laminar flow control; (3) performance evaluation of the PoC and LFSWT nozzle designs with wall heating and cooling applied at different locations and various lengths; and (4) effects of a conducted -vs- pulse wall temperature distribution for the LFSWT.
NASA Technical Reports Server (NTRS)
Waggoner, E. G.; Campbell, R. L.; Phillips, P. S.
1985-01-01
A natural laminar flow outer panel wing glove has been designed for a variable sweep fighter aircraft using state-of-the-art computational techniques. Testing of the design will yield wing pressure and boundary-layer data under actual flight conditions and environment. These data will be used to enhance the understanding of the interaction between crossflow and Tollmien-Schlichting disturbances on boundary-layer transition. The outer wing panel was contoured such that a wide range of favorable pressure gradients could be obtained on the wing upper surface. Extensive computations were performed to support the design effort which relied on two- and three-dimensional transonic design and analysis techniques. A detailed description of the design procedure that evolved during this study is presented. Results on intermediate designs at various stages in the design process demonstrate how the various physical and aerodynamic constraints were integrated into the design. Final results of the glove design analyzed as part of the complete aircraft configuration with a full-potential wing/body analysis code indicate that the aerodynamic design objectives were met.
Supersonic Laminar Flow Control Research
NASA Technical Reports Server (NTRS)
Lo, C. F.; Wiberg, Clark G.
1996-01-01
The objective of this research is to understand supersonic laminar flow stability, transition and active control. Some prediction techniques are developed or modified to analyze laminar flow stability. The effects of distributed heating and cooling as an active boundary layer control technique are studied. The primary tasks of the research apply to the NASA/Ames Proof-of-Concept (PoC) and the Laminar Flow Supersonic Wind Tunnel's (LFSWT's) nozzle design with laminar flow control and are listed as follows: (1) Predictions of supersonic laminar boundary layer stability and transition; (2) Effects of wall heating and cooling on supersonic laminar flow control on a flat plate; (3) Performance evaluation of the PoC and LFSWT nozzle designs with wall heating and cooling applied at different locations and various lengths; (4) Effects of a conducted -vs- pulse wall temperature distribution for the LFSWT; and (5) Application of wall heating and/or cooling to laminar boundary layer and flow separation control of airfoils and investigation of related active control techniques.
NASA Technical Reports Server (NTRS)
Sewall, William G.; Mcghee, Robert J.; Viken, Jeffery K.; Waggoner, Edgar G.; Walker, Betty S.; Millard, Betty F.
1985-01-01
Two dimensional wind tunnel tests were conducted on a high speed natural laminar flow airfoil in both the Langley 6 x 28 inch Transonic Tunnel and the Langley Low Turbulence Pressure Tunnel. The test conditions consisted of Mach numbers ranging from 0.10 to 0.77 and Reynolds numbers ranging from 3 x 1 million to 11 x 1 million. The airfoil was designed for a lift coefficient of 0.20 at a Mach number of 0.70 and Reynolds number of 11 x 1 million. At these conditions, laminar flow would extend back to 50 percent chord of the upper surface and 70 percent chord of the lower surface. Low speed results were also obtained with a 0.20 chord trailing edge split flap deflected 60 deg.
A Numerical Evaluation of Icing Effects on a Natural Laminar Flow Airfoil
NASA Technical Reports Server (NTRS)
Chung, James J.; Addy, Harold E., Jr.
2000-01-01
As a part of CFD code validation efforts within the Icing Branch of NASA Glenn Research Center, computations were performed for natural laminar flow (NLF) airfoil, NLF-0414. with 6 and 22.5 minute ice accretions. Both 3-D ice castings and 2-D machine-generated ice shapes were used in wind tunnel tests to study the effects of natural ice is well as simulated ice. They were mounted in the test section of the Low Turbulence Pressure Tunnel (LTPT) at NASA Langley that the 2-dimensionality of the flow can be maintained. Aerodynamic properties predicted by computations were compared to data obtained through the experiment by the authors at the LTPT. Computations were performed only in 2-D and in the case of 3-D ice, the digitized ice shape obtained at one spanwise location was used. The comparisons were mainly concentrated on the lift characteristics over Reynolds numbers ranging from 3 to 10 million and Mach numbers ranging from 0.12 to 0.29. WIND code computations indicated that the predicted stall angles were in agreement with experiment within one or two degrees. The maximum lift values obtained by computations were in good agreement with those of the experiment for the 6 minute ice shapes and the minute 3-D ice, but were somewhat lower in the case of the 22.5 minute 2-D ice. In general, the Reynolds number variation did not cause much change in the lift values while the variation of Mach number showed more change in the lift. The Spalart-Allmaras (S-A) turbulence model was the best performing model for the airfoil with the 22.5 minute ice and the Shear Stress Turbulence (SST) turbulence model was the best for the airfoil with the 6 minute ice and also for the clean airfoil. The pressure distribution on the surface of the iced airfoil showed good agreement for the 6 minute ice. However, relatively poor agreement of the pressure distribution on the upper surface aft of the leading edge horn for the 22.5 minute ice suggests that improvements are needed in the grid or
NASA Technical Reports Server (NTRS)
Doty, Wayne A.
1990-01-01
Development of Natural Laminar Flow (NLF) technology for application to general aviation-type aircraft has raised some question as to the adequacy of FAR Part 23 for certification of aircraft with significant NLF. A series of flight tests were conducted with a modified Cessna T210R to allow quantitative comparison of the aircraft's ability to meet certification requirements with significant NLF and with boundary layer transition fixed near the leading edge. There were no significant differences between the two conditions except an increasing in drag, which resulted in longer takeoff distances and reduced climb performance.
Hybrid laminar flow control study
NASA Technical Reports Server (NTRS)
1982-01-01
Hybrid laminar flow control (HLFC) in which leading edge suction is used in conjunction with wing pressure distribution tailoring to postpone boundary layer transition and reduce friction drag was examined. Airfoil design characteristics required for laminar flow control (LFC) were determined. The aerodynamic design of the HLFC wing for a 178 passenger commercial turbofan transport was developed, and a drag was estimated. Systems changes required to install HLFC were defined, and weights and fuel economy were estimated. The potential for 9% fuel reduction for a 3926-km (2120-nmi) mission is identified.
NASA Technical Reports Server (NTRS)
Murri, Daniel G.; Jordan, Frank L., Jr.
1987-01-01
An investigation was conducted in the Langley 30- by 60-Foot Wind Tunnel to evaluate the performance, stability, and control characteristics of a full-scale general aviation airplane equipped with an advanced laminar flow wing. The study focused on the effects of natural laminar flow and advanced boundary layer transition on performance, stability, and control, and also on the effects of several wing leading edge modifications on the stall/departure resistance of the configuration. Data were measured over an angle-of-attack range from -6 to 40 deg and an angle-of-sideslip range from -6 to 20 deg. The Reynolds number was varied from 1.4 to 2.4 x 10 to the 6th power based on the mean aerodynamic chord. Additional measurements were made using hot-film and sublimating chemical techniques to determine the condition of the wing boundary layer, and wool tufts were used to study the wing stall characteristics. The investigation showed that large regions of natural laminar flow existed on the wing which would significantly enhance cruise performance. Also, because of the characteristics of the airfoil section, artificially tripping the wing boundary layer to a turbulent condition did not significantly effect the lift, stability, and control characteristics. The addition of a leading-edge droop arrangement was found to increase the stall angle of attack at the wingtips and, therefore, was considered to be effective in improving the stall/departure resistance of the configuration. Also the addition of the droop arrangement resulted in only minor increases in drag.
Laminar-flow flight experiments
NASA Technical Reports Server (NTRS)
Wagner, Richard D.; Maddalon, Dal V.; Bartlett, D. W.; Collier, F. S., Jr.; Braslow, A. L.
1989-01-01
The flight testing conducted over the past 10 years in the NASA laminar-flow control (LFC) will be reviewed. The LFC program was directed towards the most challenging technology application, the high supersonic speed transport. To place these recent experiences in perspective, earlier important flight tests will first be reviewed to recall the lessons learned at that time.
Laminar flow: Challenge and potential
NASA Technical Reports Server (NTRS)
Kirchner, Mark E.
1987-01-01
Commercial air transportation has experienced revolutionary technology advances since WWII. These technology advances have resulted in an explosive growth in passenger traffic. Today, however, many technologies have matured, and maintaining a similar growth rate will be a challenge. A brief history of laminar flow technology and its application to subsonic and supersonic air transportation is presented.
Investigation of a Laminar Flow Leading Edge
NASA Technical Reports Server (NTRS)
Drake, Aaron; Kennelly, Robert A., Jr.; Koga, Dennis J.; Westphal, Russell V.; Zuniga, Fanny
1994-01-01
The recent resurgence of interest in utilizing laminar flow on aircraft surfaces for reduction in skin friction drag has generated a considerable amount of research in natural laminar flow (NLF) and hybrid laminar flow control (HLFC) on transonic aircraft wings. This research has focused primarily on airfoil design and understanding transition behavior with little concern for the surface imperfections and manufacturing variations inherent to most production aircraft. In order for laminar flow to find wide-spread use on production aircraft, techniques for constructing the wings must be found such that the large surface imperfections present in the leading edge region of current aircraft do not occur. Toward this end, a modification to existing leading edge construction techniques was devised such that the resulting surface did not contain large gaps and steps as are common on current production aircraft of this class. A lowspeed experiment was first conducted on a simulation of the surface that would result from this construction technique. Preston tube measurements of the boundary layer downstream of the simulated joint and flow visualization using sublimation chemicals validated the literature on the effects of steps on a laminar boundary layer. These results also indicated that the construction technique was indeed compatible with laminar flow. In order to fully validate the compatibility of this construction technique with laminar flow, thus proving that it is possible to build wings that are smooth enough to be used on business jets and light transports in a manner compatible with laminar flow, a flight experiment is being conducted. In this experiment Mach number and Reynolds number will be matched in a real flight environment. The experiment is being conducted using the NASA Dryden F-104 Flight Test Fixture (FTF). The FTF is a low aspect ratio ventral fin mounted beneath an F-104G research aircraft. A new nose shape was designed and constructed for this
NASA Technical Reports Server (NTRS)
1987-01-01
Renewed interest in natural laminar flow (NLF) had rekindled designer concern that manufacuring deviations may destroy the effectiveness of NLF for an operational aircraft. Experiments are summarized that attemtped to measure total drag changes associated with three different wing surface conditions on an aircraft typical of current general aviation high performance singles. The speed power technique was first used in an attempt to quantify the changes in total drag. Predicted and measured boundary layer transition locations for three different wing surface conditions were also compared, using two different forms of flow visualization. The three flight test phases included: assessment of an unpainted airframe, flight tests of the same aircraft after painstakingly filling and sanding the wings to design contours, and similar measurement after this aricraft was painted. In each flight phase, transition locations were monitored using with sublimating chemicals or pigmented oil. Two-dimensional drag coefficients were estimated using the Eppler-Somers code and measured with a wake rake in a method very similar to Jones' pitot traverse method. The net change in two-dimensional drag coefficient was approximately 20 counts between the unpainted aircraft and the hand-smoothed aircraft for typical cruise flight conditions.
Assessment of the National Transonic Facility for Laminar Flow Testing
NASA Technical Reports Server (NTRS)
Crouch, Jeffrey D.; Sutanto, Mary I.; Witkowski, David P.; Watkins, A. Neal; Rivers, Melissa B.; Campbell, Richard L.
2010-01-01
A transonic wing, designed to accentuate key transition physics, is tested at cryogenic conditions at the National Transonic Facility at NASA Langley. The collaborative test between Boeing and NASA is aimed at assessing the facility for high-Reynolds number testing of configurations with significant regions of laminar flow. The test shows a unit Reynolds number upper limit of 26 M/ft for achieving natural transition. At higher Reynolds numbers turbulent wedges emanating from the leading edge bypass the natural transition process and destroy the laminar flow. At lower Reynolds numbers, the transition location is well correlated with the Tollmien-Schlichting-wave N-factor. The low-Reynolds number results suggest that the flow quality is acceptable for laminar flow testing if the loss of laminar flow due to bypass transition can be avoided.
Selected experiments in laminar flow: An annotated bibliography
NASA Technical Reports Server (NTRS)
Drake, Aaron; Kennelly, Robert A., Jr.
1992-01-01
Since the 1930s, there have been attempts to reduce drag on airplanes by delaying laminar to turbulent boundary layer transition. Experiments conducted during the 1940's, while successful in delaying transition, were discouraging because of the careful surface preparation necessary to meet roughness and waviness requirements. The resulting lull in research lasted nearly 30 years. By the late 1970s, airframe construction techniques had advanced sufficiently that the high surface quality required for natural laminar flow (NLF) and laminar flow control (LFC) appeared possible on production aircraft. As a result, NLF and LFC research became widespread. This report is an overview of that research. The experiments summarized herein were selected for their applicability to small transonic aircraft. Both flight and wind tunnel tests are included. The description of each experiment is followed by corresponding references. Part One summarizes NLF experiments; Part Two deals with LFC and hybrid laminar flow control (HLFC) experiments.
Computational Analysis of the G-III Laminar Flow Glove
NASA Technical Reports Server (NTRS)
Malik, Mujeeb R.; Liao, Wei; Lee-Rausch, Elizabeth M.; Li, Fei; Choudhari, Meelan M.; Chang, Chau-Lyan
2011-01-01
Under NASA's Environmentally Responsible Aviation Project, flight experiments are planned with the primary objective of demonstrating the Discrete Roughness Elements (DRE) technology for passive laminar flow control at chord Reynolds numbers relevant to transport aircraft. In this paper, we present a preliminary computational assessment of the Gulfstream-III (G-III) aircraft wing-glove designed to attain natural laminar flow for the leading-edge sweep angle of 34.6deg. Analysis for a flight Mach number of 0.75 shows that it should be possible to achieve natural laminar flow for twice the transition Reynolds number ever achieved at this sweep angle. However, the wing-glove needs to be redesigned to effectively demonstrate passive laminar flow control using DREs. As a by-product of the computational assessment, effect of surface curvature on stationary crossflow disturbances is found to be strongly stabilizing for the current design, and it is suggested that convex surface curvature could be used as a control parameter for natural laminar flow design, provided transition occurs via stationary crossflow disturbances.
Boundary Layers in Laminar Vortex Flows.
NASA Astrophysics Data System (ADS)
Baker, Glenn Leslie
A detailed experimental study of the flow in an intense, laminar, axisymmetric vortex has been conducted in the Purdue Tornado Vortex Simulator. The complicated nature of the flow in the boundary layer of laboratory vortices and presumably on that encountered in full-scale tornadoes has been examined. After completing a number of modifications to the existing facility to improve the quality of the flow in the simulator, hot-film anemometry was employed for making velocity-component and turbulence-intensity measurements of both the free-stream and boundary layer portions of the flow. The measurements represent the first experimental boundary layer investigation of a well-defined vortex flow to appear in the literature. These results were compared with recent theoretical work by Burggraf, Stewartson and Belcher (1971) and with an exact similarity solution for line-sink boundary layers developed by the author. A comparison is also made with the numerical simulation of Wilson (1981) in which the boundary conditions were matched to those of the present experimental investigation. Expressions for the vortex core radius, the maximum tangential velocity and the maximum pressure drop are given in terms of dimensionless modeling parameters. References. Burggraf, O. R., K. Stewartson and R. Belcher, Boundary layer. induced by a potential vortex. Phys. Fluids 14, 1821-1833 (1971). Wilson, T., M. S. thesis, Vortex Boundary Layer Dynamics, Univ. Calif. Davis (1981).
Wing Leading Edge Joint Laminar Flow Tests
NASA Technical Reports Server (NTRS)
Drake, Aaron; Westphal, Russell V.; Zuniga, Fanny A.; Kennelly, Robert A., Jr.; Koga, Dennis J.
1996-01-01
An F-104G aircraft at NASA's Dryden Flight Research Center has been equipped with a specially designed and instrumented test fixture to simulate surface imperfections of the type likely to be present near the leading edge on the wings of some laminar flow aircraft. The simulated imperfections consisted of five combinations of spanwise steps and gaps of various sizes. The unswept fixture yielded a pressure distribution similar to that of some laminar flow airfoils. The experiment was conducted at cruise conditions typical for business-jets and light transports: Mach numbers were in the range 0.5-0.8, and unit Reynolds numbers were 1.5-2.5 million per foot. Skin friction measurements indicated that laminar flow was often maintained for some distance downstream of the surface imperfections. Further work is needed to more precisely define transition location and to extend the experiments to swept-wing conditions and a broader range of imperfection geometries.
Laminar flow control, 1976 - 1982: A selected annotated bibliography
NASA Technical Reports Server (NTRS)
Tuttle, M. H.; Maddalon, D. V.
1982-01-01
Laminar Flow Control technology development has undergone tremendous progress in recent years as focused research efforts in materials, aerodynamics, systems, and structures have begun to pay off. A virtual explosion in the number of research papers published on this subject has occurred since interest was first stimulated by the 1976 introduction of NASA's Aircraft Energy Efficiency Laminar Flow Control Program. The purpose of this selected bibliography is to list available, unclassified laminar flow (both controlled and natural) research completed from about 1975 to mid 1982. Some earlier pertinent reports are included but listed separately in the Appendix. Reports listed herein emphasize aerodynamics and systems studies, but some structures work is also summarized. Aerodynamic work is mainly limited to the subsonic and transonic sped regimes. Because wind-tunnel flow qualities, such as free stream disturbance level, play such an important role in boundary-layer transition, much recent research has been done in this area and it is also included.
Laminar Entrained Flow Reactor (Fact Sheet)
Not Available
2014-02-01
The Laminar Entrained Flow Reactor (LEFR) is a modular, lab scale, single-user reactor for the study of catalytic fast pyrolysis (CFP). This system can be employed to study a variety of reactor conditions for both in situ and ex situ CFP.
NASA Technical Reports Server (NTRS)
Vijgen, Paul M. H. W.; Holmes, Bruce J.
1987-01-01
Fuelled by a need to reduce viscous drag of airframes, significant advances have been made in the last decade to design lifting surface geometries with considerable amounts of laminar flow. In contrast to the present understanding of practical limits for natural laminar flow over lifting surfaces, limited experimental results are available examining applicability of natural laminar flow over axisymmetric and nonaxisymmetric fuselage shapes at relevantly high length Reynolds numbers. The drag benefits attainable by realizing laminar flow over nonlifting aircraft components such as fuselages and nacelles are shown. A flight experiment to investigate transition location and transition mode over the forward fuselage of a light twin engine propeller driven airplane is examined.
Laminar Flow in the Ocean Ekman Layer
NASA Astrophysics Data System (ADS)
Woods, J. T. H.
INTRODUCTION THE EFFECT OF A STABLE DENSITY GRADIENT THE FATAL FLAW FLOW VISUALIZATION THE DISCOVERY OF LAMINAR FLOW FINE STRUCTURE WAVE-INDUCED SHEAR INSTABILITY BILLOW TURBULENCE REVERSE TRANSITION REVISED PARADIGM ONE-DIMENSIONAL MODELLING OF THE UPPER OCEAN DIURNAL VARIATION BUOYANT CONVECTION BILLOW TURBULENCE IN THE DIURNAL THERMOCLINE CONSEQUENCES FOR THE EKMAN CURRENT PROFILE SOLAR RADIATION APPLICATIONS Slippery Seas of Acapulco Pollution Afternoon Effect in Sonar Patchiness Fisheries Climate DISCUSSION CONCLUSION REFERENCES
Feasibility study of laminar flow bodies in fully turbulent flow
Sarkar, T.; Sayer, P.G.; Fraser, S.M.
1994-12-31
One of the most important design requirements of long range autonomous underwater vehicles (AUVs) is to minimize propulsive power. An important and relatively easy way of achieving this is by careful selection of hull shape. Two main schools of thought in this respect are: if laminar flow can be maintained for a long length of the body, the effective drag can be reduced; it is not possible to maintain laminar flow for a significant length of the body and hull design should be based on turbulent flow conditions. In this paper, a feasibility study of laminar flow designs is undertaken under the assumption that flow will be turbulent over the entire length. For comparison two laminar flow designs X-35 and F-57 are selected and results are compared with those of two typical torpedo shaped bodies, namely AFTERBODY1 and AFTERBODY2 of DTNSRDC. It has been shown that laminar flow bodies have 10--15% higher drag when flow is turbulent over the entire length. Hence there is some hydrodynamic risk involved in adopting such laminar bodies without further consideration.
NASA Astrophysics Data System (ADS)
Kheshgi, Haroon S.
1993-11-01
Fully developed flow of an incompressible Newtonian fluid through a duct in which the orientation of the cross section is twisted about an axis parallel to an imposed pressure gradient is analyzed here with the aid of the penalty/Galerkin/finite element method. When the axis of twist is located within the duct, flow approaches limits at low and high torsion, the spatial frequency τ by which the duct is twisted. For small torsion, flow is nearly rectilinear and solutions approach previous asymptotic results for an elliptical cross section. For large torsion, flow exhibits an internal layer structure: a rotating circular-cylinder core with a nearly parabolic axial velocity profile, an internal layer of thickness τ-1 along the perimeter of the largest circular cylinder that can be inscribed in the duct, and nearly quiescent flow outside of the circular cylinder. The maximum rate of swirl in the core of a square duct is found to be at moderate torsion. The primary effect of inertia is an increase in pressure with distance from the axis, due to centrifugal acceleration. When the duct is offset from the axis of twist, inertia leads to one, two, or three primary vortices without apparent bifurcation of steady states, although stability of steady flows is lost beyond detected Hopf points.
Insect contamination protection for laminar flow surfaces
NASA Technical Reports Server (NTRS)
Croom, Cynthia C.; Holmes, Bruce J.
1986-01-01
The ability of modern aircraft surfaces to achieve laminar flow was well-accepted in recent years. Obtaining the maximum benefit of laminar flow for aircraft drag reduction requires maintaining minimum leading-edge contamination. Previously proposed insect contamination prevention methods have proved impractical due to cost, weight, or inconvenience. Past work has shown that insects will not adhere to water-wetted surfaces, but the large volumes of water required for protection rendered such a system impractical. The results of a flight experiment conducted by NASA to evaluate the performance of a porous leading-edge fluid discharge ice protection system operated as an insect contamination protections system are presented. In addition, these flights explored the environmental and atmospheric conditions most suitable for insect accumulation.
Thermal laminarization of a stratified pipe flow
Oras, J.J.; Kasza, K.E.
1984-01-01
The present work constitutes a new program that grew out of a scoping assessment by ANL to determine the propensity for pipe stratification to occur in the reactor outlet nozzles and hot-leg piping of a generic LMFBR during events producing reverse pipe flow. This paper focuses on the role that thermal buoyancy plays relative to being able to laminarize a turbulent stratified shear zone in a horizontal pipe. The preceeding can influence the behavior of a pipe stratified-backflow-recirculation zone (cold plenum water down into the hot pipe flow) which developes as the result of a temperature difference between the pipe flow and the plenum.
Application of laminar flow control to supersonic transport configurations
NASA Technical Reports Server (NTRS)
Parikh, P. G.; Nagel, A. L.
1990-01-01
The feasibility and impact of implementing a laminar flow control system on a supersonic transport configuration were investigated. A hybrid laminar flow control scheme consisting of suction controlled and natural laminar flow was developed for a double-delta type wing planform. The required suction flow rates were determined from boundary layer stability analyses using representative wing pressure distributions. A preliminary design of structural modifications needed to accommodate suction through a perforated titanium skin was carried out together with the ducting and systems needed to collect, compress and discharge the suction air. The benefits of reduced aerodynamic drag were weighed against the weight, volume and power requirement penalties of suction system installation in a mission performance and sizing program to assess the net benefits. The study showed a feasibility of achieving significant laminarization of the wing surface by use of a hybrid scheme, leading to an 8.2 percent reduction in the cruise drag. This resulted in an 8.5 percent reduction in the maximum takeoff weight and a 12 percent reduction in the fuel burn after the inclusion of the LFC system installation penalties. Several research needs were identified for a resolution of aerodynamics, structural and systems issues before these potential benefits could be realized in a practical system.
Distributed apertures in laminar flow laser turrets
NASA Astrophysics Data System (ADS)
Tousley, B. B.
1981-09-01
Assume a technology that permits undistorted laser beam propagation from the aft section of a streamlined turret. A comparison of power on a distant airborne target is made between a single aperture in a large scale streamlined turret with a turbulent boundary layer and various arrays of apertures in small scale streamlined turrets with laminar flow. The array performance is mainly limited by the size of each aperture. From an array one might expect, at best, about 40 percent as much power on the target as from a single aperture with equal area. Since the turbulent boundary layer on the large single-turret has negligible effect on beam quality, the array would be preferred (if all development efforts were essentially equal) only if a laminar wake is an operational requirement.
Preliminary aerodynamic design considerations for advanced laminar flow aircraft configurations
NASA Technical Reports Server (NTRS)
Johnson, Joseph L., Jr.; Yip, Long P.; Jordan, Frank L., Jr.
1986-01-01
Modern composite manufacturing methods have provided the opportunity for smooth surfaces that can sustain large regions of natural laminar flow (NLF) boundary layer behavior and have stimulated interest in developing advanced NLF airfoils and improved aircraft designs. Some of the preliminary results obtained in exploratory research investigations on advanced aircraft configurations at the NASA Langley Research Center are discussed. Results of the initial studies have shown that the aerodynamic effects of configuration variables such as canard/wing arrangements, airfoils, and pusher-type and tractor-type propeller installations can be particularly significant at high angles of attack. Flow field interactions between aircraft components were shown to produce undesirable aerodynamic effects on a wing behind a heavily loaded canard, and the use of properly designed wing leading-edge modifications, such as a leading-edge droop, offset the undesirable aerodynamic effects by delaying wing stall and providing increased stall/spin resistance with minimum degradation of laminar flow behavior.
Design Considerations for Laminar Flow Control Aircraft
NASA Technical Reports Server (NTRS)
Sturgeon, R. F.; Bennett, J. A.
1976-01-01
A study was conducted to investigate major design considerations involved in the application of laminar flow control to the wings and empennage of long range subsonic transport aircraft compatible with initial operation in 1985. For commercial transports with a design mission range of 10,186 km (5500 n mil) and a payload of 200 passengers, parametric configuration analyses were conducted to evaluate the effect of aircraft performance, operational, and geometric parameters on fuel efficiency. Study results indicate that major design goals for aircraft optimization include maximization of aspect ratio and wing loading and minimization of wing sweep consistent with wing volume and airport performance requirements.
Flow/Soot-Formation Interactions in Nonbuoyant Laminar Diffusion Flames
NASA Technical Reports Server (NTRS)
Dai, Z.; Lin, K.-C.; Sunderland, P. B.; Xu, F.; Faeth, G. M.
2002-01-01
This is the final report of a research program considering interactions between flow and soot properties within laminar diffusion flames. Laminar diffusion flames were considered because they provide model flame systems that are far more tractable for theoretical and experimental studies than more practical turbulent diffusion flames. In particular, understanding the transport and chemical reaction processes of laminar flames is a necessary precursor to understanding these processes in practical turbulent flames and many aspects of laminar diffusion flames have direct relevance to turbulent diffusion flames through application of the widely recognized laminar flamelet concept of turbulent diffusion flames. The investigation was divided into three phases, considering the shapes of nonbuoyant round laminar jet diffusion flames in still air, the shapes of nonbuoyant round laminar jet diffusion flames in coflowing air, and the hydrodynamic suppression of soot formation in laminar diffusion flames.
Mastering nonlinear flow dynamics for laminar flow control
NASA Astrophysics Data System (ADS)
Sattarzadeh, Sohrab S.; Fransson, Jens H. M.
2016-08-01
A laminar flow control technique based on spanwise mean velocity gradients (SVGs) has recently proven successful in delaying transition in boundary layers. Here we take advantage of a well-known nonlinear effect, namely, the interaction of two oblique waves at high amplitude, to produce spanwise mean velocity variations. Against common belief we are able to fully master the first stage of this nonlinear interaction to generate steady and stable streamwise streaks, which in turn trigger the SVG method. Our experimental results show that the region of laminar flow can be extended by up to 230%.
Mastering nonlinear flow dynamics for laminar flow control.
Sattarzadeh, Sohrab S; Fransson, Jens H M
2016-08-01
A laminar flow control technique based on spanwise mean velocity gradients (SVGs) has recently proven successful in delaying transition in boundary layers. Here we take advantage of a well-known nonlinear effect, namely, the interaction of two oblique waves at high amplitude, to produce spanwise mean velocity variations. Against common belief we are able to fully master the first stage of this nonlinear interaction to generate steady and stable streamwise streaks, which in turn trigger the SVG method. Our experimental results show that the region of laminar flow can be extended by up to 230%. PMID:27627235
Laminar natural convection under nonuniform gravity.
NASA Technical Reports Server (NTRS)
Lienhard, J.; Eichhorn, R.; Dhir, V.
1972-01-01
Laminar natural convection is analyzed for cases in which gravity varies with the distance from the leading edge of an isothermal plate. The study includes situations in which gravity varies by virtue of the varying slope of a surface. A general integral solution method which includes certain known integral solutions as special cases is developed to account for arbitrary position-dependence of gravity. A series method of solution is also developed for the full equations. Although it is more cumbersome it provides verification of the integral method.
Evaluation of the Edgegard Laminar Flow Hood
Coriell, Lewis L.; McGarrity, Gerard J.
1970-01-01
In a horizontal back-to-front flow high-efficiency particulate air-filtered laminar hood, it is shown that a Blake bottle obstruction to the air flow causes a downstream cone of turbulent air which can draw microbial contamination into the work area of the hood. In controlled experiments, contamination with T3 coliphage was reduced by a series of perforations around the open edge of the hood which eliminates the cone of turbulent air. The average reduction in phage counts was 90.75, 86.79, 91.12, and 98.92%, depending upon the site of nebulization. The phage counts were reduced in 48 of the 51 tests. Images PMID:5485728
Laminar flow control perforated wing panel development
NASA Technical Reports Server (NTRS)
Fischler, J. E.
1986-01-01
Many structural concepts for a wing leading edge laminar flow control hybrid panel were analytically investigated. After many small, medium, and large tests, the selected design was verified. New analytic methods were developed to combine porous titanium sheet bonded to a substructure of fiberglass and carbon/epoxy cloth. At -65 and +160 F test conditions, the critical bond of the porous titanium to the composite failed at lower than anticipated test loads. New cure cycles, design improvements, and test improvements significantly improved the strength and reduced the deflections from thermal and lateral loadings. The wave tolerance limits for turbulence were not exceeded. Consideration of the beam column midbay deflections from the combinations of the axial and lateral loadings and thermal bowing at -65 F, room temperature, and +160 F were included. Many lap shear tests were performed at several cure cycles. Results indicate that sufficient verification was obtained to fabricate a demonstration vehicle.
Toward a laminar-flow-control transport
NASA Technical Reports Server (NTRS)
Sturgeon, R. F.
1978-01-01
Analyses were conducted to define a practical design for an advanced technology laminar flow control (LRC) transport for initial passenger operation in the early 1990's. Mission requirements, appropriate design criteria, and level of technology for the study aircraft were defined. The characteristics of the selected configuration were established, aircraft and LFC subsystems compatible with the mission requirements were defined, and the aircraft was evaluated in terms of fuel efficiency. A wing design integrating the LFC ducting and metering system into advanced composite wing structure was developed, manufacturing procedures for the surface panel design were established, and environmental and structural testing of surface panel components were conducted. Test results revealed a requirement for relatively minor changes in the manufacturing procedures employed, but have shown the general compatibility of both the selected design and the use of composite materials with the requirements of LFC wing surface panels.
Gliding swifts attain laminar flow over rough wings.
Lentink, David; de Kat, Roeland
2014-01-01
Swifts are among the most aerodynamically refined gliding birds. However, the overlapping vanes and protruding shafts of their primary feathers make swift wings remarkably rough for their size. Wing roughness height is 1-2% of chord length on the upper surface--10,000 times rougher than sailplane wings. Sailplanes depend on extreme wing smoothness to increase the area of laminar flow on the wing surface and minimize drag for extended glides. To understand why the swift does not rely on smooth wings, we used a stethoscope to map laminar flow over preserved wings in a low-turbulence wind tunnel. By combining laminar area, lift, and drag measurements, we show that average area of laminar flow on swift wings is 69% (n = 3; std 13%) of their total area during glides that maximize flight distance and duration--similar to high-performance sailplanes. Our aerodynamic analysis indicates that swifts attain laminar flow over their rough wings because their wing size is comparable to the distance the air travels (after a roughness-induced perturbation) before it transitions from laminar to turbulent. To interpret the function of swift wing roughness, we simulated its effect on smooth model wings using physical models. This manipulation shows that laminar flow is reduced and drag increased at high speeds. At the speeds at which swifts cruise, however, swift-like roughness prolongs laminar flow and reduces drag. This feature gives small birds with rudimentary wings an edge during the evolution of glide performance. PMID:24964089
Gliding Swifts Attain Laminar Flow over Rough Wings
Lentink, David; de Kat, Roeland
2014-01-01
Swifts are among the most aerodynamically refined gliding birds. However, the overlapping vanes and protruding shafts of their primary feathers make swift wings remarkably rough for their size. Wing roughness height is 1–2% of chord length on the upper surface—10,000 times rougher than sailplane wings. Sailplanes depend on extreme wing smoothness to increase the area of laminar flow on the wing surface and minimize drag for extended glides. To understand why the swift does not rely on smooth wings, we used a stethoscope to map laminar flow over preserved wings in a low-turbulence wind tunnel. By combining laminar area, lift, and drag measurements, we show that average area of laminar flow on swift wings is 69% (n = 3; std 13%) of their total area during glides that maximize flight distance and duration—similar to high-performance sailplanes. Our aerodynamic analysis indicates that swifts attain laminar flow over their rough wings because their wing size is comparable to the distance the air travels (after a roughness-induced perturbation) before it transitions from laminar to turbulent. To interpret the function of swift wing roughness, we simulated its effect on smooth model wings using physical models. This manipulation shows that laminar flow is reduced and drag increased at high speeds. At the speeds at which swifts cruise, however, swift-like roughness prolongs laminar flow and reduces drag. This feature gives small birds with rudimentary wings an edge during the evolution of glide performance. PMID:24964089
Advanced stability theory analyses for laminar flow control
NASA Technical Reports Server (NTRS)
Orszag, S. A.
1980-01-01
Recent developments of the SALLY computer code for stability analysis of laminar flow control wings are summarized. Extensions of SALLY to study three dimensional compressible flows, nonparallel and nonlinear effects are discussed.
Radiative interactions in laminar duct flows
NASA Technical Reports Server (NTRS)
Trivedi, P. A.; Tiwari, S. N.
1990-01-01
Analyses and numerical procedures are presented for infrared radiative energy transfer in gases when other modes of energy transfer occur simultaneously. Two types of geometries are considered, a parallel plate duct and a circular duct. Fully developed laminar incompressible flows of absorbing-emitting species in black surfaced ducts are considered under the conditions of uniform wall heat flux. The participating species considered are OH, CO, CO2, and H2O. Nongray as well as gray formulations are developed for both geometries. Appropriate limiting solutions of the governing equations are obtained and conduction-radiation interaction parameters are evaluated. Tien and Lowder's wide band model correlation was used in nongray formulation. Numerical procedures are presented to solve the integro-differential equations for both geometries. The range of physical variables considered are 300 to 2000 K for temperature, 0.1 to 100.0 atm for pressure, and 0.1 to 100 cm spacings between plates/radius of the tube. An extensive parametric study based on nongray formulation is presented. Results obtained for different flow conditions indicate that the radiative interactions can be quite significant in fully developed incompressible flows.
Inductively coupled plasma torch with laminar flow cooling
Rayson, Gary D.; Shen, Yang
1991-04-30
An improved inductively coupled gas plasma torch. The torch includes inner and outer quartz sleeves and tubular insert snugly fitted between the sleeves. The insert includes outwardly opening longitudinal channels. Gas flowing through the channels of the insert emerges in a laminar flow along the inside surface of the outer sleeve, in the zone of plasma heating. The laminar flow cools the outer sleeve and enables the torch to operate at lower electrical power and gas consumption levels additionally, the laminar flow reduces noise levels in spectroscopic measurements of the gaseous plasma.
Laminar Flow Control Leading Edge Systems in Simulated Airline Service
NASA Technical Reports Server (NTRS)
Wagner, R. D.; Maddalon, D. V.; Fisher, D. F.
1988-01-01
Achieving laminar flow on the wings of a commercial transport involves difficult problems associated with the wing leading edge. The NASA Leading Edge Flight Test Program has made major progress toward the solution of these problems. The effectiveness and practicality of candidate laminar flow leading edge systems were proven under representative airline service conditions. This was accomplished in a series of simulated airline service flights by modifying a JetStar aircraft with laminar flow leading edge systems and operating it out of three commercial airports in the United States. The aircraft was operated as an airliner would under actual air traffic conditions, in bad weather, and in insect infested environments.
Current Laminar Flow Control Experiments at NASA Dryden
NASA Technical Reports Server (NTRS)
Bowers, Al
2010-01-01
An experiment to demonstrate laminar flow over the swept wing of a subsonic transport is being developed. Discrete Roughness Elements are being used to maintain laminar flow over a substantial portion of a wing glove. This passive laminar flow technology has only come to be recognized as a significant player in airliner drag reduction in the last few years. NASA is implementing this experiment and is planning to demonstrate this technology at full-scale Bight cruise conditions of a small-to-medium airliner.
A model for predicting laminar gas flow through micropassages
NASA Astrophysics Data System (ADS)
Li, Jun-Ming; Wang, Bu-Xuan; Peng, Xiao-Feng
1997-12-01
An theoretical investigation was conducted to detect the gas-solid interface effect on laminar flow characteristics for gas flowing through micropassages. In the wall-adjacent region, the change in viscosity of fluid vs the distance from the wall surface, as derived from the kinetic theory of gases result in significant influence on the flow characteristics in micropassages. A model was proposed to account for the wall effect. Analytical expressions for velocity profiles and pressure drop were derived, respectively, for laminar flow of gases in microtubes and in extremely narrow parallel plates. The Knudsen number, Kn, as a criterion, that the flow can be treated reasonably as flow in macrochannels, is discussed.
NASA Technical Reports Server (NTRS)
Braslow, A. L.
1999-01-01
The paper contains the following sections: Foreword; Preface; Laminar-Flow Control Concepts and Scope of Monograph; Early Research on Suction-Type Laminar-Flow Control (Research from the 1930s through the War Years; Research from after World War II to the Mid-1960s); Post X-21 Research on Suction-Type Laminar-Flow Control; Status of Laminar-Flow Control Technology in the Mid-1990s; Glossary; Document 1-Aeronautics Panel, AACB, R&D Review, Report of the Subpanel on Aeronautic Energy Conservation/Fuels; Document 2-Report of Review Group on X-21A Laminar Flow Control Program; Document 3-Langley Research Center Announcement, Establishment of Laminar Flow Control Working Group; Document 4-Intercenter Agreement for Laminar Flow Control Leading Edge Glove Flights, LaRC and DFRC; Document 5-Flight Report NLF-144, of AFTIF-111 Aircraft with the TACT Wing Modified by a Natural Laminar Flow Glove; Document 6-Flight Record, F-16XL Supersonic Laminar Flow Control Aircraft; Index; and About the Author.
Formation of coherent structures in 3D laminar mixing flows
NASA Astrophysics Data System (ADS)
Speetjens, Michel; Clercx, Herman
2009-11-01
Mixing under laminar flow conditions is key to a wide variety of industrial systems of size extending from microns to meters. Examples range from the traditional (and still very relevant) mixing of viscous fluids via compact processing equipment down to emerging micro-fluidics applications. Profound insight into laminar mixing mechanisms is imperative for further advancement of mixing technology (particularly for complex micro-fluidics systems) yet remains limited to date. The present study concentrates on a fundamental transport phenomenon of potential relevance to laminar mixing: the formation of coherent structures in the web of 3D fluid trajectories due to fluid inertia. Such coherent structures geometrically determine the transport properties of the flow and better understanding of their formation and characteristics may offer ways to control and manipulate the mixing properties of laminar flows. The formation of coherent structures and its impact upon 3D transport properties is demonstrated by way of examples.
Lockheed laminar-flow control systems development and applications
NASA Technical Reports Server (NTRS)
Lange, Roy H.
1987-01-01
Progress is summarized from 1974 to the present in the practical application of laminar-flow control (LFC) to subsonic transport aircraft. Those efforts included preliminary design system studies of commercial and military transports and experimental investigations leading to the development of the leading-edge flight test article installed on the NASA JetStar flight test aircraft. The benefits of LFC on drag, fuel efficiency, lift-to-drag ratio, and operating costs are compared with those for turbulent flow aircraft. The current activities in the NASA Industry Laminar-Flow Enabling Technologies Development contract include summaries of activities in the Task 1 development of a slotted-surface structural concept using advanced aluminum materials and the Task 2 preliminary conceptual design study of global-range military hybrid laminar flow control (HLFC) to obtain data at high Reynolds numbers and at Mach numbers representative of long-range subsonic transport aircraft operation.
Brief history of laminar flow clean room systems
Whitfield, W J
1981-01-01
This paper reviews the development and evolution of laminar flow clean rooms and hoods and describes the underlying principles and rationales associated with development of this type of clean room system and Federal Standard No. 209. By the mid 1970's, over a thousand hospitals in the US had installed laminar flow equipment in operating rooms. During the past several years a great deal of attention has been focused on conserving energy in clean rooms. Some gains in energy conservation have been achieved by improved design, off hours shutdown, and closer evaluation of requirements for clean rooms. By the early 1970's, the laminar flow principle had been carried from the Laboratory and applied to production hardware to create a mature industry producing and marketing a variety of laminar flow equipment in less than 10 years time. This achievement was made possible by literally dozens of persons in industry, government, military, and private individuals who developed hardware, added numerous innovations, and had the foresight to apply the technology to many fields other than industrial clean rooms. Now, with laminar flow devices available, class 100 levels are readily achievable and maintained, and at the same time require fewer operating restrictions than previously possible.
Postfragmentation density function for bacterial aggregates in laminar flow
NASA Astrophysics Data System (ADS)
Byrne, Erin; Bortz, David M.; Dzul, Steve; Solomon, Michael; Younger, John
2011-04-01
The postfragmentation probability density of daughter flocs is one of the least well-understood aspects of modeling flocculation. We use three-dimensional positional data of Klebsiella pneumoniae bacterial flocs in suspension and the knowledge of hydrodynamic properties of a laminar flow field to construct a probability density function of floc volumes after a fragmentation event. We provide computational results which predict that the primary fragmentation mechanism for large flocs is erosion. The postfragmentation probability density function has a strong dependence on the size of the original floc and indicates that most fragmentation events result in clumps of one to three bacteria eroding from the original floc. We also provide numerical evidence that exhaustive fragmentation yields a limiting density inconsistent with the log-normal density predicted in the literature, most likely due to the heterogeneous nature of K. pneumoniae flocs. To support our conclusions, artificial flocs were generated and display similar postfragmentation density and exhaustive fragmentation.
Laminar natural convection in right triangular enclosures
NASA Astrophysics Data System (ADS)
Fuad Kent, E.; Asmaz, E.; Ozerbay, S.
2007-12-01
In this study, natural convection in non-rectangular enclosures is analyzed numerically. Streamlines and isotherms are presented for different triangular enclosures with different boundary conditions and Rayleigh numbers. Mean Nusselt numbers on hot walls are also calculated in order to make comparisons between different cases. The solutions are obtained for different aspect ratios where boundary conditions represent the wintertime heating of an attic space. This made possible to investigate the effect of aspect ratio on natural convection. In this study, quarter circular enclosure, which is very similar to right triangles, is also examined. Consequently, we had the opportunity to analyze how shape changes affect the flow pattern. The results of the calculations are compared with the similar enclosures and boundary conditions.
Method and apparatus for detecting laminar flow separation and reattachment
NASA Technical Reports Server (NTRS)
Stack, John P. (Inventor); Mangalam, Sivaramakrishnan M. (Inventor)
1989-01-01
The invention is a method and apparatus for detecting laminar flow separation and flow reattachment of a fluid stream by simultaneously sensing and comparing a plurality of output signals, each representing the dynamic shear stress at one of an equal number of sensors spaced along a straight line on the surface of an airfoil or the like that extends parallel to the fluid stream. The output signals are concurrently compared to detect the sensors across which a reversal in phase of said output signal occurs, said detected sensors being in the region of laminar separation or reattachment. The novelty in this invention is the discovery and use of the phase reversal phenomena to detect laminar separation and attachment of a fluid stream from any surface such as an airfoil supported therein.
Combustion characteristics of the end burning hybrid rockets in laminar flow
NASA Astrophysics Data System (ADS)
Matsuoka, Tsuneyoshi; Nagata, Harunori
2011-01-01
In this study, we aim to clarify the blowoff mechanism for flame spreading in an opposed laminar flow in narrow solid fuel ducts. To clarify this mechanism we conducted two experiments. First, we observed the changes of the flame spread rate at various oxygen velocities, ambient pressures, and port diameters. For flame spreading in laminar flow, combustion modes could be classified into 3 distinct regimes based on the strength of the opposed flow, i.e., chemical regime, thermal regime, and stabilized regime. This result is consistent with the result in turbulent flow. In the stabilized regime, quenching distance is almost constant despite oxygen velocity. In order to investigate the effect of ambient pressure and port diameter of fuels on blowoff limit, transition oxygen velocity is observed. As a result, transition oxygen velocity is proportional to the logarithm of the ambient pressure and port diameter. This relation is applicable despite the flow condition. Furthermore, we calculated velocity gradient at the fuel surface to reveal the determining factor of the blowoff limit in laminar flow. Consequently, velocity gradient, which is considered to dominate flow separation in laminar flow, would not be constant. This is because the velocity gradient at the fuel surface could not be evaluated by only the assumption of Hagen-Poiseuille flow but other parameters, such as vaporized fuel gas and natural convection by buoyancy should be included.
Laminar/turbulent oscillating flow in circular pipes
NASA Technical Reports Server (NTRS)
Ahn, Kyung H.; Ibrahim, Mounir B.
1992-01-01
A two-dimensional oscillating flow analysis was conducted simulating the gas flow inside Stirling engine heat exchangers. Both laminar and turbulent oscillating pipe flow were investigated numerically for Re(max) = 1920 (Va = 80), 10,800 (Va = 272), 19,300 (Va = 272), and 60,800 (Va = 126). The results are compared with experimental results of previous investigators. Predictions of the flow regime are also checked by comparing velocity amplitudes and phase difference with those from laminar theory and quasi-steady profile. A high Reynolds number k-epsilon turbulence model was used for turbulent oscillating pipe flow. Finally, the performance of the k-epsilon model was evaluated to explore the applicability of quasi-steady turbulent models to unsteady oscillating flow analysis.
Biomimetic structures for fluid drag reduction in laminar and turbulent flows.
Jung, Yong Chae; Bhushan, Bharat
2010-01-27
Biomimetics allows one to mimic nature to develop materials and devices of commercial interest for engineers. Drag reduction in fluid flow is one of the examples found in nature. In this study, nano, micro, and hierarchical structures found in lotus plant surfaces, as well as shark skin replica and a rib patterned surface to simulate shark skin structure were fabricated. Drag reduction efficiency studies on the surfaces were systematically carried out using water flow. An experimental flow channel was used to measure the pressure drop in laminar and turbulent flows, and the trends were explained in terms of the measured and predicted values by using fluid dynamics models. The slip length for various surfaces in laminar flow was also investigated based on the measured pressure drop. For comparison, the pressure drop for various surfaces was also measured using air flow.
Incomplete mixing and reactions in laminar shear flow
NASA Astrophysics Data System (ADS)
Paster, A.; Aquino, T.; Bolster, D.
2015-07-01
Incomplete mixing of reactive solutes is well known to slow down reaction rates relative to what would be expected from assuming perfect mixing. In purely diffusive systems, for example, it is known that small initial fluctuations in reactant concentrations can lead to reactant segregation, which in the long run can reduce global reaction rates due to poor mixing. In contrast, nonuniform flows can enhance mixing between interacting solutes. Thus, a natural question arises: Can nonuniform flows sufficiently enhance mixing to restrain incomplete mixing effects and, if so, under what conditions? We address this question by considering a specific and simple case, namely, a laminar pure shear reactive flow. Two solution approaches are developed: a Lagrangian random walk method and a semianalytical solution. The results consistently highlight that if shear effects in the system are not sufficiently strong, incomplete mixing effects initially similar to purely diffusive systems will occur, slowing down the overall reaction rate. Then, at some later time, dependent on the strength of the shear, the system will return to behaving as if it were well mixed, but represented by a reduced effective reaction rate.
Electrostatic quadrupole focused particle accelerating assembly with laminar flow beam
Maschke, Alfred W.
1985-01-01
A charged particle accelerating assembly provided with a predetermined ratio of parametric structural characteristics and with related operating voltages applied to each of its linearly spaced focusing and accelerating quadrupoles, thereby to maintain a particle beam traversing the electrostatic fields of the quadrupoles in the assembly in an essentially laminar flow throughout the assembly.
Electrostatic quadrupole focused particle accelerating assembly with laminar flow beam
Maschke, A.W.
1984-04-16
A charged particle accelerating assembly provided with a predetermined ratio of parametric structural characteristics and with related operating voltages applied to each of its linearly spaced focusing and accelerating quadrupoles, thereby to maintain a particle beam traversing the electrostatic fields of the quadrupoles in the assembly in an essentially laminar flow through the assembly.
Application of porous materials for laminar flow control
NASA Technical Reports Server (NTRS)
Pearce, W. E.
1978-01-01
Fairly smooth porous materials were elected for study Doweave; Fibermetal; Dynapore; and perforated titanium sheet. Factors examined include: surface smoothness; suction characteristics; porosity; surface impact resistance; and strain compatibility. A laminar flow control suction glove arrangement was identified with material combinations compatible with thermal expansion and structural strain.
Analytical solution of laminar-laminar stratified two-phase flows with curved interfaces
Brauner, N.; Rovinsky, J.; Maron, D.M.
1995-09-01
The present study represents a complete analytical solution for laminar two-phase flows with curved interfaces. The solution of the Navier-Stokes equations for the two-phases in bipolar coordinates provides the `flow monograms` describe the relation between the interface curvature and the insitu flow geometry when given the phases flow rates and viscosity ratios. Energy considerations are employed to construct the `interface monograms`, whereby the characteristic interfacial curvature is determined in terms of the phases insitu holdup, pipe diameter, surface tension, fluids/wall adhesion and gravitation. The two monograms are then combined to construct the system `operational monogram`. The `operational monogram` enables the determination of the interface configuration, the local flow characteristics, such as velocity profiles, wall and interfacial shear stresses distribution as well as the integral characteristics of the two-phase flow: phases insitu holdup and pressure drop.
F-16XL-2 Supersonic Laminar Flow Control Flight Test Experiment
NASA Technical Reports Server (NTRS)
Anders, Scott G.; Fischer, Michael C.
1999-01-01
The F-16XL-2 Supersonic Laminar Flow Control Flight Test Experiment was part of the NASA High-Speed Research Program. The goal of the experiment was to demonstrate extensive laminar flow, to validate computational fluid dynamics (CFD) codes and design methodology, and to establish laminar flow control design criteria. Topics include the flight test hardware and design, airplane modification, the pressure and suction distributions achieved, the laminar flow achieved, and the data analysis and code correlation.
Transition from laminar to turbulent flow in liquid filled microtubes
NASA Astrophysics Data System (ADS)
Sharp, K. V.; Adrian, R. J.
2004-05-01
The transition to turbulent flow is studied for liquids of different polarities in glass microtubes having diameters between 50 and 247 µm. The onset of transition occurs at Reynolds numbers of ~1,800 2,000, as indicated by greater-than-laminar pressure drop and micro-PIV measurements of mean velocity and rms velocity fluctuations at the centerline. Transition at anomalously low values of Reynolds number was never observed. Additionally, the results of more than 1,500 measurements of pressure drop versus flow rate confirm the macroscopic Poiseuille flow result for laminar flow resistance to within -1% systematic and ±2.5% rms random error for Reynolds numbers less than 1,800.
Laminar Flow Supersonic Wind Tunnel primary air injector
NASA Technical Reports Server (NTRS)
Smith, Brooke Edward
1993-01-01
This paper describes the requirements, design, and prototype testing of the flex-section and hinge seals for the Laminar Flow Supersonic Wind Tunnel Primary Injector. The supersonic atmospheric primary injector operates between Mach 1.8 and Mach 2.2 with mass-flow rates of 62 to 128 lbm/s providing the necessary pressure reduction to operate the tunnel in the desired Reynolds number (Re) range.
Advanced stability analysis for laminar flow control
NASA Technical Reports Server (NTRS)
Orszag, S. A.
1981-01-01
Five classes of problems are addressed: (1) the extension of the SALLY stability analysis code to the full eighth order compressible stability equations for three dimensional boundary layer; (2) a comparison of methods for prediction of transition using SALLY for incompressible flows; (3) a study of instability and transition in rotating disk flows in which the effects of Coriolis forces and streamline curvature are included; (4) a new linear three dimensional instability mechanism that predicts Reynolds numbers for transition to turbulence in planar shear flows in good agreement with experiment; and (5) a study of the stability of finite amplitude disturbances in axisymmetric pipe flow showing the stability of this flow to all nonlinear axisymmetric disturbances.
Self-pumping suction/propulsion for laminar flow bodies
NASA Astrophysics Data System (ADS)
Rogers, K. H.; King, D. A.
1984-06-01
An analysis is presented to investigate the feasibility of a self-pumping suction system for a very low drag suction laminar flow control (SLFC) underwater test body. The nose and afterbody of a torpedo-like body are contoured such that a prominent low-pressure region in the aft part of the body can serve as a suction pump to suck the boundary layer fluid through the circumferential surface-slots and thus laminarize the entire body length forward of the aft low-pressure peak. The results indicate that it is feasible to laminarize a test body in this fashion at a design speed, such as 40 knots; but that the laminarization of a particular configuration is limited to a band of speeds at and near the design speed. If an SLFC test body with a wide range of speed capability is desired, then a controllable-speed suction pump and controllable suction distribution along the body are indicated. The analysis includes a suction system design calculation example and should be a useful reference for future development of undersea SLFC vehicles.
Application of linear stability theory in laminar flow design
NASA Technical Reports Server (NTRS)
Iyer, Venkit; Spall, Robert
1991-01-01
The linear stability of fully three-dimensional supersonic boundary layers formed over swept-wing configurations is investigated using a modified version of the linear stability code COSAL. Configurations studied include a highly swept leading-edge model to be utilized for transition studies in the LARC Low-disturbance Mach 3.5 Pilot Tunnel. The model is a representation of the leading edge of a laminar flow control wing for the F-16XL aircraft. In addition, the region over a laminar flow control glove fitted on the midportion of an F-16XL wing was studied. For each configuration, estimates of the location of the onset of transition were computed using linear stability theory and the e exp N method. The effectiveness of suction in stabilizing the boundary layer over the F-16XL wing glove was also investigated.
Development of laminar flow control wing surface porous structure
NASA Technical Reports Server (NTRS)
Klotzsche, M.; Pearce, W.; Anderson, C.; Thelander, J.; Boronow, W.; Gallimore, F.; Brown, W.; Matsuo, T.; Christensen, J.; Primavera, G.
1984-01-01
It was concluded that the chordwise air collection method, which actually combines chordwise and spanwise air collection, is the best of the designs conceived up to this time for full chord laminar flow control (LFC). Its shallower ducting improved structural efficiency of the main wing box resulting in a reduction in wing weight, and it provided continuous support of the chordwise panel joints, better matching of suction and clearing airflow requirements, and simplified duct to suction source minifolding. Laminar flow control on both the upper and lower surfaces was previously reduced to LFC suction on the upper surface only, back to 85 percent chord. The study concludes that, in addition to reduced wing area and other practical advantages, this system would be lighter because of the increase in effective structural wing thickness.
Croze, Ottavio A.; Sardina, Gaetano; Ahmed, Mansoor; Bees, Martin A.; Brandt, Luca
2013-01-01
Shear flow significantly affects the transport of swimming algae in suspension. For example, viscous and gravitational torques bias bottom-heavy cells to swim towards regions of downwelling fluid (gyrotaxis). It is necessary to understand how such biases affect algal dispersion in natural and industrial flows, especially in view of growing interest in algal photobioreactors. Motivated by this, we here study the dispersion of gyrotactic algae in laminar and turbulent channel flows using direct numerical simulation (DNS) and a previously published analytical swimming dispersion theory. Time-resolved dispersion measures are evaluated as functions of the Péclet and Reynolds numbers in upwelling and downwelling flows. For laminar flows, DNS results are compared with theory using competing descriptions of biased swimming cells in shear flow. Excellent agreement is found for predictions that employ generalized Taylor dispersion. The results highlight peculiarities of gyrotactic swimmer dispersion relative to passive tracers. In laminar downwelling flow the cell distribution drifts in excess of the mean flow, increasing in magnitude with Péclet number. The cell effective axial diffusivity increases and decreases with Péclet number (for tracers it merely increases). In turbulent flows, gyrotactic effects are weaker, but discernable and manifested as non-zero drift. These results should have a significant impact on photobioreactor design. PMID:23407572
Ground vibration test of the laminar flow control JStar airplane
NASA Technical Reports Server (NTRS)
Kehoe, M. W.; Cazier, F. W., Jr.; Ellison, J. F.
1985-01-01
A ground vibration test was conducted on a Lockheed JetStar airplane that had been modified for the purpose of conducting laminar flow control experiments. The test was performed prior to initial flight flutter tests. Both sine-dwell and single-point-random excitation methods were used. The data presented include frequency response functions and a comparison of mode frequencies and mode shapes from both methods.
Making Large Suction Panels For Laminar-Flow Control
NASA Technical Reports Server (NTRS)
Maddalon, Dal V.
1991-01-01
Perforated titanium panels used to identify and resolve issues related to manufacture. Recently, relatively large suction panels with aerodynamically satisfactory surface perforations and with surface contours and smoothness characteristics necessary for Laminar-Flow Control (LFC) designed, fabricated, and tested. Requirements of production lines for commercial transport airplanes carefully considered in development of panels. Sizes of panels representative of what is used on wing of commercial transport airplane. Tests of perforated panels in transonic wind tunnel demonstrated aerodynamic stability at flight mach numbers.
NASA Astrophysics Data System (ADS)
Krygier, Michael; Grigoriev, Roman
2015-11-01
A direct transition from laminar to turbulent flow has recently been discovered experimentally in the small-gap Taylor-Couette flow with counter-rotating cylinders. The subcritical nature of this transition is a result of relatively small aspect ratio, Γ = 5 . 26 for large Γ the transition is supercritical and involves an intermediate stable state (Coughlin & Marcus, 1996) - interpenetrating spirals (IPS). We investigate this transition numerically to probe the dynamics in regimes inaccessible to experiments for a fixed Reo = - 1000 by varying Rei . The numerics reproduce all the experimentally observed features and confirm the hysteretic nature of the transition. As Rei is increased, the laminar flow transitions to turbulence, with an unstable IPS state mediating the transition, similar to the Tollmien-Schlichting waves in plane Poiseuille flow. As Rei is decreased, turbulent flow transitions to a stable, temporally chaotic IPS state. This IPS state further transitions to either laminar or turbulent flow as Rei is decreased or increased. The stable IPS state is reminiscent of the pre-turbulent chaotic states found numerically in plane Poiseuille flow (Zammert & Eckhardt, 2015), but previously never observed experimentally.
Boundary Layer Theory. Part 1; Laminar Flows
NASA Technical Reports Server (NTRS)
Schlichting, H.
1949-01-01
The purpose of this presentation is to give you a survey of a field of aerodynamics which has for a number of years been attracting an ever growing interest. The subject is the theory of flows with friction, and, within that field, particularly the theory of friction layers, or boundary layers. As you know, a great many considerations of aerodynamics are based on the so-called ideal fluid, that is, the frictionless incompressible fluid. By neglect of compressibility and friction the extensive mathematical theory of the ideal fluid (potential theory) has been made possible.
Laminar flow of two miscible fluids in a simple network
NASA Astrophysics Data System (ADS)
Karst, Casey M.; Storey, Brian D.; Geddes, John B.
2013-03-01
When a fluid comprised of multiple phases or constituents flows through a network, nonlinear phenomena such as multiple stable equilibrium states and spontaneous oscillations can occur. Such behavior has been observed or predicted in a number of networks including the flow of blood through the microcirculation, the flow of picoliter droplets through microfluidic devices, the flow of magma through lava tubes, and two-phase flow in refrigeration systems. While the existence of nonlinear phenomena in a network with many inter-connections containing fluids with complex rheology may seem unsurprising, this paper demonstrates that even simple networks containing Newtonian fluids in laminar flow can demonstrate multiple equilibria. The paper describes a theoretical and experimental investigation of the laminar flow of two miscible Newtonian fluids of different density and viscosity through a simple network. The fluids stratify due to gravity and remain as nearly distinct phases with some mixing occurring only by diffusion. This fluid system has the advantage that it is easily controlled and modeled, yet contains the key ingredients for network nonlinearities. Experiments and 3D simulations are first used to explore how phases distribute at a single T-junction. Once the phase separation at a single junction is known, a network model is developed which predicts multiple equilibria in the simplest of networks. The existence of multiple stable equilibria is confirmed experimentally and a criterion for existence is developed. The network results are generic and could be applied to or found in different physical systems.
Laminar-flow torch for helium inductively coupled plasma spectrometry
Tan, H.; Chan, S.K.; Montaser, A.
1988-11-15
Helium inductively coupled plasmas (He ICPs) operated at atmospheric pressure, possess two advantages compared to Ar ICPs for atomic emission spectrometry (AES) and mass spectrometry (MS). First, for the elements tested so far, the detection powers for the He ICPs are superior to those for an Ar discharge. Second, the emission background spectra of the He ICPs are quite simple in the red and the near-infrared regions, thus reducing the spectral interference problems encountered with the determination of halogens and other nonmetals. Relatedly, certain mass spectral interferences noted in the detection of monoisotopic elements are eliminated when helium is used as the plasma gas instead of argon. For the most recent studies of He ICPs, the authors used a tangential-flow torch to form an annular plasma at forward power of 1500 W with a total helium gas flow of 8 L/min. The present study is concerned with the formation and preliminary characterization of a He ICP using a laminar-flow torch. The total helium gas flow for this torch is less than 2 L/min. Studies of plasmas formed in laminar-flow torches are important because of the possibility to reduce one major source of noise resulting from the rotation of the plasma gas in tangential-flow torches.
Analysis of Laminar Incompressible Flow on Semiporous Channels
NASA Technical Reports Server (NTRS)
Donoughe, Patrick L
1956-01-01
Perturbation solutions for laminar incompressible flow in semiporous and fully porous channels are compared. The perturbation parameter measures the amount of suction or blowing at the porous wall. The velocity profile and the wall friction parameter are more affected by suction or blowing for the semiporous channel than for the fully porous channel. For blowing through the wall, the pressure decreases in channel direction for both channels; with sufficiently high suction rates, the analysis showed that the pressure rises in flow direction for the fully porous channel.
Oscillating laminar electrokinetic flow in infinitely extended rectangular microchannels.
Yang, J; Bhattacharyya, A; Masliyah, J H; Kwok, D Y
2003-05-01
This paper has addressed analytically the problem of laminar flow in microchannels with rectangular cross-section subjected to a time-dependent sinusoidal pressure gradient and a sinusoidal electric field. The analytical solution has been determined based on the Debye-Hückel approximation of a low surface potential at the channel wall. We have demonstrated that Onsager's principle of reciprocity is valid for this problem. Parametric studies of streaming potential have shown the dependence of the electroviscous effect not only on the Debye length, but also on the oscillation frequency and the microchannel width. Parametric studies of electroosmosis demonstrate that the flow rate decreases due to an increase in frequency. The obtained solutions for both the streaming potential and electroosmotic flows become those for flow between two parallel plates in the limit of a large aspect ratio. PMID:12725820
Transient radiative energy transfer in incompressible laminar flows
NASA Technical Reports Server (NTRS)
Tiwari, S. N.; Singh, D. J.
1987-01-01
Analysis and numerical procedures are presented to investigate the transient radiative interactions of nongray absorbing-emitting species in laminar fully-developed flows between two parallel plates. The particular species considered are OH, CO, CO2, and H2O and different mixtures of these. Transient and steady-state results are obtained for the temperaure distribution and bulk temperature for different plate spacings, wall temperatures, and pressures. Results, in general, indicate that the rate of radiative heating can be quite high during earlier times. This information is useful in designing thermal protection systems for transient operations.
Aircraft energy efficiency laminar flow control wing design study
NASA Technical Reports Server (NTRS)
Bonner, T. F., Jr.; Pride, J. D., Jr.; Fernald, W. W.
1977-01-01
An engineering design study was performed in which laminar flow control (LFC) was integrated into the wing of a commercial passenger transport aircraft. A baseline aircraft configuration was selected and the wing geometry was defined. The LFC system, with suction slots, ducting, and suction pumps was integrated with the wing structure. The use of standard aluminum technology and advanced superplastic formed diffusion bonded titanium technology was evaluated. The results of the design study show that the LFC system can be integrated with the wing structure to provide a structurally and aerodynamically efficient wing for a commercial transport aircraft.
Predicting Transition from Laminar to Turbulent Flow over a Surface
NASA Technical Reports Server (NTRS)
Rajnarayan, Dev (Inventor); Sturdza, Peter (Inventor)
2016-01-01
A prediction of whether a point on a computer-generated surface is adjacent to laminar or turbulent flow is made using a transition prediction technique. A plurality of instability modes are obtained, each defined by one or more mode parameters. A vector of regressor weights is obtained for the known instability growth rates in a training dataset. For an instability mode in the plurality of instability modes, a covariance vector is determined. A predicted local instability growth rate at the point is determined using the covariance vector and the vector of regressor weights. Based on the predicted local instability growth rate, an n-factor envelope at the point is determined.
Low temperature high current ion beams and laminar flows
NASA Astrophysics Data System (ADS)
Cavenago, Marco
2014-07-01
Self-consistent Vlasov-Poisson equilibria for the extraction of ions with low temperature Ti are discussed, with comparison to the laminar flow case Ti = 0, in two dimensional diodes. Curvilinear coordinates aligned with laminar beam flow lines are extended to the low ion temperature case, with a reduced current density jd, expressed with cathode integrals. This generalizes one-dimensional interpolation between rays along the cathode coordinate to multidimensional integrations, including also the momentum components, so that jd is free from the granularity defect and noise, typical of standard ray tracing approach. A robust numerical solution procedure is developed, which allows studying current saturated extraction and drift tube effects. A discussion of particle initial conditions determines the emission angles and shows that temperature effect at beam edge is partly balanced by the focus electrode inclination. Results for a typical diode are described, with detail about normalized emittance, here taken strictly proportional to the x - px phase space area, for a beam with non uniform velocities. Contribution to the Topical Issue "Theory and Applications of the Vlasov Equation", edited by Francesco Pegoraro, Francesco Califano, Giovanni Manfredi and Philip J. Morrison.
Numerical simulation of laminar flow in a curved duct
Lopez, A.R.; Oberkampf, W.L.
1995-01-01
This paper describes numerical simulations that were performed to study laminar flow through a square duct with a 900 bend. The purpose of this work was two fold. First, an improved understanding was desired of the flow physics involved in the generation of secondary vortical flows in three-dimensions. Second, adaptive gridding techniques for structured grids in three- dimensions were investigated for the purpose of determining their utility in low Reynolds number, incompressible flows. It was also of interest to validate the commercial computer code CFD-ACE. Velocity predictions for both non-adaptive and adaptive grids are compared with experimental data. Flow visualization was used to examine the characteristics of the flow though the curved duct in order to better understand the viscous flow physics of this problem. Generally, moderate agreement with the experimental data was found but shortcomings in the experiment were demonstrated. The adaptive grids did not produce the same level of accuracy as the non-adaptive grid with a factor of four more grid points.
Heat transport in laminar flow of erythrocyte suspensions.
Ahuja, A S
1975-07-01
Measurements of thermal conductivity were made in laminar flow of dog and turkey erythrocyte suspensions in a stainless stell tube of about 1 mm ID. These measurements were independent of the shear rate, showing that the red cell motion relative to plasma in flowing blood had no effect on the heat transfer. Measurements of thermal conductivity were further made in suspensions of polystyrene spheres of 100 mum and were found to be dependent upon the shear rate. The Graetz solution corresponding to uniform wall temperature was used for determining the value of thermal conductivity in an apparatus calibrated with tap water. The overall accuracy of the results is within 10%. A model based on the particle rotation with the entrained fluid is proposed. It is pointed out that the diffusion of platelets, red cells, and possibly plasma proteins (such as fibrinogen) will be augmented if they happen to be in the hydrodynamic field of rotating erythrocytes. PMID:1150598
Predicting Transition from Laminar to Turbulent Flow over a Surface
NASA Technical Reports Server (NTRS)
Rajnarayan, Dev (Inventor); Sturdza, Peter (Inventor)
2013-01-01
A prediction of whether a point on a computer-generated surface is adjacent to laminar or turbulent flow is made using a transition prediction technique. A plurality of boundary-layer properties at the point are obtained from a steady-state solution of a fluid flow in a region adjacent to the point. A plurality of instability modes are obtained, each defined by one or more mode parameters. A vector of regressor weights is obtained for the known instability growth rates in a training dataset. For each instability mode in the plurality of instability modes, a covariance vector is determined, which is the covariance of a predicted local growth rate with the known instability growth rates. Each covariance vector is used with the vector of regressor weights to determine a predicted local growth rate at the point. Based on the predicted local growth rates, an n-factor envelope at the point is determined.
Laminar boundary-layer flow of non-Newtonian fluid
NASA Technical Reports Server (NTRS)
Lin, F. N.; Chern, S. Y.
1979-01-01
A solution for the two-dimensional and axisymmetric laminar boundary-layer momentum equation of power-law non-Newtonian fluid is presented. The analysis makes use of the Merk-Chao series solution method originally devised for the flow of Newtonian fluid. The universal functions for the leading term in the series are tabulated for n from 0.2 to 2. Equations governing the universal functions associated with the second and the third terms are provided. The solution together with either Lighthill's formula or Chao's formula constitutes a simple yet general procedure for the calculation of wall shear and surface heat transfer rate. The theory was applied to flows over a circular cylinder and a sphere and the results compared with published data.
Heat transport in laminar flow of erythrocyte suspensions.
Ahuja, A S
1975-07-01
Measurements of thermal conductivity were made in laminar flow of dog and turkey erythrocyte suspensions in a stainless stell tube of about 1 mm ID. These measurements were independent of the shear rate, showing that the red cell motion relative to plasma in flowing blood had no effect on the heat transfer. Measurements of thermal conductivity were further made in suspensions of polystyrene spheres of 100 mum and were found to be dependent upon the shear rate. The Graetz solution corresponding to uniform wall temperature was used for determining the value of thermal conductivity in an apparatus calibrated with tap water. The overall accuracy of the results is within 10%. A model based on the particle rotation with the entrained fluid is proposed. It is pointed out that the diffusion of platelets, red cells, and possibly plasma proteins (such as fibrinogen) will be augmented if they happen to be in the hydrodynamic field of rotating erythrocytes.
Stability theory applications to laminar-flow control
NASA Technical Reports Server (NTRS)
Malik, Mujeeb R.
1987-01-01
In order to design Laminar Flow Control (LFC) configurations, reliable methods are needed for boundary-layer transition predictions. Among the available methods, there are correlations based upon R sub e, shape factors, Goertler number and crossflow Reynolds number. The most advanced transition prediction method is based upon linear stability theory in the form of the e sup N method which has proven to be successful in predicting transition in two- and three-dimensional boundary layers. When transition occurs in a low disturbance environment, the e sup N method provides a viable design tool for transition prediction and LFC in both 2-D and 3-D subsonic/supersonic flows. This is true for transition dominated by either TS, crossflow, or Goertler instability. If Goertler/TS or crossflow/TS interaction is present, the e sup N will fail to predict transition. However, there is no evidence of such interaction at low amplitudes of Goertler and crossflow vortices.
On laminar separation at a corner point in transonic flow
NASA Astrophysics Data System (ADS)
Ruban, A. I.; Turkyilmaz, I.
2000-11-01
The separation of the laminar boundary layer from a convex corner on a rigid body contour in transonic flow is studied based on the asymptotic analysis of the Navier Stokes equations at large values of the Reynolds number. It is shown that the flow in a small vicinity of the separation point is governed, as usual, by strong interaction between the boundary layer and the inviscid part of the flow. Outside the interaction region the Kármán Guderley equation describing transonic inviscid flow admits a self-similar solution with the pressure on the body surface being proportional to the cubic root of the distance from the separation point. Analysis of the boundary layer driven by this pressure shows that as the interaction region is approached the boundary layer splits into two parts: the near-wall viscous sublayer and the main body of the boundary layer where the flow is locally inviscid. It is interesting that contrary to what happens in subsonic and supersonic flows, the displacement effect of the boundary layer is primarily due to the inviscid part. The contribution of the viscous sublayer proves to be negligible to the leading order. Consequently, the flow in the interaction region is governed by the inviscid inviscid interaction. To describe this flow one needs to solve the Kármán Guderley equation for the potential flow region outside the boundary layer; the solution in the main part of the boundary layer was found in an analytical form, thanks to which the interaction between the boundary layer and external flow can be expressed via the corresponding boundary condition for the Kármán Guderley equation. Formulation of the interaction problem involves one similarity parameter which in essence is the Kármán Guderley parameter suitably modified for the flow at hand. The solution of the interaction problem has been constructed numerically.
Transonic flight test of a laminar flow leading edge with surface excrescences
NASA Technical Reports Server (NTRS)
Zuniga, Fanny A.; Drake, Aaron; Kennelly, Robert A., Jr.; Koga, Dennis J.; Westphal, Russell V.
1994-01-01
A flight experiment, conducted at NASA Dryden Flight Research Center, investigated the effects of surface excrescences, specifically gaps and steps, on boundary-layer transition in the vicinity of a leading edge at transonic flight conditions. A natural laminar flow leading-edge model was designed for this experiment with a spanwise slot manufactured into the leading-edge model to simulate gaps and steps like those present at skin joints of small transonic aircraft wings. The leading-edge model was flown with the flight test fixture, a low-aspect ratio fin mounted beneath an F-104G aircraft. Test points were obtained over a unit Reynolds number range of 1.5 to 2.5 million/ft and a Mach number range of 0.5 to 0.8. Results for a smooth surface showed that laminar flow extended to approximately 12 in. behind the leading edge at Mach number 0.7 over a unit Reynolds number range of 1.5 to 2.0 million/ft. The maximum size of the gap-and-step configuration over which laminar flow was maintained consisted of two 0.06-in. gaps with a 0.02-in. step at a unit Reynolds number of 1.5 million/ft.
Oscillating laminar electrokinetic flow in infinitely extended circular microchannels.
Bhattacharyya, A; Masliyah, J H; Yang, J
2003-05-01
This article addresses the problem of oscillating laminar electrokinetic liquid flow in an infinitely extended circular microchannel. Based on the Debye-Huckel approximation for low surface potential at the channel wall, a complex variable approach is used to obtain an analytical solution for the flow. The complex counterparts of the flow rate and the current are linearly dependent on the pressure gradient and the external electric field. This property is used to show that Onsager's principle of reciprocity continues to be valid (involving the complex quantities) for the stated problem. During oscillating pressure-driven flow, the electroviscous effect for a given value of the normalized reciprocal electrical double-layer (EDL) thickness is observed to attain a maximum at a certain normalized frequency. In general, an increasing normalized frequency results in a reduction of EDL effects, leading to (i). a volumetric flow rate in the case of streaming potential approaching that predicted by the theory without EDL effects, and (ii). a reduction in the volumetric flow rate in the case of electroosmosis. PMID:12725819
The effect of mako sharkskin on laminar flow separation
NASA Astrophysics Data System (ADS)
Bradshaw, Michael; Lang, Amy; Motta, Philip; Habegger, Maria; Hueter, Robert
2013-11-01
Many animals possess effective performance enhancing mechanisms, such as the denticles found on the skin of the shortfin mako shark (Isurus oxyrinchus). The shortfin mako, one of the fastest sharks on the planet, is covered by small, tooth-like scales that vary in flexibility over the body. Previous biological findings have shown that the scales increase in flexibility from the leading to trailing edge over the pectoral fin as well as on various sections of the body. It is believed that the scale bristling may provide a mechanism for flow separation control that leads to decreased drag and increased maneuverability. This study involved testing a left pectoral fin of a shortfin mako shark as well as a cylinder with a sharkskin specimen applied circumferentially in a water tunnel facility under static, laminar conditions. Digital Particle Image Velocimetry (DPIV) was used to characterize the flow over the surfaces. Various Reynolds numbers were tested for both configurations, as well as several AOAs for the pectoral fin. The flow over the fin and cylinder were compared to a painted fin and a smooth PVC cylinder, respectively. The study found that the shark scales do, in fact, help to control flow separation. However, in order for the scales to bristle and trap the reversing flow, a certain magnitude of reversed flow and shear is required. This phenomenon seems to be most effective at near stall conditions and at higher Reynolds numbers. Support from REU grant 1062611 is greatfully acknowledged.
Laminar flow control leading edge glove flight test article development
NASA Technical Reports Server (NTRS)
Pearce, W. E.; Mcnay, D. E.; Thelander, J. A.
1984-01-01
A laminar flow control (LFC) flight test article was designed and fabricated to fit into the right leading edge of a JetStar aircraft. The article was designed to attach to the front spar and fill in approx. 70 inches of the leading edge that are normally occupied by the large slipper fuel tank. The outer contour of the test article was constrained to align with an external fairing aft of the front spar which provided a surface pressure distribution over the test region representative of an LFC airfoil. LFC is achieved by applying suction through a finely perforated surface, which removes a small fraction of the boundary layer. The LFC test article has a retractable high lift shield to protect the laminar surface from contamination by airborne debris during takeoff and low altitude operation. The shield is designed to intercept insects and other particles that could otherwise impact the leading edge. Because the shield will intercept freezing rain and ice, a oozing glycol ice protection system is installed on the shield leading edge. In addition to the shield, a liquid freezing point depressant can be sprayed on the back of the shield.
Aerodynamic study of a small wind turbine with emphasis on laminar and transition flows
NASA Astrophysics Data System (ADS)
Niculescu, M. L.; Cojocaru, M. G.; Crunteanu, D. E.
2016-06-01
The wind energy is huge but unfortunately, wind turbines capture only a little part of this enormous green energy. Furthermore, it is impossible to put multi megawatt wind turbines in the cities because they generate a lot of noise and discomfort. Instead, it is possible to install small Darrieus and horizontal-axis wind turbines with low tip speed ratios in order to mitigate the noise as much as possible. Unfortunately, the flow around this wind turbine is quite complex because the run at low Reynolds numbers. Therefore, this flow is usually a mixture of laminar, transition and laminar regimes with bubble laminar separation that is very difficult to simulate from the numerical point of view. Usually, transition and laminar regimes with bubble laminar separation are ignored. For this reason, this paper deals with laminar and transition flows in order to provide some brightness in this field.
Lecture Series "Boundary Layer Theory". Part I - Laminar Flows. Part 1; Laminar Flows
NASA Technical Reports Server (NTRS)
Schlichting, H.
1949-01-01
In the lecture series starting today author want to give a survey of a field of aerodynamics which has for a number of years been attracting an ever growing interest. The subject is the theory of flows with friction, and, within that field, particularly the theory of friction layers, or boundary layers. A great many considerations of aerodynamics are based on the ideal fluid, that is the frictionless incompressibility and fluid. By neglect of compressibility and friction the extensive mathematical theory of the ideal fluid, (potential theory) has been made possible. Actual liquids and gases satisfy the condition of incomressibility rather well if the velocities are not extremely high or, more accurately, if they are small in comparison with sonic velocity. For air, for instance, the change in volume due to compressibility amounts to about 1 percent for a velocity of 60 meters per second. The hypothesis of absence of friction is not satisfied by any actual fluid; however, it is true that most technically important fluids, for instance air and water, have a very small friction coefficient and therefore behave in many cases almost like the ideal frictionless fluid. Many flow phenomena, in particular most cases of lift, can be treated satisfactorily, - that is, the calculations are in good agreement with the test results, -under the assumption of frictionless fluid. However, the calculations with frictionless flow show a very serious deficiency; namely, the fact, known as d'Alembert's paradox, that in frictionless flow each body has zero drag whereas in actual flow each body experiences a drag of greater or smaller magnitude. For a long time the theory has been unable to bridge this gap between the theory of frictionless flow and the experimental findings about actual flow. The cause of this fundamental discrepancy is the viscosity which is neglected in the theory of ideal fluid; however, in spite of its extraordinary smallness it is decisive for the course of the flow
Numerical Solutions of Supersonic and Hypersonic Laminar Compression Corner Flows
NASA Technical Reports Server (NTRS)
Hung, C. M.; MacCormack, R. W.
1976-01-01
An efficient time-splitting, second-order accurate, numerical scheme is used to solve the complete Navier-Stokes equations for supersonic and hypersonic laminar flow over a two-dimensional compression corner. A fine, exponentially stretched mesh spacing is used in the region near the wall for resolving the viscous layer. Good agreement is obtained between the present computed results and experimental measurement for a Mach number of 14.1 and a Reynolds number of 1.04 x 10(exp 5) with wedge angles of 15 deg, 18 deg, and 24 deg. The details of the pressure variation across the boundary layer are given, and a correlation between the leading edge shock and the peaks in surface pressure and heat transfer is observed.
GASP cloud encounter statistics - Implications for laminar flow control flight
NASA Technical Reports Server (NTRS)
Jasperson, W. H.; Nastrom, G. D.; Davis, R. E.; Holdeman, J. D.
1984-01-01
The cloud observation archive from the NASA Global Atmospheric Sampling Program (GASP) is analyzed in order to derive the probability of cloud encounter at altitudes normally flown by commercial airliners, for application to a determination of the feasability of Laminar Flow Control (LFC) on long-range routes. The probability of cloud encounter is found to vary significantly with season. Several meteorological circulation features are apparent in the latitudinal distribution of cloud cover. The cloud encounter data are shown to be consistent with the classical midlatitude cyclone model with more clouds encountered in highs than in lows. Aircraft measurements of route-averaged time-in-clouds fit a gamma probability distribution model which is applied to estimate the probability of extended cloud encounter, and the associated loss of LFC effectiveness along seven high-density routes. The probability is demonstrated to be low.
Drag Measurements in Laminar Flows over Superhydrophobic Porous Membranes
NASA Astrophysics Data System (ADS)
Ozsun, Ozgur; Yakhot, Victor; Ekinci, Kamil L.
2012-02-01
An anomalous hydrodynamic response has recently been observed in oscillating flows on mesh-like porous superhydrophobic membranes.ootnotetextS. Rajauria, O. Ozsun, J. Lawall, V. Yakhot, and K. L. Ekinci, Phys. Rev. Lett. 107, 174501 (2011) This effect was attributed to a stable Knudsen layer of gas at the solid-liquid interface. In this study, we investigate laminar channel flow over these porous superhydrophobic membranes. We have fabricated surfaces with solid area fraction φs, which can maintain intimate contact with both air and water reservoirs on either side. Typical structures have linear dimensions of 1.5 mm x 15 mm x 1 μm and pore area of 10 μm x 10 μm. The surfaces are enclosed with precisely machined plastic microchannels, where pressure driven flow of DI water is generated. Pressure drop across the microchannels is measured as a function of flow rate. Slip lengths are inferred from the Poiseuille relation as a function of φs and compared to that of similar standard superhydrophobic surfaces, which lack intimate contact with an air reservoir.
Progress Toward Efficient Laminar Flow Analysis and Design
NASA Technical Reports Server (NTRS)
Campbell, Richard L.; Campbell, Matthew L.; Streit, Thomas
2011-01-01
A multi-fidelity system of computer codes for the analysis and design of vehicles having extensive areas of laminar flow is under development at the NASA Langley Research Center. The overall approach consists of the loose coupling of a flow solver, a transition prediction method and a design module using shell scripts, along with interface modules to prepare the input for each method. This approach allows the user to select the flow solver and transition prediction module, as well as run mode for each code, based on the fidelity most compatible with the problem and available resources. The design module can be any method that designs to a specified target pressure distribution. In addition to the interface modules, two new components have been developed: 1) an efficient, empirical transition prediction module (MATTC) that provides n-factor growth distributions without requiring boundary layer information; and 2) an automated target pressure generation code (ATPG) that develops a target pressure distribution that meets a variety of flow and geometry constraints. The ATPG code also includes empirical estimates of several drag components to allow the optimization of the target pressure distribution. The current system has been developed for the design of subsonic and transonic airfoils and wings, but may be extendable to other speed ranges and components. Several analysis and design examples are included to demonstrate the current capabilities of the system.
Numerical predictions for laminar source-sink flow in a rotating cylindrical cavity
NASA Astrophysics Data System (ADS)
Chew, J. W.; Owen, J. M.; Pincombe, J. R.
1984-06-01
Numerical solutions are presented for steady, axisymmetric, laminar, isothermal, source-sink flow in a rotating cylindrical cavity. These results, which are in good agreement with previously published experimental work, have been used to give a fresh insight into the nature of the flow and to investigate the validity of other theoretical solutions. When the fluid enters the cavity through a central uniform radial source and leaves through an outer sink, it is shown that the flow near the disks can be approximated by two known analytical solutions. If the radial source is replaced by an axial inlet, the flow becomes more complex, with a wall jet forming on the downstream disk at sufficiently high flow rates.
Laminar flow in the entrance region of elliptical ducts
NASA Astrophysics Data System (ADS)
Bhatti, M. S.
1983-06-01
A closed-form analytical solution is developed to hitherto unsolved problem of steady laminar flow of a Newtonian fluid in the entrance region of elliptical ducts. The analysis is based on the Karman-Pohlhausen integral method and entails solution of the integrated forms of the mass and the momentum balance equations. According to this analysis, the hydrodynamic entrance length based on 99 percent approach to the fully developed flow is equal to 0.5132 lambda/(l + lambda-squared) where lambda is the aspect ratio. Also, the fully developed incremental pressure defect is found to be 7/6 which is independent of the aspect ratio. In the limit when the flow becomes fully developed, the solution converges to the known exact asymptotic solution. Available, wide-ranging velocity measurements for a circular tube agree with the analytical predictions within 7 percent. Also, available pressure drop measurements near the inlet of a circular tube agree with the analytical predictions within 2 percent.
Direct numerical simulation of laminar-turbulent flow over a flat plate at hypersonic flow speeds
NASA Astrophysics Data System (ADS)
Egorov, I. V.; Novikov, A. V.
2016-06-01
A method for direct numerical simulation of a laminar-turbulent flow around bodies at hypersonic flow speeds is proposed. The simulation is performed by solving the full three-dimensional unsteady Navier-Stokes equations. The method of calculation is oriented to application of supercomputers and is based on implicit monotonic approximation schemes and a modified Newton-Raphson method for solving nonlinear difference equations. By this method, the development of three-dimensional perturbations in the boundary layer over a flat plate and in a near-wall flow in a compression corner is studied at the Mach numbers of the free-stream of M = 5.37. In addition to pulsation characteristic, distributions of the mean coefficients of the viscous flow in the transient section of the streamlined surface are obtained, which enables one to determine the beginning of the laminar-turbulent transition and estimate the characteristics of the turbulent flow in the boundary layer.
Application of laminar flow control to high-bypass-ratio turbofan engine nacelles
NASA Technical Reports Server (NTRS)
Wie, Y. S.; Collier, F. S., Jr.; Wagner, R. D.
1991-01-01
Recently, the concept of the application of hybrid laminar flow to modern commercial transport aircraft was successfully flight tested on a Boeing 757 aircraft. In this limited demonstration, in which only part of the upper surface of the swept wing was designed for the attainment of laminar flow, significant local drag reduction was measured. This paper addresses the potential application of this technology to laminarize the external surface of large, modern turbofan engine nacelles which may comprise as much as 5-10 percent of the total wetted area of future commercial transports. A hybrid-laminar-flow-control (HLFC) pressure distribution is specified and the corresponding nacelle geometry is computed utilizing a predictor/corrector design method. Linear stability calculations are conducted to provide predictions of the extent of the laminar boundary layer. Performance studies are presented to determine potential benefits in terms of reduced fuel consumption.
Characterization of Fuego for laminar and turbulent natural convection heat transfer.
Francis, Nicholas Donald, Jr.
2005-08-01
A computational fluid dynamics (CFD) analysis is conducted for internal natural convection heat transfer using the low Mach number code Fuego. The flow conditions under investigation are primarily laminar, transitional, or low-intensity level turbulent flows. In the case of turbulent boundary layers at low-level turbulence or transitional Reynolds numbers, the use of standard wall functions no longer applies, in general, for wall-bounded flows. One must integrate all the way to the wall in order to account for gradients in the dependent variables in the viscous sublayer. Fuego provides two turbulence models in which resolution of the near-wall region is appropriate. These models are the v2-f turbulence model and a Launder-Sharma, low-Reynolds number turbulence model. Two standard geometries are considered: the annulus formed between horizontal concentric cylinders and a square enclosure. Each geometry emphasizes wall shear flow and complexities associated with turbulent or near turbulent boundary layers in contact with a motionless core fluid. Overall, the Fuego simulations for both laminar and turbulent flows compared well to measured data, for both geometries under investigation, and to a widely accepted commercial CFD code (FLUENT).
The pulsating laminar flow in a rectangular channel
NASA Astrophysics Data System (ADS)
Valueva, E. P.; Purdin, M. S.
2015-11-01
The finite difference method is used to solve the task of the developed pulsating laminar flow in a rectangular channel. The optimum of the difference scheme parameters was determined. Data on the amplitude and phase of the longitudinal velocity oscillations, the hydraulic and friction drag coefficients, the shear stress on the wall have been obtained. Using the dimensionless value of the frequency pulsations two characteristic regimes — the quasisteady-state regime and the high-frequency regime have been identified. In the quasi-steady-state regime, the values of all hydrodynamic quantities at each instant of time correspond to the velocity value averaged over the cross section at a given moment of time. It is shown that in the high-frequency regime, the dependences on the dimensionless oscillation frequency of oscillating components of hydrodynamic quantities are identical for rectilinear channels with a different cross-sectional form (round pipe, flat and a rectangular channels). The effect of the aspect ratio of the rectangular channel sides channel on the pulsating flow dynamics has been analyzed.
Laminar-Turbulent Transition: A Hysteresis Curve of Two Critical Reynolds Numbers in Pipe Flow
NASA Astrophysics Data System (ADS)
Kanda, Hidesada
2006-11-01
A laminar-turbulent transition model (DFD 2004) has been constructed for pipe flows: (1) Natural transition occurs in the entrance region, and (2) Entrance shape determines a critical Reynolds number Rc. To verify the model, we have carried out experiments similar to Reynolds's color-dye experiment with 5 bellmouth entrances and a straight pipe. Then, we observed the following: (i) two different types of Rc exist, Rc1 from laminar to turbulent and Rc2 from turbulent to laminar, and (ii) the ratio of bellmouth diameter BD to pipe diameter D affects the values of Rc1 and Rc2. For each entrance, Rc1 has a maximum value Rc1(max) and Rc2 has a minimum value Rc2(min). When overlapping the two curves of Rc1(max) and Rc2(min) against BD/D, a hysteresis curve is confirmed. All Rc values exist inside this hysteresis curve. Consequently, Rc takes a minimum value Rc(min) of approximately 2000 when BD/D is at a minimum, i.e., at BD/D = 1, Rc(min) = Rc1(max) = Rc2(min) = 2000. Regarding Reynolds's Rc of 12,830, we observed Rc1(max) of approximately 13,000 at BD/D above 1.54. Therefore, the model has been partly verified.
Mechanical and statistical study of the laminar hole formation in transitional plane Couette flow
NASA Astrophysics Data System (ADS)
Rolland, Joran
2015-03-01
This article is concerned with the numerical study and modelling of two aspects the formation of laminar holes in transitional turbulence of plane Couette flow (PCF). On the one hand, we consider quenches: sudden decreases of the Reynolds number R which force the formation of holes. The Reynolds number is decreased from featureless turbulence to the range of existence of the oblique laminar-turbulent bands [ R g; R t]. The successive stages of the quench are studied by means of visualisations and measurements of kinetic energy and turbulent fraction. The behaviour of the kinetic energy is explained using a kinetic energy budget: it shows that viscosity causes quasi modal decay until lift-up equals it and creates a new balance. Moreover, the budget confirms that the physical mechanisms at play are independent of the way the quench is performed. On the other hand we consider the natural formation of laminar holes in the bands, near R g. The direct numerical simulations (DNS) show that holes in the turbulent bands provide a mechanism for the fragmented bands regime and orientation fluctuations near R g. Moreover the analysis of the fluctuations of kinetic energy toward low values demonstrates that the disappearance of turbulence in the bands can be described within the framework of large deviations. A large deviation function is extracted from the probability density function of the kinetic energy.
Warner, D.J.; Ozgur, S.A.; Haigh, W.W.
1980-04-01
The feasibility of applying laminar boundary-layer control with body shaping to a high altitude, Lighter-Than-Air vehicle was investigated. Solar-radiation-induced surface heating was shown to have a destablizing effect on laminar flow and caused the laminar flow to break down on regions of the vehicle surface exposed to high levels of solar radiation. Aerodynamic drag estimates were made for the vehicle. Surface waviness and roughness criteria for achieving laminar flow were determined.
Aircraft energy efficiency laminar flow control glove flight conceptual design study
NASA Technical Reports Server (NTRS)
Wright, A. S.
1979-01-01
A laminar flow control glove applied to the wing of a short to medium range jet transport with aft mounted engines was designed. A slotted aluminum glove concept and a woven stainless steel mesh porous glove concept suction surfaces were studied. The laminar flow control glove and a dummy glove with a modified supercritical airfoil, ducting, modified wing leading and trailing edges, modified flaps, and an LFC trim tab were applied to the wing after slot spacing suction parameters, and compression power were determined. The results show that a laminar flow control glove can be applied to the wing of a jet transport with an appropriate suction system installed.
Calculation of laminar and turbulent boundary layers for two-dimensional time-dependent flows
NASA Technical Reports Server (NTRS)
Cebeci, T.
1977-01-01
A general method for computing laminar and turbulent boundary layers for two-dimensional time-dependent flows is presented. The method uses an eddy-viscosity formulation to model the Reynolds shear-stress term and a very efficient numerical method to solve the governing equations. The model was applied to steady two-dimensional and three-dimensional flows and was shown to give good results. A discussion of the numerical method and the results obtained by the present method for both laminar and turbulent flows are discussed. Based on these results, the method is efficient and suitable for solving time-dependent laminar and turbulent boundary layers.
Development of laminar flow control wing surface composite structures
NASA Technical Reports Server (NTRS)
Lineberger, L. B.
1984-01-01
The dramatic increases in fuel costs and the potential for periods of limited fuel availability provided the impetus to explore technologies to reduce transport aircraft fuel consumption. NASA sponsored the Aircraft Energy Efficiency (ACEE) program beginning in 1976 to develop technologies to improve fuel efficiency. This report documents the Lockheed-Georgia Company accomplishments under NAS1-16235 LFC Laminar-Flow-Control Wing Panel Structural Design And Development (WSSD); Design, manufacturing, and testing activities. An in-depth preliminary design of the baseline 1993 LFC wing was accomplished. A surface panel using the Lockheed graphite/epoxy integrated LFC wing box structural concept was designed. The concept was shown by analysis to be structurally efficient and cost effective. Critical details of the surface and surface joints were demonstrated by fabricating and testing complex, concept selection specimens. Cost of the baseline LFC aircraft was estimated and compared to the turbulent aircraft. The mission fuel weight was 21.7 percent lower for the LFC aircraft. The calculation shows that the lower fuel costs for LFC offset the higher incremental costs of LFC in less than six months.
Frost Growth and Densification in Laminar Flow Over Flat Surfaces
NASA Technical Reports Server (NTRS)
Kandula, Max
2011-01-01
One-dimensional frost growth and densification in laminar flow over flat surfaces has been theoretically investigated. Improved representations of frost density and effective thermal conductivity applicable to a wide range of frost circumstances have been incorporated. The validity of the proposed model considering heat and mass diffusion in the frost layer is tested by a comparison of the predictions with data from various investigators for frost parameters including frost thickness, frost surface temperature, frost density and heat flux. The test conditions cover a range of wall temperature, air humidity ratio, air velocity, and air temperature, and the effect of these variables on the frost parameters has been exemplified. Satisfactory agreement is achieved between the model predictions and the various test data considered. The prevailing uncertainties concerning the role air velocity and air temperature on frost development have been elucidated. It is concluded that that for flat surfaces increases in air velocity have no appreciable effect on frost thickness but contribute to significant frost densification, while increase in air temperatures results in a slight increase the frost thickness and appreciable frost densification.
Distributed acoustic receptivity in laminar flow control configurations
NASA Technical Reports Server (NTRS)
Choudhari, Meelan
1992-01-01
A model problem related to distributed receptivity to free-stream acoustic waves in laminar flow control (LFC) configurations is studied, within the Orr-Sommerfield framework, by a suitable extension of the Goldstein-Ruban theory for receptivity due to localized disturbances on the airfoil surface. The results, thus, complement the earlier work on the receptivity produced by local variations in the surface suction and/or surface admittance. In particular, we show that the cumulative effect of the distributed receptivity can be substantially larger than that of a single, isolated suction strip or slot. Furthermore, even if the receptivity is spread out over very large distances, the most effective contributions come from a relatively short region in vicinity of the lower branch of the neutral stability curve. The length scale of this region is intermediate to that of the mean of these two length scales. Finally, it is found that the receptivity is effectively dominated by a narrow band of Fourier components from the wall-suction and admittance distributions, roughly corresponding to a detuning of less than ten percent with respect to the neutral instability wavenumber at the frequency under consideration. The results suggest that the drop-off in receptivity magnitudes away from the resonant wavenumber is nearly independent of the frequency parameter.
Characteristics of electrohydrodynamic roll structures in laminar planar Couette flow
NASA Astrophysics Data System (ADS)
Kourmatzis, Agisilaos; Shrimpton, John S.
2016-02-01
The behaviour of an incompressible dielectric liquid subjected to a laminar planar Couette flow with unipolar charge injection is investigated numerically in two dimensions. The computations show new morphological characteristics of roll structures that arise in this forced electro-convection problem. The charge and velocity magnitude distributions between the two parallel electrodes are discussed as a function of the top wall velocity and the EHD Rayleigh number, T for the case of strong charge injection. A wide enough parametric space is investigated such that the observed EHD roll structures progress through three regimes. These regimes are defined by the presence of a single or double-roll free convective structure as observed elsewhere (Vazquez et al 2008 J. Phys. D 41 175303), a sheared or stretched roll structure, and finally by a regime where the perpendicular velocity gradient is sufficient to prevent the generation of a roll. These three regimes have been delineated as a function of the wall to ionic drift velocity {{U}\\text{W}}/κ E , and the T number. In the stretched regime, an increase in {{U}\\text{W}}/κ E can reduce charge and momentum fluctuations whilst in parallel de-stratify charge in the region between the two electrodes. The stretched roll regime is also characterised by a substantial influence of {{U}\\text{W}}/κ E on the steady development time, however in the traditional non-stretched roll structure regime, no influence of {{U}\\text{W}}/κ E on the development time is noted.
F-16XL Supersonic Laminar Flow Test Flight
An F-16XL aircraft was used by the Dryden Flight Research Center, Edwards, California, in a NASA-wide program to improve laminar airflow on aircraft flying at sustained supersonic speeds. It was th...
Current Evidence for the Use of Laminar Flow in Reducing Infection Rates in Total Joint Arthroplasty
James, M; Khan, W.S; Nannaparaju, M.R; Bhamra, J.S; Morgan-Jones, R
2015-01-01
Since the introduction of laminar air flow in orthopaedic theatres by Sir John Charnley, it has widely become accepted as the standard during orthopaedic procedures such as joint arthroplasty. We present a review of available current literature for the use of laminar flow operating theatre ventilation during total joint arthroplasty and examines the effectiveness of laminar flow ventilated operating theatres in preventing post-operative wound infection. Results of our findings suggest that while bacterial and air particulate is reduced by laminar air flow systems, there is no conclusive effect on the reduction of post-operative wound infections following total joint arthroplasty. We conclude that a combination of strict aseptic technique, prophylactic antibiotics and good anaesthetic control during surgery remains crucial to reduce post-operative surgical infections. PMID:26587068
Analysis of Low-Speed Stall Aerodynamics of a Swept Wing with Laminar-Flow Glove
NASA Technical Reports Server (NTRS)
Bui, Trong
2013-01-01
This is the presentation related to the paper of the same name describing Reynolds Averaged Navier Stokes (RANS) computational Fluid Dynamics (CFD) analysis of low speed stall aerodynamics of a swept wing with a laminar flow wing glove.
A flight test of laminar flow control leading-edge systems
NASA Technical Reports Server (NTRS)
Fischer, M. C.; Wright, A. S., Jr.; Wagner, R. D.
1983-01-01
NASA's program for development of a laminar flow technology base for application to commercial transports has made significant progress since its inception in 1976. Current efforts are focused on development of practical reliable systems for the leading-edge region where the most difficult problems in applying laminar flow exist. Practical solutions to these problems will remove many concerns about the ultimate practicality of laminar flow. To address these issues, two contractors performed studies, conducted development tests, and designed and fabricated fully functional leading-edge test articles for installation on the NASA JetStar aircraft. Systems evaluation and performance testing will be conducted to thoroughly evaluate all system capabilities and characteristics. A simulated airline service flight test program will be performed to obtain the operational sensitivity, maintenance, and reliability data needed to establish that practical solutions exist for the difficult leading-edge area of a future commercial transport employing laminar flow control.
Design and operation of a laminar-flow electrostatic-quadrupole-focused acceleration column
Maschke, A.W.
1983-06-20
This report deals with the design principles involved in the design of a laminar-flow electrostatic-quadrupole-focused acceleration column. In particular, attention will be paid to making the parameters suitable for incorporation into a DC MEQALAC design.
A perspective of laminar-flow control. [aircraft energy efficiency program
NASA Technical Reports Server (NTRS)
Braslow, A. L.; Muraca, R. J.
1978-01-01
A historical review of the development of laminar flow control technology is presented with reference to active laminar boundary-layer control through suction, the use of multiple suction slots, wind-tunnel tests, continuous suction, and spanwise contamination. The ACEE laminar flow control program is outlined noting the development of three-dimensional boundary-layer codes, cruise-noise prediction techniques, airfoil development, and leading-edge region cleaning. Attention is given to glove flight tests and the fabrication and testing of wing box designs.
Video- Demonstration of Laminar Flow in a Liquid Onboard the International Space Station (ISS)
NASA Technical Reports Server (NTRS)
2003-01-01
Saturday Morning Science, the science of opportunity series of applied experiments and demonstrations, performed aboard the International Space Station (ISS) by Expedition 6 astronaut Dr. Don Pettit, revealed some remarkable findings. In this video clip, Pettit demonstrates laminar flow in a rotating film of water. The demonstration is done by placing tracer particles in a water film held in place by a round wire loop, then stirring the system rotationally. The resulting flow clearly demonstrates laminar 2D behavior with spiraling streamlines.
Method and applications of fiber synthesis using laminar flow
NASA Astrophysics Data System (ADS)
Burns, Bradley Justin
A Laminar Flow Reactor (LFR) using the principles of hydrodynamic focusing was created and used to fabricate functional composite polymer fibers. These fibers had the ability to conduct or serve as a carrier for singlet oxygen-generating molecules. Critical to the process was designing an easy-to-fabricate, inexpensive device and developing a repeatable method that made efficient use of the materials. The initial designs used a planar layout and hydrodynamically focused in only one dimension while later versions switched to a two-fluid concentric design. Modeling was undertaken and verified for the different device layouts. Three types of conductive particles were embedded in the formed polymer: silver, indium tin oxide (ITO) and polyaniline. The polymer was also used as a carrier to two singlet oxygen generating molecules: Methylene Blue (MB) and perylene. Both were effective in killing Bacillus thuringiensis but MB leached from the fiber into the tested cell suspension. Perylene, which is not water soluble, did not leach out and was just as effective as MB. Research that was performed at ITT is also presented. A critical need exists to detect, identify, quantify, locate, and track virus and toxin aerosols to provide early warning during both light and dark conditions. The solution presented is a remote sensing technology using seeding particles. Seeding particles developed during this program provide specific identification of threat cloud content. When introduced to the threat cloud the seeders will bind specifically to the analyte of interest and upon interrogation from a stand off laser source will fluoresce. The fluorescent signal is detected from a distance using a long-range microscope and collection optics that allow detection of low concentrations of threat aerosols.
Convective heat transfer characteristics of laminar pulsating pipe air flow
NASA Astrophysics Data System (ADS)
Habib, M. A.; Attya, A. M.; Eid, A. I.; Aly, A. Z.
Heat transfer characteristics to laminar pulsating pipe flow under different conditions of Reynolds number and pulsation frequency were experimentally investigated. The tube wall of uniform heat flux condition was considered. Reynolds number was varied from 780 to 1987 while the frequency of pulsation ranged from 1 to 29.5Hz. The results showed that the relative mean Nusselt number is strongly affected by pulsation frequency while it is slightly affected by Reynolds number. The results showed enhancements in the relative mean Nusselt number. In the frequency range of 1-4Hz, an enhancement up to 30% (at Reynolds number of 1366 and pulsation frequency of 1.4Hz) was obtained. In the frequency range of 17-25Hz, an enhancement up to 9% (at Reynolds number of 1366 and pulsation frequency of 17.5Hz) was indicated. The rate of enhancement of the relative mean Nusselt number decreased as pulsation frequency increased or as Reynolds number increased. A reduction in relative mean Nusselt number occurred outside these ranges of pulsation frequencies. A reduction in relative mean Nusselt number up to 40% for pulsation frequency range of 4.1-17Hz and a reduction up to 20% for pulsation frequency range of 25-29.5Hz for Reynolds numbers range of 780-1987 were considered. This reduction is directly proportional to the pulsation frequency. Empirical dimensionless equations have been developed for the relative mean Nusselt number that related to Reynolds number (750
Lateral Diffusion of Bedload Transport under Laminar Flow
NASA Astrophysics Data System (ADS)
Ortiz, C. P.; Houssais, M.; Purohit, P. K.; Durian, D. J.; Jerolmack, D. J.
2014-12-01
Lateral sediment transport is a key momentum-exchange mechanism to model equilibrium channel geometry and channel bar evolution. We study sediment transport from a statistical mechanical point of view akin to Furbish et al. 2012. This approach holds promise for linking grain-scale motion to macroscopic transport, but there are few data to definitively develop and test such models. We study an experimental model river, composed of monodisperse acrylic spheres dispersed in silicon oil, driven by a layer of fluid under steady shear. We choose to drive fluid flow in the laminar regime (Re < 1) to suppress fluid turbulence and isolate granular and bed structure controls. We use a refractive-index-matched laser scanning technique to observe the motion of particles at the surface of the bed as well as the particle dynamics below the surface. We study how the probability distribution of displacements varies as a function of distance from the bed surface and as a function of distance to the channel center. In the streamwise direction, in agreement with Furbish et al. 2012, we find that the dynamics can be decomposed into an advection and a diffusion term. In the lateral direction, we find a competition between diffusion and an elastic-like interaction with the bed. We study this lateral stochastic process and find a need to introduce two parameters to quantify this competition. The first parameter describes the tendency for particles to reside near the center of the channel and the second parameter describes the kinetic energy distribution of the particles. We study how the requisite averaging scales and ensemble sizes to achieve statistically convergent parameters, and we explore how these parameters depend on the driving rate.
Lubricant-impregnated surfaces for drag reduction in viscous laminar flow
NASA Astrophysics Data System (ADS)
Solomon, Brian; Khalil, Karim; Varanasi, Kripa; MIT Team
2013-11-01
For the first time, we explore the potential of lubricant impregnated surfaces (LIS) in reducing drag. LIS, inspired by the surface of the Nepenthes pitcher plant, have been introduced as a novel way of functionalizing a surface. LIS are characterized by extremely low contact angle hysteresis and have been show to effectively repel various liquids including water, oils, ketchup and blood. Motivated by the slippery nature of such surfaces, we explore the potential of LIS to reduce drag in internal flows. We observe a reduction in drag for LIS surfaces in a viscous laminar drag flow and model the impact of relevant system parameters (lubricant viscosity, working fluid viscosity, solid fraction, depth of texture, etc.).
Choudhari, Meelan; Chang, Chau-Lyan; Jiang, Li
2005-05-15
Laminar flow control (LFC) is one of the key enabling technologies for quiet and efficient supersonic aircraft. Recent work at Arizona State University (ASU) has led to a novel concept for passive LFC, which employs distributed leading edge roughness to limit the growth of naturally dominant crossflow instabilities in a swept-wing boundary layer. Predicated on nonlinear modification of the mean boundary-layer flow via controlled receptivity, the ASU concept requires a holistic prediction approach that accounts for all major stages within transition in an integrated manner. As a first step in developing an engineering methodology for the design and optimization of roughness-based supersonic LFC, this paper reports on canonical findings related to receptivity plus linear and nonlinear development of stationary crossflow instabilities on a Mach 2.4, 73 degrees swept airfoil with a chord Reynolds number of 16.3 million.
NASA Technical Reports Server (NTRS)
Goodyear, M. D.
1987-01-01
NASA sponsored the Aircraft Energy Efficiency (ACEE) program in 1976 to develop technologies to improve fuel efficiency. Laminar flow control was one such technology. Two approaches for achieving laminar flow were designed and manufactured under NASA sponsored programs: the perforated skin concept used at McDonnell Douglas and the slotted design used at Lockheed-Georgia. Both achieved laminar flow, with the slotted design to a lesser degree (JetStar flight test program). The latter design had several fabrication problems concerning springback and adhesive flow clogging the air flow passages. The Lockheed-Georgia Company accomplishments is documented in designing and fabricating a small section of a leading edge article addressing a simpler fabrication method to overcome the previous program's manufacturing problems, i.e., design and fabrication using advanced technologies such as diffusion bonding of aluminum, which has not been used on aerospace structures to date, and the superplastic forming of aluminum.
NASA Astrophysics Data System (ADS)
Ziaei-Rad, Masoud
2013-07-01
This paper concerns the study of laminar and turbulent force convection heat transfer and pressure drop between horizontal parallel plates with a nanofluid composed of Al2O3 and water. A set of governing equations are solved using a non-staggered SIMPLE procedure for the velocity-pressure coupling. For the convection-diffusion terms a power-law scheme is employed. A modified k-ɛ model with a two-layer technique for the near-wall region has been used to predict the turbulent viscosity. The effects of nanoparticle volume fraction in the base fluid on laminar and turbulent flow variables are presented and discussed. The velocity and temperature profiles, friction factor, pressure coefficient and Nusselt number at different Reynolds numbers in the entrance region for both the laminar and turbulent flow regimes are reported under different thermal boundary conditions. The results show that the effect of the presence of nanoparticles in the base fluid on hydraulic and thermal parameters for the turbulent flow is not very significant, while the rate of heat transfer for the laminar flow with nanoparticles is greater than that of the base liquid. Furthermore, the thermal boundary layer and consequently the Nusselt number more quickly reach their fully developed values by increasing the percentage of nanoparticles in the base fluid for the laminar flow regime, while no changes in the trend are observed for the turbulent flow.
Boundary-Layer Transition Results from the F-16XL-2 Supersonic Laminar Flow Control Experiment
NASA Technical Reports Server (NTRS)
Marshall, Laurie A.
1999-01-01
A variable-porosity suction glove has been flown on the F-16XL-2 aircraft to demonstrate the feasibility of this technology for the proposed High-Speed Civil Transport (HSCT). Boundary-layer transition data have been obtained on the titanium glove primarily at Mach 2.0 and altitudes of 53,000-55,000 ft. The objectives of this supersonic laminar flow control flight experiment have been to achieve 50- to 60-percent-chord laminar flow on a highly swept wing at supersonic speeds and to provide data to validate codes and suction design. The most successful laminar flow results have not been obtained at the glove design point (Mach 1.9 at an altitude of 50,000 ft). At Mach 2.0 and an altitude of 53,000 ft, which corresponds to a Reynolds number of 22.7 X 10(exp 6), optimum suction levels have allowed long runs of a minimum of 46-percent-chord laminar flow to be achieved. This paper discusses research variables that directly impact the ability to obtain laminar flow and techniques to correct for these variables.
A History of Suction-Type Laminar Flow Control with Emphasis on Flight Research
NASA Technical Reports Server (NTRS)
Braslow, Albert L.
1999-01-01
Laminar-flow control is an area of aeronautical research that has a long history at NASA's Langley Research Center, Dryden Flight Research Center, their predecessor organizations, and elsewhere. In this monograph, the author, who spent much of his career at Langley working with this research, presents a history of that portion of laminar-flow technology known as active laminar-flow control, which employs suction of a small quantity of air through airplane surfaces. This important technique offers the potential for significant reduction in drag and, thereby, for large increases in range or reductions in fuel usage for aircraft. For transport aircraft, the reductions in fuel consumed as a result of laminar-flow control may equal 30 percent of present consumption. Given such potential, it is obvious that active laminar-flow control with suction is an important technology. In this study, the author covers the early history of the subject and brings the story all the way to the mid-1990s with an emphasis on flight research, much of which has occurred at Dryden. This is an important monograph that not only encapsulates a lot of history in a brief compass but also does so in language that is accessible to non-technical readers. NASA is publishing it in a format that will enable it to reach the wide audience the subject deserves.
Low-Disturbance Flow Characteristics of the NASA-Ames Laminar Flow Supersonic Wind Tunnel
NASA Technical Reports Server (NTRS)
Wolf, Stephen W. D.; Laub, James A.; Davis, Sanford S. (Technical Monitor)
1994-01-01
A unique, low-disturbance (quiet) supersonic wind tunnel has been commissioned at the NASA-Ames Fluid Mechanics Laboratory (FML) to support Supersonic Laminar Flow Control (SLFC) research. Known as the Laminar Flow Supersonic Wind Tunnel (LFSWT), this tunnel is designed to operate at potential cruise Mach numbers and unit Reynolds numbers (Re) of the High Speed Civil Transport (HSCT). The need to better understand the receptivity of the transition phenomena on swept (HSCT) wings to attachment-line contamination and cross-flows has provided the impetus for building the LFSWT. Low-disturbance or "quiet" wind tunnels are known to be an essential part of any meaningful boundary layer transition research. In particular, the receptivity of supersonic boundary layers to wind tunnel disturbances can significantly alter the transition phenomena under investigation on a test model. Consequently, considerable effort has gone into the design of the LFSWT to provide quiet flow. The paper describes efforts to quantify the low-disturbance flows in the LFSWT operating at Mach 1.6, as a precursor to transition research on wing models. The research includes: (1) Flow measurements in both the test section and settling chamber of the LFSWT, using a full range of measurement techniques; (2) Study of the state of the test section boundary layer so far by using a single hot-wire mounted above the floor centerline, with and without boundary layer trips fitted at the test section entrance; (3) The effect of flow quality of unsteady supersonic diffuser flow, joint steps and gaps, and wall vibration.
Summary of Transition Results From the F-16XL-2 Supersonic Laminar Flow Control Experiment
NASA Technical Reports Server (NTRS)
Marshall, Laurie A.
2000-01-01
A variable-porosity suction glove has been flown on the F-16XL-2 aircraft to demonstrate the feasibility of this technology for the proposed High-Speed Civil Transport. Boundary-layer transition data on the titanium glove primarily have been obtained at speeds of Mach 2.0 and altitudes of 15,240-16,764 m (50,000-55,000 ft). The objectives of this flight experiment have been to achieve 0.50-0.60 chord laminar flow on a highly swept wing at supersonic speeds and to provide data to validate codes and suction design. The most successful laminar flow results have not been obtained at the glove design point, a speed of Mach 1.9 at an altitude of 15,240 m (50,000 ft); but rather at a speed of Mach 2.0 and an altitude of 16,154 m (53,000 ft). Laminar flow has been obtained to more than 0.46 wing chord at a Reynolds number of 22.7 x 10(exp 6). A turbulence diverter has been used to initially obtain a laminar boundary layer at the attachment line. A lower-surface shock fence was required to block an inlet shock from the wing leading edge. This paper discusses research variables that directly impact the ability to obtain laminar flow and techniques to correct for these variables.
NASA Technical Reports Server (NTRS)
1999-01-01
This document describes the aerodynamic design of an experimental hybrid laminar flow control (HLFC) wing panel intended for use on a Boeing 757 airplane to provide a facility for flight research on high Reynolds number HLFC and to demonstrate practical HLFC operation on a full-scale commercial transport airplane. The design consists of revised wing leading edge contour designed to produce a pressure distribution favorable to laminar flow, definition of suction flow requirements to laminarize the boundary layer, provisions at the inboard end of the test panel to prevent attachment-line boundary layer transition, and a Krueger leading edge flap that serves both as a high lift device and as a shield to prevent insect accretion on the leading edge when the airplane is taking off or landing.
Stability and dissipation of laminar vortex flow in superfluid 3He-B.
Eltsov, V B; de Graaf, R; Heikkinen, P J; Hosio, J J; Hänninen, R; Krusius, M; L'vov, V S
2010-09-17
A central question in the dynamics of vortex lines in superfluids is dissipation on approaching the zero temperature limit T→0. From both NMR measurements and vortex filament calculations, we find that vortex flow remains laminar up to large Reynolds numbers Re{α}∼10(3) in a cylinder filled with 3He-B. This is different from viscous fluids and superfluid 4He, where the corresponding responses are turbulent. In 3He-B, laminar vortex flow is possible in the bulk volume even in the presence of sizable perturbations from axial symmetry to below 0.2Tc. The laminar flow displays no excess dissipation beyond mutual friction, which vanishes in the T→0 limit, in contrast with turbulent vortex motion where dissipation has been earlier measured to approach a large T-independent value at T≲0.2Tc.
Parametric study on laminar flow for finite wings at supersonic speeds
NASA Technical Reports Server (NTRS)
Garcia, Joseph Avila
1994-01-01
Laminar flow control has been identified as a key element in the development of the next generation of High Speed Transports. Extending the amount of laminar flow over an aircraft will increase range, payload, and altitude capabilities as well as lower fuel requirements, skin temperature, and therefore the overall cost. A parametric study to predict the extent of laminar flow for finite wings at supersonic speeds was conducted using a computational fluid dynamics (CFD) code coupled with a boundary layer stability code. The parameters investigated in this study were Reynolds number, angle of attack, and sweep. The results showed that an increase in angle of attack for specific Reynolds numbers can actually delay transition. Therefore, higher lift capability, caused by the increased angle of attack, as well as a reduction in viscous drag, due to the delay in transition, can be expected simultaneously. This results in larger payload and range.
Control of airborne nickel welding fumes by means of a vertical laminar air flow system
NASA Astrophysics Data System (ADS)
Helms, T. C.
1980-12-01
The effectiveness of a clean room facility with laminar air flow in the control of nickel fumes is evaluated. The fumes are released from metal inert gas (MIG) and shielded metal arc (SMA) welding operations performed on mild steel using nickel filler materials. The laminar flow clean room approach to controlling welding fumes can be successful in certain small table top welding operations. However, almost any interferences that obstruct the downward airflow results in eddy currents and subsequent buildup of fumes by entrapment. Airflow patterns differ significantly when comparing table top operations to welding on large cylindrical and/or doughnut shaped items. After fifteen days of sampling, airflow was reduced to 140-150 feet per maximum. Additional prefiltering units would be required for efficient operation of a laminar air flow clean room in an actual shop situation.
Numerical solution of inviscid and viscous laminar and turbulent flow around the airfoil
NASA Astrophysics Data System (ADS)
Slouka, Martin; Kozel, Karel
2016-03-01
This work deals with the 2D numerical solution of inviscid compressible flow and viscous compressible laminar and turbulent flow around the profile. In a case of turbulent flow algebraic Baldwin-Lomax model is used and compared with Wilcox k-omega model. Calculations are done for NACA 0012 and RAE 2822 airfoil profile for the different angles of upstream flow. Numerical results are compared and discussed with experimental data.
NASA Technical Reports Server (NTRS)
Ostowari, Cyrus
1992-01-01
Preliminary studies have shown that maintenance of laminar flow through active boundary-layer control is viable. Current research activity at NASA Langley and NASA Dryden is utilizing the F-16XL-1 research vehicle fitted with a laminar-flow suction glove that is connected to a vacuum manifold in order to create and control laminar flow at supersonic flight speeds. This experimental program has been designed to establish the feasibility of obtaining laminar flow at supersonic speeds with highly swept wing and to provide data for computational fluid dynamics (CFD) code calibration. Flight experiments conducted as supersonic speeds have indicated that it is possible to achieve laminar flow under controlled suction at flight Mach numbers greater than 1. Currently this glove is fitted with a series of pressure belts and flush mounted hot film sensors for the purpose of determining the pressure distributions and the extent of laminar flow region past the stagnation point. The present mode of data acquisition relies on out-dated on board multi-channel FM analogue tape recorder system. At the end of each flight, the analogue data is digitized through a long laborious process and then analyzed. It is proposed to replace this outdated system with an on board state-of-the-art digital data acquisition system capable of a through put rate of up to 1 MegaHertz. The purpose of this study was three-fold: (1) to develop a simple algorithm for acquiring data via 2 analogue-to-digital convertor boards simultaneously (total of 32 channels); (2) to interface hot-film/wire anemometry instrumentation with a PCAT type computer; and (3) to characterize the frequency response of a flush mounted film sensor. A brief description of each of the above tasks along with recommendations are given.
NASA Astrophysics Data System (ADS)
Matsumoto, Daichi; Fukudome, Koji; Wada, Hirofumi
2016-10-01
Understanding the hydrodynamic properties of fluid flow in a curving pipe and channel is important for controlling the flow behavior in technologies and biomechanics. The nature of the resulting flow in a bent pipe is extremely complicated because of the presence of a cross-stream secondary flow. In an attempt to disentangle this complexity, we investigate the fluid dynamics in a bent channel via the direct numerical simulation of the Navier-Stokes equation in two spatial dimensions. We exploit the absence of secondary flow from our model and systematically investigate the flow structure along the channel as a function of both the bend angle and Reynolds number of the laminar-to-turbulent regime. We numerically suggest a scaling relation between the shape of the separation bubble and the flow conductance, and construct an integrated phase diagram.
Air Flow in a Separating Laminar Boundary Layer
NASA Technical Reports Server (NTRS)
Schubauer, G B
1936-01-01
The speed distribution in a laminar boundary layer on the surface of an elliptic cylinder, of major and minor axes 11.78 and 3.98 inches, respectively, has been determined by means of a hot-wire anemometer. The direction of the impinging air stream was parallel to the major axis. Special attention was given to the region of separation and to the exact location of the point of separation. An approximate method, developed by K. Pohlhausen for computing the speed distribution, the thickness of the layer, and the point of separation, is described in detail; and speed-distribution curves calculated by this method are presented for comparison with experiment.
NASA Technical Reports Server (NTRS)
Thiede, P.
1978-01-01
The transition of the laminar boundary layer into the turbulent state, which results in an increased drag, can be avoided by sucking of the boundary layer particles near the wall. The technically-interesting case of sucking the particles using individual slits is investigated for bodies of revolution in incompressible flow. The results of the variational calculations show that there is an optimum suction height, where the slot separations are maximum. Combined with favorable shaping of the body, it is possible to keep the boundary layer over bodies of revolution laminar at high Reynolds numbers using relatively few suction slits and small amounts of suction flow.
Start of fluidization of a bulk granular material in laminar flow
Rozhdestvenskii, O.I.; Bednyakov, G.E.; Zayats, E.I.; Kirillov, I.N.; Serebryakova, T.V.
1982-04-20
This report examines the usage and transformation of an equation of the form Re/sub cr/=Ar(1400+5.22/Ar) which is used in design calculations for determination of the velocity of the start of fluidization of a granular material bearing initial voidage e/sub o/=0.4. Variations of the Reynold's number corresponding to the Critical Fluidization velocity at various voidages of the granular bed and different values of the Archimedes number in laminar flow are presented. Results indicate that the equation cannot be recommended for use even for rough estimates of the bulk materials in laminar flow.
Laminar flow studies of a low-temperature space radiator model using D-shaped tubes
NASA Technical Reports Server (NTRS)
Cintula, T. C.; Prok, G. M.; Johnston, D. B.
1972-01-01
Test results of a low-temperature space radiator model are presented. Radiator performance is evaluated with a low-thermal-conductivity fluid in laminar flow in D-shaped cross-section tubes. The test covered a Reynolds number range from 50 to 4500 and a fluid temperature range from 294 to 414 K (70 to 286 F). For low-temperature radiators, the fluid-to-surface temperature differential was predominately influenced by fluid temperature in laminar flow. Heat transfer and pressure drop for the radiator tube could be predicted within engineering accuracy from existing correlations.
Feasibility and benefits of laminar flow control on supersonic cruise airplanes
NASA Technical Reports Server (NTRS)
Powell, A. G.; Agrawal, S.; Lacey, T. R.
1989-01-01
An evaluation was made of the applicability and benefits of laminar flow control (LFC) technology to supersonic cruise airplanes. Ancillary objectives were to identify the technical issues critical to supersonic LFC application, and to determine how those issues can be addressed through flight and wind-tunnel testing. Vehicle types studied include a Mach 2.2 supersonic transport configuration, a Mach 4.0 transport, and two Mach 2-class fighter concepts. Laminar flow control methodologies developed for subsonic and transonic wing laminarization were extended and applied. No intractible aerodynamic problems were found in applying LFC to airplanes of the Mach 2 class, even ones of large size. Improvements of 12 to 17 percent in lift-drag ratios were found. Several key technical issues, such as contamination avoidance and excresence criteria were identified. Recommendations are made for their resolution. A need for an inverse supersonic wing design methodology is indicated.
Technology Transfer Automated Retrieval System (TEKTRAN)
Little research has been conducted to investigate fate and transport of colloids in surface vegetation in overland flow under unfavorable chemical conditions. In this work, single collector attachment efficiency (a) of colloid capture by a simulated plant stem (i.e. cylindrical collector) in laminar...
On self-organizing during transition from a laminar to a turbulent flow for nonextensive systems
NASA Astrophysics Data System (ADS)
Zaripov, R. G.
2016-06-01
The evolution of parametric q-entropy and q-information divergence to the equilibrium state during spontaneous transitions and transitions from a laminar to a turbulent flow is considered as applied to nonextensive self-organizing systems. The S- and I-theorems on the variations of measures with constant mean energies are proved.
Laboratory and Numerical Investigations of Residence Time Distribution of Fluids in Laminar Flow Stirred Annular Photoreactor
E. Sahle-Demessie1, Siefu Bekele2, U. R. Pillai1
1U.S. EPA, National Risk Management Research Laboratory
Sustainable Technology Division,...
Performance of laminar-flow leading-edge test articles in cloud encounters
NASA Technical Reports Server (NTRS)
Davis, Richard E.; Maddalon, Dal V.; Wagner, Richard D.
1987-01-01
An extensive data bank of concurrent measurements of laminar flow (LF), particle concentration, and aircraft charging state was gathered for the first time. From this data bank, 13 flights in the simulated airline service (SAS) portion were analyzed to date. A total of 6.86 hours of data at one-second resolution were analyzed. An extensive statistical analysis, for both leading-edge test articles, shows that there is a significant effect of cloud and haze particles on the extent of laminar flow obtained. Approximately 93 percent of data points simulating LFC flight were obtained in clear air conditions; approximately 7 percent were obtained in cloud and haze. These percentages are consistent with earlier USAF and NASA estimates and results. The Hall laminar flow loss criteria was verified qualitatively. Larger particles and higher particle concentrations have a more marked effect on LF than do small particles. A particle spectrometer of a charging patch are both acceptable as diagnostic indicators of the presence of particles detrimental to laminar flow.
Modelling of laminar flow in the inlet section of rectangular microchannels
NASA Astrophysics Data System (ADS)
Martinelli, Matteo; Viktorov, Vladimir
2009-02-01
This paper is a study of laminar flow in rectangular microchannels. The behaviour of compressible and incompressible fluids in microchannels was simulated using CFD software. Numerical data were compared to experimental measurements to test the validity of CFD models. The velocity profile of flow developing inside the channel is described as a function of the Reynolds number Re, varying from 100 to 2000, and the aspect ratio h/w, ranging from 1 to 0.125. The fundamental importance of the entrance length of microchannels is highlighted. Numerical data were applied to define analytical formulae covering the minimum entrance length for fully developed laminar flow of compressible fluids, viscous stress and incremental pressure drop effect during flow development, and the velocity profiles of flow for compressible and incompressible fluids.
NASA Astrophysics Data System (ADS)
Sohn, Jeong L.
1988-08-01
The purpose of the study is the evaluation of the numerical accuracy of FIDAP (Fluid Dynamics Analysis Package). Accordingly, four test problems in laminar and turbulent incompressible flows are selected and the computational results of these problems compared with other numerical solutions and/or experimental data. These problems include: (1) 2-D laminar flow inside a wall-driven cavity; (2) 2-D laminar flow over a backward-facing step; (3) 2-D turbulent flow over a backward-facing step; and (4) 2-D turbulent flow through a turn-around duct.
NASA Technical Reports Server (NTRS)
Beckwith, I. E.; Cohen, N. B.
1963-01-01
Flat plate and stagnation flow heat transfer coefficients, similarity solutions of the laminar boundary layer for air in dissociation equilibrium and calculation of laminar heat-transfer distribution on blunt three-dimensional bodies in high speed flow
Laminar and turbulent nozzle-jet flows and their acoustic near-field
Bühler, Stefan; Obrist, Dominik; Kleiser, Leonhard
2014-08-15
We investigate numerically the effects of nozzle-exit flow conditions on the jet-flow development and the near-field sound at a diameter-based Reynolds number of Re{sub D} = 18 100 and Mach number Ma = 0.9. Our computational setup features the inclusion of a cylindrical nozzle which allows to establish a physical nozzle-exit flow and therefore well-defined initial jet-flow conditions. Within the nozzle, the flow is modeled by a potential flow core and a laminar, transitional, or developing turbulent boundary layer. The goal is to document and to compare the effects of the different jet inflows on the jet flow development and the sound radiation. For laminar and transitional boundary layers, transition to turbulence in the jet shear layer is governed by the development of Kelvin-Helmholtz instabilities. With the turbulent nozzle boundary layer, the jet flow development is characterized by a rapid changeover to a turbulent free shear layer within about one nozzle diameter. Sound pressure levels are strongly enhanced for laminar and transitional exit conditions compared to the turbulent case. However, a frequency and frequency-wavenumber analysis of the near-field pressure indicates that the dominant sound radiation characteristics remain largely unaffected. By applying a recently developed scaling procedure, we obtain a close match of the scaled near-field sound spectra for all nozzle-exit turbulence levels and also a reasonable agreement with experimental far-field data.
NASA Astrophysics Data System (ADS)
Maynes, D.; Jeffs, K.; Woolford, B.; Webb, B. W.
2007-09-01
This paper reports results of an analytical and experimental investigation of the laminar flow in a parallel-plate microchannel with ultrahydrophobic top and bottom walls. The walls are fabricated with microribs and cavities that are oriented parallel to the flow direction. The channel walls are modeled in an idealized fashion, with the shape of the liquid-vapor meniscus approximated as flat. An analytical model of the vapor cavity flow is employed and coupled with a numerical model of the liquid flow by matching the local liquid and vapor phase velocity and shear stress at the interface. The numerical predictions show that the effective slip length and the reduction in the classical friction factor-Reynolds number product increase with increasing relative cavity width, increasing relative cavity depth, and decreasing relative microrib/cavity module length. Comparisons were also made between the zero shear interface model and the liquid-vapor cavity coupled model. The results illustrate that the zero shear interface model underpredicts the overall flow resistance. Further, the deviation between the two models was found to be significantly larger for increasing values of both the relative rib/cavity module width and the cavity fraction. The trends in the frictional pressure drop predictions are in good agreement with experimental measurements made at similar conditions, with greater deviation observed at increasing size of the cavity fraction. Based on the numerical predictions, an expression is proposed in which the friction factor-Reynolds number product may be estimated in terms of the important variables.
NASA Technical Reports Server (NTRS)
Meyer, J. S.; Kosovich, J.
1973-01-01
An anesthetic gas flow pop-off valve canister is described that is airtight and permits the patient to breath freely. Once its release mechanism is activated, the exhaust gases are collected at a hose adapter and passed through activated coal for adsorption. A survey of laminar air flow clean rooms is presented and the installation of laminar cross flow air systems in operating rooms is recommended. Laminar flow ventilation experiments determine drying period evaporation rates for chicken intestines, sponges, and sections of pig stomach.
Formation of a laminar electron flow for 300 GHz high-power pulsed gyrotron
Yamaguchi, Yuusuke; Tatematsu, Yoshinori; Saito, Teruo; Ikeda, Ryosuke; Mudiganti, Jagadish C.; Ogawa, Isamu; Idehara, Toshitaka
2012-11-15
This paper describes the design of a triode magnetron injection gun for use in a 200 kW, 300 GHz gyrotron. As power and frequency increase, the performance of the gyrotron becomes quite sensitive to the quality of the electron beam. Formation of a laminar electron flow is essential for the realization of a high quality beam with a small velocity spread. In this study, a new method is developed for a quantitative evaluation of the laminarity and is applied to optimize the electrode design. The laminarity depends not only on conventional design parameters such as the cathode slant angle but also on the spatial distribution of the electric field along the beam trajectory. In the optimized design, the velocity pitch factors, {alpha}, larger than 1.2 are obtained at 65 kV, 10 A with spreads, {Delta}{alpha}, less than 5%.
Analysis and evaluation of an integrated laminar flow control propulsion system
NASA Technical Reports Server (NTRS)
Keith, Theo G., Jr.; Dewitt, Kenneth J.
1993-01-01
Reduction of drag has been a major goal of the aircraft industry as no other single quantity influences the operating costs of transport aircraft more than aerodynamic drag. It has been estimated that even modest reduction of frictional drag could reduce fuel costs by anywhere from 2 to 5 percent. Current research on boundary layer drag reduction deals with various approaches to reduce turbulent skin friction drag as a means of improving aircraft performance. One of the techniques belonging to this category is laminar flow control in which extensive regions of laminar flow are maintained over aircraft surfaces by delaying transition to turbulence through the ingestion of boundary layer air. While problems of laminar flow control have been studied in some detail, the prospect of improving the propulsion system of an aircraft by the use of ingested boundary layer air has received very little attention. An initial study for the purpose of reducing propulsion system requirements by utilizing the kinetic energy of boundary layer air was performed in the mid-1970's at LeRC. This study which was based on ingesting the boundary layer air at a single location, did not yield any significant overall propulsion benefits; therefore, the concept was not pursued further. However, since then it has been proposed that if the boundary layer air were ingested at various locations on the aircraft surface instead of just at one site, an improvement in the propulsion system might be realized. The present report provides a review of laminar flow control by suction and focuses on the problems of reducing skin friction drag by maintaining extensive regions of laminar flow over the aircraft surfaces. In addition, it includes an evaluation of an aircraft propulsion system that is augmented by ingested boundary layer air.
Features of quasistable laminar flows of He II and an additional dissipative process
NASA Astrophysics Data System (ADS)
Gritsenko, I. A.; Klokol, K. A.; Sokolov, S. S.; Sheshin, G. A.
2016-03-01
Quasistable laminar flow of He II at a temperature of 140 mK is studied experimentally. The liquid flow was excited by a vibrating quartz tuning fork with a resonance frequency of about 24 kHz. It was found that for velocities of the tuning fork oscillations from 0.046 to 0.16 m/s, the He II flow can be both quasistable laminar and turbulent. Transitions between these flow regimes were observed. When the velocity of the tuning fork oscillations increases more rapidly, the velocity at which the quasistable flow becomes unstable and undergoes a transition to a turbulent flow is higher. Mechanisms for the dissipation of the energy of the oscillating tines of the tuning fork in the quasistable laminar flow regime are analyzed. It is found that there is an additional mechanism for dissipation of the energy of the oscillating tuning fork beyond internal friction in the quartz. This mechanism is associated with mutual friction owing to scattering of thermal excitations of He II on quantized vortices and leads to a cubic dependence of the exciting force on the fluid velocity.
Correlation of Water Frost Porosity in Laminar Flow over Flat Surfaces
NASA Technical Reports Server (NTRS)
Kandula, Max
2011-01-01
A dimensionless correlation has been proposed for water frost porosity expressing its dependence on frost surface temperature and Reynolds number for laminar forced flow over a flat surface. The correlation is presented in terms of a dimensionless frost surface temperature scaled with the cold plate temperature, and the freezing temperature. The flow Reynolds number is scaled with reference to the critical Reynolds number for laminar-turbulent transition. The proposed correlation agrees satisfactorily with the simultaneous measurements of frost density and frost surface temperature covering a range of plate temperature, ambient air velocity, humidity, and temperature. It is revealed that the frost porosity depends primarily on the frost surface and the plate temperatures and the flow Reynolds number, and is only weakly dependent on the relative humidity. The results also point out the general character of frost porosity displaying a decrease with an increase in flow Reynolds number.
Response of hot element flush wall gauges in oscillating laminar flow
NASA Technical Reports Server (NTRS)
Giddings, T. A.; Cook, W. J.
1986-01-01
The time dependent response characteristics of flush-mounted hot element gauges used as instruments to measure wall shear stress in unsteady periodic air flows were investigated. The study was initiated because anomalous results were obtained from the gauges in oscillating turbulent flows for the phase relation of the wall shear stress variation, indicating possible gauge response problems. Flat plate laminar oscillating turbulent flows characterized by a mean free stream velocity with a superposed sinusoidal variation were performed. Laminar rather than turbulent flows were studied, because a numerical solution for the phase angle between the free stream velocity and the wall shear stress variation that is known to be correct can be obtained. The focus is on comparing the phase angle indicated by the hot element gauges with corresponding numerical prediction for the phase angle, since agreement would indicate that the hot element gauges faithfully follow the true wall shear stress variation.
Sedimentary microbial oxygen demand for laminar flow over a sediment bed of finite length.
Higashino, Makoto; Stefan, Heinz G
2005-09-01
Dead organic material accumulated on the bed of a lake, reservoir or wetland often provides the substrate for substantial microbial activity as well as chemical processes that withdraw dissolved oxygen (DO) from the water column. A model to estimate the actual DO profile and the "sedimentary oxygen demand (SOD)" must specify the rate of microbial or chemical activity in the sediment as well as the diffusive supply of DO from the water column through the diffusive boundary layer into the sediment. Most previous experimental and field studies have considered this problem with the assumptions that the diffusive boundary layer is (a) turbulent and (b) fully developed. These assumptions require that (a) the flow velocity above the sediment bed is fast enough to produce turbulent mixing in the boundary layer, and (b) the sediment bed is long. In this paper a model for laminar flow and SOD over a sediment bed of finite length is presented and the results are compared with those for turbulent flow. Laminar flow near a sediment bed is encountered in quiescent water bodies such as lakes, reservoirs, river backwaters, wetlands and ponds under calm wind conditions. The diffusive oxygen transfer through the laminar diffusive boundary layer above the sediment surface can restrict the microbial or chemical oxygen uptake inside the sediment significantly. The developing laminar diffusive boundary layer above the sediment/water interface is modeled based on the analogy with heat transfer, and DO uptake inside the sediment is modeled by Michaelis-Menten microbial growth kinetics. The model predicts that the rate of SOD at the beginning of the reactive sediment bed is solely dependent on microbial density in the sediment regardless of flow velocity and type. The rate of SOD, and the DO penetration depth into the sediment decrease in stream-wise direction over the length of the sediment bed, as the diffusive boundary layer above the sediment/water interface thickens. With increasing
Laskoski, Luciane Maria; Locatelli-Dittrich, Rosangela; Valadão, Carlos Augusto Araújo; Deconto, Ivan; Gonçalves, Kamila Alcala; Montiani-Ferreira, Fabiano; Brum, Juliana Sperotto; de Brito, Harald Fernando Vicente; de Sousa, Renato Silva
2015-08-01
The present study was aimed at identifying laminar lesions and leukocyte infiltration in hoof laminar tissue of horses with colic syndrome and its correlation with the total leukocyte count before death. Six healthy horses were used as control group (CG), and eighteen horses with lethal gastrointestinal disease were divided into two groups: leukopenic group (LG) with seven leukopenic horses, and non-leukopenic group (NLG) with 11 horses with total leukocyte count within reference range for the species. Leukocyte infiltration was examined by immunohistochemistry. Laminar lesions were observed in both LG and NLG, with no differences in severity between them. LG showed increase of the leukocyte infiltration in the hoof laminar tissue, when compared to CG and NLG. Horses with severe colic syndrome (LG and NLG) developed intense laminar lesions without clinical signs of laminitis, with increased leukocyte infiltration. However, the LG demonstrated an even higher increase of leukocyte infiltration compared to both CG and NLG.
Laskoski, Luciane Maria; Locatelli-Dittrich, Rosangela; Valadão, Carlos Augusto Araújo; Deconto, Ivan; Gonçalves, Kamila Alcala; Montiani-Ferreira, Fabiano; Brum, Juliana Sperotto; de Brito, Harald Fernando Vicente; de Sousa, Renato Silva
2015-08-01
The present study was aimed at identifying laminar lesions and leukocyte infiltration in hoof laminar tissue of horses with colic syndrome and its correlation with the total leukocyte count before death. Six healthy horses were used as control group (CG), and eighteen horses with lethal gastrointestinal disease were divided into two groups: leukopenic group (LG) with seven leukopenic horses, and non-leukopenic group (NLG) with 11 horses with total leukocyte count within reference range for the species. Leukocyte infiltration was examined by immunohistochemistry. Laminar lesions were observed in both LG and NLG, with no differences in severity between them. LG showed increase of the leukocyte infiltration in the hoof laminar tissue, when compared to CG and NLG. Horses with severe colic syndrome (LG and NLG) developed intense laminar lesions without clinical signs of laminitis, with increased leukocyte infiltration. However, the LG demonstrated an even higher increase of leukocyte infiltration compared to both CG and NLG. PMID:26267083
A two element laminar flow airfoil optimized for cruise. M.S. Thesis
NASA Technical Reports Server (NTRS)
Steen, Gregory Glen
1994-01-01
Numerical and experimental results are presented for a new two-element, fixed-geometry natural laminar flow airfoil optimized for cruise Reynolds numbers on the order of three million. The airfoil design consists of a primary element and an independent secondary element with a primary to secondary chord ratio of three to one. The airfoil was designed to improve the cruise lift-to-drag ratio while maintaining an appropriate landing capability when compared to conventional airfoils. The airfoil was numerically developed utilizing the NASA Langley Multi-Component Airfoil Analysis computer code running on a personal computer. Numerical results show a nearly 11.75 percent decrease in overall wing drag with no increase in stall speed at sailplane cruise conditions when compared to a wing based on an efficient single element airfoil. Section surface pressure, wake survey, transition location, and flow visualization results were obtained in the Texas A&M University Low Speed Wind Tunnel. Comparisons between the numerical and experimental data, the effects of the relative position and angle of the two elements, and Reynolds number variations from 8 x 10(exp 5) to 3 x 10(exp 6) for the optimum geometry case are presented.
Experimental study of the instability of laminar flow in a tube with deformable walls
NASA Astrophysics Data System (ADS)
Neelamegam, R.; Shankar, V.
2015-02-01
The onset of instability of laminar flow in a tube with deformable walls is studied experimentally in order to characterize how the onset is affected by the elastic (shear) modulus of the deformable wall. To this end, rectangular blocks of polydimethylsiloxane (PDMS) gels of different shear moduli are fabricated with a cylindrical hole (of diameter 1.65 mm) in which the fluid (water) flow occurs due to an imposed pressure difference. The shear moduli of the PDMS gels were in the range of 21 - 608 kPa. When fluid flows through the deformable tube, we find that the tube radius changes slowly as a function of distance along the flow, and this change is a function of Reynolds number (Re). The pressure drop between the two ends of the tube is measured, and the friction factor is calculated from this pressure drop. The friction factor vs. Re data shows that the expected laminar flow relation (f = 64/Re) for flow in a rigid tube is seen in a deformable tube at lower Re, but there is a deviation from this relation at Re < 2000. We identify the Re at which the deviation occurs as the Reynolds number at which the laminar flow in the deformable tube becomes unstable. This transition Reynolds number is as low as 500 for the 21 kPa PDMS gel, the softest gel studied in this work, and this value is much lower than the critical Reynolds number (˜2000) for transition in a rigid tube. The onset of the transition is also independently corroborated using a dye-stream visualization method, and the transition Reynolds number obtained with this method agrees well with the Reynolds number at which there is a deviation in the friction-factor data from the laminar relation. This transition in a deformable tube which happens at Reynolds number much lower than 2000 could be potentially exploited in improving mixing in microscale devices.
Wu, Y.; Welty, J.R. . Dept. of Mechanical Engineering)
1994-08-01
A two-dimensional finite difference computer program in cylindrical coordinates has been developed to solve the case of laminar natural convection in a vertical tube open to large reservoir. Such a device, the open thermosyphon, is used in a number of applications, including the cooling of gas turbines, geothermal energy extraction, and thermosyphon solar water heaters. The objective of this work were to study the nature of fluid flow and the heat transfer rate along the tube wall. A semi-implicit, time marching, finite difference solution procedure was used, satisfying continuity, momentum, and energy equations for incompressible flow. Results show three well-defined flow regimes appearing as functions of the tube length-to-radius (aspect) ratio. Fluid motion in the tube and heat transfer rates became oscillatory at long time intervals. Plots of streamlines and isotherms at selected times for different aspect ratio tubes are also presented to show the transition behavior of fluid motion.
NASA Technical Reports Server (NTRS)
Burnel, S.; Gougat, P.; Martin, F.
1981-01-01
The natural instabilities which propagate in the laminar boundary layer of a flat plate composed of intermittent wave trains are described. A spectral analysis determines the frequency range and gives a frequency and the harmonic 2 only if there is a wall deformation. This analysis provides the amplitude modulation spectrum of the instabilities. Plots of the evolution of power spectral density are compared with the numerical results obtained from the resolve of the Orr-Sommerfeld equation, while the harmonic is related to a micro-recirculating flow near the wall deformation.
Laminar Natural Convection in Vertical Tubes with One End Open to a Large Reservoir
NASA Astrophysics Data System (ADS)
Wu, Yissu
1995-01-01
The problem of laminar natural convection in vertical tubes with one end open to a large reservoir, designated open thermosyphons, is numerically and experimentally examined to predict flow behavior and the heat transfer rates. In the numerical study, a semi-implicit, time-marching, finite -volume solution procedure was adopted to solve the three governing equations--mass, momentum, and energy--sequentially. Experimental work involved the use of a Mach-Zehnder interferometer to examine the temperature field for a modified rectangular open thermosyphon through the interpretation of fringe patterns. These experimental fringe patterns were used for the qualitative comparison with those obtained from the numerical analyses. Nusselt numbers were determined from the interferometer results and compared with numerical results. Heat transfer rates through the tube wall were found to be strong functions of the tube radius, and approached an asymptotic limit as the tube radius was increased. Both experimental and numerical results exhibited an oscillatory nature for large height-to-width (aspect ratio) open cavities. comparisons between experimental and numerically-generated fringe patterns indicated good agreement. Based on experimental results, a correlation between Nusselt number, Nu, and Rayleigh number, Ra_{rm w}, for different aspect ratios, L/W, was determined to be Nu = 0.036cdotrm Ra_sp{w }{2/5}cdot(L/W)^{-1/5} .
Comparison of NACA 0012 Laminar Flow Solutions: Structured and Unstructured Grid Methods
NASA Technical Reports Server (NTRS)
Swanson, R. C.; Langer, S.
2016-01-01
In this paper we consider the solution of the compressible Navier-Stokes equations for a class of laminar airfoil flows. The principal objective of this paper is to demonstrate that members of this class of laminar flows have steady-state solutions. These laminar airfoil flow cases are often used to evaluate accuracy, stability and convergence of numerical solution algorithms for the Navier-Stokes equations. In recent years, such flows have also been used as test cases for high-order numerical schemes. While generally consistent steady-state solutions have been obtained for these flows using higher order schemes, a number of results have been published with various solutions, including unsteady ones. We demonstrate with two different numerical methods and a range of meshes with a maximum density that exceeds 8 × 106 grid points that steady-state solutions are obtained. Furthermore, numerical evidence is presented that even when solving the equations with an unsteady algorithm, one obtains steady-state solutions.
NASA Technical Reports Server (NTRS)
Brooks, Cuyler W., Jr.; Harris, Charles D.; Harvey, William D.
1991-01-01
A swept supercritical wing incorporating laminar flow control at transonic flow conditions was designed and tested. The definition of an experimental suction coefficient and a derivation of the compressible and incompressible formulas for the computation of the coefficient from measurable quantities is presented. The suction flow coefficient in the highest velocity nozzles is shown to be overpredicted by as much as 12 percent through the use of an incompressible formula. However, the overprediction on the computed value of suction drag when some of the suction nozzles were operating in the compressible flow regime is evaluated and found to be at most 6 percent at design conditions.
NASA Technical Reports Server (NTRS)
Maddalon, Dal V.; Braslow, Albert L.
1990-01-01
The effectiveness and practicality of candidate leading edge systems for suction laminar flow control transport airplanes were investigated in a flight test program utilizing a modified JetStar airplane. The leading edge region imposes the most severe conditions on systems required for any type of laminar flow control. Tests of the leading edge systems, therefore, provided definitive results as to the feasibility of active laminar flow control on airplanes. The test airplane was operated under commercial transport operating procedures from various commercial airports and at various seasons of the year.
A reduced model for unsteady laminar flow past a solid body using matched asymptotics
NASA Astrophysics Data System (ADS)
Vadivelnadar Kartheeswaran, Ponnulakshmi; Guo, Xinjun; Mandre, Shreyas
2014-11-01
We present a reduced order method for unsteady, laminar flow past a smooth but otherwise arbitrarily shaped body at high Reynolds number. Inspired by matched asymptotic expansion of Navier-Stokes equation, the flow domain is divided into two regimes: (i) an outer inviscid region where the flow field is represented using potential flow and point vortices, and (ii) a boundary layer around the body where the flow field obeys Prandtl's boundary layer equations. Since both representations of the flow field are governed by identical process (viscous effects becoming negligible sufficiently away from the solid body), it is possible to match the flow field at the interface between the two domains. Matching the flow field at the interface dictates the strength and location of vorticity shed from the boundary layer to the outer region. An approximately 100-fold increase in computational speed may be achieved using this method. In this talk, we present results for the flow surrounding a 2D oscillating elliptic hydrofoil, a configuration employed for energy extraction from tides. Simulations are performed for various pitching and heaving parameters in an effort to optimize the stroke for maximum energy extraction. A reduced model for unsteady laminar flow past a solid body using matched asymptotics.
Micro-flow separation system using an open capillary tube that works under laminar flow conditions.
Jinno, Naoya; Hashimoto, Masahiko; Tsukagoshi, Kazuhiko
2009-02-01
A micro-flow separation system was developed using an open capillary, fused-silica or polyethylene tube, and an aqueous-organic mixture (water-acetonitrile-ethyl acetate mixture) as a carrier solution. A model analyte solution containing 2,6-naphthalenedisulfonic acid and 1-naphthol was injected into the capillary tube by a gravity method. The analyte solution was subsequently delivered through the capillary tube with the carrier solution by a micro-syringe pump; the system worked under laminar flow conditions. The analytes were separated through the capillary tube and detected on-capillary by an absorption detector. 2,6-Naphthalenedisulfonic acid and 1-naphthol were detected in this order with a carrier solution of water-acetonitrile-ethyl acetate (15:3:2 volume ratio), while they were detected in the reverse order with a carrier solution of water-acetonitrile-ethyl acetate (2:5:9 volume ratio) using a fused-silica capillary tube. Similar separation behavior, i.e., that the elution times of the analytes could be easily reversed by changing the component ratio of the solvents in the carrier solution, was observed with a polyethylene capillary tube.
Curran, Stephen J; Black, Richard A
2005-03-30
Rotating wall vessel bioreactors have been proposed as a means of controlling the fluid dynamic environment during long-term culture of mammalian cells and engineered tissues. In this study, we show how the delivery of oxygen to cells in an annular flow bioreactor is enhanced by the forced convective transport afforded by Taylor vortex flows. A fiberoptic oxygen probe with negligible lag time was used to measure the dissolved oxygen concentration in real time and under carefully controlled aeration conditions. From these data, the overall mass transfer coefficients were calculated and mass transport correlations determined under laminar Couette flow conditions and discrete Taylor vortex flow regimes, including laminar, wavy, and turbulent flows. While oxygen transport in Taylor vortex flows was significantly greater, and the available oxygen exceeded that consumed by murine fibroblasts in free suspension, the proportion of cells that remained viable decreased with increasing Reynolds number (101.8 < Rei < 1018), which we attribute to the action of fluid shear stresses on the cells as opposed to any limitation in mass transport. Nevertheless, the results of this study suggest that laminar Taylor-vortex flow regimes provide an effective means of maintaining the levels of oxygen transport required for long-term cell culture. PMID:15696514
A parametric study of supersonic laminar flow for swept wings using linear stability analysis
NASA Technical Reports Server (NTRS)
Cummings, Russell M.; Garcia, Joseph A.; Tu, Eugene L.
1995-01-01
A parametric study to predict the extent of laminar flow on the upper surface of a generic swept-back wing (NACA 64A010 airfoil section) at supersonic speeds was conducted. The results were obtained by using surface pressure predictions from an Euler/Navier-Stokes computational fluid dynamics code coupled with a boundary layer code, which predicts detailed boundary layer profiles, and finally with a linear stability code to determine the extent of laminar flow. The parameters addressed are Reynolds number, angle of attack, and leading-edge wing sweep. The results of this study show that an increase in angle of attack, for specific Reynolds numbers, can actually delay transition. Therefore, higher lift capability, caused by the increased angle of attack, as well as a reduction in viscous drag due to the delay in transition is possible for certain flight conditions.
Control of airborne nickel welding fumes by means of a vertical laminar air flow system
Helms, T.C.
1980-12-08
The purpose of this study was to evaluate the effeciveness of a clean room facility with laminar air flow in the control of nickel fumes released from metal inert gas (MIG) and shielded metal arc (SMA) welding operations performed on mild steel using nickel filler materials. From data observed in these experiments, it appears that the laminar flow clean room approach to controlling welding fumes can be successful in certain small table top welding operations. However, almost any interferences that obstruct the downward airflow can result in eddy currents and subsequent build-up of fumes by entrapment. Airflow patterns differ significantly when comparing table top operations to welding on large cylindrical and/or doughnut shaped items. (JGB)
Wu, Xiaohua; Moin, Parviz; Adrian, Ronald J.; Baltzer, Jon R.
2015-06-15
We report that the precise dynamics of breakdown in pipe transition is a century-old unresolved problem in fluid mechanics. We demonstrate that the abruptness and mysteriousness attributed to the Osborne Reynolds pipe transition can be partially resolved with a spatially developing direct simulation that carries weakly but finitely perturbed laminar inflow through gradual rather than abrupt transition arriving at the fully developed turbulent state. Our results with this approach show during transition the energy norms of such inlet perturbations grow exponentially rather than algebraically with axial distance. When inlet disturbance is located in the core region, helical vortex filaments evolvemore » into large-scale reverse hairpin vortices. The interaction of these reverse hairpins among themselves or with the near-wall flow when they descend to the surface from the core produces small-scale hairpin packets, which leads to breakdown. When inlet disturbance is near the wall, certain quasi-spanwise structure is stretched into a Lambda vortex, and develops into a large-scale hairpin vortex. Small-scale hairpin packets emerge near the tip region of the large-scale hairpin vortex, and subsequently grow into a turbulent spot, which is itself a local concentration of small-scale hairpin vortices. This vortex dynamics is broadly analogous to that in the boundary layer bypass transition and in the secondary instability and breakdown stage of natural transition, suggesting the possibility of a partial unification. Under parabolic base flow the friction factor overshoots Moody’s correlation. Plug base flow requires stronger inlet disturbance for transition. Finally, accuracy of the results is demonstrated by comparing with analytical solutions before breakdown, and with fully developed turbulence measurements after the completion of transition.« less
Wu, Xiaohua; Moin, Parviz; Adrian, Ronald J.; Baltzer, Jon R.
2015-06-15
We report that the precise dynamics of breakdown in pipe transition is a century-old unresolved problem in fluid mechanics. We demonstrate that the abruptness and mysteriousness attributed to the Osborne Reynolds pipe transition can be partially resolved with a spatially developing direct simulation that carries weakly but finitely perturbed laminar inflow through gradual rather than abrupt transition arriving at the fully developed turbulent state. Our results with this approach show during transition the energy norms of such inlet perturbations grow exponentially rather than algebraically with axial distance. When inlet disturbance is located in the core region, helical vortex filaments evolve into large-scale reverse hairpin vortices. The interaction of these reverse hairpins among themselves or with the near-wall flow when they descend to the surface from the core produces small-scale hairpin packets, which leads to breakdown. When inlet disturbance is near the wall, certain quasi-spanwise structure is stretched into a Lambda vortex, and develops into a large-scale hairpin vortex. Small-scale hairpin packets emerge near the tip region of the large-scale hairpin vortex, and subsequently grow into a turbulent spot, which is itself a local concentration of small-scale hairpin vortices. This vortex dynamics is broadly analogous to that in the boundary layer bypass transition and in the secondary instability and breakdown stage of natural transition, suggesting the possibility of a partial unification. Under parabolic base flow the friction factor overshoots Moody’s correlation. Plug base flow requires stronger inlet disturbance for transition. Finally, accuracy of the results is demonstrated by comparing with analytical solutions before breakdown, and with fully developed turbulence measurements after the completion of transition.
Wu, Xiaohua; Moin, Parviz; Adrian, Ronald J; Baltzer, Jon R
2015-06-30
The precise dynamics of breakdown in pipe transition is a century-old unresolved problem in fluid mechanics. We demonstrate that the abruptness and mysteriousness attributed to the Osborne Reynolds pipe transition can be partially resolved with a spatially developing direct simulation that carries weakly but finitely perturbed laminar inflow through gradual rather than abrupt transition arriving at the fully developed turbulent state. Our results with this approach show during transition the energy norms of such inlet perturbations grow exponentially rather than algebraically with axial distance. When inlet disturbance is located in the core region, helical vortex filaments evolve into large-scale reverse hairpin vortices. The interaction of these reverse hairpins among themselves or with the near-wall flow when they descend to the surface from the core produces small-scale hairpin packets, which leads to breakdown. When inlet disturbance is near the wall, certain quasi-spanwise structure is stretched into a Lambda vortex, and develops into a large-scale hairpin vortex. Small-scale hairpin packets emerge near the tip region of the large-scale hairpin vortex, and subsequently grow into a turbulent spot, which is itself a local concentration of small-scale hairpin vortices. This vortex dynamics is broadly analogous to that in the boundary layer bypass transition and in the secondary instability and breakdown stage of natural transition, suggesting the possibility of a partial unification. Under parabolic base flow the friction factor overshoots Moody's correlation. Plug base flow requires stronger inlet disturbance for transition. Accuracy of the results is demonstrated by comparing with analytical solutions before breakdown, and with fully developed turbulence measurements after the completion of transition.
Measurements of laminar burning velocities for natural gas-hydrogen-air mixtures
Huang, Zuohua; Zhang, Yong; Zeng, Ke; Liu, Bing; Wang, Qian; Jiang, Deming
2006-07-15
Laminar flame characteristics of natural gas-hydrogen-air flames were studied in a constant-volume bomb at normal temperature and pressure. Laminar burning velocities and Markstein lengths were obtained at various ratios of hydrogen to natural gas (volume fraction from 0 to 100%) and equivalence ratios (f from 0.6 to 1.4). The influence of stretch rate on flame was also analyzed. The results show that, for lean mixture combustion, the flame radius increases with time but the increasing rate decreases with flame expansion for natural gas and for mixtures with low hydrogen fractions, while at high hydrogen fractions, there exists a linear correlation between flame radius and time. For rich mixture combustion, the flame radius shows a slowly increasing rate at early stages of flame propagation and a quickly increasing rate at late stages of flame propagation for natural gas and for mixtures with low hydrogen fractions, and there also exists a linear correlation between flame radius and time for mixtures with high hydrogen fractions. Combustion at stoichiometric mixture demonstrates the linear relationship between flame radius and time for natural gas-air, hydrogen-air, and natural gas-hydrogen-air flames. Laminar burning velocities increase exponentially with the increase of hydrogen fraction in mixtures, while the Markstein length decreases and flame instability increases with the increase of hydrogen fractions in mixture. For a fixed hydrogen fraction, the Markstein number shows an increase and flame stability increases with the increase of equivalence ratios. Based on the experimental data, a formula for calculating the laminar burning velocities of natural gas-hydrogen-air flames is proposed. (author)
The Langley 8-ft transonic pressure tunnel laminar-flow-control experiment
NASA Technical Reports Server (NTRS)
Bobbitt, Percy J.; Harvey, William D.; Harris, Charles D.; Brooks, Cuyler W., Jr.
1992-01-01
An account is given of the considerations involved in selecting the NASA-Langley transonic pressure tunnel's design and test parameters, as well as its liner and a swept wing for laminar flow control (LFC) experimentation. Attention is given to the types and locations of the instrumentation employed. Both slotted and perforated upper surfaces were tested with partial- and full-chord suction; representative results are presented for all.
Pore-scale simulation of laminar flow through porous media
NASA Astrophysics Data System (ADS)
Piller, M.; Casagrande, D.; Schena, G.; Santini, M.
2014-04-01
The experimental investigation of flow through porous media is inherently difficult due to the lack of optical access. The recent developments in the fields of X-ray micro-tomography (micro-CT hereafter), digital sample reconstruction by image-processing techniques and fluid-dynamics simulation, together with the increasing power of super-computers, allow to carry out pore-scale simulations through digitally-reconstructed porous samples. The scientific relevance of pore-scale simulations lies in the possibility of upscaling the pore-level data, yielding volume-averaged quantities useful for practical purposes. One of the best-known examples of upscaling is the calculation of absolute and relative permeability of reservoir rocks. This contribution presents a complete work-flow for setting up pore-scale simulations, starting from the micro-CT of a (in general small) porous sample. Relevant applications are discussed in order to reveal the potential of the proposed methodology.
Micropatterned biofilm formations by laminar flow-templating.
Aznaveh, Nahid Babaei; Safdar, Muhammad; Wolfaardt, Gideon; Greener, Jesse
2014-08-01
We present a microfluidic device capable of patterning linear biofilm formations using a flow templating approach. We describe the design considerations and fabrication methodology of a two level flow-templating micro-bioreactor (FT-μBR), which generates a biofilm growth stream surrounded on 3 sides by a growth inhibiting confinement stream. Through a combination of experiments and simulations we comprehensively evaluate and exploit control parameters to manipulate the biofilm growth template stream dimensions. The FT-μBR is then used to grow biofilm patterns with controllable dimensions. A proof-of-principle study using the device demonstrates its utility in conducting biofilm growth rate measurements under different shear stress environments. This opens the way for quantitative studies into the effects of the local shear environment on biofilm properties and for the synthesis of a new generation of functional biomaterials with controllable properties. PMID:24722812
Laminar flow effects in the coil planet centrifuge
NASA Technical Reports Server (NTRS)
Herrmann, F. T.
1984-01-01
The coil planet centrifuge designed by Ito employs flow of a single liquid phase, through a rotating coiled tube in a centrifugal force field, to provide a separation of particles based on sedimentation rates. Mathematical solutions are derived for the linear differential equations governing particle behavior in the coil planet centrifuge device. These solutions are then applied as the basis of a model for optimizing particle separations.
Erosion of a granular bed by laminar fluid flow
NASA Astrophysics Data System (ADS)
Orpe, Ashish; Lobovsky, Alex; Molloy, Ryan; Kudrolli, Arshad; Rothman, Daniel
2007-03-01
Motivated by examples of erosive incision of channels in sand, we investigate the motion of individual grains in a granular bed as a function of fluid flow rate to give us new insight concerning the relationship between hydrodynamic stress and surficial granular flow. A closed channel of rectangular cross section is partially filled with glass beads and a fluid and a constant flux Q is circulated through the channel. The fluid has same refractive index as the glass beads and is illuminated with a laser sheet away from the sidewalls. The bed erodes quadratically in time to a height hc which depends on Q. The Shields criterion, which is proportional to the ratio of the viscous shear stress and gravitational normal stress, describes the observed hc√Q when a height offset of approximately half a grain diameter is introduced. The offset can be interpreted as arising due to differences between the flow near a porous boundary and a smooth wall. Introducing this offset in the estimation of the shear stress yields a grain flux qx in the bed load regime proportional to (τ- τc)^2, where τ is the non-dimensional shear stress, and τc corresponds to the Shields criteria.
NASA Technical Reports Server (NTRS)
1999-01-01
This document describes the design, fabrication, and installation of the suction panel and the required support structure, ducting, valving, and high-lift system (Krueger flaps) for flight demonstration of hybrid laminar flow control on the Boeing 757 airplane.
NASA Astrophysics Data System (ADS)
Kenis, Paul
2005-03-01
Over the last decade a wide variety of research efforts in microchemical systems, in which fluid flow is laminar, has developed. The original challenge of mixing in the absence of turbulence in this laminar flow regime has been overcome through various technical approaches including zig-zag or serpentine-shaped channels (Branebjerg, Beebe et al.), lamination (e.g. Manz, Jensen et al.), hydrodynamic focusing (Austin et al.), and integrated herringbone features (Stroock et al.). Others have grasped the opportunity to utilize multistream laminar flow for example for a T-sensor for blood analysis (Weigl et al.) and in microfabrication or cell studies (Whitesides et al.). This presentation will highlight the development of (i) a membraneless fuel cell, and (ii) a microreactor for cofactor regeneration that utilize multistream laminar flow. Various performance-determining characteristics and engineering improvements will be discussed.
Shear stress related blood damage in laminar couette flow.
Paul, Reinhard; Apel, Jörn; Klaus, Sebastian; Schügner, Frank; Schwindke, Peter; Reul, Helmut
2003-06-01
Artificial organs within the blood stream are generally associated with flow-induced blood damage, particularly hemolysis of red blood cells. These damaging effects are known to be dependent on shear forces and exposure times. The determination of a correlation between these flow-dependent properties and actual hemolysis is the subject of this study. For this purpose, a Couette device has been developed. A fluid seal based on fluorocarbon is used to separate blood from secondary external damage effects. The shear rate within the gap is controlled by the rotational speed of the inner cylinder, and the exposure time by the amount of blood that is axially pumped through the device per given time. Blood damage is quantified by the index of hemolysis (IH), which is calculated from photometric plasma hemoglobin measurements. Experiments are conducted at exposure times from texp=25 - 1250 ms and shear rates ranging from tau=30 up to 450 Pa ensuring Taylor-vortex free flow characteristics. Blood damage is remarkably low over a broad range of shear rates and exposure times. However, a significant increase in blood damage can be observed for shear stresses of tau>or= 425 Pa and exposure times of texp>or= 620 ms. Maximum hemolysis within the investigated range is IH=3.5%. The results indicate generally lower blood damage than reported in earlier studies with comparable devices, and the measurements clearly indicate a rather abrupt (i.e., critical levels of shear stresses and exposure times) than gradual increase in hemolysis, at least for the investigated range of shear rates and exposure times. PMID:12780506
Laminar flow between a stationary and a rotating disk with radial throughflow
Nesreddine, H.; Nguyen, C.T.; Vo-Ngoc, D.
1995-05-01
The problem of axisymmetric laminar flow of a viscous incompressible fluid that occurs between a stationary and a rotating disk subjected to a uniform radial throughflow has been numerically investigated for a large range of flow parameters. Results show that the basic flow structure is rather complex and depends strongly on both the rotational and the flow structure is rather complex and depends strongly on both the rotational and the throughflow Reynolds numbers. In general, the basic unicellular structure has been observed. With the increase of the throughflow Reynolds number, a multicellular flow structure may be found. The phenomenon of multiple solutions has been clearly observed for cases with sufficiently high rational Re and/or high throughflow Re. Among these solutions, stable as well as unstable solutions have been determined by applying Rayleigh`s stability criterion. The influence of the starting conditions on the stability of the flow has also been investigated for various ranges of flow parameters.
Laminar flame and acoustic waves in two-dimensional flow
Zaytsev, M. L. Akkerman, V. B.
2011-03-15
The complete system of fluid dynamics equations describing the development of instability of a reaction front in a two-dimensional flow in reversed time are reduced to a closed system of equations of front dynamics by using Lagrangian variables and integrals of motion. The system can be used to analyze processes behind the front without solving the complete system of fluid dynamics and chemical kinetics equations. It is demonstrated how the gas density disturbances induced by the moving front can be described in the adiabatic approximation.
NASA Astrophysics Data System (ADS)
Crowley, Christopher; Krygier, Michael; Borrero-Echeverry, Daniel; Grigoriev, Roman; Schatz, Michael
2015-11-01
The transition to turbulence in counter-rotating Taylor-Couette flow typically occurs through a sequence of supercritical bifurcations of stable flow states (e.g. spiral vortices, interpenetrating spirals (IPS), and wavy interpenetrating spirals). Coughlin and Marcus have proposed a mechanism by which these laminar spiral flows undergo a secondary instability that leads to turbulence. We report the discovery of a counter-rotating regime (Reout = - 1000 , Rein ~ 640) of small aspect ratio/large radius ratio Taylor-Couette flow (Γ = 5 . 26 / η = 0 . 91), where the system bypasses the primary instability to stable laminar spirals and instead undergoes a direct transition to turbulence as the inner cylinder rotation rate is slowly increased. This transition is mediated by an unstable IPS state. We study the transition experimentally using flow visualization and tomographic PIV, and show that it is both highly repeatable and that it shows hysteresis as the inner cylinder rotation rate is decreased. As Rein is decreased, the turbulent flow relaminarizes into an intermediate, stable IPS state. Decreasing Rein further returns the system back to circular Couette flow. This study was supported by NSF DMS-1125302 and NSF CMMI-1234436.
Numerical simulation of laminar reacting flows with complex chemistry
Day, Marcus S.; Bell, John B.
1999-12-01
We present an adaptive algorithm for low Mach number reacting flows with complex chemistry. Our approach uses a form of the low Mach number equations that discretely conserves both mass and energy. The discretization methodology is based on a robust projection formulation that accommodates large density contrasts. The algorithm uses an operator-split treatment of stiff reaction terms and includes effects of differential diffusion. The basic computational approach is embedded in an adaptive projection framework that uses structured hierarchical grids with subcycling in time that preserves the discrete conservation properties of the underlying single-grid algorithm. We present numerical examples illustrating the performance of the method on both premixed and non-premixed flames.
Development of Advanced High Lift Leading Edge Technology for Laminar Flow Wings
NASA Technical Reports Server (NTRS)
Bright, Michelle M.; Korntheuer, Andrea; Komadina, Steve; Lin, John C.
2013-01-01
This paper describes the Advanced High Lift Leading Edge (AHLLE) task performed by Northrop Grumman Systems Corporation, Aerospace Systems (NGAS) for the NASA Subsonic Fixed Wing project in an effort to develop enabling high-lift technology for laminar flow wings. Based on a known laminar cruise airfoil that incorporated an NGAS-developed integrated slot design, this effort involved using Computational Fluid Dynamics (CFD) analysis and quality function deployment (QFD) analysis on several leading edge concepts, and subsequently down-selected to two blown leading-edge concepts for testing. A 7-foot-span AHLLE airfoil model was designed and fabricated at NGAS and then tested at the NGAS 7 x 10 Low Speed Wind Tunnel in Hawthorne, CA. The model configurations tested included: baseline, deflected trailing edge, blown deflected trailing edge, blown leading edge, morphed leading edge, and blown/morphed leading edge. A successful demonstration of high lift leading edge technology was achieved, and the target goals for improved lift were exceeded by 30% with a maximum section lift coefficient (Cl) of 5.2. Maximum incremental section lift coefficients ( Cl) of 3.5 and 3.1 were achieved for a blown drooped (morphed) leading edge concept and a non-drooped leading edge blowing concept, respectively. The most effective AHLLE design yielded an estimated 94% lift improvement over the conventional high lift Krueger flap configurations while providing laminar flow capability on the cruise configuration.
Flow/Soot-Formation Interactions in Nonbuoyant Laminar Diffusion Flames
NASA Technical Reports Server (NTRS)
Dai, Z.; Faeth, G. M.
1999-01-01
Nonpremixed (diffusion) flames are attractive for practical applications because they avoid the stability, autoignition, flashback, etc. problems of premixed flames. Unfortunately, soot formation in practical hydrocarbon-fueled diffusion flames reduces their attractiveness due to widely-recognized public health and combustor durability problems of soot emissions. For example, more deaths are attributed to the emission of soot (15,000-60,000 deaths annually in the U.S. alone) than any other combustion-generated pollutant. In addition, continuum radiation from soot-containing flames is the principle heat load to combustor components and is mainly responsible for engine durability problems of aircraft and gas turbine engines. As a result, there is considerable interest in controlling both soot concentrations within flames and soot emissions from flames. Thus, the objective of the present investigation is to study ways to control soot formation in diffusion flames by manipulating the mixing process between the fuel and oxidant streams. In order to prevent the intrusion of gravity from masking flow properties that reduce soot formation in practical flames (where effects of gravity are small), methods developed during past work will be exploited to minimize effects of buoyant motion.
Application of Laminar Flow Control Technology to Long-Range Transport Design
NASA Technical Reports Server (NTRS)
Gratzer, L. B.; George-Falvy, D.
1978-01-01
The impact of laminar flow control (LFC) technology on aircraft structural design concepts and systems was discussed and the corresponding benefits were shown in terms of performance and fuel economy. Specific topics discussed include: (1) recent advances in laminar boundary layer development and stability analysis techniques in terms of suction requirements and wing suction surface design; (2) validation of theory and realistic simulation of disturbances and off-design conditions by wind tunnel testing; (3) compatibility of aerodynamic design of airfoils and wings with LFC requirements; (4) structural alternatives involving advanced alloys or composites in combinations made possible by advanced materials processing and manufacturing techniques; (5) addition of suction compressor and drive units and their location on the aircraft; and (6) problems associated with operation of LFC aircraft, including accumulation of insects at low altitudes and environmental considerations.
Hydrodynamics and heat transfer in a laminar flow of viscoelastic fluid in a flat slot channel
NASA Astrophysics Data System (ADS)
Ananyev, D. V.; Halitova, G. R.; Vachagina, E. K.
2015-01-01
Results of the numerical study of hydrodynamics and heat transfer in a laminar flow of viscoelastic fluid in a flat slot channel are presented in the present paper. The model of nonlinear viscoelastic fluid of Phan-Thien—Tanner is used to describe the viscoelastic properties of fluid. The solution to the stated problem by software package "COMSOL Multiphysics" is considered. The method of solution is verified, and results are compared with data of the other authors. It is determined that in the flow of viscoelastic fluid in a flat slot channel, the maximal contribution of heating due to dissipation is approximately 7-8 %.
Demonstration of a plasma mirror based on a laminar flow water film
Panasenko, Dmitriy; Shu, Anthony J.; Gonsalves, Anthony; Nakamura, Kei; Matlis, Nicholas H.; Toth, Csaba; Leemans, Wim P.
2010-08-15
A plasma mirror based on a laminar water film with low flow speed (0.5-2 cm/s) has been developed and characterized, for use as an ultrahigh intensity optical reflector. The use of flowing water as a target surface automatically results in each laser pulse seeing a new interaction surface and avoids the need for mechanical scanning of the target surface. In addition, the breakdown of water does not produce contaminating debris that can be deleterious to vacuum chamber conditions and optics, such as is the case when using conventional solid targets. The mirror exhibits 70% reflectivity, while maintaining high-quality of the reflected spot.
Numerical Solution of Supersonic Laminar Flow Over an Inclined Body of Revolution
NASA Technical Reports Server (NTRS)
Hung, C. M.
1980-01-01
A mixed explicit-implicit scheme is used to solve the time-dependent thin-layer approximation of the Navier-Stokes equations for a supersonic laminar flow over an inclined body of revolution. Test cases for Mach 2.8 flow over a cylinder with 15-deg flare angle at angles of attack of 0,1, and 4 deg are calculated. Good agreement is obtained between the present computed results and experimental measurements of surface pressure. A pair of vortices on the leeward and a peak in the normal force distribution near the flared juncture are predicted; the role of circumferential communication is discussed.
Numerical solution of supersonic laminar flow over an inclined body of revolution
NASA Technical Reports Server (NTRS)
Hung, C. M.
1979-01-01
A mixed explicit-implicit scheme is used to solve the time-dependent thin-layer approximation of the Navier-Stokes equations for a supersonic laminar flow over an inclined body of revolution. Test cases for Mach 2.8 flow over a cylinder with 15 deg flare angle at angles of attack of 0, 1, and 4 deg are calculated. Good agreement is obtained between the present computed results and experimental measurements of surface pressure. A pair of vortices on the leeward and a peak in the normal force distribution near the flared juncture are predicted; the role of circumferential communication is discussed.
NASA Technical Reports Server (NTRS)
1976-01-01
The feasibility of using porous composite materials (Kevlar, Doweave, and Leno Weave) as lightweight, efficient laminar flow control (LFC) surface materials is compared to the metallic 319L stainless Dynapore surfaces and electron beam drilled composite surfaces. Areas investigated include: (1) selection of the LFC-suitable surface materials, structural materials, and fabrication techniques for the LFC aircraft skins; (2) aerodynamic static air flow test results in terms of pressure drop through the LFC panel and the corresponding effective porosity; (3) structural design definition and analyses of the panels, and (4) contamination effects on static drop and effective porosity. Conclusions are presented and discussed.
NASA Astrophysics Data System (ADS)
Kowalski, Adam; Olsen, Thomas; Wiener, Richard
2006-11-01
Previously we have presented preliminary measurements indicating that the irregular generation of new Taylor Vortex Pairs in laminar Taylor-Couette flow with hourglass geometry could be characterized as low dimensional chaos and in the corresponding case of turbulent flow the chaotic dimension was higher. We now present data from far more extended time series of the periods between vortex formation, confirming and extending our original results. We present confirmation of our computational methodology in other systems. T. Olsen, R. Bjorge, & R. Wiener, Bull. Am. Phys. Soc. 47-10, 76 (2002). T. Olsen, B. Tomlin, R. Bjorge, & R. Wiener, Bull. Am. Phys. Soc. 48-10, 111 (2003)
Demonstration of a plasma mirror based on a laminar flow water film
Panasenko, Dmitriy; Shu, Anthony; Gonsalves, Anthony; Nakamura, Kei; Matlis, Nicholas; Toth, Csaba; Leemans, Wim
2011-07-22
A plasma mirror based on a laminar water film with low flow speed 0.5-2 cm/s has been developed and characterized, for use as an ultrahigh intensity optical reflector. The use of flowing water as atarget surface automatically results in each laser pulse seeing a new interaction surface and avoids the need for mechanical scanning of the target surface. In addition, the breakdown of water does notproduce contaminating debris that can be deleterious to vacuum chamber conditions and optics, such as is the case when using conventional solid targets. The mirror exhibits 70percent reflectivity, whilemaintaining high-quality of the reflected spot.
Law Jr., C.G.; Pierini, P.; Newman, J.
1980-07-01
Experimental data and theoretical calculations are presented for the mass-transfer rate to rotating disks and rotating rings when laminar, transition, and fully developed turbulent flow exist upon different portions of the surface. Good agreement of data and the model is obtained for rotating disks and relatively thick rotating rings. Results of the calculations for thin rings generally exceed the experimental data measured in transition and turbulent flow. A y{sup +{sup 3}} form for the eddy diffusivity is used to fit the data. No improvement is noticed with a form involving both y{sup +{sup 3}} and y{sup +{sup 3}}.
Lashgari, Iman; Picano, Francesco; Breugem, Wim-Paul; Brandt, Luca
2014-12-19
The aim of this Letter is to characterize the flow regimes of suspensions of finite-size rigid particles in a viscous fluid at finite inertia. We explore the system behavior as a function of the particle volume fraction and the Reynolds number (the ratio of flow and particle inertia to viscous forces). Unlike single-phase flows, where a clear distinction exists between the laminar and the turbulent states, three different regimes can be identified in the presence of a particulate phase, with smooth transitions between them. At low volume fractions, the flow becomes turbulent when increasing the Reynolds number, transitioning from the laminar regime dominated by viscous forces to the turbulent regime characterized by enhanced momentum transport by turbulent eddies. At larger volume fractions, we identify a new regime characterized by an even larger increase of the wall friction. The wall friction increases with the Reynolds number (inertial effects) while the turbulent transport is weakly affected, as in a state of intense inertial shear thickening. This state may prevent the transition to a fully turbulent regime at arbitrary high speed of the flow.
NASA Astrophysics Data System (ADS)
Urban, O.; Jehlička, J.; Pokorný, J.; Rouzaud, J. N.
2003-08-01
In order to estimate the role of laminar flow of viscous, aromatic matter of carbonaceous precursor on microtextural preorientation in pregraphitization stage, we performed experiments with coal tar pitch (CTP). The principal hypothesis of preorientation of basic structural units (BSUs) in the case of laminar flow (pressure impregnation of CTP into porous matrix) and secondary release of volatiles during carbonization were studied. Glass microplates, planar porous medium with average distance between single microplates 5 μm were used as suitable porous matrix. Samples of CTP were carbonized up to 2500 °C. Optical microscopy reveals large flow domains in the sample of cokes carbonized between glass microplates. Raman microspectroscopy and high resolution transmission electron microscopy (HRTEM) show that at nanometric scale, the samples do not support the proposed hypotheses. With increasing temperature of pyrolysis, the graphitization of CTP impregnated into porous matrix proceeds to lower degree of structural ordering in comparison with single pyrolyzed CTP. This is explained by the release of volatile matter during carbonization in geometrically restricted spaces. More evident structural changes were discovered with the sample of single coke, where parts of fine grain mosaics, relicts of 'so called QI parts', reveal higher structural organization, in comparison with large and prolonged flow domains, similar to flow domains of cokes from microplates.
Experiments on densely-loaded non-Newtonian slurries in laminar and turbulent pipe flows
NASA Astrophysics Data System (ADS)
Park, Joel T.; Mannheimer, Richard J.; Grimley, Terrence A.; Morrow, Thomas B.
1989-06-01
An experimental description of the flow structure of non-Newtonian slurries in the laminar, transitional, and fully-developed turbulent pipe flow regimes was the primary objective of this research. Experiments were conducted in a large-scale pipe slurry flow facility with an inside diameter of 51 mm (2 inches). Approximately, 550 liters (145 gal) of slurry were necessary in the operation of the loop. Detailed velocity profile measurements by a two-color, two-component laser Doppler anemometer (LDA) were accomplished in a transparent test section with an optically transparent slurry. These velocity measurements were apparently the first ever reported for a non-Newtonian slurry with a yield value. The transparent slurry was formulated for these experiments from silica with a particle size of one to two microns, mineral oil, and Stoddard solvent. From linear regression analysis of concentric-cylinder viscometer data, the slurry exhibited yield-power-law behavior with a yield stress of 100 dynes/cm(sup 2), and an exponent of 0.630 for a solids concentration of 5.65 percent by weight. Good agreement was attained with rheological data derived from the pressure drop data in the flow loop under laminar flow conditions. The rheological properties of the transparent slurry were similar to many industrial slurries, including coal slurries, which have a yield value.
Development of quiet-flow supersonic wind tunnels for laminar-turbulent transition research
NASA Technical Reports Server (NTRS)
Schneider, Steven P.
1994-01-01
This grant supported research into quiet-flow supersonic wind-tunnels, between May 1990 and December 1994. Quiet-flow nozzles operate with laminar nozzle-wall boundary layers, in order to provide low-disturbance flow for studies of laminar-turbulent transition under conditions comparable to flight. Major accomplishments include: (1) the design, fabrication, and performance-evaluation of a new kind of quiet tunnel, a quiet-flow Ludweig tube; (2) the integration of preexisting codes for nozzle design, 2D boundary-layer computation, and transition-estimation into a single user-friendly package for quiet-nozzle design; and (3) the design and preliminary evaluation of supersonic nozzles with square cross-section, as an alternative to conventional quiet-flow nozzles. After a brief summary of (1), a description of (2) is presented. Published work describing (3) is then summarized. The report concludes with a description of recent results for the Tollmien-Schlichting and Gortler instability in one of the square nozzles previously analyzed.
The response of a laminar boundary layer in supersonic flow to small amplitude progressive waves
NASA Technical Reports Server (NTRS)
Duck, Peter W.
1989-01-01
The effect of a small amplitude progressive wave on the laminar boundary layer on a semi-infinite flat plate, due to a uniform supersonic freestream flow, is considered. The perturbation to the flow divides into two streamwise zones. In the first, relatively close to the leading edge of the plate, on a transverse scale comparable to the boundary layer thickness, the perturbation flow is described by a form of the unsteady linearized compressible boundary layer equations. In the freestream, this component of flow is governed by the wave equation, the solution of which provides the outer velocity conditions for the boundary layer. This system is solved numerically, and also the asymptotic structure in the far downstream limit is studied. This reveals a breakdown and a subsequent second streamwise zone, where the flow disturbance is predominantly inviscid. The two zones are shown to match in a proper asymptotic sense.
A laminar flow unit for the care of critically ill newborn infants
Perez, Jose MR; Golombek, Sergio G; Fajardo, Carlos; Sola, Augusto
2013-01-01
Introduction Medical and nursing care of newborns is predicated on the delicate control and balance of several vital parameters. Closed incubators and open radiant warmers are the most widely used devices for the care of neonates in intensive care; however, several well-known limitations of these devises have not been resolved. The use of laminar flow is widely used in many fields of medicine, and may have applications in neonatal care. Objective To describe the neonatal laminar flow unit, a new equipment we designed for care of ill newborns. Methods The idea, design, and development of this device was completed in Sao Paulo, Brazil. The unit is an open mobile bed designed with the objective of maintaining the advantages of the incubator and radiant warmer, while overcoming some of their inherent shortcomings; these shortcomings include noise, magnetic fields and acrylic barriers in incubators, and lack of isolation and water loss through skin in radiant warmers. The unit has a pump that aspirates environmental air which is warmed by electrical resistance and decontaminated with High Efficiency Particulate Air Filter (HEPA) filters (laminar flow). The flow is directed by an air flow directioner. The unit has an embedded humidifier to increase humidity in the infant’s microenvironment and a servo control mechanism for regulation of skin temperature. Results The laminar flow unit is open and facilitates access of care providers and family, which is not the case in incubators. It provides warming by convection at an air velocity of 0.45 m/s, much faster than an incubator (0.1 m/s). The system provides isolation 1000 class (less than 1,000 particles higher than 0.3 micron per cubic feet at all times). This is much more protection than an incubator provides and more than radiant warmers, which have no isolation whatsoever. Additionally, it provides humidification of the newborn’s microenvironment (about 60% relative humidity), which is impossible with a radiant
Lane, Whitney O; Jantzen, Alexandra E; Carlon, Tim A; Jamiolkowski, Ryan M; Grenet, Justin E; Ley, Melissa M; Haseltine, Justin M; Galinat, Lauren J; Lin, Fu-Hsiung; Allen, Jason D; Truskey, George A; Achneck, Hardean E
2012-01-01
The overall goal of this method is to describe a technique to subject adherent cells to laminar flow conditions and evaluate their response to well quantifiable fluid shear stresses. Our flow chamber design and flow circuit (Fig. 1) contains a transparent viewing region that enables testing of cell adhesion and imaging of cell morphology immediately before flow (Fig. 11A, B), at various time points during flow (Fig. 11C), and after flow (Fig. 11D). These experiments are illustrated with human umbilical cord blood-derived endothelial progenitor cells (EPCs) and porcine EPCs. This method is also applicable to other adherent cell types, e.g. smooth muscle cells (SMCs) or fibroblasts. The chamber and all parts of the circuit are easily sterilized with steam autoclaving. In contrast to other chambers, e.g. microfluidic chambers, large numbers of cells (> 1 million depending on cell size) can be recovered after the flow experiment under sterile conditions for cell culture or other experiments, e.g. DNA or RNA extraction, or immunohistochemistry (Fig. 11E), or scanning electron microscopy. The shear stress can be adjusted by varying the flow rate of the perfusate, the fluid viscosity, or the channel height and width. The latter can reduce fluid volume or cell needs while ensuring that one-dimensional flow is maintained. It is not necessary to measure chamber height between experiments, since the chamber height does not depend on the use of gaskets, which greatly increases the ease of multiple experiments. Furthermore, the circuit design easily enables the collection of perfusate samples for analysis and/or quantification of metabolites secreted by cells under fluid shear stress exposure, e.g. nitric oxide (Fig. 12).
Gas Flow Dynamics in Inlet Capillaries: Evidence for non Laminar Conditions
NASA Astrophysics Data System (ADS)
Wißdorf, Walter; Müller, David; Brachthäuser, Yessica; Langner, Markus; Derpmann, Valerie; Klopotowski, Sebastian; Polaczek, Christine; Kersten, Hendrik; Brockmann, Klaus; Benter, Thorsten
2016-09-01
In this work, the characteristics of gas flow in inlet capillaries are examined. Such inlet capillaries are widely used as a first flow restriction stage in commercial atmospheric pressure ionization mass spectrometers. Contrary to the common assumption, we consider the gas flow in typical glass inlet capillaries with 0.5 to 0.6 mm inner diameters and lengths about 20 cm as transitional or turbulent. The measured volume flow of the choked turbulent gas stream in such capillaries is 0.8 L·min-1 to 1.6 L·min-1 under typical operation conditions, which is in good agreement to theoretically calculated values. Likewise, the change of the volume flow in dependence of the pressure difference along the capillary agrees well with a theoretical model for turbulent conditions as well as with exemplary measurements of the static pressure inside the capillary channel. However, the results for the volume flow of heated glass and metal inlet capillaries are neither in agreement with turbulent nor with laminar models. The velocity profile of the neutral gas in a quartz capillary with an inner diameter similar to commercial inlet capillaries was experimentally determined with spatially resolved ion transfer time measurements. The determined gas velocity profiles do not contradict the turbulent character of the flow. Finally, inducing disturbances of the gas flow by placing obstacles in the capillary channel is found to not change the flow characteristics significantly. In combination the findings suggest that laminar conditions inside inlet capillaries are not a valid primary explanation for the observed high ion transparency of inlet capillaries under common operation conditions.
Gas Flow Dynamics in Inlet Capillaries: Evidence for non Laminar Conditions.
Wißdorf, Walter; Müller, David; Brachthäuser, Yessica; Langner, Markus; Derpmann, Valerie; Klopotowski, Sebastian; Polaczek, Christine; Kersten, Hendrik; Brockmann, Klaus; Benter, Thorsten
2016-09-01
In this work, the characteristics of gas flow in inlet capillaries are examined. Such inlet capillaries are widely used as a first flow restriction stage in commercial atmospheric pressure ionization mass spectrometers. Contrary to the common assumption, we consider the gas flow in typical glass inlet capillaries with 0.5 to 0.6 mm inner diameters and lengths about 20 cm as transitional or turbulent. The measured volume flow of the choked turbulent gas stream in such capillaries is 0.8 L·min(-1) to 1.6 L·min(-1) under typical operation conditions, which is in good agreement to theoretically calculated values. Likewise, the change of the volume flow in dependence of the pressure difference along the capillary agrees well with a theoretical model for turbulent conditions as well as with exemplary measurements of the static pressure inside the capillary channel. However, the results for the volume flow of heated glass and metal inlet capillaries are neither in agreement with turbulent nor with laminar models. The velocity profile of the neutral gas in a quartz capillary with an inner diameter similar to commercial inlet capillaries was experimentally determined with spatially resolved ion transfer time measurements. The determined gas velocity profiles do not contradict the turbulent character of the flow. Finally, inducing disturbances of the gas flow by placing obstacles in the capillary channel is found to not change the flow characteristics significantly. In combination the findings suggest that laminar conditions inside inlet capillaries are not a valid primary explanation for the observed high ion transparency of inlet capillaries under common operation conditions. Graphical Abstract ᅟ. PMID:27245455
PIV experiments in rough-wall, laminar-to-turbulent, oscillatory boundary-layer flows
NASA Astrophysics Data System (ADS)
Mujal-Colilles, Anna; Mier, Jose M.; Christensen, Kenneth T.; Bateman, Allen; Garcia, Marcelo H.
2014-01-01
Exploratory measurements of oscillatory boundary layers were conducted over a smooth and two different rough beds spanning the laminar, transitional and turbulent flow regimes using a multi-camera 2D-PIV system in a small oscillatory-flow tunnel (Admiraal et al. in J Hydraul Res 44(4):437-450, 2006). Results show how the phase lag between bed shear stress and free-stream velocity is better defined when the integral of the momentum equation is used to estimate the bed shear stress. Observed differences in bed shear stress and phase lag between bed shear stress and free-stream velocity are highly sensitive to the definition of the bed position ( y = b). The underestimation of turbulent stresses close to the wall is found to explain such differences when using the addition of Reynolds and viscous stresses to define both the bed shear stress and the phase lag. Regardless of the flow regime, in all experiments, boundary-layer thickness reached its maximum value at a phase near the flow reversal at the wall. Friction factors in smooth walls are better estimated using a theoretical equation first proposed by Batchelor (An introduction to fluid dynamics. Cambridge University Press, Cambridge, 1967) while the more recent empirical predictor of Pedocchi and Garcia (J Hydraul Res 47(4):438-444, 2009a) was found to be appropriate for estimating friction coefficients in the laminar-to-turbulent transition regime.
Validity of classical scaling laws in laminar channel flow with periodic spacer-like obstacles
NASA Astrophysics Data System (ADS)
Rohlfs, Wilko; Lienhard, John H.
2015-11-01
Laminar channel flows with periodic obstacles occur in different technical applications involving heat and mass transfer. They are present in membrane technologies such as electro-dialysis or spirally wound membrane modules. For process design, classical scaling laws of heat and mass transfer are typically used. The laws scale the transfer (Sherwood) number, Sh , to the hydrodynamic Reynolds, Re , the fluid specific Schmidt number, Sc , and to some dimensionless geometric parameters, G, in a classical form like Sh = CReα ScβGγ . However, the validity of those classical scaling laws is limited to the region where the concentration boundary layer develops as it is well known that the transfer numbers approach a constant (Reynolds and Schmidt independent) value in the developed region of a laminar channel flow. This study examines numerically the validity of the scaling laws if the channel flow is interrupted periodically by cylindrical obstacles of different size and separation distance. In the developed region, a Schmidt and Reynolds number dependency is found and associated to wall-normal flow induced by the obstacles, for which this dependency varies with obstacle size and separation distance. Funding for WR was provided by the German Academic Exchange Service DAAD.
Development of a compact laminar flow heat exchanger with stainless steel micro-tubes
NASA Astrophysics Data System (ADS)
Saji, N.; Nagai, S.; Tsuchiya, K.; Asakura, H.; Obata, M.
2001-05-01
The present paper describes the design concept and manufacturing of a new compact laminar flow heat exchanger with stainless-steel micro-tubes for helium refrigerators. In the temperature range of less than 20 K, aluminum plate fin type heat exchangers exhibit a remarkable fall of performance characteristics as a compact heat exchanger. We presented in a previous paper that some compact heat exchangers with good performance in the temperature range of less than 4 K are required for a subcooled He II refrigerator cycle to be worked with 3He turbo-compressors (F. Doty, et al., A new look at the closed brayton cycle, Proceedings, IECEC-90 Reno, NV, 1991, p. 116). For this requirement, we developed a micro-tube strip counter flow type heat exchanger, which consists of 12 elements with a total of 4800 stainless steel micro-tubes. Each element is formed with 400 tubes and a newly developed vacuum brazing method was applied for the bonding to the side plate. Each tube has an inner diameter of 0.5 mm, an outer diameter of 0.7 mm and is 310 mm long. We developed a cladding plate with two layers of gold brazing sheet sandwiched inside. In aerodynamic and thermal design of the element, the laminar flow conditions were adopted for the flows of inner and outer tubes to keep a high heat transfer rate and a low pressure loss.
NASA Astrophysics Data System (ADS)
Natrajan, V. K.; Christensen, K. T.
2009-11-01
The convective heat-transfer behavior of laminar flow through smooth- and rough-wall microchannels is investigated by performing non-intrusive measurements of fluid temperature using a microscale adaptation of two-color laser-induced fluorescent thermometry for flow through a heated copper microchannel testbed of hydraulic diameter Dh=600,μm. These measurements, in concert with pressure-drop measurements, are performed for a smooth-wall case and two different rough-wall cases with roughness that is reminiscent of the surface irregularities one might encounter due to imperfect fabrication methods. Pressure-drop measurements reveal the onset of transition above Recr=1800 for the smooth-wall case and deviation from laminar behavior at progressively lower Re with increasing surface roughness. The local Nusselt number (Nu) for smooth-wall flow over the range 200<=Re<=Recr agree well with macroscale predictions in both the thermally-developing and -developed regimes. With increasing roughness, while an enhancement in local Nu is noted in the thermally-developing regime, these differences do not exist upon attainment of a thermally- developed state. Examination of temperature profiles across the microchannel suggest that the thermal boundary layer may be regenerated by roughness, resulting in a delay in the attainment of thermally-developed flow.
Finite volume and finite element methods applied to 3D laminar and turbulent channel flows
Louda, Petr; Příhoda, Jaromír; Sváček, Petr; Kozel, Karel
2014-12-10
The work deals with numerical simulations of incompressible flow in channels with rectangular cross section. The rectangular cross section itself leads to development of various secondary flow patterns, where accuracy of simulation is influenced by numerical viscosity of the scheme and by turbulence modeling. In this work some developments of stabilized finite element method are presented. Its results are compared with those of an implicit finite volume method also described, in laminar and turbulent flows. It is shown that numerical viscosity can cause errors of same magnitude as different turbulence models. The finite volume method is also applied to 3D turbulent flow around backward facing step and good agreement with 3D experimental results is obtained.
Experimental Study of Saddle Point of Attachment in Laminar Juncture Flow
NASA Technical Reports Server (NTRS)
Coon, Michael D.; Tobak, Murray
1995-01-01
An experimental study of laminar horseshoe vortex flows upstream of a cylinder/flat plate juncture has been conducted to verify the existence of saddle-point-of-attachment topologies. In the classical depiction of this flowfield, a saddle point of separation exists on the flat plate upstream of the cylinder, and the boundary layer separates from the surface. Recent computations have indicated that the topology may actually involve a saddle point of attachment on the surface and additional singular points in the flow. Laser light sheet flow visualizations have been performed on the symmetry plane and crossflow planes to identify the saddle-point-of-attachment flowfields. The visualizations reveal that saddle-point-of-attachment topologies occur over a range of Reynolds numbers in both single and multiple vortex regimes. An analysis of the flow topologies is presented that describes the existence and evolution of the singular points in the flowfield.
On the possibility of laminar flow control on a swept wing by means of plasma actuators
NASA Astrophysics Data System (ADS)
Chernyshev, S. L.; Kuryachii, A. P.; Manuilovich, S. V.; Rusyanov, D. A.; Skvortsov, V. V.
2015-06-01
Theoretical assessment of the possibility of laminar flow control (LFC) on a swept wing owing to volumetric force and heat impact of plasma actuators is presented. The proposed approach includes numerical modeling of dielectric barrier discharge (DBD) actuators, calculation of inviscid flow over an infinite span swept wing, calculation of compressible boundary layer spatially modulated in spanwise direction, and numerical solution of linear stability problem for stationary modes of cross-flow-type disturbances. Calculations have been performed for one set of geometrical and physical parameters describing plasma actuators to estimate qualitative features of volumetric force and heat input distributions. Inviscid flow and boundary layer calculations were executed at free stream parameters corresponding to typical cruise flight conditions. Estimation of volumetric force impact necessary for noticeable influence on cross-flowtype instability is obtained.
Non-Newtonian fluid laminar flow and forced convection heat transfer in rectangular ducts
Gao, S.X.; Hartnett, J.P. . Energy Resources Center)
1992-09-01
Numerical solutions for fully developed laminar flow forced convection heat transfer of a power law non-Newtonian fluid in rectangular ducts are presented in this paper. Finite difference methods are developed for the governing equations to obtain the velocity and temperature distributions. Friction factor results are given for flow through rectangular ducts of aspect ratios of 0.2, 0.5 and 1.0 with power law index n values of 0.5 to 1.0. For the same flow conditions the Nusselt values, maximum wall temperatures, and minimum wall temperatures for the H2 thermal boundary condition for different combinations of heated and adiabatic walls are obtained. Also the Nusselt values for slug flow (n = 0) are presented for the H2 boundary condition.
NASA Technical Reports Server (NTRS)
Harris, Charles D.; Harvey, William D.; Brooks, Cuyler W., Jr.
1988-01-01
A large-chord, swept, supercritical, laminar-flow-control (LFC) airfoil was designed and constructed and is currently undergoing tests in the Langley 8 ft Transonic Pressure Tunnel. The experiment was directed toward evaluating the compatibility of LFC and supercritical airfoils, validating prediction techniques, and generating a data base for future transport airfoil design as part of NASA's ongoing research program to significantly reduce drag and increase aircraft efficiency. Unique features of the airfoil included a high design Mach number with shock free flow and boundary layer control by suction. Special requirements for the experiment included modifications to the wind tunnel to achieve the necessary flow quality and contouring of the test section walls to simulate free air flow about a swept model at transonic speeds. Design of the airfoil with a slotted suction surface, the suction system, and modifications to the tunnel to meet test requirements are discussed.
Preliminary design characteristics of a subsonic business jet concept employing laminar flow control
NASA Technical Reports Server (NTRS)
Turriziani, R. V.; Lovell, W. A.; Price, J. E.; Quartero, C. B.; Washburn, G. F.
1978-01-01
Aircraft configurations were developed with laminar flow control (LFC) and without LFC. The LFC configuration had approximately eleven percent less parasite drag and a seven percent increase in the maximum lift-to drag ratio. Although these aerodynamic advantages were partially offset by the additional weight of the LFC system, the LFC aircraft burned from six to eight percent less fuel for comparable missions. For the trans-atlantic design mission with the gross weight fixed, the LFC configuration would carry a greater payload for ten percent fuel per passenger mile.
Evaluation of laminar flow control systems concepts for subsonic commercial transport aircraft
NASA Technical Reports Server (NTRS)
Pearce, W. E.
1983-01-01
An evaluation was made of laminar flow control (LFC) system concepts for subsonic commercial transport aircraft. Configuration design studies, performance analyses, fabrication development, structural testing, wind tunnel testing, and contamination-avoidance techniques were included. As a result of trade studies, a configuration with LFC on the upper wing surface only, utilizing an electron beam-perforated suction surface, and employing a retractable high-lift shield for contamination avoidance, was selected as the most practical LFC system. The LFC aircraft was then compared with an advanced turbulent aircraft designed for the same mission. This comparison indicated significant fuel savings and reduced direct operating cost benefits would result from using LFC.
Flight evaluation of an insect contamination protection system for laminar flow wings
NASA Technical Reports Server (NTRS)
Croom, C. C.; Holmes, B. J.
1985-01-01
The maintenance of minimum wing leading edge contamination is critical to the preservation of drag-reducing laminar flow; previous methods for the prevention of leading edge contamination by insects have, however, been rendered impractical by their excessive weight, cost, or inconvenience. Attention is presently given to the results of a NASA flight experiment which evaluated the performance of a porous leading edge fluid-discharge ice protection system in the novel role of insect contamination removal; high insect contamination conditions were also noted in the experiment. Very small amounts of the fluid are found to be sufficient for insect contamination protection.
Unique laminar-flow stability limit based shallow-water theory
Chen, Cheng-lung
1993-01-01
Two approaches are generally taken in deriving the stability limit for the Froude member (Fs) for laminar sheet flow. The first approach used the Orr-Sommerfeld equation, while the second uses the cross-section-averaged equations of continuity and motion. Because both approaches are based on shallow-water theory, the values of Fs obtained from both approaches should be identical, yet in the literature they are not. This suggests that a defect exists in at least one of the two approaches. After examining the governing equations used in both approaches, one finds that the existing cross-section -averaged equation of motion is dependent on the frame of reference.
Simulated airline service experience with laminar-flow control leading-edge systems
NASA Technical Reports Server (NTRS)
Maddalon, Dal V.; Fisher, David F.; Jennett, Lisa A.; Fischer, Michael C.
1987-01-01
The first JetStar leading edge flight test was made November 30, 1983. The JetStar was flown for more than 3 years. The titanium leading edge test articles today remain in virtually the same condition as they were in on that first flight. No degradation of laminar flow performance has occurred as a result of service. The JetStar simulated airline service flights have demonstrated that effective, practical leading edge systems are available for future commercial transports. Specific conclusions based on the results of the simulated airline service test program are summarized.
The NASA Langley laminar-flow-control experiment on a swept, supercritical airfoil - Drag equations
NASA Technical Reports Server (NTRS)
Brooks, Cuyler W., Jr.; Harris, Charles D.; Harvey, William D.
1989-01-01
The Langley Research Center has designed a swept, supercritical airfoil incorporating Laminar Flow Control for testing at transonic speeds. Analytical expressions have been developed and an evaluation made of the experimental section drag, composed of suction drag and wake drag, using theoretical design information and experimental data. The analysis shows that, although the sweep-induced boundary-layer crossflow influence on the wake drag is too large to be ignored and there is not a practical method for evaluating these crossflow effects on the experimental wake data, the conventional unswept 2-D wake-drag computation used in the reduction of the experimental data is at worst 10 percent too high.
NASA Technical Reports Server (NTRS)
Harvey, William D.; Harris, Charles D.; Brooks, Cuyler W., Jr.
1989-01-01
A swept, supercritical laminar flow control (LFC) airfoil designated NASA SCLFC(1)-0513F was tested at subsonic and transonic speeds in the NASA Langley eight-foot Transonic Pressure Tunnel. This paper examines Tollmien-Schlichting and crossflow disturbance amplification for this airfoil using the linear stability method. The design methodology using linear stability analysis is evaluated and the results of the incompressible and compressible methods are compared. Experimental data on the swept, supercritical LFC airfoil and reference wind tunnel and flight results are used to correlate and evaluate the N-factor method for transition prediction over a speed range M(infinity) from zero to one.
NASA Technical Reports Server (NTRS)
Pearce, W. E.
1982-01-01
An evaluation was made of laminar flow control (LFC) system concepts for subsonic commercial transport aircraft. Configuration design studies, performance analyses, fabrication development, structural testing, wind tunnel testing, and contamination-avoidance techniques were included. As a result of trade studies, a configuration with LFC on the upper wing surface only, utilizing an electron beam-perforated suction surface, and employing a retractable high-lift shield for contamination avoidance, was selected as the most practical LFC system. The LFC aircraft was then compared with an advanced turbulent aircraft designed for the same mission. This comparison indicated significant fuel savings.
Effects of an aft facing step on the surface of a laminar flow glider wing
NASA Technical Reports Server (NTRS)
Sandlin, Doral R.; Saiki, Neal
1993-01-01
A motor glider was used to perform a flight test study on the effects of aft facing steps in a laminar boundary layer. This study focuses on two dimensional aft facing steps oriented spanwise to the flow. The size and location of the aft facing steps were varied in order to determine the critical size that will force premature transition. Transition over a step was found to be primarily a function of Reynolds number based on step height. Both of the step height Reynolds numbers for premature and full transition were determined. A hot film anemometry system was used to detect transition.
In situ analysis of dynamic laminar flow extraction using surface-enhanced Raman spectroscopy
Wang, Fei; Wang, Hua-Lin; Qiu, Yang; Chang, Yu-Long; Long, Yi-Tao
2015-01-01
In this study, we performed micro-scale dynamic laminar flow extraction and site-specific in situ chloride concentration measurements. Surface-enhanced Raman spectroscopy was utilized to investigate the diffusion process of chloride ions from an oil phase to a water phase under laminar flow. In contrast to common logic, we used SERS intensity gradients of Rhodamine 6G to quantitatively calculate the concentration of chloride ions at specific positions on a microfluidic chip. By varying the fluid flow rates, we achieved different extraction times and therefore different chloride concentrations at specific positions along the microchannel. SERS spectra from the water phase were recorded at these different positions, and the spatial distribution of the SERS signals was used to map the degree of nanoparticle aggregation. The concentration of chloride ions in the channel could therefore be obtained. We conclude that this method can be used to explore the extraction behaviour and efficiency of some ions or molecules that enhance the SERS intensity in water or oil by inducing nanoparticle aggregation. PMID:26687436
Development of high-lift laminar wing using steady active flow control
NASA Astrophysics Data System (ADS)
Clayton, Patrick J.
Fuel costs represent a large fraction of aircraft operating costs. Increased aircraft fuel efficiency is thus desirable. Laminar airfoils have the advantage of reduced cruise drag and increased fuel efficiency. Unfortunately, they cannot perform adequately during high-lift situations (i.e. takeoff and landing) due to low stall angles and low maximum lift caused by flow separation. Active flow control has shown the ability to prevent or mitigate separation effects, and increase maximum lift. This fact makes AFC technology a fitting solution for improving high-lift systems and reducing the need for slats and flap elements. This study focused on experimentally investigating the effects of steady active flow control from three slots, located at 1%, 10%, and 80% chord, respectively, over a laminar airfoil with 45 degree deflected flap. A 30-inch-span airfoil model was designed, fabricated, and then tested in the Bill James 2.5'x3' Wind Tunnel at Iowa State University. Pressure data were collected along the mid-span of the airfoil, and lift and drag were calculated. Five test cases with varying injection locations and varying Cμ were chosen: baseline, blown flap, leading edge blowing, equal blowing, and unequal blowing. Of these cases, unequal blowing achieved the greatest lift enhancement over the baseline. All cases were able to increase lift; however, gains were less than anticipated.
Three-dimensional measurement of the laminar flow field inside a static mixer
NASA Astrophysics Data System (ADS)
Speetjens, Michel; Jilisen, Rene; Bloemen, Paul
2011-11-01
Static mixers are widely used in industry for laminar mixing of viscous fluids as e.g. polymers and food stuffs. Moreover, given the similarities in flow regime, static mixers often serve as model for compact mixers for process intensification and even for micro-mixers. This practical relevance has motivated a host of studies on the mixing characteristics of static mixers and their small-scale counterparts. However, these studies are primarily theoretical and numerical. Experimental studies, in contrast, are relatively rare and typically restricted to local 2D flow characteristics or integral quantities (pressure drop, residence-time distributions). The current study concerns 3D measurements on the laminar flow field inside a static mixer using 3D Particle-Tracking Velocimetry (3D-PTV) Key challenges to the 3D-PTV image-processing procedure are the optical distortion and degradation of the particle imagery due to light refraction and reflection caused by the cylindrical boundary and the internal elements. Ways to tackle these challenges are discussed and first successful 3D measurements in an actual industrial static mixer are presented.
In situ analysis of dynamic laminar flow extraction using surface-enhanced Raman spectroscopy.
Wang, Fei; Wang, Hua-Lin; Qiu, Yang; Chang, Yu-Long; Long, Yi-Tao
2015-01-01
In this study, we performed micro-scale dynamic laminar flow extraction and site-specific in situ chloride concentration measurements. Surface-enhanced Raman spectroscopy was utilized to investigate the diffusion process of chloride ions from an oil phase to a water phase under laminar flow. In contrast to common logic, we used SERS intensity gradients of Rhodamine 6G to quantitatively calculate the concentration of chloride ions at specific positions on a microfluidic chip. By varying the fluid flow rates, we achieved different extraction times and therefore different chloride concentrations at specific positions along the microchannel. SERS spectra from the water phase were recorded at these different positions, and the spatial distribution of the SERS signals was used to map the degree of nanoparticle aggregation. The concentration of chloride ions in the channel could therefore be obtained. We conclude that this method can be used to explore the extraction behaviour and efficiency of some ions or molecules that enhance the SERS intensity in water or oil by inducing nanoparticle aggregation. PMID:26687436
Verification of Transition from Laminar to Turbulent Flow in Circular Pipe by Color-Dye Experiment
NASA Astrophysics Data System (ADS)
Kanda, Hidesada; Takayuki, Yanagiya
2003-11-01
Investigations of the flow phenomena in circular pipes have been performed by many researchers. However, the transition from laminar to turbulent flow in circular pipes is still not well understood, since the main cause of the transition depends on the growth or decay of invisible infinitesimal disturbances. Many experiments carried out in the past were performed in order to identify a main cause, and thus it was found that the transition occurs in the entrance region. In addition, we found that (i) the critical Reynolds number Rc is goverened by the bellmouth shape of the pipe inlet, and (ii) the minimum Rc is approximately 2000 when using the straight pipe without any bellmouth. Until now, it has not been considered how the bellmouth-shaped entrance affects the flow in circular pipes. If the inlet shape determines the transition, the turbulence can be controlled. These findings are verified by reproducing the Reynolds color-dye experiment.
Application of Hybrid Laminar Flow Control to Global Range Military Transport Aircraft
NASA Technical Reports Server (NTRS)
Lange, Roy H.
1988-01-01
A study was conducted to evaluate the application of hybrid laminar flow control (HLFC) to global range military transport aircraft. The global mission included the capability to transport 132,500 pounds of payload 6500 nautical miles, land and deliver the payload and without refueling return 6500 nautical miles to a friendly airbase. The preliminary design studies show significant performance benefits obtained for the HLFC aircraft as compared to counterpart turbulent flow aircraft. The study results at M=0.77 show that the largest benefits of HLFC are obtained with a high wing with engines on the wing configuration. As compared with the turbulent flow baseline aircraft, the high wing HLFC aircraft shows 17 percent reduction in fuel burned, 19.2 percent increase in lift-to-drag ratio, an insignificant increase in operating weight, and a 7.4 percent reduction in gross weight.
Laminar flow in a microchannel with superhydrophobic walls exhibiting transverse ribs
NASA Astrophysics Data System (ADS)
Davies, J.; Maynes, D.; Webb, B. W.; Woolford, B.
2006-08-01
One approach recently proposed for reducing the frictional resistance to liquid flow in microchannels is the patterning of microribs and cavities on the channel walls. When treated with a hydrophobic coating, the liquid flowing in the microchannel wets only the surfaces of the ribs, and does not penetrate the cavities, provided the pressure is not too high. The net result is a reduction in the surface contact area between channel walls and the flowing liquid. For microribs and cavities that are aligned normal to the channel axis (principal flow direction), these micropatterns form a repeating, periodic structure. This paper presents results of a study exploring the momentum transport in a parallel-plate microchannel with such microengineered walls. The investigation explored the entire laminar flow Reynolds number range and characterized the influence of the vapor cavity depth on the overall flow field. The liquid-vapor interface (meniscus) in the cavity regions is treated as flat in the numerical analysis and two conditions are explored with regard to the cavity region: (1) The liquid flow at the liquid-vapor interface is treated as shear-free (vanishing viscosity in the vapor region), and (2) the liquid flow in the microchannel core and the vapor flow within the cavity are coupled by matching the velocity and shear stress at the interface. Regions of slip and no-slip behavior exist and the velocity field shows distinct variations from classical laminar flow in a parallel-plate channel. The local streamwise velocity profiles, interfacial velocity distributions, and maximum interfacial velocities are presented for a number of scenarios and provide a sound understanding of the local flow physics. The predictions and accompanying measurements reveal that significant reductions in the frictional pressure drop (enhancement in effective fluid slip at the channel walls) can be achieved relative to the classical smooth-channel Stokes flow. Reductions in the friction
Data Analysis for the NASA/Boeing Hybrid Laminar Flow Control Crossflow Experiment
NASA Technical Reports Server (NTRS)
Eppink, Jenna L.; Wlezien, Richard
2011-01-01
The Hybrid-Laminar Flow Control (HLFC) Crossflow Experiment, completed in 1995. generated a large database of boundary layer stability and transition data that was only partially analyzed before data analysis was abruptly ended in the late 1990's. Renewed interest in laminar flow technologies prompted additional data analysis, to integrate all data, including some post-test roughness and porosity measurements. The objective is to gain new insights into the effects of suction on boundary layer stability. A number of challenges were encountered during the data analysis, and their solutions are discussed in detail. They include the effect of the probe vibration, the effect of the time-varying surface temperature on traveling crossflow instabilities, and the effect of the stationary crossflow modes on the approximation of wall location. Despite the low turbulence intensity of the wind tunnel (0.01 to 0.02%), traveling crosflow disturbances were present in the data, in some cases at amplitudes up to 1% of the freestream velocity. However, the data suggests that transition was dominated by stationary crossflow. Traveling crossflow results and stationary data in the presence of suction are compared with linear parabolized stability equations results as a way of testing the quality of the results.
Analysis of Low-Speed Stall Aerodynamics of a Swept Wing with Laminar-Flow Glove
NASA Technical Reports Server (NTRS)
Bui, Trong
2013-01-01
Reynolds-Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) analysis was conducted to study the low-speed stall aerodynamics of a GIII aircraft s swept wing modified with a laminar-flow wing glove. The stall aerodynamics of the gloved wing were analyzed and compared with the unmodified wing for the flight speed of 120 knots and altitude of 2300 ft above mean sea level (MSL). The Star-CCM+ polyhedral unstructured CFD code was first validated for wing stall predictions using the wing-body geometry from the First AIAA CFD High-Lift Prediction Workshop. It was found that the Star-CCM+ CFD code can produce results that are within the scattering of other CFD codes considered at the workshop. In particular, the Star-CCM+ CFD code was able to predict wing stall for the AIAA wing-body geometry to within 1 degree of angle of attack as compared to benchmark wind-tunnel test data. Current results show that the addition of the laminar-flow wing glove causes the gloved wing to stall much earlier than the unmodified wing. Furthermore, the gloved wing has a different stall characteristic than the clean wing, with no sharp lift drop-off at stall for the gloved wing.
Analysis of Low Speed Stall Aerodynamics of a Swept Wing with Laminar Flow Glove
NASA Technical Reports Server (NTRS)
Bui, Trong T.
2014-01-01
Reynolds-Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) analysis was conducted to study the low-speed stall aerodynamics of a GIII aircraft's swept wing modified with a laminar-flow wing glove. The stall aerodynamics of the gloved wing were analyzed and compared with the unmodified wing for the flight speed of 120 knots and altitude of 2300 ft above mean sea level (MSL). The Star-CCM+ polyhedral unstructured CFD code was first validated for wing stall predictions using the wing-body geometry from the First American Institute of Aeronautics and Astronautics (AIAA) CFD High-Lift Prediction Workshop. It was found that the Star-CCM+ CFD code can produce results that are within the scattering of other CFD codes considered at the workshop. In particular, the Star-CCM+ CFD code was able to predict wing stall for the AIAA wing-body geometry to within 1 degree of angle of attack as compared to benchmark wind-tunnel test data. Current results show that the addition of the laminar-flow wing glove causes the gloved wing to stall much earlier than the unmodified wing. Furthermore, the gloved wing has a different stall characteristic than the clean wing, with no sharp lift drop-off at stall for the gloved wing.
Analysis of Low-Speed Stall Aerodynamics of a Swept Wing with Laminar-Flow Glove
NASA Technical Reports Server (NTRS)
Bui, Trong T.
2014-01-01
Reynolds-Averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) analysis was conducted to study the low-speed stall aerodynamics of a GIII aircraft's swept wing modified with a laminar-flow wing glove. The stall aerodynamics of the gloved wing were analyzed and compared with the unmodified wing for the flight speed of 120 knots and altitude of 2300 ft above mean sea level (MSL). The Star-CCM+ polyhedral unstructured CFD code was first validated for wing stall predictions using the wing-body geometry from the First American Institute of Aeronautics and Astronautics (AIAA) CFD High-Lift Prediction Workshop. It was found that the Star-CCM+ CFD code can produce results that are within the scattering of other CFD codes considered at the workshop. In particular, the Star-CCM+ CFD code was able to predict wing stall for the AIAA wing-body geometry to within 1 degree of angle of attack as compared to benchmark wind-tunnel test data. Current results show that the addition of the laminar-flow wing glove causes the gloved wing to stall much earlier than the unmodified wing. Furthermore, the gloved wing has a different stall characteristic than the clean wing, with no sharp lift drop-off at stall for the gloved wing.
Arcara, P.C. Jr.; Bartlett, D.W.; Mccullers, L.A. Vigyan, Inc., Hampton, VA )
1991-09-01
The FLOPS aircraft conceptual design/analysis code has been used to evaluate the effects of incorporating hybrid laminar flow control (HLFC) in a 300-passenger, 6500 n. mi. range, twin-engine subsonic transport aircraft. The baseline configuration was sized to account for 50 percent chord laminar flow on the wing upper surface as well as both surfaces of the empennage airfoils. Attention is given to the additional benefits of achieving various degrees of laminar flow on the engine nacelles, and the horsepower extraction and initial weight and cost increments entailed by the HLFC system. The sensitivity of the results obtained to fuel-price and off-design range are also noted. 6 refs.
NASA Astrophysics Data System (ADS)
Sato, Makoto; Nonomura, Taku; Okada, Koichi; Asada, Kengo; Aono, Hikaru; Yakeno, Aiko; Abe, Yoshiaki; Fujii, Kozo
2015-11-01
Large-eddy simulations have been conducted to investigate the mechanisms of separated-flow control using a dielectric barrier discharge plasma actuator at a low Reynolds number. In the present study, the mechanisms are classified according to the means of momentum injection to the boundary layer. The separated flow around the NACA 0015 airfoil at a Reynolds number of 63 000 is used as the base flow for separation control. Both normal and burst mode actuations are adopted in separation control. The burst frequency non-dimensionalized by the freestream velocity and the chord length (F+) is varied from 0.25 to 25, and we discuss the control mechanism through the comparison of the aerodynamic performance and controlled flow-fields in each normal and burst case. Lift and drag coefficients are significantly improved for the cases of F+ = 1, 5, and 15 due to flow reattachment associated with a laminar-separation bubble. Frequency and linear stability analyses indicate that the F+ = 5 and 15 cases effectively excite the natural unstable frequency at the separated shear layer, which is caused by the Kelvin-Helmholtz instability. This excitation results in earlier flow reattachment due to earlier turbulent transition. Furthermore, the Reynolds stress decomposition is conducted in order to identify the means of momentum entrainment resulted from large-scale spanwise vortical structure or small-scale turbulent vortices. For the cases with flow reattachment, the large-scale spanwise vortices, which shed from the separated shear layer through plasma actuation, significantly increase the periodic component of the Reynolds stress near the leading edge. These large-scale vortices collapse to small-scale turbulent vortices, and the turbulent component of the Reynolds stress increases around the large-scale vortices. In these cases, although the combination of momentum entrainment by both Reynolds stress components results in flow reattachment, the dominant component is identified as
NASA Astrophysics Data System (ADS)
Dickinson, B. T.; Singler, J. R.; Batten, B. A.
2012-02-01
Bats possess arrays of distributed flow-sensitive hair-like mechanoreceptors on their dorsal and ventral wing surfaces. Bat wing hair receptors are known to play a significant role in flight maneuverability and are directionally most sensitive to reversed flow over the wing. In this work, we consider the mechanics of flexible hair-like structures for the time accurate detection and visualization of hydrodynamic images associated with unsteady near surface flow phenomena. A nonlinear viscoelastic model of a hair-like structure coupled to an unsteady nonuniform flow is proposed. Writing the hair model in nondimensional form, we identify five dimensionless groups that govern hair behavior. An order of magnitude analysis of the physical forces involved in the fluid-structure hair response is performed. Through the choice of hair material properties, we show how a local measure of near surface flow velocity may be obtained from hair tip displacement and resultant moment. When hair structures are placed into an array, time and space accurate hydrodynamic images may be obtained. We illustrate the imaging of reversed flow that occurs during a laminar unsteady flow separation with an array of hair-like structures.
Direct velocity measurement and enhanced mixing in laminar flows over ultrahydrophobic surfaces
NASA Astrophysics Data System (ADS)
Ou, Jia
2005-11-01
A series of experiment are presented studying the kinematics of water flowing over drag-reducing ultrahydrophobic surfaces. The surfaces are fabricated from silicon wafers using photolithography and are designed to incorporate patterns of microridges with precise spacing and alignment. These surfaces are reacted with an organosilane to achieve high hydrophobicity. Microridges with different widths, spacing and alignments are tested in a microchannel flow cell with rectangular cross-section. The velocity profile across the microchannel is measured with micro particle image velocimetry (μ-PIV) capable of resolving the flow down to length scales well below the size of the surface features. A maximum slip velocity of >60% of the average velocity in the flow is observed at the center of the air-water interface supported between these hydrophobic microridges, and the no-slip boundary condition is found at the hydrophobic microridges. The μ-PIV measurements demonstrate that slip along the shear-free air-water interface supported between the hydrophobic micron-sized ridges is the primary mechanism responsible for the drag reduction. The experiment velocity and pressure drop measurement are compared with the prediction of numerical simulation and an analytical model. By aligning the hydrophobic microridges at an acute angle to the flow direction a secondary flow is produced which can significantly enhance mixing in this laminar flow.
Analysis of laminar flow between stationary and rotating disks with inflow
NASA Technical Reports Server (NTRS)
Rohatgi, U.; Reshotko, E.
1974-01-01
The laminar flow between a rotating and a stationary disk with inflow was analyzed. Solutions to the dimensionless governing equations are sought by expanding each of the velocity components in powers of inverse radius. The equations to leading order are those for the configuration with no inflow. The subsequent orders yield sets of linear ordinary differential equations. Solutions are obtained for the first two of these subsequent orders. The solutions indicate that inflow tends to increase the magnitude of the azimuthal velocity in the flow between the two disks and to decrease the torque on the rotating disk. For Prandtl number one, an energy integral is obtained which relates the temperature distribution to the velocity distribution for all Reynolds numbers and therefore eliminates the needs for separate solution of the energy equation.
Heat transfer in pulsating laminar flow in a pipe - A constant wall temperature
NASA Astrophysics Data System (ADS)
Kita, Y.; Hirose, K.; Hayashi, T.
1982-02-01
An analytical model of heat transfer in a pulsating laminar pipe flow with a constant wall temperature is presented. Governing equations for the velocity profile and the wall shear stress are defined and the temperature field is studied for an instantaneous Nusselt number. Cases of steady and unsteady temperature fields are considered, along with the heat flux in the unsteady state, and a ratio for the Nusselt number in the steady state to that in the pulsating flow is obtained. A method for deriving the instantaneous pipe friction factor is demonstrated and the range of the pressure-gradient amplitudes is determined. Finally, conditions are formulated in which the temperature field, including the heat flux, at the wall are equal to that of the steady state.
Laminar and turbulent heat transfer in flow of supercritical CO{sub 2}
Zhou, N.; Krishnan, A.
1995-12-31
Modern military aircraft employ fuel as the primary heat sink medium for heat loads arising from sources such as the engine, the avionics, the environmental control system, and the air frame. Pressures in current fuel systems are generally above the critical pressure of the fuel. Large heat loads can cause the fuel temperature to increase beyond the critical temperature of the fuel. This necessitates the operation of the fuel in the supercritical regime. Unfortunately, little is known about the transport behavior of fuels in the supercritical regime. This study describes the integration and incorporation of models for transport properties of fluids (in the supercritical regime) into a general purpose Computational Fluid Dynamics (CFD) code to facilitate the analysis of flow and heat transfer in fuel systems. Preliminary validation studies and the application of the code to laminar and turbulent flow of supercritical CO{sub 2} are presented.
NASA Technical Reports Server (NTRS)
Karageorghis, Andreas; Phillips, Timothy N.
1990-01-01
The numerical simulation of steady planar two-dimensional, laminar flow of an incompressible fluid through an abruptly contracting channel using spectral domain decomposition methods is described. The key features of the method are the decomposition of the flow region into a number of rectangular subregions and spectral approximations which are pointwise C(1) continuous across subregion interfaces. Spectral approximations to the solution are obtained for Reynolds numbers in the range 0 to 500. The size of the salient corner vortex decreases as the Reynolds number increases from 0 to around 45. As the Reynolds number is increased further the vortex grows slowly. A vortex is detected downstream of the contraction at a Reynolds number of around 175 that continues to grow as the Reynolds number is increased further.
Experimental study of the laminar-turbulent transition of a concave wall in a parallel flow
NASA Technical Reports Server (NTRS)
Bippes, H.
1978-01-01
The instability of the laminar boundary layer flow along a concave wall was studied. Observations of these three-dimensional boundary layer phenomena were made using the hydrogen-bubble visualization technique. With the application of stereo-photogrammetric methods in the air-water system it was possible to investigate the flow processes qualitatively and quantitatively. In the case of a concave wall of sufficient curvature, a primary instability occurs first in the form of Goertler vortices with wave lengths depending upon the boundary layer thickness and the wall curvature. At the onset the amplification rate is in agreement with the linear theory. Later, during the non-linear amplification stage, periodic spanwise vorticity concentrations develop in the low velocity region between the longitudinal vortices. Then a meandering motion of the longitudinal vortex streets subsequently ensues, leading to turbulence.
NASA Technical Reports Server (NTRS)
Sturgeon, R. F.
1978-01-01
A study was conducted to evaluate the technical and economic feasibility of applying laminar flow control (LFC) to the wings and empennage of long-range subsonic transport aircraft for initial operation in 1985. For a design mission range of 5500 n mi, advanced technology LFC and turbulent-flow aircraft were developed for a 200-passenger payload, and compared on the basis of production costs, direct operating costs, and fuel efficiency. Parametric analyses were conducted to establish optimum geometry, advanced system concepts were evaluated, and configuration variations maximizing the effectiveness of LFC were developed. The final comparisons include consideation of maintenance costs and procedures, manufacturing costs and procedures, and operational considerations peculiar to LFC aircraft.
Weyand, Birgit; Israelowitz, Meir; Kramer, James; Bodmer, Christian; Noehre, Mariel; Strauss, Sarah; Schmälzlin, Elmar; Gille, Christoph; von Schroeder, Herbert P; Reimers, Kerstin; Vogt, Peter M
2015-01-01
A three-dimensional computational fluid dynamics- (CFD-) model based on a differential pressure laminar flow bioreactor prototype was developed to further examine performance under changing culture conditions. Cell growth inside scaffolds was simulated by decreasing intrinsic permeability values and led to pressure build-up in the upper culture chamber. Pressure release by an integrated bypass system allowed continuation of culture. The specific shape of the bioreactor culture vessel supported a homogenous flow profile and mass flux at the scaffold level at various scaffold permeabilities. Experimental data showed an increase in oxygen concentration measured inside a collagen scaffold seeded with human mesenchymal stem cells when cultured in the perfusion bioreactor after 24 h compared to static culture in a Petri dish (dynamic: 11% O2 versus static: 3% O2). Computational fluid simulation can support design of bioreactor systems for tissue engineering application.
NASA Astrophysics Data System (ADS)
Enjilela, Vali; Salimi, Davood; Tavasoli, Ali; Lotfi, Mohsen
2016-02-01
In the present work, the meshless local Petrov-Galerkin vorticity-stream function (MLPG-VF) method is extended to solve two-dimensional laminar fluid flow and heat transfer equations for high Reynolds and Rayleigh numbers. The characteristic-based split (CBS) scheme which uses unity test function is employed for discretization, and the moving least square (MLS) method is used for interpolation of the field variables. Four test cases are considered to evaluate the present algorithm, namely lid-driven cavity flow with Reynolds numbers up to and including 104, flow over a backward-facing step at Reynolds number of 800, natural convection in a square cavity for Rayleigh numbers up to and including 108, and natural convection in a concentric square outer cylinder and circular inner cylinder annulus for Rayleigh numbers up to and including 107. In each case, the result obtained using the proposed algorithm is either compared with the results from the literatures or with those obtained using conventional numerical techniques. The present algorithm shows stable results at lower or equal computational cost compared to the other upwinding schemes usually employed in the MLPG method. Close agreements between the compared results as well as higher accuracy of the proposed method show the ability of this stabilized algorithm.
NASA Technical Reports Server (NTRS)
Cebeci, T.; Carr, L. W.
1978-01-01
A computer program is described which provides solutions of two dimensional equations appropriate to laminar and turbulent boundary layers for boundary conditions with an external flow which fluctuates in magnitude. The program is based on the numerical solution of the governing boundary layer equations by an efficient two point finite difference method. An eddy viscosity formulation was used to model the Reynolds shear stress term. The main features of the method are briefly described and instructions for the computer program with a listing are provided. Sample calculations to demonstrate its usage and capabilities for laminar and turbulent unsteady boundary layers with an external flow which fluctuated in magnitude are presented.
Natural convective mixing flows
NASA Astrophysics Data System (ADS)
Ramos, Eduardo; de La Cruz, Luis; del Castillo, Luis
1998-11-01
Natural convective mixing flows. Eduardo Ramos and Luis M. de La Cruz, National University of Mexico and Luis Del Castillo San Luis Potosi University. The possibility of mixing a fluid with a natural convective flow is analysed by solving numerically the mass, momentum and energy equations in a cubic container. Two opposite vertical walls of the container are assumed to have temperatures that oscillate as functions of time. The phase of the oscillations is chosen in such a way that alternating corrotating vortices are formed in the cavity. The mixing efficiency of this kind of flow is examined with a Lagrangian tracking technique. This work was partially financed by CONACyT-Mexico project number GE0044
NASA Astrophysics Data System (ADS)
Kadian, Arun Kumar; Biswas, Pankaj
2015-10-01
Friction stir welding has been quite successful in joining aluminum alloy which has gained importance in almost all industrial sectors over the past two decades. It is a newer technique and therefore needs more attention in many sectors, flow of material being one among them. The material flow pattern actually helps in deciding the parameters required for particular tool geometry. The knowledge of material flow is very significant in removing defects from the weldment. In the work presented in this paper, the flow behavior of AA6061 under a threaded tool has been studied. The convective heat loss has been considered from all the surfaces, and a comparative study has been made with and without the use of temperature-dependent properties and their significance in the finite volume method model. The two types of models that have been implemented are turbulent and laminar models. Their thermal histories have been studied for all the cases. The material flow velocity has been analyzed to predict the flow of material. A swirl inside the weld material has been observed in all the simulations.
NASA Astrophysics Data System (ADS)
Geshev, P. I.
2015-05-01
A stratified laminar flow of several fluids in a channels with an arbitrarily shaped cross section is considered. It is assumed that the hydrostatic problem of finding free boundaries between different fluids is solved and domains of motion of individual fluids are known. Under the assumption that the medium motion arises under the action of an applied pressure gradient and volume gravity forces (or forces of inertia), the property of reciprocity between the applied forces F j and the flows of different components Q i , which is manifested as symmetry of the matrix of the flow rate coefficients L ij ( Q i = L ij F j ), is proved in the general form. General symmetric solutions of the problem for a plane channel and a circular tube are presented. Formulas for the coefficient of increasing of the fluid flow rate owing to the presence of a near-wall layer of the gas are derived. It is shown that the flow rate of water in a partly filled channel may exceed the flow rate in a completely filled channel by more than an order of magnitude.
Motion of cells sedimenting on a solid surface in a laminar shear flow.
Tissot, O; Pierres, A; Foa, C; Delaage, M; Bongrand, P
1992-01-01
Cell adhesion often occurs under dynamic conditions, as in flowing blood. A quantitative understanding of this process requires accurate knowledge of the topographical relationships between the cell membrane and potentially adhesive surfaces. This report describes an experimental study made on both the translational and rotational velocities of leukocytes sedimenting of a flat surface under laminar shear flow. The main conclusions are as follows: (a) Cells move close to the wall with constant velocity for several tens of seconds. (b) The numerical values of translational and rotational velocities are inconsistent with Goldman's model of a neutrally buoyant sphere in a laminar shear flow, unless a drag force corresponding to contact friction between cells and the chamber floor is added. The phenomenological friction coefficient was 7.4 millinewton.s/m. (c) Using a modified Goldman's theory, the width of the gap separating cells (6 microns radius) from the chamber floor was estimated at 1.4 micron. (d) It is shown that a high value of the cell-to-substrate gap may be accounted for by the presence of cell surface protrusions of a few micrometer length, in accordance with electron microscope observations performed on the same cell population. (e) In association with previously reported data (Tissot, O., C. Foa, C. Capo, H. Brailly, M. Delaage, and P. Bongrand. 1991. Biocolloids and Biosurfaces. In press), these results are consistent with the possibility that cell-substrate attachment be initiated by the formation of a single molecular bond, which might be considered as the rate limiting step. Images FIGURE 3 FIGURE 8 PMID:1540690
Convective heat transfer in foams under laminar flow in pipes and tube bundles
Attia, Joseph A.; McKinley, Ian M.; Moreno-Magana, David; Pilon, Laurent
2014-01-01
The present study reports experimental data and scaling analysis for forced convection of foams and microfoams in laminar flow in circular and rectangular tubes as well as in tube bundles. Foams and microfoams are pseudoplastic (shear thinning) two-phase fluids consisting of tightly packed bubbles with diameters ranging from tens of microns to a few millimeters. They have found applications in separation processes, soil remediation, oil recovery, water treatment, food processes, as well as in fire fighting and in heat exchangers. First, aqueous solutions of surfactant Tween 20 with different concentrations were used to generate microfoams with various porosity, bubble size distribution, and rheological behavior. These different microfoams were flowed in uniformly heated circular tubes of different diameter instrumented with thermocouples. A wide range of heat fluxes and flow rates were explored. Experimental data were compared with analytical and semi-empirical expressions derived and validated for single-phase power-law fluids. These correlations were extended to two-phase foams by defining the Reynolds number based on the effective viscosity and density of microfoams. However, the local Nusselt and Prandtl numbers were defined based on the specific heat and thermal conductivity of water. Indeed, the heated wall was continuously in contact with a film of water controlling convective heat transfer to the microfoams. Overall, good agreement between experimental results and model predictions was obtained for all experimental conditions considered. Finally, the same approach was shown to be also valid for experimental data reported in the literature for laminar forced convection of microfoams in rectangular minichannels and of macrofoams across aligned and staggered tube bundles with constant wall heat flux. PMID:25552745
Motion of cells sedimenting on a solid surface in a laminar shear flow.
Tissot, O; Pierres, A; Foa, C; Delaage, M; Bongrand, P
1992-01-01
Cell adhesion often occurs under dynamic conditions, as in flowing blood. A quantitative understanding of this process requires accurate knowledge of the topographical relationships between the cell membrane and potentially adhesive surfaces. This report describes an experimental study made on both the translational and rotational velocities of leukocytes sedimenting of a flat surface under laminar shear flow. The main conclusions are as follows: (a) Cells move close to the wall with constant velocity for several tens of seconds. (b) The numerical values of translational and rotational velocities are inconsistent with Goldman's model of a neutrally buoyant sphere in a laminar shear flow, unless a drag force corresponding to contact friction between cells and the chamber floor is added. The phenomenological friction coefficient was 7.4 millinewton.s/m. (c) Using a modified Goldman's theory, the width of the gap separating cells (6 microns radius) from the chamber floor was estimated at 1.4 micron. (d) It is shown that a high value of the cell-to-substrate gap may be accounted for by the presence of cell surface protrusions of a few micrometer length, in accordance with electron microscope observations performed on the same cell population. (e) In association with previously reported data (Tissot, O., C. Foa, C. Capo, H. Brailly, M. Delaage, and P. Bongrand. 1991. Biocolloids and Biosurfaces. In press), these results are consistent with the possibility that cell-substrate attachment be initiated by the formation of a single molecular bond, which might be considered as the rate limiting step.
NASA Astrophysics Data System (ADS)
Yilmaz, Alper
2015-04-01
It is intended to design compact heat exchangers which can transfer high heat flow for a given volume and temperature difference with high efficiency. This work presents the optimal design of heat exchangers for a given length or hydraulic diameter with a constraint of a certain pressure loss and constant wall temperature. Both volumetric heat transfer and heat transfer efficiency are taken into consideration for the design in laminar or turbulent flow regions. Equations are derived which easily enable optimal design for all shapes of ducts and for all Pr numbers. It is found that optimum conditions for turbulent flow is possible for all duct hydraulic diameters; however, it is possible to have optimum conditions till a certain dimensionless duct hydraulic diameter for laminar flow. Besides maximal volumetric heat flow, heat transfer efficiency should be taken into consideration in turbulent flow for optimum design.
NASA Astrophysics Data System (ADS)
Yilmaz, Alper
2014-09-01
It is intended to design compact heat exchangers which can transfer high heat flow for a given volume and temperature difference with high efficiency. This work presents the optimal design of heat exchangers for a given length or hydraulic diameter with a constraint of a certain pressure loss and constant wall temperature. Both volumetric heat transfer and heat transfer efficiency are taken into consideration for the design in laminar or turbulent flow regions. Equations are derived which easily enable optimal design for all shapes of ducts and for all Pr numbers. It is found that optimum conditions for turbulent flow is possible for all duct hydraulic diameters; however, it is possible to have optimum conditions till a certain dimensionless duct hydraulic diameter for laminar flow. Besides maximal volumetric heat flow, heat transfer efficiency should be taken into consideration in turbulent flow for optimum design.
Combined MRI and CFD analysis of fully developed steady and pulsatile laminar flow through a bend.
Weston, S J; Wood, N B; Tabor, G; Gosman, A D; Firmin, D N
1998-01-01
A combined MR and computational fluid dynamics (CFD) study is made of flow in a simple phantom laboratory flow rig consisting of a 180 degree bend with straight entry and exit sections. The aim was to investigate the potential of the use of MRI-linked CFD simulations for in vivo use. To this end, the experiment was set up for both steady and pulsatile laminar flow conditions, with Reynolds and Dean numbers and Womersley pulsatility parameter representative of resting flow in the human aorta. The geometrical images of the pipe and the velocity images at entry to the bend were used as boundary conditions for CFD simulations of the flow. The CFD results for both steady and pulsatile cases compared favorably with velocity images obtained at exit from the bend. Additional information such as pressure and wall shear stress, which either could not be measured adequately via MRI, or could not be measured at all, was also extracted from the simulation. Overall, the results were sufficiently promising to justify pursuing subsequent in vivo studies.
NASA Astrophysics Data System (ADS)
Moharana, N. R.; Speetjens, M. F. M.; Trieling, R. R.; Clercx, H. J. H.
2013-09-01
Magnetic actuation of microscopic beads is a promising technique for enhancement and manipulation of scalar transport in micro-fluidic systems. This implies laminar and essentially three-dimensional (3D) unsteady flow conditions. The present study addresses fundamental transport phenomena in such configurations in terms of 3D coherent structures formed by the Lagrangian fluid trajectories in a 3D time-periodic flow driven by a rotating sphere. The flow field is represented by an exact Stokes solution superimposed by a nonlinear closed-form perturbation. This facilitates systematic "activation" and exploration of two fundamental states: (i) invariant spheroidal surfaces accommodating essentially 2D Hamiltonian dynamics; (ii) formation of intricate 3D coherent structures (spheroidal shells interconnected by tubes) and onset to 3D dynamics upon weak perturbation of the former state. Key to the latter state is emergence of isolated periodic points and the particular foliation and interaction of the associated manifolds, which relates intimately to coherent structures of the unperturbed state. The occurrence of such fundamental states and corresponding dynamics is (qualitative) similar to findings on a realistic 3D lid-driven flow subject to weak fluid inertia. This implies, first, a universal response scenario to weak perturbations and, second, an adequate representation of physical effects by the in essence artificial perturbation. The study thus offers important new insights into a class of flow configurations with great practical potential.
A study of laminar flow of polar liquids through circular microtubes
NASA Astrophysics Data System (ADS)
Phares, Denis J.; Smedley, Gregory T.
2004-05-01
Recently, the validity of using classical flow theory to describe the laminar flow of polar liquids and electrolytic solutions through microtubes has been questioned for tube diameters as large as 500 μm [Brutin and Tadrist, Phys. Fluids 15, 653 (2003)]. This potential increase in flow resistance, which has been attributed to electrokinetic effects and enhanced surface roughness effects, is critical to the understanding of certain biofluid systems. We seek to characterize this phenomenon for a variety of capillary/liquid systems. Using a numerical solution to the Poisson-Boltzmann equation, we have calculated the electroviscous effect for the systems under consideration. We have also measured the pressure drop as a function of flow rate across well-characterized stainless steel and polyimide microtubes ranging in diameter from 120 μm to 440 μm. Deionized water, tap water, a saline solution, and a variety of glycerol/water mixtures were used. The calculations and measurements suggest that any deviation from Poiseuille flow for tubes larger than 50 microns in diameter is more likely caused by the enhanced importance of surface roughness in microtubes than by electrokinetic effects.
Zhang, Alex Ce; Gu, Yi; Han, Yuanyuan; Mei, Zhe; Chiu, Yu-Jui; Geng, Lina; Cho, Sung Hwan; Lo, Yu-Hwa
2016-06-20
Although a flow cytometer, being one of the most popular research and clinical tools for biomedicine, can analyze cells based on the cell size, internal structures such as granularity, and molecular markers, it provides little information about the physical properties of cells such as cell stiffness and physical interactions between the cell membrane and fluid. In this paper, we propose a computational cell analysis technique using cells' different equilibrium positions in a laminar flow. This method utilizes a spatial coding technique to acquire the spatial position of the cell in a microfluidic channel and then uses mathematical algorithms to calculate the ratio of cell mixtures. Most uniquely, the invented computational cell analysis technique can unequivocally detect the subpopulation of each cell type without labeling even when the cell type shows a substantial overlap in the distribution plot with other cell types, a scenario limiting the use of conventional flow cytometers and machine learning techniques. To prove this concept, we have applied the computation method to distinguish live and fixed cancer cells without labeling, count neutrophils from human blood, and distinguish drug treated cells from untreated cells. Our work paves the way for using computation algorithms and fluidic dynamic properties for cell classification, a label-free method that can potentially classify over 200 types of human cells. Being a highly cost-effective cell analysis method complementary to flow cytometers, our method can offer orthogonal tests in companion with flow cytometers to provide crucial information for biomedical samples. PMID:27163941
Evaluation of laminar flow control system concepts for subsonic commercial transport aircraft
NASA Technical Reports Server (NTRS)
1979-01-01
Results of a 2-year study are reported which were carried out to extend the development of laminar flow control (LFC) technology and evaluate LFC systems concepts. The overall objective of the LFC program is to provide a sound basis for industry decisions on the application of LFC to future commercial transports. The study was organized into major tasks to support the stated objectives through application of LFC systems concepts to a baseline LFC transport initially generated for the study. Based on competitive evaluation of these concepts, a final selection was made for incorporation into the final design of an LFC transport which also included other advanced technology elements appropriate to the 1990 time period.
Laminar Convective Boundary Layer Slip Flow over a Flat Plate using Homotopy Analysis Method
NASA Astrophysics Data System (ADS)
Daniel, Yahaya Shagaiya
2016-08-01
In the present study, the influence of velocity slip and suction at the boundary on the steady laminar convective boundary layer flow over a flat plate with convective boundary condition is analyzed. Similarity transformation is used to transform the boundary layer equations which are coupled with partial differential equations into system of ordinary differential equations, which are then solved semi-analytically by homotopy analysis method. The results obtained are presented for several values of the physical governing parameter and comparison with the results published in literature are in perfect agreement. Increase in the slip parameter increases the velocity to a point that the momentum boundary layer becomes thinner. The convective parameter increases as the plate surface temperature increases. The suction on the viscous incompressible fluid suppresses the velocity field and Prandtl number increases by decreasing the temperature and the thermal boundary layer thickness as a result of increase in fluid viscosity.
NASA Technical Reports Server (NTRS)
Pfenninger, Werner; Vemuru, Chandra S.
1988-01-01
The achievement of 70 percent laminar flow using modest boundary layer suction on the wings, empennage, nacelles, and struts of long-range LFC transports, combined with larger wing spans and lower span loadings, could make possible an unrefuelled range halfway around the world up to near sonic cruise speeds with large payloads. It is shown that supercritical LFC airfoils with undercut front and rear lower surfaces, an upper surface static pressure coefficient distribution with an extensive low supersonic flat rooftop, a far upstream supersonic pressure minimum, and a steep subsonic rear pressure rise with suction or a slotted cruise flap could alleviate sweep-induced crossflow and attachment-line boundary-layer instability. Wing-mounted superfans can reduce fuel consumption and engine tone noise.
Designing a Hybrid Laminar-Flow Control Experiment: The CFD-Experiment Connection
NASA Technical Reports Server (NTRS)
Streett, C. L.
2003-01-01
The NASA/Boeing hybrid laminar flow control (HLFC) experiment, designed during 1993-1994 and conducted in the NASA LaRC 8-foot Transonic Pressure Tunnel in 1995, utilized computational fluid dynamics and numerical simulation of complex fluid mechanics to an unprecedented extent for the design of the test article and measurement equipment. CFD was used in: the design of the test wing, which was carried from definition of desired disturbance growth characteristics, through to the final airfoil shape that would produce those growth characteristics; the design of the suction-surface perforation pattern that produced enhanced crossflow-disturbance growth: and in the design of the hot-wire traverse system that produced minimal influence on measured disturbance growth. These and other aspects of the design of the test are discussed, after the historical and technical context of the experiment is described.
Investigation of radiative interaction in laminar flows using Monte Carlo simulation
NASA Technical Reports Server (NTRS)
Liu, Jiwen; Tiwari, S. N.
1993-01-01
The Monte Carlo method (MCM) is employed to study the radiative interactions in fully developed laminar flow between two parallel plates. Taking advantage of the characteristics of easy mathematical treatment of the MCM, a general numerical procedure is developed for nongray radiative interaction. The nongray model is based on the statistical narrow band model with an exponential-tailed inverse intensity distribution. To validate the Monte Carlo simulation for nongray radiation problems, the results of radiative dissipation from the MCM are compared with two available solutions for a given temperature profile between two plates. After this validation, the MCM is employed to solve the present physical problem and results for the bulk temperature are compared with available solutions. In general, good agreement is noted and reasons for some discrepancies in certain ranges of parameters are explained.
Laminar flow modelling of a thermosyphon loop at specified wall temperatures
NASA Astrophysics Data System (ADS)
Küçüka, Serhan; Başaran, Tahsin
2007-10-01
A thermosyphon loop is analyzed in this study by use of numerical and experimental techniques. A rectangular loop was constructed using copper pipe and the sections which were heated or cooled were designed as concentric tube heat exchangers. Hot or cold water was circulated outside of these sections, and both the surface temperatures and heat transferred to and from the loop were measured. Within the numerical study both the momentum and energy equations were also solved using a SIMPLEX algorithm. Numerical results were obtained for laminar flow within the circuit when there was uniform wall temperature in the vertically heated and cooled sections of the thermosyphon. The two-dimensional numerical model provided results which agree with those found experimentally from the thermosyphon loop. In addition, a simulation model was constructed using a correlation included both the Grashof and Prandtl numbers to evaluate heat transfer through a thermosyphon loop.
Evaluation of laminar flow control system concepts for subsonic commercial transport aircraft
NASA Technical Reports Server (NTRS)
1978-01-01
A two-year study conducted to establish a basis for industry decisions on the application of laminar flow control (LFC) to future commercial transports was presented. Areas of investigation included: (1) mission definition and baseline selection; (2) concepts evaluations; and (3) LFC transport configuration selection and component design. The development and evaluation of competing design concepts was conducted in the areas of aerodynamics, structures and materials, and systems. The results of supporting wind tunnel and laboratory testing on a full-scale LFC wing panel, suction surface opening concepts and structural samples were included. A final LFC transport was configured in incorporating the results of concept evaluation studies and potential performance improvements were assessed. Remaining problems together with recommendations for future research are discussed.
Evaluation of Laminar Flow Control System Concepts for Subsonic Commercial Transport Aircraft
NASA Technical Reports Server (NTRS)
Sturgeon, R. F.
1980-01-01
Alternatives in the design of laminar flow control (LFC) subsonic commerical transport aircraft for opeation in the 1980's period were studied. Analyses were conducted to select mission parameters and define optimum aircraft configurational parameters for the selected mission, defined by a passenger payload of 400 and a design range of 12, 038 km (6500 n mi). The baseline aircraft developed for this mission was used as a vehicle for the evaluation and development of alternative LFC system concepts. Alternatices in the areas of aerodynamics, structures and materials, LFC systems, leading-edge region cleaning, and integration of auxiliary systems were studied. Relative to a similarly-optimized advanced technology turbulent transport, the final LFC configuration is approximately equal in DOC but provides descreases of 8.2% in gross weight and 21.7% in fuel consumption.
A spectral element method for fluid dynamics - Laminar flow in a channel expansion
NASA Technical Reports Server (NTRS)
Patera, A. T.
1984-01-01
A spectral element method that combines the generality of the finite element method with the accuracy of spectral techniques is proposed for the numerical solution of the incompressible Navier-Stokes equations. In the spectral element discretization, the computational domain is broken into a series of elements, and the velocity in each element is represented as a high-order Lagrangian interpolant through Chebyshev collocation points. The hyperbolic piece of the governing equations is then treated with an explicit collocation scheme, while the pressure and viscous contributions are treated implicitly with a projection operator derived from a variational principle. The implementation of the technique is demonstrated on a one-dimensional inflow-outflow advection-diffusion equation, and the method is then applied to laminar two-dimensional (separated) flow in a channel expansion. Comparisons are made with experiment and previous numerical work.
NASA Astrophysics Data System (ADS)
Goldin, Nikolas; King, Rudibert; Pätzold, Andreas; Nitsche, Wolfgang; Haller, Daniel; Woias, Peter
2013-03-01
Control strategies for laminar flow control above an unswept wing are investigated. An actuation method based on a flexible membrane displaced by multiple piezo-polymer composite elements is developed for wind tunnel experiments. A model predictive control algorithm is applied to control the multi-bar actuator. The direct negative superposition method of damping Tollmien-Schlichting waves is compared to a biomimetic approach imitating the damping mechanisms of a compliant skin. In both cases, a model predictive control algorithm is applied to control the multi-bar actuator segments. For the biomimetic approach, reduced, real-time solvable models of compliant surfaces are developed and parametrized by direct optimization and according to numerically generated optimal wall properties. Damping results of up to 85 % RMS value are achieved, shifting the onset of transition about 100 mm downstream with a single actuation membrane. Additional experiments with cascaded multiple membranes show the potential for a further shift.
Design considerations for application of laminar flow control systems to transport aircraft
NASA Technical Reports Server (NTRS)
Braslow, A. L.; Fischer, M. C.
1985-01-01
The current status of the laminar-flow control LFC technology is summarized. Factors that have previously inhibited the application of LFC are first reviewed. Involved are the effects of atmospheric ice crystals, surface irregularities, acoustical environment, and off-design operating conditions. Aircraft design trends that are different from turbulent aircraft are discussed as are various design requirements unique to the LFC systems. Current design approaches for the principal LFC systems are reviewed. These include the system for protection of the leading-edge region from surface contamination and icing and the system for removal of a portion of the boundary-layer air. The latter includes consideration of both multiple spanwise suction slots and distributed perforations and required differences between the wing-box and leading-edge box regions.
NASA Technical Reports Server (NTRS)
Bushnell, D. M.; Tuttle, M. H.
1979-01-01
A survey was conducted and a bibliography compiled on attainment of laminar flow in air through the use of favorable pressure gradient and suction. This report contains the survey, summaries of data for both ground and flight experiments, and abstracts of referenced reports. Much early information is also included which may be of some immediate use as background material for LFC applications.
An approximate method of estimating the maximum saturation, the nucleation rate, and the total number nucleated per second during the laminar flow of a hot vapour–gas mixture along a tube with cold walls is described. The basis of the approach is that the temperature an...
Numerical evaluation of laminar heat transfer enhancement in nanofluid flow in coiled square tubes.
Sasmito, Agus Pulung; Kurnia, Jundika Candra; Mujumdar, Arun Sadashiv
2011-05-09
Convective heat transfer can be enhanced by changing flow geometry and/or by enhancing thermal conductivity of the fluid. This study proposes simultaneous passive heat transfer enhancement by combining the geometry effect utilizing nanofluids inflow in coils. The two nanofluid suspensions examined in this study are: water-Al2O3 and water-CuO. The flow behavior and heat transfer performance of these nanofluid suspensions in various configurations of coiled square tubes, e.g., conical spiral, in-plane spiral, and helical spiral, are investigated and compared with those for water flowing in a straight tube. Laminar flow of a Newtonian nanofluid in coils made of square cross section tubes is simulated using computational fluid dynamics (CFD)approach, where the nanofluid properties are treated as functions of particle volumetric concentration and temperature. The results indicate that addition of small amounts of nanoparticles up to 1% improves significantly the heat transfer performance; however, further addition tends to deteriorate heat transfer performance.
Numerical simulation of laminar plasma dynamos in a cylindrical von Karman flow
Khalzov, I. V.; Brown, B. P.; Schnack, D. D.; Forest, C. B.; Ebrahimi, F.
2011-03-15
The results of a numerical study of the magnetic dynamo effect in cylindrical von Karman plasma flow are presented with parameters relevant to the Madison Plasma Couette Experiment. This experiment is designed to investigate a broad class of phenomena in flowing plasmas. In a plasma, the magnetic Prandtl number Pm can be of order unity (i.e., the fluid Reynolds number Re is comparable to the magnetic Reynolds number Rm). This is in contrast to liquid metal experiments, where Pm is small (so, Re>>Rm) and the flows are always turbulent. We explore dynamo action through simulations using the extended magnetohydrodynamic NIMROD code for an isothermal and compressible plasma model. We also study two-fluid effects in simulations by including the Hall term in Ohm's law. We find that the counter-rotating von Karman flow results in sustained dynamo action and the self-generation of magnetic field when the magnetic Reynolds number exceeds a critical value. For the plasma parameters of the experiment, this field saturates at an amplitude corresponding to a new stable equilibrium (a laminar dynamo). We show that compressibility in the plasma results in an increase of the critical magnetic Reynolds number, while inclusion of the Hall term in Ohm's law changes the amplitude of the saturated dynamo field but not the critical value for the onset of dynamo action.
Fatigue response of perforated titanium for application in laminar flow control
NASA Technical Reports Server (NTRS)
Johnson, W. Steven; Miller, Jennifer L.; Newman, Jr., James
1996-01-01
The room temperature tensile and fatigue response of non-perforated and perforated titanium for laminar flow control application was investigated both experimentally and analytically. Results showed that multiple perforations did not affect the tensile response, but did reduce the fatigue life. A two dimensional finite element stress analysis was used to determine that the stress fields from adjacent perforations did not influence one another. The stress fields around the holes did not overlap one another, allowing the materials to be modeled as a plate with a center hole. Fatigue life was predicted using an equivalent MW flow size approach to relate the experimental results to microstructural features of the titanium. Predictions using flaw sizes ranging from 1 to 15 microns correlated within a factor of 2 with the experimental results by using a flow stress of 260 MPa. By using two different flow stresses in the crack closure model and correcting for plasticity, the experimental results were bounded by the predictions for high applied stresses. Further analysis of the complex geometry of the perforations and the local material chemistry is needed to further understand the fatigue behavior of the perforated titanium.
NASA Astrophysics Data System (ADS)
Mondal, Rabindra Nath; Roy, Titob; Shaha, Poly Rani; Yanase, Shinichiro
2016-07-01
Unsteady laminar flow with convective heat transfer through a curved square duct rotating at a constant angular velocity about the center of curvature is investigated numerically by using a spectral method, and covering a wide range of the Taylor number -300≤Tr≤1000 for the Dean number Dn = 1000. A temperature difference is applied across the vertical sidewalls for the Grashof number Gr = 100, where the outer wall is heated and the inner wall cooled, the top and bottom walls being adiabatic. Flow characteristics are investigated with the effects of rotational parameter, Tr, and the pressure-driven parameter, Dn, for the constant curvature 0.001. Time evolution calculations as well as their phase spaces show that the unsteady flow undergoes through various flow instabilities in the scenario `multi-periodic → chaotic → steady-state → periodic → multi-periodic → chaotic', if Tr is increased in the positive direction. For negative rotation, however, time evolution calculations show that the flow undergoes in the scenario `multi-periodic → periodic → steady-state', if Tr is increased in the negative direction. Typical contours of secondary flow patterns and temperature profiles are obtained at several values of Tr, and it is found that the unsteady flow consists of two- to six-vortex solutions if the duct rotation is involved. External heating is shown to generate a significant temperature gradient at the outer wall of the duct. This study also shows that there is a strong interaction between the heating-induced buoyancy force and the centrifugal-Coriolis instability in the curved channel that stimulates fluid mixing and consequently enhances heat transfer in the fluid.
Laminar and turbulent flows over hydrophobic surfaces with shear-dependent slip length
NASA Astrophysics Data System (ADS)
Khosh Aghdam, Sohrab; Ricco, Pierre
2016-03-01
Motivated by extensive discussion in the literature, by experimental evidence and by recent direct numerical simulations, we study flows over hydrophobic surfaces with shear-dependent slip lengths and we report their drag-reduction properties. The laminar channel-flow and pipe-flow solutions are derived and the effects of hydrophobicity are quantified by the decrease of the streamwise pressure gradient for constant mass flow rate and by the increase of the mass flow rate for constant streamwise pressure gradient. The nonlinear Lyapunov stability analysis, first applied to a two-dimensional channel flow by Balogh et al. ["Stability enhancement by boundary control in 2-D channel flow," IEEE Trans. Autom. Control 46, 1696-1711 (2001)], is employed on the three-dimensional channel flow with walls featuring shear-dependent slip lengths. The feedback law extracted through the stability analysis is recognized for the first time to coincide with the slip-length model used to represent the hydrophobic surfaces, thereby providing a precise physical interpretation for the feedback law advanced by Balogh et al. The theoretical framework by Fukagata et al. ["A theoretical prediction of friction drag reduction in turbulent flow by superhydrophobic surfaces," Phys. Fluids 18, 051703 (2006)] is employed to model the drag-reduction effect engendered by the shear-dependent slip-length surfaces and the theoretical drag-reduction values are in very good agreement with our direct numerical simulation data. The turbulent drag reduction is measured as a function of the hydrophobic-surface parameters and is found to be a function of the time- and space-averaged slip length, irrespective of the local and instantaneous slip behaviour at the wall. For slip parameters and flow conditions that could be realized in the laboratory, the maximum computed turbulent drag reduction is 50% and the drag reduction effect degrades when slip along the spanwise direction is considered. The power spent by
DNS on control of laminar-turbulent transition in channel flow with suction and blowing
NASA Astrophysics Data System (ADS)
Yamamoto, Kiyoshi; Murase, Takeo; Floryan, J. M.
1992-11-01
Numerical simulation of laminar-turbulent transition in channel flow with spatially periodic suction/blowing from its channel walls is conducted with a spectral method based on the Fourier spectral method. Reynolds number is fixed on a subcritical value, 5,000, and the influence of both amplitude and wave number of the suction/blowing on the transition is investigated. When the amplitude is small, the transition does not occur because the suction/blowing gives only a slight effect to the basic flow and the resulted flow remains stable to all three-dimensional small disturbances. On the other hand, when the amplitude is a large value, the transition occurs in a finite time, and finally it is obtained instantaneously with a huge value of the amplitude. It is found that the suction/blowing makes the separation ridges on the wall, which may simulate a wall roughness. The transition times are obtained for the moderately large amplitudes and wave numbers, obey nearly a minus two power law dependence on the ratio of amplitude to wave number.
NASA Astrophysics Data System (ADS)
O'Hern, T. J.; Torczynski, J. R.
1993-06-01
The laminar steady flow downstream of fine-mesh screens is studied. Instead of woven-wire screens, high-uniformity screens are fabricated by photoetching holes into 50.8-micron-thick Inconel sheets. The resulting screens have minimum wire widths of 50.8 microns and inter-wire separations of 254 and 318 microns for the two screens examined. A flow facility has been constructed for experiments with these screens. Air is passed through the screens at upstream velocities yielding wire width Reynolds numbers from 2 to 35. To determine the drag coefficient, pressure drops across the screens are measured using pressure transducers and manometers. Three-dimensional flow simulations are also performed. The computational drag coefficients consistently overpredict the experimental values. However, the computational results exhibit sensitivity to the assumed wire cross section, indicating that detailed knowledge of the wire cross section is essential for unambiguous interpretation of experiments using photoetched screens. Standard semiempirical drag correlations for woven-wire screens do not predict the present experimental results with consistent accuracy.
WENO schemes on arbitrary unstructured meshes for laminar, transitional and turbulent flows
Tsoutsanis, Panagiotis Antoniadis, Antonios Foivos Drikakis, Dimitris
2014-01-01
This paper presents the development and implementation of weighted-essentially-non-oscillatory (WENO) schemes for viscous flows on arbitrary unstructured grids. WENO schemes up to fifth-order accurate have been implemented in conjunction with hybrid and non-hybrid unstructured grids. The schemes are investigated with reference to numerical and experimental results for the Taylor–Green vortex, as well as for laminar and turbulent flows around a sphere, and the turbulent shock-wave boundary layer interaction flow problem. The results show that the accuracy of the schemes depends on the arbitrariness of shape and orientation of the unstructured mesh elements, as well as the compactness of directional stencils. The WENO schemes provide a more accurate numerical framework compared to second-order and third-order total variation diminishing (TVD) methods, however, the fifth-order version of the schemes is computationally too expensive to make the schemes practically usable. On the other hand, the third-order variant offers an excellent numerical framework in terms of accuracy and computational cost compared to the fifth-order WENO and second-order TVD schemes. Parallelisation of the CFD code (henceforth labelled as UCNS3D), where the schemes have been implemented, shows that the present methods offer very good scalable performance.
Kusunose, Jiro; Zhang, Hua; Gagnon, M Karen J; Pan, Tingrui; Simon, Scott I; Ferrara, Katherine W
2013-01-01
The identification of novel, synthetic targeting ligands to endothelial receptors has led to the rapid development of targeted nanoparticles for drug, gene and imaging probe delivery. Central to development and optimization are effective models for assessing particle binding in vitro. Here, we developed a simple and cost effective method to quantitatively assess nanoparticle accumulation under physiologically-relevant laminar flow. We designed reversibly vacuum-sealed PDMS microfluidic chambers compatible with 35 mm petri dishes, which deliver uniform or gradient shear stress. These chambers have sufficient surface area for facile cell collection for particle accumulation quantitation through FACS. We tested this model by synthesizing and flowing liposomes coated with APN (K (D) ~ 300 μM) and VCAM-1-targeting (K (D) ~ 30 μM) peptides over HUVEC. Particle binding significantly increased with ligand concentration (up to 6 mol%) and decreased with excess PEG. While the accumulation of particles with the lower affinity ligand decreased with shear, accumulation of those with the higher affinity ligand was highest in a low shear environment (2.4 dyne/cm(2)), as compared with greater shear or the absence of shear. We describe here a robust flow chamber model that is applied to optimize the properties of 100 nm liposomes targeted to inflamed endothelium. PMID:22855121
A comparative study of sound generation by laminar, combusting and non-combusting jet flows
NASA Astrophysics Data System (ADS)
Talei, Mohsen; Brear, Michael J.; Hawkes, Evatt R.
2014-08-01
Sound production by two-dimensional, laminar jet flows with and without combustion is studied numerically and theoretically. The compressible Navier-Stokes, energy and progress variable equations are solved by resolving both the near field and the acoustics. The combusting jet flows are compared to non-combusting jets of the same jet Mach number, with the non-combusting, non-isothermal jets having the same steady temperature difference as the combusting jets. This infers that the magnitude of entropic and density disturbances is similar in some of the combusting and non-combusting cases. The flows are perturbed by a sinusoidal inlet velocity fluctuation at different Strouhal numbers. The computational domain is resolved to the far field in all cases, allowing direct examination of the sound radiated and its sources. Lighthill's acoustic analogy is then solved numerically using Green's functions. The radiated sound calculated using Lighthill's equation is in good agreement with that from the simulations for all cases, validating the numerical solution of Lighthill's equation. The contribution of the source terms in Dowling's reformulation of Lighthill's equation is then investigated. It is shown that the source term relating to changes in the momentum of density inhomogeneities is the dominant source term for all non-reacting, non-isothermal cases. Further, this source term has similar magnitude in the combusting cases and is one of the several source terms that have similar magnitude to the source term involving fluctuations in the heat release rate.
Inertia-driven particle migration and mixing in a wall-bounded laminar suspension flow
NASA Astrophysics Data System (ADS)
Loisel, V.; Abbas, M.; Masbernat, O.; Climent, E.
2015-12-01
Laminar pressure-driven suspension flows are studied in the situation of neutrally buoyant particles at finite Reynolds number. The numerical method is validated for homogeneous particle distribution (no lateral migration across the channel): the increase of particle slip velocities and particle stress with inertia and concentration is in agreement with former works in the literature. In the case of a two-phase channel flow with freely moving particles, migration towards the channel walls due to the Segré-Silberberg effect is observed, leading to the development of a non-uniform concentration profile in the wall-normal direction (the concentration peaks in the wall region and tends towards zero in the channel core). The particle accumulation in the region of highest shear favors the shear-induced particle interactions and agitation, the profile of which appears to be correlated to the concentration profile. A 1D model predicting particle agitation, based on the kinetic theory of granular flows in the quenched state regime when Stokes number St = O(1) and from numerical simulations when St < 1, fails to reproduce the agitation profile in the wall normal direction. Instead, the existence of secondary flows is clearly evidenced by long time simulations. These are composed of a succession of contra-rotating structures, correlated with the development of concentration waves in the transverse direction. The mechanism proposed to explain the onset of this transverse instability is based on the development of a lift force induced by spanwise gradient of the axial velocity fluctuations. The establishment of the concentration profile in the wall-normal direction therefore results from the combination of the mean flow Segré-Silberberg induced migration, which tends to stratify the suspension and secondary flows which tend to mix the particles over the channel cross section.
Inertia-driven particle migration and mixing in a wall-bounded laminar suspension flow
Loisel, V.; Abbas, M. Masbernat, O.; Climent, E.
2015-12-15
Laminar pressure-driven suspension flows are studied in the situation of neutrally buoyant particles at finite Reynolds number. The numerical method is validated for homogeneous particle distribution (no lateral migration across the channel): the increase of particle slip velocities and particle stress with inertia and concentration is in agreement with former works in the literature. In the case of a two-phase channel flow with freely moving particles, migration towards the channel walls due to the Segré-Silberberg effect is observed, leading to the development of a non-uniform concentration profile in the wall-normal direction (the concentration peaks in the wall region and tends towards zero in the channel core). The particle accumulation in the region of highest shear favors the shear-induced particle interactions and agitation, the profile of which appears to be correlated to the concentration profile. A 1D model predicting particle agitation, based on the kinetic theory of granular flows in the quenched state regime when Stokes number St = O(1) and from numerical simulations when St < 1, fails to reproduce the agitation profile in the wall normal direction. Instead, the existence of secondary flows is clearly evidenced by long time simulations. These are composed of a succession of contra-rotating structures, correlated with the development of concentration waves in the transverse direction. The mechanism proposed to explain the onset of this transverse instability is based on the development of a lift force induced by spanwise gradient of the axial velocity fluctuations. The establishment of the concentration profile in the wall-normal direction therefore results from the combination of the mean flow Segré-Silberberg induced migration, which tends to stratify the suspension and secondary flows which tend to mix the particles over the channel cross section.
Cochran, R.J.
1992-01-01
A study of the finite element method applied to two-dimensional incompressible fluid flow analysis with heat transfer is performed using a mixed Galerkin finite element method with the primitive variable form of the model equations. Four biquadratic, quadrilateral elements are compared in this study--the serendipity biquadratic element with bilinear continuous pressure interpolation (Q2(8)-Q1) and the Lagrangian biquadratic element with bilinear continuous pressure interpolation (Q2-Q1) of the Taylor-Hood form. A modified form of the Q2-Q1 element is also studied. The pressure interpolation is augmented by a discontinuous constant shape function for pressure (Q2-Q1+). The discontinuous pressure element formulation makes use of biquadratic shape functions and a discontinuous linear interpolation of the pressure (Q2-P1(3)). Laminar flow solutions, with heat transfer, are compared to analytical and computational benchmarks for flat channel, backward-facing step and buoyancy driven flow in a square cavity. It is shown that the discontinuous pressure elements provide superior solution characteristics over the continuous pressure elements. Highly accurate heat transfer solutions are obtained and the Q2-P1(3) element is chosen for extension to turbulent flow simulations. Turbulent flow solutions are presented for both low turbulence Reynolds number and high Reynolds number formulations of two-equation turbulence models. The following three forms of the length scale transport equation are studied; the turbulence energy dissipation rate ([var epsilon]), the turbulence frequency ([omega]) and the turbulence time scale (tau). It is shown that the low turbulence Reynolds number model consisting of the K - [tau] transport equations, coupled with the damping functions of Shih and Hsu, provides an optimal combination of numerical stability and solution accuracy for the flat channel flow.
NASA Astrophysics Data System (ADS)
Fang, Pingping
1998-12-01
An extended numerical investigation of fully developed, forced convective laminar flows with heat transfer in eccentric annuli has been carried out. Both Newtonian and non-Newtonian (power-law or Ostwald-de Waele) fluids are studied, representing typical applications in petrochemical, bio-chemical, personal care products, polymer/plastic extrusion and food industries. For the heat transfer problem, with an insulated outer surface, two types of thermal boundary conditions have been considered: Constant wall temperature (T), and uniform axial heat flux with constant peripheral temperature (H1) on the inner surface of the annulus. The governing differential equations for momentum and energy conservation are solved by finite-difference methods. Velocity and temperature distributions in the flow cross section, the wall shear-stress distribution, and isothermal f Re, Nu i,T and Nu i,H1 values for different eccentric annuli (0/leɛ/*/le0.6,/ 0.2/le r/sp/*/le0.8) are presented. In Newtonian flows, the eccentricity is found to have a very strong influence on the flow and temperature fields. In an annulus with relatively large inner cylinder eccentricity, the flow tends to stagnate in the narrow section and has higher peak velocities in the wide section of the annulus. There is considerable flow maldistribution in the azimuthal direction, which in turn produces greater nonuniformity in the temperature field and a consequent degradation in the average heat transfer. Also, the H1 wall condition sustains higher heat transfer coefficients relative to the T boundary condition on the inner surface. For viscous, power-law type non-Newtonian flows, both shear thinning (n<1) and shear thickening (n>1) fluids are considered. Here, the non-linear shear behavior of the fluid is found to further aggravate the flow and temperature maldistribution, and once again the eccentricity is seen to exhibit a very strong influence on the friction and heat transfer behavior. Finally, the
NASA Astrophysics Data System (ADS)
Natrajan, V. K.; Christensen, K. T.
2010-11-01
The convective heat transfer behavior of laminar flow through a smooth- and two rough-wall microchannels is investigated by performing non-intrusive and spatially resolved measurements of fluid temperature via two-color fluorescent thermometry under constant heat flux conditions at three of the four microchannel walls. Pressure-drop measurements reveal that the apparent friction factors for all surfaces agree well with established macroscale predictions for laminar flow through rectangular ducts with the onset of transition at Re > Recr = 1,800 for smooth-wall flow and deviation from laminar behavior at progressively lower Re with increasing surface roughness. The local Nu for smooth-wall flow agrees well with macroscale predictions in both the thermally developing and developed regimes. With increasing roughness, while an enhancement in local Nu is noted for flow in the thermally developing regime, no measurable influence is noted upon attainment of a thermally developed state. These observations are supported by the examination of temperature profiles across the microchannel at various axial positions and Re, which suggest that the thermal boundary layer may be regenerated locally by roughness in the thermal entrance region of the flow resulting in an increased axial distance (compared to smooth-wall behavior) at which thermally developed flow is attained in the presence of roughness. Finally, estimates of the bulk Nu indicate enhancement in convective heat transfer over the smooth-wall case for laminar flow at higher Re while the smooth-wall bulk Nu data are found to agree well with macroscale predictions.
NASA Astrophysics Data System (ADS)
Kurelek, John; Yarusevych, Serhiy
2015-11-01
The transition process in a laminar separation bubble (LSB) formed on the suction surface of a NACA 0018 airfoil at a chord Reynolds number of 100,000 and an angle of attack of 5° is studied experimentally. Both natural and forced transition are evaluated using controlled acoustic disturbances. Time-resolved Particle Image Velocimetry and surface pressure measurements are used to investigate the streamwise and spanwise flow development in the bubble. For all the cases examined, the transition process is characterized by the formation of strongly periodic shear layer vortices in the LSB due to the amplification of disturbances in the bubble's fore portion. These structures feature strong spanwise coherence at roll-up; however, they deform rapidly and begin to break down upstream of the mean reattachment point. The vortex breakup is shown to be initiated by spanwise deformation of the vortex filaments, linked to the formation of streamwise structures. This is followed by the formation of turbulent spots, which expand rapidly near mean reattachment. The results demonstrate that the acoustic disturbance environment can have a strong influence on the characteristics of the vortices and their breakup, thereby affecting flow transition and the overall dynamics of the LSB.
Laser Doppler flowmetry for measurement of laminar capillary blood flow in the horse
NASA Astrophysics Data System (ADS)
Adair, Henry S., III
1998-07-01
Current methods for in vivo evaluation of digital hemodynamics in the horse include angiography, scintigraphy, Doppler ultrasound, electromagnetic flow and isolated extracorporeal pump perfused digit preparations. These techniques are either non-quantifiable, do not allow for continuous measurement, require destruction of the horse orare invasive, inducing non- physiologic variables. In vitro techniques have also been reported for the evaluation of the effects of vasoactive agents on the digital vessels. The in vitro techniques are non-physiologic and have evaluated the vasculature proximal to the coronary band. Lastly, many of these techniques require general anesthesia or euthanasia of the animal. Laser Doppler flowmetry is a non-invasive, continuous measure of capillary blood flow. Laser Doppler flowmetry has been used to measure capillary blood flow in many tissues. The principle of this method is to measure the Doppler shift, that is, the frequency change that light undergoes when reflected by moving objects, such as red blood cells. Laser Doppler flowmetry records a continuous measurement of the red cell motion in the outer layer of the tissue under study, with little or no influence on physiologic blood flow. This output value constitutes the flux of red cells and is reported as capillary perfusion units. No direct information concerning oxygen, nutrient or waste metabolite exchange in the surrounding tissue is obtained. The relationship between the flowmeter output signal and the flux of red blood cells is linear. The principles of laser Doppler flowmetry will be discussed and the technique for laminar capillary blood flow measurements will be presented.
NASA Astrophysics Data System (ADS)
Jenkinson, Ian R.; Sun, Jun
2014-03-01
The laminar-flow viscosity of ocean and other natural waters consists of a Newtonian aqueous component contributed by water and salts, and a non-Newtonian one contributed mainly by exopolymeric polymers (EPS) derived largely from planktonic algae and bacteria. Phytoplankton and EPS form thin layers in stratified waters, often associated with density discontinuities. A recent model (Jenkinson and Sun, 2011. J. Plankton Res., 33, 373-383) investigated possible thalassorheological control of pycnocline thickness (PT) by EPS secreted by the harmful dinoflagellate Karenia mikimotoi. The model, based on published measurements of viscosity increase by this species, found that whether it can influence PT depends on the relationship between increased viscosity, deformation rates/stresses and length scale, which the present work has investigated. To do this, flow rate vs. hydrostatic pressure (and hence wall stress) was measured in cultures (relative to that in reference water) in capillaries of 5 radii 0.35-1.5 mm, close to oceanic-turbulence Kolmogorov length. We compared cultures of the potentially harmful algae, K. mikimotoi, Alexandrium catenella, Prorocentrum donghaiense, Skeletonema costatum, Phaeodactylum tricornutum and the bacterium Escherichia coli. Drag increase, ascribed to rheological thickening by EPS, occurred in the smallest capillaries, but drag reduction (DR) occurred in the largest ones. Since this occurred at Reynolds numbers Re too small for turbulence (or turbulent DR) to occur, this was laminar-flow DR. It may have been superhydrophobic DR (SDR), associated with the surfaces of the plankton and bacteria. SDR is associated with the self-cleaning Lotus-leaf Effect, in which water and dirt are repelled from surfaces bearing nm- to µm-sized irregularities coated with hydrophobic polymers. Because DR decreased measured viscosity and EPS thickening increased it, we could not validate the model. DR, however, represents hitherto unknown phenomenon in the
Structural development of laminar flow control aircraft chordwise wing joint designs
NASA Technical Reports Server (NTRS)
Fischler, J. E.; Jerstad, N. M.; Gallimore, F. H., Jr.; Pollard, T. J.
1989-01-01
For laminar flow to be achieved, any protuberances on the surface must be small enough to avoid transition to turbulent flow. However, the surface must have joints between the structural components to allow assembly or replacement of damaged parts, although large continuous surfaces can be utilized to minimize the number the number of joints. Aircraft structural joints usually have many countersunk bolts or rivets on the outer surface. To maintain no mismatch on outer surfaces, it is desirable to attach the components from the inner surface. It is also desirable for the panels to be interchangeable, without the need for shims at the joint, to avoid surface discontinuities that could cause turbulence. Fabricating components while pressing their outer surfaces against an accurate mold helps to ensure surface smoothness and continuity at joints. These items were considered in evaluating the advantages and disadvantages of the joint design concepts. After evaluating six design concepts, two of the leading candidates were fabricated and tested using many small test panels. One joint concept was also built and tested using large panels. The small and large test panel deflections for the leading candidate designs at load factors up to +1.5 g's were well within the step and waviness requirements for avoiding transition.The small panels were designed and tested for compression and tension at -65 F, at ambient conditions, and at 160 F. The small panel results for the three-rib and the sliding-joint concepts indicated that they were both acceptable. The three-rib concept, with tapered splice plates, was considered to be the most practical. A modified three-rib joint that combined the best attributes of previous candidates was designed, developed, and tested. This improved joint met all of the structural strength, surface smoothness, and waviness criteria for laminar flow control (LFC). The design eliminated all disadvantages of the initial three-rib concept except for
NASA Astrophysics Data System (ADS)
Kitagawa, A.; Kimura, K.; Endo, H.; Hagiwara, Y.
2009-02-01
Laminar mixed-convection heat transfer is widely seen in compact heat exchangers. Injection of sub-millimeter bubbles is considered as one of the efficient techniques for enhancing laminar mixed-convection heat transfer for liquids. However, the effects of sub-millimeter-bubble injection on the laminar mixed-convection heat transfer are poorly understood. In this study, we experimentally investigate flow and heat transfer characteristics of the laminar mixed-convection of water with sub-millimeter bubbles in a vertical channel. The thermocouples and a PTV (Particle Tracking Velocimetry) technique are used for the temperature and velocity measurements, respectively. Tap water is used for working fluid and hydrogen bubbles generated by electrolysis of water are used as the sub-millimeter bubbles. The Reynolds number of the main flow ranges from 100 to 150. Our results show that the ratio of the heat transfer coefficient with sub-millimeter-bubble injection to that without injection decreases as the Reynolds number increases. It is found from the liquid velocity measurements that this decrease is mainly due to a decrease in the "bubble advection effect".
Heat transfer enhancement of laminar nanofluids flow in a triangular duct using vortex generator
NASA Astrophysics Data System (ADS)
Ahmed, H. E.; Mohammed, H. A.; Yusoff, M. Z.
2012-09-01
In this work, two dimensional laminar flow of different nanofluids flow inside a triangular duct with the existence of vortex generator is numerically investigated. The governing equations of mass, momentum and energy were solved using the finite volume method (FVM). The effects of type of the nanoparticles, particle concentrations, and Reynolds number on the heat transfer coefficient and pressure drop of nanofluids are examined. Reynolds number is ranged from 100 to 800. A constant surface temperature is assumed to be the thermal condition for the upper and lower heated walls. In the present work, three nanofluids are examined which are Al2O3, CuO and SiO2 suspended in the base fluid of ethylene glycol with nanoparticles concentrations ranged from 1 to 6%. The results show that for the case of SiO2-EG, at ϕ = 6% and Re = 800, it is found that the average Nusselt number is about 50.0% higher than the case of Re = 100.
Laminar Wall Jet Flow and Heat Transfer over a Shallow Cavity
Maheandera Prabu, P.; Padmanaban, K. P.
2015-01-01
This paper presents the detailed simulation of two-dimensional incompressible laminar wall jet flow over a shallow cavity. The flow characteristics of wall jet with respect to aspect ratio (AR), step length (Xu), and Reynolds number (Re) of the shallow cavity are expressed. For higher accuracy, third-order discretization is applied for momentum equation which is solved using QUICK scheme with SIMPLE algorithm for pressure-velocity coupling. Low Reynolds numbers 25, 50, 100, 200, 400, and 600 are assigned for simulation. Results are presented for streamline contour, velocity contour, and vorticity formation at wall and also velocity profiles are reported. The detailed study of vortex formation on shallow cavity region is presented for various AR, Xu, and Re conditions which led to key findings as Re increases and vortex formation moves from leading edge to trailing edge of the wall. Distance between vortices increases when the step length (Xu) increases. When Re increases, the maximum temperature contour distributions take place in shallow cavity region and highest convection heat transfer is obtained in heated walls. The finite volume code (FLUENT) is used for solving Navier-Stokes equations and GAMBIT for modeling and meshing. PMID:26413565
Studying Molecular Interactions at the Single Bond Level with a Laminar Flow Chamber
Pierres, Anne; Benoliel, Anne-Marie; Bongrand, Pierre
2008-01-01
During the last decade, many investigators developed new methodologies allowing to study ligand-receptor interactions with unprecedented accuracy, up to the single bond level. Reported results include information on bond mechanical properties, association behaviour of surface-attached molecules, and dissection of energy landscapes and reaction pathways. The purpose of the present review is to discuss the potential and limitations of laminar flow chambers operated at low shear rates. This includes a brief review of basic principles, practical tips and problems associated with data interpretation. It is concluded that flow chambers are ideally suited to analyze weak interactions between a number of biomolecules, including the main families of adhesion receptors such as selectins, integrins, cadherins and members of the immunoglobulin superfamily. The sensitivity of the method is limited by the quality of surfaces and efficiency of the studied ligand-receptor couple rather than the hardware. Analyzing interactions with a resolution of a piconewton and a few milliseconds shows that ligand-receptor complexes may experience a number of intermediate binding states, making it necessary to examine the definition of association and dissociation rates. Finally, it is emphasized that association rates measured on surface-bound molecules are highly dependent on parameters unrelated to binding surfaces. PMID:21151952
Performance evaluation on an air-cooled heat exchanger for alumina nanofluid under laminar flow
2011-01-01
This study analyzes the characteristics of alumina (Al2O3)/water nanofluid to determine the feasibility of its application in an air-cooled heat exchanger for heat dissipation for PEMFC or electronic chip cooling. The experimental sample was Al2O3/water nanofluid produced by the direct synthesis method at three different concentrations (0.5, 1.0, and 1.5 wt.%). The experiments in this study measured the thermal conductivity and viscosity of nanofluid with weight fractions and sample temperatures (20-60°C), and then used the nanofluid in an actual air-cooled heat exchanger to assess its heat exchange capacity and pressure drop under laminar flow. Experimental results show that the nanofluid has a higher heat exchange capacity than water, and a higher concentration of nanoparticles provides an even better ratio of the heat exchange. The maximum enhanced ratio of heat exchange and pressure drop for all the experimental parameters in this study was about 39% and 5.6%, respectively. In addition to nanoparticle concentration, the temperature and mass flow rates of the working fluid can affect the enhanced ratio of heat exchange and pressure drop of nanofluid. The cross-section aspect ratio of tube in the heat exchanger is another important factor to be taken into consideration. PMID:21827644
Kamholz, A E; Yager, P
2001-01-01
The T-sensor is a microfluidic analytical device that operates at low Reynolds numbers to ensure entirely laminar flow. Diffusion of molecules between streams flowing side by side may be observed directly. The pressure-driven velocity profile in the duct-shaped device influences diffusive transport in ways that affect the use of the T-sensor to measure molecular properties. The primary effect is a position-dependent variation in the extent of diffusion that occurs due to the distribution of residence time among different fluid laminae. A more detailed characterization reveals that resultant secondary concentration gradients yield variations in the scaling behavior between diffusive displacement and elapsed time in different regions of the channel. In this study, the time-dependent evolution of analyte distribution has been quantified using a combination of one- and two-dimensional models. The results include an accurate portrayal of the shape of the interdiffusion region in a representative T-sensor assay, calculation of the diffusive scaling law across the width of the channel, and quantification of artifacts that occur when making diffusion coefficient measurements in the T-sensor. PMID:11159391
Laminar Wall Jet Flow and Heat Transfer over a Shallow Cavity.
Prabu, P Maheandera; Padmanaban, K P
2015-01-01
This paper presents the detailed simulation of two-dimensional incompressible laminar wall jet flow over a shallow cavity. The flow characteristics of wall jet with respect to aspect ratio (AR), step length (X u), and Reynolds number (Re) of the shallow cavity are expressed. For higher accuracy, third-order discretization is applied for momentum equation which is solved using QUICK scheme with SIMPLE algorithm for pressure-velocity coupling. Low Reynolds numbers 25, 50, 100, 200, 400, and 600 are assigned for simulation. Results are presented for streamline contour, velocity contour, and vorticity formation at wall and also velocity profiles are reported. The detailed study of vortex formation on shallow cavity region is presented for various AR, X u , and Re conditions which led to key findings as Re increases and vortex formation moves from leading edge to trailing edge of the wall. Distance between vortices increases when the step length (X u) increases. When Re increases, the maximum temperature contour distributions take place in shallow cavity region and highest convection heat transfer is obtained in heated walls. The finite volume code (FLUENT) is used for solving Navier-Stokes equations and GAMBIT for modeling and meshing. PMID:26413565
Greiner, G.P.; Furlong, D.A.; Bahner, M.A.
1989-05-01
This report describes ambient temperature testing of an electrostatic precipitator having a portion of the main precipitator flow drawn through porous (fabric) plates. The effects of flow through the plates (side flow) on precipitator turbulence and particulate removal efficiency are investigated. Ambient temperature particulate removal efficiency measurements are conducted on both indoor air dust, and on injected coal fly ash. 24 figs., 10 tabs.
NASA Technical Reports Server (NTRS)
Kumar, A.; Graeves, R. A.
1980-01-01
A user's guide for a computer code 'COLTS' (Coupled Laminar and Turbulent Solutions) is provided which calculates the laminar and turbulent hypersonic flows with radiation and coupled ablation injection past a Jovian entry probe. Time-dependent viscous-shock-layer equations are used to describe the flow field. These equations are solved by an explicit, two-step, time-asymptotic finite-difference method. Eddy viscosity in the turbulent flow is approximated by a two-layer model. In all, 19 chemical species are used to describe the injection of carbon-phenolic ablator in the hydrogen-helium gas mixture. The equilibrium composition of the mixture is determined by a free-energy minimization technique. A detailed frequency dependence of the absorption coefficient for various species is considered to obtain the radiative flux. The code is written for a CDC-CYBER-203 computer and is capable of providing solutions for ablated probe shapes also.
NASA Technical Reports Server (NTRS)
Kumar, A.; Tiwari, S. N.
1980-01-01
Laminar and turbulent flow-field solutions with coupled carbon-phenolic mass injection are presented for the forebody of a probe entering a nominal Jupiter atmosphere. Solutions are obtained for a 35-degree hyperboloid and for a 45-degree spherically blunted cone using a time-dependent, finite-difference method. The radiative heating rates for the coupled laminar flow are significantly reduced as compared to the corresponding no-blowing case; however, for the coupled turbulent flow, it is found that the surface radiative heating rates are substantially increased and often exceed the corresponding no-blowing values. Turbulence is found to have no effect on the surface radiative heating rates for the no-blowing solutions. The present results are compared with the other available solutions, and some additional solutions are presented.
Ambient Test Rig (ATR) flow studies: A laminar flow, reduced entrainment electrostatic precipitator
Not Available
1988-10-01
Results of flow testing on a Reduced Entrainment Precipitator Ambient Test Rig are presented. The Reduced Entrainment Precipitator concept involves drawing a portion of the main precipitator flow through hollow, porous collecting plates. The purposes of flow through porous collecting plates ( side flow'') are to provide a dust layer clamping force, and to reduce turbulence with the precipitator. Achievement of these goals should reduce re-entrainment, and result in increased precipitator efficiency. The increased efficiency should be especially evident at higher precipitator main flow velocities. Flow tests conducted included pilot tube velocity traverses, smoke (turbulence) visualization, and measurements of turbulence and velocity with a (fast-response) hot-wire anemometer. 12 refs., 13 figs.
NASA Astrophysics Data System (ADS)
Fan, Juli; Tian, Lu; Jia, Xudong
2016-06-01
Transmission of airborne bacteria is the main factor causing surgical site infection (SSI). Horizontal laminar flow screen is a kind of new clean equipment, which can prevent SSI effectively. Numerical simulation is conducted on the pollution control effect of operating table protected by horizontal laminar flow screen. A three-dimensional model is established, discrete phase model (DPM) is used for calculation. Numerical simulation is carried out to evaluate the particle trajectories with the Lagrange approach, and the dynamic mesh is used. Air movement in the case with and without people’s walking is analyzed. As a result, people’s walking would not affect the distribution of pollutants at the key area of the operating table, the vertex caused by the walking person does little influence on flow field of the whole operating room and the influence area is about 0.24m to 0.75m around the walking person. The protective effect of pollutants with horizontal laminar flow screen for the key areas of operating table is excellent. This work provides references for the study on the depuration of operating room or other occasion.
Interaction between a laminar flame and its self-generated flow
Dunn-Rankin, D.
1985-04-01
The interaction between a premixed laminar flame and its self-generated flow is experimentally studied in a closed duct. A laser Doppler anemometer measures two components of the enclosed gas velocity during the flame propagation. High-speed schlieren cinematography is used to observe changes in flame shape and location. Pressure records correlate with the qualitative schlieren movies and help quantify the progress of the combustion process. A one-dimensional model accurately predicts the unburned gas motion. The flow in the burned gas is rotational because of vorticity generated from flow deflection through the curved flame front. The density difference between the burned and unburned gas requires a velocity jump at the flame front to maintain continuity of mass flux. The measured velocity jump corresponds to this predicted value. A large flame cusp, called a ''tulip'' flame, appears during the flame propagation. Flame instability, pressure wave/flame interaction, and large scale circulation in the unburned gas are suggested explanation for the ''tulip'' flame. Velocity measurements of this work show that no large scale circulation exists in the unburned gas. The onset of the ''tulip'' process coincides with the quench of part of the flame at the sidewalls of the combustion vessel. The velocity decrease in the unburned gas and the curved flame shape at the time of quench combine to generate a vortex in the burned gas. The vortex remains in the proximity of the flame and modifies the flame shape and unburned gas field such that the flame cusp or ''tulip'' is formed.
Zizzari, A; Bianco, M; Miglietta, R; del Mercato, L L; Carraro, M; Sorarù, A; Bonchio, M; Gigli, G; Rinaldi, R; Viola, I; Arima, V
2014-11-21
Liquid flow in microchannels is completely laminar and uniaxial, with a very low Reynolds number regime and long mixing lengths. To increase fluid mixing and solubility of reactants, as well as to reduce reaction time, complex three-dimensional networks inducing chaotic advection have to be designed. Alternatively, turbulence in the liquid can be generated by active mixing methods (magnetic, acoustic waves, etc.) or adding small quantities of elastic materials to the working liquid. Here, polyelectrolyte multilayer capsules embodying a catalytic polyoxometalate complex have been suspended in an aqueous solution and used to create elastic turbulence and to propel fluids inside microchannels as an alternative to viscoelastic polymers. The overall effect is enhanced and controlled by feeding the polyoxometalate-modified capsules with hydrogen peroxide, H2O2, thus triggering an on-demand propulsion due to oxygen evolution resulting from H2O2 decomposition. The quantification of the process is done by analysing some structural parameters of motion such as speed, pressure, viscosity, and Reynolds and Weissenberg numbers, directly obtained from the capillary dynamics of the aqueous mixtures with different concentrations of H2O2. The increases in fluid speed as well as the capsule-induced turbulence effects are proportional to the H2O2 added and therefore dependent on the kinetics of H2O2 dismutation. PMID:25238401
Zizzari, A; Bianco, M; Miglietta, R; del Mercato, L L; Carraro, M; Sorarù, A; Bonchio, M; Gigli, G; Rinaldi, R; Viola, I; Arima, V
2014-11-21
Liquid flow in microchannels is completely laminar and uniaxial, with a very low Reynolds number regime and long mixing lengths. To increase fluid mixing and solubility of reactants, as well as to reduce reaction time, complex three-dimensional networks inducing chaotic advection have to be designed. Alternatively, turbulence in the liquid can be generated by active mixing methods (magnetic, acoustic waves, etc.) or adding small quantities of elastic materials to the working liquid. Here, polyelectrolyte multilayer capsules embodying a catalytic polyoxometalate complex have been suspended in an aqueous solution and used to create elastic turbulence and to propel fluids inside microchannels as an alternative to viscoelastic polymers. The overall effect is enhanced and controlled by feeding the polyoxometalate-modified capsules with hydrogen peroxide, H2O2, thus triggering an on-demand propulsion due to oxygen evolution resulting from H2O2 decomposition. The quantification of the process is done by analysing some structural parameters of motion such as speed, pressure, viscosity, and Reynolds and Weissenberg numbers, directly obtained from the capillary dynamics of the aqueous mixtures with different concentrations of H2O2. The increases in fluid speed as well as the capsule-induced turbulence effects are proportional to the H2O2 added and therefore dependent on the kinetics of H2O2 dismutation.
Self similar growth of a 1D granular fan under laminar flow near threshold
NASA Astrophysics Data System (ADS)
Guerit, Laure; Métivier, François; Devauchelle, Olivier; Lajeunesse, Eric; Barrier, Laurie
2014-05-01
Alluvial fans are major sedimentary bodies that make the transition between the reliefs and the sedimentary basins. They are found at the outlet of some drainages catchments, where rivers are free to diverge and avulse, and to depose part of their sedimentary load. Understanding their dynamics of formation and evolution is a great problem of sediment transport. Rivers and fan profiles are usually described as diffusive systems but this is only true if the shear stress exerted on the bed is high compared to the critical shear stress. This might be the case for sand bed rivers, but not for gravel bed rivers, for which it is known that the shear stress is only slightly higher than the critical one. This is why we need to develop a new model to describe the evolution of alluvial fans built by gravel bed rivers. To do this analytically, we work in 1D, with a laminar flow and one grain-size in order to be able to describe both the fluid and the sediment transport. In addition, the conditions of the experiments insured that the boundary shear stress is near the critical value for motion inception of the granular material. Using Taylor expansion, we show that for asymptotically long times, the fan growth is self-similar and can be decomposed into a triangular ``threshold" shape plus a small quadratic deviation. We performed experiments with glass beads and glycerol to test and successfully validate this theory.
Application of Entropy Concept for Shear Stress Distribution in Laminar Pipe Flow
NASA Astrophysics Data System (ADS)
Choo, Yeon Moon; Choo, Tai Ho; Jung, Donghwi; Seon, Yun Gwan; Kim, Joong Hoon
2016-04-01
In the river fluid mechanics, shear stress is calculated from frictional force caused by viscosity and fluctuating velocity. Traditional shear stress distribution equations have been widely used because of their simplicity. However, they have a critical limitation of requiring energy gradient which is generally difficult to estimate in practice. Especially, measuring velocity/velocity gradient on the boundary layer is difficult in practice. It requires point velocity throughout the entire cross section to calculate velocity gradient. This study proposes shear stress distribution equations for laminar flow based on entropy theory using mean velocity and entropy coefficient. The proposed equations are demonstrated and compared with measured shear stress distribution using Nikuradse's data. Results showed that the coefficient of determination is around 0.99 indicating that the proposed method well describes the true shear stress distribution. Therefore, it was proved that shear stress distribution can be easily and accurately estimated by using the proposed equations. (This research was supported by a gran(13AWMP-B066744-01) from Advanced Water Management Research Program funded by Ministry of Land, Infrastructure and Transport of Korean Government)
Evaluation of laminar flow control system concepts for subsonic commercial transport aircraft
NASA Technical Reports Server (NTRS)
1980-01-01
A study was conducted to evaluate alternatives in the design of laminar flow control (LFC) subsonic commercial transport aircraft for operation in the 1980's period. Analyses were conducted to select mission parameters and define optimum aircraft configurational parameters for the selected mission, defined by a passenger payload of 400 and a design range of 12,038 km (6500 n mi). The baseline aircraft developed for this mission was used as a vehicle for the evaluation and development of alternative LFC system concepts. Alternatives were evaluated in the areas of aerodynamics structures, materials, LFC systems, leading-edge region cleaning and integration of auxiliary systems. Based on these evaluations, concept in each area were selected for further development and testing and ultimate incorporation in the final study aircraft. Relative to a similarly-optimized advanced technology turbulent transport, the final LFC configuration is approximately equal in direct operating cost but provides decreases of 8.2% in gross weight and 21.7% in fuel consumption.
Frost Growth and Densification on a Flat Surface in Laminar Flow with Variable Humidity
NASA Technical Reports Server (NTRS)
Kandula, M.
2012-01-01
Experiments are performed concerning frost growth and densification in laminar flow over a flat surface under conditions of constant and variable humidity. The flat plate test specimen is made of aluminum-6031, and has dimensions of 0.3 mx0.3 mx6.35 mm. Results for the first variable humidity case are obtained for a plate temperature of 255.4 K, air velocity of 1.77 m/s, air temperature of 295.1 K, and a relative humidity continuously ranging from 81 to 54%. The second variable humidity test case corresponds to plate temperature of 255.4 K, air velocity of 2.44 m/s, air temperature of 291.8 K, and a relative humidity ranging from 66 to 59%. Results for the constant humidity case are obtained for a plate temperature of 263.7 K, air velocity of 1.7 m/s, air temperature of 295 K, and a relative humidity of 71.6 %. Comparisons of the data with the author's frost model extended to accommodate variable humidity suggest satisfactory agreement between the theory and the data for both constant and variable humidity.
Structural tests and development of a laminar flow control wing surface composite chordwise joint
NASA Technical Reports Server (NTRS)
Lineberger, L. B.
1984-01-01
The dramatic increases in fuel costs and the potential for periods of limited fuel availability provided the impetus to explore technologies to reduce transport aircraft fuel consumption. NASA sponsored the Aircraft Energy Efficiency (ACEE) program beginning in 1976 to develop technologies to improve fuel efficiency. The Lockheed-Georgia Company accomplished under NAS1-16235 Laminar-Flow-Control (LFC) Wing Panel Structural Design and Development (WSSD); design, manufacturing, and testing activities. An in-depth preliminary design of the baseline 1993 LFC wing was accomplished. A surface panel using the Lockheed graphite/epoxy integrated LFC wing box structural concept was designed. The concept was shown by analysis to be structurally efficient and cost effective. Critical details of the surface and surface joint was demonstrated by fabricating and testing complex, concept selection specimens. The Lockheed-Georgia Company accomplishments, Development of LFC Wind Surface Composite Structures (WSCS), are documented. Tests were conducted on two CV2 panels to verify the static tension and fatigue strength of LFC wing surface chordwise joints.
A transonic interactive boundary-layer theory for laminar and turbulent flow over swept wings
NASA Technical Reports Server (NTRS)
Woodson, Shawn H.; Dejarnette, Fred R.
1988-01-01
A 3-D laminar and turbulent boundary-layer method is developed for compressible flow over swept wings. The governing equations and curvature terms are derived in detail for a nonorthogonal, curvilinear coordinate system. Reynolds shear-stress terms are modeled by the Cebeci-Smith eddy-viscosity formulation. The governing equations are descretized using the second-order accurate, predictor-corrector finite-difference technique of Matsuno, which has the advantage that the crossflow difference formulas are formed independent of the sign of the crossflow velocity component. The method is coupled with a full potential wing/body inviscid code (FLO-30) and the inviscid-viscous interaction is performed by updating the original wing surface with the viscous displacement surface calculated by the boundary-layer code. The number of these global iterations ranged from five to twelve depending on Mach number, sweep angle, and angle of attack. Several test cases are computed by this method and the results are compared with another inviscid-viscous interaction method (TAWFIVE) and with experimental data.
NASA Technical Reports Server (NTRS)
Harris, Charles D.; Brooks, Cuyler W., Jr.; Clukey, Patricia G.; Stack, John P.
1992-01-01
The initial evaluation of a large-chord, swept, supercritical airfoil incorporating an active laminar-flow-control (LFC) suction system with a perforated upper surface is documented in a chronological manner, and the deficiencies in the suction capability of the perforated panels as designed are described. The experiment was conducted in the Langley 8-Foot Transonic Pressure Tunnel. Also included is an evaluation of the influence of the proximity of the tunnel liner to the upper surface of the airfoil pressure distribution.
NASA Technical Reports Server (NTRS)
Jacobs, Eastman N.
1939-01-01
Recent developments in airfoil-testing methods and fundamental air-flow investigations, as applied to airfoils, are discussed. Preliminary test results, obtained under conditions relatively free from stream turbulence and other disturbances, are presented. Suitable airfoils and airfoil-design principles were developed to take advantage of the unusually extensive laminar boundary layers that may be maintained under the improved testing conditions. The results are of interest mainly in range of below 6,000,000.
Characterization and reduction of flow separation in jet pumps for laminar oscillatory flows.
Timmer, Michael A G; Oosterhuis, Joris P; Bühler, Simon; Wilcox, Douglas; van der Meer, Theo H
2016-01-01
A computational fluid dynamics model is used to predict the oscillatory flow through tapered cylindrical tube sections (jet pumps). The asymmetric shape of jet pumps results in a time-averaged pressure drop that can be used to suppress Gedeon streaming in closed-loop thermoacoustic devices. However, previous work has shown that flow separation in the diverging flow direction counteracts the time-averaged pressure drop. In this work, the characteristics of flow separation in jet pumps are identified and coupled with the observed jet pump performance. Furthermore, it is shown that the onset of flow separation can be shifted to larger displacement amplitudes by designs that have a smoother transition between the small opening and the tapered surface of the jet pump. These design alterations also reduce the duration of separated flow, resulting in more effective and robust jet pumps. To make the proposed jet pump designs more compact without reducing their performance, the minimum big opening radius that can be implemented before the local minor losses have an influence on the jet pump performance is investigated. To validate the numerical results, they are compared with experimental results for one of the proposed jet pump designs. PMID:26827017
Characterization and reduction of flow separation in jet pumps for laminar oscillatory flows
NASA Astrophysics Data System (ADS)
Timmer, Michael A. G.; Oosterhuis, Joris P.; Bühler, Simon; Wilcox, Douglas; van der Meer, Theo H.
2016-01-01
A computational fluid dynamics model is used to predict the oscillatory flow through tapered cylindrical tube sections (jet pumps). The asymmetric shape of jet pumps results in a time-averaged pressure drop that can be used to suppress Gedeon streaming in closed-loop thermoacoustic devices. However, previous work has shown that flow separation in the diverging flow direction counteracts the time-averaged pressure drop. In this work, the characteristics of flow separation in jet pumps are identified and coupled with the observed jet pump performance. Furthermore, it is shown that the onset of flow separation can be shifted to larger displacement amplitudes by designs that have a smoother transition between the small opening and the tapered surface of the jet pump. These design alterations also reduce the duration of separated flow, resulting in more effective and robust jet pumps. To make the proposed jet pump designs more compact without reducing their performance, the minimum big opening radius that can be implemented before the local minor losses have an influence on the jet pump performance is investigated. To validate the numerical results, they are compared with experimental results for one of the proposed jet pump designs.
NASA Technical Reports Server (NTRS)
Anderson, Bianca Trujillo; Meyer, Robert R., Jr.
1990-01-01
The variable sweep transition flight experiment (VSTFE) was conducted on an F-14A variable sweep wing fighter to examine the effect of wing sweep on natural boundary layer transition. Nearly full span upper surface gloves, extending to 60 percent chord, were attached to the F-14 aircraft's wings. The results are presented of the glove 2 flight tests. Glove 2 had an airfoil shape designed for natural laminar flow at a wing sweep of 20 deg. Sample pressure distributions and transition locations are presented with the complete results tabulated in a database. Data were obtained at wing sweeps of 15, 20, 25, 30, and 35 deg, at Mach numbers ranging from 0.60 to 0.79, and at altitudes ranging from 10,000 to 35,000 ft. Results show that a substantial amount of laminar flow was maintained at all the wing sweeps evaluated. The maximum transition Reynolds number obtained was 18.6 x 10(exp 6) at 15 deg of wing sweep, Mach 0.75, and at an altitude of 10,000 ft.
Guo, Deliang; Chien, Shu; Shyy, John Y-J
2007-03-01
Steady laminar flow in the straight parts of the arterial tree is atheroprotective, whereas disturbed flow with oscillation in branch points and the aortic root are athero-prone, in part, because of the distinct roles of the flow patterns in regulating the cell cycle of vascular endothelial cells (ECs). To elucidate the molecular basis underlying the endothelial cell cycle regulated by distinct flow patterns, we conducted flow-channel experiments to investigate the effects of laminar versus oscillatory flows on activation of AMP-activated protein kinase (AMPK) and Akt in ECs. Laminar flow caused a transient activation of both AMPK and Akt, but oscillatory flow activated only Akt, with AMPK being maintained at its basal level. Constitutively active and dominant-negative mutants of AMPK and Akt were used to elucidate further the positive effect of Akt and negative role of AMPK in mediating mTOR (mammalian target of rapamycin) and its target p70S6 kinase (S6K) in response to laminar and oscillatory flows. Measurements of phosphorylation of mTOR Ser2448 and S6K Thr389 showed that AMPK, by counteracting Akt under laminar flow, resulted in a transient activation of S6K. Under oscillatory flow, because of the lack of AMPK activation to effect negative regulation, S6K was activated in a sustained manner. As a functional consequence, AMPK activation attenuated cell cycle progression in response to both laminar and oscillatory flows. In contrast, AMPK inhibition promoted EC cycle progression by decreasing the cell population in the G(0)/G(1) phase and increasing it in the S+G(2)/M phase. In vivo, phosphorylation of the promitotic S6K in mouse thoracic aorta was much less than that in mouse aortic root. In contrast, AMPK phosphorylation was higher in the thoracic aorta. These results provide a molecular mechanism by which laminar versus oscillatory flow regulates the endothelial cell cycle.
Wilson, Derek J; Konermann, Lars
2005-11-01
The adverse effects of nonvolatile salts on the electrospray (ESI) mass spectra of proteins and other biological analytes are a major obstacle for a wide range of applications. Numerous sample cleanup approaches have been devised to facilitate ESI-MS analyses. Recently developed microdialysis techniques can shorten desalting times down to several minutes, the bottleneck being diffusion of the contaminant through a semipermeable membrane. This work introduces an approach that allows the on-line desalting of macromolecule solutions within tens of milliseconds. The device does not employ a membrane; instead, it uses a two-layered laminar flow geometry that exploits the differential diffusion of macromolecular analytes and low molecular weight contaminants. To maximize desalting efficiency, diffusive exchange between the flow layers is permitted only for such a time as to allow full exchange of salt, while incurring minimal macromolecule exchange. Computer simulations and optical studies show that the device can reduce the salt concentration by roughly 1 order of magnitude, while retaining approximately 70% of the original protein concentration. Application of this approach to the on-line purification of salt-contaminated protein solutions in ESI-MS results in dramatic improvements of both the signal-to-noise ratio and the absolute signal intensity. However, efficient desalting requires the diffusion coefficients of salt and analyte to differ by roughly 1 order of magnitude or more. This technique has potential to facilitate high-throughput analyses of biological macromolecules directly from complex matrixes. In addition, it may become a valuable tool for process monitoring and for on-line kinetic studies on biological systems.
NASA Technical Reports Server (NTRS)
Shih, Ke-Gang
1987-01-01
The existence of concave solutions of Berman's equation which describes the laminar flow in channels with injection through porous walls is established. It was found that the (unique) concave solutions exist for all injection Reynolds numbers R less than 0.
Yagi, Takanobu; Sato, Ayaka; Shinke, Manabu; Takahashi, Sara; Tobe, Yasutaka; Takao, Hiroyuki; Murayama, Yuichi; Umezu, Mitsuo
2013-05-01
This study experimentally investigated the instability of flow impingement in a cerebral aneurysm, which was speculated to promote the degradation of aneurysmal wall. A patient-specific, full-scale and elastic-wall replica of cerebral artery was fabricated from transparent silicone rubber. The geometry of the aneurysm corresponded to that found at 9 days before rupture. The flow in a replica was analysed by quantitative flow visualization (stereoscopic particle image velocimetry) in a three-dimensional, high-resolution and time-resolved manner. The mid-systolic and late-diastolic flows with a Reynolds number of 450 and 230 were compared. The temporal and spatial variations of near-wall velocity at flow impingement delineated its inherent instability at a low Reynolds number. Wall shear stress (WSS) at that site exhibited a combination of temporal fluctuation and spatial divergence. The frequency range of fluctuation was found to exceed significantly that of the heart rate. The high-frequency-fluctuating WSS appeared only during mid-systole and disappeared during late diastole. These results suggested that the flow impingement induced a transition from a laminar regime. This study demonstrated that the hydrodynamic instability of shear layer could not be neglected even at a low Reynolds number. No assumption was found to justify treating the aneurysmal haemodynamics as a fully viscous laminar flow.
F-16XL Ship #2 during last flight viewed from tanker showing titanium laminar flow glove on left win
NASA Technical Reports Server (NTRS)
1996-01-01
Dryden research pilot Dana Purifoy drops NASA F-16XL #848 away from the tanker in the 44th flight in the Supersonic Laminar Flow Control program recently. The flight test portion of the program ended with the 45th and last data collection flight Nov. 26, 1996. The project demonstrated that laminar--or smooth--airflow could be achieved over a major portion of a wing at supersonic speeds by use of a suction system. The system drew turbulent boundary-layer air through millions of tiny laser-drilled holes in a titanium 'glove' fitted to the upper left wing. About 90 hours of flight time were logged by the unique aircraft during the 13-month flight research program, much of it at speeds of Mach 2. Data acquired during the program will be used to develop a design code calibration database which could assist designers in reducing aerodynamic drag of a proposed second-generation supersonic transport.
NASA Technical Reports Server (NTRS)
Egolfopoulos, Fokion N.; Campbell, Charles S.; Wu, Ming-Shin (Technical Monitor)
1999-01-01
A detailed numerical study was conducted on the dynamics and thermal response of inert spherical particles in strained, laminar, premixed hydrogen/air flames. The modeling included the solution of the steady conservation equations for both the gas and particle phases along and around the stagnation streamline of an opposed-jet configuration, and the use of detailed descriptions of chemical kinetics and molecular transport. For the gas phase, the equations of mass, momentum, energy, and species are considered, while for the particle phase, the model is based on conservation equations of the particle momentum balance in the axial and radial direction, the particle number density, and the particle thermal energy equation. The particle momentum equation includes the forces as induced by drag, thermophoresis, and gravity. The particle thermal energy equation includes the convective/conductive heat exchange between the two phases, as well as radiation emission and absorption by the particle. A one-point continuation method is also included in the code that allows for the description of turning points, typical of ignition and extinction behavior. As expected, results showed that the particle velocity can be substantially different than the gas phase velocity, especially in the presence of large temperature gradients and large strain rates. Large particles were also found to cross the gas stagnation plane, stagnate, and eventually reverse as a result of the opposing gas phase velocity. It was also shown that the particle number density varies substantially throughout the flowfield, as a result of the straining of the flow and the thermal expansion. Finally, for increased values of the particle number density, substantial flame cooling to extinction states and modification of the gas phase fluid mechanics were observed. As also expected, the effect of gravity was shown to be important for low convective velocities and heavy particles. Under such conditions, simulations
NASA Technical Reports Server (NTRS)
Egolfopoulos, Fokion N.; Campbell, Charles S.
1999-01-01
A detailed numerical study was conducted on the dynamics and thermal response of inert, spherical particles in strained, laminar, premixed hydrogen/air flames. The modeling included the solution of the steady conservation equations for both the gas and particle phases along and around the stagnation streamline of an opposed-jet configuration, and the use of detailed descriptions of chemical kinetics and molecular transport, For the gas phase, the equations of mass, momentum, energy, and species are considered, while for the particle phase, the model is based on conservation equations of the particle momentum balance in the axial and radial direction, the particle number density, and the particle thermal energy equation. The particle momentum equation includes the forces as induced by drag, thermophoresis, and gravity. The particle thermal energy equation includes the convective/conductive heat exchange between the two phases, as well as radiation emission and absorption by the particle. A one-point continuation method is also included in the code that allows for the description of turning points, typical of ignition and extinction behavior. As expected, results showed that the particle velocity can be substantially different than the gas phase velocity, especially in the presence of large temperature gradients and large strain rates. Large particles were also found to cross the gas stagnation plane, stagnate, and eventually reverse as a result of the opposing gas phase velocity. It was also shown that the particle number density varies substantially throughout the flowfield, as a result of the straining of the flow and the thermal expansion. Finally, for increased values of the particle number density, substantial flame cooling to extinction states and modification of the gas phase fluid mechanics were observed. As also expected, the effect of gravity was shown to be important for low convective velocities and heavy particles. Under such conditions, simulations
An evaluation of a partial-walled laminar-flow operating room
Whyte, W.; Shaw, B. H.; Freeman, M. A. R.
1974-01-01
This paper contains an assessment of the physical performance of a permanently installed down-flow laminar-flow operating room at the London Hospital. This system employs partial walls extending 0·76 m (2·5 ft.) from the ceiling, from which the air is allowed to issue freely downwards at an initial velocity of about 0·4 m./sec. (80 ft./min.). The usefulness of the partial wall, as compared with a free issuing system, was demonstrated and a comparison made with a fully walled system. It was shown that a fully walled system would be more efficient than a partial-walled system as there was a loss in air velocity of about 20-25% with the partial wall due to the nonconstrained flow of air. This loss would be reflected in an increase in airborne bacterial count and would mean that an increase of 20-25% in the air volume would be required to obtain the same conditions as with the full-walled system. Entrainment of contaminated air was demonstrated but it was concluded that this would be of little consequence in the centre of the clean area, i.e. at the wound site. Sterile instruments, etc., however, on the outside of the clean area, would be more liable to airborne contamination. Bacterial and dust airborne counts taken during total hip operations gave a very low average figure (0·3 bacteria/ft.3 or 10·5/m.3) from which we conclude that the system was about 30 times cleaner in terms of airborne bacteria than a well ventilated conventional operating-room. We concluded that although the partial-walled system was slightly less efficacious than a normal full-walled system, the freedom of movement and of communication for the operating team could in some circumstances outweigh this disadvantage. Sound levels were such that normal conversation was possible with little or no awareness of background noise. ImagesFig. 2Fig. 3Plate 2Plate 2Plate 3Plate 3Plate 1 PMID:4529595
Olivier, L A; Truskey, G A
1993-10-01
Exposure of spreading anchorage-dependent cells to laminar flow is a common technique to measure the strength of cell adhesion. Since cells protrude into the flow stream, the force exerted by the fluid on the cells is a function of cell shape. To assess the relationship between cell shape and the hydrodynamic force on adherent cells, we obtained numerical solutions of the velocity and stress fields around bovine aortic endothelial cells during various stages of spreading and calculated the force required to detach the cells. Morphometric parameters were obtained from light and scanning electron microscopy measurements. Cells were assumed to have a constant volume, but the surface area increased during spreading until the membrane was stretched taut. Two-dimensional models of steady flow were generated using the software packages ANSYS (mesh generation) and FIDAP (problem solution). The validity of the numerical results was tested by comparison with published results for a semicircle in contact with the surface. The drag force and torque were greatest for round cells making initial contact with the surface. During spreading, the drag force and torque declined by factors of 2 and 20, respectively. The calculated forces and moments were used in adhesion models to predict the wall shear stress at which the cells detached. Based upon published values for the bond force and receptor number, round cells should detach at shear stresses between 2.5 and 6 dyn/cm(2), whereas substantially higher stresses are needed to detach spreading and fully spread cells. Results from the simulations indicate that (1) the drag force varies little with cell shape whereas the torque is very sensitive to cell shape, and (2) the increase in the strength of adhesion during spreading is due to increased contact area and receptor densities within the contact area.
Colloidal asphaltene deposition in laminar pipe flow: Flow rate and parametric effects
NASA Astrophysics Data System (ADS)
Hashmi, S. M.; Loewenberg, M.; Firoozabadi, A.
2015-08-01
Deposition from a suspended phase onto a surface can aversely affect everyday transport processes on a variety of scales, from mineral scale corrosion of household plumbing systems to asphaltene deposition in large-scale pipelines in the petroleum industry. While petroleum may be a single fluid phase under reservoir conditions, depressurization upon production often induces a phase transition in the fluid, resulting in the precipitation of asphaltene material which readily aggregates to the colloidal scale and deposits on metallic surfaces. Colloidal asphaltene deposition in wellbores and pipelines can be especially problematic for industrial purposes, where cleanup processes necessitate costly operational shutdowns. In order to better understand the parametric dependence of deposition which leads to flow blockages, we carry out lab-scale experiments under a variety of material and flow conditions. We develop a parametric scaling model to understand the fluid dynamics and transport considerations governing deposition. The lab-scale experiments are performed by injecting precipitating petroleum fluid mixtures into a small metal pipe, which results in deposition and clogging, assessed by measuring the pressure drop across the pipe. Parametric scaling arguments suggest that the clogging behavior is determined by a combination of the Peclet number, volume fraction of depositing material, and the volume of the injection itself.
Incompressible laminar flow through hollow fibers: a general study by means of a two-scale approach
NASA Astrophysics Data System (ADS)
Borsi, Iacopo; Farina, Angiolo; Fasano, Antonio
2011-08-01
We study the laminar flow of an incompressible Newtonian fluid in a hollow fiber, whose walls are porous. We write the Navier-Stokes equations for the flow in the inner channel and Darcy's law for the flow in the fiber, coupling them by means of the Beavers-Joseph condition which accounts for the (possible) slip at the membrane surface. Then, we introduce a small parameter {\\varepsilon ≪ 1} (the ratio between the radius and the length of the fiber) and expand all relevant quantities in powers of ɛ. Averaging over the fiber cross section, we find the velocity profiles for the longitudinal flow and for the cross-flow, and eventually, we determine the explicit expression of the permeability of the system. This work is also preliminary to the study of more complex systems comprising a large number of identical fibers (e.g., ultrafiltration modules and dialysis).
NASA Astrophysics Data System (ADS)
Yapıcı, Hüseyin; Kayataş, Nesrin; Baştürk, Gamze; Kahraman, Nafiz
2006-11-01
This study presents the investigation of transient local entropy generation rate in pulsating fully developed laminar flow through an externally heated pipe. The flow inlet to the pipe is considered as pulsating at a constant period and amplitude (only the velocity oscillates). The simulations are extended to include different pulsating flow cases (sinusoidal flow, step flow, and saw-down flow). To determine the effects of the mean velocity, the period and the amplitude of the pulsating flow on the entropy generation rate, the pulsating flow is examined for various cases of these parameters. Two-dimensional flow and temperature fields are computed numerically with the help of the fluent computational fluid dynamics (CFD) code. In addition to this CFD code, a computer program has been developed to calculate numerically the entropy generation and other thermodynamic parameters by using the results of the calculations performed for the flow and temperature fields. In all investigated cases, the irreversibility due to the heat transfer dominates. The step flow constitutes the highest temperature (about 919 K) and generates the highest total entropy rate (about 0.033 W/K) within the pipe. The results of this study indicate that in the considered situations, the inverse of square of temperature (1/ T 2) is more dominant on the entropy generation than the temperature gradients, and that the increase of the mean velocity of the pulsating flow has an adverse effect on the ratio of the useful energy transfer rate to irreversibility rate.
Instabilities orginating from suction holes used for Laminar Flow Control (LFC)
NASA Technical Reports Server (NTRS)
Watmuff, Jonathan H.
1994-01-01
A small-scale wind tunnel previously used for turbulent boundary layer studies has been modified for experiments in laminar flow control. The facility incorporates suction through interchangeable porous test surfaces which are used to stabilize the boundary layer and delay transition to turbulent flow. The thin porous test surfaces are supported by a baffled plenum chamber box which also acts to gather the flow through the surface into tubes which are routed to a high pressure fan. An elliptic leading edge is attached to the assembly to establish a new layer on the test plate. A slot is used to remove the test section flow below the leading edge. The test section was lengthened and fitted with a new ceiling. Substantial modifications were also made to the 3D probe traverse. Detailed studies have been made using isolated holes to explore the underlying instability mechanisms. The suction is perturbed harmonically and data are averaged on the basis of the phase of the disturbance. Conditions corresponding to strong suction and without suction have been studied. In both cases, 3D contour surfaces in the vicinity of the hole show highly three-dimensional T-S waves that fan out away from the hole with streamwise distance. With suction, the perturbations on the centerline are much stronger and decay less rapidly, while the far field is similar to the case without suction. Downstream the contour surfaces of the bow-shaped TS waves develop spanwise irregularities which eventually form into clumps. The contours remain smooth when suction is not applied. Even without suction, the harmonic point source is challenging for CFD; e.g. DNS has been used for streamwise growth. With suction, grid resources are consumed by the hole and this makes DNS even more expensive. Limited DNS results so far indicate that the vortices which emanate from suction holes appear to be stable. The spanwise clumping observed in the experiment is evidence of a secondary instability that could be
NASA Astrophysics Data System (ADS)
Gladden, Herbert J.; Ko, Ching L.; Boddy, Douglas E.
1995-01-01
A higher-order finite-difference technique is developed to calculate the developing-flow field of steady incompressible laminar flows in the entrance regions of circular pipes. Navier-Stokes equations governing the motion of such a flow field are solved by using this new finite-difference scheme. This new technique can increase the accuracy of the finite-difference approximation, while also providing the option of using unevenly spaced clustered nodes for computation such that relatively fine grids can be adopted for regions with large velocity gradients. The velocity profile at the entrance of the pipe is assumed to be uniform for the computation. The velocity distribution and the surface pressure drop of the developing flow then are calculated and compared to existing experimental measurements reported in the literature. Computational results obtained are found to be in good agreement with existing experimental correlations and therefore, the reliability of the new technique has been successfully tested.
Rate-ratio asymptotic analysis of autoignition of n-heptane in laminar nonpremixed flows
Seshadri, K.; Peters, N.; Paczko, G.
2006-07-15
A rate-ratio asymptotic analysis is carried out to elucidate the mechanisms of autoignition of n-heptane (C{sub 7}H{sub 16}) in laminar, nonpremixed flows. It has been previously established that autoignition of n-heptane takes place in three distinct regimes. These regimes are called the low-temperature regime, the intermediate-temperature regime, and the high-temperature regime. The present analysis considers the high-temperature regime. A reduced chemical-kinetic mechanism made up of two global steps is used in the analysis. The reduced mechanism is deduced from a skeletal mechanism made up of 16 elementary reactions. The skeletal mechanism is derived from a short mechanism made up of 30 elementary reactions. The short mechanism is deduced from a detailed mechanism made up of 56 elementary reactions. In the reduced mechanism, the first global step represents a sequence of fast reactions starting from the rate-limiting elementary reaction between n-heptane and HO{sub 2}. In this global step C{sub 7}H{sub 16} is consumed and hydrogen peroxide (H{sub 2}O{sub 2}) is formed. The second global step represents a sequence of fast reactions starting from the rate-limiting elementary reaction in which H{sub 2}O{sub 2} is consumed and OH is formed. A key aspect of the second global step is that the sequence of fast reactions gives rise to consumption of fuel only without net consumption of H{sub 2}O{sub 2}. This makes the chemical system autocatalytic. The unsteady flamelet equations are used to predict the onset of autoignition. In the flamelet equations a conserved scalar quantity, Z, is used as the independent variable. On the oxidizer side of the mixing layer Z=0, and on the fuel side Z=1. The practical case where the temperature of the oxidizer stream, T{sub 2}, is much greater than the temperature of the fuel stream is considered. Therefore autoignition is presumed to take place close to Z=0. Balance equations are written for C{sub 7}H{sub 16} and H{sub 2}O{sub 2
Hyvärinen, Antti-Pekka; Brus, David; Zdímal, Vladimír; Smolík, Jiri; Kulmala, Markku; Viisanen, Yrjö; Lihavainen, Heikki
2006-06-14
Homogeneous nucleation rate isotherms of n-butanol+helium were measured in a laminar flow diffusion chamber at total pressures ranging from 50 to 210 kPa to investigate the effect of carrier gas pressure on nucleation. Nucleation temperatures ranged from 265 to 280 K and the measured nucleation rates were between 10(2) and 10(6) cm(-3) s(-1). The measured nucleation rates decreased as a function of increasing pressure. The pressure effect was strongest at pressures below 100 kPa. This negative carrier gas effect was also temperature dependent. At nucleation temperature of 280 K and at the same saturation ratio, the maximum deviation between nucleation rates measured at 50 and 210 kPa was about three orders of magnitude. At nucleation temperature of 265 K, the effect was negligible. Qualitatively the results resemble those measured in a thermal diffusion cloud chamber. Also the slopes of the isothermal nucleation rates as a function of saturation ratio were different as a function of total pressure, 50 kPa isotherms yielded the steepest slopes, and 210 kPa isotherms the shallowest slopes. Several sources of inaccuracies were considered in the interpretation of the results: uncertainties in the transport properties, nonideal behavior of the vapor-carrier gas mixture, and shortcomings of the used mathematical model. Operation characteristics of the laminar flow diffusion chamber at both under-and over-pressure were determined to verify a correct and stable operation of the device. We conclude that a negative carrier gas pressure effect is seen in the laminar flow diffusion chamber and it cannot be totally explained with the aforementioned reasons.
Hyvärinen, Antti-Pekka; Brus, David; Zdímal, Vladimír; Smolík, Jiri; Kulmala, Markku; Viisanen, Yrjö; Lihavainen, Heikki
2006-06-14
Homogeneous nucleation rate isotherms of n-butanol+helium were measured in a laminar flow diffusion chamber at total pressures ranging from 50 to 210 kPa to investigate the effect of carrier gas pressure on nucleation. Nucleation temperatures ranged from 265 to 280 K and the measured nucleation rates were between 10(2) and 10(6) cm(-3) s(-1). The measured nucleation rates decreased as a function of increasing pressure. The pressure effect was strongest at pressures below 100 kPa. This negative carrier gas effect was also temperature dependent. At nucleation temperature of 280 K and at the same saturation ratio, the maximum deviation between nucleation rates measured at 50 and 210 kPa was about three orders of magnitude. At nucleation temperature of 265 K, the effect was negligible. Qualitatively the results resemble those measured in a thermal diffusion cloud chamber. Also the slopes of the isothermal nucleation rates as a function of saturation ratio were different as a function of total pressure, 50 kPa isotherms yielded the steepest slopes, and 210 kPa isotherms the shallowest slopes. Several sources of inaccuracies were considered in the interpretation of the results: uncertainties in the transport properties, nonideal behavior of the vapor-carrier gas mixture, and shortcomings of the used mathematical model. Operation characteristics of the laminar flow diffusion chamber at both under-and over-pressure were determined to verify a correct and stable operation of the device. We conclude that a negative carrier gas pressure effect is seen in the laminar flow diffusion chamber and it cannot be totally explained with the aforementioned reasons. PMID:16784271
NASA Technical Reports Server (NTRS)
Harris, Charles D.; Brooks, Cuyler W., Jr.; Clukey, Patricia G.; Stack, John P.
1989-01-01
The effects of Mach number and Reynolds number on the experimental surface pressure distributions and transition patterns for a large chord, swept supercritical airfoil incorporating an active Laminar Flow Control suction system with spanwise slots are presented. The experiment was conducted in the Langley 8 foot Transonic Pressure Tunnel. Also included is a discussion of the influence of model/tunnel liner interactions on the airfoil pressure distribution. Mach number was varied from 0.40 to 0.82 at two chord Reynolds numbers, 10 and 20 x 1,000,000, and Reynolds number was varied from 10 to 20 x 1,000,000 at the design Mach number.
Hou Bixue; Easter, James; Krushelnick, Karl; Nees, John A.
2008-04-21
Hard x rays are generated in laminar helium flow in atmosphere (without a vacuum vessel) through the interaction of tightly focused 35 fs laser pulses of varying energy with a Cu target. The energy conversion efficiency from laser to K{alpha} x rays is measured to be 5.4x10{sup -6}, giving a flux of 5.9x10{sup 9} photons/s into 2{pi} sr from a source measuring approximately 9x12 {mu}m{sup 2} in size (verticalxhorizontal). Results are compared to those measured in vacuum and in static helium environments.
NASA Technical Reports Server (NTRS)
Sturgeon, R. F.; Bennett, J. A.; Etchberger, F. R.; Ferrill, R. S.; Meade, L. E.
1976-01-01
A study was conducted to evaluate the technical and economic feasibility of applying laminar flow control to the wings and empennage of long-range subsonic transport aircraft compatible with initial operation in 1985. For a design mission range of 10,186 km (5500 n mi), advanced technology laminar-flow-control (LFC) and turbulent-flow (TF) aircraft were developed for both 200 and 400-passenger payloads, and compared on the basis of production costs, direct operating costs, and fuel efficiency. Parametric analyses were conducted to establish the optimum geometry for LFC and TF aircraft, advanced LFC system concepts and arrangements were evaluated, and configuration variations maximizing the effectiveness of LFC were developed. For the final LFC aircraft, analyses were conducted to define maintenance costs and procedures, manufacturing costs and procedures, and operational considerations peculiar to LFC aircraft. Compared to the corresponding advanced technology TF transports, the 200- and 400-passenger LFC aircraft realized reductions in fuel consumption up to 28.2%, reductions in direct operating costs up to 8.4%, and improvements in fuel efficiency, in ssm/lb of fuel, up to 39.4%. Compared to current commercial transports at the design range, the LFC study aircraft demonstrate improvements in fuel efficiency up to 131%. Research and technology requirements requisite to the development of LFC transport aircraft were identified.
Length and time for development of laminar flow in tubes following a step increase of volume flux
NASA Astrophysics Data System (ADS)
Chaudhury, Rafeed A.; Herrmann, Marcus; Frakes, David H.; Adrian, Ronald J.
2015-01-01
Laminar flows starting up from rest in round tubes are relevant to numerous industrial and biomedical applications. The two most common types are flows driven by an abruptly imposed constant pressure gradient or by an abruptly imposed constant volume flux. Analytical solutions are available for transient, fully developed flows, wherein streamwise development over the entrance length is absent (Szymanski in J de Mathématiques Pures et Appliquées 11:67-107, 1932; Andersson and Tiseth in Chem Eng Commun 112(1):121-133, 1992, respectively). They represent the transient responses of flows in tubes that are very long compared with the entrance length, a condition that is seldom satisfied in biomedical tube networks. This study establishes the entrance (development) length and development time of starting laminar flow in a round tube of finite length driven by a piston pump that produces a step change from zero flow to a constant volume flux for Reynolds numbers between 500 and 3,000. The flows are examined experimentally, using stereographic particle image velocimetry and computationally using computational fluid dynamics, and are then compared with the known analytical solutions for fully developed flow conditions in infinitely long tubes. Results show that step function volume flux start-up flows reach steady state and fully developed flow five times more quickly than those driven by a step function pressure gradient, a 500 % change when compared with existing estimates. Based on these results, we present new, simple guidelines for achieving experimental flows that are fully developed in space and time in realistic (finite) tube geometries. To a first approximation, the time to achieve steady spatially developing flow is nearly equal to the time needed to achieve steady, fully developed flow. Conversely, the entrance length needed to achieve fully developed transient flow is approximately equal to the length needed to achieve fully developed steady flow. Beyond this
A Note on the Wave Action Density of a Viscous Instability Mode on a Laminar Free-shear Flow
NASA Technical Reports Server (NTRS)
Balsa, Thomas F.
1994-01-01
Using the assumptions of an incompressible and viscous flow at large Reynolds number, we derive the evolution equation for the wave action density of an instability wave traveling on top of a laminar free-shear flow. The instability is considered to be viscous; the purpose of the present work is to include the cumulative effect of the (locally) small viscous correction to the wave, over length and time scales on which the underlying base flow appears inhomogeneous owing to its viscous diffusion. As such, we generalize our previous work for inviscid waves. This generalization appears as an additional (but usually non-negligible) term in the equation for the wave action. The basic structure of the equation remains unaltered.
NASA Technical Reports Server (NTRS)
1999-01-01
This document describes the design of the leading edge suction system for flight demonstration of hybrid laminar flow control on the Boeing 757 airplane. The exterior pressures on the wing surface and the required suction quantity and distribution were determined in previous work. A system consisting of porous skin, sub-surface spanwise passages ("flutes"), pressure regulating screens and valves, collection fittings, ducts and a turbocompressor was defined to provide the required suction flow. Provisions were also made for flexible control of suction distribution and quantity for HLFC research purposes. Analysis methods for determining pressure drops and flow for transpiration heating for thermal anti-icing are defined. The control scheme used to observe and modulate suction distribution in flight is described.
NASA Technical Reports Server (NTRS)
Dress, David A.
1989-01-01
Low speed wind tunnel drag force measurements were taken on a laminar flow body of revolution free of support interference. This body was tested at zero incidence in the NASA Langley 13 in. Magnetic Suspension and Balance System (MSBS). The primary objective of these tests was to substantiate the drag force measuring capabilities of the 13 in. MSBS. The drag force calibrations and wind-on repeatability data provide a means of assessing these capabilities. Additional investigations include: (1) the effects of fixing transition; (2) the effects of fins installed in the tail; and (3) surface flow visualization using both liquid crystals and oil flow. Also two simple drag prediction codes were used to assess their usefulness in estimating overall body drag.
NASA Technical Reports Server (NTRS)
Vemaganti, Gururaja R.
1994-01-01
This report presents computations for the Type 4 shock-shock interference flow under laminar and turbulent conditions using unstructured grids. Mesh adaptation was accomplished by remeshing, refinement, and mesh movement. Two two-equation turbulence models were used to analyze turbulent flows. The mean flow governing equations and the turbulence governing equations are solved in a coupled manner. The solution algorithm and the details pertaining to its implementation on unstructured grids are described. Computations were performed at two different freestream Reynolds numbers at a freestream Mach number of 11. Effects of the variation in the impinging shock location are studied. The comparison of the results in terms of wall heat flux and wall pressure distributions is presented.
Tabe, Reza; Ghalichi, Farzan; Hossainpour, Siamak; Ghasemzadeh, Kamran
2016-08-12
Laminar, turbulent, transitional, or combine areas of all three types of viscous flow can occur downstream of a stenosis depending upon the Reynolds number and constriction shape parameter. Neither laminar flow solver nor turbulent models for instance the k-ω (k-omega), k-ε (k-epsilon), RANS or LES are opportune for this type of flow. In the present study attention has been focused vigorously on the effect of the constriction in the flow field with a unique way. It means that the laminar solver was employed from entry up to the beginning of the turbulent shear flow. The turbulent model (k-ω SST Transitional Flows) was utilized from starting of turbulence to relaminarization zone while the laminar model was applied again with onset of the relaminarization district. Stenotic flows, with 50 and 75% cross-sectional area, were simulated at Reynolds numbers range from 500 to 2000 employing FLUENT (v6.3.17). The flow was considered to be steady, axisymmetric, and incompressible. Achieving results were reported as axial velocity, disturbance velocity, wall shear stress and the outcomes were compared with previously experimental and CFD computations. The analogy of axial velocity profiles shows that they are in acceptable compliance with the empirical data. As well as disturbance velocity and wall shear stresses anticipated by this new approach, part by part simulation, are reasonably valid with the acceptable experimental studies.
Tabe, Reza; Ghalichi, Farzan; Hossainpour, Siamak; Ghasemzadeh, Kamran
2016-08-12
Laminar, turbulent, transitional, or combine areas of all three types of viscous flow can occur downstream of a stenosis depending upon the Reynolds number and constriction shape parameter. Neither laminar flow solver nor turbulent models for instance the k-ω (k-omega), k-ε (k-epsilon), RANS or LES are opportune for this type of flow. In the present study attention has been focused vigorously on the effect of the constriction in the flow field with a unique way. It means that the laminar solver was employed from entry up to the beginning of the turbulent shear flow. The turbulent model (k-ω SST Transitional Flows) was utilized from starting of turbulence to relaminarization zone while the laminar model was applied again with onset of the relaminarization district. Stenotic flows, with 50 and 75% cross-sectional area, were simulated at Reynolds numbers range from 500 to 2000 employing FLUENT (v6.3.17). The flow was considered to be steady, axisymmetric, and incompressible. Achieving results were reported as axial velocity, disturbance velocity, wall shear stress and the outcomes were compared with previously experimental and CFD computations. The analogy of axial velocity profiles shows that they are in acceptable compliance with the empirical data. As well as disturbance velocity and wall shear stresses anticipated by this new approach, part by part simulation, are reasonably valid with the acceptable experimental studies. PMID:27567769
NASA Technical Reports Server (NTRS)
Hackett, Charles M.
1993-01-01
The interaction between a swept shock wave and a laminar boundary layer was investigated experimentally in high-enthalpy hypersonic flow. The effect of high-temperature, real gas physics on the interaction was examined by conducting tests in air and helium. Heat transfer measurements were made on the surface of a flat plate and a shock-generating fin using thin-film resistance sensors for fin incidence angles of 0, 5, and 10 deg at Mach numbers of 6.9 in air and 7.2 in helium. The experiments were conducted in the NASA HYPULSE expansion tube, an impulse-type facility capable of generating high-enthalpy, high-velocity flow with freestream levels of dissociated species that are particularly low. The measurements indicate that the swept shock wave creates high local heat transfer levels in the interaction region, with the highest heating found in the strongest interaction. The maximum measured heating rates in the interaction are order of magnitude greater than laminar flat plate boundary layer heating levels at the same location.
On Laminar to Turbulent Transition of Arc-Jet Flow in the NASA Ames Panel Test Facility
NASA Technical Reports Server (NTRS)
Gokcen, Tahir; Alunni, Antonella I.
2012-01-01
This paper provides experimental evidence and supporting computational analysis to characterize the laminar to turbulent flow transition in a high enthalpy arc-jet facility at NASA Ames Research Center. The arc-jet test data obtained in the 20 MW Panel Test Facility include measurements of surface pressure and heat flux on a water-cooled calibration plate, and measurements of surface temperature on a reaction-cured glass coated tile plate. Computational fluid dynamics simulations are performed to characterize the arc-jet test environment and estimate its parameters consistent with the facility and calibration measurements. The present analysis comprises simulations of the nonequilibrium flowfield in the facility nozzle, test box, and flowfield over test articles. Both laminar and turbulent simulations are performed, and the computed results are compared with the experimental measurements, including Stanton number dependence on Reynolds number. Comparisons of computed and measured surface heat fluxes (and temperatures), along with the accompanying analysis, confirm that that the boundary layer in the Panel Test Facility flow is transitional at certain archeater conditions.
NASA Astrophysics Data System (ADS)
Hazbehian, Mohammad; Mohammadiun, Mohammad; Maddah, Heydar; Alizadeh, Mostafa
2016-09-01
In the present study, the theoretical and experimental results of the second law analysis on the performance of a uniform heat flux tube using are presented in the laminar flow regime. For this purpose, carbon nanotube/water nanofluids is considered as the base fluid. The experimental investigations were undertaken in the Reynolds number range from 800 to 2600, volume concentrations of 0.1-1 %. Results are verified with well-known correlations. The focus will be on the entrance region under the laminar flow conditions for SWCNT nanofluid. The results showed that the Nu number increased about 90-270 % with the enhancement of nanoparticles volume concentration compared to water. The enhancement was particularly significant in the entrance region. Based on the exergy analysis, the results show that exergetic heat transfer effectiveness is increased by 22-67 % employing nanofluids. The exergetic efficiency is increase with increase in nanoparticles concentration. On the other hand, exergy loss was reduced by 23-43 % employing nanofluids as a heat transfer medium with comparing to conventional fluid. In addition, the empirical correlation for exergetic efficiency has also been developed. The consequential results obtained from the correlation are found to be in good agreement with the experimental results within ±5 % variation.
NASA Astrophysics Data System (ADS)
Seshadri, Kalyanasundaram; Frassoldati, Alessio; Cuoci, Alberto; Faravelli, Tiziano; Niemann, Ulrich; Weydert, Patrick; Ranzi, Eliseo
2011-08-01
Experimental and kinetic modeling studies are carried out to characterize premixed combustion of jet fuels, their surrogates, and reference components in laminar nonuniform flows. In previous studies, it was established that the Aachen surrogate made up of 80 % n-decane and 20 % trimethylbenzene by weight, and surrogate C made up of 57 % n-dodecane, 21 % methylcyclohexane and 22 % o-xylene by weight, reproduce key aspects of combustion of jet fuels in laminar nonpremixed flows. Here, these surrogates and a jet fuel are tested in premixed, nonuniform flows. The counterflow configuration is employed, and critical conditions of extinction are measured. In addition, the reference components tested are n-heptane, n-decane, n-dodecane, methylcyclohexane, trimethylbenzene, and o-xylene. Measured critical conditions of extinction of the Aachen surrogate and surrogate C are compared with those for the jet fuel. In general the alkanes n-heptane, n-decane, and n-dodecane, and methylcyclohexane are found to be more reactive than the aromatics o-xylene and trimethylbenzene. Flame structure and critical conditions of extinction are predicted for the reference components and the surrogates using a semi-detailed kinetic model. The predicted values are compared with experimental data. Sensitivity analysis shows that the lower reactivity of the aromatic species arises from the formation of resonantly stabilized radicals. These radicals are found to have a scavenging effect. The present study on premixed flows together with previous studies on nonpremixed flows show that the Aachen surrogate and surrogate C reproduce many aspects of premixed and nonpremixed combustion of jet fuels.
Finite element, stream function-vorticity solution of steady laminar natural convection
NASA Astrophysics Data System (ADS)
Stevens, W. N. R.
1982-12-01
Stream function-vorticity finite element solution of two-dimensional incompressible viscous flow and natural convection is considered. Steady state solutions of the natural convection problem have been obtained for a wide range of the two independent parameters. Use of boundary vorticity formulae or iterative satisfaction of the no-slip boundary condition is avoided by application of the finite element discretization and a displacement of the appropriate discrete equations. Solution is obtained by Newton-Raphson iteration of all equations simultaneously. The method then appears to give a steady solution whenever the flow is physically steady, but it does not give a steady solution when the flow is physically unsteady. In particular, no form of asymmetric differencing is required. The method offers a degree of economy over primitive variable formulations. Physical results are given for the square cavity convection problem. The paper also reports on earlier work in which the most commonly used boundary vorticity formula was found not to satisfy the no-slip condition, and in which segregated solution procedures were attempted with very minimal success.
NASA Technical Reports Server (NTRS)
Davis, Richard E.; Maddalon, Dal V.; Wagner, Richard D.; Fisher, David F.; Young, Ronald
1989-01-01
Summary evaluations of the performance of laminar-flow control (LFC) leading edge test articles on a NASA JetStar aircraft are presented. Statistics, presented for the test articles' performance in haze and cloud situations, as well as in clear air, show a significant effect of cloud particle concentrations on the extent of laminar flow. The cloud particle environment was monitored by two instruments, a cloud particle spectrometer (Knollenberg probe) and a charging patch. Both instruments are evaluated as diagnostic aids for avoiding laminar-flow detrimental particle concentrations in future LFC aircraft operations. The data base covers 19 flights in the simulated airline service phase of the NASA Leading-Edge Flight-Test (LEFT) Program.
NASA Astrophysics Data System (ADS)
Kok, Mariana; Young, Trevor M.
2014-09-01
Surface contamination caused by insects on laminar flow wing surfaces causes a disruption of the flow, resulting in an increase in drag and fuel consumption. Consequently, the use of superhydrophobic coatings to mitigate insect residue adhesion was investigated. A range of hierarchical superhydrophobic coatings with different surface chemistry and topography was examined. Candidate coatings were characterized in terms of their morphology and hydrophobic properties by scanning electron microscopy (SEM) and static and dynamic contact angle measurements, respectively. Arithmetic mean surface roughness (Ra) values were measured using profilometry. Only superhydrophobic coatings with a specific topography showed complete mitigation against insect residue adhesion. A surface which exhibited a specific microstructure (Ra = 5.26 μm) combined with a low sliding angle (SA = 7.6°) showed the best anti-contamination properties. The dynamics of an insect impact event and its influence on the wetting and adhesion mechanisms of insect residue to a surface were discussed.
The structure and stability of the laminar counter-flow partially premixed methane/air triple flame
Lockett, R.D.; Boulanger, B.; Harding, S.C.; Greenhalgh, D.A.
1999-10-01
The flame stability map defining the regime of existence of a counter-flowing laminar partially premixed methane-air triple flame has been determined using OH planar laser-induced fluorescence (PLIF). The stability limits were determined through the observation of flame merging and flame extinction, a function of rich and lean equivalence ratios, and mean axial strain rate. Relatively quantitative OH species profiles and Rayleigh scattering profiles have been measured for three flame conditions. Axial flow velocity profiles, and nozzle exit velocity profiles have been determined for two of the three conditions using 1-D laser Doppler velocimetry (LDV). The diffusion flame extinction axial velocity profile has been measured, and the local extinction axial strain rate has been determined to be 710 s{sup {minus}1}.
NASA Astrophysics Data System (ADS)
Driss, Zied; Karray, Sarhan; Kchaou, Hedi; Abid, Mohamed Salah
2011-12-01
In this paper, the mixing performance of double helical ribbons and double helical screw ribbons impellers mounted on stirred tanks is numerical investigated. The computer simulations are conducted within a specific computational fluid dynamic (CFD) code, based on resolution of the Naviers-Stokes equations in the laminar flow with a finite volume discretization. The field velocity and the viscous dissipation rate are presented in different vessel planes. The global characteristics and the power consumption of these impellers are also studied. The numerical results showed that the velocity field is more active with the double helical screw ribbons impeller. In this case, the effectiveness of the viscous dissipation and the pumping flow has been obviously noted. Also, the pumping and the energy efficiency reach the highest values at the same Reynolds number. The good agreement between the numerical results and the experimental data quietly confirmed the analysed method.
PLIF Temperature and Velocity Distributions in Laminar Hypersonic Flat-plate Flow
NASA Technical Reports Server (NTRS)
OByrne, S.; Danehy, P. M.; Houwing, A. F. P.
2003-01-01
Rotational temperature and velocity distributions have been measured across a hypersonic laminar flat-plate boundary layer, using planar laser-induced fluorescence. The measurements are compared to a finite-volume computation and a first-order boundary layer computation, assuming local similarity. Both computations produced similar temperature distributions and nearly identical velocity distributions. The disagreement between calculations is ascribed to the similarity solution not accounting for leading-edge displacement effects. The velocity measurements agreed to within the measurement uncertainty of 2 % with both calculated distributions. The peak measured temperature was 200 K lower than the computed values. This discrepancy is tentatively ascribed to vibrational relaxation in the boundary layer.
NASA Astrophysics Data System (ADS)
Kumar, P. C. Mukesh; Kumar, J.; Suresh, S.; Babu, K. Praveen
2012-10-01
In this experimental investigation, the heat transfer coefficients of a shell and helically coiled tube heat exchanger using Al2O3/water nanofluid under laminar flow condition were studied. The Al2O3 nanoparticles were characterized by X-Ray diffraction (XRD). The Al2O3/water nanofluid at 0.1%, 0.4% and 0.8% particle volume concentration were prepared by using two step method. The prepared nanofluid was characterized by scanning electron microscope (SEM). It is observed that the overall heat transfer coefficient, inner heat transfer coefficient and experimental inner Nusselt number increase while increasing particle volume concentration and increasing inner Dean number. The enhancement of overall heat transfer coefficient was found to be 7%, 16.9% and 24.2% at 0.1%, 0.4% and 0.8% Al2O3/water nanofluid respectively when compared with water. The enhancement of tube side experimental Nusselt number was found to be 17%, 22.9% and 28% at 0.1%, 0.4% and 0.8% particle volume concentration of Al2O3/water nanofluid respectively when compared with water at fixed Dean number. The tests were conducted in the range of 1600 < De < 2700, and 5200 < Re < 8600 under laminar flow condition and counter flow configuration. These enhancements are due to higher thermal conductivity of nanofluid while increasing particle volume concentration and Brownian motion of nanoparticles. It is studied that there is no negative impact on formation of secondary flow and mixing of fluid when nanofluid passes through the helically coiled tube.
NASA Astrophysics Data System (ADS)
Yu, Jiu-Yang; Lin, Wei; Zheng, Xiao-Tao
2014-06-01
Two-dimensional numerical simulation is performed to understand the effect of flow pulsation on the flow and heat transfer from a heated square cylinder at Re = 100. Numerical calculations are carried out by using a finite volume method based on the pressure-implicit with splitting of operators algorithm in a collocated grid. The effects of flow pulsation amplitude (0.2 ≤ A ≤ 0.8) and frequency (0 ≤ f p ≤ 20 Hz) on the detailed kinematics of flow (streamlines, vorticity patterns), the macroscopic parameters (drag coefficient, vortex shedding frequency) and heat transfer enhancement are presented in detail. The Strouhal number of vortices shedding, drag coefficient for non-pulsating flow are compared with the previously published data, and good agreement is found. The lock-on phenomenon is observed for a square cylinder in the present flow pulsation. When the pulsating frequency is within the lock-on regime, time averaged drag coefficient and heat transfer from the square cylinder is substantially augmented, and when the pulsating frequency in about the natural vortex shedding frequency, the heat transfer is also substantially enhanced. In addition, the influence of the pulsating amplitude on the time averaged drag coefficient, heat transfer enhancement and lock-on occurrence is discussed in detail.
Flight-measured laminar boundary-layer transition phenomena including stability theory analysis
NASA Technical Reports Server (NTRS)
Obara, C. J.; Holmes, B. J.
1985-01-01
Flight experiments were conducted on a single-engine turboprop aircraft fitted with a 92-in-chord, 3-ft-span natural laminar flow glove at glove section lift coefficients from 0.15 to 1.10. The boundary-layer transition measurement methods used included sublimating chemicals and surface hot-film sensors. Transition occurred downstream of the minimum pressure point. Hot-film sensors provided a well-defined indication of laminar, laminar-separation, transitional, and turbulent boundary layers. Theoretical calculations of the boundary-layer parameters provided close agreement between the predicted laminar-separation point and the measured transition location. Tollmien-Schlichting (T-S) wave growth n-factors between 15 and 17 were calculated at the predicted point of laminar separation. These results suggest that for many practical airplane cruise conditions, laminar separation (as opposed to T-S instability) is the major cause of transition in predominantly two-dimensional flows.
Blanchard, M.; Schuller, T.; Sipp, D.; Schmid, P. J.
2015-04-15
The response of a laminar premixed methane-air flame subjected to flow perturbations around a steady state is examined experimentally and using a linearized compressible Navier-Stokes solver with a one-step chemistry mechanism to describe combustion. The unperturbed flame takes an M-shape stabilized both by a central bluff body and by the external rim of a cylindrical nozzle. This base flow is computed by a nonlinear direct simulation of the steady reacting flow, and the flame topology is shown to qualitatively correspond to experiments conducted under comparable conditions. The flame is then subjected to acoustic disturbances produced at different locations in the numerical domain, and its response is examined using the linearized solver. This linear numerical model then allows the componentwise investigation of the effects of flow disturbances on unsteady combustion and the feedback from the flame on the unsteady flow field. It is shown that a wrinkled reaction layer produces hydrodynamic disturbances in the fresh reactant flow field that superimpose on the acoustic field. This phenomenon, observed in several experiments, is fully interpreted here. The additional perturbations convected by the mean flow stem from the feedback of the perturbed flame sheet dynamics onto the flow field by a mechanism similar to that of a perturbed vortex sheet. The different regimes where this mechanism prevails are investigated by examining the phase and group velocities of flow disturbances along an axis oriented along the main direction of the flow in the fresh reactant flow field. It is shown that this mechanism dominates the low-frequency response of the wrinkled shape taken by the flame and, in particular, that it fully determines the dynamics of the flame tip from where the bulk of noise is radiated.
A numerical study of the laminar incompressible flow over a 6:1 prolate spheroid at 10 deg incidence
NASA Astrophysics Data System (ADS)
Rosenfeld, Moshe; Wolfshtein, Micha; Israeli, Moshe
1992-07-01
The steady incompressible laminar flowfield over a 6:1 prolate spheroid at 10 deg incidence and a Reynolds number of 1.6 x 10 exp 6 is investigated numerically by solving a reduced set of the Navier-Stokes equations. The present study moves one step beyond the boundary-layer approximation by relaxing the requirement of an imposed pressure field to permit the calculation of both attached and longitudinal vortical flowfields. The results shed light on the flow properties over slender bodies at intermediate incidence. The longitudinal vortex is found to be weak relative to vortex-dominated flows. Nevertheless, it has pronounced effects on the flow near the surface and on global features of the flowfield. A displacement velocity which describes the effect of the vortical flow on the outer inviscid flow is defined. The line on the spheroid where the displacement velocity vanishes closely follows the projection of the vortex centerline on the surface of the spheroid. It is demonstrated numerically that the convergence of the skin friction lines is not a unique criterion for identifying a vortex flow.
Trachtenberg, Shlomo; Fishelov, Dalia; Ben-Artzi, Matania
2003-01-01
The flagellar filament, the bacterial organelle of motility, is the smallest rotary propeller known. It consists of 1), a basal body (part of which is the proton driven rotary motor), 2), a hook (universal joint—allowing for off-axial transmission of rotary motion), and 3), a filament (propeller—a long, rigid, supercoiled helical assembly allowing for the conversion of rotary motion into linear thrust). Helically perturbed (so-called “complex”) filaments have a coarse surface composed of deep grooves and ridges following the three-start helical lines. These surface structures, reminiscent of a turbine or Archimedean screw, originate from symmetry reduction along the six-start helical lines due to dimerization of the flagellin monomers from which the filament self assembles. Using high-resolution electron microscopy and helical image reconstruction methods, we calculated three-dimensional density maps of the complex filament of Rhizobium lupini H13-3 and determined its surface pattern and boundaries. The helical symmetry of the filament allows viewing it as a stack of identical slices spaced axially and rotated by constant increments. Here we use the closed outlines of these slices to explore, in two dimensions, the hydrodynamic effect of the turbine-like boundaries of the flagellar filament. In particular, we try to determine if, and under what conditions, transitions from laminar to turbulent flow (or perturbations of the laminar flow) may occur on or near the surface of the bacterial propeller. To address these questions, we apply the boundary element method in a manner allowing the handling of convoluted boundaries. We tested the method on several simple, well-characterized cylindrical structures before applying it to real, highly convoluted biological surfaces and to simplified mechanical analogs. Our results indicate that under extreme structural and functional conditions, and at low Reynolds numbers, a deviation from laminar flow might occur on the
Stoodley, P; Dodds, I; De Beer, D; Scott, H Lappin; Boyle, J D
2005-01-01
Fluid flow has been shown to be important in influencing biofilm morphology and causing biofilms to flow over surfaces in flow cell experiments. However, it is not known whether similar effects may occur in porous media. Generally, it is assumed that the primary transport mechanism for biomass in porous media is through convection, as suspended particulates (cells and flocs) carried by fluid flowing through the interstices. However, the flow of biofilms over the surfaces of soils and sediment particles, may represent an important flux of biomass, and subsequently affect both biological activity and permeability. Mixed species bacterial biofilms were grown in glass flow cells packed with 1 mm diameter glass beads, under laminar or turbulent flow (porous media Reynolds number = 20 and 200 respectively). The morphology and dynamic behavior reflected those of biofilms grown in the open flow cells. The laminar biofilm was relatively uniform and after 23 d had inundated the majority of the pore spaces. Under turbulent flow the biofilm accumulated primarily in protected regions at contact points between the beads and formed streamers that trailed from the leeward face. Both biofilms caused a 2 to 3-fold increase in friction factor and in both cases there were sudden reductions in friction factor followed by rapid recovery, suggesting periodic sloughing and regrowth events. Time-lapse microscopy revealed that under both laminar and turbulent conditions biofilms flowed over the surface of the porous media. In some instances ripple structures formed. The velocity of biofilm flow was on the order of 10 mum h(-1) in the turbulent flow cell and 1.0 mum h(-1) in the laminar flow cell.
Stoodley, P; Dodds, I; De Beer, D; Scott, H Lappin; Boyle, J D
2005-01-01
Fluid flow has been shown to be important in influencing biofilm morphology and causing biofilms to flow over surfaces in flow cell experiments. However, it is not known whether similar effects may occur in porous media. Generally, it is assumed that the primary transport mechanism for biomass in porous media is through convection, as suspended particulates (cells and flocs) carried by fluid flowing through the interstices. However, the flow of biofilms over the surfaces of soils and sediment particles, may represent an important flux of biomass, and subsequently affect both biological activity and permeability. Mixed species bacterial biofilms were grown in glass flow cells packed with 1 mm diameter glass beads, under laminar or turbulent flow (porous media Reynolds number = 20 and 200 respectively). The morphology and dynamic behavior reflected those of biofilms grown in the open flow cells. The laminar biofilm was relatively uniform and after 23 d had inundated the majority of the pore spaces. Under turbulent flow the biofilm accumulated primarily in protected regions at contact points between the beads and formed streamers that trailed from the leeward face. Both biofilms caused a 2 to 3-fold increase in friction factor and in both cases there were sudden reductions in friction factor followed by rapid recovery, suggesting periodic sloughing and regrowth events. Time-lapse microscopy revealed that under both laminar and turbulent conditions biofilms flowed over the surface of the porous media. In some instances ripple structures formed. The velocity of biofilm flow was on the order of 10 mum h(-1) in the turbulent flow cell and 1.0 mum h(-1) in the laminar flow cell. PMID:16371336
NASA Astrophysics Data System (ADS)
Miao, Sha; Hendrickson, Kelli; Liu, Yuming; Subramani, Hariprasad
2015-11-01
This work presents a novel and efficient Cartesian-grid based simulation capability for the study of an incompressible, turbulent gas layer over a liquid flow with disparate Reynolds numbers in two phases. This capability couples a turbulent gas-flow solver and a liquid-layer based on a second-order accurate Boundary Data Immersion Method (BDIM) at the deformable interface. The turbulent gas flow solver solves the incompressible Navier-Stokes equations via direct numerical simulation or through turbulence closure (unsteady Reynolds-Averaged Navier-Stokes Models) for Reynolds numbers O(106). In this application, a laminar liquid layer solution is obtained from depth-integrated Navier-Stokes equations utilizing shallow water wave assumptions. The immersed boundary method (BDIM) enforces the coupling at the deformable interface, the boundary conditions to turbulence closure equations and defines the domain geometry on the Cartesian grid. Validations are made for the turbulent gas channel flow over high-viscosity liquid. This simulation capability can be applied to problems in the oil and industrial sector such as channel and pipe flows with heavy oils as well as wind wave generation in shallow waters. Sponsored by the Chevron Energy Technology Company.
NASA Astrophysics Data System (ADS)
Balankin, Alexander S.; Valdivia, Juan-Carlos; Marquez, Jesús; Susarrey, Orlando; Solorio-Avila, Marco A.
2016-08-01
In this Letter, we report experimental and theoretical studies of Newtonian fluid flow through permeable media with fractal porosity. Darcy flow experiments were performed on samples with a deterministic pre-fractal pore network. We found that the seepage velocity is linearly proportional to the pressure drop, but the apparent absolute permeability increases with the increase of sample length in the flow direction L. We claim that a violation of the Hagen-Poiseuille law is due to an anomalous diffusion of the fluid momentum. In this regard we argue that the momentum diffusion is governed by the flow metric induced by the fractal topology of the pore network. The Darcy-like equation for laminar flow in a fractal pore network is derived. This equation reveals that the apparent absolute permeability is independent of L, only if the number of effective spatial degrees of freedom in the pore-network ν is equal to the network fractal (self-similarity) dimension D, e.g. it is in the case of fractal tree-like networks. Otherwise, the apparent absolute permeability either decreases with L, if ν < D, e.g. in media with self-avoiding fractal channels, or increases with L, if ν > D, as this is in the case of the inverse Menger sponge.
NASA Technical Reports Server (NTRS)
Meng, J. C. S.
1973-01-01
The laminar base flow field of a two-dimensional reentry body has been studied by Telenin's method. The flow domain was divided into strips along the x-axis, and the flow variations were represented by Lagrange interpolation polynomials in the transformed vertical coordinate. The complete Navier-Stokes equations were used in the near wake region, and the boundary layer equations were applied elsewhere. The boundary conditions consisted of the flat plate thermal boundary layer in the forebody region and the near wake profile in the downstream region. The resulting two-point boundary value problem of 33 ordinary differential equations was then solved by the multiple shooting method. The detailed flow field and thermal environment in the base region are presented in the form of temperature contours, Mach number contours, velocity vectors, pressure distributions, and heat transfer coefficients on the base surface. The maximum heating rate was found on the centerline, and the two-dimensional stagnation point flow solution was adquate to estimate the maximum heating rate so long as the local Reynolds number could be obtained.
Heating Augmentation in Laminar Flow Due to Heat-Shield Cavities on the Project Orion CEV
NASA Technical Reports Server (NTRS)
Hollis, Brian R.
2008-01-01
An experimental study has been conducted to assess the effects of compression pad cavities on the aeroheating environment of the Project Orion CEV heat-shield at laminar conditions. Testing was conducted in Mach 6 and Mach 10 perfect-gas wind tunnels to obtain heating measurements on and around the compression pads using global phosphor thermography. Consistent trends in heating augmentation levels were observed in the data and correlations of average and maximum heating at the cavities were formulated in terms of the local boundary-layer parameters and cavity dimensions. Additional heating data from prior testing of Genesis and Mars Science Laboratory models were also examined to extend the parametric range of cavity heating correlations.
Continuous Laminar-Smoke Generator
NASA Technical Reports Server (NTRS)
Weinstein, L. M.
1985-01-01
Single smoke filament used to study flow in low-speed wind tunnels. Use of small-diameter single laminar smoke stream allows examination of flow structures at higher resolution, and continuous operation facilitates use.
NASA Technical Reports Server (NTRS)
Swinford, G. R.
1976-01-01
The results of an aircraft wing design study are reported. The selected study airplane configuration is defined. The suction surface, ducting, and compressor systems are described. Techniques of manufacturing suction surfaces are identified and discussed. A wing box of graphite/epoxy composite is defined. Leading and trailing edge structures of composite construction are described. Control surfaces, engine installation, and landing gear are illustrated and discussed. The preliminary wing design is appraised from the standpoint of manufacturing, weight, operations, and durability. It is concluded that a practical laminar flow control (LFC) wing of composite material can be built, and that such a wing will be lighter than an equivalent metal wing. As a result, a program of suction surface evaluation and other studies of configuration, aerodynamics, structural design and manufacturing, and suction systems are recommended.
Kim, Dongwan; Popescu, Paula; Harfouche, Mark; Sendowski, Jacob; Dimotsantou, Maria-Eleni; Flagan, Richard C; Yariv, Amnon
2015-09-01
We propose an on-chip integrated differential optical microring refractive index sensing platform which leverages laminar flow conditions. Close spacing between a sensing and a reference resonator, and sharing the same microfluidic channel allows the two resonators to experience similar environmental disturbances, such as temperature fluctuations and fluidic-induced transients, achieving reliable and sensitive sensing performance. We obtain a noise floor of 80.0 MHz (0.3 pm) and a bulk refractive index sensitivity of 17.0 THz per refractive index unit (RIU) (64.2 nm/RIU), achieving a limit of detection of 1.4×10(-5) RIU in a 30 min and an 8°C window.
NASA Technical Reports Server (NTRS)
Swift, G.; Mungur, P.
1979-01-01
General procedures for the prediction of component noise levels incident upon airframe surfaces during cruise are developed. Contributing noise sources are those associated with the propulsion system, the airframe and the laminar flow control (LFC) system. Transformation procedures from the best prediction base of each noise source to the transonic cruise condition are established. Two approaches to LFC/acoustic criteria are developed. The first is a semi-empirical extension of the X-21 LFC/acoustic criteria to include sensitivity to the spectrum and directionality of the sound field. In the second, the more fundamental problem of how sound excites boundary layer disturbances is analyzed by deriving and solving an inhomogeneous Orr-Sommerfeld equation in which the source terms are proportional to the production and dissipation of sound induced fluctuating vorticity. Numerical solutions are obtained and compared with corresponding measurements. Recommendations are made to improve and validate both the cruise noise prediction methods and the LFC/acoustic criteria.
NASA Technical Reports Server (NTRS)
Deissler, Robert G
1951-01-01
Relations were analytically obtained for the prediction of radial distributions of velocity and temperature for fully developed laminar flow of gases and of liquid metals in tubes with fluid properties variable along the radius. The relations are applicable to both heating and cooling of the fluid. By use of the relations for velocity and temperature distributions, relations were obtained among Nusselt number, friction parameter, and ratio of wall to bulk temperature. The Nusselt number and friction parameter were found to be independent of Reynolds number and Prandtl number. The effects of ratio of wall to bulk temperature on Nusselt number and friction parameter could be eliminated by evaluating the fluid properties at specified temperatures in the fluid.
NASA Technical Reports Server (NTRS)
Tibbetts, J. G.
1979-01-01
Methods for predicting noise at any point on an aircraft while the aircraft is in a cruise flight regime are presented. Developed for use in laminar flow control (LFC) noise effects analyses, they can be used in any case where aircraft generated noise needs to be evaluated at a location on an aircraft while under high altitude, high speed conditions. For each noise source applicable to the LFC problem, a noise computational procedure is given in algorithm format, suitable for computerization. Three categories of noise sources are covered: (1) propulsion system, (2) airframe, and (3) LFC suction system. In addition, procedures are given for noise modifications due to source soundproofing and the shielding effects of the aircraft structure wherever needed. Sample cases, for each of the individual noise source procedures, are provided to familiarize the user with typical input and computed data.
NASA Technical Reports Server (NTRS)
Harris, J. E.; Blanchard, D. K.
1982-01-01
A numerical algorithm and computer program are presented for solving the laminar, transitional, or turbulent two dimensional or axisymmetric compressible boundary-layer equations for perfect-gas flows. The governing equations are solved by an iterative three-point implicit finite-difference procedure. The software, program VGBLP, is a modification of the approach presented in NASA TR R-368 and NASA TM X-2458, respectively. The major modifications are: (1) replacement of the fourth-order Runge-Kutta integration technique with a finite-difference procedure for numerically solving the equations required to initiate the parabolic marching procedure; (2) introduction of the Blottner variable-grid scheme; (3) implementation of an iteration scheme allowing the coupled system of equations to be converged to a specified accuracy level; and (4) inclusion of an iteration scheme for variable-entropy calculations. These modifications to the approach presented in NASA TR R-368 and NASA TM X-2458 yield a software package with high computational efficiency and flexibility. Turbulence-closure options include either two-layer eddy-viscosity or mixing-length models. Eddy conductivity is modeled as a function of eddy viscosity through a static turbulent Prandtl number formulation. Several options are provided for specifying the static turbulent Prandtl number. The transitional boundary layer is treated through a streamwise intermittency function which modifies the turbulence-closure model. This model is based on the probability distribution of turbulent spots and ranges from zero to unity for laminar and turbulent flow, respectively. Several test cases are presented as guides for potential users of the software.
Huang, Bin; Chen, Chang-Ting; Chen, Chi-Shia; Wang, Yun-Ming; Hsieh, Hsyue-Jen; Wang, Danny Ling
2015-09-01
Laminar shear flow triggers a signaling cascade that maintains the integrity of endothelial cells (ECs). Hydrogen sulfide (H2S), a new gasotransmitter is regarded as an upstream regulator of nitric oxide (NO). Whether the H2S-generating enzymes are correlated to the enzymes involved in NO production under shear flow conditions remains unclear as yet. In the present study, the cultured ECs were subjected to a constant shear flow (12 dyn/cm(2)) in a parallel flow chamber system. We investigated the expression of three key enzymes for H2S biosynthesis, cystathionine-γ-lyase (CSE), cystathionine-β-synthase (CBS), and 3-mercapto-sulfurtransferase (3-MST). Shear flow markedly increased the level of 3-MST. Shear flow enhanced the production of H2S was determined by NBD-SCN reagent that can bind to cysteine/homocystein. Exogenous treatment of NaHS that can release gaseous H2S, ECs showed an increase of phosphorylation in Akt(S473), ERK(T202/Y204) and eNOS(S1177). This indicated that H2S can trigger the NO-production signaling cascade. Silencing of CSE, CBS and 3-MST genes by siRNA separately attenuated the phosphorylation levels of Akt(S473) and eNOS(S1177) under shear flow conditions. The particular mode of shear flow increased H2S production. The interplay between H2S and NO-generating enzymes were discussed in the present study. PMID:26212441
Brus, David; Hyvärinen, Antti-Pekka; Zdímal, Vladimír; Lihavainen, Heikki
2005-06-01
Isothermal homogeneous nucleation rates of 1-butanol were measured both in a thermal diffusion cloud chamber and in a laminar flow diffusion chamber built recently at the Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, Prague, Czech Republic. The chosen system 1-butanol-helium can be studied reasonably well in both devices, in the overlapping range of temperatures. The results were compared with those found in the literature and those measured by Lihavainen in a laminar flow diffusion chamber of a similar design. The same isotherms measured with the thermal diffusion cloud chamber occur at highest saturation ratios of the three devices. Isotherms measured with the two laminar flow diffusion chambers are reasonably close together; the measurements by Lihavainen occur at lowest saturation ratios. The temperature dependences observed were similar in all three devices. The molecular content of critical clusters was calculated using the nucleation theorem and compared with the Kelvin equation. Both laminar flow diffusion chambers provided very similar sizes slightly above the Kelvin equation, whereas the thermal diffusion cloud chamber suggests critical cluster sizes significantly smaller. The results found elsewhere in the literature were in reasonable agreement with our results.
Brus, David; Hyvärinen, Antti-Pekka; Zdímal, Vladimír; Lihavainen, Heikki
2005-06-01
Isothermal homogeneous nucleation rates of 1-butanol were measured both in a thermal diffusion cloud chamber and in a laminar flow diffusion chamber built recently at the Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, Prague, Czech Republic. The chosen system 1-butanol-helium can be studied reasonably well in both devices, in the overlapping range of temperatures. The results were compared with those found in the literature and those measured by Lihavainen in a laminar flow diffusion chamber of a similar design. The same isotherms measured with the thermal diffusion cloud chamber occur at highest saturation ratios of the three devices. Isotherms measured with the two laminar flow diffusion chambers are reasonably close together; the measurements by Lihavainen occur at lowest saturation ratios. The temperature dependences observed were similar in all three devices. The molecular content of critical clusters was calculated using the nucleation theorem and compared with the Kelvin equation. Both laminar flow diffusion chambers provided very similar sizes slightly above the Kelvin equation, whereas the thermal diffusion cloud chamber suggests critical cluster sizes significantly smaller. The results found elsewhere in the literature were in reasonable agreement with our results. PMID:15974753
NASA Technical Reports Server (NTRS)
Carter, J. E.
1972-01-01
Numerical solutions have been obtained for the supersonic, laminar flow over a two-dimensional compression corner. These solutions were obtained as steady-state solutions to the unsteady Navier-Stokes equations using the finite difference method of Brailovskaya, which has second-order accuracy in the spatial coordinates. Good agreement was obtained between the computed results and wall pressure distributions measured experimentally for Mach numbers of 4 and 6.06, and respective Reynolds numbers, based on free-stream conditions and the distance from the leading edge to the corner. In those calculations, as well as in others, sufficient resolution was obtained to show the streamline pattern in the separation bubble. Upstream boundary conditions to the compression corner flow were provided by numerically solving the unsteady Navier-Stokes equations for the flat plate flow field, beginning at the leading edge. The compression corner flow field was enclosed by a computational boundary with the unknown boundary conditions supplied by extrapolation from internally computed points.
DNS on control of laminar-turbulent transition in a channel flow with a periodic suction and blowing
NASA Astrophysics Data System (ADS)
Yamamoto, Kiyoshi; Murase, Takeo; Floryan, J. M.
Numerical simulation of laminar-turbulent transition in a channel flow with a spatially periodic suction/blowing on the channel walls is conducted with a spectral method based on the Fourier spectral method. The Reynolds number is fixed on a subcritical value of 5000 and the influence of both amplitude and wave number of the suction/blowing on the transition is investigated. When the amplitude is small, the transition does not occur because the suction/blowing has only a slight effect to the basic flow and the resulting flow remains stable to all 3D small disturbances. On the other hand, when the amplitude has a large value the transition occurs in a finite time and is obtained instantaneously with a huge value of the amplitude. It is found that the suction/blowing makes the separation ridges on the wall, perhaps simulating the wall roughness. The transition times are obtained for moderately large amplitudes and wave numbers and they show nearly a -2 power law dependence of the ratio of amplitude to wave number.
NASA Astrophysics Data System (ADS)
Thorson, Michael R.; Brushett, Fikile R.; Timberg, Chris J.; Kenis, Paul J. A.
2012-11-01
The influence of electrode length on performance is investigated in an air-breathing alkaline direct methanol laminar flow fuel cell (LFFC). Depletion of methanol at the electrode surface along the direction of flow hinders reaction kinetics and consequently also cell performance. Reducing the electrode length can decrease the influence of boundary layer depletion, and thereby, improve both the current and power densities. Here, the effect of boundary layer depletion was found to play a significant effect on performance within the first 18 mm of an electrode length. To further utilize the increased power densities provided by shorter electrode lengths, alternative electrode aspect ratios (electrode length-to-width) and electrode arrangements were explored experimentally. Furthermore, by fitting an empirical model based on experimentally obtained data, we demonstrate that a configuration comprised of a series of short electrodes and operated at low flow rates can achieve higher current and power outputs. The analysis of optimal electrode aspect ratio and electrode arrangements can also be applied to other microfluidic reactor designs in which reaction depletion boundary layers occur due to surface reactions.
NASA Technical Reports Server (NTRS)
Srokowski, A. J.
1994-01-01
The computer program SALLY was developed to compute the incompressible linear stability characteristics and integrate the amplification rates of boundary layer disturbances on swept and tapered wings. For some wing designs, boundary layer disturbance can significantly alter the wing performance characteristics. This is particularly true for swept and tapered laminar flow control wings which incorporate suction to prevent boundary layer separation. SALLY should prove to be a useful tool in the analysis of these wing performance characteristics. The first step in calculating the disturbance amplification rates is to numerically solve the compressible laminar boundary-layer equation with suction for the swept and tapered wing. A two-point finite-difference method is used to solve the governing continuity, momentum, and energy equations. A similarity transformation is used to remove the wall normal velocity as a boundary condition and place it into the governing equations as a parameter. Thus the awkward nonlinear boundary condition is avoided. The resulting compressible boundary layer data is used by SALLY to compute the incompressible linear stability characteristics. The local disturbance growth is obtained from temporal stability theory and converted into a local growth rate for integration. The direction of the local group velocity is taken as the direction of integration. The amplification rate, or logarithmic disturbance amplitude ratio, is obtained by integration of the local disturbance growth over distance. The amplification rate serves as a measure of the growth of linear disturbances within the boundary layer and can serve as a guide in transition prediction. This program is written in FORTRAN IV and ASSEMBLER for batch execution and has been implemented on a CDC CYBER 70 series computer with a central memory requirement of approximately 67K (octal) of 60 bit words. SALLY was developed in 1979.
NASA Technical Reports Server (NTRS)
Back, L. H.
1972-01-01
The laminar flow equations in differential form are solved numerically on a digital computer for flow of a very high temperature gas through the entrance region of an externally cooled tube. The solution method is described and calculations are carried out in conjunction with experimental measurements. The agreement with experiment is good, with the result indicating relatively large energy and momentum losses in the highly cooled flows considered where the pressure is nearly uniform along the flow and the core flow becomes non-adiabatic a few diameters downstream of the inlet. The effects of a large range of Reynolds number and Mach number (viscous dissipation) are also investigated.
Laurent, Christian M.; Palmer, Colin; Boardman, Richard P.; Dyke, Gareth; Cook, Richard B.
2014-01-01
Flight feathers have evolved under selective pressures to be sufficiently light and strong enough to cope with the stresses of flight. The feather shaft (rachis) must resist these stresses and is fundamental to this mode of locomotion. Relatively little work has been done on rachis morphology, especially from a mechanical perspective and never at the nanoscale. Nano-indentation is a cornerstone technique in materials testing. Here we use this technique to make use of differentially oriented fibres and their resulting mechanical anisotropy. The rachis is established as a multi-layered fibrous composite material with varying laminar properties in three feathers of birds with markedly different flight styles; the Mute Swan (Cygnus olor), the Bald Eagle (Haliaeetus leucocephalus) and the partridge (Perdix perdix). These birds were chosen not just because they are from different clades and have different flight styles, but because they have feathers large enough to gain meaningful results from nano-indentation. Results from our initial datasets indicate that the proportions and orientation of the laminae are not fixed and may vary either in order to cope with the stresses of flight particular to the bird or with phylogenetic lineage. PMID:25339689
Laurent, Christian M; Palmer, Colin; Boardman, Richard P; Dyke, Gareth; Cook, Richard B
2014-12-01
Flight feathers have evolved under selective pressures to be sufficiently light and strong enough to cope with the stresses of flight. The feather shaft (rachis) must resist these stresses and is fundamental to this mode of locomotion. Relatively little work has been done on rachis morphology, especially from a mechanical perspective and never at the nanoscale. Nano-indentation is a cornerstone technique in materials testing. Here we use this technique to make use of differentially oriented fibres and their resulting mechanical anisotropy. The rachis is established as a multi-layered fibrous composite material with varying laminar properties in three feathers of birds with markedly different flight styles; the Mute Swan (Cygnus olor), the Bald Eagle (Haliaeetus leucocephalus) and the partridge (Perdix perdix). These birds were chosen not just because they are from different clades and have different flight styles, but because they have feathers large enough to gain meaningful results from nano-indentation. Results from our initial datasets indicate that the proportions and orientation of the laminae are not fixed and may vary either in order to cope with the stresses of flight particular to the bird or with phylogenetic lineage.
Laurent, Christian M; Palmer, Colin; Boardman, Richard P; Dyke, Gareth; Cook, Richard B
2014-12-01
Flight feathers have evolved under selective pressures to be sufficiently light and strong enough to cope with the stresses of flight. The feather shaft (rachis) must resist these stresses and is fundamental to this mode of locomotion. Relatively little work has been done on rachis morphology, especially from a mechanical perspective and never at the nanoscale. Nano-indentation is a cornerstone technique in materials testing. Here we use this technique to make use of differentially oriented fibres and their resulting mechanical anisotropy. The rachis is established as a multi-layered fibrous composite material with varying laminar properties in three feathers of birds with markedly different flight styles; the Mute Swan (Cygnus olor), the Bald Eagle (Haliaeetus leucocephalus) and the partridge (Perdix perdix). These birds were chosen not just because they are from different clades and have different flight styles, but because they have feathers large enough to gain meaningful results from nano-indentation. Results from our initial datasets indicate that the proportions and orientation of the laminae are not fixed and may vary either in order to cope with the stresses of flight particular to the bird or with phylogenetic lineage. PMID:25339689
Chevrons formation in laminar erosion
NASA Astrophysics Data System (ADS)
Devauchelle, Olivier; Josserand, Christophe; Lagree, Pierre-Yves; Zaleski, Stephane; Nguyen, Khanh-Dang; Malverti, Luce; Lajeunesse, Eric
2007-11-01
When eroded by laminar free-surface flows, granular substrates may generate a rich variety of natural patterns. Among them are dunes, similar to the ones observed by Charru and Hinch in a Couette cell (Charru F, Hinch EJ ; Ripple formation on a particle bed sheared by a viscous liquid. Part 1. Steady flow ; JOURNAL OF FLUID MECHANICS 550: 111-121 MAR 10 2006). Chevron-shaped instabilities as those found on the sea-shore, can also be observed, sometimes in competition against dunes formation. These were first pointed out by Daerr et al. when pulling a plate covered with granular material out of a bath of water (Daerr A, Lee P, Lanuza J, et al. ; Erosion patterns in a sediment layer ; PHYSICAL REVIEW E 67 (6): Art. No. 065201 Part 2 JUN 2003). Both instabilities can grow in laminar open-channel flows, an experimental set-up which is more easily controlled. The mechanisms leading to the formation of these patterns are investigated and compared. Whereas dunes formation requires vertical inertia effects, we show that chevrons may result from the non-linear evolution of bars instability, which may grow even in purely viscous flows.
Linear and nonlinear instability and ligament dynamics in 3D laminar two-layer liquid/liquid flows
NASA Astrophysics Data System (ADS)
Ó Náraigh, Lennon; Valluri, Prashant; Scott, David; Bethune, Iain; Spelt, Peter
2013-11-01
We consider the linear and nonlinear stability of two-phase density-matched but viscosity contrasted fluids subject to laminar Poiseuille flow in a channel, paying particular attention to the formation of three-dimensional waves. The Orr-Sommerfeld-Squire analysis is used along with DNS of the 3D two-phase Navier-Stokes equations using our newly launched TPLS Solver (http://edin.ac/10cRKzS). For the parameter regimes considered, we demonstrate the existence of two distinct mechanisms whereby 3D waves enter the system, and dominate at late time. There exists a direct route, whereby 3D waves are amplified by the standard linear mechanism; for certain parameter classes, such waves grow at a rate less than but comparable to that of most-dangerous two-dimensional mode. Additionally, there is a weakly nonlinear route, whereby a purely spanwise wave couples to a streamwise mode and grows exponentially. We demonstrate these mechanisms in isolation and in concert. Consideration is also given to the ultimate state of these waves: persistent three-dimensional nonlinear waves are stretched and distorted by the base flow, thereby producing regimes of ligaments, ``sheets,'' or ``interfacial turbulence.'' HECToR RAP/dCSE Project e174, HPC-Europa 2.
NASA Astrophysics Data System (ADS)
Mittal, Nitesh; Lundell, Fredrik; Soderberg, Daniel
2015-11-01
There are several fiber production technologies that are based on wet-spinning processes. Many such processes rely on the transformation of a liquid solution into a solid filament. The kinetics of solidification depends largely on the diffusion of the solvents, additives and polymer molecules, which make such systems quite complex and differ from a system to another as a function of the specific chemical, physical and structural features of the used material components. Moreover, tuning the orientation of the polymers in the liquid suspensions makes it further possible to control their structure, which in turn can lead to materials having improved properties. By keeping in mind the facts mentioned above, the aim of the current study is to utilize benefits of a flow focusing approach to align carboxymethylated cellulose nanofibrils (CNF), as a colloidal dispersion, with the help of a laminar elongational flow-field followed by the solidification using different solidifying agents or molecules (with dissimilar diffusion behavior based on their size and charges) to synthesize fibers with enhanced mechanical properties. CNF are charged elongated particles obtained from woods with diameter of 4-10 nm and length of 1-1.5 μm, and they are completely biodegradable.
NASA Technical Reports Server (NTRS)
Kuhn, G. D.
1971-01-01
A computer program was developed to do the calculations for two-dimensional or axisymmetric configurations from low speeds to hypersonic speeds with arbitrary streamwise pressure, temperature, and Mach number distributions. Options are provided for obtaining initial conditions either from experimental information or from a theoretical similarity solution. The transition region can be described either by an arbitrary distribution of intermittency or by a function based on Emmons' probability theory. Correlations were developed for use in estimating the parameters of the theoretical intermittency function. Correlations obtained from other sources are used for estimating the transition point. Comparisons were made between calculated and measured boundary layer quantities for laminar, transitional, and turbulent flows on flat plates, cones, cone flares, and a waisted body of revolution. Excellent agreement was obtained between the present theory and two other theories based on the method of finite differences. The intermittency required to reproduce some experimental heat transfer results in hypersonic flow was found to be quite different from the theoretical function. It is suggested that the simple probability theory of Emmons may not be valid for representing the intermittency of hypersonic transitional boundary layers and that the program could be useful as a tool for detailed study of the intermittency of the transition region.
NASA Astrophysics Data System (ADS)
Wagner, S.; Klein, M.; Kathrotia, T.; Riedel, U.; Kissel, T.; Dreizler, A.; Ebert, V.
2012-06-01
Acetylene (C2H2), as an important precursor for chemiluminescence species, is a key to understand, simulate and model the chemiluminescence and the related reaction paths. Hence we developed a high resolution spectrometer based on direct Tunable Diode Laser Absorption Spectroscopy (TDLAS) allowing the first quantitative, calibration-free and spatially resolved in situ C2H2 measurement in an atmospheric non-premixed counter-flow flame supported on a Tsuji burner. A fiber-coupled distributed feedback diode laser near 1535 nm was used to measure several absolute C2H2 concentration profiles (peak concentrations up to 9700 ppm) in a laminar non-premixed CH4/air flame ( T up to 1950 K) supported on a modified Tsuji counter-flow burner with N2 purge slots to minimize end flames. We achieve a fractional optical resolution of up to 5×10-5 OD (1 σ) in the flame, resulting in temperature-dependent acetylene detection limits for the P17e line at 6513 cm-1 of up to 2.1 ppmṡm. Absolute C2H2 concentration profiles were obtained by translating the burner through the laser beam using a DC motor with 100 μm step widths. Intercomparisons of the experimental C2H2 profiles with simulations using our new hydrocarbon oxidation mechanisms show excellent agreement in position, shape and in the absolute C2H2 values.
Development of the technology for the fabrication of reliable laminar flow control panels
NASA Technical Reports Server (NTRS)
Weiss, D. D.; Lindh, D. V.
1977-01-01
Various configurations of porous, perforated and slotted materials were flow tested to determine if they would meet the LFC surface smoothness and flow requirements. The candidate materials were then tested for susceptibility to clogging and for resistance to corrosion. Of the materials tested, perforated titanium, porous polyimide, and slotted assemblies demonstrated a much greater resistance to clogging than other porous materials.
NASA Astrophysics Data System (ADS)
Carlson, Henry Andrew
1995-01-01
Chapter 1: An algorithm has been developed which extends the scope of spectral methods to include solution of non-canonical channel flows arising from more complicated wall geometries, providing an accurate tool for the investigation of flows over three-dimensional surfaces which move in time. Through a time-dependent, curvilinear transformation a general domain is mapped to one which permits spectral representation of the solution and preserves exact boundary conditions. Static and dynamic tests of one-dimensional flow over a perturbed wall confirm the accuracy of the time-dependent transformation. Results from a higher Reynolds number simulation of separated flow behind a three-dimensional Gaussian protuberance match well with a solution from Mason and Morton (1.27). Chapter 2: Direct simulation of laminar flow over a rising obstacle (an actuator) reveals the presence of vortical structures identical to those found in flow over a stationary obstacle, intensified and stretched by the upward velocity of the boundary. Following deceleration of the actuator (to a stationary position) this amplification leads to one vortex shedding event. Three obstacle shapes are analyzed--one is streamwise symmetric, two skew-symmetric. The symmetric actuator is also raised into a higher Reynolds number flow and at half-speed into the low Reynolds number flow. Results indicate that the time scale of the transient is independent of Reynolds number, depending primarily upon the rising time of the actuator and to a lesser degree its shape. Chapter 3: Direct simulations facilitate an investigation of smart skin control in a turbulent boundary layer (with drag reduction as the goal). The test bed is a minimal flow unit, containing one pair of coherent structures in the near wall region: a high- and a low-speed streak. The controlling device consists of an actuator, Gaussian in shape and approximately twelve wall units in height, which emerges from one of the channel walls. Raising the
A new friction factor correlation for laminar, single-phase flows through rock fractures
NASA Astrophysics Data System (ADS)
Nazridoust, Kambiz; Ahmadi, Goodarz; Smith, Duane H.
2006-09-01
SummarySingle-phase flow through fractured media occurs in various situations, such as transport of dissolved contaminants through geological strata, sequestration of carbon dioxide in depleted gas reservoirs, and in primary oil recovery. In the present study, fluid flows through a rock fracture were simulated. The fracture geometry was obtained from the CT scans of a rock fracture produced by the Brazilian method in a sandstone sample. A post-processing code using a CAD package was developed and used to generate the three-dimensional fracture from the CT scan data. Several sections along the fracture were considered and the Gambit™ code was used to generate unstructured grids for flow simulations. FLUENT™ was used to analyze the flow conditions through the fracture section for different flow rates. Because of the small aperture of the fractures, the gravitational effects could be neglected. It was confirmed that the pressure drop was dominated by the smallest aperture passages of the fracture. The accuracy of parallel plate models for estimating the pressure drops through fractures was studied. It was shown that the parallel plate flow model with the use of an appropriate effective fracture aperture and inclusion of the tortuosity factor could provide reasonable estimates for pressure drops in the fracture. On the basis of the CFD simulation data, a new expression for the friction factor for flows through fractures was developed. The new model predictions were compared with the simulation results and favorable agreement was found. It was shown that when the length of the fracture and the mean and standard deviation of the fracture are known, the pressure loss as a function of the flow rate could be estimated. These findings may prove useful for design of lab experiments, computational studied of flows through real rock fractures, or inclusions in simulators for large-scale flows in highly fractured rocks.
A new friction factor correlation for laminar, single-phase flows through rock fractures
Nazridoust, K.; Ahmadi, G.; Smith, D.H.
2006-09-30
Single-phase flow through fractured media occurs in various situations, such as transport of dissolved contaminants through geological strata, sequestration of carbon dioxide in depleted gas reservoirs, and in primary oil recovery. In the present study, fluid flows through a rock fracture were simulated. The fracture geometry was obtained from the CT scans of a rock fracture produced by the Brazilian method in a sandstone sample. A post-processing code using a CAD package was developed and used to generate the three-dimensional fracture from the CT scan data. Several sections along the fracture were considered and the GambitTM code was used to generate unstructured grids for flow simulations. FLUENTTM was used to analyze the flow conditions through the fracture section for different flow rates. Because of the small aperture of the fractures, the gravitational effects could be neglected. It was confirmed that the pressure drop was dominated by the smallest aperture passages of the fracture. The accuracy of parallel plate models for estimating the pressure drops through fractures was studied. It was shown that the parallel plate flow model with the use of an appropriate effective fracture aperture and inclusion of the tortuosity factor could provide reasonable estimates for pressure drops in the fracture. On the basis of the CFD simulation data, a new expression for the friction factor for flows through fractures was developed. The new model predictions were compared with the simulation results and favorable agreement was found. It was shown that when the length of the fracture and the mean and standard deviation of the fracture are known, the pressure loss as a function of the flow rate could be estimated. These findings may prove useful for design of lab experiments, computational studied of flows through real rock fractures, or inclusions in simulators for large-scale flows in highly fractured rocks.
NASA Astrophysics Data System (ADS)
Tyliszczak, Artur
2014-11-01
The paper presents a novel, efficient and accurate algorithm for laminar and turbulent flow simulations. The spatial discretisation is performed with help of the compact difference schemes (up to 10th order) for collocated and half-staggered grid arrangements. The time integration is performed by a predictor-corrector approach combined with the projection method for pressure-velocity coupling. At this stage a low order discretisation is introduced which considerably decreases the computational costs. It is demonstrated that such approach does not deteriorate the solution accuracy significantly. Following Boersma B.J. [13] the interpolation formulas developed for staggered uniform meshes are used also in the computations with a non-uniform strongly varying nodes distribution. In the proposed formulation of the projection method such interpolation is performed twice. It is shown that it acts implicitly as a high-order low pass filter and therefore the resulting algorithm is very robust. Its accuracy is first demonstrated based on simple 2D and 3D problems: an inviscid vortex advection, a decay of Taylor-Green vortices, a modified lid-driven cavity flow and a dipole-wall interaction. In periodic flow problems (the first two cases) the solution accuracy exhibits the 10th order behaviour, in the latter cases the 3rd and the 4th order is obtained. Robustness of the proposed method in the computations of turbulent flows is demonstrated for two classical cases: a periodic channel with Reτ=395 and Reτ=590 and a round jet with Re=21 000. The solutions are obtained without any turbulence model and also without any explicit techniques aiming to stabilise the solution. The results are in a very good agreement with literature DNS and LES data, both the mean and r.m.s. values are predicted correctly.
Hypersonic Laminar Viscous Flow Past Spinning Cones at Angle of Attack
NASA Technical Reports Server (NTRS)
Agarwal, Ramesh; Rakich, John V.
1982-01-01
Computational results are presented for hypersonic viscous flow past spinning sharp and blunt cones of angle of attack, obtained with a parabolic Navier-Stokes marching code. The code takes into account the asymmetries in the flowfield resulting from spinning motion and computes the asymmetric shock shape, cross-flow and streamwise shear, heat transfer, cross-flow separation, and vortex structure. The Magnus force and moments are also computed. Comparisons are made with other theoretical analyses based on boundary-layer and boundary-region equations, and an anomaly is discovered in the displacement thickness contribution to the Magnus force when compared with boundary-layer results.
Natural gas flow through critical nozzles
NASA Technical Reports Server (NTRS)
Johnson, R. C.
1969-01-01
Empirical method for calculating both the mass flow rate and upstream volume flow rate through critical flow nozzles is determined. Method requires knowledge of the composition of natural gas, and of the upstream pressure and temperature.
An experimental evaluation of slots versus porous strips for laminar-flow applications
NASA Technical Reports Server (NTRS)
Cornelius, Kenneth C.
1987-01-01
Detailed mean velocity and disturbance amplitude measurements were conducted in a Blasius boundary-layer flow with wall suction applied at three downstream locations. The main emphasis was a direct comparison of the growth rate of the instability wave with discrete spanwise slots versus wide porous strips. The results demonstrate that the local effects of suction through slots or very narrow porous strips have a greater beneficial effect on the stability of the boundary-layer flow relative to the suction influence of a wide porous strip. Codes which use continuous suction for the growth rates of the instability waves to determine the suction quantities for a multiple series of slots will be quite conservative in the estimation of the suction quantity. Guidelines were provided for suction-chamber design and flow rates to minimize internal oscillations which propagate into the boundary-layer flow.
Transport in vertical mixed convection flows and natural convection flows in cold water
NASA Astrophysics Data System (ADS)
Carey, V. P.
Computed similarity solutions are presented for thermally-driven natural convection flow adjacent to a vertical isothermal surface in cold pure or saline water. These calculations specifically explore the flow behavior at temperature conditions for which the buoyancy force reverses across the thermal transport region due to the presence of a density extremum within the region. Computed similarity solutions are given for the laminar natural convection flow adjacent to a vertical ice surface melting in saline water. The most recent transport property data and a very accurate equation of state for saline water are used to analyze the transport of momentum, salt and thermal energy in such flows. Interface motion effects are included and the interface conditions are determined from the transport. Time exposure photographs of the flow adjacent to a vertical ice surface melting in 10% saline water are presented for ambient water temperatures between 1 C and 15 C. A perturbation analysis is presented of mixed convection flow over a vertical semi infinite surface with uniform heat flux.
Knopf, Daniel A; Pöschl, Ulrich; Shiraiwa, Manabu
2015-04-01
Flow reactors, denuders, and sampling tubes are essential tools for many applications in analytical and physical chemistry and engineering. We derive a new method for determining radial diffusion effects and the penetration or transmission of gas molecules and aerosol particles through cylindrical tubes under laminar flow conditions using explicit analytical equations. In contrast to the traditional Brown method [Brown, R. L. J. Res. Natl. Bur. Stand. (U. S.) 1978, 83, 1-8] and CKD method (Cooney, D. O.; Kim, S. S.; Davis, E. J. Chem. Eng. Sci. 1974, 29, 1731-1738), the new approximation developed in this study (known as the KPS method) does not require interpolation or numerical techniques. The KPS method agrees well with the CKD method under all experimental conditions and also with the Brown method at low Sherwood numbers. At high Sherwood numbers corresponding to high uptake on the wall, flow entry effects become relevant and are considered in the KPS and CKD methods but not in the Brown method. The practical applicability of the KPS method is demonstrated by analysis of measurement data from experimental studies of rapid OH, intermediate NO3, and slow O3 uptake on various organic substrates. The KPS method also allows determination of the penetration of aerosol particles through a tube, using a single equation to cover both the limiting cases of high and low deposition described by Gormley and Kennedy (Proc. R. Ir. Acad., Sect. A. 1949, 52A, 163-169). We demonstrate that the treatment of gas and particle diffusion converges in the KPS method, thus facilitating prediction of diffusional loss and penetration of gases and particles, analysis of chemical kinetics data, and design of fluid reactors, denuders, and sampling lines. PMID:25744622
NASA Astrophysics Data System (ADS)
Liakos, Anastasios; Malamataris, Nikolaos A.
2014-05-01
The topology and evolution of flow around a surface mounted cubical object in three dimensional channel flow is examined for low to moderate Reynolds numbers. Direct numerical simulations were performed via a home made parallel finite element code. The computational domain has been designed according to actual laboratory experiment conditions. Analysis of the results is performed using the three dimensional theory of separation. Our findings indicate that a tornado-like vortex by the side of the cube is present for all Reynolds numbers for which flow was simulated. A horseshoe vortex upstream from the cube was formed at Reynolds number approximately 1266. Pressure distributions are shown along with three dimensional images of the tornado-like vortex and the horseshoe vortex at selected Reynolds numbers. Finally, and in accordance to previous work, our results indicate that the upper limit for the Reynolds number for which steady state results are physically realizable is roughly 2000.
Sensitivity of aerodynamic forces in laminar and turbulent flow past a square cylinder
NASA Astrophysics Data System (ADS)
Meliga, Philippe; Boujo, Edouard; Pujals, Gregory; Gallaire, François
2014-10-01
We use adjoint-based gradients to analyze the sensitivity of the drag force on a square cylinder. At Re = 40, the flow settles down to a steady state. The quantity of interest in the adjoint formulation is the steady asymptotic value of drag reached after the initial transient, whose sensitivity is computed solving a steady adjoint problem from knowledge of the stable base solution. At Re = 100, the flow develops to the time-periodic, vortex-shedding state. The quantity of interest is rather the time-averaged mean drag, whose sensitivity is computed integrating backwards in time an unsteady adjoint problem from knowledge of the entire history of the vortex-shedding solution. Such theoretical frameworks allow us to identify the sensitive regions without computing the actually controlled states, and provide a relevant and systematic guideline on where in the flow to insert a secondary control cylinder in the attempt to reduce drag, as established from comparisons with dedicated numerical simulations of the two-cylinder system. For the unsteady case at Re = 100, we also compute an approximation to the mean drag sensitivity solving a steady adjoint problem from knowledge of only the mean flow solution, and show the approach to carry valuable information in view of guiding relevant control strategy, besides reducing tremendously the related numerical effort. An extension of this simplified framework to turbulent flow regime is examined revisiting the widely benchmarked flow at Reynolds number Re = 22 000, the theoretical predictions obtained in the frame of unsteady Reynolds-averaged Navier-Stokes modeling being consistent with experimental data from the literature. Application of the various sensitivity frameworks to alternative control objectives such as increasing the lift and reducing the fluctuating drag and lift is also discussed and illustrated with a few selected examples.
Rising of a single Taylor drop in a stagnant liquid—2D laminar flow and axisymmetry limits
NASA Astrophysics Data System (ADS)
Direito, F. J. N.; Campos, J. B. L. M.; Miranda, J. M.
2016-05-01
A numerical (computational fluid dynamics (CFD)) study concerning the rise of individual liquid Taylor drops through vertical columns of stagnant heavier liquids is presented in this paper. CFD simulations were performed in Ansys Fluent, using its implementation of volume of fluid method, assuming the flow to be axisymmetric and laminar. Different physical conditions were tested, corresponding to different combinations of relevant dimensionless parameters and the numerical method was validated through experimental data available in the literature. The viscosity ratio between the lighter and the heavier liquid was within the range 0.01-40 and Eötvös number was between 8 and 30. Morton number was within the interval of 2.32 × 10-6-100. Froude number results were compared to data from a literature correlation. The accordance is acceptable for the ranges studied. Velocity profiles in significant regions are reported (drop nose, drop bottom and continuous phase liquid film). The influence of changing one dimensionless parameter alone was assessed. For small and large viscosity ratios, axisymmetric behavior is not a valid assumption.
NASA Technical Reports Server (NTRS)
Turriziani, R. V.; Lovell, W. A.; Price, J. E.; Quartero, C. B.; Washburn, S. F.
1979-01-01
Two aircraft were evaluated, using a derated TF34-GE-100 turbofan engine one with laminar flow control (LFC) and one without. The mission of the remotely piloted vehicles (RPV) is one of high-altitude loiter at maximum endurance. With the LFC system maximum mission time increased by 6.7 percent, L/D in the loiter phase improved 14.2 percent, and the minimum parasite drag of the wing was reduced by 65 percent resulting in a 37 percent reduction for the total airplane. Except for the minimum parasite drag of the wing, the preceding benefits include the offsetting effects of weight increase, suction power requirements, and drag of the wing-mounted suction pods. In a supplementary study using a scaled-down, rather than derated, version of the engine, on the LFC configuration, a 17.6 percent increase in mission time over the airplane without LFC and an incremental time increase of 10.2 percent over the LFC airplane with derated engine were attained. This improvement was due principally to reductions in both weight and drag of the scaled engine.
Görke, Hanna; Neitola, Kimmo; Hyvärinen, Antti-Pekka; Lihavainen, Heikki; Wölk, Judith; Strey, Reinhard; Brus, David
2014-05-01
Nucleation rates of n-propanol were investigated in the Laminar Flow Diffusion Chamber. Nucleation temperatures between 270 and 300 K and rates between 10(0) and 10(6) cm(-3) s(-1) were achieved. Since earlier measurements of n-butanol and n‑pentanol suggest a dependence of nucleation rates on carrier gas pressure, similar conditions were adjusted for these measurements. The obtained data fit well to results available from literature. A small positive pressure effect was found which strengthen the assumption that this effect is attributed to the carbon chain length of the n-alcohol [D. Brus, A. P. Hyvärinen, J. Wedekind, Y. Viisanen, M. Kulmala, V. Ždímal, J. Smolík, and H. Lihavainen, J. Chem. Phys. 128, 134312 (2008)] and might be less intensive for substances in the homologous series with higher equilibrium vapor pressure. A comparison with the theoretical approach by Wedekind et al. [Phys. Rev. Lett. 101, 12 (2008)] shows that the effect goes in the same direction but that the intensity is much stronger in experiments than in theory. PMID:24811635
Mass-transfer enhancement via chaotic laminar flow within a droplet
NASA Astrophysics Data System (ADS)
Bryden, Michelle D.; Brenner, Howard
1999-01-01
The Stokes flow occurring within a non-neutrally buoyant spherical droplet translating by buoyancy through an immiscible liquid which is undergoing simple shear is shown to be chaotic under many circumstances for which the droplet translates by buoyancy through the entraining fluid. This flow is easily produced, for example, when the droplet rises (or falls) through the annular space of a vertical concentric-cylinder Couette viscometer or through a vertical Poiseuille flow. The parameters studied include: (i) droplet/bulk fluid viscosity ratio; (ii) shear strength/bubble rise velocity ratio; and (iii) the angle between the translational bubble velocity vector and the vorticity vector characterizing the undisturbed shear. Streamlines existing within a droplet that translates perpendicular to this vorticity vector are shown to be non-chaotic for all choices of physical parameters. Other relative orientations frequently contain chaotic trajectories. When solute initially dissolved within the droplet is extracted into the bulk fluid, the resulting overall mass-transfer coefficient (calculated via generalized Taylor dispersion theory) quantifying the extraction rate at asymptotically long times is shown to be significantly higher in the chaotic flow case.
Linear and nonlinear instability in vertical counter-current laminar gas-liquid flows
NASA Astrophysics Data System (ADS)
Schmidt, Patrick; Ó Náraigh, Lennon; Lucquiaud, Mathieu; Valluri, Prashant
2016-04-01
We consider the genesis and dynamics of interfacial instability in vertical gas-liquid flows, using as a model the two-dimensional channel flow of a thin falling film sheared by counter-current gas. The methodology is linear stability theory (Orr-Sommerfeld analysis) together with direct numerical simulation of the two-phase flow in the case of nonlinear disturbances. We investigate the influence of two main flow parameters on the interfacial dynamics, namely the film thickness and pressure drop applied to drive the gas stream. To make contact with existing studies in the literature, the effect of various density contrasts is also examined. Energy budget analyses based on the Orr-Sommerfeld theory reveal various coexisting unstable modes (interfacial, shear, internal) in the case of high density contrasts, which results in mode coalescence and mode competition, but only one dynamically relevant unstable interfacial mode for low density contrast. A study of absolute and convective instability for low density contrast shows that the system is absolutely unstable for all but two narrow regions of the investigated parameter space. Direct numerical simulations of the same system (low density contrast) show that linear theory holds up remarkably well upon the onset of large-amplitude waves as well as the existence of weakly nonlinear waves. For high density contrasts, corresponding more closely to an air-water-type system, linear stability theory is also successful at determining the most-dominant features in the interfacial wave dynamics at early-to-intermediate times. Nevertheless, the short waves selected by the linear theory undergo secondary instability and the wave train is no longer regular but rather exhibits chaotic motion. The same linear stability theory predicts when the direction of travel of the waves changes — from downwards to upwards. We outline the practical implications of this change in terms of loading and flooding. The change in direction of the
NASA Technical Reports Server (NTRS)
Landau, U.
1984-01-01
The finite difference computation method was investigated for solving problems of interaction between a shock wave and a laminar boundary layer, through solution of the complete Navier-Stokes equations. This method provided excellent solutions, was simple to perform and needed a relatively short solution time. A large number of runs for various flow conditions could be carried out from which the interaction characteristics and principal factors that influence interaction could be studied.
Syrjaelae, S.
1996-10-01
Forced convection heat transfer to hydrodynamically and thermally fully developed laminar flow of power-law non-Newtonian fluid in rectangular ducts has been studied for the H1 and T thermal boundary conditions. The solutions for the velocity and temperature fields were obtained numerically using the finite element method with quartic triangular elements. From these solutions, very accurate Nusselt number values were determined. Computations were performed over a range of power-law indices and duct aspect ratios.
Influence of neighboring particles on the drag of a particle suspended in laminar flows
NASA Astrophysics Data System (ADS)
Roig, Adam Vincent
Understanding particle-fluid flows is very important for the areas of sedimentation in river beds, fluidized bed reactors, and other fields of multiphase flow. The effect of one particle on another in a fluid flow is not very well understood nor does a correlation exist to describe the behavior of the drag coefficient between particles. The use of Proteus was validated by comparison to previous studies to the result obtained through simulations in Proteus, including analysis of the wake structure of a single sphere. Two particles were then analyzed for various Reynolds numbers less than 250 but greater than 5 and for the dimensionless gap of L/D ≥ 2, where L is the distance between the two particle centers and D is the diameter of the particles. Two arrangements were used for simulation, with the particles spaced horizontally or vertically within the fluid flow. Both orientations were evaluated for the effects of the dimensionless gap on the drag coefficient. The wake structure at higher Reynolds numbers were also evaluated for effects due to neighboring particles. A correlation was developed for the case of the horizontal particles at a dimensionless gap, L/D ≥ 2 for the range of Reynolds numbers described. The orientation effect is then studied at a fixed distance for offsets of thirty, forty-five and sixty degrees from the horizontal. Results are also presented to evaluate the effect of the diameter of a neighboring particle. The current results are restricted to the case described in the work. Future studies may build on the current work to extend the work to other effects of neighboring particles and multiple particle influence.
A comparison of measured and modeled velocity fields for a laminar flow in a porous medium
NASA Astrophysics Data System (ADS)
Wood, B. D.; Apte, S. V.; Liburdy, J. A.; Ziazi, R. M.; He, X.; Finn, J. R.; Patil, V. A.
2015-11-01
Obtaining highly-resolved velocity data from experimental measurements in porous media is a significant challenge. The goal of this work is to compare the velocity fields measured in a randomly-packed porous medium obtained from particle image velocimetry (PIV) with corresponding fields predicted from direct numerical simulation (DNS). Experimentally, the porous medium was comprised of 15 mm diameter spherical beads made of optical glass placed in a glass flow cell to create the packed bed. A solution of ammonium thiocyanate was refractive-index matched to the glass creating a medium that could be illuminated with a laser sheet without distortion. The bead center locations were quantified using the imaging system so that the geometry of the porous medium was known very accurately. Two-dimensional PIV data were collected and processed to provide high-resolution velocity fields at a single plane within the porous medium. A Cartesian-grid-based fictitious domain approach was adopted for the direct numerical simulation of flow through the same geometry as the experimental measurements and without any adjustable parameters. The uncertainties associated with characterization of the pore geometry, PIV measurements, and DNS predictions were all systematically quantified. Although uncertainties in bead position measurements led to minor discrepancies in the comparison of the velocity fields, the axial and normal velocity deviations exhibited normalized root mean squared deviations (NRMSD) of only 11.32% and 4.74%, respectively. The high fidelity of both the experimental and numerical methods have significant implications for understanding and even for engineering the micro-macro relationship in porous materials. The ability to measure and model sub-pore-scale flow features also has relevance to the development of upscaled models for flow in porous media, where physically reasonable closure models must be developed at the sub-pore scale. These results provide valuable data
Interaction of a laminar flame with its self-generated flow during constant volume combustion
Dunn-Rankin, D.; Sawyer, R.F.
1985-02-01
The formation of cusp shaped or ''tulip'' flames during closed tube flame propagation has been recorded by combustion researchers for nearly sixty years. Flame instability, pressure wave/flame interaction, and large scale circulation in the unburned gas have been suggested as explanations for the ''tulip'' flame phenomenon, but the cause of the ''tulip'' flame has not been conclusively determined. This work uses laser Doppler anemometer measurements of the flow field during flame propagation in a closed tube to describe the combustion generated flow and to support a fluid mechanical explanation for the ''tulip'' flame formation. The flame behaves as a fluid mechanical discontinuity which deflects the velocity of the gas passing through it. As the flame quenches at the side walls of the combustion vessel, the flow deflection generates a vortex in the burned gas. The vortex remains in the proximity of the flame and modifies the unburned gas field such that the flame propagates more quickly near the wall than at the center. The discrepancy in propagation rates leads to the ''tulip'' flame.
NASA Astrophysics Data System (ADS)
Liakos, Anastasios; Malamataris, Nikolaos
2014-11-01
The topology and evolution of flow around a surface mounted cubical object in three dimensional channel flow is examined for low to moderate Reynolds numbers. Direct numerical simulations were performed via a home made parallel finite element code. The computational domain has been designed according to actual laboratory experimental conditions. Analysis of the results is performed using the three dimensional theory of separation. Our findings indicate that a tornado-like vortex by the side of the cube is present for all Reynolds numbers for which flow was simulated. A horse-shoe vortex upstream from the cube was formed at Reynolds number approximately 1266. Pressure distributions are shown along with three dimensional images of the tornado-like vortex and the horseshoe vortex at selected Reynolds numbers. Finally, and in accordance to previous work, our results indicate that the upper limit for the Reynolds number for which steady state results are physically realizable is roughly 2000. Financial support of author NM from the Office of Naval Research Global (ONRG-VSP, N62909-13-1-V016) is acknowledged.
NASA Ames Laminar Flow Supersonic Wind Tunnel (LFSWT) Tests of a 10 deg Cone at Mach 1.6
NASA Technical Reports Server (NTRS)
Wolf, Stephen W. D.; Laub, James A.
1997-01-01
This work is part of the ongoing qualification of the NASA Ames Laminar Flow Supersonic Wind Tunnel (LFSWT) as a low-disturbance (quiet) facility suitable for transition research. A 10 deg cone was tested over a range of unit Reynolds numbers (Re = 2.8 to 3.8 million per foot (9.2 to 12.5 million per meter)) and angles of incidence (O deg to 10 deg) at Mach 1.6. The location of boundary layer transition along the cone was measured primarily from surface temperature distributions, with oil flow interferometry and Schlieren flow visualization providing confirmation measurements. With the LFSWT in its normal quiet operating mode, no transition was detected on the cone in the test core, over the Reynolds number range tested at zero incidence and yaw. Increasing the pressure disturbance levels in the LFSWT test section by a factor of five caused transition onset on the cone within the test core, at zero incidence and yaw. When operating the LFSWT in its normal quiet mode, transition could only be detected in the test core when high angles of incidence (greater than 5 deg) for cones were set. Transition due to elevated pressure disturbances (Tollmien-Schlichting) and surface trips produced a skin temperature rise of order 4 F (2.2 C). Transition due to cross flows on the leeward side of the cone at incidence produced a smaller initial temperature rise of only order 2.5 F (1.4 C), which indicates a slower transition process. We can conclude that these cone tests add further proof that the LFSWT test core is normally low-disturbance (pressure fluctuations greater than 0.1%), as found by associated direct flow quality measurements discussed in this report. Furthermore, in a quiet test environment, the skin temperature rise is sensitive to the type of dominant instability causing transition. The testing of a cone in the LFSWT provides an excellent experiment for the development of advanced transition detection techniques.
NASA Technical Reports Server (NTRS)
Taylor, C. (Editor); Chin, J. H. (Editor); Homsy, G. M. (Editor)
1991-01-01
Consideration is given to the impulse response of a laminar boundary layer and receptivity; numerical transition to turbulence in plane Poiseuille flow; large eddy simulation of turbulent wake flow; a viscous model and loss calculation of a multisplitter cascade; vortex initiation during dynamic stall of an airfoil; a numerical analysis of isothermal flow in a combustion chamber; and compressible flow calculations with a two-equation turbulence model and unstructured grids. Attention is also given to a 2D calculation of a buoyant flow around a burning sphere, a fast multigrid method for 3D turbulent incompressible flows, a streaming flow induced by an oscillating cascade of circular cylinders, an algebraic multigrid scheme for solving the Navier-Stokes equations on unstructured meshes; and nonlinear coupled multigrid solutions to thermal problems employing different nodal grid arrangements and convective transport approximations.
NASA Technical Reports Server (NTRS)
Harris, Charles D.; Brooks, Cuyler W., Jr.
1988-01-01
Modifications to the NASA Langley 8 Foot Transonic Pressure Tunnel in support of the Lamina Flow Control (LFC) Experiment included the installation of a honeymoon and five screens in the settling chamber upstream of the test section 41-long test section liner that extended from the upstream end of the test section contraction region, through the best section, and into the diffuser. The honeycomb and screens were installed as permanent additions to the facility, and the liner was a temporary addition to be removed at the conclusion of the LFC Experiment. These modifications are briefly described.
"Ladder" structure in tonal noise generated by laminar flow around an airfoil.
Chong, Tze Pei; Joseph, Phillip
2012-06-01
The presence of a "ladder" structure in the airfoil tonal noise was discovered in the 1970s, but its mechanism hitherto remains a subject of continual investigation in the research community. Based on the measured noise results and some numerical analysis presented in this letter, the variations of four types of airfoil tonal noise frequencies with the flow velocity were analyzed individually. The ladder structure is proposed to be caused by the acoustic/hydrodynamic frequency lag between the scattering of the boundary layer instability noise and the discrete noise produced by an aeroacoustic feedback loop.
An experimental investigation of pressure drop of aqueous foam in laminar tube flow
NASA Astrophysics Data System (ADS)
Blackwell, B. F.; Sobolik, K. B.
1987-04-01
This report is the first of two detailing pressure-drop and heat-transfer measurements made at the Foam Flow Heat Transfer Loop. The work was motivated by a desire to extend the application of aqueous foam from petroleum drilling to geothermal drilling. Pressure-drop measurements are detailed in this report; a forthcoming report (SAND85-1922) will describe the heat-transfer measurements. The pressure change across a 2.4-m (8-ft) length of the 2.588-cm (1.019-in.) ID test section was measured for liquid volume fractions between 0.05 and 0.35 and average velocities between 0.12 and 0.80 m/s (0.4 and 2.6 ft/s). The resulting pressure-drop/flow-rate data were correlated to a theoretical model for a Bingham plastic. Simple expressions for the dynamic viscosity and the yield stress as a function of liquid volume fraction were estimated.
NASA Astrophysics Data System (ADS)
Tumin, Anatoli
2015-11-01
Zavol'skii and Reutov (1983), Luchini (2008, 2010), Fedorov (2010, 2012, 2014) explored potential role of kinetic fluctuations (KF) in incompressible and calorically perfect gas boundary layer flows. The results indicate that role of KF is comparable with other disturbance sources in flight experiments and in quiet wind tunnels. The analysis is based on the Landau and Lifshitz (1957) concept of fluctuating hydrodynamics representing the dissipative fluxes as an average and fluctuating parts. We are extending analysis of the receptivity problem to the fluctuating dissipative fluxes in chemically reacting nonequilibrium boundary layer flows of binary mixtures. There are new terms in the energy, and the species equations. The species conservation equation includes the dissipative diffusion flux and the species generation due to dissociation. The momentum equation includes fluctuating stress tensor. The energy equation includes fluctuating heat flux, energy flux due to diffusion of the species, and fluctuating dissipative flux due to viscosity. The effects are compared for the cases stemming from constraints of the HTV project (Klentzman and Tumin, AIAA Paper 2013-2882). Supported by AFOSR.
Hooper, G J; Rothwell, A G; Frampton, C; Wyatt, M C
2011-01-01
We have investigated whether the use of laminar-flow theatres and space suits reduced the rate of revision for early deep infection after total hip (THR) and knee (TKR) replacement by reviewing the results of the New Zealand Joint Registry at ten years. Of the 51 485 primary THRs and 36 826 primary TKRs analysed, laminar-flow theatres were used in 35.5% and space suits in 23.5%. For THR there was a significant increase in early infection in those procedures performed with the use of a space suit compared with those without (p < 0.0001), in those carried out in a laminar-flow theatre compared with a conventional theatre (p < 0.003) and in those undertaken in a laminar-flow theatre with a space suit (p < 0.001) when compared with conventional theatres without such a suit. The results were similar for TKR with the use of a space suit (p < 0.001), in laminar-flow theatres (p < 0.019) and when space suits were used in those theatres (p < 0.001). These findings were independent of age, disease and operating time and were unchanged when the surgeons and hospital were analysed individually. The rate of revision for early deep infection has not been reduced by using laminar flow and space suits. Our results question the rationale for their increasing use in routine joint replacement, where the added cost to the health system seems to be unjustified.
Drag phenomena within a torque converter driven automotive transmission - laminar flow approach
NASA Astrophysics Data System (ADS)
Alexa, O.; Marinescu, M.; Olaru, Gh; Costache, D.; Ilie, C. O.; Vinturis, V.
2015-11-01
When discussing a torque converter driven, automotive transmission with respect to the vehicle's coasting mode, automotive engineers have to take into account the slip between the converter's propeller and turbine. If the turbine isn't locked to the propellers during coasting process, drag phenomena within the converter's fluid occur and they have to be properly assessed when computing the coasting process dynamics. The best way to make the needed evaluation is to have a separate torque converter and test it on a test bench, if the data provided by the manufacturer, in this respect, weren't available. But there are several issues that could baffle this action. Among them, one could find the lack of information from the manufacturer, missing (bankrupted) manufacturer, classified information, old (out of date) products and so on. An even more challenging situation consists in dealing with a military special vehicle. Actually, the vehicle that would be subjected to the following topic is a military tracked, heavy vehicle (MBT) with a planetary driveline, driven by its engine via a hydraulic torque converter. In the attempt to assess its’ coasting dynamic performances, we faced the problem of the reverse rotation of the torque converter that strongly influences the general drag of the vehicle's motion. Hence, this paper tries to provide a method to determine the transmission overall drag considering the torque converter as being its main contributor. The method is based on the experimental research our team has performed in the last several months. Using high-quality software and adjacent mathematics while assuming a certain sort of flow type within the torque converter, we aimed at determining the parameter of interest of the flow. The method can be successfully used for all type of hydrodynamic components of the transmission under the condition of developing the necessary experimental research. As far as the test were concerned, they were the typical ones designed
Seshadri, K; Lu, T; Herbinet, O; Humer, S; Niemann, U; Pitz, W J; Law, C K
2008-01-09
Methyl decanoate is a large methyl ester that can be used as a surrogate for biodiesel. In this experimental and computational study, the combustion of methyl decanoate is investigated in nonpremixed, nonuniform flows. Experiments are performed employing the counterflow configuration with a fuel stream made up of vaporized methyl decanoate and nitrogen, and an oxidizer stream of air. The mass fraction of fuel in the fuel stream is measured as a function of the strain rate at extinction, and critical conditions of ignition are measured in terms of the temperature of the oxidizer stream as a function of the strain rate. It is not possible to use a fully detailed mechanism for methyl decanoate to simulate the counterflow flames because the number of species and reactions is too large to employ with current flame codes and computer resources. Therefore a skeletal mechanism was deduced from a detailed mechanism of 8555 elementary reactions and 3036 species using 'directed relation graph' method. This skeletal mechanism has only 713 elementary reactions and 125 species. Critical conditions of ignition were calculated using this skeletal mechanism and are found to agree well with experimental data. The predicted strain rate at extinction is found to be lower than the measurements. In general, the methyl decanoate mechanism provides a realistic kinetic tool for simulation of biodiesel fuels.
NASA Astrophysics Data System (ADS)
Chen, Wen Ruey
2016-10-01
This paper studies the steady laminar natural convection of micropolar fluids in the complex annuli between the inner sphere and outer vertical cylinder to present a numerical analysis of the flow and heat transfer characteristics with buoyancy effects. Computations were carried out systematically by the several different parameters of geometric ratio, micropolar material parameter and Rayleigh number to determine the average Nusselt number and the skin friction coefficient on the flow and the thermal fields.
NASA Technical Reports Server (NTRS)
Eckert, E R; Livingood, John N B
1953-01-01
The solution of heat-transfer problems has become vital for many aeronautical applications. The shapes of objects to be cooled can often be approximated by cylinders of various cross sections with flow normal to the axis as, for instance heat transfer on gas-turbine blades and on air foils heated for deicing purposes. A laminar region always exists near the stagnation point of such objects. A method previously presented by E. R. G. Eckert permits the calculation of local heat transfer around the periphery of cylinders of arbitrary cross section in the laminar region for flow of a fluid with constant property values with an accuracy sufficient for engineering purposes. The method is based on exact solutions of the boundary-layer equations for incompressible wedge-type flow and on the postulate that at any point on the cylinder the boundary-layer growth is the same as that on a wedge with comparable flow conditions. This method is extended herein to take into account the influence of large temperature differences between the cylinder wall and the flow as well as the influence of transpiration cooling when the same medium as the outside flow is used as coolant.
Kuang, C.; Chen, M.; McMurry, P. H.; Wang, J.
2011-10-01
This paper describes simple modifications to thermally diffusive laminar flow ultrafine condensation particle counters (UCPCs) that allow detection of {approx}1 nm condensation nuclei with much higher efficiencies than have been previously reported. These nondestructive modifications were applied to a commercial butanol based UCPC (TSI 3025A) and to a diethylene glycol-based UCPC (UMN DEG-UCPC). Size and charge dependent detection efficiencies using the modified UCPCs (BNL 3025A and BNL DEGUCPC) were measured with high resolution mobility classified aerosols composed of NaCl, W, molecular ion standards of tetraalkyl ammonium bromide, and neutralizer-generated ions. With negatively charged NaCl aerosol, the BNL 3025A and BNL DEGUCPC achieved detection efficiencies of 37% (90x increase over TSI 3025A) at 1.68 nm mobility diameter (1.39 nm geometric diameter) and 23% (8x increase over UMN DEG-UCPC) at 1.19 nm mobility diameter (0.89 nm geometric diameter), respectively. Operating conditions for both UCPCs were identified that allowed negatively charged NaCl and W particles, but not negative ions of exactly the same mobility size, to be efficiently detected. This serendipitous material dependence, which is not fundamentally understood, suggests that vapor condensation might sometimes allow for the discrimination between air 'ions' and charged 'particles.' As a detector in a scanning mobility particle spectrometer (SMPS), a UCPC with this strong material dependence would allow for more accurate measurements of sub-2 nm aerosol size distributions due to the reduced interference from neutralizer-generated ions and atmospheric ions, and provide increased sensitivity for the determination of nucleation rates and initial particle growth rates.
NASA Astrophysics Data System (ADS)
Heris, Saeed Zeinali; Farzin, Farshad; Sardarabadi, Hamideh
2015-04-01
The aim of the present study was to investigate heat transfer characteristics of turbine oil-based nanofluids inside a circular tube in laminar flow under a constant heat flux boundary condition. Oil-based nanofluids were prepared dispersing less than 1 % volume concentrations of CuO, , and nanoparticles in turbine oil using a two-step method. The primary objective was to evaluate and compare the effect of different volume concentrations and nanoparticle types on convective heat transfer. An experimental apparatus was designed and constructed to measure the heat transfer coefficient and the Nusselt number of the samples. Due to the high Prandtl number of the nanofluids (about 350), it was concluded that the nanofluids were in the developing region. Experimental results clearly indicated that all of the added nanoparticles improved both the heat transfer coefficient and the Nusselt number of the turbine oil. A nanofluid is more capable than a single-phase fluid insofar as removing heat from high heat flux surfaces. The highest values of the Nusselt number and the Nusselt number ratio (the ratio of the nanofluid Nusselt number to that of the pure turbine oil) belonged to the CuO/turbine oil nanofluid. Among the sample nanofluids, the highest Nusselt number ratios belonged to CuO/turbine oil (0.50 %), /turbine oil (0.50 %), /turbine oil (0.50 %), and a Reynolds number of about 800 which were 1.38, 1.31, and 1.15, respectively. Moreover, so as to determine the efficiency of a nanofluid, the ratio of the pressure drop and Nusselt number of three nanofluid samples were compared with that of the base fluid. A third parameter (performance index) was evaluated to determine the possibility of practically using such for rating nanofluids. All the obtained performance indexes for CuO/turbine oil and /turbine oil were more than one, meaning the employment of such nanofluids leads to a higher quality turbine oil.
Nehmé, Hala; Nehmé, Reine; Lafite, Pierre; Routier, Sylvain; Morin, Philippe
2013-11-01
A capillary electrophoresis (CE)-based enzyme assay method has been developed to screen protein kinase inhibitors. Four human kinases GSK3β, DYRK1A, CDK5/p25 and CDK1/cyclin B were chosen to test this novel method. These enzymes have been identified as very promising targets to develop treatments against cancer and neurodegenerative diseases. The efficiency of drugs against these relevant biological targets has never been carried out by CE. For this proposal, the capillary was used as a nanoreactor in which four reactants (the enzyme, its two substrates and its potential inhibitor) were successively injected, mixed by using transverse diffusion of laminar flow profiles and incubated. The adenosine 5'-diphosphate (ADP) formed during the enzymatic reaction was detected by UV and quantified. The efficiency of the developed CE method was validated by determining the IC50 values of a wide variety of inhibitors covering a large domain of affinity toward kinases and containing representative and chemically divergent skeletons. Excellent agreement was found between the results obtained by CE and those reported in the literature when using conventional radiometric enzyme assays. Moreover, CE was successfully used to determine the inhibitory effect of several potential inhibitors that was not yet assessed by conventional methods and is crucial for structure activity relation studies. This novel CE method is simple, rapid, very economic (few tens of nanoliters per IC50) and eco-friendly since no radioactivity was required. It could be extended to high-throughput screening of kinase inhibitors, which is of great interest for biomedical and pharmaceutical research fields. PMID:24075461
Mixed convection laminar flow and heat transfer of liquids in horizontal internally finned tubes
Shome, B.
1998-01-01
Energy and material savings, as well as economic incentives, have led to concentrated efforts over the past several decades in the field of heat transfer enhancement to produce more efficient and compact heat exchangers. Internally finned tubes are widely used for heat transfer enhancement, particularly in chemical process and petroleum industries. A finned tube heat exchanger with optimum geometry could offer 35--40% increase in heat duty for equal pumping power and size over a smooth tube heat exchanger or a comparable decrease in the heat exchanger size for a given heat duty. Developing mixed convection flow in internally finned tubes with variable viscosity was numerically investigated for a fin geometry range of 8 {le} N {le} 24, 0.1 {le} H {le} 0.3 and an operating condition range of 50 {le} Pr{sub in} {le} 1,250, 0 {le} Ra{sub in} {le} 10{sup 7}, and 0 {le} q{sub w}d/k{sub in} {le} 2,000. The numerical model was validated by comparison with existing numerical and experimental data. Internal finning was found to produce a complex two-cell, buoyancy-induced vortex structure. The results show that coring (retarded velocity in the interfin region) leads to poor heat transfer performance of tubes with large numbers of fins or with tall fins. The overall results indicated that large enhancement in the heat transfer can be obtained in the entrance region. Furthermore, variable viscosity effects are seen to have a pronounced effect on the friction factor and Nusselt number predictions.
NASA Technical Reports Server (NTRS)
Campbell, R. L.
1982-01-01
Tests were conducted in the Langley High-Speed 7- by 10-Foot Tunnel using a 1/10-scale model of an executive jet to examine the effects of the nacelles on the wing pressures and model longitudinal aerodynamic characteristics. For the present investigation, each wing panel was modified with a simulated, partial-chord, laminar-flow-control glove. Horizontal-tail effects were also briefly examined. The tests covered a range of Mach numbers from 0.40 to 0.82 and lift coefficients from 0.20 to 0.55. Oil-flow photographs of the wing at selected conditions are included.
NASA Technical Reports Server (NTRS)
Anderson, E. C.; Moss, J. N.
1975-01-01
The viscous shock layer equations applicable to hypersonic laminar, transitional, and turbulent flows of a perfect gas over two-dimensional plane or axially symmetric blunt bodies are presented. The equations are solved by means of an implicit finite difference scheme, and the results are compared with a turbulent boundary layer analysis. The agreement between the two solution procedures is satisfactory for the region of flow where streamline swallowing effects are negligible. For the downstream regions, where streamline swallowing effects are present, the expected differences in the two solution procedures are evident.
NASA Technical Reports Server (NTRS)
Iyer, Venkit
1993-01-01
The theory, formulation, and solution of three-dimensional, compressible attached laminar flows, applied to swept wings in subsonic or supersonic flow are discussed. Several new features and modifications to an earlier general procedure described in NASA CR 4269, Jan. 1990 are incorporated. Details of interfacing the boundary-layer computation with solution of the inviscid Euler equations are discussed. A description of the computer program, complete with user's manual and example cases, is also included. Comparison of solutions with Navier-Stokes computations with or without boundary-layer suction is given. Output of solution profiles and derivatives required in boundary-layer stability analysis is provided.
NASA Technical Reports Server (NTRS)
Yeo, S. H.; Dancey, C. L.
1991-01-01
Measurements of the axial and radial components of velocity on the air side of stagnation in an axisymmetric H2/Air laminar counter-flow diffusion flame are reported. Results include the two-dimensional velocity field and computed velocity gradients (strain rates) along the stagnation streamline at two 'characteristic' strain rates, below the extinction limit. The measurements generally verify the modeling assumptions appropriate to the model of Kee et al. (1988). The 'traditional' potential flow model is not consistent with the measured results.
NASA Technical Reports Server (NTRS)
Li, Fei; Choudhari, Meelan M.; Chang, Chau-Lyan; Streett, Craig L.; Carpenter, Mark H.
2011-01-01
A combination of parabolized stability equations and secondary instability theory has been applied to a low-speed swept airfoil model with a chord Reynolds number of 7.15 million, with the goals of (i) evaluating this methodology in the context of transition prediction for a known configuration for which roughness based crossflow transition control has been demonstrated under flight conditions and (ii) of analyzing the mechanism of transition delay via the introduction of discrete roughness elements (DRE). Roughness based transition control involves controlled seeding of suitable, subdominant crossflow modes, so as to weaken the growth of naturally occurring, linearly more unstable crossflow modes. Therefore, a synthesis of receptivity, linear and nonlinear growth of stationary crossflow disturbances, and the ensuing development of high frequency secondary instabilities is desirable to understand the experimentally observed transition behavior. With further validation, such higher fidelity prediction methodology could be utilized to assess the potential for crossflow transition control at even higher Reynolds numbers, where experimental data is currently unavailable.
NASA Astrophysics Data System (ADS)
Falconi, C. J.; Lehrenfeld, C.; Marschall, H.; Meyer, C.; Abiev, R.; Bothe, D.; Reusken, A.; Schlüter, M.; Wörner, M.
2016-01-01
The vertically upward Taylor flow in a small square channel (side length 2 mm) is one of the guiding measures within the priority program "Transport Processes at Fluidic Interfaces" (SPP 1506) of the German Research Foundation (DFG). This paper presents the results of coordinated experiments and three-dimensional numerical simulations (with three different academic computer codes) for typical local flow parameters (bubble shape, thickness of the liquid film, and velocity profiles) in different cutting planes (lateral and diagonal) for a specific co-current Taylor flow. For most quantities, the differences between the three simulation results and also between the numerical and experimental results are below a few percent. The experimental and computational results consistently show interesting three-dimensional flow effects in the rear part of the liquid film. There, a local back flow of liquid occurs in the fixed frame of reference which leads to a temporary reversal of the direction of the wall shear stress during the passage of a Taylor bubble. Notably, the axial positions of the region with local backflow and those of the minimum vertical velocity differ in the lateral and the diagonal liquid films. By a thorough analysis of the fully resolved simulation results, this previously unknown phenomenon is explained in detail and, moreover, approximate criteria for its occurrence in practical applications are given. It is the different magnitude of the velocity in the lateral film and in the corner region which leads to azimuthal pressure differences in the lateral and diagonal liquid films and causes a slight deviation of the bubble from the rotational symmetry. This deviation is opposite in the front and rear parts of the bubble and has the mentioned significant effects on the local flow field in the rear part of the liquid film.
NASA Technical Reports Server (NTRS)
Kumar, A.; Graves, R. A., Jr.
1980-01-01
A user's guide is provided for a computer code which calculates the laminar and turbulent hypersonic flows about blunt axisymmetric bodies, such as spherically blunted cones, hyperboloids, etc., at zero and small angles of attack. The code is written in STAR FORTRAN language for the CDC-STAR-100 computer. Time-dependent, viscous-shock-layer-type equations are used to describe the flow field. These equations are solved by an explicit, two-step, time asymptotic, finite-difference method. For the turbulent flow, a two-layer, eddy-viscosity model is used. The code provides complete flow-field properties including shock location, surface pressure distribution, surface heating rates, and skin-friction coefficients. This report contains descriptions of the input and output, the listing of the program, and a sample flow-field solution.
NASA Technical Reports Server (NTRS)
Brown, R. D.; Jakubowski, A. K.
1974-01-01
Heat-transfer and pressure distributions were measured for laminar separated flows downstream of rearward-facing steps with and without mass suction. The flow conditions were such that the boundary-layer thickness was comparable to or larger than the step height. For both suction and no-suction cases, an increase in the step height resulted in a sharp decrease in the initial heat-transfer rates behind the step. Downstream, however, the heat transfer gradually recovered back to less than or near attached-flow values. Mass suction from the step base area increased the local heat-transfer rates; however, this effect was relatively weak for the laminar flows considered. Even removal of the entire approaching boundary layer raised the post-step heat-transfer rates only about 10 percent above the flatplate values. Post-step pressure distributions were found to depend on the entrainment conditions at separation. In the case of the solid-faced step, a sharp pressure drop behind the step was followed by a very short plateau and relatively fast recompression. For the slotted-step connected to a large plenum but without suction, the pressure drop at the base was much smaller and the downstream recompression more gradual than that for solid-faced step.
Supersonic laminar flow control
NASA Technical Reports Server (NTRS)
Bushnell, D. M.
1992-01-01
A development status evaluation is presented for the theoretical understanding and design conceptualization of boundary layer control (BLC) systems applicable to supersonic transports, such as the currently envisioned NASA High Speed Civil Transport. By reducing fuel burned, supersonic BLC techniques could expand ranges to Pacific-crossing scales, while lowering sonic boom effects and upper-atmosphere pollution and even reducing skin friction temperature. The critical consideration for supersonic BLC is the presence of wave effects.
NASA Technical Reports Server (NTRS)
Hamilton, H. Harris, II; Millman, Daniel R.; Greendyke, Robert B.
1992-01-01
A computer code was developed that uses an implicit finite-difference technique to solve nonsimilar, axisymmetric boundary layer equations for both laminar and turbulent flow. The code can treat ideal gases, air in chemical equilibrium, and carbon tetrafluoride (CF4), which is a useful gas for hypersonic blunt-body simulations. This is the only known boundary layer code that can treat CF4. Comparisons with experimental data have demonstrated that accurate solutions are obtained. The method should prove useful as an analysis tool for comparing calculations with wind tunnel experiments and for making calculations about flight vehicles where equilibrium air chemistry assumptions are valid.
NASA Technical Reports Server (NTRS)
Klopfer, Goetz H.
1993-01-01
The work performed during the past year on this cooperative agreement covered two major areas and two lesser ones. The two major items included further development and validation of the Compressible Navier-Stokes Finite Volume (CNSFV) code and providing computational support for the Laminar Flow Supersonic Wind Tunnel (LFSWT). The two lesser items involve a Navier-Stokes simulation of an oscillating control surface at transonic speeds and improving the basic algorithm used in the CNSFV code for faster convergence rates and more robustness. The work done in all four areas is in support of the High Speed Research Program at NASA Ames Research Center.
NASA Technical Reports Server (NTRS)
Dress, David A.
1988-01-01
Low-speed wind tunnel drag force measurements were taken on a laminar flow body of revolution free of support interference. This body was tested at zero incidence in the NASA Langley 13 inch Magnetic Suspension and Balance System (MSBS). The primary objective of these tests was to substantiate the drag force measuring capabilities of the 13 inch MSBS. A secondary objective was to obtain support interference free drag measurements on an axisymmetric body of interest. Both objectives were met. The drag force calibrations and wind-on repeatability data provide a means of assessing the drag force measuring capabilities of the 13 inch MSBS. The measured drag coefficients for this body are of interest to researchers actively involved in designing minimum drag fuselage shapes. Additional investigations included: the effects of fixing transition; the effects of fins installed in the tail; surface flow visualizations using both liquid crystals and oil flow; and base pressure measurements using a one-channel telemetry system. Two drag prediction codes were used to assess their usefulness in estimating overall body drag. These theoretical results did not compare well with the measured values because of the following: incorrect or non-existent modeling of a laminar separation bubble on the body and incorrect of non-existent estimates of base pressure drag.
NASA Technical Reports Server (NTRS)
Bobbitt, Percy J.; Ferris, James C.; Harvey, William D.; Goradia, Suresh H.
1992-01-01
A description is given of the development of, and results from, the hybrid laminar flow control (HLFC) experiment conducted in the NASA LaRC 8 ft Transonic Pressure Tunnel on a 7 ft chord, 23 deg swept model. The methods/codes used to obtain the contours of the HLFC model surface and to define the suction requirements are outlined followed by a discussion of the model construction, suction system, instrumentation, and some example results from the wind tunnel tests. Included in the latter are the effects of Mach number, suction level, and the extent of suction. An assessment is also given of the effect of the wind tunnel environment on the suction requirements. The data show that, at or near the design Mach number, large extents of laminar flow can be achieved with suction mass flows over the first 25 percent, or less, of the chord. Top surface drag coefficients with suction extending from the near leading edge to 20 percent of the chord were approximately 40 percent lower than those obtained with no suction. The results indicate that HLFC can be designed for transonic speeds with lift and drag coefficients approaching those of LFC designs but with much smaller extents and levels of suction.
NASA Technical Reports Server (NTRS)
Miner, E. W.; Anderson, E. C.; Lewis, C. H.
1971-01-01
A computer program is described in detail for laminar, transitional, and/or turbulent boundary-layer flows of non-reacting (perfect gas) and reacting gas mixtures in chemical equilibrium. An implicit finite difference scheme was developed for both two dimensional and axisymmetric flows over bodies, and in rocket nozzles and hypervelocity wind tunnel nozzles. The program, program subroutines, variables, and input and output data are described. Also included is the output from a sample calculation of fully developed turbulent, perfect gas flow over a flat plate. Input data coding forms and a FORTRAN source listing of the program are included. A method is discussed for obtaining thermodynamic and transport property data which are required to perform boundary-layer calculations for reacting gases in chemical equilibrium.
Yamashita, Kenichi; Miyazaki, Masaya; Yamaguchi, Yoshiko; Nakamura, Hiroyuki; Maeda, Hideaki
2008-07-01
This paper presents the capability of changing the activation energy of chemical reactions using microchannel laminar flow. Kinetic parameters of the duplex-coil equilibrium of DNA oligomers were studied by measuring the hysteresis between denaturation-renaturation curves using an in-house temperature-controllable microchannel-type flow cell. For this study, DNA oligomers were used because they allow physicochemical analysis and theoretical discussion. Kinetic parameters of the duplex-coil equilibrium of DNA oligomers were obtained by measuring the denaturation-renaturation hysteresis curves. Both cooling and heating curves were shifted to the high-temperature side at higher flow rates. The renaturation reaction was influenced by a slower flow rate. The effect of the slower flow rate was more pronounced for renaturation than denaturation reactions. The magnitude of the activation energies of association decreased as the flow rate increased, but that of the activation energies of the dissociation increased as the flow rate increased. Overall, these results suggest that chemical reactions' change of activation energy depends on the flow rate and the DNA molecular size. PMID:18584094
Eiamsa-ard, Smith; Seemawute, Panida; Wongcharee, Khwanchit
2010-09-15
Effects of peripherally-cut twisted tape insert on heat transfer, friction loss and thermal performance factor characteristics in a round tube were investigated. Nine different peripherally-cut twisted tapes with constant twist ratio (y/W = 3.0) and different three tape depth ratios (DR = d/W = 0.11, 0.22 and 0.33), each with three different tape width ratios (WR = w/W = 0.11, 0.22 and 0.33) were tested. Besides, one typical twisted tape was also tested for comparison. The measurement of heat transfer rate was conducted under uniform heat flux condition while that of friction factor was performed under isothermal condition. Tests were performed with Reynolds number in a range from 1000 to 20,000, using water as a working fluid. The experimental results revealed that both heat transfer rate and friction factor in the tube equipped with the peripherally-cut twisted tapes were significantly higher than those in the tube fitted with the typical twisted tape and plain tube, especially in the laminar flow regime. The higher turbulence intensity of fluid in the vicinity of the tube wall generated by the peripherally-cut twisted tape compared to that induced by the typical twisted tape is referred as the main reason for achieved results. The obtained results also demonstrated that as the depth ratio increased and width ratio decreased, the heat transfer enhancement increased. Over the range investigated, the peripherally-cut twisted tape enhanced heat transfer rates in term of Nusselt numbers up to 2.6 times (turbulent regime) and 12.8 times (laminar regime) of that in the plain tube. These corresponded to the maximum performance factors of 1.29 (turbulent regime) and 4.88 (laminar regime). (author)
NASA Astrophysics Data System (ADS)
Kozhumal Shijin, Puthiyaparambath; Raghavan, Vasudevan; Babu, Viswanathan
2016-07-01
Flame stabilisation in a combustor having vortices generated by flame holding devices constitutes an interesting fundamental problem. The presence of vortices in many practical combustors ranging from industrial burners to high speed propulsion systems induces vortex-flame interactions and complex stabilisation conditions. The scenario becomes more complex if the flame sustains after separating itself from the flame holder. In a recent study [P.K. Shijin, S.S. Sundaram, V. Raghavan, and V. Babu, Numerical investigation of laminar cross-flow non-premixed flames in the presence of a bluff-body, Combust. Theory Model. 18, 2014, pp. 692-710], the authors reported details of the regimes of flame stabilisation of non-premixed laminar flames established in a cross-flow combustor in the presence of a square cylinder. In that, the separated flame has been shown to be three dimensional and highly unsteady. Such separated flames are investigated further in the present study. Flame-vortex interactions in separated methane-air cross flow flames established behind three bluff bodies, namely a square cylinder, an isosceles triangular cylinder and a half V-gutter, have been analysed in detail. The mixing process in the reactive flow has been explained using streamlines of species velocities of CH4 and O2. The time histories of z-vorticity, net heat release rate and temperature are analysed to reveal the close relationship between z-vorticity and net heat release rate spectra. Two distinct fluctuating layers are visible in the proper orthogonal decomposition and discrete Fourier transform of OH mass fraction data. The upper fluctuating layer observed in the OH field correlates well with that of temperature. A detailed investigation of the characteristics of OH transport has also been carried out to show the interactions between factors affecting fluid dynamics and chemical kinetics that cause multiple fluctuating layers in the OH.
Identifying natural flow regimes using fish communities
NASA Astrophysics Data System (ADS)
Chang, Fi-John; Tsai, Wen-Ping; Wu, Tzu-Ching; Chen, Hung-kwai; Herricks, Edwin E.
2011-10-01
SummaryModern water resources management has adopted natural flow regimes as reasonable targets for river restoration and conservation. The characterization of a natural flow regime begins with the development of hydrologic statistics from flow records. However, little guidance exists for defining the period of record needed for regime determination. In Taiwan, the Taiwan Eco-hydrological Indicator System (TEIS), a group of hydrologic statistics selected for fisheries relevance, is being used to evaluate ecological flows. The TEIS consists of a group of hydrologic statistics selected to characterize the relationships between flow and the life history of indigenous species. Using the TEIS and biosurvey data for Taiwan, this paper identifies the length of hydrologic record sufficient for natural flow regime characterization. To define the ecological hydrology of fish communities, this study connected hydrologic statistics to fish communities by using methods to define antecedent conditions that influence existing community composition. A moving average method was applied to TEIS statistics to reflect the effects of antecedent flow condition and a point-biserial correlation method was used to relate fisheries collections with TEIS statistics. The resulting fish species-TEIS (FISH-TEIS) hydrologic statistics matrix takes full advantage of historical flows and fisheries data. The analysis indicates that, in the watersheds analyzed, averaging TEIS statistics for the present year and 3 years prior to the sampling date, termed MA(4), is sufficient to develop a natural flow regime. This result suggests that flow regimes based on hydrologic statistics for the period of record can be replaced by regimes developed for sampled fish communities.
Punjabi, Sangeeta B.; Sahasrabudhe, S. N.; Das, A. K.; Joshi, N. K.; Mangalvedekar, H. A.; Kothari, D. C.
2014-01-15
This paper provides 2D comparative study of results obtained using laminar and turbulent flow model for RF (radio frequency) Inductively Coupled Plasma (ICP) torch. The study was done for the RF-ICP torch operating at 50 kW DC power and 3 MHz frequency located at BARC. The numerical modeling for this RF-ICP torch is done using ANSYS software with the developed User Defined Function. A comparative study is done between laminar and turbulent flow model to investigate how temperature and flow fields change when using different operating conditions such as (a) swirl and no swirl velocity for sheath gas flow rate, (b) variation in sheath gas flow rate, and (c) variation in plasma gas flow rate. These studies will be useful for different material processing applications.
NASA Astrophysics Data System (ADS)
Varol, Yasin; Öztop, Hakan F.; Özgen, Filiz; Koca, Ahmet
2012-01-01
Natural convection heat transfer in an inclined fin attached square enclosure is studied both experimentally and numerically. Bottom wall of enclosure has higher temperature than that of top wall while vertical walls are adiabatic. Inclined fin has also adiabatic boundary conditions. Numerical solutions have been done by writing a computer code in Fortran platform and results are compared with Fluent commercial code and experimental method. Governing parameters are Rayleigh numbers (8.105 ≤ Ra ≤ 4 × 106) and inclination angle (30° ≤ and ≤ 120°). The temperature measurements are done by using thermocouples distributed uniformly at the wall of the enclosure. Remarkably good agreement is obtained between the predicted results and experimental data. A correlation is also developed including all effective parameters on heat transfer and fluid flow. It was observed that heat transfer can be controlled by attaching an inclined fin onto wall.
Measurements of natural ice nuclei with a continuous flow diffusion chamber
NASA Technical Reports Server (NTRS)
Rogers, D. C.
1983-01-01
A description is given of a continuous flow diffusion chamber technique for measuring the atmospheric concentrations of natural C-F nuclei. It is noted that the same device can also measure deposition nuclei; these two modes can thus be separated and compared. The laminar flow characteristics allow the temperature and supersaturation to be calculated with a high degree of precision and confidence. The method avoids the problems of a supporting substrate and of concentrating the sample into a small volume (as for membrane filters). The present measurements of natural ice nucleus concentrations at +1 percent water supersaturation are found to be comparable to research aircraft measurements of ice crystal concentrations in winter cap clouds over Elk Mountain, Wyoming (Vali et al., 1982).
NASA Astrophysics Data System (ADS)
Seong, Sehyun; Kim, Sug-Whan; Kim, Sangmin; Ryu, Dongok; Kang, Ho Gyun
2014-10-01
We present the apparent optical performance variation of an infrared sensor caused by laminar flow field surrounding a highly supersonic projectile with cone shape head. An optical ray tracing model was constructed and numerical simulations of the aero-optical effects were performed by computational fluid dynamics (CFD) analysis and isodensity surface based ray tracing computation. To maximize modeling and computation efficiency, the number of sampling isodensity layers was reduced to less than 5 for improved discretization of the inhomogeneous gradient index (GRIN) media. Using this method, the simulation results show that the BSE is smaller than about 2.8 arcsec when the projectile flies at 25, 35, 50 km in altitude, Mach 4, 6 in speed, and 0°, 10° in angle of attack. The technical details and implications of the optical ray tracing model are presented together with the simulation results.
NASA Technical Reports Server (NTRS)
Harvey, W. D.
1975-01-01
Results are presented of a coordinated experimental and theoretical study of a sound shield concept which aims to provide a means of noise reduction in the test section of supersonic wind tunnels at high Reynolds numbers. The model used consists of a planar array of circular rods aligned with the flow, with adjustable gaps between them for boundary layer removal by suction, i.e., laminar flow control. One of the basic requirements of the present sound shield concept is to achieve sonic cross flow through the gaps in order to prevent lee-side flow disturbances from penetrating back into the shielded region. Tests were conducted at Mach 6 over a local unit Reynolds number range from about 1.2 x 10 to the 6th power to 13.5 x 10 to the 6th power per foot. Measurements of heat transfer, static pressure, and sound levels were made to establish the transition characteristics of the boundary layer on the rod array and the sound shielding effectiveness.