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.
Natural laminar flow application to transport aircraft
NASA Technical Reports Server (NTRS)
Gratzer, Louis B.
1990-01-01
A major goal of NASA during the last 15 years has been the development of laminar flow technology for aircraft drag reduction. Of equal importance is achieving a state of readiness that will allow the successful application of this technology by industry to large, long-range aircraft. Recent progress in achieving extensive laminar flow with limited suction on the Boeing 757 has raised the prospects from practical application of the hybrid laminar flow control (HLFC) concept to subsonic aircraft. Also, better understanding of phenomena affecting laminar flow stability and response to disturbances has encouraged consideration of natural laminar flow (NLF), obtained without suction or active mechanical means, for application to transport aircraft larger than previously thought feasible. These ideas have inspired the current NASA/ASEE project with goals as follows: explore the feasibility of extensive NLF for aircraft at high Reynolds number under realistic flight conditions; determine the potential applications of NLF technology and the conditions under which they may be achieved; and identify existing aircraft that could be adapted to carry out flight experiments to validate NLF technology application. To achieve these objectives, understanding of the physical limits to natural laminar flow and possible ways to extend these limits was sought. The primary factors involved are unit Reynolds number, Mach number, wing sweep, thickness, and lift coefficients as well as surface pressure gradients and curvature. Based on previous and ongoing studies using laminar boundary layer stability theory, the interplay of the above factors and the corresponding transition limits were postulated.
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.
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 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.
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 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.
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-Fidelity Aerodynamic Shape Optimization for Natural Laminar Flow
NASA Astrophysics Data System (ADS)
Rashad, Ramy
To ensure the long-term sustainability of aviation, serious effort is underway to mitigate the escalating economic, environmental, and social concerns of the industry. Significant improvement to the energy efficiency of air transportation is required through the research and development of advanced and unconventional airframe and engine technologies. In the quest to reduce airframe drag, this thesis is concerned with the development and demonstration of an effective design tool for improving the aerodynamic efficiency of subsonic and transonic airfoils. The objective is to advance the state-of-the-art in high-fidelity aerodynamic shape optimization by incorporating and exploiting the phenomenon of laminar-turbulent transition in an efficient manner. A framework for the design and optimization of Natural Laminar Flow (NLF) airfoils is developed and demonstrated with transition prediction capable of accounting for the effects of Reynolds number, freestream turbulence intensity, Mach number, and pressure gradients. First, a two-dimensional Reynolds-averaged Navier-Stokes (RANS) flow solver has been extended to incorporate an iterative laminar-turbulent transition prediction methodology. The natural transition locations due to Tollmien-Schlichting instabilities are predicted using the simplified eN envelope method of Drela and Giles or, alternatively, the compressible form of the Arnal-Habiballah-Delcourt criterion. The boundary-layer properties are obtained directly from the Navier-Stokes flow solution, and the transition to turbulent flow is modeled using an intermittency function in conjunction with the Spalart-Allmaras turbulence model. The RANS solver is subsequently employed in a gradient-based sequential quadratic programming shape optimization framework. The laminar-turbulent transition criteria are tightly coupled into the objective and gradient evaluations. The gradients are obtained using a new augmented discrete-adjoint formulation for non-local transition
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
Computational wing design studies relating to natural laminar flow
NASA Technical Reports Server (NTRS)
Waggoner, Edgar G.
1986-01-01
Two research studies are described which directly relate to the application of natural laminar flow (NLF) technology to transonic transport-type wing planforms. Each involved using state-of-the-art computational methods to design three-dimensional wing contours which generate significant runs of favorable pressure gradients. The first study supported the Variable Sweep Transition Flight Experiment and involves design of a full-span glove which extends from the leading edge to the spoiler hinge line on the upper surface of an F-14 outer wing panel. A wing was designed computationally for a corporate transport aircraft in the second study. The resulting wing design generated favorable pressure gradients from the leading edge aft to the mid-chord on both upper and lower surfaces at the cruise design point. Detailed descriptions of the computational design approach are presented along with the various constraints imposed on each of the designs.
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.
Natural laminar flow and airplane stability and control
NASA Technical Reports Server (NTRS)
Vandam, Cornelis P.
1986-01-01
Location and mode of transition from laminar to turbulent boundary layer flow have a dominant effect on the aerodynamic characteristics of an airfoil section. The influences of these parameters on the sectional lift and drag characteristics of three airfoils are examined. Both analytical and experimental results demonstrate that when the boundary layer transitions near the leading edge as a result of surface roughness, extensive trailing-edge separation of the turbulent boundary layer may occur. If the airfoil has a relatively sharp leading-edge, leading-edge stall due to laminar separation can occur after the leading-edge suction peak is formed. These two-dimensional results are used to examine the effects of boundary layer transition behavior on airplane longitudinal and lateral-directional stability and control.
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.
Laminar boundary layer in conditions of natural transition to turbulent flow
NASA Technical Reports Server (NTRS)
Polyakov, N. F.
1986-01-01
Results of experimental study of regularities of a natural transition of a laminar boundary layer to a turbulent layer at low subsonic air flow velocities are presented, analyzed and compared with theory and model experiments.
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.
Observations and implications of natural laminar flow on practical airplane surfaces
NASA Technical Reports Server (NTRS)
Holmes, B. J.; Obara, C. J.
1982-01-01
The results of natural laminar flow (NLF) experiments conducted by NASA to determine if modern aircraft structures can benefit from NLF as do sailplanes are presented. Seven aircraft, ranging from a Cessna 210 to a Learjet 28/29, with relatively stiff skins were flown in production configurations with no modifications. Measurements were made of the boundary-layer laminar to turbulent transition locations on various aerodynamic surfaces, the effect of a total loss of laminar flow, the effect of the propeller slipstream on the wing boundary-layer transition and the boundary-layer profiles, the wing section profile drag, the effect of flight through clouds, and insect debris contamination effects. Favorable pressure gradients for NLF were concluded to be feasible up to a transition Reynolds number of 11 million. Laminar flows were observed in propeller slipstreams, and insects were found to cause transition 1/4 of the time.
Design and Experimental Results for a Natural-Laminar-Flow Airfoil for General Aviation Applications
NASA Technical Reports Server (NTRS)
Somers, D. M.
1981-01-01
A natural-laminar-flow airfoil for general aviation applications, the NLF(1)-0416, was designed and analyzed theoretically and verified experimentally in the Langley Low-Turbulence Pressure Tunnel. The basic objective of combining the high maximum lift of the NASA low-speed airfoils with the low cruise drag of the NACA 6-series airfoils was achieved. The safety requirement that the maximum lift coefficient not be significantly affected with transition fixed near the leading edge was also met. Comparisons of the theoretical and experimental results show excellent agreement. Comparisons with other airfoils, both laminar flow and turbulent flow, confirm the achievement of the basic objective.
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.
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.
F-15B in flight showing Supersonic Natural Laminar Flow (SS-NLF) experiment attached vertically to t
NASA Technical Reports Server (NTRS)
1999-01-01
In-flight photo of the F-15B equipped with the Supersonic Natural Laminar Flow (SS-NLF) experiment. During four research flights, laminar flow was achieved over 80 percent of the test wing at speeds approaching Mach 2. This was accomplished as the sole result of the shape of the wing, without the use of suction gloves, such as on the F-16XL. Laminar flow is a condition in which air passes over a wing in smooth layers, rather than being turbulent The greater the area of laminar flow, the lower the amount of friction drag on the wing, thus increasing an aircraft's range and fuel economy. Increasing the area of laminar flow on a wing has been the subject of research by engineers since the late 1940s, but substantial success has proven elusive. The SS-NLF experiment was intended to provide engineers with the data by which to design natural laminar flow wings.
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.
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.
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.
NASA Astrophysics Data System (ADS)
Vermeersch, Olivier; Yoshida, Kenji; Ueda, Yoshine; Arnal, Daniel
2015-11-01
In the framework of next supersonic transport airplane generation, the Japan Aerospace eXploration Agency (JAXA) has developed a new natural laminar flow highly swept wing. The design has been experimentally validated firstly in a supersonic wind tunnel and secondly accomplishing flight test. These experimental data were then analyzed and completed by numerical stability analyses in a joint research program between Onera and JAXA. At the design condition, for a Mach number M=2 at an altitude of h=18 km, results have confirmed the laminar design of the wing due to a strong attenuation of cross-flow instabilities ensuring an extended laminar zone. As the amplification of disturbances inside the boundary layer and transition process is very sensitive to external parameters, the impact of wall roughness of the models and the influence of Reynolds number on transition process have been carefully analyzed.
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.
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.
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.
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.
Tzeng, P.Y.; Soong, C.Y.; Sheu, T.S.
1997-02-07
The present work is concerned with a numerical investigation of transient laminar natural convection and the associated flow-mode transition in a two-dimensional rectangular enclosure. Navier-Stokes/Boussinesq equations for fluid flow and energy balance are solved by using the SIMPLE-C algorithm. Air of Pr = 0.71 in a differentially heated enclose of length-to-height aspect ratio As = 4 and at Ra = 5,000 is chosen as the flow model to examine the influences of the inclination. Calculations of time accuracy are performed to investigate the transient procedure of the flow-mode transition with increasing or decreasing inclination. The present results reveal that, at some critical situations, natural convection in inclined enclosures is very sensitive to the change in tilt angle, and the associated heat transfer rates are closely related to the correspondent cellular flow patterns.
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.
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.
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.
NASA Technical Reports Server (NTRS)
Somers, D. M.
1981-01-01
A flapped natural laminar flow airfoil for general aviation applications, the NLF(1)-0215F, has been designed and analyzed theoretically and verified experimentally in the Langley Low Turbulence Pressure Tunnel. The basic objective of combining the high maximum lift of the NASA low speed airfoils with the low cruise drag of the NACA 6 series airfoils has been achieved. The safety requirement that the maximum lift coefficient not be significantly affected with transition fixed near the leading edge has also been met. Comparisons of the theoretical and experimental results show generally good agreement.
Certification aspects of airplanes which may operate with significant natural laminar flow
NASA Technical Reports Server (NTRS)
Gabriel, Edward A.; Tankesley, Earsa L.
1986-01-01
Recent research by NASA indicates that extensive natural laminar flow (NLF) is attainable on modern high performance airplanes currently under development. Modern airframe construction methods and materials, such as milled aluminum skins, bonded aluminum skins, and composite materials, offer the potential for production of aerodynamic surfaces having waviness and roughness below the values which are critical for boundary layer transition. Areas of concern with the certification aspects of Natural Laminar Flow (NLF) are identified to stimulate thought and discussion of the possible problems. During its development, consideration has been given to the recent research information available on several small business and experimental airplanes and the certification and operating rules for general aviation airplanes. The certification considerations discussed are generally applicable to both large and small airplanes. However, from the information available at this time, researchers expect more extensive NLF on small airplanes because of their lower operating Reynolds numbers and cleaner leading edges (due to lack of leading-edge high lift devices). Further, the use of composite materials for aerodynamic surfaces, which will permit incorporation of NLF technology, is currently beginning to appear in small airplanes.
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…
Supersonic laminar flow control research
NASA Technical Reports Server (NTRS)
Lo, C. 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 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 POC and LFSWT's nozzle design with laminar flow control are as follows: (1) supersonic laminar boundary layer stability and transition prediction; (2) effects of heating and cooling for supersonic laminar flow control; and (3) POC and LFSWT nozzle design with heating and cooling effects combining wall contour and length changes.
Computational design of natural laminar flow wings for transonic transport application
NASA Technical Reports Server (NTRS)
Waggoner, Edgar G.; Campbell, Richard L.; Phillips, Pamela S.; Viken, Jeffrey K.
1986-01-01
Two research programs are described which directly relate to the application of natural laminar flow (NLF) technology to transonic transport-type wind planforms. Each involved using state-of-the-art computational methods to design three-dimensional wing contours which generate significant runs of favorable pressure gradients. The first program supported the Variable Sweep Transition Flight Experiment and involves design of a full-span glove which extends from the leading edge to the spoiler hinge line on the upper surface of an F-14 outer wing panel. Boundary-layer and static-pressure data will be measured on this design during the supporting wind-tunnel and flight tests. These data will then be analyzed and used to infer the relationship between crossflow and Tollmein-Schlichting disturbances on laminar boundary-layer transition. A wing was designed computationally for a corporate transport aircraft in the second program. The resulting wing design generated favorable pressure gradients from the leading edge aft to the mid-chord on both upper and lower surfaces at the cruise design point. Detailed descriptions of the computational design approach are presented along with the various constraints imposed on each of the designs. Wing surface pressure distributions, which support the design objective and were derived from transonic three-dimensional analyses codes, are also presented. Current status of each of the research programs is included in the summary.
Chouikh, R.; Guizani, A.; Maalej, M.; Belghith, A.
1999-04-01
The amount of work accomplished in the area of natural convection heat transfer in interacting flow fields around an array of cylinders has increased in the last years. There is a growing demand for a better understanding of this phenomenon in areas like heat exchangers, electronic devices, solar heating and storing technology among others. Here, natural convection heat transfer from an array of heated cylinders has received attention in recent years. However, most of the previous investigations has been experimental and has been restricted to the influence of geometrical parameters on the overall heat transfer. The present work is devoted to the numerical study of laminar natural convection flow from an array of two horizontal isothermal cylinders. This work, that enters within the framework of general study dealing with an array of several cylinders, states the problem in Cartesian coordinates system, involves the use of a control-volume method and solves the full vorticity transport equation together with the stream function and energy equations. The modifications of the average Nusselt number evolution compared with the single cylinder are explained in terms of velocity and temperature fields of the flow around the cylinders. Results are obtained for variety of combinations of spacing and numbers of Rayleigh.
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.
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.
Supersonic laminar flow control research
NASA Technical Reports Server (NTRS)
Lo, Ching F.; Wiberg, Clark G.
1995-01-01
The objective 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 Proof of Concept (PoC) and 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, (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 versus pulse wall temperature distribution for the LFSWT.
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)
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.
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.
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)
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.
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)
Kolesar, C. E.
1987-01-01
Research activity on an airfoil designed for a large airplane capable of very long endurance times at a low Mach number of 0.22 is examined. Airplane mission objectives and design optimization resulted in requirements for a very high design lift coefficient and a large amount of laminar flow at high Reynolds number to increase the lift/drag ratio and reduce the loiter lift coefficient. Natural laminar flow was selected instead of distributed mechanical suction for the measurement technique. A design lift coefficient of 1.5 was identified as the highest which could be achieved with a large extent of laminar flow. A single element airfoil was designed using an inverse boundary layer solution and inverse airfoil design computer codes to create an airfoil section that would achieve performance goals. The design process and results, including airfoil shape, pressure distributions, and aerodynamic characteristics are presented. A two dimensional wind tunnel model was constructed and tested in a NASA Low Turbulence Pressure Tunnel which enabled testing at full scale design Reynolds number. A comparison is made between theoretical and measured results to establish accuracy and quality of the airfoil design technique.
NASA Astrophysics Data System (ADS)
Rogers, David F.
1992-10-01
The major thrust of this book is to present a technique of analysis that aids the formulation, understanding, and solution of problems of viscous flow. The intent is to avoid providing a "canned" program to solve a problem, offering instead a way to recognize the underlying physical, mathematical, and modeling concepts inherent in the solutions. The reader must first choose a mathematical model and derive governing equations based on realistic assumptions, or become aware of the limitations and assumptions associated with existing models. An appropriate solution technique is then selected. The solution technique may be either analytical or numerical. Computer-aided analysis algorithms supplement the classical analyses. The book begins by deriving the Navier-Stokes equation for a viscous compressible variable property fluid. The second chapter considers exact solutions of the incompressible hydrodynamic boundary layer equations solved with and without mass transfer at the wall. Forced convection, free convection, and the compressible laminar boundary layer are discussed in the remaining chapters. The text unifies the various topics by tracing a logical progression from simple to complex governing differential equations and boundary conditions. Numerical, parametric, and directed analysis problems are included at the end of each chapter.
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.
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.
Supersonic laminar-flow control
NASA Technical Reports Server (NTRS)
Bushnell, Dennis M.; Malik, Mujeeb R.
1987-01-01
Detailed, up to date systems studies of the application of laminar flow control (LFC) to various supersonic missions and/or vehicles, both civilian and military, are not yet available. However, various first order looks at the benefits are summarized. The bottom line is that laminar flow control may allow development of a viable second generation SST. This follows from a combination of reduced fuel, structure, and insulation weight permitting operation at higher altitudes, thereby lowering sonic boom along with improving performance. The long stage lengths associated with the emerging economic importance of the Pacific Basin are creating a serious and renewed requirement for such a vehicle. Supersonic LFC techniques are discussed.
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.
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.
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.
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.
Natural laminar-turbulent transition delay by dielectric barrier discharge
NASA Astrophysics Data System (ADS)
Ustinov, Maxim; Kogan, Mikhail; Litvinov, Vladimir; Uspensky, Alexander
2011-12-01
The use dielectric barrier discharge for the delay of laminar turbulent transition excited by natural flow disturbances in a quiet wind-tunnel was investigated experimentally. Optimal electrodes location and the operational regime of high-voltage impulse generator provided maximal downstream shift of transition location were found. It was demonstrated that the 10% increase of the laminar part of boundary layer can be obtained using barrier discharge with the cross-flow electrodes. This gives up to 20% friction drag reduction.
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.
Laminar Flow Breakdown due to Particle Interactions
2012-08-01
effect on the boundary layer when encountering cirrus cloud , is incomplete. The observed performance degradations [5, 9] have been attributed to the...crystals as occurring in cirrus cloud would have a detrimental effect on the performance of Laminar Flow Control (LFC) systems. During flight tests of...full chord suction type LFC systems aboard two X-21 aircraft, laminar flow was entirely lost when entering thick cirrus cloud and degraded even in
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.
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.
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.
Roughness and waviness requirements for laminar flow surfaces
NASA Technical Reports Server (NTRS)
Obara, Clifford J.; Holmes, Bruce J.
1986-01-01
Many modern metal and composite airframe manufacturing techniques can provide surface smoothness which is compatible with natural laminar flow (NLF) requirements. An important consideration is manufacturing roughness of the surface in the form of steps and gaps perpendicular to the freestream. The principal challenge to the design and manufacture of laminar flow surfaces today appears to be in the installation of leading-edge panels on wing, nacelle, and empennage surfaces. A similar challenge is in the installation of access panels, doors, windows, fuselage noses, and engine nacelles. Past work on roughness and waviness manufacturing tolerances and comparisons with more recent experiments are reviewed.
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.
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
Steady laminar flow of fractal fluids
NASA Astrophysics Data System (ADS)
Balankin, Alexander S.; Mena, Baltasar; Susarrey, Orlando; Samayoa, Didier
2017-02-01
We study laminar flow of a fractal fluid in a cylindrical tube. A flow of the fractal fluid is mapped into a homogeneous flow in a fractional dimensional space with metric induced by the fractal topology. The equations of motion for an incompressible Stokes flow of the Newtonian fractal fluid are derived. It is found that the radial distribution for the velocity in a steady Poiseuille flow of a fractal fluid is governed by the fractal metric of the flow, whereas the pressure distribution along the flow direction depends on the fractal topology of flow, as well as on the fractal metric. The radial distribution of the fractal fluid velocity in a steady Couette flow between two concentric cylinders is also derived.
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.
Evaluation of laminar flow microbiological safety cabinets.
Staat, R H; Beakley, J W
1968-10-01
The microbiological control efficiency of two class 100 laminar down-flow hoods was determined by using aerosols of Bacillus subtilis var. niger spores. The first unit challenged utilized a slanted eyelid to partially enclose the front work opening. This hood showed nearly perfect control of ambient organisms in the work area. It also gave a 10(6) or greater drop in the number of organisms passing out of the exhaust system. However, when the interior work area of the hood was challenged, significant numbers of spores penetrated the air barrier and escaped into the ambient air. A redesigned laminar flow hood was built incorporating a vertical eyelid and a reduced opening to the work area. This hood showed the same excellent characteristics for controlling ambient contamination. Exhaust system leakage was also extremely low. Air barrier efficiency for the newer hood was increased with lower amounts of spore penetration into the ambient air.
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.
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.
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.
Geometries for roughness shapes in laminar flow
NASA Technical Reports Server (NTRS)
Holmes, Bruce J. (Inventor); Martin, Glenn L. (Inventor); Domack, Christopher S. (Inventor); Obara, Clifford J. (Inventor); Hassan, Ahmed A. (Inventor)
1986-01-01
A passive interface mechanism between upper and lower skin structures, and a leading edge structure of a laminar flow airfoil is described. The interface mechanism takes many shapes. All are designed to be different than the sharp orthogonal arrangement prevalent in the prior art. The shapes of the interface structures are generally of two types: steps away from the centerline of the airfoil with a sloping surface directed toward the trailing edge and, the other design has a gap before the sloping surface. By properly shaping the step, the critical step height is increased by more than 50% over the orthogonal edged step.
Elliptic Length Scales in Laminar, Two-Dimensional Supersonic Flows
2015-06-01
AFRL-RQ-WP-TP-2015-0109 ELLIPTIC LENGTH SCALES IN LAMINAR, TWO- DIMENSIONAL SUPERSONIC FLOWS James H. Miller Vehicle Technology Branch...SUBTITLE ELLIPTIC LENGTH SCALES IN LAMINAR, TWO-DIMENSIONAL SUPERSONIC FLOWS 5a. CONTRACT NUMBER In-house 5b. GRANT NUMBER 5c. PROGRAM ELEMENT...ANSI Std. Z39-18 1 Approved for public release; distribution unlimited. Elliptic Length Scales in Laminar, Two-Dimensional Supersonic Flows
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.
Base pressure in laminar supersonic flow.
NASA Technical Reports Server (NTRS)
Messiter, A. F.; Hough, G. R.; Feo, A.
1973-01-01
An asymptotic description is proposed for supersonic laminar flow over a wedge or a backward-facing step, for large Reynolds number and for a base or step height which is small compared with the boundary-layer length. The analysis is carried out for adiabatic wall conditions and a viscosity coefficient proportional to temperature. In a particular limit corresponding to a very thick boundary layer, a similarity law is obtained for the base pressure. For a thinner boundary layer an asymptotic form for the base pressure is obtained which shows the dependence on the parameters explicitly and which permits good agreement with experiment. This latter result is based on an inviscid-flow approximation for the corner expansion and for reattachment with viscous forces important primarily in a thin sublayer about the dividing streamline. A prediction of the pressure distribution at reattachment is given and the result is compared with experimental pressure distributions.
Evaluation of the Edgegard laminar flow hood.
Coriell, L L; McGarrity, G J
1970-09-01
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.
Laminar flow past a rotating circular cylinder
NASA Astrophysics Data System (ADS)
Kang, Sangmo; Choi, Haecheon; Lee, Sangsan
1999-11-01
The present study numerically investigates two-dimensional laminar flow past a circular cylinder rotating with a constant angular velocity, for the purpose of controlling vortex shedding and understanding the underlying flow mechanism. Numerical simulations are performed for flows with Re=60, 100, and 160 in the range of 0⩽α⩽2.5, where α is the circumferential speed at the cylinder surface normalized by the free-stream velocity. Results show that the rotation of a cylinder can suppress vortex shedding effectively. Vortex shedding exists at low rotational speeds and completely disappears at α>αL, where αL is the critical rotational speed which shows a logarithmic dependence on Re. The Strouhal number remains nearly constant regardless of α while vortex shedding exists. With increasing α, the mean lift increases linearly and the mean drag decreases, which differ significantly from those predicted by the potential flow theory. On the other hand, the amplitude of lift fluctuation stays nearly constant with increasing α (<αL), while that of drag fluctuation increases. Further studies from the instantaneous flow fields demonstrate again that the rotation of a cylinder makes a substantial effect on the flow pattern.
Laminar Flow past a Rotating Sphere
NASA Astrophysics Data System (ADS)
Kim, Dongjoo; Choi, Haecheon
2000-11-01
In this study, laminar flow past a rotating sphere is numerically investigated to understand the effect of the streamwise rotation on the flow characteristics behind a sphere. The present numerical method is based on a newly developed immersed boundary method in a cylindrical coordinate. Numerical simulations are performed at Re =100, 250 and 300 in the range of 0 <= ω^* <= 1.0, where ω^* is the maximum circumferential speed at the sphere surface normalized by the free-stream velocity. At ω^*=0 (without rotation), the flow past a sphere experiences steady axisymmetry, steady plane-symmetry, and unsteady plane-symmetry, respectively, at Re =100, 250 and 300. When the rotational speed increases, the drag increases for all the Reynolds numbers investigated, whereas the lift shows a non-monotonic behavior depending on the Reynolds number. At Re =100, the flow past a sphere shows steady axisymmetry for all the rotational speeds considered and thus the lift is zero. On the other hand, at Re =250 and 300, the flow becomes unsteady with rotation. With increasing rotational speed, the lift first decreases and then increases, showing a local minimum of lift at a specific rotational speed. The three-dimensional vortical structures behind a sphere are significantly modified by the streamwise rotation. For example, the vortical structures at Re =300 are completely changed and phase locked with rotation at ω^*=0.6.
Laminar flow control SPF/08 feasibility demonstration
NASA Technical Reports Server (NTRS)
Ecklund, R. C.; Williams, N. R.
1981-01-01
The feasibility of applying superplastic forming/diffusion bonding (SPF/DB) technology to laminar flow control (LFC) system concepts was demonstrated. Procedures were developed to produce smooth, flat titanium panels, using thin -0.016 inch sheets, meeting LFC surface smoothness requirements. Two large panels 28 x 28 inches were fabricated as final demonstration articles. The first was flat on the top and bottom sides demonstrating the capability of the tooling and the forming and diffusion bonding procedures to produce flat, defect free surfaces. The second panel was configurated for LFC porous panel treatment by forming channels with dimpled projections on the top side. The projections were machined away leaving holes extending into the panel. A perforated titanium sheet was adhesively bonded over this surface to complete the LFC demonstration panel. The final surface was considered flat enough to meet LFC requirements for a jet transport aircraft in cruising flight.
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.
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.
NASA F-16XL supersonic laminar flow control program overview
NASA Technical Reports Server (NTRS)
Fischer, Michael C.
1992-01-01
The viewgraphs and discussion of the NASA supersonic laminar flow control program are provided. Successful application of laminar flow control to a High Speed Civil Transport (HSCT) offers significant benefits in reductions of take-off gross weight, mission fuel burn, cruise drag, structural temperatures, engine size, emissions, and sonic boom. The ultimate economic success of the proposed HSCT may depend on the successful adaption of laminar flow control, which offers the single most significant potential improvements in lift drag ratio (L/D) of all the aerodynamic technologies under consideration. The F-16XL Supersonic Laminar Flow Control (SLFC) Experiment was conceived based on the encouraging results of in-house and NASA supported industry studies to determine if laminar flow control is feasible for the HSCT. The primary objective is to achieve extensive laminar flow (50-60 percent chord) on a highly swept supersonic wing. Data obtained from the flight test will be used to validate existing Euler and Navier Stokes aerodynamic codes and transition prediction boundary layer stability codes. These validated codes and developed design methodology will be delivered to industry for their use in designing supersonic laminar flow control wings. Results from this experiment will establish preliminary suction system design criteria enabling industry to better size the suction system and develop improved estimates of system weight, fuel volume loss due to wing ducting, turbocompressor power requirements, etc. so that benefits and penalties can be more accurately assessed.
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.
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.
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.
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.
Design Guide for Laminar Flow Fluidic Amplifiers and Sensors.
1982-04-27
input * and output characteristics for the geometry of any amplifier . The only constraint is that the flow out of the supply nozzle remains laminar and...supply pressure in the range of 2 to 20 MPa. Although turbulent flow jet deflection amplifiers have useful characteristics , their low gain and low dynamic...simple proportional fluidic controllers using turbulent flow amplifiers indicated that the characteristics of these devices would restrict the
LAMINAR TRANSITIONAL AND TURBULENT BOUNDARY LAYERS FOR COMPRESSIBLE AXISYMMETRIC FLOW
NASA Technical Reports Server (NTRS)
Albers, J. A.
1994-01-01
This is a finite-difference program for calculating the viscous compressible boundary layer flow over either planar or axisymmetric surfaces. The flow may be initially laminar and progress through a transitional zone to a fully turbulent flow, or it may remain laminar, depending on the imposed boundary conditions, laws of viscosity, and numerical solution of the momentum and energy equations. The flow may also be forced into a turbulent flow at a chosen spot by the data input. The input may contain factors of arbitrary Reynolds number, free-stream Mach number, free stream turbulence, wall heating or cooling, longitudinal wall curvature, wall suction or blowing, and wall roughness. The solution may start from an initial Falkner-Skan similarity profile, an approximate equilibrium turbulent profile, or an initial arbitrary input profile. This program has been implemented on the IBM 7094/7044 Direct Couple System. This program is written in FORTRAN IV and was developed in 1974.
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.
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.
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.
On laminar-turbulent transition in nanofluid flows
NASA Astrophysics Data System (ADS)
Rudyak, V. Ya.; Minakov, A. V.; Guzey, D. V.; Zhigarev, V. A.; Pryazhnikov, M. I.
2016-09-01
The paper presents experimental data on the laminar-turbulent transition in the nanofluid flow in the pipe. The transition in the flows of such fluids is shown to have lower Reynolds numbers than in the base fluid. The degree of the flow destabilization increases with an increase in concentration of nanoparticles and a decrease in their size. On the other hand, in the turbulent flow regime, the presence of particles in the flow leads to the suppression of smallscale turbulent fluctuations. The correlation of the measured viscosity coefficient of considered nanofluids is presented.
NASA Technical Reports Server (NTRS)
Manuel, G. S.; Carraway, D. L.; Lee, C. C.
1991-01-01
Reduction of viscous drag on airplanes explores limits of practical applications of natural laminar flow. Wind-tunnel and flight tests conducted to explore abilities of hot-film sensors to identify separation of laminar flow as principal mode of amplification of instability leading to transition from laminar to turbulent flow. Two different laminar-separation-sensor configurations developed and used to detect boundary-layer transitions. Results show hot-film laminar-separation-sensor technique viable means for detecting existence of transition as well as for indicating reversed flow in laminar-separation bubble. Refinement of sensor configurations provides tools necessary to explore, in all speed regimes, practical limits of laminar-flow applications and viscous-drag-reduction technology.
Hydrodynamic Fluctuations in Laminar Fluid Flow. II. Fluctuating Squire Equation
NASA Astrophysics Data System (ADS)
Ortiz de Zárate, José M.; Sengers, Jan V.
2013-02-01
We use fluctuating hydrodynamics to evaluate the enhancement of thermally excited fluctuations in laminar fluid flow using plane Couette flow as a representative example. In a previous publication (J. Stat. Phys. 144:774, 2011) we derived the energy amplification arising from thermally excited wall-normal fluctuations by solving a fluctuating Orr-Sommerfeld equation. In the present paper we derive the energy amplification arising from wall-normal vorticity fluctuation by solving a fluctuating Squire equation. The thermally excited wall-normal vorticity fluctuations turn out to yield the dominant contribution to the energy amplification. In addition, we show that thermally excited streaks, even in the absence of any externally imposed perturbations, are present in laminar fluid flow.
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.
Laminar flow downregulates Notch activity to promote lymphatic sprouting.
Choi, Dongwon; Park, Eunkyung; Jung, Eunson; Seong, Young Jin; Yoo, Jaehyuk; Lee, Esak; Hong, Mingu; Lee, Sunju; Ishida, Hiroaki; Burford, James; Peti-Peterdi, Janos; Adams, Ralf H; Srikanth, Sonal; Gwack, Yousang; Chen, Christopher S; Vogel, Hans J; Koh, Chester J; Wong, Alex K; Hong, Young-Kwon
2017-04-03
The major function of the lymphatic system is to drain interstitial fluid from tissue. Functional drainage causes increased fluid flow that triggers lymphatic expansion, which is conceptually similar to hypoxia-triggered angiogenesis. Here, we have identified a mechanotransduction pathway that translates laminar flow-induced shear stress to activation of lymphatic sprouting. While low-rate laminar flow commonly induces the classic shear stress responses in blood endothelial cells and lymphatic endothelial cells (LECs), only LECs display reduced Notch activity and increased sprouting capacity. In response to flow, the plasma membrane calcium channel ORAI1 mediates calcium influx in LECs and activates calmodulin to facilitate a physical interaction between Krüppel-like factor 2 (KLF2), the major regulator of shear responses, and PROX1, the master regulator of lymphatic development. The PROX1/KLF2 complex upregulates the expression of DTX1 and DTX3L. DTX1 and DTX3L, functioning as a heterodimeric Notch E3 ligase, concertedly downregulate NOTCH1 activity and enhance lymphatic sprouting. Notably, overexpression of the calcium reporter GCaMP3 unexpectedly inhibited lymphatic sprouting, presumably by disturbing calcium signaling. Endothelial-specific knockouts of Orai1 and Klf2 also markedly impaired lymphatic sprouting. Moreover, Dtx3l loss of function led to defective lymphatic sprouting, while Dtx3l gain of function rescued impaired sprouting in Orai1 KO embryos. Together, the data reveal a molecular mechanism underlying laminar flow-induced lymphatic sprouting.
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
Croze, Ottavio A; Sardina, Gaetano; Ahmed, Mansoor; Bees, Martin A; Brandt, Luca
2013-04-06
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.
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.
A Redefined Hydraulic Diameter for Laminar Flow.
1986-12-01
entrance, down the duct, and either into a weighing tank or back into the reservoir, depending on the selector valve setting. A mercury manometer board...station alonq the duct . 28 •S is presented on the mercury manometer board. The weighing tank is used to measure the mass flow of oil for a specific
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.
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.
Experiments on Laminar to Turbulence Transition and Relaminarization in Pulsatile Flows
NASA Astrophysics Data System (ADS)
Gomez, Joan; Goushcha, Oleg; Andreopoulos, Yiannis
2016-11-01
Biological flows display laminar-turbulence-laminar transitions due to the cyclic nature of a beating heart. Addressing the question of how turbulence appears, decays and is suppressed in the cardiovascular system, particularly in the large arteries, is challenging due to flow unsteadiness, very complicated geometry and flow-wall interaction. In the present work we have designed and tested a facility to simulate unsteady pulsatile flows and the onset of transition under varying Reynolds and Womersley numbers. A moving piston is used to generate a flow pulsation and control the velocity amplitude. Time-Resolved Particle Image Velocimetry (TR-PIV) techniques were used to acquire velocity data on the plane of a CW laser illumination. Two different decompositions were applied to analyze the non-stationary and non-linear time-dependent data, the Empirical Mode Decomposition (EMD) and the Trend Removal Method (TRM). Two flow regimes were found, one in which the pulsatile flow exhibits phase-locked turbulence which is associated with the stabilizing effects of longitudinal straining during acceleration and a second where transition occurs very close to the wall while the core remains laminar.
Laminar flow transition: A large-eddy simulation approach
NASA Technical Reports Server (NTRS)
Biringen, S.
1982-01-01
A vectorized, semi-implicit code was developed for the solution of the time-dependent, three dimensional equations of motion in plane Poiseuille flow by the large-eddy simulation technique. The code is tested by comparing results with those obtained from the solutions of the Orr-Sommerfeld equation. Comparisons indicate that finite-differences employed along the cross-stream direction act as an implicit filter. This removes the necessity of explicit filtering along this direction (where a nonhomogeneous mesh is used) for the simulation of laminar flow transition into turbulence in which small scale turbulence will be accounted for by a subgrid scale turbulence model.
Laminar flow over a backward-facing step
NASA Astrophysics Data System (ADS)
Zebib, A.; Homsy, G. M.
1984-09-01
The steady, two-dimensional flow of an incompressible fluid over a backward-facing step is computed by a finite difference procedure. The flow depends upon the Reynolds number, Re, based on the inlet flow conditions, and on the dimensionless step height, s. Spatially resolved, accurate solutions are obtained for a range of s for Reynolds numbers as high as 350. The primary flow feature is a steady separated region immediately in back of the step. Additionally, a secondary separated vortex can appear on the top, straight wall of the channel. A region is delineated in the (s,Re) plane where laminar separation occurs on the top surface. It is concluded that there is no flow reversal on the top surface if Re is less than about 200, regardless of the step height s. The occurrence of this secondary vortex is associated with laminar separation of the top boundary layer produced by an adverse pressure gradient along the top of the channel.
NASA Technical Reports Server (NTRS)
Fischer, Michael C.; Vemuru, Chandra S.
1991-01-01
The NASA Supersonic Laminar Flow Control (SLFC) program encompasses the development of refined CFD methods and boundary layer stability codes for the highly 3D supersonic flow conditions encountered by the F-16XL technology demonstration aircraft and the prospective High Speed Civil Transport (HSCT). While the F-16XL-1 aircraft continues to gather SLFC data, work is under way on the F-16XL-2 aircraft: which will furnish attach-line design criteria, code-calibration data, and an improved understanding of the flowfield over a wing that will add confidence to the design of HSCTs' boundary layer-controlling air-suction panels.
Superhydrophobic drag reduction in laminar flows: a critical review
NASA Astrophysics Data System (ADS)
Lee, Choongyeop; Choi, Chang-Hwan; Kim, Chang-Jin
2016-12-01
A gas in between micro- or nanostructures on a submerged superhydrophobic (SHPo) surface allows the liquid on the structures to flow with an effective slip. If large enough, this slippage may entail a drag reduction appreciable for many flow systems. However, the large discrepancies among the slippage levels reported in the literature have led to a widespread misunderstanding on the drag-reducing ability of SHPo surfaces. Today we know that the amount of slip, generally quantified with a slip length, is mainly determined by the structural features of SHPo surfaces, such as the pitch, solid fraction, and pattern type, and further affected by secondary factors, such as the state of the liquid-gas interface. Reviewing the experimental data of laminar flows in the literature comprehensively and comparing them with the theoretical predictions, we provide a global picture of the liquid slip on structured surfaces to assist in rational design of SHPo surfaces for drag reduction. Because the trapped gas, called plastron, vanishes along with its slippage effect in most application conditions, lastly we discuss the recent efforts to prevent its loss. This review is limited to laminar flows, for which the SHPo drag reduction is reasonably well understood.
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.
A 'similarity' solution for laminar swirling core flows
NASA Astrophysics Data System (ADS)
Ross, D. G.
1984-05-01
The far downstream region of laminar core flows with weak, strong, or very strong swirl embedded in a uniform parallel following stream is investigated analytically. Linearized similarity solutions based on the small-axial-disturbance-velocity assumption of Oseen are obtained using methods similar to those employed by Batchelor (1964) for strong trailing vortices. Strong swirl is shown to reduce axial velocity on and near the core axis, with two reversals as distance from the axis increases. Very strong swirl (a momentumless jet) is associated with an axial velocity profile having its maximum off the center line.
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.
Airborne drug levels in a laminar-flow hood
Kleinberg, M.L.; Quinn, M.J.
1981-09-01
The airborne levels of fluorouracil and cefazolin sodium injections after manipulation of these drug products inside a horizontal laminar-flow hood were measured. The Biotest RCS Centrifugal Air Sampler, generally used to measure microbial levels in air, was adapted with a paper filter to measure drug levels in air. In each of nine trials, five ampuls of fluorouracil were opened in the hood and transferred to empty vials. Likewise, in each of nine trials, 50 vials of cefazolin sodium 1 g were reconstituted and transferred to small-volume i.v. solutions. Drug manipulations were performed between the hood's filter and the Biotest, which was placed inside the hood. Drug collected on the filter in the Biotest was assayed with ultraviolet spectrophotometry after extraction. The range of fluorouracil collected by the Biotest was from 0 to 14 microgram, corresponding to 0-0.07 microgram/liter of sample air. Recovered cefazolin sodium ranged from 28 to 131 microgram, or 0.02-0.11 microgram/liter of sampled air. Following routine manipulation of drug products in a laminar-flow hood, the drug can contaminate, the air flowing over the product.
Airborne drug levels in a laminar-flow hood.
Kleinberg, M L; Quinn, M J
1981-09-01
The airborne levels of fluorouracil and cefazolin sodium injections after manipulation of these drug products inside a horizontal laminar-flow hood were measured. The Biotest RCS Centrifugal Air Sampler, generally used to measure microbial levels in air, was adapted with a paper filter to measure drug levels in air. In each of nine trials, five ampuls of fluorouracil were opened in the hood and transferred to empty vials. Likewise, in each of nine trials, 50 vials of cefazolin sodium 1 g were reconstituted and transferred to small-volume i.v. solutions. Drug manipulations were performed between the hood's filter and the Biotest, which was placed inside the hood. Drug collected on the filter in the Biotest was assayed with ultraviolet spectrophotometry after extraction. The range of fluorouracil collected by the Biotest was from 0 to 14 microgram, corresponding to 0-0.07 microgram/liter of sample air. Recovered cefazolin sodium ranged from 28 to 131 microgram, or 0.02-0.11 microgram/liter of sampled air. Following routine manipulation of drug products in a laminar-flow hood, the drug can contaminate, the air flowing over the product.
NASA Technical Reports Server (NTRS)
Albers, J. A.; Gregg, J. L.
1974-01-01
Finite-difference computer program calculates viscous compressible boundary layer flow over either planar or axisymmetric surfaces. Flow may be initially laminar and progress through transitional zone to fully turbulent flow, or it may remain laminar, depending on imposed boundary conditions, laws of viscosity, and numerical solution of momentum and energy equations.
Laminar-flow fluid mixer for fast fluorescence kinetics studies.
Pabit, Suzette A; Hagen, Stephen J
2002-01-01
The ability to mix aqueous liquids on microsecond time scales, while consuming minimal amounts of sample and maintaining UV-visible optical access to the mixing region, is highly desirable for a range of biophysical studies of fast protein and nucleic acid interactions and folding. We have constructed a laminar coaxial jet mixer that allows the measurement of UV-excited fluorescence from nanoliter and microliter quantities of material, mixed at microsecond rates. The mixer injects a narrow cylindrical stream (radius a < 1 microm) of fluorescent sample into a larger flow of diluting buffer that moves through a capillary (100 microm i.d.) at a speed approximately 20 cm/s, under laminar flow conditions (Re approximately equal to 14). Construction from a fused silica capillary allows the laser excitation (at 266 nm) and detection (at 350 nm) of tryptophan fluorescence at reasonably low working concentrations, without interference from background fluorescence. Using this mixer we have measured sub-millisecond fluorescence quenching kinetics while consuming fluorescent sample at rates no greater than 6 nl/s. Consumption of the diluting buffer is also very modest (approximately 1-3 microl/s) in comparison with other rapid mixer designs. PMID:12414719
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.
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.
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.
A Realistic Theoretical Model for Laminar Flow over a Flat Plate
2010-09-14
laminar flow over a flat plate. For 111= I and a= I, thi s equation reduces to the Hiemenz [6] equation for laminar 2-D stagnation point flow. 6...New York, 1979. [6] K. Hiemenz , "Die Grenzschicht an eimen in den gleichformigen Fllissigkeitsstrom eingetauchten geraden Kreiszylinder," Dingler’s
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
Nam, Young Gyu; Najera, Maria Alejandra; Lee, Sang Woo; Strickler, J. Rudi; Chang, Woo-Jin
2016-01-01
The liquid streams in a microchannel are hardly mixed to form laminar flow, and the mixing issue is well described by a low Reynolds number scheme. The staggered herringbone mixer (SHM) using repeated patterns of grooves in the microchannel have been proved to be an efficient passive micro-mixer. However, only a negative pattern of the staggered herringbone mixer has been used so far after it was first suggested, to the best of our knowledge. In this study, the mixing efficiencies from negative and positive staggered herringbone mixer patterns as well as from opposite flow directions were tested to investigate the effect of the micro-structure geometry on the surrounding laminar flow. The positive herringbone pattern showed better mixing efficiency than the conventionally used negative pattern. Also, generally used forward flow gives better mixing efficiency than reverse flow. The mixing was completed after two cycles of staggered herringbone mixer with both forward and reverse flow in a positive pattern. The traditional negative pattern showed complete mixing after four and five cycles in forward and reverse flow direction, respectively. The mixing effect in all geometries was numerically simulated, and the results confirmed more efficient mixing in the positive pattern than the negative. The results can further enable the design of a more efficient microfluidic mixer, as well as in depth understanding of the phenomena of positive and negative patterns existing in nature with regards to the surrounding fluids. PMID:27814386
Kwak, Tae Joon; Nam, Young Gyu; Najera, Maria Alejandra; Lee, Sang Woo; Strickler, J Rudi; Chang, Woo-Jin
2016-01-01
The liquid streams in a microchannel are hardly mixed to form laminar flow, and the mixing issue is well described by a low Reynolds number scheme. The staggered herringbone mixer (SHM) using repeated patterns of grooves in the microchannel have been proved to be an efficient passive micro-mixer. However, only a negative pattern of the staggered herringbone mixer has been used so far after it was first suggested, to the best of our knowledge. In this study, the mixing efficiencies from negative and positive staggered herringbone mixer patterns as well as from opposite flow directions were tested to investigate the effect of the micro-structure geometry on the surrounding laminar flow. The positive herringbone pattern showed better mixing efficiency than the conventionally used negative pattern. Also, generally used forward flow gives better mixing efficiency than reverse flow. The mixing was completed after two cycles of staggered herringbone mixer with both forward and reverse flow in a positive pattern. The traditional negative pattern showed complete mixing after four and five cycles in forward and reverse flow direction, respectively. The mixing effect in all geometries was numerically simulated, and the results confirmed more efficient mixing in the positive pattern than the negative. The results can further enable the design of a more efficient microfluidic mixer, as well as in depth understanding of the phenomena of positive and negative patterns existing in nature with regards to the surrounding fluids.
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).
Material development for laminar flow control wing panels
NASA Technical Reports Server (NTRS)
Meade, L. E.
1977-01-01
The absence of suitable porous materials or techniques for the economic perforation of surface materials has previously restricted the design of laminar flow control (LFC) wing panels to a consideration of mechanically slotted LFC surfaces. A description is presented of a program which has been conducted to exploit recent advances in materials and manufacturing technology for the fabrication of reliable porous or perforated LFC surface panels compatible with the requirements of subsonic transport aircraft. Attention is given to LFC design criteria, surface materials, surface concepts, the use of microporous composites, perforated composites, and perforated metal. The described program was successful in that fabrication processes were developed for producing predictable perforated panels both of composite and of metal.
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.
Eddy genesis and manipulation in plane laminar shear flow
NASA Astrophysics Data System (ADS)
Scholle, M.; Haas, A.; Aksel, N.; Wilson, M. C. T.; Thompson, H. M.; Gaskell, P. H.
2009-07-01
Eddy formation and presence in a plane laminar shear flow configuration consisting of two infinitely long plates orientated parallel to each other is investigated theoretically. The upper plate, which is planar, drives the flow; the lower one has a sinusoidal profile and is fixed. The governing equations are solved via a full finite element formulation for the general case and semianalytically at the Stokes flow limit. The effects of varying geometry (involving changes in the mean plate separation or the amplitude and wavelength of the lower plate) and inertia are explored separately. For Stokes flow and varying geometry, excellent agreement between the two methods of solution is found. Of particular interest with regard to the flow structure is the importance of the clearance that exists between the upper plate and the tops of the corrugations forming the lower one. When the clearance is large, an eddy is only present at sufficiently large amplitudes or small wavelengths. However, as the plate clearance is reduced, a critical value is found, which triggers the formation of an eddy in an otherwise fully attached flow for any finite amplitude and arbitrarily large wavelength. This is a precursor to the primary eddy to be expected in the lid-driven cavity flow, which is formed in the limit of zero clearance between the plates. The influence of the flow driving mechanism is assessed by comparison with corresponding solutions for the case of gravity-driven fluid films flowing over an undulating substrate. When inertia is present, the flow generally becomes asymmetrical. However, it is found that for large mean plate separations the flow local to the lower plate becomes effectively decoupled from the inertia dominated overlying flow if the wavelength of the lower plate is sufficiently small. In such cases the local flow retains its symmetry. A local Reynolds number based on the wavelength is shown to be useful in characterizing these large-gap flows. As the mean plate
On the effect of riblets in fully developed laminar channel flows
NASA Technical Reports Server (NTRS)
Choi, Haecheon; Moin, Parviz; Kim, John
1991-01-01
The effect of longitudinal riblet surfaces on viscous drag in fully developed laminar channel flows was investigated. Unlike turbulent flows, drag reduction was not obtained in the laminar flows. Results were independent of Reynolds number. Wall-shear rates on most regions of the cross-sectional perimeter of riblets were smaller than that of corresponding plane channel flow even though the net drag was increased.
Heat exchange at laminar flow in rectangular channels
NASA Astrophysics Data System (ADS)
Valueva, E. P.; Purdin, M. S.
2016-11-01
Numerical modeling of heat exchange at a laminar stationary and pulsatile flow in rectangular channels with different aspect ratios of side lengths γ has been carried out by a finite difference method for two boundary conditions: a constant wall temperature and a constant heat flux density on the wall. For the boundary condition of the first kind, the similarity of distributions of the heat flux density and shear stress on the walls over the channel perimeter has been established. The reasons for a nonmonotonous dependence of the initial thermal interval length on γ are discussed. For the boundary condition of the second kind, the difference of the Nusselt number averaged over the perimeter at γ → 0 from its value for a flow in a flat channel has been explained. An increase in the Nusselt number averaged over the perimeter and the period of oscillations has been revealed for a pulsatile flow in the quasi-stationary regime at large amplitudes of the oscillations of the velocity averaged over the cross section.
Factors influencing flow steadiness in laminar boundary layer shock interactions
NASA Astrophysics Data System (ADS)
Tumuklu, Ozgur; Levin, Deborah A.; Gimelshein, Sergey F.; Austin, Joanna M.
2016-11-01
The Direct Simulation Monte Carlo method has been used to model laminar shock wave boundary interactions of hypersonic flow over a 30/55-deg double-wedge and "tick-shaped" model configurations studied in the Hypervelocity Expansion Tube facility and T-ADFA free-piston shock tunnel, respectively. The impact of thermochemical effects on these interactions by changing the chemical composition from nitrogen to air as well as argon for a stagnation enthalpy of 8.0 MJ/kg flow are investigated using the 2-D wedge model. The simulations are found to reproduce many of the classic features related to Edney Type V strong shock interactions that include the attached, oblique shock formed over the first wedge, the detached bow shock from the second wedge, the separation zone, and the separation and reattachment shocks that cause complex features such as the triple point for both cases. However, results of a reacting air flow case indicate that the size of the separation length, and the movement of the triple point toward to the leading edge is much less than the nitrogen case.
Active control of instabilities in laminar boundary-layer flow. Part 1: An overview
NASA Technical Reports Server (NTRS)
Joslin, Ronald D.; Erlebacher, Gordon; Hussaini, M. Yousuff
1994-01-01
This paper (the first in a series) focuses on using active-control methods to maintain laminar flow in a region of the flow in which the natural instabilities, if left unattended, lead to turbulent flow. The authors review previous studies that examine wave cancellation (currently the most prominent method) and solve the unsteady, nonlinear Navier-Stokes equations to evaluate this method of controlling instabilities. It is definitely shown that instabilities are controlled by the linear summation of waves (i.e., wave cancellation). Although a mathematically complete method for controlling arbitrary instabilities has been developed (but not yet tested), the review, duplication, and physical explanation of previous studies are important steps for providing an independent verification of those studies, for establishing a framework for subsequent work which will involve automated transition control, and for detailing the phenomena by which the automated studies can be used to expand knowledge of flow control.
Velocity fluctuations and energy amplification in laminar fluid flows
NASA Astrophysics Data System (ADS)
Ortiz de Zarate, Jose M.; Sengers, Jan V.
2008-11-01
We present a systematic procedure for evaluating the intrinsic velocity fluctuations and the resulting intrinsic energy amplification that are always present in laminar fluid flows. For this purpose we formulate a stochastic Orr-Sommerfeld equation and a stochastic Squire equation by applying a fluctuation-dissipation theorem for the random part of the dissipative stresses. From the solution of the stochastic Orr- Sommerfeld and Squire equations the intrinsic energy amplification can be deduced. As an illustration of the procedure we present an explicit solution for the case of planar Couette flow. We first solve the fluctuating hydrodynamics equations in the bulk, obtaining an exact representation of the spatial spectrum of the velocity fluctuations valid for large wave numbers. The resulting energy amplification is proportional to Re^3/2. Next, we show how to a good approximation confinement can be incorporated by a simple Galerkin projection technique. The effect of the boundary conditions is to reduce the energy amplification to a logarithmic dependence on Re. We shall also indicate how an exact solution for the case of confined geometries can be obtained by an expansion into a set of hydrodynamic modes, conveniently expressed in terms of Airy functions.
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.
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.
Rheology of sediment transported by a laminar flow
NASA Astrophysics Data System (ADS)
Houssais, M.; Ortiz, C. P.; Durian, D. J.; Jerolmack, D. J.
2016-12-01
Understanding the dynamics of fluid-driven sediment transport remains challenging, as it occurs at the interface between a granular material and a fluid flow. Boyer, Guazzelli, and Pouliquen [Phys. Rev. Lett. 107, 188301 (2011)], 10.1103/PhysRevLett.107.188301 proposed a local rheology unifying dense dry-granular and viscous-suspension flows, but it has been validated only for neutrally buoyant particles in a confined and homogeneous system. Here we generalize the Boyer, Guazzelli, and Pouliquen model to account for the weight of a particle by addition of a pressure P0 and test the ability of this model to describe sediment transport in an idealized laboratory river. We subject a bed of settling plastic particles to a laminar-shear flow from above, and use refractive-index-matching to track particles' motion and determine local rheology—from the fluid-granular interface to deep in the granular bed. Data from all experiments collapse onto a single curve of friction μ as a function of the viscous number Iv over the range 3 ×10-5 ≤Iv≤2 , validating the local rheology model. For Iv<3 ×10-5 , however, data do not collapse. Instead of undergoing a jamming transition with μ →μs as expected, particles transition to a creeping regime where we observe a continuous decay of the friction coefficient μ ≤μs as Iv decreases. The rheology of this creep regime cannot be described by the local model, and more work is needed to determine whether a nonlocal rheology model can be modified to account for our findings.
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.
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.
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.
Hydrodynamics and heat transfer for pulsating laminar flow in channels
NASA Astrophysics Data System (ADS)
Valueva, E. P.; Purdin, M. S.
2015-09-01
The problem about laminar pulsating flow and heat transfer with high pulsation amplitudes of average cross-section velocity in a round tube and in a flat channel is solved using the finite element method. The difference scheme's optimal parameters are determined. Data on the pulsation amplitude and phase are obtained for the hydraulic friction coefficient, tangential stress on the wall, liquid temperature, heat flux on the wall q w (at ϑw = const), and wall temperature ϑw (at q w = const) are obtained. Two characteristic modes, namely, quasi steady-state and high-frequency ones are separated based on the value of dimensionless pulsation frequency. During operation in the quasi steady-state mode, the values of all hydrodynamic and thermal quantities correspond to the values of time-average velocity at the given time instant. For operation in the high-frequency mode, it is shown that the dependences of the pulsating components of hydrodynamic and thermal quantities on the dimensionless pulsation frequency have the same pattern for rectilinear channels having different shapes of their cross section. It is found that certain nodal points exist on the distribution of thermal characteristics along the tube (liquid temperature, heat flux density on the wall at ϑw = const, and wall temperature at q w = const) in which the values of these quantities remain unchanged. The distances between the nodal points decrease with increasing the pulsation frequency. The pulsations of thermal quantities decay over the tube length.
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.
2005-06-01
AFRL-VA-WP-TR-2005-3060 AIR VEHICLES TECHNOLOGY INTEGRATION PROGRAM (AVTIP) Delivery Order 0020 : Prediction Of... Technology Integration Program (AVTIP) 5b. GRANT NUMBER Delivery Order 0020 : Prediction Of Manufacturing Tolerances For Laminar Flow 5c. PROGRAM
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...
Laminar flow control research at TsAGI: Past and present
NASA Astrophysics Data System (ADS)
Chernyshev, S. L.; Kiselev, A. Ph.; Kuryachii, A. P.
2011-04-01
This paper presents a brief review of activities in laminar flow control being performed at the Central Aerohydrodynamic Institute named after Prof. N.E. Zhukovsky (TsAGI). These efforts are focused on the improvement of the existing laminar flow control methods and on the development of new ones. The investigations have demonstrated the effectiveness of aircraft surface laminarization applications with the aim of friction drag reduction. The opportunity of considerable delaying of laminar-turbulent transition due to special wing profile geometry and using boundary layer suction and surface cooling has been verified at sub- and supersonic speeds through various wind tunnel testing at TsAGI and during flying laboratory experiments at the Flight Research Institute (LII). The investigations on using hybrid laminar flow control systems for friction drag reduction were also carried out. New techniques of laminar flow control were proposed, in particular, the method of local heating of the wing leading edge, boundary layer laminarization by means of receptivity control, and electrohydrodynamic methods of boundary layer stability control.
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.
NASA Astrophysics Data System (ADS)
Novak, Milos H.; Nowak, Edwin S.
1993-12-01
To analyze the laminar natural convection heat transfer and fluid flow distribution in vertical rectangular cavities with or without inner partitions, the personal computer finite difference program entitled CAV is used. The CAV program was tested successfully for slender cavities with aspect ratios as high as R = H/ L = 90 and for the Grashof numbers, based on the cavity height, up to GrH = 3 x10 9. To make the CAV program useful for a number of applications, various types of boundary conditions can also be imposed on the program calculations. Presented are program applications dealing with the 2-D numerical analysis of natural convection heat transfer in very slender window cavities with and without small inner partitions and recommendations are made for window design.
Heat transfer by laminar flow in a vertical pipe with twisted-tape inserts
NASA Astrophysics Data System (ADS)
Klaczak, A.
Heat transfer for laminar flow of water in an air-cooled vertical copper pipe with four twisted-tape inserts was determined experimentally. The tests were executed for laminar flow within 110<=Re<=1500, 8.1<=Gz <= 82.0 and 1.62<=y<=5.29. The correlation equation for heat transfer was defined for the tested range. The obtained results were compared to the results of other authors.
A preliminary design study on an acoustic muffler for the laminar flow transition research apparatus
NASA Technical Reports Server (NTRS)
Abrahamson, A. L.
1984-01-01
An acoustic muffler design of a research tool for studying laminar flow and the mechanisms of transition, the Laminar Flow and Transition Research Apparatus (LFTRA) is investigated. Since the presence of acoustic pressure fluctuations is known to affect transition, low background noise levels in the test section of the LFTRA are mandatory. The difficulties and tradeoffs of various muffler design concepts are discussed and the most promising candidates are emphasized.
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.
A fundamental study of suction for Laminar Flow Control (LFC)
NASA Technical Reports Server (NTRS)
Watmuff, Jonathan H.
1992-01-01
This report covers the period forming the first year of the project. The aim is to experimentally investigate the effects of suction as a technique for Laminar Flow Control. Experiments are to be performed which require substantial modifications to be made to the experimental facility. Considerable effort has been spent developing new high performance constant temperature hot-wire anemometers for general purpose use in the Fluid Mechanics Laboratory. Twenty instruments have been delivered. An important feature of the facility is that it is totally automated under computer control. Unprecedently large quantities of data can be acquired and the results examined using the visualization tools developed specifically for studying the results of numerical simulations on graphics works stations. The experiment must be run for periods of up to a month at a time since the data is collected on a point-by-point basis. Several techniques were implemented to reduce the experimental run-time by a significant factor. Extra probes have been constructed and modifications have been made to the traverse hardware and to the real-time experimental code to enable multiple probes to be used. This will reduce the experimental run-time by the appropriate factor. Hot-wire calibration drift has been a frustrating problem owing to the large range of ambient temperatures experienced in the laboratory. The solution has been to repeat the calibrations at frequent intervals. However the calibration process has consumed up to 40 percent of the run-time. A new method of correcting the drift is very nearly finalized and when implemented it will also lead to a significant reduction in the experimental run-time.
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.
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.).
Method and apparatus for detecting laminar flow separation and reattachment
NASA Technical Reports Server (NTRS)
Stack, John P. (Inventor); Mangalam, Sivaramakrishnan M. (Inventor)
1990-01-01
The invention is a method and apparatus for simultaneously detecting laminar separation and reattachment of a fluid stream such as an airstream from and to the upper surface of an airfoil by simultaneously sensing and comparing a plurality of output signals. Each signal represents the dynamic shear stress at one of an equal number of sensors spaced along a straight line on the surface of the airfoil that extends parallel to the airstream. The output signals are simultaneously 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.
Topologically Derived Separation Conditions for Two- and Three-Dimensional Laminar Flows
NASA Technical Reports Server (NTRS)
Tobak, Murray; Davis, Sanford S. (Technical Monitor)
1996-01-01
Topological concepts are used to derive separation conditions for two- and three-dimensional laminar flows. The result for two-dimensional flow reproduces the form of the well-known Stratford criterion. An extension makes the form applicable to the symmetry plane of a three-dimensional flow.
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.
Ledezma, G.A.; Campo, A.
1999-04-01
The utilization of internal longitudinal finned tubes has received unparallel attention in the heat transfer literature over the years as a result of its imminent application in high performance compact heat exchangers to enhance the heat transfer between laminar streams of viscous fluids and tube walls. Here, the central goal of this paper is to report a simple approximate way for the prediction of the two asymptotes for the local Nusselt number in laminar forced convection flows inside internal longitudinal finned tubes. The computational attributes of the Method Of Lines (MOL) are propitious for the determination of asymptotic temperature solutions and corresponding heat transfer rates (one for Z {r_arrow} 0 and the other for z {r_arrow} {infinity}). The two local Nusselt number sub-distributions, namely Nu{sub z{r_arrow}0} and Nu{sub z{r_arrow}{infinity}}, blend themselves into an approximate Nusselt number distribution that covers the entire z-domain in a natural way.
Flight experiments on laminar flow control in swept-wing boundary layers
NASA Astrophysics Data System (ADS)
Saric, William; Reed, Helen; Carpenter, Andrew; Kluzek, Celine; Hunt, Lauren; Schouten, Shane
2006-11-01
Data are presented on boundary-layer transition to turbulence in low-disturbance environments. It uses a combination of hotfilm anemometry and infra-red thermography to study a variety of roughness related issues in flight. The hotfilm measurements give the important passband and spanwise scales while the thermography gives transition location. A swept-wing model is mounted on the wing of a Cessna O-2 aircraft. An Euler code is used calculate the aircraft flowfield while parabolized stability equations correlate the stability measurements and transition locations. The laminarization scheme of spanwise-periodic distributed roughness elements is investigated at chord Reynolds numbers of 7.5 million. In the past year, a number of flight tests have been conducted. Measurements were made to determine the pressure distribution on the model and the transition locations for clean configurations, and transition locations for enhanced surface roughness that simulates an operational surface finish. For clean configurations, natural laminar flow was achieved over 80% of the surface of a 30^o swept-wing model at chord Reynolds numbers of 7.55 million. The corresponding amplification factors were at N = 14.
Flight experiments on laminar flow control in swept-wing boundary layers.
NASA Astrophysics Data System (ADS)
Saric, William; Carpenter, Andrew; Reed, Helen
2007-11-01
Data are presented on boundary-layer transition to turbulence in low-disturbance environments. The measurements include infra-red thermography to study roughness related issues of boundary-layer transition in flight. A swept-wing model is mounted on the wing of a Cessna O-2 aircraft where an Euler code is used calculate the aircraft flowfield a nonlinear parabolized stability equations correlate the stability measurements and transition locations. The laminarization scheme of spanwise-periodic distributed roughness elements (DRE) is investigated at chord Reynolds numbers of 8 million. Measurements were made to determine the transition locations for clean configurations and transition locations for enhanced surface roughness that simulates an operational surface finish. For clean configurations, natural laminar flow was achieved over 80% of the surface of a 37 swept-wing model at chord Reynolds numbers of 8.1 million. With a background surface roughness of 1.1 μm rms, transition moved forward to 30% chord. The DRE moved transition to 60% chord.
Numerical Study of Laminar Flow over Acoustic Cavities
NASA Astrophysics Data System (ADS)
Owen, Matthew; Cheng, Gary
2016-11-01
Fluid flow over an open cavity often emits acoustic waves with certain natural frequencies dependent on the geometry of the cavity and the properties and flow conditions of the fluid. Numerical studies of this kind, Computational Aeroacoustics (CAA), pose a grave challenge to the accuracy and efficiency of numerical methods. This project examines the Space-Time Conservation Element Solution Element (CESE) method developed by Dr. S.C. Chang at NASA GRC and compares numerical results of two-dimensional flow to previous experimental data found in literature. The conclusion the project reached is that the test data agrees well with one of the modes of the predicted frequencies, and that further testing is needed to be able to match experimental results. Funding from NSF REU site Grant EEC 1358991 is greatly appreciated.
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.
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 laminar flow electroporation system for efficient DNA and siRNA delivery.
Wei, Zewen; Zhao, Deyao; Li, Xueming; Wu, Mengxi; Wang, Wei; Huang, Huang; Wang, Xiaoxia; Du, Quan; Liang, Zicai; Li, Zhihong
2011-08-01
By introducing a hydrodynamic mechanism into a microfluidics-based electroporation system, we developed a novel laminar flow electroporation system with high performance. The laminar buffer flow implemented in the system separated the cell suspension flow from the electrodes, thereby excluding many unfavorable effects due to electrode reaction during electroporation, such as hydrolysis, bubble formation, pH change, and heating. Compared to conventional microfluidic electroporation systems, these improvements significantly enhanced transfection efficiency and cell viability. Furthermore, successful electrotransfection of plasmid DNA and, more importantly, synthetic siRNA, was demonstrated in several hard-to-transfect cell types using this system.
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.
NASA Technical Reports Server (NTRS)
Srokowski, A. J.
1978-01-01
The problem of obtaining accurate estimates of suction requirements on swept laminar flow control wings was discussed. A fast accurate computer code developed to predict suction requirements by integrating disturbance amplification rates was described. Assumptions and approximations used in the present computer code are examined in light of flow conditions on the swept wing which may limit their validity.
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.
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.
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.
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.
Quinlan, Nathan J; Dooley, Patrick N
2007-08-01
Viscous shear stress and Reynolds stress are often used to predict hemolysis and thrombosis due to flow-induced stress on blood elements in cardiovascular devices. These macroscopic stresses are distinct from the true stress on an individual cell, which is determined by the local microscale flow field. In this paper the flow-induced stress on blood cells is calculated for laminar and turbulent flow, using simplified models for cells and for turbulent eddies. The model is applied to estimate shear stress on red blood cells in flow through a prosthetic heart valve, using the energy spectral density measured by Liu et al. [J. Biomech. Eng. 122:118-124, 2000]. Results show that in laminar flow, the maximum stress on a cell is approximately equal to the macroscopic viscous shear stress. In turbulent flow through a prosthetic heart valve, the estimated root mean square of flow-induced stress on a cell is at least an order of magnitude less than the Reynolds stress. The results support the hypothesis that smaller turbulent eddies cause higher stress on cells. However, the stress due to an eddy depends on the velocity scale of the eddy as well as its length scale. For the heart valve flow investigated, turbulence contributes to flow-induced stress on cells almost equally across a broad range of the frequency spectrum. The model suggests that Reynolds stress alone is not an adequate predictor of cell damage in turbulent flow, and highlights the importance of the energy spectral density.
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 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.
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.
A Numerical Investigation of Controllably Flexible Hydrofoil in Laminar Flows
NASA Astrophysics Data System (ADS)
He, G. Y.; Zhang, X.; Zhang, S. G.; He, G. W.
Aquatic animals, such as fishes, whales, seals and penguins, are naturally born to be flexible and deformable, which promise their effective locomotion through water. They are able to produce hydrodynamic thrust by active control of their body configurations. That is, the aquatic animals could wiggle their flexible bodies at an appropriate frequency and amplitude suitable to the hydrodynamics surrounding them. However, the mechanism for the active controls has not been adequately understood yet and attracts current research. One obstacle which hinders such investigation is the difficulty in experimental measurements of the flows around the wiggling bodies, and thus numerical simulation is becoming an indispensable alternative. In the paper, an immersed boundary method is developed to simulate the NACA 65-10 hydrofoil. It is observed that a wiggling hydrofoil exhibits a higher thrust while a stationary hydrofoil offers little improvement.
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.
NASA Technical Reports Server (NTRS)
Sohn, Jeong L.
1988-01-01
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.
The silent base flow and the sound sources in a laminar jet.
Sinayoko, Samuel; Agarwal, Anurag
2012-03-01
An algorithm to compute the silent base flow sources of sound in a jet is introduced. The algorithm is based on spatiotemporal filtering of the flow field and is applicable to multifrequency sources. It is applied to an axisymmetric laminar jet and the resulting sources are validated successfully. The sources are compared to those obtained from two classical acoustic analogies, based on quiescent and time-averaged base flows. The comparison demonstrates how the silent base flow sources shed light on the sound generation process. It is shown that the dominant source mechanism in the axisymmetric laminar jet is "shear-noise," which is a linear mechanism. The algorithm presented here could be applied to fully turbulent flows to understand the aerodynamic noise-generation mechanism.
NASA Technical Reports Server (NTRS)
Albers, J. A.; Gregg, J. L.
1974-01-01
A finite-difference program is described for calculating the viscous compressible boundary layer flow over either planar or axisymmetric surfaces. The flow may be initially laminar and progress through a transitional zone to fully turbulent flow, or it may remain laminar, depending on the imposed boundary conditions, laws of viscosity, and numerical solution of the momentum and energy equations. The flow may also be forced into a turbulent flow at a chosen spot by the data input. The input may contain the factors of arbitrary Reynolds number, free-stream Mach number, free-stream turbulence, wall heating or cooling, longitudinal wall curvature, wall suction or blowing, and wall roughness. The solution may start from an initial Falkner-Skan similarity profile, an approximate equilibrium turbulent profile, or an initial arbitrary input profile.
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.
Effect of laminar air flow and clean-room dress on contamination rates of intravenous admixtures.
Brier, K L; Latiolais, C J; Schneider, P J; Moore, T D; Buesching, W J; Wentworth, B C
1981-08-01
The effect of laminar air flow conditions and clean-room dress on the microbial contamination rates of intravenous admixtures was investigated. Intravenous admixtures were prepared by one investigator using aseptic technique under four environmental conditions: laminar air flow conditions with clean-room dress; laminar air flow without clean-room dress; clean table top with clean-room dress; and clean table top without clean-room dress. In each environmental condition, 350 admixtures were compounded. Negative-control samples (n = 150) were also tested, as were 10 positive-control samples. Samples were tested in each of two growth media and incubated at 35 degrees C for 14 days or until growth occurred. The incidence of contamination of admixtures compounded in laminar air flow conditions was significantly less than the contamination of those compounded on a clean table top (p less than 0.05) regardless of the operator's dress. The incidence of contamination of admixtures compounded while wearing clean-room dress was not significantly different from those prepared while not wearing clean-room dress regardless of the environment in which the admixture was prepared. The overall low level of contamination [0.79% (11/1400)] was inconclusive regarding the effect of dress on the incidence of contamination when admixtures were prepared under LAF conditions. It is concluded that, when one adheres to aseptic technique, the environment in which admixtures are compounded is the most important variable affecting the microbial contamination rate.
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,...
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...
Laminar and turbulent nozzle-jet flows and their acoustic near-field
NASA Astrophysics Data System (ADS)
Bühler, Stefan; Obrist, Dominik; Kleiser, Leonhard
2014-08-01
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 ReD = 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.
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 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.
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.
Experiments on densely-loaded non-Newtonian slurries in laminar and turbulent pipe flows
NASA Astrophysics Data System (ADS)
Park, J. T.; Mannheimer, R. J.; Grimley, T. A.; Morrow, T. B.
1988-02-01
An experimental description of the flow structure of non-Newtonian slurries in the laminar, transitional, and full turbulent pipe flow regimes is the primary objective of this research. Measurements include rheological characterization of the fluid and local fluid velocity measurements with a laser Doppler velocimeter (LDV). Optical access to the flow is gained through a test section and model slurry which are both transparent. The model slurry is formulated from silica gel particles and hydrocarbon liquid mixture whose indices of refraction are matched so that light is not scattered from the particles. Experiments are being conducted in a large-scale pipe slurry flow facility with an inside pipe diameter of 51 mm (2 inches). Detailed flow measurements including turbulence quantities such as Reynolds stress were measured with a two-component two-color LDV. The present research indicates that non-Newtonian slurries are possible with concentrations of a few percent by weight of small particles whose sizes are one micron or less. A non-Newtonian slurry from small particles could maintain large particles (100 micron size) at high concentrations in suspension almost indefinitely. Such a slurry would prevent particle fallout and its associated problems. Velocity profiles were acquired by the LDV in the laminar, transitional, and turbulent flow regimes. The velocity profile for laminar flow was in agreement with theory. The range of the transition region was 21 percent of the transition velocity in comparison to 50 percent for a Newtonian fluid.
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
The response of an elastic splitter plate attached to a cylinder to laminar pulsatile flow
NASA Astrophysics Data System (ADS)
Kundu, Anup; Soti, Atul K.; Bhardwaj, Rajneesh; Thompson, Mark C.
2017-01-01
The flow-induced deformation of a thin, elastic splitter plate attached to the rear of a circular cylinder and subjected to laminar pulsatile inflow is investigated. The cylinder and elastic splitter plate are contained within a narrow channel and the Reynolds number is mostly restricted to Re = 100, primarily covering the two-dimensional flow regime. An in-house fluid-structure interaction code is employed for simulations, which couples a sharp-interface immersed boundary method for the fluid dynamics with a finite-element method to treat the structural dynamics. The structural solver is implicitly (two-way) coupled with the flow solver using a partitioned approach. This implicit coupling ensures numerical stability at low structure-fluid density ratios. A power spectrum analysis of the time-varying plate displacement shows that the plate oscillates at more than a single frequency for pulsatile inflow, compared to a single frequency observed for steady inflow. The multiple frequencies obtained for the former case can be explained by beating between the applied and plate oscillatory signals. The plate attains a self-sustained time-periodic oscillation with a plateau amplitude in the case of steady flow, while the superimposition of pulsatile inflow with induced plate oscillation affects the plateau amplitude. Lock-in of the plate oscillation with the pulsatile inflow occurs at a forcing frequency that is twice of the plate natural frequency in a particular mode and this mode depends on the plate length. The plate displacement as well as pressure drag increases at the lock-in condition. The percentage change in the maximum plate displacement, and skin-friction and pressure drag coefficients on the plate, due to pulsatile inflow is quantified. The non-linear dynamics of the plate and its coupling with the pulsatile flow are briefly discussed.
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.
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)
Active Flow Control on Laminar flow over a Backward facing step
NASA Astrophysics Data System (ADS)
Mushyam, Aditya; Bergada, Josep M.
2015-09-01
In the present study, two dimensional flow over a backward-facing step in laminar flow regime with application of active flow control (AFC) technique is analysed. The aim of the present work is to gauge the effectiveness of implementing AFC to reduce drag and study its effects on flow characteristics. In order to analyse the influence of AFC on the boundary layer and the downstream vortex shedding, two different kinds of AFC techniques have been used in this study namely zero net mass flow actuators and fluidic actuators. A parametric non dimensional analysis has been carried out by varying the frequency from 0.025 to 0.1 and jet amplitude from 0.05 and 1. Four different positions of the groove were simulated; groove was respectively located at 0.024a, 0.047a, 0.072a and 0.097a, measured upstream from the right side upper edge. Three different non dimensional groove widths 0.023a, 0.048a and 0.073a were also evaluated, where a is the step height. The idea behind this study was to determine an optimal configuration to reduce the drag on the step and to suppress the vortex dissipation in the wake of the step. It was observed that when using an AFC frequency ± 10% of the vortex shedding one, was causing the maximum drag reduction. When comparing the effects of zero net mass flow actuators with the fluidic actuators, it was observed that zero net mass flow actuators were more effective.
Grid-refinement study of hypersonic laminar flow over a 2-D ramp
NASA Technical Reports Server (NTRS)
Thomas, James L.; Rudy, David H.; Kumar, Ajay; Van Leer, Bram
1991-01-01
Computations were made for those test cases of Problem 3 which were designated as laminar flows, viz., test cases 3.1, 3.2, 3.4, and 3.5. These test cases corresponded to flows over a flat plate and a compression ramp at high Mach number and at high Reynolds number. The computations over the compression ramps indicate a substantial streamwise extent of separation. Based on previous experience with separated laminar flows at high Mach numbers which indicated a substantial effect with spatial grid refinement, a series of computations with different grid sizes were performed. Also, for the flat plate, comparisons of the results for two different algorithms were made.
Stability analysis for laminar flow control, part 1
NASA Technical Reports Server (NTRS)
Benney, D. J.; Orszag, S. A.
1977-01-01
The basic equations for the stability analysis of flow over three dimensional swept wings are developed and numerical methods for their solution are surveyed. The equations for nonlinear stability analysis of three dimensional disturbances in compressible, three dimensional, nonparallel flows are given. Efficient and accurate numerical methods for the solution of the equations of stability theory were surveyed and analyzed.
NASA Technical Reports Server (NTRS)
Wood, Richard M. (Inventor); Bauer, Steven X. S. (Inventor)
1992-01-01
The invention is a natural flow wing and a method for constructing the same. The method comprises contouring a three-dimensional upper surface and a three-dimensional lower surface of the natural flow wing independently of one another into a prescribed shape. Experimental data and theoretical analysis show that flow and pressure-loading over an upper surface of a wing tend to be conical about an apex of the wing, producing favorable and unfavorable regions of performance based on drag. The method reduces these unfavorable regions by shaping the upper surface such that the maximum thickness near a tip of the natural flow wing moves aft, thereby, contouring the wing to coincide more closely with the conical nature of the flow on the upper surface. Nearly constant compressive loading characterizes the flow field over a lower surface of the conventional wing. Magnitude of these compressive pressures on the lower surface depends on angle of attack and on a streamwise curvature of the lower surface of the wing and not on a cross-sectional spanwise curvature. The method, thereby, shapes the lower surface to create an area as large as possible with negative slopes. Any type of swept wing may be used to obtain the final, shaped geometry of the upper and lower surfaces of the natural flow wing.
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.
On the flow structures and hysteresis of laminar swirling jets
NASA Astrophysics Data System (ADS)
Ogus, G.; Baelmans, M.; Vanierschot, M.
2016-12-01
In this paper different flow patterns of an annular jet with a stepped-conical nozzle as well as the transition between these patterns are numerically investigated as a function of the swirl number S which is the ratio of tangential momentum flux to axial momentum flux. The Reynolds number of the jet based on the axial velocity and the nozzle hydraulic diameter is 180. The 3D Navier Stokes equations are solved using the direct numerical simulation. Four different flow patterns are identified and their associated flow structures are discussed. Starting from an annular jet at zero swirl, spinning vortices around the central axis originate with increasing swirl. As the swirl is further increased, the onset of vortex breakdown occurs, followed by jet attachment to the nozzle. Decreasing the swirl number back from this flow pattern, the Coanda effect near the nozzle outlet creates a wall jet. This wall jet remains till the decreasing swirl number equals to zero, showing hysteresis in flow patterns between an increase and a subsequent decrease in swirl. The determined flow states are experimentally validated. Potential applications related to these flow patterns and their hysteretic behavior are also briefly discussed.
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.
The Stability of Particulate Ladden Laminar Boundary-Layer Flows
NASA Technical Reports Server (NTRS)
Acrivos, Andreas
1996-01-01
During the course of this investigation, the following two topics were studied theoretically: (1) forced convection and sedimentation past a flat plate, and (2) the effect of rain on airfoil performance. The prototype of the first topic is that of air flowing past the wing section of an aircraft under heavy rain and high windshear. The long-range objective of this project was to identify the various factors determining the dynamics of the flow and then to develop a theoretical framework for modeling such systems. The second topic focused on the idea that the presence of the gas-liquid interface (being the air flow around the airfoil and the thin liquid film created by the rain) accelerates flow separation and thus induces performance losses.
Global pressure relaxation for laminar two-dimensional internal flow
NASA Technical Reports Server (NTRS)
Rosenbaum, D.; Rubin, S. G.
1990-01-01
This study extends the reduced Navier-Stokes (RNS) global pressure relaxation procedure developed by Rubin and co-workers for external flow to internal flow applications. The streamwise pressure gradient is split into a backward-differenced or initial value component, as in boundary layer marching, and a forward-differenced or boundary value component that represents the elliptic downstream effects. The streamwise convection terms are upwind-differenced and all other streamwise derivatives are backward-differenced. A standard boundary layer marching technique imbedded in a conventional line relaxation technique is obtained. For compressible flow the pressure iteration determines the interior flow interaction as well as the inlet mass flux that is consistent with the outflow pressure boundary condition. Results have been computed for incompressible flow in both rectangular and curved channels, and for subsonic compressible flow in the simulation of an aerofoil in a wind tunnel. Converged solutions were obtained over a range of Reynolds numbers generating small to moderately large separation bubbles.
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.
Wu, Xiaohua; Moin, Parviz; Adrian, Ronald J.; ...
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.
The stability of laminar flow past a sphere
NASA Technical Reports Server (NTRS)
Pretsch, J
1942-01-01
As a contribution to the problem of turbulence on a surface of rotation, the method of small oscillation is applied to the flow past a sphere. It was found that the method developed for two-dimensional flow is applicable without modifications. The frictional layer in the vicinity of the stagnation point of a surface of rotation is less stable against small two-dimensional disturbances than in the stagnation point itself, as proved from an analysis of the velocity distribution made by Homann.
A laminar flow microfluidic fuel cell for detection of hexavalent chromium concentration
Ye, Dingding; Yang, Yang; Li, Jun; Zhu, Xun; Liao, Qiang; Zhang, Biao
2015-01-01
An electrochemical hexavalent chromium concentration sensor based on a microfluidic fuel cell is presented. The correlation between current density and chromium concentration is established in this report. Three related operation parameters are investigated, including pH values, temperature, and external resistance on the sensor performance. The results show that the current density increases with increasing temperature and the sensor produces a maximum regression coefficient at the catholyte pH value of 1.0. Moreover, it is found that the external resistance has a great influence on the linearity and current densities of the microfluidic sensor. Owing to the membraneless structure and the steady co-laminar flow inside the microchannel, the microfluidic sensor exhibits short response time to hexavalent chromium concentration. The laminar flow fuel cell sensor provides a new and simple method for detecting hexavalent chromium concentration in the industrial wastewater. PMID:26649130
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.
NASA Astrophysics Data System (ADS)
Wu, Xiaohua; Moin, Parviz; Adrian, Ronald; Baltzer, Jon; Hickey, Jean-Pierre
2012-11-01
The most fundamental internal flow, smooth pipe from a slightly perturbed laminar inlet state continuously through bypass transition to fully-developed turbulence, has been computed using DNS over an axial domain length of 250 pipe radii. In the fully-developed turbulent region, mean and second-order turbulent statistics including the rate of viscous dissipation show excellent agreement with those obtained from an additional simulation using the conventional streamwise periodic boundary condition over an axial domain length of 30 pipe radii. Friction factor follows analytical solution prior to breakdown, and agrees with Moody's correlation after the completion of transition. During transition it exhibits an overshoot. Breakdown of the laminar pipe flow is characterized by the formation of large Lambda-shaped vortices pointing upstream, followed by their subsequent generation of small hairpin packets inclined towards the downstream direction.
Design aspects of long range supersonic LFC airplanes with highly swept wings. [laminar flow control
NASA Technical Reports Server (NTRS)
Pfenninger, W.; Vemuru, C. S.
1990-01-01
Studies on supersonic long-range LFC (laminar flow control) aircraft were performed with the aim of maximizing L/D and alleviating sonic boom during supersonic cruise. It is found that configurations with highly swept LFC wings of very high structural aspect ratio, with the sweep increasing toward the wing root and braced externally by wide chord laminarized struts, appear especially promising. In the supersonic cruise design condition the wing upper surface isobars are swept such that the flow in the direction normal to them is transonic with embedded supersonic zones and practically shock-free over most of the span, with M-perpendicular equal to the two-dimensional design values of advanced SC LFC airfoils, e.g., of the X-787 or X-6 type.
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)
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.
Simulation of two-dimensional fully developed laminar flow for a magneto-hydrodynamic (MHD) pump.
Wang, Pei-Jen; Chang, Chia-Yuan; Chang, Ming-Lang
2004-07-30
MHD micro-pumps circumvent the wear and fatigue caused by high pressure-drop across the check valves of mechanical micro-pumps in micro-fluidic systems. Early analyses of the fluid flow for MHD micro-pumps were mostly made possible by the Poiseuille flow theory; however, this conventional laminar approach cannot illustrate the effects of various channel sizes and shapes. This paper, therefore, presents a simplified MHD flow model based upon steady state, incompressible and fully developed laminar flow theory to investigate the characteristics of a MHD pump. Inside the pump, flowing along the channel is the electrically conducting fluid flowing driven by the Lorentz forces in the direction perpendicular to both dc magnetic field and applied electric currents. The Lorentz forces were converted into a hydrostatic pressure gradient in the momentum equations of the MHD channel flow model. The numerical simulations conducted with the explicit finite difference method show that the channel dimensions and the induced Lorentz forces have significant influences on the flow velocity profile. Furthermore, the simulation results agree well with the experimental results published by other researchers.
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.
Analysis of first stage ignition delay times of dimethyl ether in a laminar flow reactor
NASA Astrophysics Data System (ADS)
Wada, Tomoya; Sudholt, Alena; Pitsch, Heinz; Peters, Norbert
2013-10-01
The combustion chemistry of the first stage ignition and chemistry/flow interactions are studied for dimethyl ether (DME) with a mathematical analysis of two systems: a plug flow reactor study is used to reduce the reaction chemistry systematically. A skeletal reaction mechanism for the low temperature chemistry of DME until the onset of ignition is derived on the basis of the detailed DME mechanism of the Lawrence Livermore National Laboratory - see Curran, Fischer and Dryer, Int. J. Chem. Kinetics, Vol. 32 (2000). It is shown that reasonably good results for ignition delay times can be reached using a simple system of three ordinary differential equations and that the resulting analytical solution depends only on two reaction rates and the initial fuel concentration. The stepwise reduction of the system based on assumptions yields an understanding on why these reactions are so important. Furthermore, the validation of the assumptions yields insight into the influence of the fuel and the oxygen concentration on the temperature during the induction phase. To investigate the influence of chemistry/flow interactions, a 2D model with a laminar Hagen-Poiseuille flow and 2D-polynomial profiles for the radial species concentration is considered. For the 2D model, it is found that only the diffusion coefficients and the reactor radius need to be taken into consideration additionally to describe the system sufficiently. Also, the coupling of flow and chemistry is clarified in the mathematical analysis. The insight obtained from the comparison of the 2D model and the plug flow model is used to establish an average velocity for the conversion of ignition locations to ignition delay times in a laminar flow reactor. Finally, the 2D analytical solution is compared against new experimental data, obtained in such a laminar flow reactor for an undiluted DME/air mixture with an equivalence ratio of φ = 0.835 and a temperature range of 555 to 585 K at atmospheric pressure.
Adhesion of Streptococcus mutans to various dental materials in a laminar flow chamber system.
Rosentritt, Martin; Hahnel, Sebastian; Gröger, Gerhard; Mühlfriedel, Bastian; Bürgers, Ralf; Handel, Gerhard
2008-07-01
Newly developed dental materials have to be tested for their susceptibility to adhere bacteria causing caries and periodontitis. The objective of this study was to establish an in vitro laminar flow chamber assay for dental material evaluation with regard to the adhesion of oral bacteria. Test specimens of commonly used dental materials (ceramic (five brands of ceramics, n = 15/brand), composite (eight brands of composites, n = 15/brand), and alloy (two brands of alloys, n = 15/brand) specimens) were inserted in a laminar flow chamber system and rinsed with artificial saliva (2 h) and Streptococcus mutans NCTC 10,449 suspension (4 h) successively. The amount of adhered bacteria was quantified using a Resazurin reduction assay (Alamar Blue). Statistical analysis was performed using the Mann-Whitney U-test (alpha = 0.05). Regarding adhesion of Streptococcus mutans, significant differences between the various material classes were found. Highest fluorescence values (ranging from 973 to 3145), correlating with high bacterial adhesion, were found on composite samples, and lowest values (173-272) were found on the alloys. Ceramic specimens showed an intermediate adhesion of Streptococcus mutans (fluorescence values from 532 to 1326). Streptococcus mutans NCTC 10449 adhered differently to the various classes of dental materials. The established laminar flow chamber device provides a suitable method for evaluating the adhesion of oral bacteria to dental material surfaces.
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.
Spatial variation of the magnetic field inside laminar flows of a perfect conductive fluid
NASA Astrophysics Data System (ADS)
Duka, Bejo; Boçi, Sonila
2017-01-01
The steady state of a perfect conductive fluid in laminar flow resulting from the ‘Hall effect’ is studied. Using the Maxwell equations, the spatial variation of the magnetic field in the steady state is calculated for three cases of different fluid flow geometries: flow between two infinite parallel planes, flow between two coaxial infinite-long cylinders and flow between two concentric spheres. According to our calculation of the three cases, the spatial variation of the magnetic field depends on the flow velocity. The magnetic field is strengthened in layers where the velocity is greater, but this dependency is negligible for non relativistic flows. Our approach in this study provides an example of how to receive interesting results using only basic knowledge of physics and mathematics.
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.
A Laminar Flow-Based Microfluidic Tesla Pump via Lithography Enabled 3D Printing.
Habhab, Mohammed-Baker; Ismail, Tania; Lo, Joe Fujiou
2016-11-23
Tesla turbine and its applications in power generation and fluid flow were demonstrated by Nicholas Tesla in 1913. However, its real-world implementations were limited by the difficulty to maintain laminar flow between rotor disks, transient efficiencies during rotor acceleration, and the lack of other applications that fully utilize the continuous flow outputs. All of the aforementioned limits of Tesla turbines can be addressed by scaling to the microfluidic flow regime. Demonstrated here is a microscale Tesla pump designed and fabricated using a Digital Light Processing (DLP) based 3D printer with 43 µm lateral and 30 µm thickness resolutions. The miniaturized pump is characterized by low Reynolds number of 1000 and a flow rate of up to 12.6 mL/min at 1200 rpm, unloaded. It is capable of driving a mixer network to generate microfluidic gradient. The continuous, laminar flow from Tesla turbines is well-suited to the needs of flow-sensitive microfluidics, where the integrated pump will enable numerous compact lab-on-a-chip applications.
A Laminar Flow-Based Microfluidic Tesla Pump via Lithography Enabled 3D Printing
Habhab, Mohammed-Baker; Ismail, Tania; Lo, Joe Fujiou
2016-01-01
Tesla turbine and its applications in power generation and fluid flow were demonstrated by Nicholas Tesla in 1913. However, its real-world implementations were limited by the difficulty to maintain laminar flow between rotor disks, transient efficiencies during rotor acceleration, and the lack of other applications that fully utilize the continuous flow outputs. All of the aforementioned limits of Tesla turbines can be addressed by scaling to the microfluidic flow regime. Demonstrated here is a microscale Tesla pump designed and fabricated using a Digital Light Processing (DLP) based 3D printer with 43 µm lateral and 30 µm thickness resolutions. The miniaturized pump is characterized by low Reynolds number of 1000 and a flow rate of up to 12.6 mL/min at 1200 rpm, unloaded. It is capable of driving a mixer network to generate microfluidic gradient. The continuous, laminar flow from Tesla turbines is well-suited to the needs of flow-sensitive microfluidics, where the integrated pump will enable numerous compact lab-on-a-chip applications. PMID:27886051
Laminar Flow About a Rotating Body of Revolution in an Axial Airstream
NASA Technical Reports Server (NTRS)
Schlichting, H.
1956-01-01
We have set ourselves the problem of calculating the laminar flow on a body of revolution in an axial flow which simultaneously rotates about its axis. The problem mentioned above, the flow about a rotating disk in a flow, which we solved some time ago, represents the first step in the calculation of the flow on the rotating body of revolution in a flow insofar as, in the case of a round nose, a small region about the front stagnation point of the body of revolution may be replaced by its tangential plane. In our problem regarding the rotating body of revolution in a flow, for laminar flow, one of the limiting cases is known: that of the body which is in an axial approach flow but does not rotate. The other limiting case, namely the flow in the neighborhood of a body which rotates but is not subjected to a flow is known only for the rotating circular cylinder, aside from the rotating disk. In the case of the cylinder one deals with a distribution of the circumferential velocity according to the law v = omega R(exp 2)/r where R signifies the cylinder radius, r the distance from the center, and omega the angular velocity of the rotation. The velocity distribution as it is produced here by the friction effect is therefore the same as in the neighborhood of a potential vortex. When we treat, in what follows, the general case of the rotating body of revolution in a flow according to the calculation methods of Prandtl's boundary-layer theory, we must keep in mind that this solution cannot contain the limiting case of the body of revolution which only rotates but is not subjected to a flow. However, this is no essential limitation since this case is not of particular importance for practical purposes.
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.
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
Two experimental supercritical laminar-flow-control swept-wing airfoils
NASA Technical Reports Server (NTRS)
Allison, Dennis O.; Dagenhart, J. Ray
1987-01-01
Two supercritical laminar-flow-control airfoils were designed for a large-chord swept-wing experiment in the Langley 8-Foot Transonic Pressure Tunnel where suction was provided through most of the model surface for boundary-layer control. The first airfoil was derived from an existing full-chord laminar airfoil by extending the trailing edge and making changes in the two lower-surface concave regions. The second airfoil differed from the first one in that it was designed for testing without suction in the forward concave region of the lower surface. Differences between the first airfoil and the one from which it was derived as well as between the first and second airfoils are discussed. Airfoil coordinates and predicted pressure distributions for the design normal Mach number of 0.755 and section lift coefficient of 0.55 are given for the three airfoils.
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.
Bacteriological testing of a modified laminar flow microbiological safety cabinet.
Heidt, P J
1982-01-01
A modified microbiological safety cabinet which can be used as a class II and a class III safety cabinet has been bacteriologically tested. This cabinet makes use of a high-speed down-flow air curtain in the front opening to minimize the amount of air escaping over the arms of the operator. By using artificial aerosols and a dummy or a test person placing his arms into the working opening of the cabinet, a transfer from the inside to the environment was detected only when the highest concentration of the test aerosol was used. Since the number of bacteria detected was very low, this is considered to be acceptable. When the cabinet was used as a class III type, with a glove panel mounted in the front opening, leakage from the environment occurred. This could be completely prevented by fixing tape over the hinge of the front panel. The conclusion is drawn that this type of biohazard hood can be safely used as a class II and a class III microbiological safety cabinet, provided the construction of the hinge of the front panel will be adapted to prevent transfer from the environment to the working area.
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.
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}}.
Analysis of laminar flow heat transfer in uniform temperature circular tubes with tape inserts
NASA Astrophysics Data System (ADS)
Manglik, R. M.; Bergles, A. E.
1986-05-01
Constant property, laminar flow heat transfer in a semicircular tube with uniform wall temperature has been analyzed to define the lower bound of heat transfer augmentation in circular tubes with twisted-tape inserts. Two thermal boundary conditions, which correspond to the two extremes of the fin effect of twisted tapes encountered in practical applications, are considered. Numerical solutions, employing finite-difference formulations for the governing momentum and energy equations were carried out for the thermal entrance region and for fully developed flow.
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.
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.
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.
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.
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.
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.
Development of a convective diffusion model for lead pipe rigs operating in laminar flow.
Cardew, P T
2006-06-01
As part of achieving lower lead standards water undertakers are utilising lead pipe rigs to quantify the benefit of treatment measures. A convective diffusion model is developed for lead pipe rigs operating in laminar flow, and applied to the three operating steps of flushing, sampling and stagnation. The model is used to determine the appropriate time-scales for each stage, and the sensitivity of the measure to variations in flow-rate. In contrast to rigs operating in turbulent flow the average lead observed leaving the pipe and that in the pipe, after a period of stagnation, are substantially different. Equations are derived for both, and take into account the residual distribution of lead left in the pipe after flushing. It is shown that the lead concentration observed leaving the pipe is well approximated by a single exponential term in contrast to the concentration within the pipe. Predictions are made on the residual lead concentration that can be achieved through flushing, and its dependence on flow-rate. The relevance of the laminar flow model to that in domestic lead pipes is discussed.
Prediction of laminar and turbulent primary and secondary flows in strongly curved ducts
NASA Technical Reports Server (NTRS)
Kreskovsky, J. P.; Briley, W. R.; Mcdonald, H.
1981-01-01
The analysis is based on a primary secondary velocity decomposition in a given coordinate system, and leads to approximate governing equations which correct an a priori inviscid solution for viscous effects, secondary flows, total pressure distortion, heat transfer, and internal flow blockage and losses. Solution of the correction equations is accomplished as an initial value problem in space using an implicit forward marching technique. The overall solution procedure requires significantly less computational effort than Navier-Stokes algorithms. The solution procedure is effective even with the extreme local mesh resolution which is necessary to solve near wall sublayer regions in turbulent flow calculations. Computed solutions for both laminar and turbulent flow compared very favorably with available analytical and experimental results. The overall method appears very promising as an economical procedure for making detailed predictions of viscous primary and secondary flows in highly curved passages.
Correlations for laminar mixed convection flows on vertical, inclined, and horizontal flat plates
NASA Astrophysics Data System (ADS)
Chen, T. S.; Armaly, B. F.; Ramachandran, N.
1986-11-01
Local Nusselt numbers for laminar mixed convection flows along isothermal vertical, inclined, and horizontal flat plates are presented for the entire mixed convection regime for a wide range of Prandtl numbers. Simple correlation equations for the local and average mixed convection Nusselt numbers are developed, which are found to agree well with the numerically predicted values and available experimental data for both buoyancy assisting and opposing flow conditions. The threshold values of significant buoyancy effects on forced convection and forced flow effects on free convection, as well as the maximum increase in the local mixed convection Nusselt number from the respective pure convection limits, are also presented for all flow configurations. It is found that the buoyancy or forced flow effect can increase the surface heat transfer rate from pure forced or pure free convection by about 20 percent.
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.
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 stresses1. 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 EPCs2,3. 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 microscopy5. 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)6. PMID:22297325
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
2012-01-17
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).
Interaction theory of hypersonic laminar near-wake flow behind an adiabatic circular cylinder
NASA Astrophysics Data System (ADS)
Hinman, W. Schuyler; Johansen, C. T.
2016-11-01
The separation and shock wave formation on the aft-body of a hypersonic adiabatic circular cylinder were studied numerically using the open source software OpenFOAM. The simulations of laminar flow were performed over a range of Reynolds numbers (8× 10^3 < Re < 8× 10^4) at a free-stream Mach number of 5.9. Off-body viscous forces were isolated by controlling the wall boundary condition. It was observed that the off-body viscous forces play a dominant role compared to the boundary layer in displacement of the interaction onset in response to a change in Reynolds number. A modified free-interaction equation and correlation parameter has been presented which accounts for wall curvature effects on the interaction. The free-interaction equation was manipulated to isolate the contribution of the viscous-inviscid interaction to the overall pressure rise and shock formation. Using these equations coupled with high-quality simulation data, the underlying mechanisms resulting in Reynolds number dependence of the lip-shock formation were investigated. A constant value for the interaction parameter representing the part of the pressure rise due to viscous-inviscid interaction has been observed at separation over a wide range of Reynolds numbers. The effect of curvature has been shown to be the primary contributor to the Reynolds number dependence of the free-interaction mechanism at separation. The observations in this work have been discussed here to create a thorough analysis of the Reynolds number-dependent nature of the lip-shock.
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.
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.
Membraneless laminar flow cell for electrocatalytic CO2 reduction with liquid product separation
NASA Astrophysics Data System (ADS)
Monroe, Morgan M.; Lobaccaro, Peter; Lum, Yanwei; Ager, Joel W.
2017-04-01
The production of liquid fuel products via electrochemical reduction of CO2 is a potential path to produce sustainable fuels. However, to be practical, a separation strategy is required to isolate the fuel-containing electrolyte produced at the cathode from the anode and also prevent the oxidation products (i.e. O2) from reaching the cathode. Ion-conducting membranes have been applied in CO2 reduction reactors to achieve this separation, but they represent an efficiency loss and can be permeable to some product species. An alternative membraneless approach is developed here to maintain product separation through the use of a laminar flow cell. Computational modelling shows that near-unity separation efficiencies are possible at current densities achievable now with metal cathodes via optimization of the spacing between the electrodes and the electrolyte flow rate. Laminar flow reactor prototypes were fabricated with a range of channel widths by 3D printing. CO2 reduction to formic acid on Sn electrodes was used as the liquid product forming reaction, and the separation efficiency for the dissolved product was evaluated with high performance liquid chromatography. Trends in product separation efficiency with channel width and flow rate were in qualitative agreement with the model, but the separation efficiency was lower, with a maximum value of 90% achieved.
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.
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.
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.
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.
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.
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.
Analysis of a laminar boundary layer flow over a flat plate with injection or suction
NASA Astrophysics Data System (ADS)
Sadri, S.; Babaelahi, M.
2013-01-01
An analysis is performed to study a laminar boundary layer flow over a porous flat plate with injection or suction imposed at the wall. The basic equations of this problem are reduced to a system of nonlinear ordinary differential equations by means of appropriate transformations. These equations are solved analytically by the optimal homotopy asymptotic method (OHAM), and the solutions are compared with the numerical solution (NS). The effect of uniform suction/injection on the heat transfer and velocity profile is discussed. A constant surface temperature in thermal boundary conditions is used for the horizontal flat plate.
Modification of flow perturbations in a laminar separation bubble by heat transfer
NASA Astrophysics Data System (ADS)
Boiko, A. V.; Dovgal, A. V.; Sorokin, A. M.
2017-02-01
Laminar boundary layer separation in conditions of localized heat transfer is investigated at low subsonic velocity through wind-tunnel measurements and linear stability analysis. A backward-facing step flow is subjected to a stationary temperature variation generated by Peltier elements installed on the test model directly downstream of the separation line. The experimental and theoretical data clarify the response of velocity disturbances in the separation region to the temperature variation, the latter appearing primarily as a modifier of the initial wave spectrum of the amplifying separated layer oscillations.
A method for calculating heat transfer in the laminar flow region of bodies
NASA Technical Reports Server (NTRS)
Allen, H Julian; Look, Bonne C
1943-01-01
This report has been prepared to provide a practical method for determining the chordwise distribution of the rate of heat transfer from the surface of a wing or body of revolution to air. The method is limited in use to the determination of heat transfer from the forward section of such bodies when the flow is laminar. A comparison of the calculated average heat-transfer coefficient for the nose section of the wing of a Lockheed 12-A airplane with that experimentally determined shows a satisfactory agreement. A sample calculation is appended.
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.
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.
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.
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.
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.
Computation of laminar viscous-inviscid interactions in high-speed internal flows
NASA Technical Reports Server (NTRS)
Rudy, David H.; Thomas, James L.; Kumar, Ajay
1991-01-01
A review is given of computations for a series of nominally 2-D laminar viscous-inviscid interactions. Comparisons were made with detailed experimental shock tunnel results. The shock wave boundary layer interactions considered were induced by a compression ramp in one case and by an externally generated incident shock in the second case. In general, good agreement was reached between the grid refined calculations and experiment for the incipient and small separation conditions. For the highly separated flow, 3-D calculations which included the finite span effects of the experiment were required in order to obtain agreement with the data.
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.
Experimental study of supersonic laminar base flow with and without suction
NASA Technical Reports Server (NTRS)
Jakubowski, A. K.; Lewis, C. H.
1973-01-01
Heat-transfer and pressure distributions in laminar separated flows downstream of rearward-facing steps with and without mass suction were investigated at Mach numbers around 4 for the conditions when the boundary-layer thickness was comparable to or larger than the step height. In both suction and no-suction cases, an increase of the step height resulted in a sharp drop of the base heating rates, which then gradually recovered to less than or near attached-flow values obtained with flat-plate configuration. Mass suction from the step base area increased the local heating rates; this effect, however, was relatively weak for laminar flows tested, and the competing effect of the step height clearly predominated. It was found that even removal of the entire incoming boundary layer was not sufficient to raise the poststep heating rates above the flat-plate values. The base pressure in the no-suction, solid-step case correlated reasonably well with the step height-to-boundary-layer thickness ratio and with the Reynolds number based on the step height.
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.
NASA Technical Reports Server (NTRS)
Kim, Sang-Wook
1988-01-01
A velocity-pressure integrated, mixed interpolation, Galerkin finite element method for the Navier-Stokes equations is presented. In the method, the velocity variables were interpolated using complete quadratic shape functions and the pressure was interpolated using linear shape functions. For the two dimensional case, the pressure is defined on a triangular element which is contained inside the complete biquadratic element for velocity variables; and for the three dimensional case, the pressure is defined on a tetrahedral element which is again contained inside the complete tri-quadratic element. Thus the pressure is discontinuous across the element boundaries. Example problems considered include: a cavity flow for Reynolds number of 400 through 10,000; a laminar backward facing step flow; and a laminar flow in a square duct of strong curvature. The computational results compared favorable with those of the finite difference methods as well as experimental data available. A finite elememt computer program for incompressible, laminar flows is presented.
Fully developed laminar slip and no-slip flow in rough microtubes
NASA Astrophysics Data System (ADS)
Akyildiz, F. Talay; Siginer, Dennis A.
2011-08-01
The effect of surface roughness on developed laminar flow in microtubes is investigated. The tube boundary is defined by {r=R[{1+\\varepsilon sin( {λ θ })}]}, with R representing the reference radius and {\\varepsilon} and λ the roughness parameters. The momentum equation is solved using Fourier-Galerkin-Tau method with slip at the boundary. A novel semi-analytical method is developed to predict friction factor and pressure drop in corrugated rough microtubes for continuum flow and slip flow that are not restricted to small values of {\\varepsilon λ } . The analytical solution collapses onto the perturbation solution ofDuan and Muzychka (J. Fluids Eng., 130:031102, 2008) for small enough values of {\\varepsilon λ }.
Simulations of granular bed erosion due to laminar shear flow near the critical Shields number
NASA Astrophysics Data System (ADS)
Derksen, J. J.
2011-11-01
Direct numerical simulations of granular beds consisting of uniformly sized spherical particles being eroded by a shear flow of Newtonian liquid have been performed. The lattice-Boltzmann method has been used for resolving the flow of the interstitial liquid. Fluid and solid dynamics are fully coupled with the particles having finite size and undergoing hard-sphere collisions. Only laminar flow has been considered with particle-based Reynolds numbers in the range 0.02 to 0.6. The parameter range of the simulations covers the transition between static and mobilized beds. The transition occurs for 0.10<θ<0.15 with θ the Shields number. The transition is insensitive of the Reynolds number and the solid-over-liquid density ratio. Incipient bed motion has been interpreted in terms of the probability density functions of the hydrodynamic forces acting on the spheres in the upper layer of the bed.
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-turbulent patterning in wall-bounded shear flows: a Galerkin model
NASA Astrophysics Data System (ADS)
Seshasayanan, K.; Manneville, P.
2015-06-01
On its way to turbulence, plane Couette flow-the flow between counter-translating parallel plates-displays a puzzling steady oblique laminar-turbulent pattern. We approach this problem via Galerkin modelling of the Navier-Stokes equations. The wall-normal dependence of the hydrodynamic field is treated by means of expansions on functional bases fitting the boundary conditions exactly. This yields a set of partial differential equations for spatiotemporal dynamics in the plane of the flow. Truncating this set beyond the lowest nontrivial order is numerically shown to produce the expected pattern, therefore improving over what was obtained at the cruder effective wall-normal resolution. Perspectives opened by this approach are discussed.
Response of hot element wall shear stress gages in laminar oscillating flows
NASA Technical Reports Server (NTRS)
Cook, W. J.; Murphy, J. D.; Giddings, T. A.
1986-01-01
An experimental investigation of the time-dependent response of hot element wall shear stress gages in unsteady periodic air flows is reported. The study has focused on wall shear stress in laminar oscillating flows produced on a flat plate by a free stream velocity composed of a mean component and a superposed sinusoidal variation. Two types of hot element gages, platinum film and flush wire, were tested for values of reduced frequency ranging from 0.14 to 2.36. Values of the phase angle of the wall shear stress variation relative to the free stream velocity, as indicated by the hot element gages, are compared with numerical prediction. The comparisons show that the gages indicate a wall shear stress variation that lags the true variation, and that the gages will also not indicate the correct wall shear stress variation in periodic turbulent flows.
Special considerations in the use of vertical laminar-flow workbenches.
Avis, K E; Levchuk, J W
1984-01-01
The design, operation, and proper use of vertical laminar-flow workbenches are reviewed. Vertical-flow hoods are different from horizontal-flow units in several important ways that must be considered by operators who may have been trained to use the horizontal-flow type. Air in vertical-flow units provides practically no resistance to ingress of air propelled by body motions of the operator or passers-by or from nearby ventilation ducts. The HEPA-filtered air hits the work surface perpendicularly and must travel horizontally to reach the exhaust ducts; thus, manipulations should not be performed close to the work surface. Turbulence patterns around objects in the vertical flow hood will be different from that in horizontal-flow units. Manipulative technique is also different in a vertical-flow hood. Supplies may be arranged to the sides and the back of the area in which manipulations will be performed. Items not sterile, including fingers and hands, must be kept downstream from critical sites. Masks do not have to be worn because of the hood's glass panel. Operators must be cognizant of basic differences between vertical- and horizontal-flow hoods.
Stochastic analysis of the time evolution of laminar-turbulent bands of plane Couette flow.
Rolland, Joran
2015-11-01
This article is concerned with the time evolution of the oblique laminar-turbulent bands of transitional plane Couette flow under the influence of turbulent noise. Our study is focused on the amplitude of modulation of turbulence (the bands). In order to guide the numerical study of the flow, we first perform an analytical and numerical analysis of a Stochastic Ginzburg-Landau (GL) equation for a complex order parameter. The modulus of this order parameter models the amplitude of modulation of turbulence. Firstly, we compute the autocorrelation function of said modulus once the band is established. Secondly, we perform a calculation of average and fluctuations around the exponential growth of the order parameter. This type of analysis is similar to the Stochastic Structural Stability Theory (S3T). We then perform numerical simulations of the Navier-Stokes equations in order to confront these predictions with the actual behaviour of the bands. Computation of the autocorrelation function of the modulation of turbulence shows quantitative agreement with the model: in the established band regime, the amplitude of modulation follows an Ornstein-Uhlenbeck process. In order to test the S3T predictions, we perform quench experiments, sudden decreases of the Reynolds number from uniform turbulence, in which modulation appears. We compute the average evolution of the amplitude of modulation and the fluctuations around it. We find good agreement between numerics and modeling. The average trajectory grows exponentially, at a rate clearly smaller than that of the formation of laminar holes. Meanwhile, the actual time evolution remains in a flaring envelope, centered on the average, and expanding at the same rate. These results provide further validation of the stochastic modeling for the time evolution of the bands for further studies. Besides, they stress on the difference between the oblique band formation and the formation of laminar holes.
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.
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.
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.
Detection near 1-nm with a laminar-flow, water-based condensation particle counter
Hering, Susanne V.; Lewis, Gregory S.; Spielman, Steven R.; Eiguren-Fernandez, Arantzazu; Kreisberg, Nathan M.; Kuang, Chongai; Attoui, Michel
2016-11-18
Presented is a laminar-flow, water-based condensation particle counter capable of particle detection near 1 nm. This instrument employs a three-stage, laminar-flow growth tube with a “moderator” stage that reduces the temperature and water content of the output flow without reducing the peak supersaturation, and makes feasible operation at the large temperature differences necessary for achieving high supersaturations. The instrument has an aerosol flow of 0.3 L/min, and does not use a filtered sheath flow. It is referred to as a “versatile” water condensation particle counter, or vWCPC, as operating temperatures can be adjusted in accordance with the cut-point desired. When operated with wall temperatures of ~2°C, >90°C, and ~22°C for the three stages, respectively, the vWCPC detects particles generated from a heated nichrome wire with a 50% efficiency cut-point near 1.6 nm mobility diameter. At these operating temperatures, it also detects 10–20% of large molecular ions formed from passing filtered ambient air through a bipolar ion source. Decreasing the temperature difference between the first two stages, with the first and second stages operated at 10 and 90°C, respectively, essentially eliminates the response to charger ions, and raises the 50% efficiency cut-point for the nichrome wire particles to 1.9 nm mobility diameter. Here, the time response, as measured by rapid removal of an inlet filter, yields a characteristic time constant of 195 ms.
Detection near 1-nm with a laminar-flow, water-based condensation particle counter
Hering, Susanne V.; Lewis, Gregory S.; Spielman, Steven R.; ...
2016-11-18
Presented is a laminar-flow, water-based condensation particle counter capable of particle detection near 1 nm. This instrument employs a three-stage, laminar-flow growth tube with a “moderator” stage that reduces the temperature and water content of the output flow without reducing the peak supersaturation, and makes feasible operation at the large temperature differences necessary for achieving high supersaturations. The instrument has an aerosol flow of 0.3 L/min, and does not use a filtered sheath flow. It is referred to as a “versatile” water condensation particle counter, or vWCPC, as operating temperatures can be adjusted in accordance with the cut-point desired. Whenmore » operated with wall temperatures of ~2°C, >90°C, and ~22°C for the three stages, respectively, the vWCPC detects particles generated from a heated nichrome wire with a 50% efficiency cut-point near 1.6 nm mobility diameter. At these operating temperatures, it also detects 10–20% of large molecular ions formed from passing filtered ambient air through a bipolar ion source. Decreasing the temperature difference between the first two stages, with the first and second stages operated at 10 and 90°C, respectively, essentially eliminates the response to charger ions, and raises the 50% efficiency cut-point for the nichrome wire particles to 1.9 nm mobility diameter. Here, the time response, as measured by rapid removal of an inlet filter, yields a characteristic time constant of 195 ms.« less
NASA Technical Reports Server (NTRS)
Arcara, P. C., Jr.; Bartlett, D. W.; Mccullers, L. A.
1991-01-01
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.
NASA Astrophysics Data System (ADS)
Masciopinto, Costantino; Volpe, Angela; Palmiotta, Domenico; Cherubini, Claudia
2010-09-01
A combination of a parallel fracture model with the PHREEQC-2 geochemical model was developed to simulate sequential flow and chemical transport with reactions in fractured media where both laminar and turbulent flows occur. The integration of non-laminar flow resistances in one model produced relevant effects on water flow velocities, thus improving model prediction capabilities on contaminant transport. The proposed conceptual model consists of 3D rock-blocks, separated by horizontal bedding plane fractures with variable apertures. Particle tracking solved the transport equations for conservative compounds and provided input for PHREEQC-2. For each cluster of contaminant pathways, PHREEQC-2 determined the concentration for mass-transfer, sorption/desorption, ion exchange, mineral dissolution/precipitation and biodegradation, under kinetically controlled reactive processes of equilibrated chemical species. Field tests have been performed for the code verification. As an example, the combined model has been applied to a contaminated fractured aquifer of southern Italy in order to simulate the phenol transport. The code correctly fitted the field available data and also predicted a possible rapid depletion of phenols as a result of an increased biodegradation rate induced by a simulated artificial injection of nitrates, upgradient to the sources.
Masciopinto, Costantino; Volpe, Angela; Palmiotta, Domenico; Cherubini, Claudia
2010-09-20
A combination of a parallel fracture model with the PHREEQC-2 geochemical model was developed to simulate sequential flow and chemical transport with reactions in fractured media where both laminar and turbulent flows occur. The integration of non-laminar flow resistances in one model produced relevant effects on water flow velocities, thus improving model prediction capabilities on contaminant transport. The proposed conceptual model consists of 3D rock-blocks, separated by horizontal bedding plane fractures with variable apertures. Particle tracking solved the transport equations for conservative compounds and provided input for PHREEQC-2. For each cluster of contaminant pathways, PHREEQC-2 determined the concentration for mass-transfer, sorption/desorption, ion exchange, mineral dissolution/precipitation and biodegradation, under kinetically controlled reactive processes of equilibrated chemical species. Field tests have been performed for the code verification. As an example, the combined model has been applied to a contaminated fractured aquifer of southern Italy in order to simulate the phenol transport. The code correctly fitted the field available data and also predicted a possible rapid depletion of phenols as a result of an increased biodegradation rate induced by a simulated artificial injection of nitrates, upgradient to the sources.
Transient effects of orthogonal pipe oscillations on laminar developing incompressible flow
NASA Astrophysics Data System (ADS)
Benhamou, B.; Galanis, N.; Laneville, A.
2000-12-01
This paper presents a numerical study of the transient developing laminar flow of a Newtonian incompressible fluid in a straight horizontal pipe oscillating around the vertical diameter at its entrance. The flow field is influenced by the tangential and Coriolis forces, which depend on the through-flow Reynolds number, the oscillation Reynolds number and the angular amplitude of the pipe oscillation. The impulsive start of the latter generates a transient pulsating flow, whose duration increases with axial distance. In any cross-section, this flow consists of a pair of symmetrical counter-rotating vortices, which are alternatively clockwise and anti-clockwise. The circumferentially averaged friction factor and the axial pressure gradient fluctuate with time and are always larger than the corresponding values for a stationary pipe. On the other hand, local axial velocities and local wall shear stress can be smaller than the corresponding stationary pipe values during some part of the pipe oscillation. The fluctuation amplitude of these local variables increases with axial distance and can be as high as 50% of the corresponding stationary pipe value, even at short distances from the pipe entrance. Eventually, the flow field reaches a periodic regime that depends only on the axial position. The results show that the transient flow field depends on the pipe oscillation pattern (initial position and/or direction of initial movement). Copyright
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. PMID:26301245
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.
Laminar forced convection from a rotating horizontal cylinder in cross flow
NASA Astrophysics Data System (ADS)
Chandran, Prabul; Venugopal, G.; Jaleel, H. Abdul; Rajkumar, M. R.
2017-04-01
The influence of non-dimensional rotational velocity, flow Reynolds number and Prandtl number of the fluid on laminar forced convection from a rotating horizontal cylinder subject to constant heat flux boundary condition is numerically investigated. The numerical simulations have been conducted using commercial Computational Fluid Dynamics package CFX available in ANSYS Workbench 14. Results are presented for the non-dimensional rotational velocity α ranging from 0 to 4, flow Reynolds number from 25 to 40 and Prandtl number of the fluid from 0.7 to 5.4. The rotational effects results in reduction in heat transfer compared to heat transfer from stationary heated cylinder due to thickening of boundary layer as consequence of the rotation of the cylinder. Heat transfer rate increases with increase in Prandtl number of the fluid.
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)
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.
Structural Effects of Biodiesel on Soot Volume Fraction in a Laminar Co-Flow Diffusion Flame
NASA Astrophysics Data System (ADS)
Weingarten, Jason
An experimental study was performed to determine the structural effects of biodiesel on soot volume fraction in a laminar co-flow diffusion flame. These include the effects of the ester function group, the inclusion of a double bond, and its positional effect. The soot volume fraction and temperature profiles of a biodiesel surrogate, n-Decane, 1-Decene, and 5-Decene fuels were measured. Improvements were made to existing laser extinction and rapid thermocouple insertion apparatus and were used to measure soot volume fraction and temperature profiles respectively. Flow rates of each fuel were determined in order to keep the temperature effects on soot negligible. Using n-Decane as a baseline, the double bond increased soot production and was further increased with a more centrally located double bond. The ester function group containing oxygen decreased soot production. The order of most to least sooting fuels were as follows 5-Decene > 1-Decene > n-Decane > Biodiesel Surrogate.
NASA Astrophysics Data System (ADS)
Zhang, Heng-Yun; Ge, Xin-Shi
1997-03-01
Heat transfer in the evacuated collector tube is a three-dimensional laminar natural convection problem driven by buoyancy. Because of its complexity, no effective theoretical model is available despite of limited experimental work which is confined to one aspect. The present work aims to depict the convective heat transfer inside a two-ended inclined tube with East-West symmetric heat input using numerical methods. Based on reasonable assumptions, governing equations of the inside fluid are established. The corresponding discretizated equations are solved by employing numerical methods. The calculated results are displayed for velocity and temperature profiles on different cross-sectional planes, which present the flow pattern characterized by upflow and downflow along the axial direction and adherent flow along the peripheral direction, and the heat transfer process from the wall to the center. Furthermore, the transient Nusselt number and average temperature level are shown and discussed. Finally, the parametric effects of the tube radius and the heat input on the flow and heat transfer are also given.
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.
Further analyses of laminar flow heat transfer in circular sector ducts
Lei, Q.M.; Trupp, A.C. )
1989-11-01
Heat transfer in circular sector ducts is often encountered in multipassage tubes. Certain flow characteristics of circular sector ducts for apex angles up to {pi} have been determined as documented by Shah and London (1978). Recently, Lei and Trupp (1989) have more completely analyzed the flow characteristics of fully developed laminar flow for apex angles up to 2{pi}, including the location of the maximum velocity. Heat transfer results of fully developed laminar flow in circular sector ducts are also available for certain boundary conditions. Trupp and Lau (1984) numerically determined the average Nusselt number (Nu{sub T}) for isothermal walls. Eckert et al. (1958) initially derived an analytical expression for the temperature profile for the case of H1. Sparrow and Haji-angles up to {pi}. However, the above work required numerical integration (or equivalent) to obtain a value for Nu{sub H1}. Regarding the H1{sub ad} boundary condition, Date (1974) numerically obtained a limiting value of Nu{sub H1}{sub ad} for the semicircular duct from the prediction of circular tubes containing a twisted tape (straight and nonconducting tape). Hong and Bergles (1976) also reported an asymptotic value of Nu{sub H1}{sub ad} for the semicircular duct from their entrance region solution. Otherwise it appears that there are no published analytical results of Nu{sub H1}{sub ad} for circular sector ducts. The purpose of this technical note is to communicate these results. In addition, a novel series expression for Nu{sub H1} is presented together with results for apex angles up to 2{pi}.
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)
Arndt, Ralf; Gaulke, Alexander
2008-03-01
Thermography (IR) allows global visualization of temperature distribution on surfaces with high accuracy. This potential can be used for visualization of fluid mechanics effects at the intersection of laminar and turbulent flows, where temperature jumps appear due to convection and friction i.e. for the optimization in the design of airplane geometries. In civil engineering too it is the aspiration of the modern engineer of light weight structures to meet singular loads like wind peaks rather by intelligent structures and materials than by massive structures. Therefore the "Institute of Conceptual and Structural Design" of the Technical University of Berlin (TUB) is working on the development of adaptive structures, optimized geometry and intelligent microstructures on surfaces of structural elements. The paper shows the potential of modern computational fluid dynamics (CFD) in combination with thermography (IR) to optimize structures by visualization of laminar-tumultuous border layer currents. Therefore CFD simulations and IR wind tunnel experiments will be presented and discussed. For simulations and experiments - artificial and structural elements of the cable-stayed Strelasund Bridge, Germany, are used.
Convective heat transfer in foams under laminar flow in pipes and tube bundles.
Attia, Joseph A; McKinley, Ian M; Moreno-Magana, David; Pilon, Laurent
2012-12-01
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.
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
NASA Astrophysics Data System (ADS)
Loisel, Vincent; Abbas, Micheline; Masbernat, Olivier; Climent, Eric
2013-12-01
The presence of finite-size particles in a channel flow close to the laminar-turbulent transition is simulated with the Force Coupling Method which allows two-way coupling with the flow dynamics. Spherical particles with channel height-to-particle diameter ratio of 16 are initially randomly seeded in a fluctuating flow above the critical Reynolds number corresponding to single phase flow relaminarization. When steady-state is reached, the particle volume fraction is homogeneously distributed in the channel cross-section (ϕ ≅ 5%) except in the near-wall region where it is larger due to inertia-driven migration. Turbulence statistics (intensity of velocity fluctuations, small-scale vortical structures, wall shear stress) calculated in the fully coupled two-phase flow simulations are compared to single-phase flow data in the transition regime. It is observed that particles increase the transverse r.m.s. flow velocity fluctuations and they break down the flow coherent structures into smaller, more numerous and sustained eddies, preventing the flow to relaminarize at the single-phase critical Reynolds number. When the Reynolds number is further decreased and the suspension flow becomes laminar, the wall friction coefficient recovers the evolution of the laminar single-phase law provided that the suspension viscosity is used in the Reynolds number definition. The residual velocity fluctuations in the suspension correspond to a regime of particulate shear-induced agitation.
Experiments on densely-loaded non-Newtonian slurries in laminar and turbulent pipe flows
NASA Astrophysics Data System (ADS)
Park, J. T.; Mannheimer, R. J.; Grimley, T. A.; Morrow, T. B.
1987-10-01
An experimental description of the flow structure of non-Newtonian slurries in the laminar, transitional, and full turbulent pipe flow regimes is the primary objective of this research. Measurements include rheological characterization of the fluid and local fluid velocity measurements with a laser Doppler velocimeter (LDV). Optical access to the flow is gained through a test section and model slurry which are both transparent. The model slurry is formulated from silica gel particles and hydrocarbon liquid mixture whose indices of refraction are matched so that light is not scattered from the particles. Experiments are being conducted in a large-scale pipe slurry flow facility with an inside pipe diameter of 51 mm (2 inches). Detailed flow measurements including turbulence quantities such as Reynolds stress will be taken with a two-component two-color LDV. The present research indicates that non-Newtonian slurries are possible with concentrations of a few percent by weight of small particles whose sizes are one micron or less. A non-Newtonian slurry from small particles could maintain large particles (100 micron size) at high concentrations in suspension almost indefinitely. Such a slurry would prevent particle fallout and its associated problems.
Pattern formation of Dictystelium discoideum in the presence of laminar flow and cAMP pulses
NASA Astrophysics Data System (ADS)
Gholami, Azam; Steinbock, Oliver; Zykov, Vladimir; Bodenschatz, Eberhard
2014-03-01
Dictyostelium discoideum (D.d) amobae undergo starvation-induced multicellular development in which single cells aggregate chemotactically towards cAMP signals emitted periodically from an aggregation center. We are investigating spatiotemporal pattern formation of D.d. cells under the presence of a laminar flow. Starved cells are loaded into a straight millifluidic device with an external flow and cell response to the signaling molecule cAMP is monitored indirectly using dark-field microscopy. The observed contraction waves develop simultaneously over the entire channel, are propagating only in flow direction, and have curved wave fronts resembling the parabolic flow profile. The wave dynamics analysis shows that the wave velocity is locked to the flow velocity and yields a wave period of T0 6 min, which matches the typical oscillation period of extracellular cAMP in spatial homogeneous, well-stirred systems. We apply a small cAMP perturbation at the inlet region of the channel and observe the spatiotemporal response of the cells as the pulse is propagating down the channel. The results show that D.d. cells are in the oscillatory regime and the system can be forced within resonance tongue. We compared our results with analytical and numerical analysis of Goldbeter model.
2004-10-01
Center Room 342 Mechanical and Aerospace Engineering, Box 87-6106 Tempe, Arizona 85287-6106 USA Email: william.solomon@ngc.com /aaron.drake@ngc.com...wing laminar flow, which is the focus of this paper. 1.2 General Relationships Between Instability Mechanisms and Wing Sweep Angles Boundary-layer...transition in 3-D flows is a complicated process involving complex flow structures, multiple instability mechanisms , and nonlinear interactions. Four
Effects of 2HZ Imposed Bulk Flow Unsteadiness on Laminar/Turbulent Transition in a Straight Channel
1989-12-01
stainless steel tube ( hypodermic needle ) which allows the wire to move freely. The smoke wire is connected to an A/C-D/C converter and this in turn has...describe the onset of transition is the Reynolds number. In channel flows, linear stability theory predicts that the laminar flow becomes unstable to...linear theory indicates that the flow is stable. Experimental clarification of these points is needed, along with the verification of the sequence of
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.
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.
Similarity solutions for magneto-forced-unsteady free convective laminar boundary-layer flow
NASA Astrophysics Data System (ADS)
Abd-El-Malek, Mina B.; Helal, Medhat M.
2008-09-01
The group theoretic method is applied for solving problem of a unsteady free-convective laminar boundary-layer flow on a non-isothermal vertical plate under the effect of an external velocity and a magnetic field normal to the plate. The application of two-parameter transformation group reduces the number of independent variables, by two, and consequently the system of governing partial differential equations with the boundary and initial conditions reduces to a system of ordinary differential equations with appropriate corresponding conditions. The Runge-Kutta shooting method used to find the numerical solution of the velocity field, shear stress, heat transfer and heat flux has been obtained. The effect of the magnetic field on the velocity field and the Prandtl number on the heat transfer and heat flux has been discussed.
Hybrid solution for the laminar flow of power-law fluids inside rectangular ducts
NASA Astrophysics Data System (ADS)
Lima, J. A.; Pereira, L. M.; Macêdo, E. N.; Chaves, C. L.; Quaresma, J. N. N.
The so-called generalized integral transform technique (GITT) is employed in the hybrid numerical-analytical solution of two-dimensional fully-developed laminar flow of non-Newtonian power-law fluids inside rectangular ducts. The characteristic of the automatic and straightforward global error control procedure inherent to this approach, permits the determination of fully converged benchmark results to assess the performance of purely numerical techniques. Therefore, numerical results for the product Fanning friction factor-generalized Reynolds number are computed for different values of power-law index and aspect ratio, which are compared with previously reported results in the literature, providing critical comparisons among them as well as illustrating the powerfulness of the integral transform approach. The resulting velocity profiles computed by using this methodology are also compared with those calculated by approximated methods for power-law fluids, within the range of governing parameters studied.
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.
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.
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.
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.
F-16XL Ship #2 in hangar for Laminar Flow Glove mounting
NASA Technical Reports Server (NTRS)
1995-01-01
NASA's two-seat F-16XL research aircraft is shown in the modification hangar at the Dryden Flight Research Center, Edwards, California, during installation of a titanium 'glove' on the upper surface of its modified left wing. The aircraft subsequently concluded a 13 month-long, 45-flight research program which investigated drawing off a small portion of the boundary-layer air in order to provide laminar -- or smooth -- flow over a major portion of a wing flying at supersonic speeds. A turbo-compressor in the aircraft's fuselage provided suction to draw air through more than 10 million tiny laser-drilled holes in the glove via a manifold system employing 20 valves. Data obtained during the program could assist designers of future high-speed aircraft in developing a more efficient civil transport.
NASA Astrophysics Data System (ADS)
Sarracino, A.; Cecconi, F.; Puglisi, A.; Vulpiani, A.
2016-10-01
We study the mobility and the diffusion coefficient of an inertial tracer advected by a two-dimensional incompressible laminar flow, in the presence of thermal noise and under the action of an external force. We show, with extensive numerical simulations, that the force-velocity relation for the tracer, in the nonlinear regime, displays complex and rich behaviors, including negative differential and absolute mobility. These effects rely upon a subtle coupling between inertia and applied force that induces the tracer to persist in particular regions of phase space with a velocity opposite to the force. The relevance of this coupling is revisited in the framework of nonequilibrium response theory, applying a generalized Einstein relation to our system. The possibility of experimental observation of these results is also discussed.
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.
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...
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.
Three-layer interactive method for computing supersonic laminar separated flows
NASA Technical Reports Server (NTRS)
Brandeis, J.; Rom, J.
1980-01-01
An interactive model for numerical computation of complicated two-dimensional flowfields including regions of reversed flow is proposed. The present approach is one of dividing the flowfield into three regions, in each of which a simplified mathematical model is applied: (1) outer, supersonic flow for which the full potential equation (hyperbolic) is used; (2) viscous, laminar layer in which the compressible boundary-layer model (parabolic) is used; and (3) recirculating flow modeled by the incompressible Navier-Stokes equations (elliptic). For matching of the numerical solutions in the three layers, two interaction models are developed: one for pressure interaction, the other for interaction between the shear layer and the recirculating flow. The uniform solution for the whole flowfield is then obtained by iteration of the local solutions under the constraints imposed by matching. The three-layer interactive model is used for solution of the flowfield past an asymmetric cavity. The method is shown to be capable of dealing with backflow without encountering problems at separation, characteristic to the boundary-layer approach.
Experiments on densely-loaded non-Newtonian slurries in laminar and turbulent pipe flows
NASA Astrophysics Data System (ADS)
Park, J. T.; Mannheimer, R. J.; Grimley, T. A.; Morrow, T. B.
1988-05-01
An experimental description of the flow structure of non-Newtonian slurries in the laminar, transitional, and full turbulent pipe flow regimes is the primary objective of this research. Measurements include rheological characterization of the fluid and local fluid velocity measurements with a Laser Doppler Velocimeter (LDV). Optical access to the flow is gained through a test section and model slurry which are both transparent. The model slurry is formulated from silica gel particles and hydrocarbon liquid mixture whose indices of refraction are matched so that light is not scattered from the particles. Experiments are being conducted in a large-scale pipe slurry. Flow measurements including turbulence quantities such as Reynolds stress were measured with a two-component two-color LDV. The present research indicates that non-Newtonian slurries are possible with concentrations of a few percent by weight of small particles whose sizes are two microns or less. A non-Newtonian slurry from small particles could maintain large particles (one millimeter size) at high concentrations in suspension almost indefinitely. Such a slurry would prevent particle fallout and its associated problems.
Experimental and numerical study of direct laminar-turbulent transition in Taylor-Couette flow
NASA Astrophysics Data System (ADS)
Crowley, Christopher J.; Krygier, Michael; Borrero-Echeverry, Daniel; Grigoriev, Roman O.; Schatz, Michael F.
2016-11-01
The transition to turbulence in large aspect ratio Taylor-Couette flow (TCF) occurs via a sequence of supercritical bifurcations of stable flow states (e.g. spiral vortices, interpenetrating spirals (IPS), and wavy interpenetrating spirals). We previously reported the discovery of a direct laminar-turbulent transition in a TCF system with counter-rotating cylinders (Reo = - 1000 , Rei 640) and a small aspect ratio (Γ = 5 . 26) as Rei is slowly increased. This transition is mediated by an unstable IPS state. As Rei is decreased, the turbulent flow first relaminarizes into an intermediate, stable IPS state, before returning to circular Couette flow. In this talk we will present the study of this transition experimentally using tomographic PIV and direct numerical simulations with realistic boundary conditions, and show that it is both highly repeatable and that it shows hysteresis. The transition between both the IPS and turbulent states exhibits statistics consistent with chaotic attractor transitioning to a chaotic repeller. The IPS state is accessed from a subcritical transition and is inaccessible when the inner cylinder is originally accelerated on the way up to turbulence, suggesting that a finite amplitude perturbation is required to reach it. This work is supported in part by the Army Research Office (Contract # W911NF-16-1-0281).
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.
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.
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 evaluation of laminar heat transfer enhancement in nanofluid flow in coiled square tubes
2011-01-01
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. PMID:21711901
Effect of laminar unsteady fluid flows on mass transfer in electrochemical systems
NASA Astrophysics Data System (ADS)
Shehata, Ahmed Kamal
1999-11-01
A numerical study of mass transfer in steady as well as unsteady two-dimensional laminar channel flows is investigated. When a circular cylinder is suspended in a steady flow stream, the flow becomes unsteady and oscillates periodically for Reynolds numbers, Re, between 200 and 800 (where Re is based on the channel height) due to the formation of the Karman vortex street. This well- characterized unsteady periodic flow is utilized to study mass transfer rates at different positions downstream of the blocking cylinder. The study consisted of mass transfer to a channel wall and mass transfer to the bottom surface of rectangular cavities, of different depth/width ratios. All investigated positions, including cavity position, are located downstream of the blocking cylinder. The study also included the mass transfer to a channel wall in a steady fully-developed flow when a hemi-cylindrical bump is located at the lower wall. The results of the numerical simulations are then compared to the experimental data. The numerical and experimental results are found to be generally in good agreement. Structured multi-block grids are utilized for the fluid flow simulations. It is shown that grids can be created differently with different block topologies. Solution accuracy is shown to be strongly affected by the shape as well as the densities of the resulting grids. The finite element method is used to simulate the fluid flow while for the concentration field a procedure based on the finite volume method is used. The strength of the flow at the cavity mouth was found to scale linearly with wall shear in the absence of the cavity for steady channel flow. The flow at the cavity mouth was also found to be independent of the cavity depth for both steady and unsteady flows. Based on these observations it is possible to predict cavity flows and cavity mass transfer without computing the flow in the entire channel plus cavity domain when studying different cavity aspect ratios. A
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.
Mangalappalli-Illathu, Anil K; Lawrence, John R; Swerhone, George D W; Korber, Darren R
2008-03-31
Salmonella enterica serovar Enteritidis is a significant biofilm-forming pathogen. The influence of a 10-fold difference in nutrient laminar flow velocity on the dynamics of Salmonella Enteritidis biofilm formation and protein expression profiles were compared in order to ascertain how flow velocity influenced biofilm structure and function. Low-flow (0.007 cm s(-1)) biofilms consisted of diffusely-arranged microcolonies which grew until merging by approximately 72 h. High-flow (0.07 cm s(-1)) biofilms were significantly thicker (36+/-3 microm (arithmetic mean+/-standard error; n=225) versus 16+/-2 microm for low-flow biofilms at 120 h) and consisted of large bacterial mounds interspersed by water channels. Lectin-binding analysis of biofilm exopolymers revealed a significantly higher (P<0.05) proportion of N-acetylgalactosamine (GalNAc) in low-flow biofilms (55.2%), relative to only 1.2% in high-flow biofilms. Alternatively, the proportions of alpha-L-fucose and N-acetylglucosamine (GlcNAc2)-N-acetylneuraminic acid (NeuNAc) polymer-conjugates were significantly higher (P<0.05) in high-flow biofilms (69.1% and 29.6%, respectively) than low-flow biofilms (33.1% and 11.7%, respectively). Despite an apparent flow rate-based physiologic effect on biofilm structure and exopolymer composition, no major shift in whole-cell protein expression patterns was seen between 168 h-old low-flow and high-flow biofilms, and notably did not include any response involving the stress response proteins, DnaK, SodB, and Tpx. Proteins involved in degradation and energy metabolism (PduA, GapA, GpmA, Pgk, and RpiA), RNA and protein biosynthesis (Tsf, TufA, and RpoZ), cell processes (Crr, MalE, and PtsH), and adaptation (GrcA), and some hypothetical proteins (YcbL and YnaF) became up-regulated in both biofilm systems relative to a 168 h-old planktonic cell control. Our results indicate that Salmonella Enteritidis biofilms altered their structure and extracellular glycoconjugate composition
Experiments on densely-loaded non-Newtonian slurries in laminar and turbulent pipe flows
NASA Astrophysics Data System (ADS)
Mannheimer, R. J.; Grimley, T. A.; Park, J. T.; Morrow, T. B.
1987-04-01
The structure of non-Newtonian slurries in laminar, transitional, and turbulent flow regimes in pipes is studied. Experiments are conducted in a large-scale pipe slurry flow facility with an inside pipe diameter of 51 mm. Flow measurements including turbulence quantities such as Reynolds stress are taken with a two-component laser-Doppler velocimeter in a transparent test section with a transparent model slurry. Two transparent model slurries have been developed with non-Newtonian rheological properties. Silica gel particles with diameters on the order of one micron are suspended in two different hydrocarbon liquid mixtures with viscosities of 1.19 and 6.39 cS. In rheological measurements with a concentric cylinder viscometer, slurries from both liquid mixtures exhibited slip. From a linear regression analysis with a power-law model, slurries with the higher viscosity fluid had yield values of 80 and 30 dyn/sq cm for silica gel concentrations of 5.6 and 4.0% by weight, respectively, and the exponents were 0.584 and 0.763. The measured refractive index for the transparent slurries is 1.454 where the difference in refractive index between the fluid and silica gel is estimated to be less than 0.001. Bench scale tests with large diameter silica gel particles on the order of 100 microns have produced slurries with excessive turbidity. A silica gel manufactured by a different process which may form a less turbid slurry is currently under investigation.
NASA Astrophysics Data System (ADS)
Guido, Joseph D.
1992-09-01
An experimental study of laminar flow heat transfer of an ethylene glycol/water mixture in an electrically heated horizontal tube using wire mesh (HEATEX) and twisted tape inserts was investigated. Twelve thermocouples, inserted in the tube wall at four longitudinal locations, enabled a mean inside experimental heat-transfer coefficient to be accurately measured. A constant wall heat flux boundary condition was placed on the wall by wrapping six 200 W flexible heater tapes tightly around the tube. The ethylene glycol/water mixture provided a coolant Reynolds number between 200-5000 and a Prandtl number between 30-140. Two smooth inside diameters and a roped tube profile were tested with and without the inserts. Heat-transfer correlations for tubes without inserts were developed and compared with theory for both thermally and hydrodynamically developing flow. Correlations were also developed for the two types of inserts. Nusselt numbers for fully developed flow were found to be a function of Reynolds and Prandtl numbers for the wire mesh insert and a function of tape twist ratio, Reynolds and Prandtl numbers for the twisted tape insert. Heat transfer enhancements of over 7 for the wire mesh insert and over 4 for the twisted tape insert at high Reynolds numbers were obtained over the empty tube.
NASA Technical Reports Server (NTRS)
Cook, W. J.
1975-01-01
The laminar boundary layer has been theoretically studied for six gases for flows over cold walls with zero pressure gradient at Mach numbers between 5.5 and 12.5 to correlate boundary layer quantities for the various gases. The flow conditions considered correspond to those that can be generated in test facilities such as the shock tunnel and the expansion tube. Computed results obtained using real gas properties indicate that the Eckert number based on edge conditions serves to correlate the results in terms of the wall shear stress and enthalpy gradient, the Stanton number, and the momentum thickness for the various gases within plus or minus 10 per cent for Te = Tw and Te approximately 3Tw. Computed Reynolds analogy factors exhibit very good agreement with those predicted by the Colburn analogy. Velocity and displacement thicknesses correlate well with Eckert number for Te = Tw, but fail to correlate for Te approximately 3Tw. Differences in results are traced to property variations. Results show that the Eckert number is a significant correlating variable for the flows considered.
Zero absolute vorticity: insight from experiments in rotating laminar plane Couette flow.
Suryadi, Alexandre; Segalini, Antonio; Alfredsson, P Henrik
2014-03-01
For pressure-driven turbulent channel flows undergoing spanwise system rotation, it has been observed that the absolute vorticity, i.e., the sum of the averaged spanwise flow vorticity and system rotation, tends to zero in the central region of the channel. This observation has so far eluded a convincing theoretical explanation, despite experimental and numerical evidence reported in the literature. Here we show experimentally that three-dimensional laminar structures in plane Couette flow, which appear under anticyclonic system rotation, give the same effect, namely, that the absolute vorticity tends to zero if the rotation rate is high enough. It is shown that this is equivalent to a local Richardson number of approximately zero, which would indicate a stable condition. We also offer an explanation based on Kelvin's circulation theorem to demonstrate that the absolute vorticity should remain constant and approximately equal to zero in the central region of the channel when going from the nonrotating fully turbulent state to any state with sufficiently high rotation.
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.
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.
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.
Saarenrinne, Pentti
2016-01-01
ABSTRACT The boundary layers of rainbow trout, Oncorhynchus mykiss [0.231±0.016 m total body length (L) (mean±s.d.); N=6], swimming at 1.6±0.09 L s−1 (N=6) in an experimental flow channel (Reynolds number, Re=4×105) with medium turbulence (5.6% intensity) were examined using the particle image velocimetry technique. The tangential flow velocity distributions in the pectoral and pelvic surface regions (arc length from the rostrum, lx=71±8 mm, N=3, and lx=110±13 mm, N=4, respectively) were approximated by a laminar boundary layer model, the Falkner−Skan equation. The flow regime over the pectoral and pelvic surfaces was regarded as a laminar flow, which could create less skin-friction drag than would be the case with turbulent flow. Flow separation was postponed until vortex shedding occurred over the posterior surface (lx=163±22 mm, N=3). The ratio of the body-wave velocity to the swimming speed was in the order of 1.2. This was consistent with the condition of the boundary layer laminarization that had been confirmed earlier using a mechanical model. These findings suggest an energy-efficient swimming strategy for rainbow trout in a turbulent environment. PMID:27815242
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.
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
Nagata, Maria Portia B; Yamashita, Kenichi; Miyazaki, Masaya; Nakamura, Hiroyuki; Maeda, Hideaki
2009-07-01
This article reports the enhancement of thermal stability involving normal duplex and mutation-carrying DNA duplexes in microchannel laminar flow. The application of an in-house temperature-controllable microchannel-type flow cell is demonstrated for improved discrimination of mismatch base pairs such as A-G and T-G that are difficult to distinguish due to the rather small thermal destabilizations. Enhancement in thermal stability is reflected by an increased thermal melting temperature achieved in microchannel laminar flow as compared with batch reactions. To examine the kinetics and thermodynamics of duplex-coil equilibrium of DNA oligomers, denaturation-renaturation hysteresis curves were measured. The influence of microchannel laminar flow on DNA base mismatch analysis was described from the kinetic and thermodynamic perspectives. An increasing trend was observed for association rate constant as flow rate increased. In contrast, an apparent decrease in dissociation rate constant was observed with increasing flow rate. The magnitudes of the activation energies of dissociation were nearly constant for both the batch and microchannel laminar flow systems at all flow rates. In contrast, the magnitudes of activation energies of association decreased as flow rate increased. These results clearly show how microchannel laminar flow induces change in reaction rate by effecting change in activation energy. We anticipate, therefore, that this approach based on microchannel laminar flow system holds great promise for improved mismatch discrimination in DNA analyses, particularly on single-base-pair mismatch, by pronouncedly enhancing thermal stability.
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
Performance evaluation on an air-cooled heat exchanger for alumina nanofluid under laminar flow.
Teng, Tun-Ping; Hung, Yi-Hsuan; Teng, Tun-Chien; Chen, Jyun-Hong
2011-08-09
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.
Analysis of a laminar-flow diffusional mixer for directed self-assembly of liposomes.
Kennedy, Matthew J; Ladouceur, Harold D; Moeller, Tiffany; Kirui, Dickson; Batt, Carl A
2012-01-01
The present work describes the operation and simulation of a microfluidic laminar-flow mixer. Diffusive mixing takes place between a core solution containing lipids in ethanol and a sheath solution containing aqueous buffer, leading to self assembly of liposomes. Present device architecture hydrodynamically focuses the lipid solution into a cylindrical core positioned at the center of a microfluidic channel of 125 × 125-μm(2) cross-section. Use of the device produces liposomes in the size range of 100-300 nm, with larger liposomes forming at greater ionic strength in the sheath solution and at lower lipid concentration in the core solution. Finite element simulations compute the concentration distributions of solutes at axial distances of greater than 100 channel widths. These simulations reduce computation time and enable computation at long axial distances by utilizing long hexahedral elements in the axial flow region and fine tetrahedral elements in the hydrodynamic focusing region. Present meshing technique is generally useful for simulation of long microfluidic channels and is fully implementable using comsol Multiphysics. Confocal microscopy provides experimental validation of the simulations using fluorescent solutions containing fluorescein or enhanced green fluorescent protein.
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
Analysis of a laminar-flow diffusional mixer for directed self-assembly of liposomes
Kennedy, Matthew J.; Ladouceur, Harold D.; Moeller, Tiffany; Kirui, Dickson; Batt, Carl A.
2012-01-01
The present work describes the operation and simulation of a microfluidic laminar-flow mixer. Diffusive mixing takes place between a core solution containing lipids in ethanol and a sheath solution containing aqueous buffer, leading to self assembly of liposomes. Present device architecture hydrodynamically focuses the lipid solution into a cylindrical core positioned at the center of a microfluidic channel of 125 × 125-μm2 cross-section. Use of the device produces liposomes in the size range of 100–300 nm, with larger liposomes forming at greater ionic strength in the sheath solution and at lower lipid concentration in the core solution. Finite element simulations compute the concentration distributions of solutes at axial distances of greater than 100 channel widths. These simulations reduce computation time and enable computation at long axial distances by utilizing long hexahedral elements in the axial flow region and fine tetrahedral elements in the hydrodynamic focusing region. Present meshing technique is generally useful for simulation of long microfluidic channels and is fully implementable using comsol Multiphysics. Confocal microscopy provides experimental validation of the simulations using fluorescent solutions containing fluorescein or enhanced green fluorescent protein. PMID:24348890
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
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.
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 Astrophysics Data System (ADS)
Kumar, A.; Graeves, R. A.
1980-06-01
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.
Effects of Prandtl number on the laminar cross flow past a heated cylinder
NASA Astrophysics Data System (ADS)
Ajith Kumar, S.; Mathur, Manikandan; Sameen, A.; Anil Lal, S.
2016-11-01
Flow past a heated cylinder at constant surface temperature is computationally simulated and analyzed in the laminar regime at moderate buoyancy. The parameters governing the flow dynamics are the Reynolds number, Re, the Richardson number, Ri, and the Prandtl number, Pr. We perform our computations in the range 10 ≤ Re ≤ 35, for which the flow past an unheated cylinder results in a steady separation bubble, and vary the other two parameters in the range 0 ≤ Ri ≤ 2, 0.25 ≤ Pr ≤ 100. The heat transfer from the entire cylinder surface, quantified by the average Nusselt number Nuavg, is shown to obey Nuavg = 0.7435Re0.44Pr0.346 in the mixed convection regime we investigate. For a fixed Re and Pr, the flow downstream of the cylinder becomes asymmetric as Ri is increased from zero, followed by a complete disappearance of the vortices in the recirculation bubble beyond a threshold value of Ri. For a fixed Re and Ri, the vortices in the recirculation bubble are again observed to disappear beyond a threshold Pr, but with the reappearance of both the vortices above a larger threshold of Pr. In the limit of large Pr, the time-averaged flow outside the thermal boundary layer but within the near-wake region regains symmetry about the centerline and ultimately converges to a flow field similar to that of Ri = 0; in the far-wake region, however, we observe asymmetric vortex shedding for moderate Pr. The thermal plume structure in the cylinder wake is then discussed, and the plume generation is identified at points on the cylinder where the Nusselt number is a local minimum. The difference between the plume generation and the flow separation locations on the cylinder is shown to converge to zero in the limit of large Pr. We conclude by plotting the lift and drag coefficients as a function of Ri and Pr, observing that CD decreases with Ri for Pr < Prt (and vice versa for Pr > Prt), where Prt ≈ 7.5.
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.
Meier, Matthias; Lucchetta, Elena M; Ismagilov, Rustem F
2010-08-21
In this article, we developed a "plant on a chip" microfluidic platform that can control the local chemical environment around live roots of Arabidopsis thaliana with high spatial resolution using multi-laminar flow. We characterized the flow profile around the Arabidopsis root, and verified that the shear forces within the device ( approximately 10 dyne cm(-2)) did not impede growth of the roots. Our platform was able to deliver stimuli to the root at a spatial resolution of 10-800 microm. Further, the platform was validated by exposing desired regions of the root with a synthetic auxin derivative, 2,4-dichlorophenoxyacetic acid (2,4-D), and its inhibitor N-1-naphthylphthalamic acid (NPA). The response to the stimuli was observed using a DR5::GFP Arabidopsis line, where GFP expression is coupled to the auxin response regulator DR5. GFP expression in the root matched the position of the flow-focused stream containing 2,4-D. When the regions around the 2,4-D stimulus were exposed to the auxin transport inhibitor NPA, the active and passive transport mechanisms of auxin could be differentiated, as NPA blocks active cell-to-cell transport of auxin. Finally, we demonstrated that local 2,4-D stimulation in a approximately 10 microm root segment enhanced morphological changes such as epidermal hair growth. These experiments were proof-of-concept and agreed with the results expected based on known root biology, demonstrating that this "root on a chip" platform can be used to test how root development is affected by any chemical component of interest, including nitrogen, phosphate, salts, and other plant hormones.
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.
On the Mach number Effects on Droplet Breakup in Laminar Flow
NASA Astrophysics Data System (ADS)
Syahdan, Irfan Miladi
A Volume of Fluid (VOF) multiphase numerical study was conducted using the commercial simulation software ANSYS Fluent to understand the effects of compressibility on droplet breakup in the laminar flow regime. A 2D axisymmetric domain which consists of four subdomains was used for the simulations. Validation of the setup and mesh was conducted by comparing to analytical shock tube equation, Engel's, and Boger et al.'s work. Two regimes of flows, subsonic and supersonic, were used and were obtained by selection of the operating pressure, velocity, density, dynamic viscosity, and temperature to keep the Reynolds, Weber, and Mach numbers at fixed values between cases. The Reynolds number was held constant at 100. Significant differences within the stripping breakup mode between the supersonic and subsonic cases for similar values of the Weber and Reynolds numbers were observed. The difference was observed in terms of droplet deformation, droplet deformed shape, and droplet lifetime. A Weber number effect is also observed to influence the droplet lifetime. Differences in the pressure distribution were found to drive the different degrees of vertical elongation while the viscous stress mainly acts to bend the droplet downstream. The pressure was found to be the major factor while viscous stress acts as the smaller factor in the physics during most of the deformation process, but viscous stress shows to be the major role at the beginning of the process. Comparison to the solid sphere case provided confirmation of the pressure distribution difference observed between supersonic and subsonic case was expected. Comparison to solid sphere also shows how droplet deformation itself plays a role in effecting the flow field.
NASA Astrophysics Data System (ADS)
Venezuela, A. L.; Pérez-Guerrero, J. S.; Fontes, S. R.
2009-03-01
The confined flows in tubes with permeable surfaces are associated to tangential filtration processes (microfiltration or ultrafiltration). The complexity of the phenomena do not allow for the development of exact analytical solutions, however, approximate solutions are of great interest for the calculation of the transmembrane outflow and estimate of the concentration polarization phenomenon. In the present work, the generalized integral transform technique (GITT) was employed in solving the laminar and permanent flow in permeable tubes of Newtonian and incompressible fluid. The mathematical formulation employed the parabolic differential equation of chemical species conservation (convective-diffusive equation). The velocity profiles for the entrance region flow, which are found in the connective terms of the equation, were assessed by solutions obtained from literature. The velocity at the permeable wall was considered uniform, with the concentration at the tube wall regarded as variable with an axial position. A computational methodology using global error control was applied to determine the concentration in the wall and concentration boundary layer thickness. The results obtained for the local transmembrane flux and the concentration boundary layer thickness were compared against others in literature.
NASA Astrophysics Data System (ADS)
Simakov, N. N.
2016-12-01
An early drag crisis can occur at high turbulence of incoming gas flow to a sphere. To study the influence of a crisis on heat transfer from a sphere to gas, a numerical experiment was carried out in which the free gas flow around a sphere with a temperature lower than the sphere temperature was simulated for two cases. The flow was laminar in the first case and highly turbulent in the second case. To take into account turbulence, the kinematic coefficient of turbulent viscosity with a value, which is much higher (up to 2000 times) than that for physical viscosity, was introduced. The results of calculations show that the early drag crisis occurs at Reynolds numbers of about 100 and results in considerable (by four to seven times) decrease in the hydrodynamic force and sphere drag coefficient C d . The early drag crisis is also accompanied by the crisis of heat transfer from a sphere to gas with a decrease in Nusselt numbers Nu by three to six times.
NASA Technical Reports Server (NTRS)
Price, J. M.; Harris, J. F.
1972-01-01
A computer program is described which solves the compressible laminar, transitional, or turbulent boundary-layer equations for planar or axisymmetric flows. Three-point implicit difference relations are used to reduce the momentum and energy equations to finite-difference form. These equations are solved simultaneously without iteration. Turbulent flow is treated by the inclusion of either a two-layer eddy-viscosity model or a mixing-length formulation. The eddy conductivity is related to the eddy viscosity through a static turbulent Prandtl number which may be an arbitrary function of the distance from the wall boundary. The transitional boundary layer is treated by the inclusion of an intermittency function which modifies the fully turbulent model. The laminar-boundary-layer equations are recovered when the intermittency is zero, and the fully turbulent equations are solved when the intermittency is unity.
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.
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.
NASA Astrophysics Data System (ADS)
Huh, Keon; Oh, Darong; Son, Seok Young; Yoo, Hyung Jung; Song, Byeonghwa; Cho, Dong-il Dan; Seo, Jong-Mo; Kim, Sung Jae
2016-12-01
The concepts of microrobots has been drawn significant attentions recently since its unprecedented applicability in nanotechnology and biomedical field. Bacteria attached microparticles presented in this work are one of pioneering microrobot technology for self-propulsion or producing kinetic energy from ambient for their motions. Microfluidic device, especially utilizing laminar flow characteristics, were employed for anisotropic attachment of Salmonella typhimurium flagellated chemotactic bacteria to 30 um × 30 um and 50 um × 50 um microparticles that made of biodegradable polymer. Any toxic chemicals or harmful treatments were excluded during the attachment process and it finished within 100 s for the anisotropic attachment. The attachments were directly confirmed by fluorescent intensity changes and SEM visualization. Chemotaxis motions were tracked using aspartate and the maximum velocity of the bacteria-attached microrobot was measured to be 5 um/s which is comparable to prior state of art technologies. This reusable and scalable method could play a key role in chemotaxis delivery of functional microparticles such as drug delivery system.
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)
DNA detection on a power-free microchip with laminar flow-assisted dendritic amplification.
Hosokawa, Kazuo; Sato, Takahiro; Sato, Yasunobu; Maeda, Mizuo
2010-01-01
In this paper, we describe DNA detection experiments using our two original technologies, power-free microchip and laminar flow-assisted dendritic amplification (LFDA), which were previously applied to immunoassays. A microchip was fabricated by combining a poly(dimethylsiloxane) (PDMS) part having microchannel patterns and a glass plate modified with probe DNA. We carried out two kinds of experiments: the detection of 21-base biotinylated target DNA and the detection of single-nucleotide polymorphism (SNP) in 56-base unlabeled target DNA by sandwich hybridization with biotinylated probe DNA. For both of the experiments, the necessary solutions were injected into microchannels not by an external power source, but by air dissolution into the PDMS part. After a hybridization reaction, the LFDA was started by injecting FITC-labeled streptavidin and biotinylated anti-streptavidin antibody onto the reaction site. With a detection time of 20 min, the limit of detection (LOD) for the biotinylated target was 2.2 pM, and the LOD for the SNP was 10-30 pM, depending on the SNP type.
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.
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.
Manica, Drew P; Ewing, Andrew G
2002-11-01
Two novel methods are described for the fabrication of components for microchip capillary electrophoresis with electrochemical detection (microchip CEEC) on glass substrates. First, rapid marker masking is introduced as a completely nonphotolithographic method of patterning and fabricating integrated thin-film metal electrodes onto a glass substrate. The process involves applying the pattern directly onto the metal layer with a permanent marker that masks the ensuing chemical etch. The method is characterized, and the performance of the resulting electrode is evaluated using catecholamines. The response compares well with photolithographically defined electrodes and exhibits detection limits of 648 nM and 1.02 microM for dopamine and catechol, respectively. Second, laminar flow etching is introduced as a partially nonphotolithographic method of replicating channel networks onto glass substrates. The replication process involves applying a poly(dimethylsiloxane) (PDMS) mold of the channel network onto a slide coated with a sacrificial metal layer and then pulling solutions of metal etchants through the channels to transfer the pattern onto the sacrificial layer. The method is tested, and prototype channel networks are shown. These methods serve to overcome the time and cost involved in fabricating glass-based microchips, thereby making the goal of a disposable high performance lab-on-a-chip more attainable.
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.
Frequency selection mechanisms in the flow of a laminar boundary layer over a shallow cavity
NASA Astrophysics Data System (ADS)
Qadri, Ubaid Ali; Schmid, Peter J.
2017-01-01
We investigate the flow over shallow cavities as a representative configuration for modeling small surface irregularities in wall-bounded shear flows. Due to the globally stable nature of the flow, we perform a frequency response analysis, which shows a significant potential for the amplification of disturbance kinetic energy by harmonic forcing within a certain frequency band. Shorter and more shallow cavities exhibit less amplified responses, while energy from the base flow can be extracted predominantly from forcing that impacts the cavity head on. A structural sensitivity analysis, combined with a componentwise decomposition of the sensitivity tensor, reveals the regions of the flow that act most effectively as amplifiers. We find that the flow inside the cavity plays a negligible role, whereas boundary layer modifications immediately upstream and downstream of the cavity edges contribute significantly to the frequency response. The same regions constitute preferred locations for implementing active or passive control strategies to manipulate the frequency response of the flow.
2003-10-01
FBPF Fan blade passing frequency F. S. Fuselage station FTF Flight test fixture GASP Global atmospheric sampling program HARV High Alpha...indicated airspeed KKK Kryo-Windkanal Köln LC Liquid crystal LDA Laser Doppler anemometer LEFT Leading-edge flight test LF Laminar flow LFC... test aircraft has such a power system, then care should be used to isolate the anemometer circuits from this source of anemometer output signal
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.
Minor, C.L. )
1989-04-01
The battery industry, with its complexity of operations and processes, uses a number of toxic chemical compounds and substances. The use of these materials results in the dissemination of fumes and dusts into the plant air. Effective and well designed ventilation offers a solution where protection to the workers is needed under such environmental exposure. The author describes laminar flow-plenums and recirculation systems and reviews applications of these technologies.
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.
NASA Technical Reports Server (NTRS)
Shih, K. G.
1986-01-01
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 number R < 0.
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.
NASA Astrophysics Data System (ADS)
Cochran, Robert James
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 Q-2Q1 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 (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. Attempts to extend the formulation beyond the flat channel were not successful due to oscillatory
NASA Astrophysics Data System (ADS)
Amin, Abolfazl
2011-12-01
Frictional resistance reduction of liquid flow over surfaces has recently become a more important topic of research in the field of fluid dynamics. Scientific and technological progress and continued interest in nano and micro-technology have required new developments and approaches related to reducing frictional resistance, especially in liquid flow through nano and micro-channels. The application of superhydrophobic surfaces could be very effective in achieving the desired flow through such small channels. Superhydrophobic surfaces are created by intentionally creating roughnesses on the surface and applying a uniform hydrophobic coating to the entire surface. Liquid droplet tests have revealed that because of the trapped air within the cavities such surfaces could have contact angles as high as 179º. Such a property gives superhydrophobic surfaces liquid repelling characteristics making them very suitable for frictional resistance reduction in liquid flow through nano or micro-channels, provided wetting of the cavities could be avoided. This study presents 3-D numerical simulation results of liquid laminar flow over post patterned superhydrophobic surfaces. The research was performed in three phases, 1) pressure-driven flow with square micro-posts, 2) Couette flow with square micro-posts, and 3) pressure-driven flow with rectangular micro-posts at various aspect ratios. In phases (1) and (2) the influences of important parameters such as the cavity fraction, in the range of 0.0-0.9998, and the relative module width, from 0.01 to 1.5, on frictional resistance reduction in the creeping flow regime were explored. Phase (1) also addressed the effect of varying Reynolds number from 1 to 2500 on frictional resistance. Phase (3) was conducted for aspect ratios of 1/8, 1/4, 1/2, 2, 4, and 8 also in the creeping flow regime. The obtained results suggest that important parameters such as cavity fraction (relative area of the cavities), relative module width (combined
NASA Technical Reports Server (NTRS)
Gougat, P.; Martin, F.
1981-01-01
Natural instability related to negative wall deformation was studied. It was shown that natural instabilities which propagate in a laminar boundary layer of a flat plate are in agreement with stability theory. It is found that if a wall has a deformation, a second frequency does exist, which is not predicted and is twice the first frequency. This second instable frequency only appears if there is a negative velocity gradient. The phenomenon is located very closely to the wall and drops off rapidly when moved away from it.
Nilsson, K-G; Lundholm, R; Friberg, S
2010-11-01
The area in a vertical ultraclean laminar air flow (LAF) theatre is usually too small to accommodate all the equipment needed for major surgery. We investigated the addition of an instrument table supplied with fixed ultraclean LAF and placed alongside the existing main LAF unit, to determine its physical and bacteriological effect on the main unit. In phase 1, with two investigators but without a patient, smoke tests showed no intrusion of air from the table into the main unit and particle counts did not show any adverse effect on the main LAF unit. In phase 2, during patients undergoing two total knee replacements, the LAF table and a table without LAF were placed alongside the main LAF unit. The tables were subjected to the activity of an extra operating room (OR) nurse working from inside the main LAF vigorously simulating handling of instruments. During this activity, the >5μm particle counts were 275/m(3) at the instrument table with LAF and 8550/m(3) at the table without LAF (P<0.0001). Also, without the OR nurse activity, the particle counts, just inside the main unit and adjacent to the LAF table, were significantly reduced (P<0.03-0.003). Sedimentation plates on the LAF table and in the main unit registered 22 and 25cfu/m(2)/h respectively compared with 45cfu/m(2)/h at the instrument table without LAF. In conclusion, the results from the smoke tests, particle counts and bacteriological evaluation showed that the additional instrument table supplied with LAF is efficient and can be safely used as an extension additional to a main OR LAF unit.
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
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 Astrophysics Data System (ADS)
Herwig, H.
Theoretical investigations of stationary incompressible two-dimensional laminar flows with finite regions of catastrophic separation, applying the method of matched asymptotic expansions, are presented. The difficulties associated with the Goldstein singularity are attacked in two ways, corresponding to the limiting values of a complex parameter kappa. Each case is applied to a unified model geometry using triple-deck equations. The flow model of Batchelor (1955) is shown not to fulfill the asymptotic-expansion assumptions; the model of Kirchhoff (1869), actually a degenerate version of the Batchelor model for the case omega-0 = 0, is found to be the uniquely valid one under these conditions.
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.
NASA Astrophysics Data System (ADS)
Fukushima, Naoya
2016-11-01
In the present study, Direct Numerical Simulation of turbulent flow in rhombic ducts have been carried out to investigate effects of the corner angle on the friction and heat transfer. Due to secondary flow of the second kind, the friction and heat transfer are enhanced in the corner, while turbulence enhances momentum and heat transfer near the wall away from the corner. In previous studies, turbulence and secondary flows are supposed to enhance momentum and heat transfer, qualitatively. The quantitative estimation of their contribution has not been clarified yet. Fukagata, Iwamoto and Kasagi (2002) have theoretically driven the FIK-identity to evaluate quantitative contributions of laminar and turbulence to the friction in turbulent channel. In this study, the FIK-identity has been numerically applied to DNS data in the rhombic ducts to evaluate quantitative contributions of laminar, turbulence and secondary flow to the momentum and heat transfer. From the results, it is quantitatively clarified that the contributions of turbulence and secondary flow to heat transfer are larger than that to friction in the rhombic ducts.
Brady, John F
2013-04-01
Though widely used in steady-flow heat transfer applications, the Nusselt number-a dimensionless heat transfer coefficient-has not been studied as thoroughly in oscillating flows and is therefore not generally used in thermoacoustic applications. This paper presents expressions for the Nusselt numbers of laminar oscillating flows within the pores of stacks and regenerators, derived from thermoacoustic theory developed by Rott and Swift. These expressions are based on bulk (velocity-weighted, cross-sectionally averaged) temperature, rather than the cross-sectionally averaged temperature. Results are shown for parallel plates, circular pores, rectangular pores, and within the boundary layer limit. It is shown that bulk temperature does not become infinite during an acoustic cycle and that the Nusselt number is a complex constant at all times. In addition, steady-flow Nusselt numbers are recovered when velocity and temperature profiles are like those in steady flows.
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 Technical Reports Server (NTRS)
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.
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
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
Description of fluid dynamics and coupled transports in models of a laminar flow diffusion chamber.
Trávníčková, Tereza; Havlica, Jaromír; Ždímal, Vladimír
2013-08-14
The aim of this study is to assess how much the results of nucleation experiments in a laminar flow diffusion chamber (LFDC) are influenced by the complexity of the model of the transport properties. The effects of the type of fluid dynamic model (the steady state compressible Navier-Stokes system for an ideal gas/parabolic profile approximation) and the contributions of the coupled terms describing the Dufour effects and thermodiffusion on the predicted magnitude of the nucleation maxima and its location were investigated. This study was performed on the model of the homogeneous nucleation of an n-butanol-He vapor mixture in a LFDC. The isothermal dependencies of the nucleation rate on supersaturation were determined at three nucleation temperatures: 265 K, 270 K, and 280 K. For this purpose, the experimental LFDC data measured by A. P. Hyvärinen et al. [J. Chem. Phys. 124, 224304 (2006)] were reevaluated using transport models at different levels of complexity. Our results indicate that the type of fluid dynamical model affects both the position of the nucleation maxima in the LFDC and the maximum value of the nucleation rate. On the other hand, the Dufour effects and thermodiffusion perceptibly influence only the value of the maximal nucleation rate. Its position changes only marginally. The dependence of the maximum experimental nucleation rate on the saturation ratio and nucleation temperature was acquired for each case. Based on this dependence, we presented a method for the comparison and evaluation of the uncertainties of simpler models' solutions for the results, where we assumed that the model with Navier-Stokes equations and both coupled effects taken into account was the basis. From this comparison, it follows that an inappropriate choice of mathematical models could lead to relative errors of the order of several hundred percent in the maximum experimental nucleation rate. In the conclusion of this study, we also provide some general recommendations
Description of fluid dynamics and coupled transports in models of a laminar flow diffusion chamber
NASA Astrophysics Data System (ADS)
Trávníčková, Tereza; Havlica, Jaromír; Ždímal, Vladimír
2013-08-01
The aim of this study is to assess how much the results of nucleation experiments in a laminar flow diffusion chamber (LFDC) are influenced by the complexity of the model of the transport properties. The effects of the type of fluid dynamic model (the steady state compressible Navier-Stokes system for an ideal gas/parabolic profile approximation) and the contributions of the coupled terms describing the Dufour effects and thermodiffusion on the predicted magnitude of the nucleation maxima and its location were investigated. This study was performed on the model of the homogeneous nucleation of an n-butanol-He vapor mixture in a LFDC. The isothermal dependencies of the nucleation rate on supersaturation were determined at three nucleation temperatures: 265 K, 270 K, and 280 K. For this purpose, the experimental LFDC data measured by A. P. Hyvärinen et al. [J. Chem. Phys. 124, 224304 (2006), 10.1063/1.2200341] were reevaluated using transport models at different levels of complexity. Our results indicate that the type of fluid dynamical model affects both the position of the nucleation maxima in the LFDC and the maximum value of the nucleation rate. On the other hand, the Dufour effects and thermodiffusion perceptibly influence only the value of the maximal nucleation rate. Its position changes only marginally. The dependence of the maximum experimental nucleation rate on the saturation ratio and nucleation temperature was acquired for each case. Based on this dependence, we presented a method for the comparison and evaluation of the uncertainties of simpler models' solutions for the results, where we assumed that the model with Navier-Stokes equations and both coupled effects taken into account was the basis. From this comparison, it follows that an inappropriate choice of mathematical models could lead to relative errors of the order of several hundred percent in the maximum experimental nucleation rate. In the conclusion of this study, we also provide some
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.
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.
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
Transition Induced by Fixed and Freely Convecting Spherical Particles in Laminar Boundary Layers
1993-08-01
91-J-1646 Sperical Particles in Laminar Boundary Layers " .AUTW0WS) H. L. Petrie, P. J. Morris, A. R. Bajwa, D. C. Vincent 7. PIMowG onuOaxnZ.ON NAWIS ...92 3.5.3 Method of Solution ......................... 94 3.5.4 Results and Discussion ....................... 94 3.5.4.1 Wake...laminar to turbulent flow is an important aspect of fluid dynamics in numerous engineering applications. Natural transition in laminar boundary layers
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.
NASA Astrophysics Data System (ADS)
Shalaev, V. I.
2016-10-01
Singularities appearing in solutions of 3D laminar boundary layer (BL) equations, when two streamline families are collided, are discussed. For conical bodies, equations are investigated using asymptotic methods. Analytical solutions are obtained for the outer BL region; their singularities in the runoff plane are studied. The asymptotic flow structure near the singularity is constructed on the base of Navier-Stokes equations at large Reynolds numbers. For different flow regions analytical solutions are found and are matched with BL equation solutions. Properties of BL equations for the near-wall region in the runoff plane are investigated and a criterion of the solution disappearing is found. It is shown that this criterion separates two different topological flow structures and corresponds to the singularity appearance in this plane in solutions of full equations. Calculations confirmed obtained results are presented.
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)
Lee, Cynthia C.; Obara, Clifford J.; Vijgen, Paul M.; Wusk, Michael S.
1991-01-01
Flight test results are reported from an experiment designed to study the detailed growth of disturbances in the laminar boundary layer. A gloved wing section incorporating closely-spaced flush-mounted streamwise-located instrumentation for measuring instability frequencies and amplitude growths as well as pressure distributions was used. The growth of Tollmien-Schlichting (T-S) and crossflow instabilities is predicted by the linear e exp n method and compared to the measured boundary-layer disturbance frequencies. The predictions showed good agreement with the measured data. The results exhibited fair agreement with previous n(T-S) and n(CF) flight correlations for several of the conditions analyzed. It is inferred from the high n(T-S) values for these data that moderately swept wings at compressible speeds can withstand higher combinations of n(T-S) and n(CF) values and still remain laminar than previously thought.
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.
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 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.
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.
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)
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.
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.
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.
Natural Flow Air Cooled Photovoltaics
NASA Astrophysics Data System (ADS)
Tanagnostopoulos, Y.; Themelis, P.
2010-01-01
Our experimental study aims to investigate the improvement in the electrical performance of a photovoltaic installation on buildings through cooling of the photovoltaic panels with natural air flow. Our experimental study aims to investigate the improvement in the electrical performance of a photovoltaic installation on buildings through cooling of the photovoltaic panels with natural air flow. We performed experiments using a prototype based on three silicon photovoltaic modules placed in series to simulate a typical sloping building roof with photovoltaic installation. In this system the air flows through a channel on the rear side of PV panels. The potential for increasing the heat exchange from the photovoltaic panel to the circulating air by the addition of a thin metal sheet (TMS) in the middle of air channel or metal fins (FIN) along the air duct was examined. The operation of the device was studied with the air duct closed tightly to avoid air circulation (CLOSED) and the air duct open (REF), with the thin metal sheet (TMS) and with metal fins (FIN). In each case the experiments were performed under sunlight and the operating parameters of the experimental device determining the electrical and thermal performance of the system were observed and recorded during a whole day and for several days. We collected the data and form PV panels from the comparative diagrams of the experimental results regarding the temperature of solar cells, the electrical efficiency of the installation, the temperature of the back wall of the air duct and the temperature difference in the entrance and exit of the air duct. The comparative results from the measurements determine the improvement in electrical performance of the photovoltaic cells because of the reduction of their temperature, which is achieved by the naturally circulating air.
NASA Astrophysics Data System (ADS)
Saha, Sujoy Kumar; Dayanidhi, G. L.
2012-12-01
The experimental friction factor and Nusselt number data for laminar flow through a circular duct having integral helical corrugation and fitted with centre-cleared twisted-tape has been presented. Predictive friction factor and Nusselt number correlations have also been presented. The thermohydraulic performance has been evaluated. The major findings of this experimental investigation are that the centre-cleared twisted tapes in combination with integral helical corrugation perform better than the individual enhancement technique acting alone for laminar flow through a circular duct up to a certain amount of twisted-tape centre-clearance.
NASA Astrophysics Data System (ADS)
Pal, Sagnik; Saha, Sujoy Kumar
2015-08-01
The experimental friction factor and Nusselt number data for laminar flow of viscous oil through a circular duct having integral axial corrugation roughness and fitted with twisted tapes with oblique teeth have been presented. Predictive friction factor and Nusselt number correlations have also been presented. The thermohydraulic performance has been evaluated. The major findings of this experimental investigation are that the twisted tapes with oblique teeth in combination with integral axial corrugation roughness perform significantly better than the individual enhancement technique acting alone for laminar flow through a circular duct up to a certain value of fin parameter.
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.
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.
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.
Hong, Minsung; Jo, Hansu; Ankeny, Randell F; Holliday-Ankeny, Casey J; Kim, Hyengseok; Khang, Gilson; Nerem, Robert M
2013-01-01
The interactions between endothelial cells (ECs) and smooth muscle cells (SMCs) in a complex hemodynamic environment play an important role in the control of blood vessel function. Since autologous SMCs are not readily available for the tissue engineering of a blood vessel substitute, a substitute for SMCs, such as human adult bone marrow-derived mesenchymal stem cells (MSCs), is needed. The objective of this study was to use a three-dimensional coculture model of the blood vessel wall, comprised of ECs and MSCs, to determine how the presence of MSCs affects EC function. Two vascular coculture models with an EC monolayer were created using type I collagen. All models were exposed to steady laminar flow with a shear stress of 15 dyn/cm(2) for up to 48 h. ECs in both the MSC and SMC coculture models expressed up-regulated EC-specific markers compared to the EC-only control model. The most dramatic difference observed between the two coculture models was in the experiments assessing monocyte adhesion. Here, fewer monocytes bound after laminar shear compared to static conditions; however, the number of bound monocytes was much lower for the EC-MSC coculture model than the EC-SMC coculture model for both static and shear conditions. These results suggest the feasibility of developing a tissue-engineered blood vessel substitute using MSCs as a substitute for SMCs.
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.
Trachtenberg, Shlomo; Fishelov, Dalia; Ben-Artzi, Matania
2003-09-01
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 flagellar
NASA Astrophysics Data System (ADS)
Punjabi, Sangeeta B.; Sahasrabudhe, S. N.; Joshi, N. K.; Mangalvedekar, H. A.; Das, A. K.; Kothari, D. C.
2014-01-01
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 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.
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.
Heat transfer of laminar flow over a 2-D backward facing step with isotropic porous floor segments
Abu-Hijleh, B.A.K
1997-07-01
Forced convection due to fluid flow over a backward facing step has been studied extensively. Flow through porous media occurs in a wide range of engineering applications such as the flow through insulation material, grain storage, and water movement through a geothermal reservoir. Control of the heat transfer characteristics is desirable, and the control mechanism can be either active or passive. Here, the incompressible laminar (Re{sub H} = 100) reattaching flow over a 2-D backward facing step with different length porous floor segments was solved numerically using the finite element method. The focus of this study is the change in the forced convection heat transfer characteristics of the flow field due to the addition of porous floor segments. Several isotropic porous floor segment configurations with different lengths and depths were studied. The porosity of the segments was varied over a wide range by changing the value of the pressure loss coefficient (KP = 10{sup {minus}2}--10{sup 6}). The changes in the local and overall Nusselt number are reported and discussed. Depending on the configuration, axial variation of the local Nusselt number could be altered. For all configurations, the overall Nusselt number decreased by as much as 16% while the maximum local Nusselt number increased by as much as 170%, both relative to their respective values for the reference case of solid floor.
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.
Laurent, Christian M; Palmer, Colin; Boardman, Richard P; Dyke, Gareth; Cook, Richard B
2014-12-06
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.
2014-01-01
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
Laminar boundary layer flow of a nanofluid along a wedge in the presence of suction/injection
NASA Astrophysics Data System (ADS)
Kasmani, R. Md.; Muhaimin, I.; Kandasamy, R.
2013-05-01
The behavior of an incompressible laminar boundary layer flow over a wedge in a nanofluid with suction or injection has been investigated. The model used for the nanofluid integrates the effects of the Brownian motion and thermophoresis parameters. The governing partial differential equations of this problem, subjected to their boundary conditions, are solved by the Runge-Kutta-Gill technique with the shooting method for finding the skin friction and the rate of heat and mass transfer. The result are presented in the form of velocity, temperature, and volume fraction profiles for different values of the suction/injection parameter, Brownian motion parameter, thermophoresis parameter, pressure gradient parameter, Prandtl number, and Lewis number. The conclusion is drawn that these parameters significantly affect the temperature and volume fraction profiles, but their influence on the velocity profile is comparatively smaller.
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.
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.
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.
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.
Hawley, J.T.; Chiu, C.; Rohsenow, W.M.; Todreas, N.E.
1980-08-01
Correlations are presented for subchannel and bundle friction factors and flowsplit parameters for laminar, transition and turbulent longitudinal flows in wire wrap spaced hexagonal arrays. These results are obtained from pressure drop models of flow in individual subchannels. For turbulent flow, an existing pressure drop model for flow in edge subchannels is extended, and the resulting edge subchannel friction factor is identified. Using the expressions for flowsplit parameters and the equal pressured drop assumption, the interior subchannel and bundle friction factors are obtained. For laminar flow, models are developed for pressure drops of individual subchannels. From these models, expressions for the subchannel friction factors are identified and expressions for the flowsplit parameters are derived.
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.
Vishwakarma, Niraj K; Singh, Ajay K; Hwang, Yoon-Ho; Ko, Dong-Hyeon; Kim, Jin-Oh; Babu, A Giridhar; Kim, Dong-Pyo
2017-03-06
Simultaneous capture of carbon dioxide (CO2) and its utilization with subsequent work-up would significantly enhance the competitiveness of CO2-based sustainable chemistry over petroleum-based chemistry. Here we report an interfacial catalytic reaction platform for an integrated autonomous process of simultaneously capturing/fixing CO2 in gas-liquid laminar flow with subsequently providing a work-up step. The continuous-flow microreactor has built-in silicon nanowires (SiNWs) with immobilized ionic liquid catalysts on tips of cone-shaped nanowire bundles. Because of the superamphiphobic SiNWs, a stable gas-liquid interface maintains between liquid flow of organoamines in upper part and gas flow of CO2 in bottom part of channel. The intimate and direct contact of the binary reagents leads to enhanced mass transfer and facilitating reactions. The autonomous integrated platform produces and isolates 2-oxazolidinones and quinazolines-2,4(1H,3H)-diones with 81-97% yields under mild conditions. The platform would enable direct CO2 utilization to produce high-valued specialty chemicals from flue gases without pre-separation and work-up steps.
Vishwakarma, Niraj K.; Singh, Ajay K.; Hwang, Yoon-Ho; Ko, Dong-Hyeon; Kim, Jin-Oh; Babu, A. Giridhar; Kim, Dong-Pyo
2017-01-01
Simultaneous capture of carbon dioxide (CO2) and its utilization with subsequent work-up would significantly enhance the competitiveness of CO2-based sustainable chemistry over petroleum-based chemistry. Here we report an interfacial catalytic reaction platform for an integrated autonomous process of simultaneously capturing/fixing CO2 in gas–liquid laminar flow with subsequently providing a work-up step. The continuous-flow microreactor has built-in silicon nanowires (SiNWs) with immobilized ionic liquid catalysts on tips of cone-shaped nanowire bundles. Because of the superamphiphobic SiNWs, a stable gas–liquid interface maintains between liquid flow of organoamines in upper part and gas flow of CO2 in bottom part of channel. The intimate and direct contact of the binary reagents leads to enhanced mass transfer and facilitating reactions. The autonomous integrated platform produces and isolates 2-oxazolidinones and quinazolines-2,4(1H,3H)-diones with 81–97% yields under mild conditions. The platform would enable direct CO2 utilization to produce high-valued specialty chemicals from flue gases without pre-separation and work-up steps. PMID:28262667
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.
NASA Astrophysics Data System (ADS)
Vishwakarma, Niraj K.; Singh, Ajay K.; Hwang, Yoon-Ho; Ko, Dong-Hyeon; Kim, Jin-Oh; Babu, A. Giridhar; Kim, Dong-Pyo
2017-03-01
Simultaneous capture of carbon dioxide (CO2) and its utilization with subsequent work-up would significantly enhance the competitiveness of CO2-based sustainable chemistry over petroleum-based chemistry. Here we report an interfacial catalytic reaction platform for an integrated autonomous process of simultaneously capturing/fixing CO2 in gas-liquid laminar flow with subsequently providing a work-up step. The continuous-flow microreactor has built-in silicon nanowires (SiNWs) with immobilized ionic liquid catalysts on tips of cone-shaped nanowire bundles. Because of the superamphiphobic SiNWs, a stable gas-liquid interface maintains between liquid flow of organoamines in upper part and gas flow of CO2 in bottom part of channel. The intimate and direct contact of the binary reagents leads to enhanced mass transfer and facilitating reactions. The autonomous integrated platform produces and isolates 2-oxazolidinones and quinazolines-2,4(1H,3H)-diones with 81-97% yields under mild conditions. The platform would enable direct CO2 utilization to produce high-valued specialty chemicals from flue gases without pre-separation and work-up steps.
NASA Technical Reports Server (NTRS)
Wolf, Stephen W. D.; Laub, James A.
1997-01-01
Flow quality measurements have been performed in the unique Laminar Flow Supersonic Wind Tunnel (LFSWT) to examine both mean and dynamic characteristics. The intent was to provide the necessary flow information about this ground test facility, to support meaningful transition research at Mach 1.6 and flight unit Reynolds numbers. This paper is intended to assist other experimentalists with similar goals of characterizing low-supersonic test environments. An array of instrumentation has been used to highlight the importance of proper selection of pressure instruments and data acquisition procedures. We conclude that the test section is low-disturbance (based on classical standards of pressure disturbances less than 0.1% with no specified data bandwidth), and has uniform flow. This is confirmation that the quiet design features of the LFSWT are effective. However, characterization of the test section flow over a 0.25k-5Ok bandwidth shows that the disturbance levels can be greater than classical standards particularly for stagnation pressures less than 9.5 psia (0.65 bar) with low stagnation temperatures. Variability of the flow disturbances in the settling chamber and test section is contained in a narrow frequency bandwidth below 5k Hz, which is associated with resonant frequencies from the pressure reduction system. So far, these disturbances have not impacted transition along the tunnel walls or a 10 degrees cone. However, continual vigilance is required to maintain a known low-disturbance environment for transition research in the LFSWT. Furthermore, the formation of standards for flow quality measurements is strongly recommended, so that transition research can be better isolated from tunnel disturbances.
The effect of twisted-tape width on heat transfer and pressure drop for fully developed laminar flow
Chakroun, W.M.; Al-Fahed, S.F.
1996-07-01
A series of experiments was conducted to study the effect of twisted-tape width on the heat transfer and pressure drop with laminar flow in tubes. Data for three twisted-tape wavelengths, each with five different widths, have been collected with constant wall temperature boundary condition. Correlations for the friction factor and Nusselt number are also available. The correlations predict the experimental data to within 10 to 15 percent for the heat transfer and friction factor, respectively. The presence of the twisted tape has caused the friction factor to increase by a factor of 3 to 7 depending on Reynolds number and the twisted-tape geometry. Heat transfer results have shown an increase of 1.5 to 3 times that of plain tubes depending on the flow conditions and the twisted-tape geometry. The width shows no effect on friction factor and heat transfer in the low range of Reynolds number but has a more pronounced effect on heat transfer at the higher range of Reynolds number. It is recommended to use loose-fit tapes for low Reynolds number flows instead of tight-fit in the design of heat exchangers because they are easier to install and remove for cleaning purposes.
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.
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.
Effect of laminar and turbulent fluid flow on mass transfer in some electrochemical systems
NASA Astrophysics Data System (ADS)
Chen, Qian
2000-10-01
The influence of fluid flow on electrode-shape change that results from electrodeposition in the presence of a model leveling agent is simulated and discussed. The treatment is more rigorous than past studies in that flow and concentration fields are recalculated as the electrode shape changes. It is shown that uncertainties due to approximate treatments of fluid flow may be as significant as existing discrepancies between experiment and theory. The mass transfer characteristics of a turbulent slot jet impinging normally on a target wall are examined using numerical simulations. Fluid flow is modeled using the k-turbulence model of Wilcox [1]. The computations are validated against existing experimental fluid flow, heat transfer and mass transfer data. The range of Reynolds numbers examined is from 450 to 20,000 with Prandtl or Schmidt numbers from 1 to 2,400. The distance of the target plate from the slot jet varies between 2 to 8 times the slot jet width. The study reveals computational aspects that are unique to the solution of flow and mass transfer problems with the combination of high Schmidt numbers and turbulent flows. A low order "coherent structure" near-wall flow model first proposed by Chapman and Kuhn [2] is used to obtain the near-wall fluid flow field. This flow field is then used to compute high Schmidt number mass transfer for a turbulent boundary layer flow. It is shown that useful insight can be obtained into high Schmidt number mass transfer for a turbulent fluid flow using this model. The boundary conditions for this near-wall field for more complicated flow or geometries may be obtained either from experimental turbulent velocity and frequency data or from a k-o type of turbulence model.
Quasi-3D Modeling and Efficient Simulation of Laminar Flows in Microfluidic Devices.
Islam, Md Zahurul; Tsui, Ying Yin
2016-10-03
A quasi-3D model has been developed to simulate the flow in planar microfluidic systems with low Reynolds numbers. The model was developed by decomposing the flow profile along the height of a microfluidic system into a Fourier series. It was validated against the analytical solution for flow in a straight rectangular channel and the full 3D numerical COMSOL Navier-Stokes solver for flow in a T-channel. Comparable accuracy to the full 3D numerical solution was achieved by using only three Fourier terms with a significant decrease in computation time. The quasi-3D model was used to model flows in a micro-flow cytometer chip on a desktop computer and good agreement between the simulation and the experimental results was found.
Quasi-3D Modeling and Efficient Simulation of Laminar Flows in Microfluidic Devices
Islam, Md. Zahurul; Tsui, Ying Yin
2016-01-01
A quasi-3D model has been developed to simulate the flow in planar microfluidic systems with low Reynolds numbers. The model was developed by decomposing the flow profile along the height of a microfluidic system into a Fourier series. It was validated against the analytical solution for flow in a straight rectangular channel and the full 3D numerical COMSOL Navier-Stokes solver for flow in a T-channel. Comparable accuracy to the full 3D numerical solution was achieved by using only three Fourier terms with a significant decrease in computation time. The quasi-3D model was used to model flows in a micro-flow cytometer chip on a desktop computer and good agreement between the simulation and the experimental results was found. PMID:27706104
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 Astrophysics Data System (ADS)
Fabbiane, Nicolò; Simon, Bernhard; Grundmann, Sven; Bagheri, Shervin; Henningson, Dan S.
2014-11-01
This work compares two of the mostly investigated reactive-control techniques in delaying the laminar-to-turbulence transition in boundary-layer (BL) flows: a Linear Quadratic Gaussian (LQG) regulator and a Filtered-X Least Mean Squares (FXLMS) algorithm. The two compensators are compared on damping 2D TS-waves excited via both single-frequency and white-noise disturbances in a zero-pressure-gradient BL flow. Surface hot-wire sensors are used to detect the incoming waves and measure the effectiveness of the control action that is provided by a dielectric-barrier-discharge plasma actuator positioned between the two sensors. Based on DNS of the experimental set-up a linear reduced order model is built using the Eigensystem Realization Algorithm and used for the LQG design. The two control techniques show comparable performances when tested at their design condition. However, when tested off-design the LQG compensator shows a stronger sensitivity to model variations. If the free-stream velocity is changed, the LQG regulator estimates a wrong phase information of the incoming disturbance resulting in a less effective control action. The FXLMS compensator, instead, is capable to adapt to the new condition and prescribe the correct phase information with no significant performance loss.
Lan, Wenjie; Li, Shaowei; Lu, Yangcheng; Xu, Jianhong; Luo, Guangsheng
2009-11-21
This article describes a simple method for the fabrication of microscale polymer tubes. A double co-axial microchannel device was designed and fabricated. Liquid/liquid/liquid multiphase co-laminar flows were realized in a microchannel by choosing working systems. Three kinds of polymeric solutions were selected as the middle phase while a polyethyleneglycol aqueous solution was used as the inner and outer phases in the microfluidic process. The outer and inner phases acted as extractants of the polymer solvent. A stable double core-annular flow was formed by optimizing the composition of the outer and inner phases, and highly uniform tubes were successfully fabricated by the solvent extraction method. Both the outer diameter of the tubes and the wall thickness could be adjusted from 300 microm to 900 microm and from 40 microm to 150 microm by varying the flux of the fluids and the rolling velocity of the collection roller. In addition, titanium dioxide (TiO2) nanoparticles were successfully encapsulated into the polymer tubes with this technique. This technology has the potential to generate hollow fiber membranes for applications in separation and reaction processes.
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.
A Simple Multichannel Fluidic System for Laminar Flow over Planar Substrates
2006-04-21
amplification or preconcentration steps, using a variety of complex sample matrices such as blood and food products [19]. Although the use of magnetic...custom microliter volume flow cells made of quartz or molded from polydimethylsiloxane (PDMS), as well as a multi-well, flow-through hybridization chamber
Spectral element simulations of laminar and turbulent flows in complex geometries
NASA Technical Reports Server (NTRS)
Karniadakis, George EM
1989-01-01
Spectral element methods are high-order weighted residual techniques based on spectral expansions of variables and geometry for the Navier-Stokes (NS) and transport equations. Here, practical aspects of these methods and their efficient implementation are examined, and several examples of flows in truly complex geometries are presented. The spectral element discretization for NS equations is introduced, and the convergence of the method is addressed. An efficient data management scheme is discussed in the context of parallel processing computations. The method is validated by comparing the spectral element solutions with the exact eigensolutions for the Orr-Sommerfeld equations in two and three dimensions. Computer-aided flow visualizations are presented for an impulsive flow past a sharp edge wedge. Three-dimensional states of channel flow disrupted by an array of cylindrical eddy promoters are studied, and the results of a direct simulation of the turbulent flow in a plane channel are presented.
Laminar flow at a three-dimensional stagnation point with large rates of injection
NASA Technical Reports Server (NTRS)
Libby, P. A.
1976-01-01
Exact calculations of the titled flow are presented and compared to the predictions of an asymptotic analysis for large rates of injection. The inner layer of the boundary layer is found to involve outflow in both orthogonal directions whether the external flow along the y axis is inward or outward. As a result, the flow at a nearly two-dimensional stagnation point involves drastic changes as a weak outflow changes to a weak inflow. It is also found that the velocity profiles in the two directions in the inner layer are quite different.
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.
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.
NASA Astrophysics Data System (ADS)
Borisevich, V. D.; Potanin, E. P.
2016-11-01
The rotation of a conducting viscous medium near a dielectric disk in a homogeneous magnetic field in the presence of an external flow and a suction is considered. On the basis of the Dorodnitsyn transformation, an analytical solution of the system of boundary-layer and heat-conduction equations has been obtained. It is shown that the direction of the radial flow in the boundary layer of the disk can be changed by changing the ratio between the angular velocities of the external flow and the disk and the ratio between the temperatures in the external flow and on the disk as well as by varying the hydrodynamic Prandtl number. The influence of the magnetic field on the intensity of circulation of the viscous medium was investigated.
Calibration of sonic valves for the laminar flow control, leading-edge flight test
NASA Technical Reports Server (NTRS)
Petley, D. H.; Alexander, W., Jr.; Wright, A. S., Jr.; Vallas, M.
1985-01-01
Sonic needle valves were calibrated to measure and control airflow in the suction system for the leading-edge flight test. The procedure and results for the calibration flow test of 4:41 flight valves are given. Mass-flow rates, which ranged from 0.001 to 0.012 lbm/sec, and maximum back pressure were measured for total temperatures from -30 F to 75 F and total pressures from 120 to 540 psf. Correlating equations are obtained for mass-flow rate as a function of total pressure, total temperature, and valve opening length. The most important aspect of flow measurement and control is found to be the measurement of valve opening length.
Turbulent-like laminar flows sustained and controlled by multiscale electromagnetic forces
NASA Astrophysics Data System (ADS)
Hascoet, Erwan; Rossi, Lionel; Christos Vassilicos, John
2006-11-01
We perform DNS of electromagnetically fractal-forced and Rayleigh-damped 2D flows and compare the results with a recent laboratory experiment of a similarly forced quais-2D thin layer of brine (JFM (2006) vol. 558 p. 207). We determine a range of DNS parameters where the multiscale streamline topology is the same as in the laboratory. It is possible to vary flow intensity whilst keeping multiscale flow topology constant. Our simulations show broad band power law energy spectra E(k)˜k^-p. When the fractal distribution of magnets is as in the laboratory experiment then p 2.5 in agreement with the experiment. When the fractal distribution of magnets is changed, then p is found to vary linearly with Df, the fractal dimension of the magnet set up. Hence, fractal control of the energy spectrum is possible. The multiscale flow imposed by the fractal electromagnetic forcing resembles a deterministic β-model of turbulence which also predicts a linear relation between p and the fractal dimension of the multiscale flow. In both cases, p increases as the fractal dimension decreases. In the power-law range the Rayleigh damping balances the fractal forcing's energy input rate scale by scale. The small difference between the two equals the interscale energy transfer function which is severely depleted. The energy flux oscillates between positive and negative values and the wavenumbers where it cancels are a direct reflection of the multiscale stagnation point structure of the flow.
Ground effects on separated laminar flows past an inclined flat plate
NASA Astrophysics Data System (ADS)
Li, Zhen; Lan, Chuanjin; Jia, Laibing; Ma, Yanbao
2017-04-01
The appearance of a ground surface can play an important role in the flow structures for the flows past a flat plate. We conduct two-dimensional numerical simulations on viscous flows past a flat plate inclined at an angle of attack of 20° with ground effects using a finite-volume method. Results show that the effects on the separated flow from the ground are highly dependent on the gap ( G) between the plate and the ground. As the gap decreases, the strength of vortices generated from the trailing edge is restrained, which is consistent with experimental observations. Further decrease in the gap even eliminates the vortex shedding and yields a steady flow. It is also found that the flow between the gap can either be accelerated at large gap ratios ({G/L >1}, G is the gap, L is the plate length), or be decelerated at small gap ratios ({G/L <1}). Furthermore, the numerical results show that the wake flow behind the plate can significantly change the distribution of surface shear stress on the ground. Specifically, the mean shear stress on the ground in the downstream region at a gap ratio G/L = 2.0 is one order of magnitude larger than that at a small gap ratio G/L = 0.3, and the length of the downstream region where the shear stress can be effectively changed is much larger than the plate length, which provides a guideline to manipulate the ground wall surface shear stress using an inclined plate in the vicinity of the wall.
Ground effects on separated laminar flows past an inclined flat plate
NASA Astrophysics Data System (ADS)
Li, Zhen; Lan, Chuanjin; Jia, Laibing; Ma, Yanbao
2016-10-01
The appearance of a ground surface can play an important role in the flow structures for the flows past a flat plate. We conduct two-dimensional numerical simulations on viscous flows past a flat plate inclined at an angle of attack of 20° with ground effects using a finite-volume method. Results show that the effects on the separated flow from the ground are highly dependent on the gap (G) between the plate and the ground. As the gap decreases, the strength of vortices generated from the trailing edge is restrained, which is consistent with experimental observations. Further decrease in the gap even eliminates the vortex shedding and yields a steady flow. It is also found that the flow between the gap can either be accelerated at large gap ratios ({G/L >1} , G is the gap, L is the plate length), or be decelerated at small gap ratios ({G/L <1} ). Furthermore, the numerical results show that the wake flow behind the plate can significantly change the distribution of surface shear stress on the ground. Specifically, the mean shear stress on the ground in the downstream region at a gap ratio G/L = 2.0 is one order of magnitude larger than that at a small gap ratio G/L = 0.3 , and the length of the downstream region where the shear stress can be effectively changed is much larger than the plate length, which provides a guideline to manipulate the ground wall surface shear stress using an inclined plate in the vicinity of the wall.
The effective slip length and vortex formation in laminar flow over a rough surface
NASA Astrophysics Data System (ADS)
Niavarani, Anoosheh; Priezjev, Nikolai
2008-11-01
The flow of viscous incompressible fluid over a periodically corrugated surface is considered by the numerical solution of the Navier-Stokes equation. We define the effective slip length with respect to the level of the mean height of the surface roughness. With increasing corrugation amplitude the effective no-slip boundary plane is shifted towards the bulk of the fluid what implies a negative effective slip length. Analysis of the flow streamlines shows that a flow circulation is developed in the grooves of the rough surface provided that the local boundary condition is no-slip. By applying a local slip boundary condition, the location of vortex is displaced towards the bottom the grooves and the effective slip length increases. For values of the local slip length larger than the period of the surface corrugation, the vortical structure disappears, the flow streamlines are deformed to follow the surface curvature, and the effective slip length saturates to a constant value. Inertial effects promote vortex flow formation in the grooves and reduce the effective slip length.
Taylor-Aris dispersion in time-dependent laminar channel flows
NASA Astrophysics Data System (ADS)
Vedel, Søren; Bruus, Henrik
2010-11-01
The effective axial diffusion of solute concentrations advected in channel flows is known as Taylor-Aris dispersion [1,2]. Due to the no-slip condition, particles near the walls are displaced less than those close to the channel center axis, leading to concentration gradient perpendicular to the axis and an enhanced axial diffusivity. In many applications the velocity field is unsteady, but concentration dispersion in such time-dependent flows is largely unexplored, except for transient dispersion of an initial concentration profile in a steady flow [3], and dispersion in a velocity field with one harmonically oscillating component superimposed on a steady component [4]. We present a mathematical theory for Taylor-Aris dispersion in a straight channel with an arbitrary time- dependent flow, based on Fourier expansion of the velocity field, valid for all times and all values of the P'eclet number. The theory is applied to different time-dependent flows in channels of different cross sections, and we discuss the new phenomena arising by adding an increasing number of higher harmonics. [1] Taylor, Proc. Roy. Soc. Lond. A 219, 186 (1953)[2] Aris, Proc. Roy. Soc. Lond. A 235, 67 (1956)[3] Barton, J. Fluid Mech. 126, 205 (1983)[4] Mukherjee and Mazumder, Acta Mech. 74, 107 (1988)
Special session: computational predictability of natural convection flows in enclosures
Christon, M A; Gresho, P M; Sutton, S B
2000-08-14
Modern thermal design practices often rely on a ''predictive'' simulation capability--although predictability is rarely quantified and often difficult to confidently achieve in practice. The computational predictability of natural convection in enclosures is a significant issue for many industrial thermal design problems. One example of this is the design for mitigation of optical distortion due to buoyancy-driven flow in large-scale laser systems. In many instances the sensitivity of buoyancy-driven enclosure flows can be linked to the presence of multiple bifurcation points that yield laminar thermal convective processes that transition from steady to various modes of unsteady flow. This behavior is brought to light by a problem as ''simple'' as a differentially-heated tall rectangular cavity (8:1 height/width aspect ratio) filled with a Boussinesq fluid with Pr = 0.71--which defines, at least partially, the focus of this special session. For our purposes, the differentially-heated cavity provides a virtual fluid dynamics laboratory.
Laminar flow across an unbounded square cylinder with suction or injection
NASA Astrophysics Data System (ADS)
Pantokratoras, Asterios
2017-02-01
The flow around a horizontal square cylinder with uniform suction or injection at the front and rear sides is considered in the present paper. The problem is investigated numerically with a finite volume method using the SIMPLE algorithm. This flow has been investigated in the past for Reynolds numbers greater than 70. In the present work, the investigation is extended to very low Reynolds numbers (up to 0.001, Stokes flow) including eight different cases concerning suction-injection at the two sides. It is found that the drag coefficient takes negative and zero values in many cases and varies linearly at low Re numbers. In all eight cases, the vortices around the cylinder have been calculated. It is found that at low Re numbers, some vortices are symmetrical both about the horizontal and vertical cylinder axes.
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.
Laminar supersonic flow over a backstep - A numerical solution at higher Reynolds numbers
NASA Technical Reports Server (NTRS)
Kronzon, Y.; Rom, J.; Seginer, A.
1976-01-01
The Allen-Cheng solution of the flow over a backward facing step is extended to Reynolds numbers up to 16,000 and to inflow boundary-layer height ratios as low as 0.1 by moving the downstream boundary into the recompression region and by smoothing the resulting errors. The boundary conditions in the supersonic outer flow and the downstream boundary conditions in the wake are determined by an extrapolation procedure. Computational results are compared with relevant experimental data. Fair agreement is found between the calculated base pressures and the experimental values, whereas agreement between heat transfer rates appears to be qualitative only.
NASA Astrophysics Data System (ADS)
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 100 and 106 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.
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.
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.
The effective slip length and vortex formation in laminar flow over a rough surface
NASA Astrophysics Data System (ADS)
Niavarani, Anoosheh; Priezjev, Nikolai V.
2009-05-01
The flow of viscous incompressible fluid over a periodically corrugated surface is investigated numerically by solving the Navier-Stokes equation with the local slip and no-slip boundary conditions. We consider the effective slip length which is defined with respect to the level of the mean height of the surface roughness. With increasing corrugation amplitude the effective no-slip boundary plane is shifted toward the bulk of the fluid, which implies a negative effective slip length. The analysis of the wall shear stress indicates that a flow circulation is developed in the grooves of the rough surface provided that the local boundary condition is no-slip. By applying a local slip boundary condition, the center of the vortex is displaced toward the bottom of the grooves and the effective slip length increases. When the intrinsic slip length is larger than the corrugation amplitude, the flow streamlines near the surface are deformed to follow the boundary curvature, the vortex vanishes, and the effective slip length saturates to a constant value. Inertial effects promote vortex flow formation in the grooves and reduce the effective slip length.
Three-Dimensional, Laminar Flow Past a Short, Surface-Mounted Cylinder
NASA Astrophysics Data System (ADS)
Liakos, Anastasios; Malamataris, Nikolaos
2016-11-01
The topology and evolution of three-dimensional flow past a cylinder of slenderness ratio SR = 1 mounted in a wind tunnel is examined for 0 . 1 <= Re <= 325 (based on the diameter of the cylinder) where steady-state solutions have been obtained. Direct numerical simulations were computed using an in-house parallel finite element code. Results indicate that symmetry breaking occurs at Re = 1 , while the first prominent structure is a horseshoe vortex downstream from the cylinder. At Re = 150 , two foci are observed, indicating the formation of two tornadolike vortices downstream. Concurrently, another horseshoe vortex is formed upstream from the cylinder. For higher Reynolds numbers, the flow downstream is segmented to upper and lower parts, whereas the topology of the flow on the solid boundaries remains unaltered. Pressure distributions show that pressure, the key physical parameter in the flow, decreases everywhere except immediately upstream from the cylinder. In addition, creation of critical points from saddle-node-type bifurcations occur when the streamwise component of the pressure gradient changes sign. Finally, at Re = 325 , an additional horseshoe vorrtex is formed at the wake of the cylinder
Huh, Yun Suk; Jeong, Chang-Moon; Chang, Ho Nam; Lee, Sang Yup; Hong, Won Hi; Park, Tae Jung
2010-01-01
A protein separation technology using the microfluidic device was developed for the more rapid and effective analysis of target protein. This microfluidic separation system was carried out using the aqueous two-phase system (ATPS) and the ionic liquid two-phase system (ILTPS) for purification method of the protein sample, and the three-flow desalting system was used for the removal of salts from the sucrose-rich sample. Partitioning of the protein sample was observed in ATPS or ILTPS with the various pHs. The microdialysis system was applied to remove small molecules, such as sucrose and salts in the microfluidic channel with the different flow rates of buffer phase. A complex purification method, which combines microdialysis and ATPS or ILTPS, was carried out for the effective purification of bacteriorhodopsin (BR) from the purple membrane of Halobacterium salinarium, which was then analyzed by sodium dodecyl sulfatepolyacrylamide gel electrophoresis and matrix-assisted laser desorption∕ionization time-of-flight. Furthermore, we were able to make a stable three-phase flow controlling the flow rate in the microfluidic channel. Our complex purification methods were successful in purifying and recovering the BR to its required value. PMID:20644672
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.
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
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
Navier-Stokes computations of laminar compressible and incompressible vortex flows in a channel
NASA Astrophysics Data System (ADS)
Brockmeier, U.; Mitra, N. K.; Fiebig, M.
To investigate the structure of compressible and incompressible vortices behind a small delta wing in a channel at low Reynolds and Mach numbers, computer programs have been developed to solve complete three-dimensional Navier-Stokes and energy equations. Results show qualitatively similar vortex formation, flattening of the vortex core, and movement of the core away from the channel center and towards the bottom wall for both incompressible and compressible flows.
Numerical study of laminar-turbulent transition in particle-laden channel flow
NASA Astrophysics Data System (ADS)
Klinkenberg, Joy; Sardina, Gaetano; de Lange, H. C.; Brandt, Luca
2013-04-01
We present direct numerical simulations of subcritical transition to turbulence in a particle-laden channel flow, with particles assumed rigid, spherical, and heavier than the fluid. The equations describing the fluid flow are solved with an Eulerian mesh, whereas those describing the particle dynamics are solved by Lagrangian tracking. Two-way coupling between fluid and particles is modeled with Stokes drag. The numerical code is first validated against previous results from linear stability: the nonmodal growth of streamwise vortices resulting in streamwise streaks is still the most efficient mechanism for linear disturbance amplification at subcritical conditions as for the case of a single phase fluid. To analyze the full nonlinear transition, we examine two scenarios well studied in the literature: (1) transition initiated by streamwise independent counter-rotating streamwise vortices and one three-dimensional mode and (2) oblique transition, initiated by the nonlinear interaction of two symmetric oblique waves. The threshold energy for transition is computed, and it is demonstrated that for both scenarios the transition may be facilitated by the presence of particles at low number density. This is due to the fact that particles may introduce in the system detrimental disturbances of length scales not initially present. At higher concentrations, conversely, we note an increase of the disturbance energy needed for transition. The threshold energy for the oblique scenario shows a more significant increase in the presence of particles, by a factor about four. Interestingly, for the streamwise-vortex scenario the time at which transition occurs increases with the particle volume fraction when considering disturbances of equal initial energy. These results are explained by considering the reduced amplification of oblique modes in the two-phase flow. The results from these two classical scenarios indicate that, although linear stability analysis shows hardly any
The effect of three-dimensional obstacles on marginally separated laminar boundary layer flows
NASA Astrophysics Data System (ADS)
Braun, Stefan; Kluwick, Alfred
2002-06-01
We consider the steady viscous/inviscid interaction of a two-dimensional, nearly separated, boundary layer with an isolated three-dimensional surface-mounted obstacle, for example in the large Reynolds number flow around the leading edge of a slender airfoil at a small angle of attack. An integro-differential equation describing the effect of the obstacle on the wall shear stress valid within the interaction regime is derived and solved numerically by means of a spectral method, which is outlined in detail. Typical solutions of this equation are presented for different values of the spanwise width B of the obstacle including the limiting cases B [rightward arrow] 0 and B [rightward arrow] [infty infinity]. Special emphasis is placed on the occurrence of non-uniqueness. On the main (upper) solution branch the disturbances to the flow field caused by the obstacle decay in the lateral direction. Conversely a periodic flow pattern, having no decay in the spanwise direction, was found to form on the lower solution branch. These branches are connected by a bifurcation point, which characterizes the maximum (critical) angle of attack for which a solution of the strictly plane interaction problem exists. An asymptotic investigation of the interaction equation, in the absence of any obstacle, for small deviations of this critical angle clearly reflects the observed behaviour of the numerical results corresponding to the different branches. As a result we can conclude that the primarily local interaction process breaks down in a non-local manner even in the limit of vanishing (three-dimensional local) disturbances of the flow field.