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1

Design of minimum drag bodies in incompressible laminar flow

The problem of modifying the shape of a two-dimensional body to reduce its drag while maintaining its section area (volume per unit span) constant is addressed. Two-dimensional, incompressible, laminar flow governed by the steady-state Navier-Stokes equations is assumed about the body. In this study, a set of “adjoint” equations are solved which permits the calculation of the direction and relative

Jianchun Huan; Vijay Modi

1996-01-01

2

Analysis of Laminar Incompressible Flow on Semiporous Channels

NASA Technical Reports Server (NTRS)

Perturbation solutions for laminar incompressible flow in semiporous and fully porous channels are compared. The perturbation parameter measures the amount of suction or blowing at the porous wall. The velocity profile and the wall friction parameter are more affected by suction or blowing for the semiporous channel than for the fully porous channel. For blowing through the wall, the pressure decreases in channel direction for both channels; with sufficiently high suction rates, the analysis showed that the pressure rises in flow direction for the fully porous channel.

Donoughe, Patrick L

1956-01-01

3

Laminar Incompressible Flow Past Parabolic Bodies at Angles of Attack

NASA Astrophysics Data System (ADS)

Numerical solutions of a two-dimensional steady laminar incompressible flow over semi-infinite parabolic bodies at angles of attack are obtained. All solutions are found by using a modified numerical approach to solve the time-dependent Navier-Stokes equations. A check of our solutions to those that exist in the literature at zero angle of attack showed excellent agreement. In addition, at zero angle of attack far from the leading edge, an expected correspondence to Blasius flow was found. At large enough angles of attack, the flow separated on the suction surface. In all the cases examined, the flow separation was followed by a reattachment that defined a separation zone. An almost linear increase in the streamwise extent of the separation zone occurred with increasing angle of attack. The separation location and extent of the separation zone was a function of the nose Reynolds number. The results indicated that the shape factor could be used to provide a criterion for separation and reattachment in these cases. The characteristics of the separation zone for this geometry proved to be an excellent basic flow to document the effect of leading-edge flow separation on acoustic receptivity of boundary layer instabilities.

Erturk, Ercan; Corke, Thomas; Haddad, Osamah

2003-11-01

4

Finite point solver for the simulation of 2-D laminar incompressible unsteady flows

A finite point solver has been developed to simulate 2-D laminar incompressible unsteady flow fields in the low Reynolds number regime (Reynolds of the order of 100–1000). Grid points, without connectivity in the classic sense, are scattered all over the computational domain, and a certain flow functional behaviour is assumed to hold in a small region around each point. Two

B. Mendez; A. Velazquez

2004-01-01

5

Transient radiative energy transfer in incompressible laminar flows

NASA Technical Reports Server (NTRS)

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.

Tiwari, S. N.; Singh, D. J.

1987-01-01

6

NASA Technical Reports Server (NTRS)

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.

Thiede, P.

1978-01-01

7

Optimum design of minimum drag bodies in incompressible laminar flow using a control theory approach

The problem of modifying the shape of a two-dimensional body to reduce its drag while maintaining its section area (volume per unit span) constant is addressed. Two-dimensional, incompressible, laminar flow governed by the steady-state Navier-Stokes equations is assumed about the body. In this paper, a set of “adjoint” equations is obtained, the solution to which permits the calculation of the

Jianchun Huan; Vijay Modi

1994-01-01

8

A finite difference scheme for three-dimensional steady laminar incompressible flow

NASA Technical Reports Server (NTRS)

A finite difference scheme for three-dimensional steady laminar incompressible flows is presented. The Navier-Stokes equations are expressed conservatively in terms of velocity and pressure increments (delta form). First order upwind differences are used for first order partial derivatives of velocity increments resulting in a diagonally dominant matrix system. Central differences are applied to all other terms for second order accuracy. The SIMPLE pressure correction algorithm is used to satisfy the continuity equation. Numerical results are presented for cubic cavity flow problems for Reynolds numbers up to 2000 and are in good agreement with other numerical results.

Hwang, Danny P.; Huynh, Hung T.

1987-01-01

9

NASA Technical Reports Server (NTRS)

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.

Sohn, Jeong L.

1988-01-01

10

Incompressible laminar flow through hollow fibers: a general study by means of a two-scale approach

NASA Astrophysics Data System (ADS)

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 ?. 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).

Borsi, Iacopo; Farina, Angiolo; Fasano, Antonio

2011-08-01

11

NASA Astrophysics Data System (ADS)

The laminar and fully developed flows of two immiscible fluids confined in a thin slit of constant wall heat fluxes are analyzed in terms of entropy generations due to irreversibility of forced convection heat transfer. The governing equations are analytically derived using expressions for velocity distributions. The derived equation for the dimensionless entropy generation number is used to interpret the relative importance of frictions to conduction by varying irreversibility distribution ratio ?. It is found that the minimum entropy generation takes place at the dimensionless half transverse distance (?) of 0.3 for values of ? higher than zero. The entropy generation near the plate increases more rapidly in fluid I than in fluid II as viscous dissipation effects becomes more important. The velocity profiles are found to be in agreement with the distributions of the dimensionless entropy generation number ( N S ) for two-immiscible incompressible flows in the slit.

Kam??l?, Fethi; Öztop, Hakan F.

2008-04-01

12

Natural laminar flow and laminar flow control

NASA Technical Reports Server (NTRS)

The present volume discusses the development history and basic concepts of laminar flow control, laminar flow flight experiments, subsonic laminar-flow airfoils, and a design philosophy for long-range laminar flow-control commercial transports with advanced supercritical airfoils. Also discussed are the relationship of wave-interaction theory to laminar flow control, supersonic laminar flow control, and the NASA-Langley 8-ft Transonic Pressure Tunnel.

Barnwell, R. W. (editor); Hussaini, M. Y. (editor)

1992-01-01

13

The laminar and fully developed flows of two immiscible fluids confined in a thin slit of constant wall heat fluxes are analyzed\\u000a in terms of entropy generations due to irreversibility of forced convection heat transfer. The governing equations are analytically\\u000a derived using expressions for velocity distributions. The derived equation for the dimensionless entropy generation number\\u000a is used to interpret the

Fethi Kamisli; Hakan F. Öztop

2008-01-01

14

Laminar Flow Aircraft Certification

NASA Technical Reports Server (NTRS)

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.

Williams, Louis J. (compiler)

1986-01-01

15

NASA Astrophysics Data System (ADS)

The paper presents a novel, efficient and accurate algorithm for laminar and turbulent flow simulations. The spatial discretisation is performed with help of the compact difference schemes (up to 10th order) for collocated and half-staggered grid arrangements. The time integration is performed by a predictor-corrector approach combined with the projection method for pressure-velocity coupling. At this stage a low order discretisation is introduced which considerably decreases the computational costs. It is demonstrated that such approach does not deteriorate the solution accuracy significantly. Following Boersma B.J. [13] the interpolation formulas developed for staggered uniform meshes are used also in the computations with a non-uniform strongly varying nodes distribution. In the proposed formulation of the projection method such interpolation is performed twice. It is shown that it acts implicitly as a high-order low pass filter and therefore the resulting algorithm is very robust. Its accuracy is first demonstrated based on simple 2D and 3D problems: an inviscid vortex advection, a decay of Taylor-Green vortices, a modified lid-driven cavity flow and a dipole-wall interaction. In periodic flow problems (the first two cases) the solution accuracy exhibits the 10th order behaviour, in the latter cases the 3rd and the 4th order is obtained. Robustness of the proposed method in the computations of turbulent flows is demonstrated for two classical cases: a periodic channel with Re?=395 and Re?=590 and a round jet with Re=21 000. The solutions are obtained without any turbulence model and also without any explicit techniques aiming to stabilise the solution. The results are in a very good agreement with literature DNS and LES data, both the mean and r.m.s. values are predicted correctly.

Tyliszczak, Artur

2014-11-01

16

Aircraft laminar flow control (LFC) from the 1930s through the 1990s 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

Ronald D. Joslin

1998-01-01

17

A numerical study of incompressible juncture flows

NASA Technical Reports Server (NTRS)

The laminar, steady juncture flow around single or multiple posts mounted between two flat plates is simulated using the three dimensional incompressible Navier-Stokes code, INS3D. The three dimensional separation of the boundary layer and subsequent formation and development of the horseshoe vortex is computed. The computed flow compares favorably with the experimental observation. The recent numerical study to understand and quantify the juncture flow relevant to the Space Shuttle main engine power head is summarized.

Kwak, D.; Rogers, S. E.; Kaul, U. K.; Chang, J. L. C.

1986-01-01

18

NASA Technical Reports Server (NTRS)

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.

Joslin, Ronald D.

1998-01-01

19

NASA Technical Reports Server (NTRS)

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.

Somers, Dan M. (Inventor)

2005-01-01

20

Supersonic laminar flow control research

NASA Technical Reports Server (NTRS)

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.

Lo, C. F.

1994-01-01

21

Supersonic laminar flow control research

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)

Ching F. Lo

1994-01-01

22

Development of a flow-condition-based interpolation 9-node element for incompressible flows

The Navier-Stokes equations are widely used for the analysis of incompressible laminar flows. If the Reynolds number is increased to certain values, oscillations appear in the finite element solution of the Navier-Stokes ...

Banijamali, Bahareh

2006-01-01

23

Unified approach for incompressible flows

NASA Technical Reports Server (NTRS)

A unified approach for solving incompressible flows has been investigated in this study. The numerical CTVD (Centered Total Variation Diminishing) scheme used in this study was successfully developed by Sanders and Li for compressible flows, especially for the high speed. The CTVD scheme possesses better mathematical properties to damp out the spurious oscillations while providing high-order accuracy for high speed flows. It leads us to believe that the CTVD scheme can equally well apply to solve incompressible flows. Because of the mathematical difference between the governing equations for incompressible and compressible flows, the scheme can not directly apply to the incompressible flows. However, if one can modify the continuity equation for incompressible flows by introducing pseudo-compressibility, the governing equations for incompressible flows would have the same mathematical characters as compressible flows. The application of the algorithm to incompressible flows thus becomes feasible. In this study, the governing equations for incompressible flows comprise continuity equation and momentum equations. The continuity equation is modified by adding a time-derivative of the pressure term containing the artificial compressibility. The modified continuity equation together with the unsteady momentum equations forms a hyperbolic-parabolic type of time-dependent system of equations. Thus, the CTVD schemes can be implemented. In addition, the physical and numerical boundary conditions are properly implemented by the characteristic boundary conditions. Accordingly, a CFD code has been developed for this research and is currently under testing. Flow past a circular cylinder was chosen for numerical experiments to determine the accuracy and efficiency of the code. The code has shown some promising results.

Chang, Tyne-Hsien

1995-01-01

24

Supersonic laminar flow control research

NASA Technical Reports Server (NTRS)

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.

Lo, Ching F.

1994-01-01

25

Unified approach for incompressible flows

NASA Technical Reports Server (NTRS)

An unified approach for solving both compressible and incompressible flows was investigated in this study. The difference in CFD code development between incompressible and compressible flows is due to the mathematical characteristics. However, if one can modify the continuity equation for incompressible flows by introducing pseudocompressibility, the governing equations for incompressible flows would have the same mathematical characters as compressible flows. The application of a compressible flow code to solve incompressible flows becomes feasible. Among numerical algorithms developed for compressible flows, the Centered Total Variation Diminishing (CTVD) schemes possess better mathematical properties to damp out the spurious oscillations while providing high-order accuracy for high speed flows. It leads us to believe that CTVD schemes can equally well solve incompressible flows. In this study, the governing equations for incompressible flows include the continuity equation and momentum equations. The continuity equation is modified by adding a time-derivative of the pressure term containing the artificial compressibility. The modified continuity equation together with the unsteady momentum equations forms a hyperbolic-parabolic type of time-dependent system of equations. The continuity equation is modified by adding a time-derivative of the pressure term containing the artificial compressibility. The modified continuity equation together with the unsteady momentum equations forms a hyperbolic-parabolic type of time-dependent system of equations. Thus, the CTVD schemes can be implemented. In addition, the boundary conditions including physical and numerical boundary conditions must be properly specified to obtain accurate solution. The CFD code for this research is currently in progress. Flow past a circular cylinder will be used for numerical experiments to determine the accuracy and efficiency of the code before applying this code to more specific applications.

Chang, Tyne-Hsien

1993-01-01

26

Overview of Laminar Flow Control

The history of Laminar Flow Control (LFC) from the 1930s through the1990s is reviewed and the current status of the technology is assessed. Early studiesrelated to the natural laminar boundary-layer flow physics, manufacturingtolerances for laminar flow, and insect-contamination avoidance are discussed.Although most of this publication is about slot-, porous-, and perforated-suctionLFC concept studies in wind tunnel and flight experiments, some

Ronald D. Joslin

1998-01-01

27

Supersonic Laminar Flow Control Research

NASA Technical Reports Server (NTRS)

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.

Lo, Ching F.; Wiberg, Clark G.

1996-01-01

28

Supersonic laminar flow control research

NASA Technical Reports Server (NTRS)

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.

Lo, Ching F.; Wiberg, Clark G.

1995-01-01

29

Flight experiences with laminar flow

NASA Technical Reports Server (NTRS)

A review of natural laminar flow (NLF) flight experiences over the period from the 1930's to the present has been given to provide information on the achievability and maintainability of NLF in typical airplane operating environments. Significant effects of loss of laminar flow on airplane performance have been observed for several airplanes, indicating the importance of providing information on these changes to laminar flow airplane operators. Significant changes in airplane stability and control and maximum lift were observed in flight experiments with the loss of laminar flow. However, these effects can be avoided by proper selection of airfoils. Conservative laminar flow airfoil designs should be employed which do not experience significant loss of lift (caused by flow separation) upon the loss of laminar flow. Mechanisms have been observed for the effects of insect accumulation, flight through clouds and precipitation, and propeller slipstreams on laminar flow behavior. Fixed transition testing, in addition to free transition testing, is recommended as a new standard procedure for airplanes with surfaces designed to support laminar flow.

Holmes, Bruce J.

1986-01-01

30

Supersonic laminar flow control research

NASA Technical Reports Server (NTRS)

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.

Lo, Ching F.; Wiberg, Clark G.

1995-01-01

31

COMPUTATIONAL FLUID DYNAMICS INCOMPRESSIBLE FLOW

LECTURES in COMPUTATIONAL FLUID DYNAMICS of INCOMPRESSIBLE FLOW: Mathematics, Algorithms 1991, 2003, 2007 #12;PROLOGUE Computational fluid dynamics (CFD) can be traced to the early attempts Race" with the (former) Soviet Union, beginning in the late 1950s. The terminology "computational fluid

McDonough, James M.

32

Laminar flow control - viscous simulation

Laminar flow control which offers the possibility of major reductions in aircraft drag is described. The theoretical background for the possible stabilizations of the laminar boundary layer due to shaping, suction and cooling is presented. The effects of vehicle and environmental factors on the implementation of that technology are examined. Viscous simulation is the technology of adjusting boundary layer conditions

E. Reshotko

1984-01-01

33

Supersonic Laminar Flow Control Research

NASA Technical Reports Server (NTRS)

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.

Lo, C. F.; Wiberg, Clark G.

1996-01-01

34

Laminar flow control is maturing

NASA Technical Reports Server (NTRS)

Recent research demonstrates that laminar flow (LF) can be reliable in flight and that the support system need not be complex. Shaping produces favorable pressure gradients for maintaining natural laminar flow (NLF), and laminar flow control (LFC) techniques such as full chord suction promise a fuel-saving payoff of up to 30 percent on long-range missions. For large aircraft, current research is concentrated on hybrid LFC concepts which combine suction and pressure-gradient control. At NASA Ames, an F-14 with variable wing sweep has been flight tested with smooth surface gloves on the wings; preliminary results indicate high transition Reynolds numbers to sweep angles as large as 25 deg. In addition, a 757 was flight tested with an NLF glove on the right wing just outboard of the engine pylon; and the LF was found to be suprisingly robust.

Wagner, Richard D.; Bartlett, Dennis W.; Maddalon, Dal V.

1988-01-01

35

Hybrid laminar flow control study

NASA Technical Reports Server (NTRS)

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.

1982-01-01

36

Supersonic laminar-flow control

NASA Technical Reports Server (NTRS)

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.

Bushnell, Dennis M.; Malik, Mujeeb R.

1987-01-01

37

Computational Challenges of Viscous Incompressible Flows

NASA Technical Reports Server (NTRS)

Over the past thirty years, numerical methods and simulation tools for incompressible flows have been advanced as a subset of the computational fluid dynamics (CFD) discipline. Although incompressible flows are encountered in many areas of engineering, simulation of compressible flow has been the major driver for developing computational algorithms and tools. This is probably due to the rather stringent requirements for predicting aerodynamic performance characteristics of flight vehicles, while flow devices involving low-speed or incompressible flow could be reasonably well designed without resorting to accurate numerical simulations. As flow devices are required to be more sophisticated and highly efficient CFD took become increasingly important in fluid engineering for incompressible and low-speed flow. This paper reviews some of the successes made possible by advances in computational technologies during the same period, and discusses some of the current challenges faced in computing incompressible flows.

Kwak, Dochan; Kiris, Cetin; Kim, Chang Sung

2004-01-01

38

Laminar flow control for transport aircraft applications

NASA Technical Reports Server (NTRS)

The incorporation of laminar flow control into transport aircraft is discussed. Design concepts for the wing surface panel of laminar flow control transport aircraft are described. The development of small amounts of laminar flow on small commercial transports with natural or hybrid flow control is examined. Techniques for eliminating the insect contamination problem in the leading-edge region are proposed.

Wagner, R. D.

1986-01-01

39

Smart Suction for Laminar Flow Control on Swept Wings

Results of high-order direct numerical simulations are summarized for the evolution of crossflow disturbances in incompressible wing-generic boundary-layers with suction at the wall. The concept of smart suction, an adapted combination of the upstream-flow-deform- ation (UFD) technique and suction, is presented for laminar flow control. In the UFD technique, relatively tightly spaced, useful crossflow vortices (CFVs) are excited once, grow

Tillmann A. Friederich; Markus J. Kloker

2008-01-01

40

Laminar-flow flight experiments

NASA Technical Reports Server (NTRS)

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.

Wagner, Richard D.; Maddalon, Dal V.; Bartlett, D. W.; Collier, F. S., Jr.; Braslow, A. L.

1989-01-01

41

Laminar flow: Challenge and potential

NASA Technical Reports Server (NTRS)

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.

Kirchner, Mark E.

1987-01-01

42

Radiative interactions in laminar duct flows

NASA Technical Reports Server (NTRS)

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.

Trivedi, P. A.; Tiwari, S. N.

1990-01-01

43

Application of the e sup N method to calculations of laminar flow control

The e sup N method was applied to two-dimensional, incompressible laminar boundary layers with and without suction with the aim of developing an aerodynamic design method for a laminar flow control airfoil. The method consisted of an airfoil, boundary layer and e sup N codes, respectively. The airfoil code used the vortex singularity method and the boundary layer code Keller's

Y. Ishida; N. Itoh

1985-01-01

44

Operational considerations for laminar flow aircraft

NASA Technical Reports Server (NTRS)

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.

Maddalon, Dal V.; Wagner, Richard D.

1986-01-01

45

Accurate solution algorithms for incompressible multiphase flows

A number of advances in modeling multiphase incompressible flow are described. These advances include high-order Godunov projection methods, piecewise linear interface reconstruction and tracking and the continuum surface force model. Examples are given.

Rider, W.J.; Kothe, D.B.; Mosso, S.J.; Cerutti, J.H. [Los Alamos National Lab., NM (United States); Hochstein, J.I. [Memphis State Univ., TN (United States). Dept. of Mechanical Engineering

1994-10-19

46

Laminar and Turbulent Flow in Water

ERIC Educational Resources Information Center

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…

Riveros, H. G.; Riveros-Rosas, D.

2010-01-01

47

Investigation of an incompressible flow along a corner by an alternating direction implicit method

NASA Technical Reports Server (NTRS)

The axial corner flow is analyzed for the incompressible laminar boundary layer flow. The governing equations are derived from the Navier-Stokes equations by neglecting second derivative terms of the axial direction. An alternating direction implicit method is used to solve the equations in primitive variables.

Goglia, G. L.; Patel, D. K.

1977-01-01

48

The current paper reports on the development and validation of a localized collocation meshless method (LCMM) to model laminar incompressible flows. A high order upwinding scheme was devised to dampen the numerical oscillations arising in convection-dominated flows. Subsequently, the LCMM was analytically validated and demonstrated to yield third-order accurate solutions when compared to a benchmark analytical decaying vortex solution. Numerical

Z. El Zahab; E. Divo; A. J. Kassab

2009-01-01

49

Supersonic laminar flow control on commercial transports

NASA Technical Reports Server (NTRS)

This paper provides an overview of the status of supersonic laminar flow control. Existing research into the aerodynamic problems of subsonic and supersonic laminar flow control is first reviewed to provide a prospective for subsequent discussions of recent studies to evaluate the potential performance benefits of the application of laminar flow control to supersonic transports. A flight research program to provide a realistic assessment of the technical feasibility is then described.

Wagner, R. D.; Fischer, M. C.; Collier, F. S., Jr.; Pfenninger, W.

1990-01-01

50

Laminar Flow Control at High Speeds

Laminar flow control has always meant controlling the amplitude of linearly unstable waves before transition can occur. In many physical cases, the control of linear Tollmien-Schlichting (T-S) waves is sufficient to prevent transition and many successful demonstrations, including natural laminar flow airfoils, have occurred. Supersonic flight presents another set of challenges that complicates the control process. One has the possibilities

William Saric

2003-01-01

51

Laminar motion of the incompressible fluids in self-acting thrust bearings with spiral grooves.

We analyze the laminar motion of incompressible fluids in self-acting thrust bearings with spiral grooves with inner or external pumping. The purpose of the study is to find some mathematical relations useful to approach the theoretical functionality of these bearings having magnetic controllable fluids as incompressible fluids, in the presence of a controllable magnetic field. This theoretical study approaches the permanent motion regime. To validate the theoretical results, we compare them to some experimental results presented in previous papers. The laminar motion of incompressible fluids in bearings is described by the fundamental equations of fluid dynamics. We developed and particularized these equations by taking into consideration the geometrical and functional characteristics of these hydrodynamic bearings. Through the integration of the differential equation, we determined the pressure and speed distributions in bearings with length in the "pumping" direction. These pressure and speed distributions offer important information, both quantitative (concerning the bearing performances) and qualitative (evidence of the viscous-inertial effects, the fluid compressibility, etc.), for the laminar and permanent motion regime. PMID:24526896

Velescu, Cornel; Popa, Nicolae Calin

2014-01-01

52

Efficient solutions of two-dimensional incompressible steady viscous flows

NASA Technical Reports Server (NTRS)

A simple, efficient, and robust numerical technique is provided for solving two dimensional incompressible steady viscous flows at moderate to high Reynolds numbers. The proposed approach employs an incremental multigrid method and an extrapolation procedure based on minimum residual concepts to accelerate the convergence rate of a robust block-line-Gauss-Seidel solver for the vorticity-stream function Navier-Stokes equations. Results are presented for the driven cavity flow problem using uniform and nonuniform grids and for the flow past a backward facing step in a channel. For this second problem, mesh refinement and Richardson extrapolation are used to obtain useful benchmark solutions in the full range of Reynolds numbers at which steady laminar flow is established.

Morrison, J. H.; Napolitano, M.

1986-01-01

53

Laminar Flow Control Flight Experiment Design

this envelope, flight conditions are determined which meet evaluation criteria for minimum lift coefficient and crossflow transition location. The angle of attack data band is determined, and the natural laminar flow characteristics are evaluated. Finally, DRE...

Tucker, Aaron 1975-

2012-11-29

54

Numerical study of asymmetric laminar flow of micropolar fluids in a porous channel

A numerical study is presented for the two-dimensional flow of a micropolar fluid in a porous channel. The channel walls are of different permeability. The fluid motion is superimposed by the large injection at the two walls and is assumed to be steady, laminar and incompressible. The micropolar model due to Eringen is used to describe the working fluid. The

Muhammad Ashraf; M. Anwar Kamal; K. S. Syed

2009-01-01

55

The dynamics of a laminar flow in a symmetric channel with a sudden expansion

Bifurcation analysis, linear stability study, and direct numerical simulations of the dynamics of a two-dimensional, incompressible, and laminar flow in a symmetric long channel with a sudden expansion with right angles and with an expansion ratio D=d (d is the width of the channel inlet section and D is the width of the outlet section) are presented. The bifurcation analysis

T. H AWA; Z. R USAK

2001-01-01

56

An acoustic analogy applied to the laminar upstream flow over an open 2D cavity

NASA Astrophysics Data System (ADS)

In this work a modified version of the Lighthill-Curle's analogy is applied to study the near field acoustics of an upstream laminar flow past an open cavity. Three incompressible cases have been computed and are compared against the corresponding compressible results. The three incompressible cases are carried out with different time-step sizes, distances from the cavity trailing edge to the outlet and spatial resolution in the streamwise direction. The aim of the work is to study the differences in compressible and incompressible sources in Lighthill-Curle's equation and their influence on the sound radiated. To cite this article: J. Ask, L. Davidson, C. R. Mecanique 333 (2005).

Ask, Jonas; Davidson, Lars

2005-09-01

57

Research in natural laminar flow and laminar-flow control, part 3

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.

Hefner, J.N.; Sabo, F.E.

1987-12-01

58

Research in natural laminar flow and laminar-flow control, part 3

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

J. N. Hefner; F. E. Sabo

1987-01-01

59

NASA Technical Reports Server (NTRS)

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.

Brooks, Cuyler W., Jr.; Harris, Charles D.; Harvey, William D.

1991-01-01

60

Spiral Laminar Flow: A revolution in understanding?

Blood Flow Spiral laminar flow #12;Spiral flow in the Aorta (MRI) Computational Fluid Dynamics 0 10 20 = Stent failure Turbulence associated with: - Altered wall shear stress - Damage lining artery - Cellular downstream intimal thickening Results -Downstream Disease Progression #12;Summary Spiral Stent Turbulence

Greenaway, Alan

61

Stability theory for laminar flow control design

Both passive and active techniques of laminar-flow control (LFC) require reliable methods for prediction of boundary layer transitions, as well as for quantification of LFC sensitivity to such control parameters as Mach number, pressure gradient, wall temperature, angle of attack, sweep, flow history, surface curvature, volume rotation, and flow chemistry. An account is presently given to a linear stability theory-based

Mujeeb R. Malik

1990-01-01

62

High-End Computing for Incompressible Flows

NASA Technical Reports Server (NTRS)

The objective of the First MIT Conference on Computational Fluid and Solid Mechanics (June 12-14, 2001) is to bring together industry and academia (and government) to nurture the next generation in computational mechanics. The objective of the current talk, 'High-End Computing for Incompressible Flows', is to discuss some of the current issues in large scale computing for mission-oriented tasks.

Kwak, Dochan; Kiris, Cetin

2001-01-01

63

Advanced stability analysis for laminar flow control

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

S. A. Orszag

1981-01-01

64

Flow Solver for Incompressible Rectangular Domains

NASA Technical Reports Server (NTRS)

This is an extension of the Flow Solver for Incompressible 2-D Drive Cavity software described in the preceding article. It solves the Navier-Stokes equations for incompressible flow using finite differencing on a uniform, staggered grid. There is a runtime choice of either central differencing or modified upwinding for the convective term. The domain must be rectangular, but may have a rectangular walled region within it. Currently, the position of the interior region and exterior boundary conditions are changed by modifying parameters in the code and recompiling. These features make it possible to solve a variety of classical fluid flow problems such as an L-shaped cavity, channel flow, or wake flow past a square cylinder. The code uses fourth-order Runge-Kutta time-stepping and overall second-order spatial accuracy. This software permits the walled region to be positioned such that flow past a square cylinder, an L-shaped cavity, and the flow over a back-facing step can all be solved by reconfiguration. Also, this extension has an automatic detection of periodicity, as well as use of specialized data structure for ease of configuring domain decomposition and computing convergence in overlap regions.

Kalb, Virginia L.

2008-01-01

65

Laminar flow control - Introduction and overview

NASA Technical Reports Server (NTRS)

A development history and a development-trends evaluation are presented for laminar flow controlled airfoil technologies and design concepts, including the search for 'natural' laminar flow and actively controlled flow via suction through small pores on the airfoil surface. While most NASA activities in this field have been concerned with subsonic aircraft, it has been projected that the control of boundary layer turbulence may be even more critical to the aerodynamic efficiency of supersonic aircraft. Developmental programs for these techniques have been conducted with several modified conventional aircraft.

Hefner, Jerry N.

1992-01-01

66

Multiscale laminar flows with turbulentlike properties.

By applying fractal electromagnetic force fields on a thin layer of brine, we generate steady quasi-two-dimensional laminar flows with multiscale stagnation point topology. This topology is shown to control the evolution of pair separation (Delta) statistics by imposing a turbulentlike locality based on the sizes and strain rates of hyperbolic stagnation points when the flows are fast enough, in which case Delta(2) approximately t(gamma) is a good approximation with gamma close to 3. Spatially multiscale laminar flows with turbulentlike spectral and stirring properties are a new concept with potential applications in efficient and microfluidic mixing. PMID:17155255

Rossi, Lionel; Vassilicos, J C; Hardalupas, Yannis

2006-10-01

67

Transition caused by the laminar flow separation

NASA Technical Reports Server (NTRS)

An experimental investigation of the effects of the geometry of body surface, Reynolds number, stream turbulence, and a roughness element (wire) on the reattachment of separated laminar boundary-layer flow on a bent flat plate is presented and discussed. The flow mechanisms determining reattachment of the boundary layer are analyzed and discussed.

Maekawa, T; Atsumi, Shoichi

1952-01-01

68

Method for the evaluation of minor losses in pulsatile laminar fluid flow

NASA Astrophysics Data System (ADS)

This article focuses on description and evaluation of the size of the minor losses in pulsatile laminar flow. It describes a method for determination of minor losses with respect to the phase delay between pressure waveforms and flow waveforms. The whole evaluation method is presented on the example of minor loss in the sharp 90° bend in the channel with constant square cross-section in pulsatile laminar flow of an incompressible Newtonian fluid. For this example, the minor loss coefficient is expressed depending on the dimensionless flow parameters. Total minor loss was calculated numerically. An analytical solution was used for quantification of the head loss in the developed laminar flow in the straight channel. Unsteady flow conditions were controlled by the sinusoidal flow.

Net?ebská, H.; Mat?cha, J.; Schmirler, M.; Manoch, L.; Adamec, J.

2014-03-01

69

Wing Leading Edge Joint Laminar Flow Tests

NASA Technical Reports Server (NTRS)

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.

Drake, Aaron; Westphal, Russell V.; Zuniga, Fanny A.; Kennelly, Robert A., Jr.; Koga, Dennis J.

1996-01-01

70

Progress In Incompressible Pump Flow Calculations

NASA Technical Reports Server (NTRS)

Steady and unsteady flows for propulsion systems are efficiently simulated by solving the incompressible Navier-Stokes equations. The solution method is based on the pseudo compressibility approach and uses an implicit-upwind differencing scheme together with the Gauss-Seidel line relaxation method. Current computations use one equation Baldwin-Barth turbulence model which is derived from a simplified form of the standard kappa - epsilon model equations. The resulting computer code is applied to the flow analysis inside an advanced rocket pump impeller in steadily rotating reference frames. Numerical results are compared with experimental measurements. The effects of exit and shroud cavities with the leak-age flow are investigated. Time-accurate incompressible Navier-Stokes formulation with the overlapped grid scheme capability was evaluated by using MIT flapping foil experiment. The grid dependency, turbulence model effects, and the effect of order of differencing were investigated. Numerical results were compared against experimental data. The resulting procedure were applied to unsteady flapping foil calculations. Two upstream NACA 0025 foils perform high frequency synchronized motion and generate unsteady flow conditions to the downstream larger stationary foil. Comparison between unsteady experimental data and numerical results from two different moving boundary procedures will be presented.

Kiris, Cetin; Kwak, Dochan; Kutler, Paul (Technical Monitor)

1994-01-01

71

On the flow of a viscous incompressible fluid between two coaxial rotating porous cylinders

Exact solution of the Navier-Stokes equations for the laminar flow of a viscous incompressible fluid between two coaxial rotating\\u000a porous cylinders, kept at constant temperatures, has been studied. The rate of injection at one cylinder is taken to be the\\u000a same as the rate of suction at the other. Expressions for the velocity and temperature distributions and for the torque

N. C. Jain; J. L. Bansal

1973-01-01

72

Skin-Friction Measurements in Incompressible Flow

NASA Technical Reports Server (NTRS)

Experiments have been conducted to measure the local surface-shear stress and the average skin-friction coefficient in Incompressible flow for a turbulent boundary layer on a smooth flat plate having zero pressure gradient. Data were obtained for a range of Reynolds numbers from 1 million to 45 million. The local surface-shear stress was measured by a floating-element skin-friction balance and also by a calibrated total head tube located on the surface of the test wall. The average skin-friction coefficient was obtained from boundary-layer velocity profiles.

Smith, Donald W.; Walker, John H.

1959-01-01

73

Multigrid Approach to Incompressible Viscous Cavity Flows

NASA Technical Reports Server (NTRS)

Two-dimensional incompressible viscous driven-cavity flows are computed for Reynolds numbers on the range 100-20,000 using a loosely coupled, implicit, second-order centrally-different scheme. Mesh sequencing and three-level V-cycle multigrid error smoothing are incorporated into the symmetric Gauss-Seidel time-integration algorithm. Parametrics on the numerical parameters are performed, achieving reductions in solution times by more than 60 percent with the full multigrid approach. Details of the circulation patterns are investigated in cavities of 2-to-1, 1-to-1, and 1-to-2 depth to width ratios.

Wood, William A.

1996-01-01

74

Direct Numerical Simulation of SweptWing Laminar Flow Control Using Pinpoint Suction

\\u000a Recent investigations of laminar flow control for swept-wing boundary-layer flows provide promising results with respect to\\u000a crossflow-transition delay using a technique called pinpoint suction. Strong, localized suction through holes accurately positioned with respect to the crossflow-vortex position can directly\\u000a weaken the growth of secondary instabilities that are responsible for the final laminar breakdown. With our incompressible\\u000a code N3D extremely resolved

Tillmann A. Friederich; Markus J. Kloker

75

Passive laminar flow control of crossflow vorticity

A passive laminar flow crossflow vorticity control system includes an aerodynamic or hydrodynamic surface having geometric perturbations. The perturbations include peaks and valleys having a predetermined spacing and aligned approximately in a streamline direction to force the formation of crossflow vortices. This minimizes amplification and growth of the vortices, thus delaying transition to turbulence and reducing overall drag.

Bruce J. Holmes

1990-01-01

76

Helicity in laminar and turbulent flow

A general theoretical review of helicity in flows that are laminar or turbulent is presented with references to corresponding experimental investigations. The topological nature of the helicity invariant is examined, and the turbulent dynamo mechanism is discussed in relation to the phenomenon of helicity. Helicity is also discussed in terms of being a topological constraint in relaxation to equilibrium, and

H. K. Moffatt; A. Tsinober

1992-01-01

77

Research in natural laminar flow and laminar-flow control, part 1

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.

Hefner, J.N.; Sabo, F.E.

1987-12-01

78

Research in Natural Laminar Flow and Laminar-Flow Control, part 1

NASA Technical Reports Server (NTRS)

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.

Hefner, Jerry N. (compiler); Sabo, Frances E. (compiler)

1987-01-01

79

AIAA 2004-2311 Toward Practical Laminar Flow Control--

AIAA 2004-2311 Toward Practical Laminar Flow Control-- Remaining Challenges William S. Saric Arizona State University Tempe AZ 85287-6106 ABSTRACT Different laminar flow control strategies instability has been the primary challenge for laminar flow control. Favorable pressure gradients used

80

Algebraic Flux Correction III. Incompressible Flow Problems

NASA Astrophysics Data System (ADS)

Algebraic FEM-FCT and FEM-TVD schemes are integrated into incompressible flow solvers based on the `Multilevel Pressure Schur Complement' (MPSC) approach. It is shown that algebraic flux correction is feasible for nonconforming (rotated bilinear) finite element approximations on unstructured meshes. Both (approximate) operator-splitting and fully coupled solution strategies are introduced for the discretized Navier-Stokes equations. The need for development of robust and efficient iterative solvers (outer Newton-like schemes, linear multigrid techniques, optimal smoothers/preconditioners) for implicit high-resolution schemes is emphasized. Numerical treatment of extensions (Boussinesq approximation, ? — ? turbulence model) is addressed and pertinent implementation details are given. Simulation results are presented for three-dimensional benchmark problems as well as for prototypical applications including multiphase and granular flows.

Turek, Stefan; Kuzmin, Dmitri

81

Laminar Flow in the Ocean Ekman Layer

NASA Astrophysics Data System (ADS)

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

Woods, J. T. H.

82

Adjoint operator approach to shape design for internal incompressible flows

NASA Technical Reports Server (NTRS)

The problem of determining the profile of a channel or duct that provides the maximum static pressure rise is solved. Incompressible, laminar flow governed by the steady state Navier-Stokes equations is assumed. Recent advances in computational resources and algorithms have made it possible to solve the direct problem of determining such a flow through a body of known geometry. It is possible to obtain a set of adjoint equations, the solution to which permits the calculation of the direction and relative magnitude of change in the diffuser profile that leads to a higher pressure rise. The solution to the adjoint problem can be shown to represent an artificially constructed flow. This interpretation provides a means to construct numerical solutions to the adjoint equations that do not compromise the fully viscous nature of the problem. The algorithmic and computational aspects of solving the adjoint equations are addressed. The form of these set of equations is similar but not identical to the Navier-Stokes equations. In particular some issues related to boundary conditions and stability are discussed.

Cabuk, H.; Sung, C.-H.; Modi, V.

1991-01-01

83

NITSCHE'S METHOD FOR A TRANSPORT PROBLEM IN TWOPHASE INCOMPRESSIBLE FLOWS

parabolic convectionÂdi#usion equations in the two subdomains# 1 and# 2 . The di#usion coe#cient is assumedNITSCHE'S METHOD FOR A TRANSPORT PROBLEM IN TWOÂPHASE INCOMPRESSIBLE FLOWS ARNOLD REUSKEN AND TRUNG of a dissolved species in twoÂphase incompressible flow problems. Due to the soÂcalled Henry interface condition

84

Numerical simulation of incompressible flows with particle-laden interfaces

#12;Standard model for two-phase flows We assume that the interface is a sharp dividing surface. We assume the fluid to be incompressible, viscous, Newtonian, pure, and isothermal. Fluid dynamics: Navier-phase flows We assume that the interface is a sharp dividing surface. We assume the fluid to be incompressible

85

Investigation of a Laminar Flow Leading Edge

NASA Technical Reports Server (NTRS)

The recent resurgence of interest in utilizing laminar flow on aircraft surfaces for reduction in skin friction drag has generated a considerable amount of research in natural laminar flow (NLF) and hybrid laminar flow control (HLFC) on transonic aircraft wings. This research has focused primarily on airfoil design and understanding transition behavior with little concern for the surface imperfections and manufacturing variations inherent to most production aircraft. In order for laminar flow to find wide-spread use on production aircraft, techniques for constructing the wings must be found such that the large surface imperfections present in the leading edge region of current aircraft do not occur. Toward this end, a modification to existing leading edge construction techniques was devised such that the resulting surface did not contain large gaps and steps as are common on current production aircraft of this class. A lowspeed experiment was first conducted on a simulation of the surface that would result from this construction technique. Preston tube measurements of the boundary layer downstream of the simulated joint and flow visualization using sublimation chemicals validated the literature on the effects of steps on a laminar boundary layer. These results also indicated that the construction technique was indeed compatible with laminar flow. In order to fully validate the compatibility of this construction technique with laminar flow, thus proving that it is possible to build wings that are smooth enough to be used on business jets and light transports in a manner compatible with laminar flow, a flight experiment is being conducted. In this experiment Mach number and Reynolds number will be matched in a real flight environment. The experiment is being conducted using the NASA Dryden F-104 Flight Test Fixture (FTF). The FTF is a low aspect ratio ventral fin mounted beneath an F-104G research aircraft. A new nose shape was designed and constructed for this experiment. This nose shape provides an accelerating pressure gradient in the leading edge region. By flying the aircraft at appropriate Mach numbers and altitudes, this nose shape simulates the leading edge region of a laminar flow wing for a business jet or light transport. Manufactured into the nose shape is a spanwise slot located approximately four inches downstream of the leading edge. The slot, which is an inch wide and one-eighth of an inch deep allows the simulation of surface imperfections, such as gaps and steps at skin joints, which will occur on aircraft using this new construction technique. By placing strips of aluminum of various sizes and shapes in the slot, the effect on the boundary layer of different sizes and shapes of steps and gaps will be examined. It is planned to use five different configurations, differing primarily in the size and number of gaps. Downstream of the slot, the state of the boundary layer is determined using hot film gages and Stanton gages. Agreement between these two very different techniques of measuring boundary layer properties is considered important to being able to state with confidence the effects on the boundary layer of the simulated manufacturing imperfections. To date, the aircraft has not flown. First flights of the aircraft are on schedule to begin October 4, 1993. Low-speed, preliminary experiments at matching Reynolds numbers have been completed.

Drake, Aaron; Kennelly, Robert A., Jr.; Koga, Dennis J.; Westphal, Russell V.; Zuniga, Fanny

1994-01-01

86

Laminar flow instability in nuclear rockets

Laminar flow instability (LFI) is a rarely encountered phenomenon, occurring in gaseous heated channels with high exit-to-inlet temperature ratios and a laminar Reynolds Number at the channel exit, as may be experienced in a nuclear rocket. Analytical techniques were developed and programmed for parametric evaluation that had been previously validated by comparison with available experimental data. The four types of transients associated with LFI are described in terms of the governing equations. Parametric evaluations of solid core prismatic and particle bed fuel configurations were made to determine their sensitivities to LFI from temperature ratio, flow rate, orificing, transition Reynolds Number, pressure level, presence of an exit sonic nozzle, power density and heat flux shape. The flow rate at the point of neutral stability and the growth rate of the excursive transient are calculated. The full power design point and the cooldown phases of operation were both evaluated.

Black, D.L. (628 C Street, S. E., Washington, DC 20003-4302 (United States))

1993-01-20

87

Incompressible flows with piecewise constant density

We investigate the incompressible Navier-Stokes equations with variable density. The aim is to prove existence and uniqueness results in the case of discontinuous ini- tial density. In dimension n = 2, 3, assuming only that the initial density is bounded and bounded away from zero, and that the initial velocity is smooth enough, we get the local-in-time existence of unique solutions. Uniqueness holds in any dimension and for a wider class of velocity fields. Let us emphasize that all those results are true for piecewise constant densities with arbitrarily large jumps. Global results are established in dimension two if the density is close enough to a positive constant, and in n-dimension if, in addition, the initial velocity is small. The Lagrangian formula- tion for describing the flow plays a key role in the analysis that is proposed in the present paper.

Danchin, Raphaël

2012-01-01

88

Incompressible Flows with Piecewise Constant Density

NASA Astrophysics Data System (ADS)

We investigate the incompressible Navier-Stokes equations with variable density. The aim is to prove existence and uniqueness results in the case of discontinuous initial density. In dimension n = 2,3, assuming only that the initial density is bounded and bounded away from zero, and that the initial velocity is smooth enough, we get the local-in-time existence of unique solutions. Uniqueness holds in any dimension and for a wider class of velocity fields. In particular, all those results are true for piecewise constant densities with arbitrarily large jumps. Global results are established in dimension two if the density is close enough to a positive constant, and in n dimensions if, in addition, the initial velocity is small. The Lagrangian formulation for describing the flow plays a key role in the analysis that is proposed in the present paper.

Danchin, Raphaël; Mucha, Piotr Bogus?aw

2013-03-01

89

Laminar Flow Through Circular Tubes with Side Inlets

NASA Astrophysics Data System (ADS)

We discuss experimental results on steady axisymmetric flow of a Newtonian incompressible fluid through circular pipes with side inlets. Circular tubes with a set of holes along their sidewalls are used in a number of medical procedures as straight catheters to transfer fluid into or out of the human body. For example, because of the small size of the incision required, they are commonly used in peritoneal dialysis. The internal diameter and the diameter of the side holes are often 1 mm and less, and as a result, the fluid flow is laminar in a typical medical procedure. An understanding of the flow inside the catheter tube in terms of its geometric parameters will be key in designing new catheters with optimal clinical performance for specific applications. In the experiments, water is withdrawn from a smooth tube with side holes and the local axial pressure and flow rates through the side holes are measured for different flow conditions. A nondimensionalization of the data shows a power-law behavior in only some cases. Using numerical simulations, it is shown how the interaction of the axial flow with the impinging jets from the side holes can change the overall behavior of the flow for a given suction pressure.

Abedian, Behrouz; Muhlanger, Eric

2004-11-01

90

Local pressure preconditioning method for steady incompressible flows

The convergence and accuracy characteristics of the preconditioned incompressible Euler and Navier–Stokes equations are studied. An object-oriented C++ numerical code has been developed for solving the inviscid and viscous, steady, incompressible flows problems. The code is based on the cell-centred finite volume method. In this scheme, two-dimensional incompressible Euler and Navier–Stokes equations are modified by a robust artificial compressibility (AC)

V. Esfahanian; P. Akbarzadeh

2010-01-01

91

Laminar flow control SPF\\/08 feasibility demonstration

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

R. C. Ecklund; N. R. Williams

1981-01-01

92

Laminar nanofluid flow in microheat-sinks

In response to the ever increasing demand for smaller and lighter high-performance cooling devices, steady laminar liquid nanofluid flow in microchannels is simulated and analyzed. Considering two types of nanofluids, i.e., copper-oxide nanospheres at low volume concentrations in water or ethylene glycol, the conjugated heat transfer problem for microheat-sinks has been numerically solved. Employing new models for the effective thermal

J. Koo; C. Kleinstreuer

2005-01-01

93

Transition to turbulence in laminar hypersonic flow

NASA Technical Reports Server (NTRS)

Progress in a recently started project aimed at the prediction of transition to turbulence in hypersonic flow is briefly discussed. The prediction of transition to turbulence is a very important issue in the design of space vessels. Two space vehicles currently under investigation, namely the aeroassisted transfer vehicle (AOTV) and the trans-atmospheric vehicle (TAV), suffer from strong aerodynamic heating. This heating is strongly influenced by the boundary layer structure. These aerospace vehicles fly in the upper atmospheric layer at a Mach number between 10 and 30 at very low atmospheric pressures. At very high altitudes the flow is laminar, but when the space vessel returns to a lower orbit, the flow becomes turbulent and the heating is dramatically increased. The prediction of this transition process is commonly done by means of experiments. The experimental facilities available nowadays cannot model the hypersonic flow field accurately enough by limitations in Mach and Reynolds number. These facilities also have a large free stream disturbance level which makes it very difficult to investigate transition accurately. An alternative approach is to study transition by theoretical means. Up to now numerical studies of hypersonic flow only discussed steady laminar or turbulent flow. This theoretical approach is extended to the study of transition in hypersonic flow by means of direct numerical simulations and additional theoretical investigations to explain the mechanisms leading to transition. A brief outline of how this research is to be performed is given.

Vandervegt, Jaap

1989-01-01

94

AN IMMERSED BOUNDARY METHOD FOR COMPLEX INCOMPRESSIBLE FLOWS

An immersed boundary method for time-dependant, three- dimensional, incompressible flows is presented in this paper. The incompressible Navier-Stokes equations are discretized using a low-diffusion flux splitting method for the inviscid fluxes and a second order central differenc...

95

Research in Natural Laminar Flow and Laminar-Flow Control, part 2

NASA Technical Reports Server (NTRS)

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.

Hefner, Jerry N. (compiler); Sabo, Frances E. (compiler)

1987-01-01

96

Research in natural laminar flow and laminar-flow control, part 2

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.

Hefner, J.N.; Sabo, F.E.

1987-12-01

97

Research in natural laminar flow and laminar-flow control, part 2

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.

J. N. Hefner; F. E. Sabo

1987-01-01

98

Advanced stability analysis for laminar flow control

NASA Astrophysics Data System (ADS)

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.

Orszag, S. A.

1981-02-01

99

Advanced stability analysis for laminar flow control

NASA Technical Reports Server (NTRS)

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.

Orszag, S. A.

1981-01-01

100

NASA supercritical laminar flow control airfoil experiment

NASA Technical Reports Server (NTRS)

The design and goals of experimental investigations of supercritical LFC airfoils conducted in the NASA Langley 8-ft Transonic Pressure Tunnel beginning in March 1982 are reviewed. Topics addressed include laminarization aspects; flow-quality requirements; simulation of flight parameters; the setup of screens, honeycomb, and sonic throat; the design cycle; theoretical pressure distributions and shock-free limits; drag divergence and stability analysis; and the LFC suction system. Consideration is given to the LFC airfoil model, the air-flow control system, airfoil-surface instrumentation, liner design and hardware, and test options. Extensive diagrams, drawings, graphs, photographs, and tables of numerical data are provided.

Harvey, W. D.

1982-01-01

101

Suction laminarization of highly swept supersonic laminar flow control wings

NASA Technical Reports Server (NTRS)

An evaluation is made of a suction-based method for the laminarization of highly-swept supersonic wings at cruise Mach numbers in the 2.0-2.5 range, in the interest of the reduction of wave drag due to lift. The laminar boundary layer development, as well as Tollmien-Schlichting and crossflow instabilities, have been analyzed for the case of an X66 supercritical airfoil at 60 and 72 deg sweep, for Mach numbers of 1.56 and 2.52, respectively. Strong suction is found to be needed at the front part of the upper surface and both the upper and lower rear pressure-rise areas.

Pfenninger, W.; Vemuru, C. S.

1988-01-01

102

Mixed finite element methods for incompressible flow: Stationary ...

basic equations for incompressible Newtonian flows consist of. ? ... This discretization has two obvious advantages: (i) accurate approximation to physical quantities .... Otherwise, assume that there exist positive constants ?0 and ?1 such that.

2010-04-14

103

Lattice Boltzmann method for incompressible flows with large pressure gradients.

Conventional lattice Boltzmann Bhatnagar-Gross-Krook (LBGK) models can simulate incompressible flows correctly only if the Mach number M and the density variation deltarho are negligibly small. However, the equation of state p=RTrho resulting from the conventional models limits their application to incompressible flows with a rather small pressure gradient. In this paper, based on the Enskog equation, we propose a finite difference lattice BGK model for isothermal incompressible flows with the resulting equation of state and transport properties suitable for nonideal fluids. We validated this model by simulating the plane Poiseuille flow, the two dimensional Womersley flow, and the backward-facing step flow and found that the numerical results obtained by the proposed model are more accurate than those by the conventional LBGK models when the pressure gradient imposed on the flows increases. PMID:16605480

Shi, Yong; Zhao, T S; Guo, Z L

2006-02-01

104

A numerical study of three-dimensional incompressible flow around multiple posts

NASA Technical Reports Server (NTRS)

The incompressible laminar flow around single and double rows of an infinite number of posts between two flat plates has been calculated numerically. A C-grid with periodic boundary conditions has been used. The angle of attack, measured from the line normal to the row of posts, was varied between zero and less than 90 deg. The pressure loading was computed for all of the posts in each of these cases. Most of these calculations have been carried out on the Numerical Aerodynamic Simulation Cray 2 at NASA Ames Research Center.

Rogers, S. E.; Kwak, D.; Kaul, U.

1986-01-01

105

NASA Technical Reports Server (NTRS)

The calculation of pressures when the penalty-function approximation is used in finite-element solutions of laminar incompressible flows is addressed. A Poisson equation for the pressure is formulated that involves third derivatives of the velocity field. The second derivatives appearing in the weak formulation of the Poisson equation are calculated from the C0 velocity approximation using a least-squares method. The present scheme is shown to be efficient, free of spurious oscillations, and accurate. Examples of applications are given and compared with results obtained using mixed formulations.

Sohn, J. L.; Heinrich, J. C.

1990-01-01

106

Laminar flow control, 1976 - 1982: A selected annotated bibliography

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.

M. H. Tuttle; D. V. Maddalon

1982-01-01

107

Durability of hybrid laminar flow control (HLFC) surfaces

As a part of the European Commission sponsored HYLTEC (Hybrid Laminar Flow Technology) project, a SAAB 2000 aircraft – fitted with a number of small laser drilled panels on the wing leading edge – completed 20 months of routine service; the objective being to investigate contamination and durability aspects of Hybrid Laminar Flow Control (HLFC) suction surfaces. A post-flight test

Trevor Young; Brian Mahony; Bryan Humphreys; Ernst Totland; Alan McClafferty; Julie Corish

2003-01-01

108

Roughness and waviness requirements for laminar flow surfaces

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

Clifford J. Obara; Bruce J. Holmes

1986-01-01

109

Optimized Natural-Laminar-Flow Airfoils and D. W. Zingg

Optimized Natural-Laminar-Flow Airfoils J. Driver and D. W. Zingg University of Toronto Institute-averaged Navier-Stokes equations. The algorithm is applied to the design of airfoils with maximum lift-drag ratio natural-laminar-flow airfoils. In particular, the optimization algorithm is able to design an airfoil

Zingg, David W.

110

On Nonhydrostatic Twolayer Models of Incompressible Flow

Burton Wendroff z August 6, 1996 Abstract Several reduced dimension two layer models of incompressible of the variation of the vertical component of the velocity vector. To derive the usual shallow water model, the vertical acceleration is taken to be zero implyÂ ing the hydrostatic balance of pressure forces

111

Progress in natural laminar flow research

NASA Technical Reports Server (NTRS)

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.

Holmes, B. J.

1984-01-01

112

Laminar flow control perforated wing panel development

NASA Technical Reports Server (NTRS)

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.

Fischler, J. E.

1986-01-01

113

Laminar flow control SPF/08 feasibility demonstration

NASA Technical Reports Server (NTRS)

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.

Ecklund, R. C.; Williams, N. R.

1981-01-01

114

Gliding swifts attain laminar flow over rough wings.

Swifts are among the most aerodynamically refined gliding birds. However, the overlapping vanes and protruding shafts of their primary feathers make swift wings remarkably rough for their size. Wing roughness height is 1-2% of chord length on the upper surface--10,000 times rougher than sailplane wings. Sailplanes depend on extreme wing smoothness to increase the area of laminar flow on the wing surface and minimize drag for extended glides. To understand why the swift does not rely on smooth wings, we used a stethoscope to map laminar flow over preserved wings in a low-turbulence wind tunnel. By combining laminar area, lift, and drag measurements, we show that average area of laminar flow on swift wings is 69% (n?=?3; std 13%) of their total area during glides that maximize flight distance and duration--similar to high-performance sailplanes. Our aerodynamic analysis indicates that swifts attain laminar flow over their rough wings because their wing size is comparable to the distance the air travels (after a roughness-induced perturbation) before it transitions from laminar to turbulent. To interpret the function of swift wing roughness, we simulated its effect on smooth model wings using physical models. This manipulation shows that laminar flow is reduced and drag increased at high speeds. At the speeds at which swifts cruise, however, swift-like roughness prolongs laminar flow and reduces drag. This feature gives small birds with rudimentary wings an edge during the evolution of glide performance. PMID:24964089

Lentink, David; de Kat, Roeland

2014-01-01

115

Gliding Swifts Attain Laminar Flow over Rough Wings

Swifts are among the most aerodynamically refined gliding birds. However, the overlapping vanes and protruding shafts of their primary feathers make swift wings remarkably rough for their size. Wing roughness height is 1–2% of chord length on the upper surface—10,000 times rougher than sailplane wings. Sailplanes depend on extreme wing smoothness to increase the area of laminar flow on the wing surface and minimize drag for extended glides. To understand why the swift does not rely on smooth wings, we used a stethoscope to map laminar flow over preserved wings in a low-turbulence wind tunnel. By combining laminar area, lift, and drag measurements, we show that average area of laminar flow on swift wings is 69% (n?=?3; std 13%) of their total area during glides that maximize flight distance and duration—similar to high-performance sailplanes. Our aerodynamic analysis indicates that swifts attain laminar flow over their rough wings because their wing size is comparable to the distance the air travels (after a roughness-induced perturbation) before it transitions from laminar to turbulent. To interpret the function of swift wing roughness, we simulated its effect on smooth model wings using physical models. This manipulation shows that laminar flow is reduced and drag increased at high speeds. At the speeds at which swifts cruise, however, swift-like roughness prolongs laminar flow and reduces drag. This feature gives small birds with rudimentary wings an edge during the evolution of glide performance. PMID:24964089

Lentink, David; de Kat, Roeland

2014-01-01

116

Laminar Flow Control by Suction at Mach 2

\\u000a Laminar flow control by suction of crossflow-dominated laminar-turbulent transition at Mach 2 was studied experimentally and\\u000a numerically as part of the EU project SUPERTRAC. The measurements were performed in the Ludwieg Tube Facility (RWG) at DLR\\u000a Göttingen. With a suction panel manufactured from porous sinter material a significant delay of laminar-turbulent transition\\u000a could be achieved. Transition N-factors in the range

S. Hein; E. Schülein; A. Hanifi; J. Sousa; D. Arnal

2010-01-01

117

On the characteristics-based ACM for incompressible flows

NASA Astrophysics Data System (ADS)

In this paper, the revised characteristics-based (CB) method for incompressible flows recently derived by Neofytou [P. Neofytou, Revision of the characteristic-based scheme for incompressible flows, J. Comput. Phys. 222 (2007) 475-484] has been further investigated. We have derived all the formulas for pressure and velocities from this revised CB method, which is based on the artificial compressibility method (ACM) [A.J. Chorin, A numerical solution for solving incompressible viscous flow problems, J. Comput. Phys. 2 (1967) 12]. Then we analyze the formulations of the original CB method [D. Drikakis, P.A. Govatsos, D.E. Papatonis, A characteristic based method for incompressible flows, Int. J. Numer. Meth. Fluids 19 (1994) 667-685; E. Shapiro, D. Drikakis, Non-conservative and conservative formulations of characteristics numerical reconstructions for incompressible flows, Int. J. Numer. Meth. Eng. 66 (2006) 1466-1482; D. Drikakis, P.K. Smolarkiewicz, On spurious vortical structures, J. Comput. Phys. 172 (2001) 309-325; F. Mallinger, D. Drikakis, Instability in three-dimensional, unsteady stenotic flows, Int. J. Heat Fluid Flow 23 (2002) 657-663; E. Shapiro, D. Drikakis, Artificial compressibility, characteristics-based schemes for variable density, incompressible, multi-species flows. Parts I. Derivation of different formulations and constant density limit, J. Comput. Phys. 210 (2005) 584-607; Y. Zhao, B. Zhang, A high-order characteristics upwind FV method for incompressible flow and heat transfer simulation on unstructured grids, Comput. Meth. Appl. Mech. Eng. 190 (5-7) (2000) 733-756] to investigate their consistency with the governing flow equations after convergence has been achieved. Furthermore we have implemented both formulations in an unstructured-grid finite volume solver [Y. Zhao, B. Zhang, A high-order characteristics upwind FV method for incompressible flow and heat transfer simulation on unstructured grids, Comput. Meth. Appl. Mech. Eng. 190 (5-7) (2000) 733-756]. Detailed numerical experiments show that both methods give almost identical solutions and convergence rates. Both can generate solutions which agree well with published results and experimental measurements. We thus conclude that both methods, being upwind schemes designed for the ACM, have the same performances in terms of accuracy and convergence speed, even though the revised method is more complex with less stringent assumptions made, while the original CB method is simpler due to the use of extra simplifying assumptions.

Su, Xiaohui; Zhao, Yong; Huang, Xiaoyang

2007-11-01

118

Two Dimensional Incompressible Ideal Flow Around a Small Obstacle

In this article we study the asymptotic behavior of incompressible, ideal, time-dependent two dimensional flow in the exterior of a single smooth obstacle when the size of the obstacle becomes very small. Our main purpose is to identify the equation satisfied by the limit flow. We will see that the asymptotic behavior depends on ?, the circulation around the obstacle.

D. Iftimie; M. C. Lopes Filho; H. J. Nussenzveig Lopes

2003-01-01

119

CFD validation of a supersonic laminar flow control concept

NASA Technical Reports Server (NTRS)

A three-dimensional Navier-Stokes code is used in conjunction with a linear compressible stability analysis code to develop a numerical procedure for prediction of laminar flow transition. The procedure is applied to a modified F-16XL fighter with a laminar flow control glove at supersonic speed. Details of boundary layer stability analysis indicate that, computationally, laminar flow could be realized on the highly swept wing in the absence of the leading edge attachment-line contamination. Effects of the three-dimensionality of the flow were shown to be important in the boundary layer stability analysis. The numerically predicted surface pressures compare favorably with the flight test data.

Woan, Chung-Jin; Gingrich, Philip B.; George, Michael W.

1991-01-01

120

NASA Technical Reports Server (NTRS)

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.

Kim, Sang-Wook

1988-01-01

121

Numerical study of laminar and turbulent flows inside a turnaround duct with and without guide vanes

NASA Technical Reports Server (NTRS)

The purpose of this study is to examine in detail incompressible laminar and turbulent flows inside a turnaround duct with and without guide vanes and to investigate the effects of vanes on the flow characteristics. To perform this study, an implicit finite difference code cast in general curvilinear coordinates is further developed. The code is based on the method of pseudo-compressibility and utilize ADI or implicit approximate factorization algorithm to achieve computational efficiency. Method of segmental sweeping is developed to overcome the multiple-zone problem due to imposition of guide vanes. In the present study, several test cases have been computed. These test cases include laminar and turbulent flows inside a turnaround duct without and with two or three guide vanes. The study reveals that: (1) there exists large recirculation zones inside the duct if no vanes are present; (2) properly shaped and positional guide vanes are effective in eliminating flow separation; and (3) laminar and turbulent flows have similar flow features. But turbulent flow has less total pressure drop.

Lin, S.-J.; Chang, James L. C.

1987-01-01

122

A Numerical Method for Incompressible Flow with Heat Transfer

NASA Technical Reports Server (NTRS)

A numerical method for the convective heat transfer problem is developed for low speed flow at mild temperatures. A simplified energy equation is added to the incompressible Navier-Stokes formulation by using Boussinesq approximation to account for the buoyancy force. A pseudocompressibility method is used to solve the resulting set of equations for steady-state solutions in conjunction with an approximate factorization scheme. A Neumann-type pressure boundary condition is devised to account for the interaction between pressure and temperature terms, especially near a heated or cooled solid boundary. It is shown that the present method is capable of predicting the temperature field in an incompressible flow.

Sa, Jong-Youb; Kwak, Dochan

1997-01-01

123

Numerical and experimental studies on laminar flow control

This paper gives an overview of numerical and experimental investigations performed in the framework of laminar flow control studies. After a description of the transition mechanisms that are likely to occur on swept wings, different techniques to delay the onset of laminar-turbulent transition are presented. Application of these techniques is illustrated by numerical results, wind tunnel experiments and free flight

Daniel Arnal

1999-01-01

124

Propulsion system optimization for suction laminar flow control bodies

Equations are derived for comparing propulsion systems for a suction laminar flow control (LFC) vehicle such as a torpedo when propelled by: (1) suction pump efflux only, and (2) suction pump augmented by external propeller. In an example, with nonlaminar\\/laminar drag ratio J = 0.43, the drag of a suction LFC vehicle is 17 percent of the drag of a

K. H. Rogers

1979-01-01

125

Natural laminar flow airfoil analysis and trade studies

NASA Technical Reports Server (NTRS)

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.

1979-01-01

126

Turning waves and breakdown for incompressible flows

We consider the evolution of an interface generated between two immiscible, incompressible, and irrotational fluids. Specifically we study the Muskat and water wave problems. We show that starting with a family of initial data given by (?,f0(?)), the interface reaches a regime in finite time in which is no longer a graph. Therefore there exists a time t? where the solution of the free boundary problem parameterized as (?,f(?,t)) blows up: ???f?L?(t?) = ?. In particular, for the Muskat problem, this result allows us to reach an unstable regime, for which the Rayleigh–Taylor condition changes sign and the solution breaks down.

Castro, Angel; Cordoba, Diego; Fefferman, Charles L.; Gancedo, Francisco; Lopez-Fernandez, Maria

2011-01-01

127

Current Laminar Flow Control Experiments at NASA Dryden

NASA Technical Reports Server (NTRS)

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.

Bowers, Al

2010-01-01

128

Laminar Flow Control Leading Edge Systems in Simulated Airline Service

NASA Technical Reports Server (NTRS)

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.

Wagner, R. D.; Maddalon, D. V.; Fisher, D. F.

1988-01-01

129

NASA Technical Reports Server (NTRS)

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.

Harvey, William D.; Harris, Charles D.; Brooks, Cuyler W., Jr.

1989-01-01

130

Assessment of the National Transonic Facility for Laminar Flow Testing

NASA Technical Reports Server (NTRS)

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.

Crouch, Jeffrey D.; Sutanto, Mary I.; Witkowski, David P.; Watkins, A. Neal; Rivers, Melissa B.; Campbell, Richard L.

2010-01-01

131

Summary A numerical investigation is made to establish whether multiple solutions exist for laminar, incompressible, steady flow in a parallel plate porous channel with uniform suction at both walls. For values of the wall suction Reynolds number,R, greater than 12.165 three numerical solutions are observed for eachR, while forR less than 12.165 only one solution for eachR can be found.

W. A. Robinson

1976-01-01

132

Unified Computational Schemes for Incompressible and Weakly Compressible Flows

, liquid impact and jet cutting. Moreover, some flows contain both compressible and incompressible regions. Belblidia and M. F. Webster* Institute of Non-Newtonian Fluid Mechanics, Department of Computer Science. In fluid mechanics, Mach number characterise compressibility effects conveying the ratio between fluid

Grant, P. W.

133

An upwind method for incompressible flows with heat transfer

Purpose – The purpose of this paper is to present a novel numerical method to solve incompressible flows with natural and mixed convections using pseudo-compressibility formulation. Design\\/methodology\\/approach – The present method is derived using the framework of Harten Lax and van Leer with contact (HLLC) method of Toro, Spruce and Spears, that was originally developed for compressible gas dynamics equations.

Jadav Chandra Mandal; Anesh S. Iyer

2011-01-01

134

An update on projection methods for transient incompressible viscous flow

Introduced in 1990 was the biharmonic equation (for the pressure) and the concomitant biharmonic miracle when transient incompressible viscous flow is solved approximately by a projection method. Herein is introduced the biharmonic catastrophe that sometimes occurs with these same projection methods.

Gresho, P.M.; Chan, S.T.

1995-07-01

135

Robust vortex methods for three-dimensional incompressible flows

NASA Technical Reports Server (NTRS)

Vortex methods for the numerical simulation of incompressible three-dimensional flows at high Reynolds number are discussed. Particular emphasis is placed on schemes that prevent the excessive generation of mesh elements, include viscous effects, and are relatively inexpensive even as the number of elements becomes large. Several simulations are presented involving the interaction of vortex rings.

Chua, K.; Leonard, A.; Pepin, F.; Winckelmans, G.

1988-01-01

136

Modeling Low Reynolds Number Incompressible Flows Using SPH

NASA Astrophysics Data System (ADS)

The method of smoothed particle hydrodynamics (SPH) is extended to model incompressible flows of low Reynolds number. For such flows, modification of the standard SPH formalism is required to minimize errors associated with the use of a quasi-incompressible equation of state. Treatment of viscosity, state equation, kernel interpolation, and boundary conditions are described. Simulations using the method show close agreement with series solutions for Couette and Poiseuille flows. Furthermore, comparison with finite element solutions for flow past a regular lattice of cylinders shows close agreement for the velocity and pressure fields. The SPH results exhibit small pressure fluctuations near curved boundaries. Further improvements to the boundary conditions may be possible which will reduce these errors. A similar method to that used here may permit the simulation of other flows at low Reynolds numbers using SPH. Further development will be needed for cases involving free surfaces or substantially different equations of state.

Morris, Joseph P.; Fox, Patrick J.; Zhu, Yi

1997-09-01

137

ANALYSIS OF AN EXTENDED PRESSURE FINITE ELEMENT SPACE FOR TWO-PHASE INCOMPRESSIBLE FLOWS

model for describing incompressible two-phase flows consists of the Navier-Stokes equationsANALYSIS OF AN EXTENDED PRESSURE FINITE ELEMENT SPACE FOR TWO-PHASE INCOMPRESSIBLE FLOWS ARNOLD REUSKEN Abstract. We consider a standard model for incompressible two-phase flows in which a localized

138

ANALYSIS OF AN EXTENDED PRESSURE FINITE ELEMENT SPACE FOR TWOPHASE INCOMPRESSIBLE FLOWS

ANALYSIS OF AN EXTENDED PRESSURE FINITE ELEMENT SPACE FOR TWOÂPHASE INCOMPRESSIBLE FLOWS ARNOLD REUSKEN # Abstract. We consider a standard model for incompressible twoÂphase flows in which a localized twoÂphase incompressible flow probÂ lem. Let# # R 3 be a convex polyhedral domain containing two di

139

Design of fuselage shapes for natural laminar flow

NASA Technical Reports Server (NTRS)

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.

Dodbele, S. S.; Vandam, C. P.; Vijgen, P. M. H. W.

1986-01-01

140

NASA Technical Reports Server (NTRS)

In this report, a numerical method for solving the equations of motion of three-dimensional incompressible flows in nonorthogonal body-fitted coordinate (BFC) systems has been developed. The equations of motion are transformed to a generalized curvilinear coordinate system from which the transformed equations are discretized using finite difference approximations in the transformed domain. The hybrid scheme is used to approximate the convection terms in the governing equations. Solutions of the finite difference equations are obtained iteratively by using a pressure-velocity correction algorithm (SIMPLE-C). Numerical examples of two- and three-dimensional, laminar and turbulent flow problems are employed to evaluate the accuracy and efficiency of the present computer code. The user's guide and computer program listing of the present code are also included.

Chen, Y. S.

1986-01-01

141

Conservative properties of finite difference schemes for incompressible flow

NASA Technical Reports Server (NTRS)

The purpose of this research is to construct accurate finite difference schemes for incompressible unsteady flow simulations such as LES (large-eddy simulation) or DNS (direct numerical simulation). In this report, conservation properties of the continuity, momentum, and kinetic energy equations for incompressible flow are specified as analytical requirements for a proper set of discretized equations. Existing finite difference schemes in staggered grid systems are checked for satisfaction of the requirements. Proper higher order accurate finite difference schemes in a staggered grid system are then proposed. Plane channel flow is simulated using the proposed fourth order accurate finite difference scheme and the results compared with those of the second order accurate Harlow and Welch algorithm.

Morinishi, Youhei

1995-01-01

142

Laminar: Practical Fine-Grained Decentralized Information Flow Control

Laminar: Practical Fine-Grained Decentralized Information Flow Control Indrajit Roy Donald E information flow control (DIFC) is a promising model for writing programs with powerful, end-to-end security information flow control using a single set of abstrac- tions for OS resources and heap-allocated objects

McKinley, Kathryn S.

143

An extended pressure finite element space for two-phase incompressible flows with surface tension

An extended pressure finite element space for two-phase incompressible flows with surface tension Aachen Abstract We consider a standard model for incompressible two-phase flows in which a localized in ). The interface is denoted by (t) = Â¯1(t) Â¯2(t). The standard model for describing incompressible two- phase

144

Stability analysis for laminar flow control, part 2

Topics covered include: (1) optimization of the numerics of the SALLY stability analysis code; (2) relation between temporal and spatial stability theory; (3) compressible flow stability calculations; (4) spectral methods for the boundary layer equations; and (5) numerical study of nonlinear, nonparallel stability of incompressible flows. Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find Similar

S. A. Orszag

1980-01-01

145

A Taylor-Galerkin-based algorithm for viscous incompressible flow

NASA Astrophysics Data System (ADS)

The development and behavior of a new finite element algorithm for viscous incompressible flow is presented. The stability and background theory are discussed, and the numerical performance is considered for some benchmark problems. The Taylor-Galerkin approach naturally leads to a time-stepping algorithm which is shown to perform well for a wide range of Reynolds numbers (1-400). Various modifications to the algorithm are investigated, particularly with respect to their effects on stability and accuracy.

Hawken, D. M.; Tamaddon-Jahromi, H. R.; Townsend, P.; Webster, M. F.

1990-02-01

146

A sharp interface method for incompressible two-phase flows

We present a sharp interface method for computing incompressible immiscible two-phase flows. It couples the level-set and volume-of-fluid techniques and retains their advantages while overcoming their weaknesses. It is stable and robust even for large density and viscosity ratios on the order of 1000 to 1. The numerical method is an extension of the second-order method presented by Sussman [M.

M. Sussman; K. M. Smith; M. Y. Hussaini; M. Ohta; R. Zhi-Wei

2007-01-01

147

Incompressible Turbulent Wing-Body Junction Flow

NASA Technical Reports Server (NTRS)

The overall objective of this study is to contribute to the optimized design of fan bypass systems in advanced turbofan engines. Increasing the engine bypass ratios have provided a major boost in engine performance improvement over the last fifty years. An engine with high bypass ratio (11-16:1) such as the Advanced Ducted Propulsion (ADP) is being developed and is expected to provide an additional 25% improvement in overall efficiency over the early turbofans. Such significant improvements in overall efficiency would reduce the cost per seat mile, which is a major government and Industry challenge for the 21th century. The research is part of the Advanced Subsonic Technology (AST) program that involves a NASA, U.S. Industry and FAA partnership with the goal of a safe and highly productive global air transportation system. The immediate objective of the study is to perform numerical simulation of duct-strut interactions to elucidate the loss mechanisms associated with this configuration that is typical of advanced turbofan engines such as ADP. However, at present experimental data for a duct-strut configuration are not available. Thus, as a first step a wing-body junction flow would be studied and is the specific objective of the present study. At the outset it is to be recognized that while duct-strut interaction flow is similar to that of wing-body junction flows, there are some differences owing to the presence of a wall at both ends of the strut. Likewise, some differences are due to the sheared inflow (as opposed to a uniform inflow) velocity profile. It is however expected that some features of a wing-body junction flow would persist. Next, some of the salient aspects of the complex flow near a wing-body junction, as revealed by various studies reported in the literature will be reviewed. One of the principle characteristics of the juncture flow, is the presence of the mean flow components in a plane perpendicular to the direction of the oncoming free-stream flow. The lateral curvature of the wing/strat causes the oncoming turbulent layer to skew about am axis (x-axis) parallel to the plane (xz-plane) of the mean shear. This is the principle mechanism for the generation of secondary flow. Such skew-induced secondary flows are slow to be attenuated by Reynolds stresses. Additional contribution to the generation of secondary flow comes from anisotropies in Reynolds stresses. Upstream of the strut, the mean-vorticity is directed span wise (along the y-direction). The presence of secondary flow in the vicinity of the strut causes the vorticity to stretch around the obstacle in a horse-shoe shape, with each leg having a vorticity of the opposite sense. The blockage effect of the strut imposes a severe adverse pressure gradient on the oncoming turbulent shear layer, causing boundary layer separation ahead of the leading edge, resulting in a vortex that rolls up and flows downstream into the juncture region. The separation vortices trailing in the wake of the wing can alter the lift or drag characteristics of the surfaces downstream of the wing-body juncture. Likewise, on submarines, the wake flow behind the appendage can degrade the performance of the propeller located downstream. The complex nature of this flow is caused by the presence of all six components of Reynolds stresses. Devenport and Simpson report that in the vicinity of the horse-shoe vortex there is intense recirculation with turbulent stresses being much larger than those normally observed in turbulent flows. These features contribute to making this flow a challenge to predict numerically. Some of the past studies provide useful insights into this flow that would guide our numerical efforts. In measurements reported by Shabaka and Bradshaw, the eddy viscosity tensor is seen to be non-isotropic and has negative components in certain regions. In an effort to evaluate the closure assumptions of various turbulence models, Devenport and Simpson used their own extensive measurements in juncture flows around the nose of a wing-body junction. Measured values of me

Krishnamurthy, R.; Cagle, Corey D.; Chandra, S.

1998-01-01

148

RIPPLE: A new model for incompressible flows with free surfaces

A new free surface flow model, RIPPLE, is summarized. RIPPLE obtains finite difference solutions for incompressible flow problems having strong surface tension forces at free surfaces of arbitrarily complex topology. The key innovation is the Continuum Surface Force (CSF) model which represents surface tension as a (strongly) localized volume force. Other features include a high-order momentum advection model, a volume-of-fluid free surface treatment, and an efficient two-step projection solution method. RIPPLE'S unique capabilities are illustrated with two example problems: low-gravity jet-induced tank flow, and the collision and coalescence of two cylindrical rods. 17 refs., 7 figs.

Kothe, D.B.; Mjolsness, R.C.

1991-01-01

149

Laminar flow control, 1976 - 1982: A selected annotated bibliography

NASA Technical Reports Server (NTRS)

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.

Tuttle, M. H.; Maddalon, D. V.

1982-01-01

150

A computational code is developed using cell-centered finite volume method with a non-uniform grid for solving the incompressible viscous and inviscid flows. The method has been used to determine the steady incompressible inviscid flows past a cylinder in free stream, the steady incompressible inviscid flows past a circular bump through a channel, and also the steady incompressible viscous flows past

Vahid Esfahanian; Pooria Akbarzadeh

2008-01-01

151

Laminar flow integration: Flight tests status and plans

NASA Technical Reports Server (NTRS)

Under the Aircraft Energy Efficiency - Laminar Flow Control Program, there are currently three flight test programs under way to address critical issues concerning laminar flow technology application to commercial transports. The Leading-Edge Flight Test (LEFT) with a JetStar aircraft is a cooperative effort with the Ames/Dryden Flight Research Facility to provide operational experience with candidate leading-edge systems representative of those that might be used on a future transport. In the Variable Sweep Transition Flight Experiment (VSTFE), also a cooperative effort between Langley and Ames/Dryden, basic transition data on an F-14 wing with variable sweep will be obtained to provide a data base for laminar flow wing design. Finally, under contract to the Boeing Company, the acoustic environment on the wing of a 757 aircraft will be measured and the influence of engine noise on laminar flow determined with a natural laminar flow glove on the wing. The status and plans for these programs are reported.

Wagner, R. D.; Fisher, D. F.; Fischer, M. C.; Bartlett, D. W.; Meyer, R. R., Jr.

1986-01-01

152

Brief history of laminar flow clean room systems

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.

Whitfield, W J

1981-01-01

153

Incompressible Navier-Stokes computations of vortical flows over double-delta wings

NASA Technical Reports Server (NTRS)

An implicit flux-difference splitting scheme is used to compute incompressible laminar vortical flows about a thin round-edged double-delta wing with 80 deg and 60 deg leading-edged sweep for the strake and the main wing respectively. The numerical scheme combines approximate factorization in crossflow planes with a symmetric planar Gauss-Seidel relaxation in the remaining spatial direction. It is second-order accurate spatially by applying TVD-like upwind discretization to the inviscid fluxes and central differencing to the viscous shear fluxes. The interaction between the two primary vortices emanating from the apex and kink leading-edges is successfully simulated. The computed trajectories of vortical cores compare well with experimental data.

Hsu, Chung-Hao; Hartwich, Peter-Michael; Liu, C. H.

1987-01-01

154

Efficient computation of compressible and incompressible flows

NASA Astrophysics Data System (ADS)

The combination of explicit Runge-Kutta time integration with the solution of an implicit system of equations, which in earlier work demonstrated increased efficiency in computing compressible flow on highly stretched meshes, is extended toward conditions where the free stream Mach number approaches zero. Expressing the inviscid flux Jacobians in terms of Mach number, an artificial speed of sound as in low Mach number preconditioning is introduced into the Jacobians, leading to a consistent formulation of the implicit and explicit parts of the discrete equations. Besides extension to low Mach number flows, the augmented Runge-Kutta/Implicit method allowed the admissible Courant-Friedrichs-Lewy number to be increased from O(1 0 0) to O(1 0 0 0). The implicit step introduced into the Runge-Kutta framework acts as a preconditioner which now addresses both, the stiffness in the discrete equations associated with highly stretched meshes, and the stiffness in the analytical equations associated with the disparity in the eigenvalues of the inviscid flux Jacobians. Integrated into a multigrid algorithm, the method is applied to efficiently compute different cases of inviscid flow around airfoils at various Mach numbers, and viscous turbulent airfoil flow with varying Mach and Reynolds number. Compared to well tuned conventional methods, computation times are reduced by half an order of magnitude.

Rossow, Cord-Christian

2007-01-01

155

Advanced stability theory analyses for laminar flow control

Recent developments of the SALLY computer code for stability analysis of laminar flow control wings are summarized. Extensions of SALLY to study three dimensional compressible flows, nonparallel and nonlinear effects are discussed. Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find Similar Abstracts: Use: Authors Title Keywords (in text query field) Abstract Text Return: Query Results

S. A. Orszag

1980-01-01

156

Laminar Flow Control and Aerodynamic Shape Optimization

Summary A gradient-based optimization method used to minimize the total drag of airfoils is presented. The viscous drag is minimized by delaying the laminar-turbulent transition. The gradients are obtained solving the adojoint of the Euler, boundary-layer and stability equations. The optimization is subjected to constraints such as restriction on geometry, lift and pitch moment. The geometry is parametrised using radial

A. Hani; O. Amoignon; M. Chevalier

157

Roughness and waviness requirements for laminar flow surfaces

NASA Astrophysics Data System (ADS)

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.

Obara, Clifford J.; Holmes, Bruce J.

1986-12-01

158

Viscous Incompressible Flow Computations for 3-D Steady and Unsteady Flows

NASA Technical Reports Server (NTRS)

This viewgraph presentation gives an overview of viscous incompressible flow computations for three-dimensional steady and unsteady flows. Details are given on the use of computational fluid dynamics (CFD) as an engineering tool, solution methods for incompressible Navier-Stokes equations, numerical and physical characteristics of the primitive variable approach, and the role of CFD in the past and in current engineering and research applications.

Kwak, Dochan

2001-01-01

159

Computational Optimization of a Natural Laminar Flow Experimental Wing Glove

NASA Technical Reports Server (NTRS)

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.

Hartshom, Fletcher

2012-01-01

160

Flight Tests of a Supersonic Natural Laminar Flow Airfoil

NASA Technical Reports Server (NTRS)

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.

Frederick, M. A.; Banks, D. W.; Garzon, G. A.; Matisheck, J. R.

2014-01-01

161

Laminar/turbulent oscillating flow in circular pipes

NASA Technical Reports Server (NTRS)

A two-dimensional oscillating flow analysis was conducted simulating the gas flow inside Stirling engine heat exchangers. Both laminar and turbulent oscillating pipe flow were investigated numerically for Re(max) = 1920 (Va = 80), 10,800 (Va = 272), 19,300 (Va = 272), and 60,800 (Va = 126). The results are compared with experimental results of previous investigators. Predictions of the flow regime are also checked by comparing velocity amplitudes and phase difference with those from laminar theory and quasi-steady profile. A high Reynolds number k-epsilon turbulence model was used for turbulent oscillating pipe flow. Finally, the performance of the k-epsilon model was evaluated to explore the applicability of quasi-steady turbulent models to unsteady oscillating flow analysis.

Ahn, Kyung H.; Ibrahim, Mounir B.

1992-01-01

162

Design of a hybrid laminar flow control nacelle

NASA Technical Reports Server (NTRS)

Consideration is given to the potential application of hybrid-laminar-flow control to the external surface of a modern, high-bypass-ratio (HBR) turbofan engine nacelle. With the advent of advanced ultra-HBR fans (with bypass ratios of 10-15), the wetted areas of these nacelles approach 10 percent of the total wetted area of future commercial transports. A hybrid-laminar-flow-control pressure distribution is specified and the corresponding nacelle geometry is computed utilizing a predictor/corrector design method. Linear stability calculations are conducted to provide predictions of the extent of the laminar boundary layer. Performance studies on an advanced twin-engine transport configuration are presented to determine potential benefits in terms of reduced fuel consumption.

Wie, Yong-Sun; Collier, Fayette S., Jr.; Wagner, Richard D.; Viken, Jeffery K.; Pfenninger, Werner

1992-01-01

163

Method and apparatus for detecting laminar flow separation and reattachment

NASA Technical Reports Server (NTRS)

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.

Stack, John P. (inventor); Mangalam, Sivaramakrishnan M. (inventor)

1989-01-01

164

Some observations regarding steady laminar flows past bluff bodies.

Steady laminar flows past simple objects, such as a cylinder or a sphere, have been studied for well over a century. Theoretical, experimental and numerical methods have all contributed fundamentally towards our understanding of the resulting flows. This article focuses on developments during the past few decades, when mostly numerical and asymptotical advances have provided insights also for steady, although unstable, high-Reynolds-numbers flow regimes. PMID:24936017

Fornberg, Bengt; Elcrat, Alan R

2014-07-28

165

High order parallel numerical schemes for solving incompressible flows

NASA Technical Reports Server (NTRS)

The use of parallel computers for numerically solving flow fields has gained much importance in recent years. This paper introduces a new high order numerical scheme for computational fluid dynamics (CFD) specifically designed for parallel computational environments. A distributed MIMD system gives the flexibility of treating different elements of the governing equations with totally different numerical schemes in different regions of the flow field. The parallel decomposition of the governing operator to be solved is the primary parallel split. The primary parallel split was studied using a hypercube like architecture having clusters of shared memory processors at each node. The approach is demonstrated using examples of simple steady state incompressible flows. Future studies should investigate the secondary split because, depending on the numerical scheme that each of the processors applies and the nature of the flow in the specific subdomain, it may be possible for a processor to seek better, or higher order, schemes for its particular subcase.

Lin, Avi; Milner, Edward J.; Liou, May-Fun; Belch, Richard A.

1992-01-01

166

High order parallel numerical schemes for solving incompressible flows

NASA Astrophysics Data System (ADS)

The use of parallel computers for numerically solving flow fields has gained much importance in recent years. This paper introduces a new high order numerical scheme for computational fluid dynamics (CFD) specifically designed for parallel computational environments. A distributed MIMD system gives the flexibility of treating different elements of the governing equations with totally different numerical schemes in different regions of the flow field. The parallel decomposition of the governing operator to be solved is the primary parallel split. The primary parallel split was studied using a hypercube like architecture having clusters of shared memory processors at each node. The approach is demonstrated using examples of simple steady state incompressible flows. Future studies should investigate the secondary split because, depending on the numerical scheme that each of the processors applies and the nature of the flow in the specific subdomain, it may be possible for a processor to seek better, or higher order, schemes for its particular subcase.

Lin, Avi; Milner, Edward J.; Liou, May-Fun; Belch, Richard A.

1992-02-01

167

F-16XL-2 Supersonic Laminar Flow Control Flight Test Experiment

NASA Technical Reports Server (NTRS)

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.

Anders, Scott G.; Fischer, Michael C.

1999-01-01

168

Transverse Diffusion of Laminar Flow Profiles To Produce Capillary Nanoreactors

for mixing two or more reactants inside capillaries. Conceptually, solutions of reactants are injected inside the capillary by pressure as a series of consecutive plugs. Due to the laminar nature of flow inside mixtures inside the capillary, TDLFP lowers reagent consumption to nanoliters (microliters are required

Krylov, Sergey

169

A perturbation approach for suction laminar flow control applications

A new method for computing the hydrodynamic stability eigenvalue problem in the presence of wall suction by using the eigenvalue and eigenfunctions of the no-suction problem is presented. The perturbation approach is computationally efficient in comparison with the direct approach; it is potentially applicable in various ways to hydrodynamic stability, particularly in laminar flow control.

Jamal A. Masad; Mujeeb R. Malik

1994-01-01

170

Boundary layer receptivity mechanisms relevant to laminar flow control

Receptivity processes by which free-stream acoustic waves generate instability waves in boundary layers are investigated. Concentration is placed on mechanisms associated with local regions of short scale variation in wall suction or admittance distribution. These mechanisms are relevant to laminar flow control technology, in which suction is utilized to control the growth of boundary layer instabilities. The receptivity process requires

Meelan Choudhari

1990-01-01

171

An overview of recent subsonic laminar flow control flight experiments

NASA Technical Reports Server (NTRS)

This paper presents an overview of wind-tunnel investigations and flight research activities in the United States and Europe devoted to advancing the state-of-the-art and reducing the risk associated with the application of laminar flow control (LFC) technology. The paper highlights LFC research conducted within the last five years.

Collier, F. S., Jr.

1993-01-01

172

A fundamental study of suction for Laminar Flow Control (LFC)

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

Jonathan H. Watmuff

1992-01-01

173

Application of laminar flow control to supersonic transport configurations

NASA Technical Reports Server (NTRS)

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.

Parikh, P. G.; Nagel, A. L.

1990-01-01

174

Application of porous materials for laminar flow control

NASA Technical Reports Server (NTRS)

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.

Pearce, W. E.

1978-01-01

175

Hydromagnetic Laminar Flow through Conducting Parallel Porous Walls

The steady state solution for the laminar flow of an electrically conducting liquid in the presence of transverse magnetic field has been investigated in detail. Taking into account the porosity of the walls we have obtained the velocity profiles for the induced magnetic and electric fields. Consideration has also been given to the rectangular channels in the following two cases:

P. Govinda Reddy; M. K. Jain

1967-01-01

176

Flow Solver for Incompressible 2-D Drive Cavity

NASA Technical Reports Server (NTRS)

This software solves the Navier-Stokes equations for the incompressible driven cavity flow problem. The code uses second-order finite differencing on a staggered grid using the Chorin projection method. The resulting intermediate Poisson equation is efficiently solved using the fast Fourier transform. Time stepping is done using fourth-order Runge-Kutta for stability at high Reynolds numbers. Features include check-pointing, periodic field snapshots, ongoing reporting of kinetic energy and changes between time steps, time histories at selected points, and optional streakline generation.

Kalb, Virginia L.

2008-01-01

177

Pseudo-compressibility methods for the incompressible flow equations

NASA Technical Reports Server (NTRS)

Preconditioning methods to accelerate convergence to a steady state for the incompressible fluid dynamics equations are considered. The analysis relies on the inviscid equations. The preconditioning consists of a matrix multiplying the time derivatives. Thus the steady state of the preconditioned system is the same as the steady state of the original system. The method is compared to other types of pseudo-compressibility. For finite difference methods preconditioning can change and improve the steady state solutions. An application to viscous flow around a cascade with a non-periodic mesh is presented.

Turkel, Eli; Arnone, A.

1993-01-01

178

Preconditioning and the limit to the incompressible flow equations

NASA Technical Reports Server (NTRS)

The use of preconditioning methods to accelerate the convergence to a steady state for both the incompressible and compressible fluid dynamic equations are considered. The relation between them for both the continuous problem and the finite difference approximation is also considered. The analysis relies on the inviscid equations. The preconditioning consists of a matrix multiplying the time derivatives. Hence, the steady state of the preconditioned system is the same as the steady state of the original system. For finite difference methods the preconditioning can change and improve the steady state solutions. An application to flow around an airfoil is presented.

Turkel, E.; Fiterman, A.; Vanleer, B.

1993-01-01

179

Numerical simulations of incompressible viscous flows in realistic configurations are increasingly important in many scientific and engineering fields. In Aeronautics, for instance, relatively cheap numerical computations ...

Marques, Alexandre Noll

2012-01-01

180

Natural-Laminar-Flow Airfoil and Wing Design by Adjoint Method and Automatic Transition Prediction

describes the application of optimization technique based on control theory for natural-laminar-flow airfoilNatural-Laminar-Flow Airfoil and Wing Design by Adjoint Method and Automatic Transition Prediction that an airfoil can be designed to have the desired favorable pressure gradient for laminar flow and the new

Jameson, Antony

181

Nature of laminar-turbulence intermittency in shear flows.

In pipe, channel, and boundary layer flows turbulence first occurs intermittently in space and time: at moderate Reynolds numbers domains of disordered turbulent motion are separated by quiescent laminar regions. Based on direct numerical simulations of pipe flow we argue here that the spatial intermittency has its origin in a nearest neighbor interaction between turbulent regions. We further show that in this regime turbulent flows are intrinsically intermittent with a well-defined equilibrium turbulent fraction but without ever assuming a steady pattern. This transition scenario is analogous to that found in simple models such as coupled map lattices. The scaling observed implies that laminar intermissions of the turbulent flow will persist to arbitrarily large Reynolds numbers. PMID:23848777

Avila, M; Hof, B

2013-06-01

182

Filter-matrix lattice Boltzmann model for incompressible thermal flows.

In this study, a new filter-matrix lattice Boltzmann (FMLB) model is proposed and extended to include incompressible thermal flows. A new equilibrium solution is found in the improved FMLB model, which is derived from the Hermite expansion. As a result, the velocity-dependent pressure is removed, which is an inherent defect of Somers's FMLB model. In addition, the improved model is extended to include incompressible thermal flows by introducing a class of temperature-distribution function for evaluating the temperature field. Two different temperature-distribution functions are discussed. The improved FMLB model and the temperature-evaluation equation are combined into one coupled model. Numerical simulations are performed on the two-dimensional (2D) lid-driven square cavity flow and the 2D natural convection flow in a square cavity using the improved FMLB model and the two coupled models, respectively. The numerical results of the 2D lid-driven square cavity flow show that the improved FMLB model is superior to the lattice Bhatnagar-Gross-Krook (LBGK) model in terms of both accuracy and stability. When compared with the multi-relaxation-time (MRT) model, the similar accuracy and slightly enhanced stability can be obtained by the improved model. The advantage of the improved model is that it no longer relies on difficult selection of the free parameters requested by the MRT model; in addition, the force term is already included in the collision operator of the improved model. In the case of 2D natural convection flow, the numerical results of the two present models are almost the same, and both exhibit good agreement with the benchmark solution. PMID:22680602

Zhuo, Congshan; Zhong, Chengwen; Cao, Jun

2012-04-01

183

Laminar Flow Supersonic Wind Tunnel primary air injector

NASA Technical Reports Server (NTRS)

This paper describes the requirements, design, and prototype testing of the flex-section and hinge seals for the Laminar Flow Supersonic Wind Tunnel Primary Injector. The supersonic atmospheric primary injector operates between Mach 1.8 and Mach 2.2 with mass-flow rates of 62 to 128 lbm/s providing the necessary pressure reduction to operate the tunnel in the desired Reynolds number (Re) range.

Smith, Brooke Edward

1993-01-01

184

Laminar backward-facing step flow using the finite element method

Laminar, incompressible flow over a backward-facing step is calculated using a finite element spatial discretization with a piecewise continuous pressure approximation and an explicit time marching algorithm. The time-accurate evolution to steady state is demonstrated for both two-dimensional (2D) and three-dimensional (3D) simulations. This approach is shown to accurately predict the lengths of the recirculation zone on the top wall and at the step for various meshes and domain lengths, for a Reynolds number of 800 based on the average inlet velocity and twice the inlet channel height. The instantaneous and steady-state results are investigated. The steady-state solutions are evaluated by comparison to published numerical and experimental results.

Kornblum, B.; McCallen, R. [Lawrence Livermore National Lab., CA (United States); Christon, M.A. [Sandia National Labs., Albuquerque, NM (United States); Kollmann, W. [Univ. of California, Davis, CA (United States) Dept. of Mechanical and Aeronautical Engineering] [and others

1995-11-01

185

A particle-gridless hybrid method for incompressible flows

NASA Astrophysics Data System (ADS)

A particle-gridless hybrid method for the analysis of incompressible flows is presented. The numerical scheme consists of Lagrangian and Eulerian phases as in an arbitrary Lagrangian-Eulerian (ALE) method, where a new-time physical property at an arbitrary position is determined by introducing an artificial velocity. For the Lagrangian calculation, the moving-particle semi-implicit (MPS) method is used. Diffusion and pressure gradient terms of the Navier-Stokes equation are calculated using the particle interaction models of the MPS method. As an incompressible condition, divergence of velocity is used while the particle number density is kept constant in the MPS method. For the Eulerian calculation, an accurate and stable convection scheme is developed. This convection scheme is based on a flow directional local grid so that it can be applied to multi-dimensional convection problems easily. A two-dimensional pure convection problem is calculated and a more accurate and stable solution is obtained compared with other schemes. The particle-gridless hybrid method is applied to the analysis of sloshing problems. The amplitude and period of sloshing are predicted accurately by the present method. The range of the occurrence of self-induced sloshing predicted by the present method shows good agreement with the experimental data. Calculations have succeeded even for the higher injection velocity range, where the grid method fails to simulate. Copyright

Yoon, Han Young; Koshizuka, Seiichi; Oka, Yoshiaki

1999-06-01

186

A SIMPLE based discontinuous Galerkin solver for steady incompressible flows

NASA Astrophysics Data System (ADS)

In this paper we present how the well-known SIMPLE algorithm can be extended to solve the steady incompressible Navier-Stokes equations discretized by the discontinuous Galerkin method. The convective part is discretized by the local Lax-Friedrichs fluxes and the viscous part by the symmetric interior penalty method. Within the SIMPLE algorithm, the equations are solved in an iterative process. The discretized equations are linearized and an equation for the pressure is derived on the discrete level. The equations obtained for each velocity component and the pressure are decoupled and therefore can be solved sequentially, leading to an efficient solution procedure. The extension of the proposed scheme to the unsteady case is straightforward, where fully implicit time schemes can be used. Various test cases are carried out: the Poiseuille flow, the channel flow with constant transpiration, the Kovasznay flow, the flow into a corner and the backward-facing step flow. Using a mixed-order formulation, i.e. order k for the velocity and order k-1 for the pressure, the scheme is numerically stable for all test cases. Convergence rates of k+1 and k in the L2-norm are observed for velocity and pressure, respectively. A study of the convergence behavior of the SIMPLE algorithm shows that no under-relaxation for the pressure is needed, which is in strong contrast to the application of the SIMPLE algorithm in the context of the finite volume method or the continuous finite element method. We conclude that the proposed scheme is efficient to solve the steady incompressible Navier-Stokes equations in the context of the discontinuous Galerkin method comprising hp-accuracy.

Klein, Benedikt; Kummer, Florian; Oberlack, Martin

2013-03-01

187

We report a hydroelasticity-based microfluidic oscillator that converts otherwise steady laminar flow to oscillatory flow. It incorporates an elastic diaphragm to enhance nonlinearity of the flow. Negative differential flow resistance is observed. High-frequency oscillatory flow is produced passively through interactions among hydrodynamic, elastic and inertial forces, without resorting to external actuators and control equipment. Driven by fluid flow and pressure, this device can operate in either steady laminar flow or oscillatory flow states, or work as a valve. Its applications for flow control and operation, and mixing enhancement are demonstrated. PMID:22048176

Xia, H M; Wang, Z P; Fan, W; Wijaya, A; Wang, W; Wang, Z F

2012-01-01

188

Preliminary aerodynamic design considerations for advanced laminar flow aircraft configurations

NASA Technical Reports Server (NTRS)

Modern composite manufacturing methods have provided the opportunity for smooth surfaces that can sustain large regions of natural laminar flow (NLF) boundary layer behavior and have stimulated interest in developing advanced NLF airfoils and improved aircraft designs. Some of the preliminary results obtained in exploratory research investigations on advanced aircraft configurations at the NASA Langley Research Center are discussed. Results of the initial studies have shown that the aerodynamic effects of configuration variables such as canard/wing arrangements, airfoils, and pusher-type and tractor-type propeller installations can be particularly significant at high angles of attack. Flow field interactions between aircraft components were shown to produce undesirable aerodynamic effects on a wing behind a heavily loaded canard, and the use of properly designed wing leading-edge modifications, such as a leading-edge droop, offset the undesirable aerodynamic effects by delaying wing stall and providing increased stall/spin resistance with minimum degradation of laminar flow behavior.

Johnson, Joseph L., Jr.; Yip, Long P.; Jordan, Frank L., Jr.

1986-01-01

189

Oblique laminar-turbulent interfaces in plane shear flows.

Localized structures such as turbulent stripes and turbulent spots are typical features of transitional wall-bounded flows in the subcritical regime. Based on an assumption for scale separation between large and small scales, we show analytically that the corresponding laminar-turbulent interfaces are always oblique with respect to the mean direction of the flow. In the case of plane Couette flow, the mismatch between the streamwise flow rates near the boundaries of the turbulence patch generates a large-scale flow with a nonzero spanwise component. Advection of the small-scale turbulent fluctuations (streaks) by the corresponding large-scale flow distorts the shape of the turbulence patch and is responsible for its oblique growth. This mechanism can be easily extended to other subcritical flows such as plane Poiseuille flow or Taylor-Couette flow. PMID:23373928

Duguet, Yohann; Schlatter, Philipp

2013-01-18

190

Laminar flow control research at TsAGI: Past and present

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

S. L. Chernyshev; A. Ph. Kiselev; A. P. Kuryachii

2011-01-01

191

Incompressible flow computations over moving boundary using a novel upwind method

In this paper a novel method for simulating unsteady incompressible viscous flow over a moving boundary is described. The numerical model is based on a 2D Navier–Stokes incompressible flow in artificial compressibility formulation with Arbitrary Lagrangian Eulerian approach for moving grid and dual time stepping approach for time accurate discretization. A higher order unstructured finite volume scheme, based on a

J. C. Mandal; C. R. Sonawane; A. S. Iyer; S. J. GosaviInamdar

2011-01-01

192

An extended pressure finite element space for twophase incompressible flows with surface tension

An extended pressure finite element space for twoÂphase incompressible flows with surface tension Aachen Abstract We consider a standard model for incompressible twoÂphase flows in which a localized containing the two phases are denoted by# 1 (t) and# 2 (t) with â?¢# = â?¢# 1 # â?¢# 2 and# 1 ## 2 = #. We assume

193

NITSCHE'S METHOD FOR A TRANSPORT PROBLEM IN TWO-PHASE INCOMPRESSIBLE FLOWS

-diffusion equations in the two subdomains 1 and 2. The diffusion coefficient is assumed to be piecewise constantNITSCHE'S METHOD FOR A TRANSPORT PROBLEM IN TWO-PHASE INCOMPRESSIBLE FLOWS ARNOLD REUSKEN AND TRUNG of a dissolved species in two-phase incompressible flow problems. Due to the so-called Henry interface condition

194

Computational Evaluation of a Transonic Laminar-Flow Wing Glove Design

The aerodynamic benefits of laminar flow have long made it a sought-after attribute in aircraft design. By laminarizing portions of an aircraft, such as the wing or empennage, significant reductions in drag could be achieved, reducing fuel burn...

Roberts, Matthew William

2012-07-16

195

Gyrotactic trapping in laminar and turbulent Kolmogorov flow

Phytoplankton patchiness, namely the heterogeneous distribution of microalgae over multiple spatial scales, dramatically impacts marine ecology. A spectacular example of such heterogeneity occurs in thin phytoplankton layers (TPLs), where large numbers of photosynthetic microorganisms are found within a small depth interval. Some species of motile phytoplankton can form TPLs by gyrotactic trapping due to the interplay of their particular swimming style (directed motion biased against gravity) and the transport by a flow with shear along the direction of gravity. Here we consider gyrotactic swimmers in numerical simulations of the Kolmogorov shear flow, both in laminar and turbulent regimes. In the laminar case, we show that the swimmer motion is integrable and the formation of TPLs can be fully characterized by means of dynamical systems tools. We then study the effects of rotational Brownian motion or turbulent fluctuations (appearing when the Reynolds number is large enough) on TPLs. In both cases we show that TPLs become transient, and we characterize their persistence.

Francesco Santamaria; Filippo De Lillo; Massimo Cencini; Guido Boffetta

2014-10-07

196

Gyrotactic trapping in laminar and turbulent Kolmogorov flow

Phytoplankton patchiness, namely the heterogeneous distribution of microalgae over multiple spatial scales, dramatically impacts marine ecology. A spectacular example of such heterogeneity occurs in thin phytoplankton layers (TPLs), where large numbers of photosynthetic microorganisms are found within a small depth interval. Some species of motile phytoplankton can form TPLs by gyrotactic trapping due to the interplay of their particular swimming style (directed motion biased against gravity) and the transport by a flow with shear along the direction of gravity. Here we consider gyrotactic swimmers in numerical simulations of the Kolmogorov shear flow, both in laminar and turbulent regimes. In the laminar case, we show that the swimmer motion is integrable and the formation of TPLs can be fully characterized by means of dynamical systems tools. We then study the effects of rotational Brownian motion or turbulent fluctuations (appearing when the Reynolds number is large enough) on TPLs. In both cases we show t...

Santamaria, Francesco; Cencini, Massimo; Boffetta, Guido

2014-01-01

197

Self-pumping suction/propulsion for laminar flow bodies

NASA Astrophysics Data System (ADS)

An analysis is presented to investigate the feasibility of a self-pumping suction system for a very low drag suction laminar flow control (SLFC) underwater test body. The nose and afterbody of a torpedo-like body are contoured such that a prominent low-pressure region in the aft part of the body can serve as a suction pump to suck the boundary layer fluid through the circumferential surface-slots and thus laminarize the entire body length forward of the aft low-pressure peak. The results indicate that it is feasible to laminarize a test body in this fashion at a design speed, such as 40 knots; but that the laminarization of a particular configuration is limited to a band of speeds at and near the design speed. If an SLFC test body with a wide range of speed capability is desired, then a controllable-speed suction pump and controllable suction distribution along the body are indicated. The analysis includes a suction system design calculation example and should be a useful reference for future development of undersea SLFC vehicles.

Rogers, K. H.; King, D. A.

1984-06-01

198

Distributed acoustic receptivity in laminar flow control configurations

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

Meelan Choudhari

1992-01-01

199

Distributed acoustic receptivity in laminar flow control configurations

A model problem related to distributed receptivity to free-stream acoustic waves in laminar flow control (LFC) configurations is studied within the Orr–Sommerfeld framework, by developing a suitable extension of the Goldstein–Ruban theory for receptivity due to localized disturbances on the airfoil surface. One advantage of the proposed method is that it easily permits the prediction of receptivity due to a

Meelan Choudhari

1994-01-01

200

Ground vibration test of the laminar flow control JStar airplane

NASA Technical Reports Server (NTRS)

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.

Kehoe, M. W.; Cazier, F. W., Jr.; Ellison, J. F.

1985-01-01

201

DNS Study of spatial discrete suction for Laminar Flow Control

By means of spatial direct numerical simulations (DNS) based on the complete Navier-Stokes equations the effect of three-dimensional\\u000a discrete suction on the spatial development of a laminar boundary-layer flow generic for the front part of a swept-back airliner\\u000a wing has been investigated. The baseflow is an accelerated Falkner-Skan-Cooke boundary layer, on a swept wedge with semi-opening\\u000a angle of 45 (Hartree

Ralf Messing; Markus Kloker

202

Making Large Suction Panels For Laminar-Flow Control

NASA Technical Reports Server (NTRS)

Perforated titanium panels used to identify and resolve issues related to manufacture. Recently, relatively large suction panels with aerodynamically satisfactory surface perforations and with surface contours and smoothness characteristics necessary for Laminar-Flow Control (LFC) designed, fabricated, and tested. Requirements of production lines for commercial transport airplanes carefully considered in development of panels. Sizes of panels representative of what is used on wing of commercial transport airplane. Tests of perforated panels in transonic wind tunnel demonstrated aerodynamic stability at flight mach numbers.

Maddalon, Dal V.

1991-01-01

203

Aerodynamic Design for Swept-wing Laminar Flow

Improvement (AFRL/NGC) AFRL Air Force Research Laboratory ATTAS Advanced Technologies Testing Aircraft System (German Aerospace Center) BL Wing buttock line, measured in inches from aircraft centerline CAD Computer-aided design CC Complex conjugate CFD... PSE Parabolized stability equations xi RMS Root-mean-square SARGE Subsonic Aircraft Roughness Glove Experiment SCRAT Subsonic Research Aircraft Testbed SWIFT Swept-Wing In-Flight Testing (AFRL/TAMU) SWLFC Swept-wing laminar flow control TAMU Texas A...

Belisle, Michael Joseph

2013-11-08

204

Experimental investigation of oxide nanofluids laminar flow convective heat transfer

In the present investigation nanofluids containing CuO and Al2O3 oxide nanoparticles in water as base fluid in different concentrations produced and the laminar flow convective heat transfer through circular tube with constant wall temperature boundary condition were examined. The experimental results emphasize that the single phase correlation with nanofluids properties (Homogeneous Model) is not able to predict heat transfer coefficient

S. Zeinali Heris; S. Gh. Etemad; M. Nasr Esfahany

2006-01-01

205

Incompressible SPH method for simulating Newtonian and non-Newtonian flows with a free surface

An incompressible smoothed particle hydrodynamics (SPH) method is presented to simulate Newtonian and non-Newtonian flows with free surfaces. The basic equations solved are the incompressible mass conservation and Navier–Stokes equations. The method uses prediction–correction fractional steps with the temporal velocity field integrated forward in time without enforcing incompressibility in the prediction step. The resulting deviation of particle density is then

Songdong Shao; Edmond Y. M. Lo

2003-01-01

206

Laminar flow of two miscible fluids in a simple network

NASA Astrophysics Data System (ADS)

When a fluid comprised of multiple phases or constituents flows through a network, nonlinear phenomena such as multiple stable equilibrium states and spontaneous oscillations can occur. Such behavior has been observed or predicted in a number of networks including the flow of blood through the microcirculation, the flow of picoliter droplets through microfluidic devices, the flow of magma through lava tubes, and two-phase flow in refrigeration systems. While the existence of nonlinear phenomena in a network with many inter-connections containing fluids with complex rheology may seem unsurprising, this paper demonstrates that even simple networks containing Newtonian fluids in laminar flow can demonstrate multiple equilibria. The paper describes a theoretical and experimental investigation of the laminar flow of two miscible Newtonian fluids of different density and viscosity through a simple network. The fluids stratify due to gravity and remain as nearly distinct phases with some mixing occurring only by diffusion. This fluid system has the advantage that it is easily controlled and modeled, yet contains the key ingredients for network nonlinearities. Experiments and 3D simulations are first used to explore how phases distribute at a single T-junction. Once the phase separation at a single junction is known, a network model is developed which predicts multiple equilibria in the simplest of networks. The existence of multiple stable equilibria is confirmed experimentally and a criterion for existence is developed. The network results are generic and could be applied to or found in different physical systems.

Karst, Casey M.; Storey, Brian D.; Geddes, John B.

2013-03-01

207

Incompressible Navier-Stokes Calculations in Pump Flows

NASA Technical Reports Server (NTRS)

Flow through pump components, such as the SSME-HPFTP Impeller and an advanced rocket pump impeller, is efficiently simulated by solving the incompressible Navier-Stokes equations. The solution method is based on the pseudo compressibility approach and uses an implicit-upwind differencing scheme together with the Gauss-Seidel line relaxation method. The equations are solved in steadily rotating reference frames and the centrifugal force and the Coriolis force are added to the equation of motion. Current computations use one-equation Baldwin-Barth turbulence model which is derived from a simplified form of the standard k-epsilon model equations. The resulting computer code is applied to the flow analysis inside an 11-inch SSME High Pressure Fuel Turbopump impeller, and an advanced rocket pump impeller. Numerical results of SSME-HPFTP impeller flow are compared with experimental measurements. In the advanced pump impeller, the effects of exit and shroud cavities are investigated. Flow analyses at design conditions will be presented.

Kiris, Cetin; Chang, Leon; Kwak, Dochan

1993-01-01

208

Incompressible Navier-Stokes calculations in pump flows

NASA Astrophysics Data System (ADS)

Flow through pump components, such as the SSME-HPFTP Impeller and an advanced rocket pump impeller, is efficiently simulated by solving the incompressible Navier-Stokes equations. The solution method is based on the pseudo compressibility approach and uses an implicit-upwind differencing scheme together with the Gauss-Seidel line relaxation method. The equations are solved in steadily rotating reference frames and the centrifugal force and the Coriolis force are added to the equation of motion. Current computations use one-equation Baldwin-Barth turbulence model which is derived from a simplified form of the standard k-epsilon model equations. The resulting computer code is applied to the flow analysis inside an 11-inch SSME High Pressure Fuel Turbopump impeller, and an advanced rocket pump impeller. Numerical results of SSME-HPFTP impeller flow are compared with experimental measurements. In the advanced pump impeller, the effects of exit and shroud cavities are investigated. Flow analyses at design conditions will be presented.

Kiris, Cetin; Chang, Leon; Kwak, Dochan

1993-07-01

209

Transition-Sensitized Turbulence Models for Compressible and Incompressible Flows

NASA Technical Reports Server (NTRS)

During the grant period from January 1,2002 to December 31,2002 work was carried out on three projects to extend the range of applicability of advanced turbulence models. First, a new transition-sensitized turbulence model was tested and refined. Second, the influence of compressibility on the pressure-strain rate correlation was studied. Third, the relationship between time-filtered large eddy simulation (TLES) and Reynolds-averaged Navier Stokes (RANS) modeling was investigated leading to submission of the article. The transition-sensitized turbulence model encompasses the early-stage transition and turbulent flow regimes describing the evolution of the ensemble mean disturbance energy and dissipation rate. It is founded on a consistent mathematical description of the laminar regime with its linear disturbances and the fully turbulent regime with its stochastic fluctuations. The unified description is provided by the ensemble viewpoint.

Thacker, William D.

2003-01-01

210

NASA Technical Reports Server (NTRS)

The turbulent, incompressible reattaching flow over a rearward-facing step has been studied by many researchers over the years. One of the principal quantities determined in these experiments has been the distance from the step to the point (or region) where the separated shear layer reattaches to the surface (x(r)). The values for x(r)/h, where h is the step height, have covered a wider range than can reasonably be attributed to experimental technique or inaccuracy. Often the reason for a largely different value of x(r)/h can be attributed to an incompletely developed turbulent layer, or a transitional or laminar boundary layer. However, for the majority of experiments where the boundary layer is believed to be fully developed and turbulent, x(r)/h still varies several step heights; generally, 5 1/2 approximately < x(r)/h approximately < 7 1/2. This observed variation has usually been attributed to such variables as l/h (step length to height, h/delta (step height to initial boundary-layer thickness), R(e)(theta)), or the experimental technique for determining reattachment location. However, there are so many different combinations of variables in the previous experiments that it was not possible to sort out the effects of particular conditions on the location of reattachment. In the present experiment velocity profiles have been measured in and around the region of separated flow. Results show a large influence of adverse pressure gradient on the reattaching flow over a rearward-facing step that has not been reported previously. Further, the many previous experiments for fully developed, turbulent flow in parallel-walled channels have shown a range of reattachment location that has not been explained by differences in initial flow conditions. Although these initial flow conditions might contribute to the observed variation of reattachment location, it appears that the pressure gradient effect can explain most of that variation.

Kuehn, Donald M.

1980-01-01

211

Natural laminar flow experiments on modern airplane surfaces

NASA Technical Reports Server (NTRS)

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.

Holmes, B. J.; Obara, C. J.; Yip, L. P.

1984-01-01

212

Natural laminar flow and airplane stability and control

NASA Technical Reports Server (NTRS)

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.

Vandam, Cornelis P.

1986-01-01

213

General Methodologies for Incompressible Flow Design Problems O. Soto and R. Lohner

. The present article describes two approximate adjoint formu- lations for the incompressible NS equations be written as: R = (Ru Rp), where Ru is the momentum equation for two or three-dimensional problems, and RpGeneral Methodologies for Incompressible Flow Design Problems O. Soto and R. Lohner CSI

LÃ¶hner, Rainald

214

Active Control of Instabilities in Laminar BoundaryLayer Flow--Part I: An Overview

Active Control of Instabilities in Laminar BoundaryÂLayer Flow-- Part I: An Overview Ronald D laminar flow in a region of the flow in which the natural instabilities, if left unattended, lead the phenomena byÂwhich the automated studies can be used to expand knowledge of flow control. 1 This research

Erlebacher, Gordon

215

NASA Technical Reports Server (NTRS)

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.

Gladden, Herbert J.; Ko, Ching L.; Boddy, Douglas E.

1995-01-01

216

NASA Technical Reports Server (NTRS)

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.

Fischer, Michael C.; Vemuru, Chandra S.

1991-01-01

217

Topology of advective-diffusive scalar transport in laminar flows.

The present study proposes a unified Lagrangian transport template for topological description of advective fluid transport and advective-diffusive scalar transport in laminar flows. The key to this unified description is the expression of scalar transport as purely advective transport by the total scalar flux. This admits generalization of the concept of transport topologies known from laminar mixing studies to scalar transport. The study is restricted to two-dimensional systems and the fluid and scalar transport topologies, as a consequence, prove to be Hamiltonian. The unified Lagrangian transport template is demonstrated and investigated for a heat-transfer problem with nonadiabatic boundaries, representing generic scalar transport with permeable boundaries. The fluid and thermal transport topologies under steady conditions both accommodate islands (constituting isolated flow and thermal regions) that undergo Hamiltonian disintegration into chaotic seas upon introducing time periodicity. The thermal transport topology invariably comprises transport conduits that connect the nonadiabatic boundaries and facilitate wall-wall and wall-fluid heat transfer. For steady conditions these transport conduits are regular; for time-periodic conditions these conduits may, depending on degree of diffusion, be regular or chaotic. Regular conduits connect nonadiabatic walls only with specific flow regions; chaotic heat conduits establish connection (and thus heat exchange) of the nonadiabatic walls with the entire flow domain. PMID:18352124

Speetjens, M F M

2008-02-01

218

Early development of karst systems, 1. Preferential flow path enlargement under laminar flow

Modeling of flow and solutional processes within networks of interconnected conduits in limestone aquifers indicates that enlargement occurs very selectively during the early stages of karst aquifer development under laminar flow. If initial flow paths are uniform in size, almost all enlargement occurs along a single set of connected conduits that lie along a direct path between recharge and discharge

Christopher G. Groves; Alan D. Howard

1994-01-01

219

Early development of karst systems: 1. Preferential flow path enlargement under laminar flow

Modeling of flow and solutional processes within networks of interconnected conduits in limestone aquifers indicates that enlargement occurs very selectively during the early stages of karst aquifer development under laminar flow. If initial flow paths are uniform in size, almost all enlargement occurs along a single set of connected conduits that lie along a direct path between recharge and discharge

Christopher G. Groves; Alan D. Howard

1994-01-01

220

Numerical Simulation of an Aortic Flow Based on a HLLC Type Incompressible Flow Solver

In this study, a three-dimensional artificial compressibility solver based on the average-state Harten-Lax-van Leer-Contact (HLLC) (13) type Riemann solution is first proposed and developed to solve the time-dependent incompressible flow equa- tions. To implement unsteady flow calculations, a dual time stepping strategy in- cluding the LU decomposition method is used in the pseudo-time iteration and the second-order accurate backward difference

Yang-Yao Niu; Chih-Hung Chang; Wen-Yih I. Tseng; Hsu-Hsia Peng; Hsi-Yu Yu

2009-01-01

221

NASA Technical Reports Server (NTRS)

A method for the solution of the incompressible nonviscous flow through a centrifugal impeller, including the inlet region, is presented. Several numerical solutions are obtained for four weight flows through an impeller at one operating speed. These solutions are refined in the leading-edge region. The results are presented in a series of figures showing streamlines and relative velocity contours. A comparison is made with the results obtained by using a rapid approximate method of analysis.

Kramer, James J; Prian, Vasily D; Wu, Chung-Hua

1956-01-01

222

Aircraft energy efficiency laminar flow control wing design study

NASA Technical Reports Server (NTRS)

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.

Bonner, T. F., Jr.; Pride, J. D., Jr.; Fernald, W. W.

1977-01-01

223

Hybrid laminar flow control applied to advanced turbofan engine nacelles

NASA Technical Reports Server (NTRS)

The potential application of hybrid laminar flow control (HLFC) to the external surface of an advanced, high bypass ratio turbofan engine nacelle with a wetted area that approaches 15 percent of the wing total wetted area of future commercial transports is presented. A pressure distribution compatible with HLFC is specified and the corresponding nacelle geometry is computed employing a predictor/corrector design technique. Performance evaluations on an advanced twin-engine transport configuration are discussed to determine potential benefits in terms of reduced fuel consumption.

Collier, F. S., Jr.; Arcara, P. C., Jr.; Wie, Y. S.

1992-01-01

224

Laminar flow control leading edge systems in simulated airline service

NASA Technical Reports Server (NTRS)

The feasibility of two candidate leading-edge flow laminarization systems applicable to airline service was tested using representative airline operational conditions with respect to air traffic, weather, and airport insect infestation. One of the systems involved a perforated Ti alloy suction surface with about 1 million 0.0025-in. diameter holes drilled by electron beam, as well as a Krueger-type flap that offered protective shielding against insect impingement; the other supplied surface suction through a slotted Ti alloy skin with 27 spanwise slots on the upper and lower surface.

Wagner, R. D.; Maddalon, D. V.; Fisher, D. F.

1988-01-01

225

Developing steady laminar flow through uniform straight tubes with varying wall cross curvature.

Numerical calculations are used to determine not only the wall shear stress but also the entry length in a laminar steady flow of an incompressible Newtonian fluid. The fluid is conveyed through rigid straight tubes with axially uniform cross sections, which mimic collapsed vessels. For each tube configuration, the "Navier-Stokes" equations are solved using the finite element method. The numerical tests are performed with the same value of the volume flow-rate whatever the tube configuration for three "Reynolds numbers". The wall shear stress is computed and determined along the axis of the tube, then the entry length is estimated by introducing two indexes by using: (i) the axial fluid velocity, and (ii) the wall shear stress. The results are analysed in order to exhibit the mechanical environment of cultured endothelial cells in the flow chamber for which the test conditions will be well-defined. For example, in a tube configuration where the opposite walls are in contact for which the inner perimeter and the area of the cross section are respectively given by 45 mm and 37.02 mm(2), the computed entry lengths with the criteria defined by (i) and (ii) are equals to about 118 and 126 mm, respectively for R(e0) = 500. PMID:15621652

Naili, S; Thiriet, M; Ribreau, C

2004-12-01

226

Passive and Active Device for Laminar Flow Control of Swept Wing

Summary Laminar flow control of aircraft gains importance due to both economic and environmental aspects. In this paper several solutions for passive devices and one proposal for an active device for laminar flow control on swept wings are presented. The passive devices concern the anti contamination devices (ACD) which are capable to stop the spanwise propagation of fuselage-induced contaminated flow

J. V. Krier; T. Sucipto; J. P. Godard; R. Donelli; D. Arnal

227

Pressure-Driven Laminar Flow in Tangential Microchannels: an Elastomeric Microfluidic

Pressure-Driven Laminar Flow in Tangential Microchannels: an Elastomeric Microfluidic Switch Rustem, Massachusetts 02138 This paper describes laminar fluid flow through a three- dimensional elastomeric-to-face (typically at a 90Â° angle), with the fluid flows in tangential contact. There are two ways to control fluid

Prentiss, Mara

228

The exact calculation of quadrupole sources for some incompressible flows

NASA Technical Reports Server (NTRS)

This paper is concerned with the application of the acoustic analogy of Lighthill to the acoustic and aerodynamic problems associated with moving bodies. The Ffowcs Williams-Hawkings equation, which is an interpretation of the acoustic analogy for sound generation by moving bodies, manipulates the source terms into surface and volume sources. Quite often in practice the volume sources, or quadrupoles, are neglected for various reasons. Recently, Farassat, Long and others have attempted to use the FW-H equation with the quadrupole source and neglected to solve for the surface pressure on the body. The purpose of this paper is to examine the contribution of the quadrupole source to the acoustic pressure and body surface pressure for some problems for which the exact solution is known. The inviscid, incompressible, 2-D flow, calculated using the velocity potential, is used to calculate the individual contributions of the various surface and volume source terms in the FW-H equation. The relative importance of each of the sources is then assessed.

Brentner, Kenneth S.

1988-01-01

229

(y) c | ln |x - y|| x, y , |x - y| fluid shows `shear thinning' behavior, while Newtonian behavior holds for p(x) = 2, and `shear thickening' behavior is relatedCONVERGENCE ANALYSIS FOR INCOMPRESSIBLE GENERALIZED NEWTONIAN FLUID FLOWS WITH NONSTANDARD

TÃ¼bingen, UniversitÃ¤t

230

Boundary asymptotic analysis for an incompressible viscous flow: Navier wall laws

and incompressible fluid, whose Reynolds number is of order 1/, flowing in a domain with rugosities of thinness, and assuming an homogeneous Dirichlet boundary condition on the boundary of these rugosities. Using

Boyer, Edmond

231

A predicable condition for boundary layer separation of 2-D incompressible fluid flows

In this paper, the solutions of Navier-Stokes equations with Dirichlet boundary conditions governing 2-D incompressible fluid flows are considered. A condition for boundary layer separation, which is determined by initial values and external forces, is obtained. More importantly, the condition can predict directly when and where boundary layer separation will occur. The main technical tool is geometric theory of incompressible flows developed by T. Ma and S.Wang.

Luo, Hong; Ma, Tian

2014-01-01

232

Accurate and robust methods for variable density incompressible flows with discontinuities

We are interested in the solution of incompressible flows which are characterized by large density variations, interfacial physics, arbitrary material topologies and strong vortical content. The issues present in constant density incompressible flow are exacerbated by the presence of density discontinuities. A much greater premium requirement is placed the positivity of computed quantities The mechanism of baroclinc vorticity generation exists ({gradient}p x {gradient}p) to further complicate the physics.

Rider, W.J.; Kothe, D.B.; Puckett, E.G.

1996-09-01

233

Air-breathing laminar flow-based microfluidic fuel cell.

This communication reports the design and characterization of an air-breathing laminar flow-based microfluidic fuel cell (LFFC). The performance of previous LFFC designs was cathode-limited due to the poor solubility and slow transport of oxygen in aqueous media. Introduction of an air-breathing gas diffusion electrode as the cathode addresses these mass transfer issues. With this design change, the cathode is exposed to a higher oxygen concentration, and more importantly, the rate of oxygen replenishment in the depletion boundary layer on the cathode is greatly enhanced as a result of the 4 orders of magnitude higher diffusion coefficient of oxygen in air as opposed to that in aqueous media. The power densities of the present air-breathing LFFCs are 5 times higher (26 mW/cm2) than those for LFFCs operated using formic acid solutions as the fuel stream and an oxygen-saturated aqueous stream at the cathode ( approximately 5 mW/cm2). With the performance-limiting issues at the cathode mitigated, these air-breathing LFFCs can now be further developed to fully exploit their advantages of direct control over fuel crossover and the ability to individually tailor the chemical composition of the cathode and anode media to enhance electrode performance and fuel utilization, thus increasing the potential of laminar flow-based fuel cells. PMID:16316201

Jayashree, Ranga S; Gancs, Lajos; Choban, Eric R; Primak, Alex; Natarajan, Dilip; Markoski, Larry J; Kenis, Paul J A

2005-12-01

234

Laminar boundary-layer flow of non-Newtonian fluid

NASA Technical Reports Server (NTRS)

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.

Lin, F. N.; Chern, S. Y.

1979-01-01

235

Investigation B: Laminar confined coaxial entrance flow with heat generation

NASA Technical Reports Server (NTRS)

The results of a parametric study on the entrance flow region in a gas core nuclear reactor are presented. The physical system is modeled as laminar confined, coaxial flow with heat generation in the inner fluid. The governing equations include the boundary layer approximations and the assumptions of only radial radiative transport of energy represented as an energy diffusion term. The Von Mises transformation and a zeta transformation are used to transform the equations into nonlinear nonhomogeneous convective-diffusion equations. A unique combination of forward and backward difference equations which yields accurate results at moderate computational times, is used in the numerical method. Results show that the rapidly accelerating, heat generating inner stream actually shrinks in radius as it expands axially.

Bobba, G. K. M.; Weinstein, H.

1975-01-01

236

Flight Tests of a Supersonic Natural Laminar Flow Airfoil

NASA Technical Reports Server (NTRS)

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

Frederick, Mike; Banks, Dan; Garzon, Andres; Matisheck, Jason

2014-01-01

237

These applications all rely on multistream laminar flow, which enables control over local chemical composition withinÂliquid interface between fluids of different densities flowing side-by-side in pressure-driven laminar flow growing number of microchemical systems that utilize multistream laminar flow for performing spatially

Kenis, Paul J. A.

238

NASA Technical Reports Server (NTRS)

A general integral form of the boundary-layer equation, valid for either laminar or turbulent incompressible boundary-layer flow, is derived. By using the experimental finding that all velocity profiles of the turbulent boundary layer form essentially a single-parameter family, the general equation is changed to an equation for the space rate of change of the velocity-profile shape parameter. The lack of precise knowledge concerning the surface shear and the distribution of the shearing stress across turbulent boundary layers prevented the attainment of a reliable method for calculating the behavior of turbulent boundary layers.

Tetervin, Neal; Lin, Chia Chiao

1951-01-01

239

An experimental study of a laminar flow control airfoil with suction through a perforated surface at low speed was made. The airfoil section was designed to be a natural laminar flow airfoil which can delay the boundary layer transition as far downstream as possible. The effects of suction quantity and position of sucked area on transition delay were examined. It

Yoji Ishida; Masayoshi Noguchi

1988-01-01

240

The Phase Relationship in Laminar Channel Flow Controlled by Traveling Wave-Like Blowing/Suction

The Phase Relationship in Laminar Channel Flow Controlled by Traveling Wave-Like Blowing (2006)] in a two-dimensional laminar Poiseuille flow is investigated. The investigation is done disturbances in- duced by a traveling wave-like blowing/suction control [T. Min et al., J. Fluid Mech. 558, 309

Hoepffner, JÃ©rÃ´me

241

Application of laminar flow control to high-bypass-ratio turbofan engine nacelles

Recently, the concept of the application of hybrid laminar flow to modern commercial transport aircraft was successfully flight tested on a Boeing 757 aircraft. In this limited demonstration, in which only part of the upper surface of the swept wing was designed for the attainment of laminar flow, significant local drag reduction was measured. This paper addresses the potential application

Y. S. Wie; F. S. Jr. Collier; R. D. Wagner

1991-01-01

242

Numerical solution of the Navier-Stokes equations for laminar, transonic flows

An implicit finite difference solution of the Navier-Stokes equations yielded time histories of the transonic laminar flow development about a circular cylinder and NACA-0018 airfoil. Reynolds numbers ranged from those corresponding to purely laminar flow to those corresponding to significant turbulence in the boundary layer. Body thermal conditions of an adiabatic wall and a specified body temperature were considered. Versatility

L. Turner III

1979-01-01

243

Smart Suction — an Advanced Concept for Laminar Flow Control of Three-Dimensional Boundary Layers

A new method combining classical boundary-layer suction with the recently developed technique of Upstream Flow Deformation\\u000a is proposed to delay laminar-turbulent transition in three-dimensional boundary-layer flows. By means of direct numerical\\u000a simulations details of the flow physics are investigated to maintain laminar flow even under strongly changing chordwise flow\\u000a conditions. Simulations reveal that steady crossflow modes are less amplified than

Ralf Messing; Markus Kloker

244

Overview of supersonic laminar flow control research on the F-16XL ships 1 and 2

NASA Technical Reports Server (NTRS)

NASA is directing research to develop technology for a high-speed civil transport. Supersonic laminar flow control has been identified as a program element, since it offers significant drag-reduction benefits and is one of the more promising technologies for producing an economically viable aircraft design. NASA is using two prototype F-16XL aircraft to research supersonic laminar flow control. The F-16XL planform is similar to design planforms of high-speed civil transports. The planform makes the aircraft ideally suited for developing technology pertinent to high-speed transports. The supersonic laminar flow control research programs for both aircraft are described. Some general results of the ship-1 program demonstrate that significant laminar flow was obtained using laminar flow control on a highly swept wing at supersonic speeds.

Anderson, Bianca T.; Bohn-Meyer, Marta

1992-01-01

245

This research develops a technique for the solution of incompressible equivalents to planar steady subsonic potential flows. Riemannian geometric formalism is used to develop a gauge transformation of the length measure followed by a curvilinear coordinate transformation to map the given subsonic flow into a canonical Laplacian flow with the same boundary conditions. The effect of the transformation is to

Brian Joseph German

2007-01-01

246

The viscous incompressible medium (water, air) flow past a circular cylinder is considered with regard for the temperature T dependent viscosity v. The influence of different boundary conditions for temperature on flow structure, the drag coefficient and its components due to the pressure and viscosity is investigated in the problem of the flow past a cylinder at rest for the

M. N. Zakharenkov

2007-01-01

247

An efficient algorithm for incompressible N-phase flows

NASA Astrophysics Data System (ADS)

We present an efficient algorithm within the phase field framework for simulating the motion of a mixture of N (N?2) immiscible incompressible fluids, with possibly very different physical properties such as densities, viscosities, and pairwise surface tensions. The algorithm employs a physical formulation for the N-phase system that honors the conservations of mass and momentum and the second law of thermodynamics. We present a method for uniquely determining the mixing energy density coefficients involved in the N-phase model based on the pairwise surface tensions among the N fluids. Our numerical algorithm has several attractive properties that make it computationally very efficient: (i) it has completely de-coupled the computations for different flow variables, and has also completely de-coupled the computations for the (N-1) phase field functions; (ii) the algorithm only requires the solution of linear algebraic systems after discretization, and no nonlinear algebraic solve is needed; (iii) for each flow variable the linear algebraic system involves only constant and time-independent coefficient matrices, which can be pre-computed during pre-processing, despite the variable density and variable viscosity of the N-phase mixture; (iv) within a time step the semi-discretized system involves only individual de-coupled Helmholtz-type (including Poisson) equations, despite the strongly-coupled phase-field system of fourth spatial order at the continuum level; (v) the algorithm is suitable for large density contrasts and large viscosity contrasts among the N fluids. Extensive numerical experiments have been presented for several problems involving multiple fluid phases, large density contrasts and large viscosity contrasts. In particular, we compare our simulations with the de Gennes theory, and demonstrate that our method produces physically accurate results for multiple fluid phases. We also demonstrate the significant and sometimes dramatic effects of the gravity, density ratios, pairwise surface tensions, and drop sizes on the N-phase configurations and dynamics. The numerical results show that the method developed herein is capable of dealing with N-phase systems with large density ratios, large viscosity ratios, and pairwise surface tensions, and that it can be a powerful tool for studying the interactions among multiple types of fluid interfaces.

Dong, S.

2014-11-01

248

GASP cloud encounter statistics - Implications for laminar flow control flight

NASA Technical Reports Server (NTRS)

The cloud observation archive from the NASA Global Atmospheric Sampling Program (GASP) is analyzed in order to derive the probability of cloud encounter at altitudes normally flown by commercial airliners, for application to a determination of the feasability of Laminar Flow Control (LFC) on long-range routes. The probability of cloud encounter is found to vary significantly with season. Several meteorological circulation features are apparent in the latitudinal distribution of cloud cover. The cloud encounter data are shown to be consistent with the classical midlatitude cyclone model with more clouds encountered in highs than in lows. Aircraft measurements of route-averaged time-in-clouds fit a gamma probability distribution model which is applied to estimate the probability of extended cloud encounter, and the associated loss of LFC effectiveness along seven high-density routes. The probability is demonstrated to be low.

Jasperson, W. H.; Nastrom, G. D.; Davis, R. E.; Holdeman, J. D.

1984-01-01

249

Postfragmentation density function for bacterial aggregates in laminar flow

NASA Astrophysics Data System (ADS)

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.

Byrne, Erin; Bortz, David M.; Dzul, Steve; Solomon, Michael; Younger, John

2011-04-01

250

Lift-to-drag ratio and laminar flow control of a morphing laminar wing in a wind tunnel

A new hardware-in-the-loop control strategy to enhance the aerodynamic performance of a two-dimensional morphing laminar wing prototype was developed and tested. The testing was performed in a wind tunnel under cruise flight flow conditions: Mach number ranging from 0.2 to 0.3 and angle of attack from - 1° to 0.5°. For each set of flow conditions, the shape of the

Daniel Coutu; Vladimir Brailovski; Patrick Terriault; Mahmoud Mamou; Youssef Mébarki; Éric Laurendeau

2011-01-01

251

Laminar flow around corners triggers the formation of biofilm streamers.

Bacterial biofilms have an enormous impact on medicine, industry and ecology. These microbial communities are generally considered to adhere to surfaces or interfaces. Nevertheless, suspended filamentous biofilms, or streamers, are frequently observed in natural ecosystems where they play crucial roles by enhancing transport of nutrients and retention of suspended particles. Recent studies in streamside flumes and laboratory flow cells have hypothesized a link with a turbulent flow environment. However, the coupling between the hydrodynamics and complex biofilm structures remains poorly understood. Here, we report the formation of biofilm streamers suspended in the middle plane of curved microchannels under conditions of laminar flow. Experiments with different mutant strains allow us to identify a link between the accumulation of extracellular matrix and the development of these structures. Numerical simulations of the flow in curved channels highlight the presence of a secondary vortical motion in the proximity of the corners, which suggests an underlying hydrodynamic mechanism responsible for the formation of the streamers. Our findings should be relevant to the design of all liquid-carrying systems where biofilms are potentially present and provide new insights on the origins of microbial streamers in natural and industrial environments. PMID:20356880

Rusconi, Roberto; Lecuyer, Sigolene; Guglielmini, Laura; Stone, Howard A

2010-09-01

252

NASA Astrophysics Data System (ADS)

Laminar velocity and temperature fields in a rectangular channel with a row of built-in vortex generators in the form of slender delta wings and winglet pairs have been calculated by means of a zonal method consisting of zones of complete and partially parabolized Navier-Stokes and energy equations. A modified version of SOLA for incompressible as well as for variable-density, small-Mach number flows has been used to solve the basic equations. Each wing or winglet pair generates counterrotating longitudinal vortices that, in contrast to similar vortices in an unbounded medium, show an elliptic deformation, a wakelike axial velocity distribution in the core, and an absence of breakdown even at angles of attack as large as 50 deg. The spiraling motion induced by these vortices in the channel can locally enhance the heat transfer coefficient by a factor of 3 compared to its value in a wingless channel. The temperature dependence of density can reduce this enhancement by roughly 10 percent when the ratio of gas-to-wall temperature is 1.3.

Fiegib, M.; Brockmeier, U.; Mitra, N. K.; Guentermann, T.

253

Hybrid Laminar Flow Control (HLFC) is an active drag reduction technique that requires a small amount of air to be sucked through a porous skin surface, thus stabilising the boundary layer and permitting extended laminar flow along the wing surface. Contamination of the laminar flow surfaces by insects is a major concern for this technology. An overview of insect contamination

D O'Donoghue; T. M Young; J. T Pembroke; T. F O'Dwyer

2002-01-01

254

Predictions and observations of the flow field induced by laminar flow control microperforations

Hybrid laminar flow control (HLFC) aims to reduce aircraft skin friction drag by controlling the boundary-layer characteristics through a combination of surface suction and surface profile shaping. Suction is applied through an array of microperforations in the surface; and, to enable HLFC design criteria to be established with confidence, a full understanding of how these suction perforations affect the boundary

David G. MacManus; John A. Eaton

1996-01-01

255

Application of laminar flow control to high-bypass-ratio turbofan engine nacelles

NASA Technical Reports Server (NTRS)

Recently, the concept of the application of hybrid laminar flow to modern commercial transport aircraft was successfully flight tested on a Boeing 757 aircraft. In this limited demonstration, in which only part of the upper surface of the swept wing was designed for the attainment of laminar flow, significant local drag reduction was measured. This paper addresses the potential application of this technology to laminarize the external surface of large, modern turbofan engine nacelles which may comprise as much as 5-10 percent of the total wetted area of future commercial transports. A hybrid-laminar-flow-control (HLFC) pressure distribution is specified and the corresponding nacelle geometry is computed utilizing a predictor/corrector design method. Linear stability calculations are conducted to provide predictions of the extent of the laminar boundary layer. Performance studies are presented to determine potential benefits in terms of reduced fuel consumption.

Wie, Y. S.; Collier, F. S., Jr.; Wagner, R. D.

1991-01-01

256

Computations for laminar flow control in swept-wing boundary layers

The laminarization of a swept-wing boundary layer by the introduction of passive spanwise-periodic roughness elements (DRE) near the leading edge is modeled by linear stability theory and nonlinear parabolized stability equations. Studies predict that, for chord Reynolds numbers of 8 million and with an appropriate pressure coefficient design, the crossflow instability can be stabilized and laminar flow achieved. Sensitivity to

Helen Reed; Richard Rhodes; William Saric

2007-01-01

257

Inverse formulation for incompressible viscous two-dimensional and axisymmetric flow problems

The inverse problem of an incompressible viscous axisymmetric flow is formulated using the orthogonal curvilinear coordinate system, including a two dimensional flow. The Stokes stream function or stream function and the coordinate which is constant along the orthogonal trajectories of streamlines or stream tubes are the independent variables. The Navier-Stokes equations and the vorticity transport equation are transformed into the

Tetsuhiro Tsukiji

1993-01-01

258

Direct calibration framework of triple-hole pressure probes for incompressible flow

This paper carries out a mathematical analysis of the limits and data reduction techniques of three-hole pressure (THP) probes operating in a 'non-nulling' mode for incompressible flow. As a result of this analysis, a direct procedure is advanced, based on the distinction of several zones within the angular range, where different relations can be applied to obtain the flow variables.

K. M. Argüelles Díaz; J. M. Fernández Oro; E. Blanco Marigorta

2008-01-01

259

Direct calibration framework of triple-hole pressure probes for incompressible flow

This paper carries out a mathematical analysis of the limits and data reduction techniques of three-hole pressure (THP) probes operating in a ‘non-nulling’ mode for incompressible flow. As a result of this analysis, a direct procedure is advanced, based on the distinction of several zones within the angular range, where different relations can be applied to obtain the flow variables.

K M Argüelles Díaz; J M Fernández Oro; E Blanco Marigorta

2008-01-01

260

Immersed interface methods for incompressible flow with moving interfaces

We introduce a class of immersed interface methods for incompressible Navier-Stokes equations with singular forces. The algorithms are developed using a new hybrid finite volume\\/finite difference projection method. This projection method uses the high-resolution finite-volume method from CLAWPACK to advect the cell-centered velocity using the divergence-free edge velocity. Then a finite difference method is used for the diffusion and the

Long Lee

2002-01-01

261

Front Speed Enhancement by Incompressible Flows in Three or Higher Dimensions

NASA Astrophysics Data System (ADS)

We study, in dimensions N ? 3, the family of first integrals of an incompressible flow: these are functions whose level surfaces are tangential to the streamlines of the advective incompressible field. One main motivation for this study comes from earlier results proving that the existence of nontrivial first integrals of an incompressible flow q is the main key that leads to a "linear speed up" by a large advection of pulsating traveling fronts solving a reaction-advection-diffusion equation in a periodic heterogeneous framework. The family of first integrals is not well understood in dimensions N ? 3 due to the randomness of the trajectories of q and this is in contrast with the case N = 2. By looking at the domain of propagation as a union of different components produced by the advective field, we provide more information about first integrals and we give a class of incompressible flows which exhibit "ergodic components" of positive Lebesgue measure (and hence are not shear flows) and which, under certain sharp geometric conditions, speed up the KPP fronts linearly with respect to the large amplitude. In the proofs, we establish a link between incompressibility, ergodicity, first integrals and the dimension to give a sharp condition about the asymptotic behavior of the minimal KPP speed in terms of the configuration of ergodic components.

El Smaily, Mohammad; Kirsch, Stéphane

2014-07-01

262

Aircraft energy efficiency laminar flow control glove flight conceptual design study

NASA Technical Reports Server (NTRS)

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.

Wright, A. S.

1979-01-01

263

NASA Technical Reports Server (NTRS)

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.

Carmichael, B. H.

1979-01-01

264

Erosion of a granular bed driven by laminar fluid flow

Motivated by examples of erosive incision of channels in sand, we investigate the motion of individual grains in a granular bed driven by a laminar fluid to give us new insights into the relationship between hydrodynamic stress and surface granular flow. A closed cell of rectangular cross-section is partially filled with glass beads and a constant fluid flux $Q$ flows through the cell. The refractive indices of the fluid and the glass beads are matched and the cell is illuminated with a laser sheet, allowing us to image individual beads. The bed erodes to a rest height $h_r$ which depends on $Q$. The Shields threshold criterion assumes that the non-dimensional ratio $\\theta$ of the viscous stress on the bed to the hydrostatic pressure difference across a grain is sufficient to predict the granular flux. Furthermore, the Shields criterion states that the granular flux is non-zero only for $\\theta >\\theta_c$. We find that the Shields criterion describes the observed relationship $h_r \\propto Q^{1/2}$ when the bed height is offset by approximately half a grain diameter. Introducing this offset in the estimation of $\\theta$ yields a collapse of the measured Einstein number $q^*$ to a power-law function of $\\theta - \\theta_c$ with exponent $1.75 \\pm 0.25$. The dynamics of the bed height relaxation are well described by the power law relationship between the granular flux and the bed stress.

A. E. Lobkovsky; A. V. Orpe; R. Molloy; A. Kudrolli; D. H. Rothman

2008-05-01

265

LAMINAR FLOW ELEMENT: ITS USE AS A FLOW STANDARD

A standard device to measure flows accurately and precisely was required by the U.S. Environmental Protection Agency (EPA) to establish an air pollution field auditing system capable of generating pollutant concentrations in the parts per million and parts per billion range. he e...

266

This paper discusses incompressible Navier-Stokes solution methods with an emphasis on the pseudocompressibility method. A steady-state flow solver based on the pseudocompressibility approach is then described. This flow solver code has been used to analyze the internal flow in the Space Shuttle main engine hot-gas manifold. Salient features associated with this three-dimensional realistic flow simulation are discussed. Numerical solutions relevant

J. L. C. Chang; D. Kwak; S. E. Rogers; R.-J. Yang

1988-01-01

267

Incompressible Navier-Stokes solution methods are discussed with an emphasis on the pseudocompressibility method. A steady-state flow solver based on the pseudocompressibility approach is then described. This flow-solver code was used to analyze the internal flow in the Space Shuttle main engine hot-gas manifold. Salient features associated with this three-dimensional realistic flow simulation are discussed. Numerical solutions relevant to the current

J. L. C. Chang; D. Kwak; S. E. Rogers; R.-J. Yang

1988-01-01

268

Multi-material incompressible flow simulation using the moment-of-fluid method

The Moment-of-Fluid interface reconstruction technique is implemented in a second order accurate, unstructured finite element variable density incompressible Navier-Stokes solver. For flows with multiple materials, MOF significantly outperforms existing first and second order interface reconstruction techniques. For two material flows, the performance of MOF is similar to other interface reconstruction techniques. For strongly driven bouyant flows, the errors in the flow solution dominate and all the interface reconstruction techniques perform similarly.

Garimella, R V [Los Alamos National Laboratory; Schofield, S P [Los Alamos National Laboratory; Lowrie, R B [Los Alamos National Laboratory; Swartz, B K [Los Alamos National Laboratory; Christon, M A [SIMULIA; Dyadechko, V [EXXON-MOBIL

2009-01-01

269

Laminar Flow of a Sheared Vortex Crystal: Scars in Flat Geometry

NASA Astrophysics Data System (ADS)

We consider the laminar flow of a vortex crystal in the Corbino disk geometry. Laminar flow can be induced by thermal fluctuations melting the crystal, but also by shear stress after applying a large current at zero temperature. While the velocity profile is the same in the two cases, the underlying vortex structure is completely different. A vortex crystal in this geometry can flow in a laminar fashion whenever the appropriate curvature is established in the vortex lattice. This curvature requires the presence of geometrically necessary disclinations, which here migrate from the boundary to the bulk of the crystal in the form of current-induced grain boundary scars in flat geometry. We provide an estimate of the characteristic current needed to initiate such a laminar flow regime in the vortex crystal and show that the result is in good agreement with simulations.

Miguel, M.-Carmen; Mughal, Adil; Zapperi, Stefano

2011-06-01

270

Design and operation of a laminar-flow electrostatic-quadrupole-focused acceleration column

This report deals with the design principles involved in the design of a laminar-flow electrostatic-quadrupole-focused acceleration column. In particular, attention will be paid to making the parameters suitable for incorporation into a DC MEQALAC design.

Maschke, A.W.

1983-06-20

271

Distributed acoustic receptivity in laminar flow control configurations

NASA Technical Reports Server (NTRS)

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.

Choudhari, Meelan

1992-01-01

272

Frost Growth and Densification in Laminar Flow Over Flat Surfaces

NASA Technical Reports Server (NTRS)

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.

Kandula, Max

2011-01-01

273

NASA Technical Reports Server (NTRS)

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.

Srokowski, A. J.

1994-01-01

274

A perspective of laminar-flow control. [aircraft energy efficiency program

NASA Technical Reports Server (NTRS)

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.

Braslow, A. L.; Muraca, R. J.

1978-01-01

275

A coarse-grid projection method for accelerating incompressible flow computations

NASA Astrophysics Data System (ADS)

We present a coarse-grid projection (CGP) method for accelerating incompressible flow computations, which is applicable to methods involving Poisson equations as incompressibility constraints. The CGP methodology is a modular approach that facilitates data transfer with simple interpolations and uses black-box solvers for the Poisson and advection-diffusion equations in the flow solver. After solving the Poisson equation on a coarsened grid, an interpolation scheme is used to obtain the fine data for subsequent time stepping on the full grid. A particular version of the method is applied here to the vorticity-stream function, primitive variable, and vorticity-velocity formulations of incompressible Navier-Stokes equations. We compute several benchmark flow problems on two-dimensional Cartesian and non-Cartesian grids, as well as a three-dimensional flow problem. The method is found to accelerate these computations while retaining a level of accuracy close to that of the fine resolution field, which is significantly better than the accuracy obtained for a similar computation performed solely using a coarse grid. A linear acceleration rate is obtained for all the cases we consider due to the linear-cost elliptic Poisson solver used, with reduction factors in computational time between 2 and 42. The computational savings are larger when a suboptimal Poisson solver is used. We also find that the computational savings increase with increasing distortion ratio on non-Cartesian grids, making the CGP method a useful tool for accelerating generalized curvilinear incompressible flow solvers.

San, Omer; Staples, Anne E.

2013-01-01

276

FIELD DESCRIPTIONS FOR A DEVELOPING LAMINAR TUBE FLOW WITH AND WITHOUT A CONCENTRICALLY LOCATED SPHERICAL OBSTACLE A Thesis by CLARK DOUGLAS MIKKELSEN Submitted to the Graduate College of Texas ASM University in partial fulfillment... of the requirement for the degree of MASTER OF SCIENCE December 1972 Major Subject: Mechanical Engineering FIELD DESCRIPTIONS FOR A DEVELOPING LAMINAR TUBE FLOW WITH AND WITHOUT A CONCENTRICALLY LOCATED SPHERICAL OBSTACLE A Thesis by CLARK DOUGLAS MIKKELSEN...

Mikkelsen, Clark Douglas

2012-06-07

277

Equations of turbulence in an incompressible two-phase flow in the absence of mass transfer

The problem of an incompressible two-phase flow without mass transfer is examined. In order to adapt methods used in modeling monophase flows (Lumley, 1975) to the analysis of turbulence in a two-phase flow, equations describing the evolution of the Reynolds tensor, dissipation and pressure fluctuation in each phase are derived and combined with the general equations used in treating two-phase

M. Lance; J.-L. Marie; G. Charnay; J. Bataille

1979-01-01

278

Stability Analysis of Large-Scale Incompressible Flow Calculations on Massively Parallel Computers

A set of linear and nonlinear stability analysis tools have been developed to analyze steady state incompressible flows in 3D geometries. The algorithms have been implemented to be scalable to hundreds of parallel processors. The linear stability of steady state flows are determined by calculating the rightmost eigenvalues of the associated generalize eigenvalue problem. Nonlinear stability is studied by bifurcation analysis techniques. The boundaries between desirable and undesirable operating conditions are determined for buoyant flow in the rotating disk CVD reactor.

LEHOUCQ,RICHARD B.; ROMERO,LOUIS; SALINGER,ANDREW G.

1999-10-25

279

The viscous incompressible medium (water, air) flow past a circular cylinder is considered with regard for the temperature\\u000a T dependent viscosity v. The influence of different boundary conditions for temperature on flow structure, the drag coefficient and its components\\u000a due to the pressure and viscosity is investigated in the problem of the flow past a cylinder at rest for the

M. N. Zakharenkov

2007-01-01

280

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...

281

NASA Technical Reports Server (NTRS)

Development of an incompressible Navier-Stokes solution procedure was performed for the analysis of a liquid rocket engine pump components and for the mechanical heart assist devices. The solution procedure for the propulsion systems is applicable to incompressible Navier-Stokes flows in a steadily rotating frame of reference for any general complex configurations. The computer codes were tested on different complex configurations such as liquid rocket engine inducer and impellers. As a spin-off technology from the turbopump component simulations, the flow analysis for an axial heart pump was conducted. The baseline Left Ventricular Assist Device (LVAD) design was improved by adding an inducer geometry by adapting from the liquid rocket engine pump. The time-accurate mode of the incompressible Navier-Stokes code was validated with flapping foil experiment by using different domain decomposition methods. In the flapping foil experiment, two upstream NACA 0025 foils perform high-frequency synchronized motion and generate unsteady flow conditions for a downstream larger stationary foil. Fairly good agreement was obtained between unsteady experimental data and numerical results from two different moving boundary procedures. Incompressible Navier-Stokes code (INS3D) has been extended for heat transfer applications. The temperature equation was written for both forced and natural convection phenomena. Flow in a square duct case was used for the validation of the code in both natural and forced convection.

Kiris, Cetin

1995-01-01

282

INFORMATION ISSN 1343-4500 Computing an Incompressible Viscous Fluid Flow Using Neural Network Based

INFORMATION ISSN 1343-4500 Computing an Incompressible Viscous Fluid Flow Using Neural Network Based on Modified Adaptive Smoothing Errors Nameer N. EL-Emam* and Riadh H. Al-Rabeh** *Computer Science Neural Networks (ANN) with Modified Adaptive Smoothing Errors (MASE) based on back-propagation algorithm

283

Numerical approximation of the Voigt regularization of incompressible NSE and MHD flows

Numerical approximation of the Voigt regularization of incompressible NSE and MHD flows Paul-regularizations for the Navier-Stokes and MHD equations in the presence of physical boundary conditions. We develop the first of the Voigt regularization can be made from a simple change to existing NSE and MHD codes, and moreover

Larios, Adam

284

of classical mechanics, thermodynamics, and laws of conservation of mass, momentum, and energy govern the motion of fluid. Law of conservation of momentum for in- compressible, viscous flow in a region of conservation of mass for incompressible fluids gives rise to Â¨AÂ¤CBEDGF Â¢IH (2) Viscosity of the fluid imposes

Sarin, Vivek

285

h-p adaptive finite element methods for compressible and incompressible flows

NASA Technical Reports Server (NTRS)

A unified approach based on h-p approximation in space variables and various time discretization schemes for solving both incompressible and compressible flows is presented. Two different techniques for a posteriori error estimation and accompanying h-p adaptive strategies are discussed.

Oden, J. T.; Demkowicz, L.; Liszka, T.; Rachowicz, W.

1990-01-01

286

A splitting method for numerical simulation of free surface flows of incompressible fluids The paper studies a splitting method for the numerical time-integration of the system of partial and a suitable energy estimate for numerical solutions. Under certain assumptions on the smoothness of the free

Olshanskii, Maxim A.

287

We develop an effective domain decomposition meshless methodology for conjugate heat transfer problems modeled by convecting fully viscous incompressible fluid interacting with conducting solids. The meshless formulation for fluid flow modeling is based on a radial basis function interpolation using Hardy inverse Multiquadrics and a time-progression decoupling of the equations using a Helmholtz potential. The domain decomposition approach effectively reduces

Eduardo Divo; Alain Kassab

2006-01-01

288

Numerical simulation of the incompressible internal flow through a tilting disk valve

NASA Astrophysics Data System (ADS)

A numerical simulation of the incompressible viscous flow through a prosthetic tilting disk heart valve is presented in order to demonstrate the current capability to model unsteady flows with moving boundaries. Both steady and unsteady flow calculations are performed by solving the incompressible Navier-Stokes equations in three-dimensional generalized curvilinear coordinates. In order to handle the moving boundary problems, the chimera grid embedding scheme which decomposes a complex computational domain into several simple subdomains is used. An algebraic turbulence model for internal flows is incorporated to reach the physiological values of Reynolds number. Good agreement is obtained between the numerical results and experimental measurements. It is found that the tilting disk valve causes large regions of separated flow, and regions of high shear.

Chang, I.-Dee; Rogers, Stuart E.; Kwak, Dochan; Kiris, Cetin

1990-01-01

289

Flow visualization of supersonic laminar flow over a backward-facing step via NPLS

NASA Astrophysics Data System (ADS)

An experimental study on a supersonic laminar flow over a backward-facing step of 5 mm height was undertaken in a low-noise indraft wind tunnel. To investigate the fine structures of Ma = 3.0 and 3.8 laminar flow over a backward-facing step, nanotracer planar laser scattering was adopted for flow visualization. Flow structures, including supersonic laminar boundary layer, separation, reattachment, redeveloping turbulent boundary layer, expansion wave fan and reattachment shock, were revealed in the transient flow fields. In the Ma = 3.0 BFS (backward-facing step) flow, by measuring four typical regions, it could be found that the emergence of weak shock waves was related to the K-H (Kelvin-Helmholtz) vortex which appeared in the free shear layer and that the convergence of these waves into a reattachment shock was distinct. Based on large numbers of measurements, the structure of time-averaging flow field could be gained. Reattachment occurred at the location downstream from the step, about 7-7.5 h distance. After reattachment, the recovery boundary layer developed into turbulence quickly and its thickness increased at an angle of 4.6°. At the location of X = 14 h, the redeveloping boundary layer was about ten times thicker than its original thickness, but it still had not changed into fully developed turbulence. However, in the Ma = 3.8 flow, the emergence of weak shock waves could be seen seldom, due to the decrease of expansion. The reattachment point was thought to be near X = 15 h according to the averaging result. The reattachment shock was not legible, which meant the expansion and compression effects were not intensive.

Chen, Z.; Yi, S. H.; Tian, L. F.; He, L.; Zhu, Y. Z.

2013-07-01

290

An Approach to the Constrained Design of Natural Laminar Flow Airfoils

NASA Technical Reports Server (NTRS)

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.

Green, Bradford E.

1997-01-01

291

Simultaneously developing laminar flow in an isothermal micro-tube with slip flow models

NASA Astrophysics Data System (ADS)

In this study, a two-dimensional steady state simultaneously developing laminar flow inside a micro-tube is investigated numerically under slip flow conditions. The first and second-order slip flow models have been implemented for the case where the viscous dissipation and axial conduction are included and a constant wall temperature boundary condition is specified. The results are obtained for several combinations of the Knudsen number Kn, the coefficient ? and the Brinkman number Br. The study reveals a significant impact of slip flow and temperature jump on the hydrodynamic and thermal fields. A comparison of the first and second-order slip flow shows a considerable variation of the hydrodynamic flow and a weak impact on the thermal field particularly when the flow is fully developed.

Loussif, Nizar; Orfi, Jamel

2014-04-01

292

A fundamental study of suction for Laminar Flow Control (LFC)

NASA Technical Reports Server (NTRS)

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.

Watmuff, Jonathan H.

1992-01-01

293

Convective heat transfer characteristics of laminar pulsating pipe air flow

NASA Astrophysics Data System (ADS)

Heat transfer characteristics to laminar pulsating pipe flow under different conditions of Reynolds number and pulsation frequency were experimentally investigated. The tube wall of uniform heat flux condition was considered. Reynolds number was varied from 780 to 1987 while the frequency of pulsation ranged from 1 to 29.5Hz. The results showed that the relative mean Nusselt number is strongly affected by pulsation frequency while it is slightly affected by Reynolds number. The results showed enhancements in the relative mean Nusselt number. In the frequency range of 1-4Hz, an enhancement up to 30% (at Reynolds number of 1366 and pulsation frequency of 1.4Hz) was obtained. In the frequency range of 17-25Hz, an enhancement up to 9% (at Reynolds number of 1366 and pulsation frequency of 17.5Hz) was indicated. The rate of enhancement of the relative mean Nusselt number decreased as pulsation frequency increased or as Reynolds number increased. A reduction in relative mean Nusselt number occurred outside these ranges of pulsation frequencies. A reduction in relative mean Nusselt number up to 40% for pulsation frequency range of 4.1-17Hz and a reduction up to 20% for pulsation frequency range of 25-29.5Hz for Reynolds numbers range of 780-1987 were considered. This reduction is directly proportional to the pulsation frequency. Empirical dimensionless equations have been developed for the relative mean Nusselt number that related to Reynolds number (750

Habib, M. A.; Attya, A. M.; Eid, A. I.; Aly, A. Z.

294

A fundamental study of suction for Laminar Flow Control (LFC)

NASA Astrophysics Data System (ADS)

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.

Watmuff, Jonathan H.

1992-10-01

295

Interpolation between DarcyWeisbach and Darcy for laminar and turbulent flows

. If the flow is turbulent the square of the velocity is proportional to the hydraulic gradient and if the flow is laminar, which is the usual case, the velocity is proportional to the hydraulic gradient. This last result of the appropriate DarcyÂWeisbach equation, e.g. see [2Â4], which states that the flow velocity, V, is proportional

Walter, M.Todd

296

Electrohydrodynamic instability of the laminar flow of a fluid film adjacent to a gas stream

The equations derived describe, in a long-wave approximation, the flow of a conducting fluid film in a transverse electric field in the presence of a tangential gas flow. They are applied to the problem of convective instability of the laminar flow at a flat interface. It is shown that the spectrum of perturbation frequencies contains a critical frequency that depends

V. M. Korovin

1976-01-01

297

Hybrid laminar flow control tests in the Boeing Research Wind Tunnel

NASA Technical Reports Server (NTRS)

The hybrid laminar flow control (HLFC) concept has undergone wind tunnel testing at near full-scale Reynolds number on an infinite wing of 30-deg sweep on which boundary-layer suction was furnished over the first 20 percent of chord of the upper surface. Depending on the external pressure distribution, the HLFC extended the laminarity of the boundary layer as far back as 45 percent of chord; this corresponds to a transition Reynolds number of about 11 million. The maximum chordwise extent of laminar run was found to be insensitive to the suction level over a wide range.

Parikh, P. G.; Lund, D. W.; George-Falvy, D.; Nagel, A. L.

1990-01-01

298

On a modification of GLS stabilized FEM for solving incompressible viscous flows

NASA Astrophysics Data System (ADS)

We deal with 2D flows of incompressible viscous fluids with high Reynolds numbers. Galerkin Least Squares technique of stabilization of the finite element method is studied and its modification is described. We present a number of numerical results obtained by the developed method, showing its contribution to solving flows with high Reynolds numbers. Several recommendations and remarks are included. We are interested in positive as well as negative aspects of stabilization, which cannot be divorced.

Burda, P.; Novotný, J.; Ístek, J.

2006-07-01

299

Unsteady incompressible two-dimensional and axisymmetric turbulent boundary layer flows

Summary The unsteady turbulent incompressible boundary-layer flow over two-dimensional and axisymmetric bodies with pressure gradient has been studied. An eddy-viscosity model has been used to model the Reynolds shear stress. The unsteadiness is due to variations in the free stream velocity with time. The nonlinear partial differential equation with three independent variables governing the flow has been solved using Keller's

M. Kumari

1986-01-01

300

A Unified Method for Computing Incompressible and Compressible Flows in Boundary-Fitted Coordinates

A unified method for computing incompressible and compressible flows with Mach-uniform accuracy and efficiency is described. The method is equally applicable to stationary and nonstationary flows. A pressure-based discretisation on a staggered grid in general boundary-fitted coordinates is used for the Euler equations. Extension to Navier--Stokes is straightforward. Dimensionless variables that remain finite for all Mach numbers are used. Mach

Hester Bijl; Pieter Wesseling

1998-01-01

301

On the Roughness-Induced Effective Boundary Conditions for an Incompressible Viscous Flow

We consider the laminar viscous channel flow with the lateral surface of the channel containing surface irregularities. It is supposed that a uniform pressure gradient is maintained in the longitudinal direction of the channel. After studying the corresponding boundary layers, we obtain rigorously the Navier friction condition. It is valid when the size and amplitude of the imperfections tend to

Willi Jäger; Andro Mikeli?

2001-01-01

302

Direct pore-level modeling of incompressible fluid flow in porous media

NASA Astrophysics Data System (ADS)

We present a dynamic particle-based model for direct pore-level modeling of incompressible viscous fluid flow in disordered porous media. The model is capable of simulating flow directly in three-dimensional high-resolution micro-CT images of rock samples. It is based on moving particle semi-implicit (MPS) method. We modify this technique in order to improve its stability for flow in porous media problems. Using the micro-CT image of a rock sample, the entire medium, i.e., solid and fluid, is discretized into particles. The incompressible Navier-Stokes equations are then solved for each particle using the MPS summations. The model handles highly irregular fluid-solid boundaries effectively. An algorithm to split and merge fluid particles is also introduced. To handle the computational load, we present a parallel version of the model that runs on distributed memory computer clusters. The accuracy of the model is validated against the analytical, numerical, and experimental data available in the literature. The validated model is then used to simulate both unsteady- and steady-state flow of an incompressible fluid directly in a representative elementary volume (REV) size micro-CT image of a naturally-occurring sandstone with 3.398 ?m resolution. We analyze the quality and consistency of the predicted flow behavior and calculate absolute permeability using the steady-state flow rate.

Ovaysi, Saeed; Piri, Mohammad

2010-09-01

303

Direct pore-level modeling of incompressible fluid flow in porous media

We present a dynamic particle-based model for direct pore-level modeling of incompressible viscous fluid flow in disordered porous media. The model is capable of simulating flow directly in three-dimensional high-resolution micro-CT images of rock samples. It is based on moving particle semi-implicit (MPS) method. We modify this technique in order to improve its stability for flow in porous media problems. Using the micro-CT image of a rock sample, the entire medium, i.e., solid and fluid, is discretized into particles. The incompressible Navier-Stokes equations are then solved for each particle using the MPS summations. The model handles highly irregular fluid-solid boundaries effectively. An algorithm to split and merge fluid particles is also introduced. To handle the computational load, we present a parallel version of the model that runs on distributed memory computer clusters. The accuracy of the model is validated against the analytical, numerical, and experimental data available in the literature. The validated model is then used to simulate both unsteady- and steady-state flow of an incompressible fluid directly in a representative elementary volume (REV) size micro-CT image of a naturally-occurring sandstone with 3.398 {mu}m resolution. We analyze the quality and consistency of the predicted flow behavior and calculate absolute permeability using the steady-state flow rate.

Ovaysi, Saeed, E-mail: sovaysi@uwyo.ed [Department of Chemical and Petroleum Engineering, University of Wyoming, Laramie, WY 82071-2000 (United States); Piri, Mohammad, E-mail: mpiri@uwyo.ed [Department of Chemical and Petroleum Engineering, University of Wyoming, Laramie, WY 82071-2000 (United States)

2010-09-20

304

NASA Technical Reports Server (NTRS)

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.

Goodyear, M. D.

1987-01-01

305

Method and apparatus for detecting laminar flow separation and reattachment

NASA Technical Reports Server (NTRS)

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.

Stack, John P. (inventor); Mangalam, Sivaramakrishnan M. (inventor)

1990-01-01

306

NASA Astrophysics Data System (ADS)

This paper concerns the study of laminar and turbulent force convection heat transfer and pressure drop between horizontal parallel plates with a nanofluid composed of Al2O3 and water. A set of governing equations are solved using a non-staggered SIMPLE procedure for the velocity-pressure coupling. For the convection-diffusion terms a power-law scheme is employed. A modified k-? model with a two-layer technique for the near-wall region has been used to predict the turbulent viscosity. The effects of nanoparticle volume fraction in the base fluid on laminar and turbulent flow variables are presented and discussed. The velocity and temperature profiles, friction factor, pressure coefficient and Nusselt number at different Reynolds numbers in the entrance region for both the laminar and turbulent flow regimes are reported under different thermal boundary conditions. The results show that the effect of the presence of nanoparticles in the base fluid on hydraulic and thermal parameters for the turbulent flow is not very significant, while the rate of heat transfer for the laminar flow with nanoparticles is greater than that of the base liquid. Furthermore, the thermal boundary layer and consequently the Nusselt number more quickly reach their fully developed values by increasing the percentage of nanoparticles in the base fluid for the laminar flow regime, while no changes in the trend are observed for the turbulent flow.

Ziaei-Rad, Masoud

2013-07-01

307

Time-accurate, fully 3D numerical simulations and particle image velocity laboratory experiments are carried out for flow through a fully open bileaflet mechanical heart valve under steady (nonpulsatile) inflow conditions. Flows at two different Reynolds numbers, one in the laminar regime and the other turbulent (near-peak systole flow rate), are investigated. A direct numerical simulation is carried out for the laminar flow case while the turbulent flow is investigated with two different unsteady statistical turbulence modeling approaches, unsteady Reynolds-averaged Navier-Stokes (URANS) and detached-eddy simulation (DES) approach. For both the laminar and turbulent cases the computed mean velocity profiles are in good overall agreement with the measurements. For the turbulent simulations, however, the comparisons with the measurements demonstrate clearly the superiority of the DES approach and underscore its potential as a powerful modeling tool of cardiovascular flows at physiological conditions. The study reveals numerous previously unknown features of the flow. PMID:16248308

Ge, Liang; Leo, Hwa-Liang; Sotiropoulos, Fotis; Yoganathan, Ajit P

2005-10-01

308

NASA Astrophysics Data System (ADS)

The full Navier-Stokes equations for incompressible turbulent flow must be solved to accurately represent all flow phenomena which occur in a high Reynolds number incompressible flow. A two layer algebraic eddy viscosity turbulence model is used to represent the Reynolds stress in the primitive variable formulation. The development of the boundary-fitted coordinate systems makes the numerical solution of these equations feasible for arbitrarily shaped bodies. The nondimensional time averaged Navier-Stokes equations, including the turbulence mode, are represented by finite difference approximations in the transformed plane. The resulting coupled system of nonlinear algebraic equations is solved using a point successive over relaxation iteration. The test case considered was a NACA 64A010 airfoil section at an angle of attack of two degrees and a Reynolds number of 2,000,000.

Thompson, D. S.

1980-05-01

309

An accurate method for the simulation of three-dimensional incompressible heated pipe flow

A numerical scheme using Fourier expansions in the streamwise and azimuthal directions and Jacobi polynomials in the radial direction for the direct numerical simulation of three-dimensional incompressible pipe flow with heating is presented. The proposed basis and test functions for the thermal field in conjunction with those for the velocity field set forth by Leonard and Wary offer an accurate representation of flow variables in transitional flow. A simple test to a linear stability problem demonstrates that this method yields very accurate results with relatively few radial modes and is well suited for the simulation of nonisothermal pipe flow transition.

Su, Y.C.; Wang, C.S.; Chung, J.N.; Lee, S.T.

2000-05-01

310

HYBRID LAMINAR FLOW TECHNOLOGY (HYLTEC) Partner: EADS Airbus (D) (Coordinator), Apparatebau Gauting: Â· Reduced aircraft operating costs Â· Reduced aircraft noise Â· Reduced aircraft engine emmissions 3 E

Berlin,Technische UniversitÃ¤t

311

Boundary-Layer Transition Results from the F-16XL-2 Supersonic Laminar Flow Control Experiment

NASA Technical Reports Server (NTRS)

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.

Marshall, Laurie A.

1999-01-01

312

A unifying method for sizing throttling valves under laminar or transitional flow conditions

The mass flow passing through a given valve will decrease in Reynolds number ranges below approximately 10,000 due to the transition from fully developed turbulent to laminar flow. The objective of this study is to provide a uniform prediction method to establish, with reasonable accuracy, the ratio between the turbulent and transitional or laminar flow rate passing through a given valve, taking into account the valve's hydraulic diameter and the initial turbulent velocity head loss coefficient. Experimental data from prior research tends to support a proposed unified sizing method that is applicable for all single-stage valves regardless of size or type.

Baumann, H.D. (H.D. Baumann Assoc., Ltd., Portsmouth, NH (United States))

1993-03-01

313

Measurement of fluid velocity development in laminar pipe flow using laser Doppler velocimetry

NASA Astrophysics Data System (ADS)

In this paper we present a non-intrusive experimental approach for obtaining velocity gradient profiles in a transparent smooth pipe under laminar flow conditions (Re = 925) using a laser Doppler velocimeter (LDV). Measurements were taken within the entrance region of the pipe at l = 300 mm and l = 600 mm from the pipe inlet, in addition to measurements of the fully developed flow at l = 1800 mm. The obtained results show how the velocity profile from upstream of the pipe develops into a classical laminar profile downstream, which matches the theoretical profile well. Additionally, a brief summary of historical information about the development of flow measurement techniques, in particular LDV, is provided.

Molki, Arman; Khezzar, Lyes; Goharzadeh, Afshin

2013-09-01

314

Low-Disturbance Flow Characteristics of the NASA-Ames Laminar Flow Supersonic Wind Tunnel

NASA Technical Reports Server (NTRS)

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.

Wolf, Stephen W. D.; Laub, James A.; Davis, Sanford S. (Technical Monitor)

1994-01-01

315

High Order Parallel Numerical Schemes for Solving Incompressible Flows.

National Technical Information Service (NTIS)

The use of parallel computers for numerically solving flow fields has gained much importance in recent years. This paper introduces a new high order numerical scheme for computational fluid dynamics (CFD) specifically designed for parallel computational e...

A. Lin, E. J. Milner, M. Liou, R. A. Belch

1992-01-01

316

Finite Difference Solutions of Incompressible Flow Problems with Corner Singularities

Two problems that include corner singularities are considered. The first concerns the flow of a viscous fluid in a channel driven by a constant pressure gradient, when the velocity satisfies a two-dimensional Poisson equation. The second is Stokes flow in a two-dimensional region when the stream-function satisfies the biharmonic equation. For both problems the boundaries of the domains contain corners.

Huaxiong Huang; Brian R. Seymour

2000-01-01

317

Interpolation between DarcyWeisbach and Darcy for laminar and turbulent flows

the square of the velocity is proportional to the hydraulic gradient and if the flow is laminar, which is the usual case, the velocity is proportional to the hydraulic gradient. This last result is in agreement DarcyÂWeisbach equation, e.g. see [2Â4], which states that the flow velocity, V, is proportional

Walter, M.Todd

318

LAMINAR FLOW BASED MICROREACTOR FOR EFFICIENT REGENERATION OF NICOTINAMIDE COFACTORS FOR BIOCATALYIS

LAMINAR FLOW BASED MICROREACTOR FOR EFFICIENT REGENERATION OF NICOTINAMIDE COFACTORS were run in potentiostatic mode using a PGSTAT 30 potentiostat (Autolab). In order to control as a reference electrode. Fluid flow in all experiments is pressure driven and regulated using a syringe pump

Kenis, Paul J. A.

319

Application of stability theory to laminar flow control - Progress and requirements

Paper briefly summarizes the current status of linear stability theory as applied to laminar flow control for aerodynamics. Results indicate that the conventional 'N factor' method of correlating stability theory and transition has a broad application range, including low- and high-speeds, two- and three-dimensional mean flow and TS, Gortler and crossflow disturbance modes. Linear theory is particularly applicable to the

D. M. Bushnell; M. R. Malik

1987-01-01

320

A Parallel Processing Approach to Transition Prediction for Laminar Flow Control System Design

The performance of transport aircraft can be consider- ably improved if the process by which the wing boundary- layer becomes turbulent can be controlled and extensive areas of laminar flow maintained. In order to design lami- nar flow control systems, it is necessary to be able to pre- dict the movement of the transition location in response to changes in

Rupert W. Ford; D. I. A. Poll

1995-01-01

321

NASA Technical Reports Server (NTRS)

The Method of Integral Relations is extended to apply to the calculation of Unsteady Flow in a Laminar Boundary Layer. The effectiveness of the method is demonstrated in an application to uniform flow past a circular cylinder, resulting from an impulsive start. Both first and second approximations are worked out, the latter showing good agreement with results of previous calculations.

Holt, M.; Chan, W.-K.

1975-01-01

322

Heat transfer in laminar tube flow of beef cattle manure slurries

This report describes a concentric-tube heat exchanger and presents the preliminary results of the study of the heat transfer characteristics of the beef cattle manure slurries flowing in laminar region in the inner pipe of the concentric tube heat exchanger with hot water flowing concurrently in the annual space and serving as a heat source.

Chen, Y.R.

1986-01-01

323

Classification of the Flow Produced by an Oscillating Fence in a Laminar Boundary Layer

Flow visualization has revealed that an oscillating fence produces a range of vortical structures in a flat plate laminar boundary layer. The structure can be classified by the ratio phi0 of the fence oscillation frequency to the fundamental shedding frequency of the static fence. Particle image velocimetry was used to quantitatively investigate the flow structures of each classification regime. Fences

Michael Hind; William Lindberg; Jonathan Naughton

2009-01-01

324

Higher-Order Compact Schemes for Numerical Simulation of Incompressible Flows

NASA Technical Reports Server (NTRS)

A higher order accurate numerical procedure has been developed for solving incompressible Navier-Stokes equations for 2D or 3D fluid flow problems. It is based on low-storage Runge-Kutta schemes for temporal discretization and fourth and sixth order compact finite-difference schemes for spatial discretization. The particular difficulty of satisfying the divergence-free velocity field required in incompressible fluid flow is resolved by solving a Poisson equation for pressure. It is demonstrated that for consistent global accuracy, it is necessary to employ the same order of accuracy in the discretization of the Poisson equation. Special care is also required to achieve the formal temporal accuracy of the Runge-Kutta schemes. The accuracy of the present procedure is demonstrated by application to several pertinent benchmark problems.

Wilson, Robert V.; Demuren, Ayodeji O.; Carpenter, Mark

1998-01-01

325

Hybrid finite element\\/volume method for 3D incompressible flows with heat transfer

An implicit hybrid finite element (FE)\\/volume solver has been extended to incompressible flows coupled with the energy equation. The solver is based on the segregated pressure correction or projection method on staggered unstructured hybrid meshes. An intermediate velocity field is first obtained by solving the momentum equations with the matrix-free implicit cell-centred finite volume (FV) method. The pressure Poisson equation

Shahrouz Aliabadi; Christopher Bigler; Erdal Yilmaz; Sridhar Palle; Bela Soni

2011-01-01

326

Periodic homogenization of the inviscid G-equation for incompressible flows

G-equations are popular front propagation models in combustion literature and\\u000adescribe the front motion law of normal velocity equal to a constant plus the normal projection of fluid\\u000avelocity. G-equations are Hamilton-Jacobi equations with convex but non-coercive Hamiltonians. We\\u000aprove homogenization of the inviscid G-equation for space periodic incompressible flows. This extends\\u000aa two space dimensional result in \\

Jack Xin; Yifeng Yu

2010-01-01

327

Equation-free\\/Galerkin-free POD-assisted computation of incompressible flows

We present a Galerkin-free, proper orthogonal decomposition (POD)-assisted computational methodology for numerical simulations of the long-term dynamics of the incompressible Navier–Stokes equations. The approach is based on the “equation-free” framework: we use short, appropriate initialized bursts of full direct numerical simulations (DNS) of the Navier–Stokes equations to observe, estimate, and accelerate, through “projective integration”, the evolution of the flow dynamics.

Sirod Sirisup; George Em Karniadakis; Dongbin Xiu; Ioannis G. Kevrekidis

2005-01-01

328

An adaptive levelset method for computing solutions to incompressible two-phase flows

We present an adaptive level set method for computing 2d axisymmetric and fully 3d incompressible two-phase flow. Our methodology is specifically targeted at problems characterized by large density and viscosity jumps (e.g. air\\/water) and stiff, singular source terms, such as those due to surface tension. One such application is the modeling of ink-jet printers in which one wants to accurately

Mark Sussman; Emad Fatemi; Peter Smereka; Stan Osher

1997-01-01

329

An Adaptive Levelset Method for Computing Solutions to Incompressible Two-Phase Flows

We present an adaptive level set method for computing 2d axisymmetric and fully 3d incompressible two-phase flow. Our methodology is specifically targeted at problems characterized by large density and viscosity jumps (e.g. air\\/water) and stiff, singular source terms, such as those due to surface tension. One such application is the modeling of ink-jet printers in which one wants to accurately

Mark Sussman

1997-01-01

330

An implicit centered scheme for steady and unsteady incompressible one and two-phase flows

Based on artificial compressibility and dual time-stepping, an implicit scheme is developed for solving the steady and unsteady incompressible Navier-Stokes equations for one and two-phase flows. The scheme is centered but, due to its internal dissipation, it needs no staggered grid or upwinding to be stable. Its stability with respect to pseudo and physical times and convergence to a steady

Benoit Granier; Alain Lerat; Zi-Niu Wu

1997-01-01

331

Flight investigation of natural laminar flow on the Bellanca Skyrocket II

NASA Technical Reports Server (NTRS)

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.

Holmes, B. J.; Obara, C. J.; Gregorek, G. M.; Hoffman, M. J.; Freuhler, R. J.

1983-01-01

332

Parametric study on laminar flow for finite wings at supersonic speeds

NASA Technical Reports Server (NTRS)

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.

Garcia, Joseph Avila

1994-01-01

333

The feasibility of applying laminar boundary-layer control with body shaping to a high altitude, Lighter-Than-Air vehicle was investigated. Solar-radiation-induced surface heating was shown to have a destablizing effect on laminar flow and caused the laminar flow to break down on regions of the vehicle surface exposed to high levels of solar radiation. Aerodynamic drag estimates were made for the vehicle.

D. J. Warner; S. A. Ozgur; W. W. Haigh

1980-01-01

334

Some General Characteristics of Two-Dimensional Incompressible Magnetohydrodynamic Flows

The velocity field of a liquid conductor will be planar, with all field quantities being invariant in the normal (z) direction, for two different categories of conditions. (1) Planar components of B and J are parallel. This poses a strong restriction on the electrical and magnetic boundary conditions. The magnetic field has a nontrivial influence on the flow field only

C. H. T. Pan

1962-01-01

335

NASA Technical Reports Server (NTRS)

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.

Ostowari, Cyrus

1992-01-01

336

Start of fluidization of a bulk granular material in laminar flow

This report examines the usage and transformation of an equation of the form Re/sub cr/=Ar(1400+5.22/Ar) which is used in design calculations for determination of the velocity of the start of fluidization of a granular material bearing initial voidage e/sub o/=0.4. Variations of the Reynold's number corresponding to the Critical Fluidization velocity at various voidages of the granular bed and different values of the Archimedes number in laminar flow are presented. Results indicate that the equation cannot be recommended for use even for rough estimates of the bulk materials in laminar flow.

Rozhdestvenskii, O.I.; Bednyakov, G.E.; Zayats, E.I.; Kirillov, I.N.; Serebryakova, T.V.

1982-04-20

337

Computation of Steady Incompressible Flows in Unbounded Domains

In this study we revisit the problem of computing steady Navier-Stokes flows in two-dimensional unbounded domains. Precise quantitative characterization of such flows in the high-Reynolds number limit remains an open problem of theoretical fluid dynamics. Following a review of key mathematical properties of such solutions related to the slow decay of the velocity field at large distances from the obstacle, we develop and carefully validate a spectrally-accurate computational approach which ensures the correct behavior of the solution at infinity. In the proposed method the numerical solution is defined on the entire unbounded domain without the need to truncate this domain to a finite box with some artificial boundary conditions prescribed at its boundaries. Since our approach relies on the streamfunction-vorticity formulation, the main complication is the presence of a discontinuity in the streamfunction field at infinity which is related to the slow decay of this field. We demonstrate how this difficulty ca...

Gustafsson, Jonathan

2014-01-01

338

Fully consistent CFD methods for incompressible flow computations

NASA Astrophysics Data System (ADS)

Nowadays collocated grid based CFD methods are one of the most efficient tools for computations of the flows past wind turbines. To ensure the robustness of the methods they require special attention to the well-known problem of pressure-velocity coupling. Many commercial codes to ensure the pressure-velocity coupling on collocated grids use the so-called momentum interpolation method of Rhie and Chow [1]. As known, the method and some of its widely spread modifications result in solutions, which are dependent of time step at convergence. In this paper the magnitude of the dependence is shown to contribute about 0.5% into the total error in a typical turbulent flow computation. Nevertheless if coarse grids are used, the standard interpolation methods result in much higher non-consistent behavior. To overcome the problem, a recently developed interpolation method, which is independent of time step, is used. It is shown that in comparison to other time step independent method, the method may enhance the convergence rate of the SIMPLEC algorithm up to 25 %. The method is verified using turbulent flow computations around a NACA 64618 airfoil and the roll-up of a shear layer, which may appear in wind turbine wake.

Kolmogorov, D. K.; Shen, W. Z.; Sørensen, N. N.; Sørensen, J. N.

2014-06-01

339

Phase relationship in laminar channel flow controlled by traveling-wave-like blowing or suction Mech. 558, 309 2006 in a two- dimensional laminar Poiseuille flow is investigated. The investigation-normal velocity disturbances induced by a traveling-wave-like blowing or suction control T. Min et al., J. Fluid

Hoepffner, JÃ©rÃ´me

340

Large eddy simulation of incompressible turbulent channel flow

NASA Technical Reports Server (NTRS)

The three-dimensional, time-dependent primitive equations of motion were numerically integrated for the case of turbulent channel flow. A partially implicit numerical method was developed. An important feature of this scheme is that the equation of continuity is solved directly. The residual field motions were simulated through an eddy viscosity model, while the large-scale field was obtained directly from the solution of the governing equations. An important portion of the initial velocity field was obtained from the solution of the linearized Navier-Stokes equations. The pseudospectral method was used for numerical differentiation in the horizontal directions, and second-order finite-difference schemes were used in the direction normal to the walls. The large eddy simulation technique is capable of reproducing some of the important features of wall-bounded turbulent flows. The resolvable portions of the root-mean square wall pressure fluctuations, pressure velocity-gradient correlations, and velocity pressure-gradient correlations are documented.

Moin, P.; Reynolds, W. C.; Ferziger, J. H.

1978-01-01

341

Air Flow in a Separating Laminar Boundary Layer

NASA Technical Reports Server (NTRS)

The speed distribution in a laminar boundary layer on the surface of an elliptic cylinder, of major and minor axes 11.78 and 3.98 inches, respectively, has been determined by means of a hot-wire anemometer. The direction of the impinging air stream was parallel to the major axis. Special attention was given to the region of separation and to the exact location of the point of separation. An approximate method, developed by K. Pohlhausen for computing the speed distribution, the thickness of the layer, and the point of separation, is described in detail; and speed-distribution curves calculated by this method are presented for comparison with experiment.

Schubauer, G B

1936-01-01

342

Biomimetic structures for fluid drag reduction in laminar and turbulent flows

NASA Astrophysics Data System (ADS)

Biomimetics allows one to mimic nature to develop materials and devices of commercial interest for engineers. Drag reduction in fluid flow is one of the examples found in nature. In this study, nano, micro, and hierarchical structures found in lotus plant surfaces, as well as shark skin replica and a rib patterned surface to simulate shark skin structure were fabricated. Drag reduction efficiency studies on the surfaces were systematically carried out using water flow. An experimental flow channel was used to measure the pressure drop in laminar and turbulent flows, and the trends were explained in terms of the measured and predicted values by using fluid dynamics models. The slip length for various surfaces in laminar flow was also investigated based on the measured pressure drop. For comparison, the pressure drop for various surfaces was also measured using air flow.

Jung, Yong Chae; Bhushan, Bharat

2010-01-01

343

Dispersion of swimming algae in laminar and turbulent channel flows: theory and simulations

Algal swimming is often biased by environmental cues, e.g. gravitational and viscous torques drive cells towards downwelling fluid (gyrotaxis). In view of biotechnological applications, it is important to understand how such biased swimming affects cell dispersion in a flow. Here, we study the dispersion of gyrotactic swimming algae in laminar and turbulent channel flows. By direct numerical simulation (DNS) of cell motion within upwelling and downwelling channel flows, we evaluate time-dependent measures of dispersion for increasing values of the flow Peclet (Reynolds) numbers, Pe (Re). Furthermore, we derive an analytical `swimming Taylor-Aris dispersion' theory, using flow-dependent transport parameters given by existing microscopic models. In the laminar regime, DNS results and analytical predictions compare very well, providing the first confirmation that cells' response to flow is best described by the generalized-Taylor-dispersion microscopic model. We predict that cells drift along a channel faster th...

Croze, O A; Ahmed, M; Bees, M A; Brandt, L

2012-01-01

344

Stochastic finite difference lattice Boltzmann method for steady incompressible viscous flows

With the advent of state-of-the-art computers and their rapid availability, the time is ripe for the development of efficient uncertainty quantification (UQ) methods to reduce the complexity of numerical models used to simulate complicated systems with incomplete knowledge and data. The spectral stochastic finite element method (SSFEM) which is one of the widely used UQ methods, regards uncertainty as generating a new dimension and the solution as dependent on this dimension. A convergent expansion along the new dimension is then sought in terms of the polynomial chaos system, and the coefficients in this representation are determined through a Galerkin approach. This approach provides an accurate representation even when only a small number of terms are used in the spectral expansion; consequently, saving in computational resource can be realized compared to the Monte Carlo (MC) scheme. Recent development of a finite difference lattice Boltzmann method (FDLBM) that provides a convenient algorithm for setting the boundary condition allows the flow of Newtonian and non-Newtonian fluids, with and without external body forces to be simulated with ease. Also, the inherent compressibility effect in the conventional lattice Boltzmann method, which might produce significant errors in some incompressible flow simulations, is eliminated. As such, the FDLBM together with an efficient UQ method can be used to treat incompressible flows with built in uncertainty, such as blood flow in stenosed arteries. The objective of this paper is to develop a stochastic numerical solver for steady incompressible viscous flows by combining the FDLBM with a SSFEM. Validation against MC solutions of channel/Couette, driven cavity, and sudden expansion flows are carried out.

Fu, S.C., E-mail: mm.scfu@polyu.edu.h [Mechanical Engineering Department, Hong Kong Polytechnic University, Hung Hom (Hong Kong); So, R.M.C. [Building Services Engineering Department, Hong Kong Polytechnic University, Hung Hom (Hong Kong); Mechanical Engineering Department, Purdue University, West Lafayette, IN 47907 (United States); Leung, W.W.F. [Research Institute of Innovative Products and Technologies, Hong Kong Polytechnic University, Hung Hom (Hong Kong)

2010-08-20

345

NASA Astrophysics Data System (ADS)

A high-order accurate, finite-difference method for the numerical solution of incompressible flows is presented. This method is based on the artificial compressibility formulation of the incompressible Navier-Stokes equations. Fourth- or sixth-order accurate discretizations of the metric terms and the convective fluxes are obtained using compact, centred schemes. The viscous terms are also discretized using fourth-order accurate, centred finite differences. Implicit time marching is performed for both steady-state and time-accurate numerical solutions. High-order, spectral-type, low-pass, compact filters are used to regularize the numerical solution and remove spurious modes arising from unresolved scales, non-linearities, and inaccuracies in the application of boundary conditions. The accuracy and efficiency of the proposed method is demonstrated for test problems.

Ekaterinaris, John A.

2004-08-01

346

Challenges and Accomplishments of Viscous Incompressible Flow Computations in Aerospace and Beyond

NASA Technical Reports Server (NTRS)

Recent progress in incompressible Navier-Stokes solution methods will be presented. Discussions are focused on the methods designed for complex geometry applications in three dimensions, and thus are limited to primitive variable formulation. Both steady- and unsteady-solution algorithms and their salient features are discussed. A summary of our recent progress in flow solver development is given followed by numerical studies of a few example problems of our current interest. Solvers discussed here are based on structured-grid approach using finite-difference or finite-volume frame work. This short course will be delivered in three one-our lectures. The material in the course are collected from the work performed by the Incompressible Navier-Stokes group at NASA Ames Research Center over the past several years, and can be found in our publications widely disseminated in the US and abroad. This short course is sponsored by AGARD Consultant and Exchange Program under Support Project P-110.

Kwak, Dochan

1996-01-01

347

A Quantitative Comparison of Leading-edge Vortices in Incompressible and Supersonic Flows

NASA Technical Reports Server (NTRS)

When requiring quantitative data on delta-wing vortices for design purposes, low-speed results have often been extrapolated to configurations intended for supersonic operation. This practice stems from a lack of database owing to difficulties that plague measurement techniques in high-speed flows. In the present paper an attempt is made to examine this practice by comparing quantitative data on the nearwake properties of such vortices in incompressible and supersonic flows. The incompressible flow data are obtained in experiments conducted in a low-speed wind tunnel. Detailed flow-field properties, including vorticity and turbulence characteristics, obtained by hot-wire and pressure probe surveys are documented. These data are compared, wherever possible, with available data from a past work for a Mach 2.49 flow for the same wing geometry and angles-of-attack. The results indicate that quantitative similarities exist in the distributions of total pressure and swirl velocity. However, the streamwise velocity of the core exhibits different trends. The axial flow characteristics of the vortices in the two regimes are examined, and a candidate theory is discussed.

Wang, F. Y.; Milanovic, I. M.; Zaman, K. B. M. Q.

2002-01-01

348

A Quantitative Comparison of Leading-Edge Vortices in Incompressible and Supersonic Flows

NASA Technical Reports Server (NTRS)

When requiring quantitative data on delta-wing vortices for design purposes, low-speed results have often been extrapolated to configurations intended for supersonic operation. This practice stems from a lack of database owing to difficulties that plague measurement techniques in high-speed flows. In the present paper an attempt is made to examine this practice by comparing quantitative data on the nearwake properties of such vortices in incompressible and supersonic flows. The incompressible flow data are obtained in experiments conducted in a low-speed wind tunnel. Detailed flow-field properties, including vorticity and turbulence characteristics, obtained by hot-wire and pressure probe surveys are documented. These data are compared, wherever possible, with available data from a past work for a Mach 2.49 flow for the same wing geometry and angles-of-attack. The results indicate that quantitative similarities exist in the distributions of total pressure and swirl velocity. However, the streamwise velocity of the core exhibits different trends. The axial flow characteristics of the vortices in the two regimes are examined, and a candidate theory is discussed.

Wang, F. Y.; Milanovic, I. M.; Zaman, K. B. M. Q.

2002-01-01

349

Incompressible spatially-developing free-shear flows

NASA Technical Reports Server (NTRS)

The first goal of this research is to understand the dynamics of three dimensional vortical structures, especially the interaction of the ribs and two dimensional rollers. Because of vortex stretching effects, this requires accurate and well resolved simulations. Another goal is to distinguish temporally- and spatially-growing shear layers in terms of the dynamics and observed vortical structures. This is important since the former is much easier to compute, but the error incurred in using temporal results for certain applications is unknown. The third goal is to investigate the effects of asymmetry on passive scalar mixing and fast-chemistry product formation. In this report a brief summary of a new numerical method is presented, followed by results for mixing layers and wake flows.

Buell, J. C.

1990-01-01

350

Numerical study of heat transfer in a laminar mist flow over a isothermal flat plate

A model for predicting heat and mass transfer in a laminar two-phase gas–vapor–drop mist flow over a flat isothermal flat is developed. Using this model, a numerical study is performed to examine the influence of thermal and flow parameters, i.e., Reynolds number, flow velocity, temperature ratio, concentration of the liquid phase, and drop size, on the profiles of velocity, temperature,

V. I. Terekhov; M. A. Pakhomov

2002-01-01

351

Two-dimensional MRT LB model for compressible and incompressible flows

NASA Astrophysics Data System (ADS)

In the paper we extend the Multiple-Relaxation-Time (MRT) Lattice Boltzmann (LB) model proposed in [ Europhys. Lett., 2010, 90: 54003] so that it is suitable also for incompressible flows. To decrease the artificial oscillations, the convection term is discretized by the flux limiter scheme with splitting technique. A new model is validated by some well-known benchmark tests, including Riemann problem and Couette flow, and satisfying agreements are obtained between the simulation results and analytical ones. In order to show the merit of LB model over traditional methods, the non-equilibrium characteristics of system are solved. The simulation results are consistent with the physical analysis.

Chen, Feng; Xu, Ai-Guo; Zhang, Guang-Cai; Wang, Yong-Long

2014-04-01

352

Adaptive Mesh Generation for Solution of Incompressible Fluid Flows using High Order Gradients

NASA Astrophysics Data System (ADS)

A new method of adaptive mesh generation for the computation of fluid flows is investigated. The method utilizes gradients of the flow solution to adapt the size and stretching of elements or volumes in the computational mesh as is commonly done in the conventional Hessian approach. However, in the new method, higher-order gradients are used in place of the Hessian. The method is applied to the finite element solution of the incompressible Navier-Stokes equations on model problems. Results indicate that a significant efficiency benefit is realized.

Shortridge, Randall

353

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

2013-01-01

354

Notes on Newton-Krylov based Incompressible Flow Projection Solver

The purpose of the present document is to formulate Jacobian-free Newton-Krylov algorithm for approximate projection method used in Hydra-TH code. Hydra-TH is developed by Los Alamos National Laboratory (LANL) under the auspices of the Consortium for Advanced Simulation of Light-Water Reactors (CASL) for thermal-hydraulics applications ranging from grid-to-rod fretting (GTRF) to multiphase flow subcooled boiling. Currently, Hydra-TH is based on the semi-implicit projection method, which provides an excellent platform for simulation of transient single-phase thermalhydraulics problems. This algorithm however is not efficient when applied for very slow or steady-state problems, as well as for highly nonlinear multiphase problems relevant to nuclear reactor thermalhydraulics with boiling and condensation. These applications require fully-implicit tightly-coupling algorithms. The major technical contribution of the present report is the formulation of fully-implicit projection algorithm which will fulfill this purpose. This includes the definition of non-linear residuals used for GMRES-based linear iterations, as well as physics-based preconditioning techniques.

Robert Nourgaliev; Mark Christon; J. Bakosi

2012-09-01

355

NASA Astrophysics Data System (ADS)

The viscous incompressible medium (water, air) flow past a circular cylinder is considered with regard for the temperature T dependent viscosity v. The influence of different boundary conditions for temperature on flow structure, the drag coefficient and its components due to the pressure and viscosity is investigated in the problem of the flow past a cylinder at rest for the (diameter-based) Reynolds number ReD = 40. A relation between the viscosity gradient along a normal to the body surface and the integral vorticity flux from the body surface into the boundary layer is discussed. Unlike the constant viscosity case the vorticity flux may be different from zero, which must lead because of the integral conservation law for the vorticity to an alteration of the far-field boundary conditions for the velocity. In the same connection, the problem is analysed on the heat spot entry into the computational region under consideration for the flow past a circular cylinder. The examples of the symmetrization of separated flow past a cylinder performing rotation oscillations in a uniform free stream (the Taneda problem) are considered. A comparison with flow computations for low Mach numbers M « 1 for the flow of a medium past a cylinder at rest is carried out. At the computation of the equation for heat transfer under the assumption of incompressibility of such media as air, it is proposed to retain the pressure derivative, which is typical of gases. In this case, a better agreement with the computations of compressible flows (for M « 1) is achieved, for example, at the determination of the sizes of a symmetric zone of flow separation past a circular cylinder. An unsteady flow in the neighborhood of the point of joining the zero streamline bounding a closed region of separated flow (the cavity) in a wake of the cylinder at rest is obtained by a numerical simulation at the Reynolds number equal to 40.

Zakharenkov, M. N.

2007-12-01

356

The silent base flow and the sound sources in a laminar jet.

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. PMID:22423693

Sinayoko, Samuel; Agarwal, Anurag

2012-03-01

357

Lift due to thickness for low aspect ratio wings in incompressible flow

NASA Technical Reports Server (NTRS)

The problem under consideration is a numerical study of the effects of thickness on lift for low aspect ratio wings in steady incompressible inviscid flow at moderate angles of attack. At these angles of attack the flow separates along the leading edge giving rise to a lift substantially higher than that computed by classical attached flow potential theory. The problem is treated as a perturbation expansion in a small thickness parameter. The lifting elements of the flow are modeled using a nonlinear vortex lattice method which replaces the leading and trailing edge vortex sheets by segmented straight vortex filaments. The thickness elements of the flow are modeled with a mean plane source distribution and a modification to the wing boundary conditions. Results are obtained for wings with biconvex and NACA 0012 sections which compare well with available experimental data. The important observation that the effect of thickness is to decrease the lift is made.

Dodbele, S. S.; Plotkin, A.

1985-01-01

358

Loss of lift due to thickness for low-aspect-ratio wings in incompressible flow

NASA Technical Reports Server (NTRS)

The problem under consideration is a numerical study of the effects of thickness on lift for low-aspect-ratio wings in steady incompressible inviscid flow at moderate angles of attack. At these angles of attack the flow separates along the leading edge giving rise to a lift substantially higher than that computed by classical attached-flow potential theory. The problem is treated as a perturbation expansion in a small thickness parameter. The lifting elements of the flow are modeled using a nonlinear vortex-lattice method which replaces the leading and trailing-edge vortex sheets by segmented straight vortex filaments. The thickness elements of the flow are modeled with a mean-plane source distribution and a modification to the wing boundary conditions. Results are obtained for wings with biconvex and NACA 0012 sections which compare well with available experimental data. The important observation that the effect of thickness is to decrease the lift is made.

Dodbele, S. S.; Plotkin, A.

1987-01-01

359

NASA Astrophysics Data System (ADS)

A new flow configuration has been proposed in which a bilateral mixing-layer exists in the junction between co-flowing laminar and turbulent plane Couette flows. Contrary to a classical plane mixing-layer, the present mixing-layer did neither grow in time nor in streamwise direction. However, the mixing zone varied with the distance from the stationary wall. A direct numerical simulation showed that very-large-scale flow structures were found in the turbulent part of the flow with Reynolds number 1300 based on half the velocity U1 of the fastest-moving wall and half of the distance 2h between the walls. The laminar-turbulent interface exhibited a large-scale meandering motion with frequency 0.014U1/h and wavelength about 25h. Large-scale Taylor-Görtler-like roll cells were observed in the nominally laminar flow region with Reynolds number 260. This tailor-made flow is particularly well suited for explorations of momentum transfer and intermittency in the vicinity of the laminar-turbulent interface.

Narasimhamurthy, Vagesh D.; Andersson, Helge I.; Pettersen, Bjørnar

2014-03-01

360

AIR-BREATHING LAMINAR FLOW BASED MICROFLUIDIC FUEL CELL Ranga S. Jayashree1

catalyst ink for the anode side was prepared by sonicating the required amounts of Pd black nanoparticles of the laminar flow-based microfluidic fuel cell. A 5-mm thick graphite plate (anode, fuel cell grade graphite. The catalyst ink was added drop wise onto the exposed area of the graphite plate, between the second inlet

Kenis, Paul J. A.

361

Supersonic Laminar Flow Control on Swept Wings Using Distributed Roughness Experiments

A new technology development that can lead to drag reduction on supersonic aircraft by means of laminar flow control is addressed. The principal control problem concerns the crossflow instability, which up to now was thought to be controlled only by boundary-layer suction. It has been demonstrated in a series of low-speed experiments at Arizona State University, that distributed roughness near

William Saric; Helen Reed; Chang-Kwon Kang; Robert Gladden; Pierre Gabet; Dan Clevenger

2001-01-01

362

Laminar flow control (LFC) is one of the key enabling technologies for quiet and efficient supersonic aircraft. Recent work at Arizona State University (ASU) has led to a novel concept for passive LFC, which employs distributed leading edge roughness to limit the growth of naturally dominant crossflow instabilities in a swept-wing boundary layer. Predicated on nonlinear modification of the mean

Meelan Choudhari; Chau-Lyan Chang; Li Jiang

2005-01-01

363

Experiments on Laminar Flow Control at Mach 2.4 using Distributed Roughness

A new technique for the passive laminar flow control, in the supersonic regime, over highly swept wings beyond the characteristic Mach angle is here studied. A series of previous low-speed experiments at Arizona State University has demonstrated the possibility to control stationary crossflow waves by distributed roughness near the attachment line, provided the roughness spacing is below a critical value.

Simone Zuccher; Lloyd McNeil; Elizabeth Bennett; William Saric; Helen Reed

2002-01-01

364

Current status of the use of wall compliance for laminar-flow control

This paper presents a brief review of some recent work on the the use of wall compliance for laminar-flow control. Four main topics are covered. Firstly comparisons between theory and experiment for instability and transition in flat-plate boundary layers over compliant walls are considered. Good agreement is found for the Gaster experiments in water. But the theory does not corroborate

Peter W Carpenter

1998-01-01

365

Unsteady laminar flow in a circular tube: A test of the HERCOL (Hermitian collocation) computer code

HERCOL, a computer code for the integration of second-order differential equations in one space dimension by Hermitian collocation was used to calculate the unsteady velocity profiles for laminar flow in a circular tube. The code was tested for stability and accuracy for the problem for which an analytical solution exists prior to application to a like problem in which the

James F. Welch; James A. Hurley; Michael P. Glover; Ryan D. Nassimbene; Marilyn R. Yetzbacher

1991-01-01

366

Thermophoresis in laminar flow over cold inclined plates with variable properties

This paper deals with the analysis of two dimensional laminar thermophoretic flow over inclined plates. Cold wall conditions are assumed and the governing equations are solved by a finite difference marching technique. Results for the hydrodynamic, thermal and particle concentration boundary layers are obtained over a wide range of parameters. Special emphasis is placed on the external aerosol particle deposition

S. Jayaraj

1995-01-01

367

A macroscopic agglomeration kernel model for gibbsite precipitation in turbulent and laminar flows

A macroscopic agglomeration kernel model has been developed that is capable of describing gibbsite agglomeration over a broad range of process conditions, including both the laminar and turbulent flow regimes. The agglomeration kernel model was derived using chemical reaction engineering principles and data from an extensive experimental program covering a wide range of temperatures, supersaturations, seed sizes, shear rates and

I. Livk; D. Ilievski

2007-01-01

368

Performance optimisation of laminar fully developed flow through square ducts with rounded corners

A study on combined first and second law based optimisation of thermal-hydraulic performance of laminar fully developed flow through square ducts with rounded corners has been presented in this paper. The objective functions have been considered according to suggestions of Webb and Bergles [7]. Four specific geometric constraints have been imposed on the shape of the ducts and these ducts

Subhadeep Chakraborty; Subhashis Ray

2011-01-01

369

Second Law Analysis of Laminar Flow In A Channel Filled With Saturated Porous Media

The entropy generation rate in a laminar flow through a channel filled with saturated porous media is investigated. The upper surface of the channel is adiabatic and the lower wall is assumed to have a constant heat flux. The Brinkman model is employed. Velocity and temperature profiles are obtained for large Darcy number (Da) and used to obtain the entropy

O. D. Makinde; E. Osalusi

2005-01-01

370

EXPERIMENTS WITH HEAVY GAS JETS IN LAMINAR AND TURBULENT CROSS-FLOWS

A wind tunnel study was performed to determine the dispersion characteristics of gas jets with densities heavier than that of air. he experiments were done in a laminar cross-flow and then repeated in a turbulent boundary layer. ll major boundary-layer characteristics were measur...

371

Design of a Slotted, Natural-Laminar-Flow Airfoil for Business-Jet Applications

NASA Technical Reports Server (NTRS)

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.

Somers, Dan M.

2012-01-01

372

Theory and Experiments of Transport at Channel Microband Electrodes under Laminar Flows.

the design of devices and selecting the best hydrodynamic conditions. For this purpose, we undertook a series measurements. Part I of this series (Anal. Chem. 2007, 79, 8502- 8510) evaluated the common case of a single microband electrode embedded within a microchannel under laminar flow. The present work (Part 2

Paris-Sud XI, UniversitÃ© de

373

In this article a semianalytical approach is employed to obtain dimensionless heat transfer correlations for forced convection over three geometries—sphere, cone, and cylinder with unity aspect ratio in laminar axial air flow. The comparison of the present results for a sphere with the previous work shows very good agreement. For example, the average difference between the results of the present

Yaser Hadad; Khosrow Jafarpur

2012-01-01

374

NASA Technical Reports Server (NTRS)

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.

Meyer, J. S.; Kosovich, J.

1973-01-01

375

NASA Astrophysics Data System (ADS)

Computation of flow generated noise is increasingly possible due to the availability of increasingly detailed numerical solutions to the flow. The most general way to compute the noise radiation by a turbulent flow is to numerically solve the Navier-Stokes equation. The computation needs to be performed over a large spatial domain for long time intervals, simultaneously, with the ability to resolve small scales. This requirement overwhelms present day computing power. However, depending on the speed and nature of the flow, certain simplifications can be used to make the computations feasible. For low Mach number flows in which there is no significant back reaction from the acoustics on the flow, the noise calculations can be reduced to a two step procedure: (1) Computation of the underlying flow. (2) Acoustic computations. Since Mach number of the underlying flow is small, incompressibility is still a valid assumption for the flow simulation. The second step can be accomplished by Acoustic Analogy or Kirchhoff's method with the sources calculated from the solution available from the first step. The present work uses the two step procedure just outlined, with the numerical solution to the flow problem obtained by solving the incompressible, time dependent Reynolds Averaged Navier Stokes equation. Experiments were conducted at the Glenn L. Martin Wind Tunnel to ascertain the accuracy of the computational simulation. The acoustic solution is obtained by solving the two dimensional Lighthill's wave equation which is transformed to the Helmholtz equation for the generalized body fitted coordinate system and reduced to a finite number of algebraic equations using the Finite Analytic technique. The two step procedure is demonstrated for the case of a half cylinder in and out of ground effect by enforcing the Dirichlet boundary condition derived from the computational simulations. The computed far field noise radiation shows dipole patterns for both the lift and drag type for the free stream case with a considerable change in the directivity pattern when the ground is present.

Kumarasamy, Sanjay

376

An efficient numerical model for incompressible two-phase flow in fractured media Hussein Hoteit a,1

-phase flow Water injection Fractured media Heterogeneous media Capillary pressure Discrete fractured modelAn efficient numerical model for incompressible two-phase flow in fractured media Hussein Hoteit a methods have been used in the literature to simulate single and multiphase flow in fractured media

Firoozabadi, Abbas

377

NASA Technical Reports Server (NTRS)

In order to extend the useful range of Reynolds numbers of airfoils designed to take advantage of the extensive laminar boundary layers possible in an air stream of low turbulence, tests were made of the NACA 2412-34 and 1412-34 sections in the NACA low-turbulence tunnel. Although the possible extent of the laminar boundary layer on these airfoils is not so great as for specially designed laminar-flow airfoils, it is greater than that for conventional airfoils, and is sufficiently extensive so that at Reynolds numbers above 11,000,000 the laminar region is expected to be limited by the permissible 'Reynolds number run' and not by laminar separation as is the case with conventional airfoils. Drag measurements by the wake-survey method and pressure-distribution measurements were made at several lift coefficients through a range of Reynolds numbers up to 11,400,000. The drag scale-effect curve for the NACA 1412-34 is extrapolated to a Reynolds number of 30,000,000 on the basis of theoretical calculations of the skin friction. Comparable skin-friction calculations were made for the NACA 23012. The results indicate that, for certain applications at moderate values of the Reynolds number, the NACA 1412-34 and 2412-34 airfoils offer some advantages over such conventional airfoils as the NACA 23012. The possibility of maintaining a more extensive laminar boundary layer on these airfoils should result in a small drag reduction, and the absence of pressure peaks allows higher speeds to be reached before the compressibility burble is encountered. At lower Reynold numbers, below about 10,000,000, these airfoils have higher drags than airfoils designed to operate with very extensive laminar boundary layers.

Jacobs, E.N.; Abbott, Ira H.; von Doenhoff, A.E.

1939-01-01

378

An implicit finite difference code cast in general curvilinear coordinates is further developed for three-dimensional incompressible turbulent flows. The code is based on the method of pseudocompressibility and utilizes the Beam and Warming implicit approximate factorization algorithm to achieve computational efficiency. A multiple-zone method is further extended to include composite-grids to overcome the excessive computer memory required for solving turbulent

J. L. C. Chang; R. Rosen; S. C. Dao; D. Kwak

1985-01-01

379

Analysis and evaluation of an integrated laminar flow control propulsion system

NASA Technical Reports Server (NTRS)

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.

Keith, Theo G., Jr.; Dewitt, Kenneth J.

1993-01-01

380

Analysis and evaluation of an integrated laminar flow control propulsion system

NASA Astrophysics Data System (ADS)

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.

Keith, Theo G., Jr.; Dewitt, Kenneth J.

1993-02-01

381

Cauchy's almost forgotten Lagrangian formulation of the Euler equation for 3D incompressible flow

NASA Astrophysics Data System (ADS)

Two prized papers, one by Augustin Cauchy in 1815, presented to the French Academy and the other by Hermann Hankel in 1861, presented to Göttingen University, contain major discoveries on vorticity dynamics whose impact is now quickly increasing. Cauchy found a Lagrangian formulation of 3D ideal incompressible flow in terms of three invariants that generalize to three dimensions the now well-known law of conservation of vorticity along fluid particle trajectories for two-dimensional flow. This has very recently been used to prove analyticity in time of fluid particle trajectories for 3D incompressible Euler flow and can be extended to compressible flow, in particular to cosmological dark matter. Hankel showed that Cauchy's formulation gives a very simple Lagrangian derivation of the Helmholtz vorticity-flux invariants and, in the middle of the proof, derived an intermediate result which is the conservation of the circulation of the velocity around a closed contour moving with the fluid. This circulation theorem was to be rediscovered independently by William Thomson (Kelvin) in 1869. Cauchy's invariants were only occasionally cited in the 19th century - besides Hankel, foremost by George Stokes and Maurice Lévy - and even less so in the 20th until they were rediscovered via Emmy Noether's theorem in the late 1960, but reattributed to Cauchy only at the end of the 20th century by Russian scientists.

Frisch, Uriel; Villone, Barbara

2014-09-01

382

Correlation of Water Frost Porosity in Laminar Flow over Flat Surfaces

NASA Technical Reports Server (NTRS)

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.

Kandula, Max

2011-01-01

383

Response of hot element flush wall gauges in oscillating laminar flow

NASA Technical Reports Server (NTRS)

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.

Giddings, T. A.; Cook, W. J.

1986-01-01

384

Implicit/Multigrid Algorithms for Incompressible Turbulent Flows on Unstructured Grids

NASA Technical Reports Server (NTRS)

An implicit code for computing inviscid and viscous incompressible flows on unstructured grids is described. The foundation of the code is a backward Euler time discretization for which the linear system is approximately solved at each time step with either a point implicit method or a preconditioned Generalized Minimal Residual (GMRES) technique. For the GMRES calculations, several techniques are investigated for forming the matrix-vector product. Convergence acceleration is achieved through a multigrid scheme that uses non-nested coarse grids that are generated using a technique described in the present paper. Convergence characteristics are investigated and results are compared with an exact solution for the inviscid flow over a four-element airfoil. Viscous results, which are compared with experimental data, include the turbulent flow over a NACA 4412 airfoil, a three-element airfoil for which Mach number effects are investigated, and three-dimensional flow over a wing with a partial-span flap.

Anderson, W. Kyle; Rausch, Russ D.; Bonhaus, Daryl L.

1997-01-01

385

Sedimentary microbial oxygen demand for laminar flow over a sediment bed of finite length.

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 length of the sediment bed both SOD rate and DO penetration depth into the sediment tend towards zero if the flow is laminar, but tend towards a finite value if the flow is turbulent. That value can be determined as a function of both flow velocity and microbial density. The effect of the developing laminar boundary layer on SOD is strongest at the very lowest flow velocity and/or highest microbial density inside the sediment. Under quiescent conditions, the effective SOD exerted by a reactive sediment bed of a lake or wetland approaches zero, i.e. no or very little oxygen demand is exerted on the overlying water column, except at the leading edge. PMID:16054191

Higashino, Makoto; Stefan, Heinz G

2005-09-01

386

The laminar steady flow downstream of fine-mesh screens is studied. Instead of woven-wire screens, high-uniformity screens are fabricated by photoetching holes into 50.8 µm thick Inconel sheets. The resulting screens have minimum wire widths of 50.8 µm and inter-wire separations of 254 µm and 318 µm for the two screens examined. A flow facility has been constructed for experiments with

T. J. O'Hern; J. R. Torczynski

1993-01-01

387

Heat transfer to viscoplastic materials flowing laminarly in the entrance region of tubes

Heat transfer in the entrance-region flow of viscoplastic materials inside tubes is analyzed. The flow is laminar and the material viscosity is modeled by the Herschel–Bulkley equation. The conservation equations are solved numerically via a finite volume method. Two different thermal boundary conditions are considered, namely, uniform wall temperature and uniform wall heat flux. The effect of temperature-dependent properties is

Márcia Soares; Mônica F. Naccache; Paulo R. Souza Mendes

1999-01-01

388

Heat transfer to non-Newtonian fluids in laminar flow through rectangular ducts

Heat transfer to non-newtonian fluids flowing laminarly through rectangular ducts is examined. The conservation equations of mass, momentum, and energy are solved numerically with the aid of a finite volume technique. The viscoelastic behavior of the fluid is represented by the Criminale-Ericksen-Filbey (CEF) constitutive equation. Secondary flows occur due to the elastic behavior of the fluid, and, consequently, heat transfer

Mônica F. Naccache; Paulo R. Souza Mendes

1996-01-01

389

Energy-Conserving Simulation of Incompressible Electro-Osmotic and Pressure-Driven Flow

. A numerical model for electro-osmotic flow is described. The advecting velocity field is computed by solving the incompressible\\u000a Navier–Stokes equation. The method uses a semi-implicit multigrid algorithm to compute the divergence-free velocity at each\\u000a grid point. The finite differences are second-order accurate and centered in space; however, the traditional second-order\\u000a compact finite differencing of the Poisson equation for the pressure field

Jahrul Alam; John C. Bowman

2002-01-01

390

Energy stable, collocated high order schemes for incompressible flows on distorted grids

NASA Astrophysics Data System (ADS)

An energy preserving finite difference scheme for incompressible, constant density flows is presented. It is building on the idea of the skew-symmetric rewriting of the non-linear transport term. In contrast to former schemes collocated grids can be used, while exactly preserving the energy conservation and still avoiding the odd-even decoupling of the Laplacian. High order derivatives can be utilized. A formulation for curvilinear grids is discussed and strict skew-symmetry and perfect conservation is found for arbitrary transformations in two dimensions and quite general, but not fully general transformations in three dimensions.

Reiss, Julius

2012-09-01

391

Wave Number Selection for Incompressible Parallel Jet Flows Periodic in Space

NASA Technical Reports Server (NTRS)

The temporal instability of a spatially periodic parallel flow of an incompressible inviscid fluid for various jet velocity profiles is studied numerically using Floquet Analysis. The transition matrix at the end of a period is evaluated by direct numerical integration. For verification, a method based on approximating a continuous function by a series of step functions was used. Unstable solutions were found only over a limited range of wave numbers and have a band type structure. The results obtained are analogous to the behavior observed in systems exhibiting complexity at the edge of order and chaos.

Miles, Jeffrey Hilton

1997-01-01

392

A coarse-grid projection method for accelerating incompressible flow computations

NASA Astrophysics Data System (ADS)

We present a coarse-grid projection (CGP) algorithm for accelerating incompressible flow computations, which is applicable to methods involving Poisson equations as incompressibility constraints. CGP methodology is a modular approach that facilitates data transfer with simple interpolations and uses black-box solvers for the Poisson and advection-diffusion equations in the flow solver. Here, we investigate a particular CGP method for the vorticity-stream function formulation that uses the full weighting operation for mapping from fine to coarse grids, the third-order Runge-Kutta method for time stepping, and finite differences for the spatial discretization. After solving the Poisson equation on a coarsened grid, bilinear interpolation is used to obtain the fine data for consequent time stepping on the full grid. We compute several benchmark flows: the Taylor-Green vortex, a vortex pair merging, a double shear layer, decaying turbulence and the Taylor-Green vortex on a distorted grid. In all cases we use either FFT-based or V-cycle multigrid linear-cost Poisson solvers. Reducing the number of degrees of freedom of the Poisson solver by powers of two accelerates these computations while, for the first level of coarsening, retaining the same level of accuracy in the fine resolution vorticity field.

San, Omer; Staples, Anne

2011-11-01

393

Application of stability theory to laminar flow control - Progress and requirements

NASA Technical Reports Server (NTRS)

Paper briefly summarizes the current status of linear stability theory as applied to laminar flow control for aerodynamics. Results indicate that the conventional 'N factor' method of correlating stability theory and transition has a broad application range, including low- and high-speeds, two- and three-dimensional mean flow and TS, Gortler and crossflow disturbance modes. Linear theory is particularly applicable to the laminar flow control problem as, for system efficiency, control must be exercised and disturbances maintained in the linear regime. Current areas of concern for LFC, which require further stability theory research, include TS-crossflow interaction, combined disturbance fields (roughness, waviness, noise) and suction-induced disturbances. Some results on wave-interactions are presented.

Bushnell, D. M.; Malik, M. R.

1987-01-01

394

Laminar-Turbulent Transition: The Change of the Flow State Temperature with the Reynolds Number

NASA Astrophysics Data System (ADS)

Using the previously developed model to describe laminar/turbulent states of a viscous fluid flow, which treats the flow as a collection of coherent structures of various size (Chekmarev, Chaos, 2013, 013144), the statistical temperature of the flow state is determined as a function of the Reynolds number. It is shown that at small Reynolds numbers, associated with laminar states, the temperature is positive, while at large Reynolds numbers, associated with turbulent states, it is negative. At intermediate Reynolds numbers, the temperature changes from positive to negative as the size of the coherent structures increases, similar to what was predicted by Onsager for a system of parallel point-vortices in an inviscid fluid. It is also shown that in the range of intermediate Reynolds numbers the temperature exhibits a power-law divergence characteristic of second-order phase transitions.

Chekmarev, Sergei F.

2014-09-01

395

High order essentially non-oscillatory (ENO) schemes, originally designed for compressible flow and in general for hyperbolic conservation laws, are applied to incompressible Euler and Navier-Stokes equations with periodic boundary conditions. The projection to divergence-free velocity fields is achieved by fourth-order central differences through fast Fourier transforms (FFT) and a mild high-order filtering. The objective of this work is to assess the resolution of ENO schemes for large scale features of the flow when a coarse grid is used and small scale features of the flow, such as shears and roll-ups, are not fully resolved. It is found that high-order ENO schemes remain stable under such situations and quantities related to large scale features, such as the total circulation around the roll-up region, are adequately resolved. 13 refs., 6 figs., 3 tabs.

Weinan, E. (Institute of Advanced Study, Princeton, NJ (United States)); Shu, Chi-Wang (Brown Univ., Providence, RI (United States))

1994-01-01

396

Nonhomogeneous Incompressible Herschel-Bulkley Fluid Flows Between Two Eccentric Cylinders

NASA Astrophysics Data System (ADS)

The equations for the nonhomogeneous incompressible Herschel-Bulkley fluid are considered and existence of a weak solution is proved for a boundary-value problem which describes three-dimensional flows between two eccentric cylinders when in each two-dimensional cross-section annulus the flow characteristics are the same. The rheology of such a fluid is defined by a yield stress ?* and a discontinuous stress-strain law. A fluid volume stiffens if its local stresses do not exceed ?*, and a fluid behaves like a nonlinear fluid otherwise. The flow equations are formulated in the stress-velocity-density-pressure setting. Our approach is different from that of Duvaut-Lions developed for the classical Bingham viscoplastic fluids. We do not apply the variational inequality but make use of an approximation of the generalized Bingham fluid by a non-Newtonian fluid with a continuous constitutive law.

Amirat, Youcef; Shelukhin, Vladimir V.

2013-12-01

397

Numerical studies of incompressible flow around delta and double-delta wings

NASA Technical Reports Server (NTRS)

The subject has been jointly investigated at NASA Langley Research Center and the Aerodynamisches Institut of the RWTH Aachen over a substantial period. The aim of this investigation has been to develop numerical integration procedures for the Navier-Stokes equations - particularly for incompressible three-dimensional viscous flows about simple and double delta wings - and to study the low speed flow behavior, with its complex vortex structures on the leeward side of the wing. The low speed flight regime poses unusual problems because high incidence flight conditions may, for example, encounter symmetric and asymmetric vortex breakdown. Because of the many difficulties to be expected in solving the problem, it was divided into two - analysis of the flow without vortex breakdown and analysis of the breakdown of isolated vortices. The major results obtained so far on the two topics are briefly described.

Krause, E.; Liu, C. H.

1989-01-01

398

NASA Technical Reports Server (NTRS)

Using the decomposition for the infinite-space, the issue of the nonuniqueness of the Helmholtz decomposition for the problem of the three-dimensional unsteady incompressible flow around a body is considered. A representation for the velocity that is valid for both the fluid region and the region inside the boundary surface is employed, and the motion of the boundary is described as the limiting case of a sequence of impulsive accelerations. At each instant of velocity discontinuity, vorticity is shown to be generated by the boundary condition on the normal component of the velocity, for both inviscid and viscous flows. In viscous flows, the vorticity is shown to diffuse into the surroundings, and the no-slip conditions are automatically satisfied. A trailing edge condition must be satisfied for the solution to the Euler equations to be the limit of the solution of the Navier-Stokes equations.

Morino, L.

1986-01-01

399

NASA Technical Reports Server (NTRS)

High order essentially non-oscillatory (ENO) schemes, originally designed for compressible flow and in general for hyperbolic conservation laws, are applied to incompressible Euler and Navier-Stokes equations with periodic boundary conditions. The projection to divergence-free velocity fields is achieved by fourth-order central differences through fast Fourier transforms (FFT) and a mild high-order filtering. The objective of this work is to assess the resolution of ENO schemes for large scale features of the flow when a coarse grid is used and small scale features of the flow, such as shears and roll-ups, are not fully resolved. It is found that high-order ENO schemes remain stable under such situations and quantities related to large scale features, such as the total circulation around the roll-up region, are adequately resolved.

Weinan, E.; Shu, Chi-Wang

1994-01-01

400

NASA Technical Reports Server (NTRS)

High order essentially non-oscillatory (ENO) schemes, originally designed for compressible flow and in general for hyperbolic conservation laws, are applied to incompressible Euler and Navier-Stokes equations with periodic boundary conditions. The projection to divergence-free velocity fields is achieved by fourth order central differences through Fast Fourier Transforms (FFT) and a mild high-order filtering. The objective of this work is to assess the resolution of ENO schemes for large scale features of the flow when a coarse grid is used and small scale features of the flow, such as shears and roll-ups, are not fully resolved. It is found that high-order ENO schemes remain stable under such situations and quantities related to large-scale features, such as the total circulation around the roll-up region, are adequately resolved.

Weinan, E.; Shu, Chi-Wang

1992-01-01

401

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

R. F. Sturgeon; J. A. Bennett; F. R. Etchberger; R. S. Ferrill; L. E. Meade

1976-01-01

402

Viscid-inviscid interaction associated with incompressible flow past wedges at high Reynolds number

NASA Technical Reports Server (NTRS)

An analytical method is suggested for the study of the viscid inviscid interaction associated with incompressible flow past wedges with arbitrary angles. It is shown that the determination of the nearly constant pressure (base pressure) prevailing within the near wake is really the heart of the problem, and the pressure can only be established from these interactive considerations. The basic free streamline flow field is established through two discrete parameters which adequately describe the inviscid flow around the body and the wake. The viscous flow processes such as the boundary layer buildup, turbulent jet mixing, and recompression are individually analyzed and attached to the inviscid flow in the sense of the boundary layer concept. The interaction between the viscous and inviscid streams is properly displayed by the fact that the aforementioned discrete parameters needed for the inviscid flow are determined by the viscous flow condition at the point of reattachment. It is found that the reattachment point behaves as a saddle point singularity for the system of equations describing the recompressive viscous flow processes, and this behavior is exploited for the establishment of the overall flow field. Detailed results such as the base pressure, pressure distributions on the wedge, and the geometry of the wake are determined as functions of the wedge angle.

Warpinski, N. R.; Chow, W. L.

1977-01-01

403

NASA Technical Reports Server (NTRS)

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.

Maddalon, Dal V.; Braslow, Albert L.

1990-01-01

404

Stability analysis for laminar flow control, part 1

NASA Technical Reports Server (NTRS)

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.

Benney, D. J.; Orszag, S. A.

1977-01-01

405

Efficient simulation of incompressible viscous flow over multi-element airfoils

NASA Technical Reports Server (NTRS)

The incompressible, viscous, turbulent flow over single and multi-element airfoils is numerically simulated in an efficient manner by solving the incompressible Navier-Stokes equations. The solution algorithm employs the method of pseudo compressibility and utilizes an upwind differencing scheme for the convective fluxes, and an implicit line-relaxation scheme. The motivation for this work includes interest in studying high-lift take-off and landing configurations of various aircraft. In particular, accurate computation of lift and drag at various angles of attack up to stall is desired. Two different turbulence models are tested in computing the flow over an NACA 4412 airfoil; an accurate prediction of stall is obtained. The approach used for multi-element airfoils involves the use of multiple zones of structured grids fitted to each element. Two different approaches are compared; a patched system of grids, and an overlaid Chimera system of grids. Computational results are presented for two-element, three-element, and four-element airfoil configurations. Excellent agreement with experimental surface pressure coefficients is seen. The code converges in less than 200 iterations, requiring on the order of one minute of CPU time on a CRAY YMP per element in the airfoil configuration.

Rogers, Stuart E.; Wiltberger, N. Lyn; Kwak, Dochan

1993-01-01

406

Efficient simulation of incompressible viscous flow over multi-element airfoils

NASA Technical Reports Server (NTRS)

The incompressible, viscous, turbulent flow over single and multi-element airfoils is numerically simulated in an efficient manner by solving the incompressible Navier-Stokes equations. The computer code uses the method of pseudo-compressibility with an upwind-differencing scheme for the convective fluxes and an implicit line-relaxation solution algorithm. The motivation for this work includes interest in studying the high-lift take-off and landing configurations of various aircraft. In particular, accurate computation of lift and drag at various angles of attack, up to stall, is desired. Two different turbulence models are tested in computing the flow over an NACA 4412 airfoil; an accurate prediction of stall is obtained. The approach used for multi-element airfoils involves the use of multiple zones of structured grids fitted to each element. Two different approaches are compared: a patched system of grids, and an overlaid Chimera system of grids. Computational results are presented for two-element, three-element, and four-element airfoil configurations. Excellent agreement with experimental surface pressure coefficients is seen. The code converges in less than 200 iterations, requiring on the order of one minute of CPU time (on a CRAY YMP) per element in the airfoil configuration.

Rogers, Stuart E.; Wiltberger, N. Lyn; Kwak, Dochan

1992-01-01

407

An adaptive level set approach for incompressible two-phase flows

In Sussman, Smereka and Osher, a numerical method using the level set approach was formulated for solving incompressible two-phase flow with surface tension. In the level set approach, the interface is represented as the zero level set of a smooth function; this has the effect of replacing the advection of density, which has steep gradients at the interface, with the advection of the level set function, which is smooth. In addition, the interface can merge or break up with no special treatment. The authors maintain the level set function as the signed distance from the interface in order to robustly compute flows with high density ratios and stiff surface tension effects. In this work, they couple the level set scheme to an adaptive projection method for the incompressible Navier-Stokes equations, in order to achieve higher resolution of the interface with a minimum of additional expense. They present two-dimensional axisymmetric and fully three-dimensional results of air bubble and water drop computations.

Sussman, M.; Almgren, A.S.; Bell, J.B. [and others

1997-04-01

408

Experimental study of ``laminar'' bubbly flows in a vertical pipe

NASA Astrophysics Data System (ADS)

Measurement of bubbly two-phase flow parameters in a vertical pipe were performed. To keep the pipe Reynolds number below that for single-phase turbulent transition, a water-glycerin solution was used as the test liquid. Local void fraction and liquid velocity profiles along with the wall shear stress were measured by an electrochemical method. Experiments were made with bubbles of two different sizes. As the gas flow rate was increased, a gradual development of the liquid velocity profile from the parabolic Poiseuille flow to a flattened two-phase profile was observed. The evolution of the wall shear stress and of the velocity fluctuations were also quantified.

Kashinsky, O. N.; Timkin, L. S.; Cartellier, A.

1993-09-01

409

Viscous Sublayering for Shallow Water Flows Jorn Thies Frings

Analyzing the non-dimensional, incompressible Navier-Stokes equations assum- ing mostly laminar Shallow scheme based on the Roe solver. Starting from the Navier-Stokes equations for incompressible flows, we Water flow we deduct a set of equations modeling the evolution of mass and discharge including

410

Parallel solution of high-order numerical schemes for solving incompressible flows

NASA Technical Reports Server (NTRS)

A new parallel numerical scheme for solving incompressible steady-state flows is presented. The algorithm uses a finite-difference approach to solving the Navier-Stokes equations. The algorithms are scalable and expandable. They may be used with only two processors or with as many processors as are available. The code is general and expandable. Any size grid may be used. Four processors of the NASA LeRC Hypercluster were used to solve for steady-state flow in a driven square cavity. The Hypercluster was configured in a distributed-memory, hypercube-like architecture. By using a 50-by-50 finite-difference solution grid, an efficiency of 74 percent (a speedup of 2.96) was obtained.

Milner, Edward J.; Lin, Avi; Liou, May-Fun; Blech, Richard A.

1993-01-01

411

Performance of under-resolved two-dimensional incompressible flow simulations, II

This paper presents a study of the behavior of several difference approximations for the incompressible Navier-Stokes equations as a function of the computational mesh resolution. In particular, the under-resolved case is considered. The methods considered include a Godunov projection method, a primitive variable ENO method, an upwind vorticity stream-function method, centered difference methods of both a pressure-Poisson and vorticity stream-function formulation. and a pseudospectral method. It is demonstrated that all these methods produce spurious, nonphysical vortices of the type described by Brown and Minion for a Godunov projection method when the flow is sufficiently under-resolved. The occurrence of these artifacts appears to be due to a nonlinear effect in which the truncation error of the difference method initiates a vortex instability in the computed flow. The implications of this study for adaptive mesh refinement strategies are also discussed. 29 refs., 14 figs., 2 tabs.

Minion, M.L. [Univ. of North Carolina, Chapel Hill, NC (United States)] [Univ. of North Carolina, Chapel Hill, NC (United States); Brown, D.L. [Los Alamos National Lab., NM (United States)] [Los Alamos National Lab., NM (United States)

1997-12-01

412

Multiple-relaxation-time lattice Boltzmann modeling of incompressible flows in porous media

In this paper, a two-dimensional eight-velocity (D2Q8) multiple-relaxation-time (MRT) lattice Boltzmann (LB) model is proposed for incompressible porous flows at the representative elementary volume scale based on the Brinkman-Forchheimer-extended Darcy formulation. In the model, the porosity is included into the pressure-based equilibrium moments, and the linear and nonlinear drag forces of the porous media are incorporated into the model by adding a forcing term to the MRT-LB equation in the moment space. Through the Chapman-Enskog analysis, the generalized Navier-Stokes equations can be recovered exactly without artificial compressible errors. Numerical simulations of several typical two-dimensional porous flows are carried out to validate the present MRT-LB model. The numerical results of the present MRT-LB model are in good agreement with the analytical solutions and/or other numerical solutions reported in the literature.

Qing Liu; Ya-Ling He; Chao He

2013-11-28

413

NASA Astrophysics Data System (ADS)

An efficient high-order compact scheme is presented for computing unsteady incompressible viscous flows. The scheme is constructed on a staggered Cartesian grid. Using the fractional step framework, the Navier-Stokes equations are advanced in time with the second-order Adams-Bashforth method without considering the pressure terms in the predictor step. The velocity field is then corrected so that the continuity equation is satisfied through a pressure Poisson equation. Since the efficiency of the fractional step method depends on the Poisson solver, a Mehrstellen-based V-cycle multigrid acceleration is implemented in the solution of the Poisson equation to enhance the computational efficiency. The method is validated by simulating a decaying Taylor-Green vortex. The results show that the method has high resolving efficiency, drastically reduced computational time, and high-order accuracy, making it applicable for the simulation of complex turbulent flows.

San, Omer; Staples, Anne

2009-11-01

414

Higher-order finite element discretizations in a benchmark problem for incompressible flows

NASA Astrophysics Data System (ADS)

We present a numerical study of several finite element discretizations applied to a benchmark problem for the two-dimensional steady state incompressible Navier-Stokes equations defined in Schäfer and Turek (The benchmark problem Flow around a cylinder. In Flow Simulation with High-Performance Computers II. Notes on Numerical Fluid Mechanics, vol. 52, Hirschel EH (ed.). Vieweg: Wiesbaden, 1996; 547-566). The discretizations are compared with respect to the accuracy of the computed benchmark parameters. Higher-order isoparametric finite element discretizations turned out to be by far the most accurate. The discrete systems obtained with higher-order discretizations are solved with a modified coupled multigrid method whose behaviour within the benchmark problem is also studied numerically. Copyright

John, Volker; Matthies, Gunar

2001-12-01

415

A High Order Discontinuous Galerkin Method for 2D Incompressible Flows

NASA Technical Reports Server (NTRS)

In this paper we introduce a high order discontinuous Galerkin method for two dimensional incompressible flow in vorticity streamfunction formulation. The momentum equation is treated explicitly, utilizing the efficiency of the discontinuous Galerkin method The streamfunction is obtained by a standard Poisson solver using continuous finite elements. There is a natural matching between these two finite element spaces, since the normal component of the velocity field is continuous across element boundaries. This allows for a correct upwinding gluing in the discontinuous Galerkin framework, while still maintaining total energy conservation with no numerical dissipation and total enstrophy stability The method is suitable for inviscid or high Reynolds number flows. Optimal error estimates are proven and verified by numerical experiments.

Liu, Jia-Guo; Shu, Chi-Wang

1999-01-01

416

The Langley 8-ft transonic pressure tunnel laminar-flow-control experiment

NASA Technical Reports Server (NTRS)

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.

Bobbitt, Percy J.; Harvey, William D.; Harris, Charles D.; Brooks, Cuyler W., Jr.

1992-01-01

417

DESIGNING A HYBRID LAMINAR-FLOW CONTROL EXPERIMENT - THE CFD-EXPERIMENT CONNECTION

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

C. L. Streett

418

Recent Progress in the Use of Compliant Walls for Laminar Flow Control

It has been known for some time that an appropriately designed compliant wall (artificial dolphin skin) is highly effective\\u000a for laminar flow control in low-disturbance environments. Unfortunately, compliant walls are not really practical for aeronautical\\u000a applications. Accordingly, we focus here on marine applications. The marine environment tends to have much higher levels of\\u000a freestream turbulence than found in flight conditions

Peter W. Carpenter

419

Hybrid laminar flow control experiments in the NASA - Ames, 11-foot tunnel

It was proposed to design and conduct experiments in the NASA-Ames Research Center, 11-foot wind tunnel, that would assess the role of freestream turbulence and surface roughness on swept-wing transition to turbulence. The work was to be a cooperative effort that had direct application to hybrid laminar flow control (HLFC) airfoils. The first part of the proposed work, initiated in

William S. Saric

1995-01-01

420

Heat transfer properties of nanoparticle-in-fluid dispersions (nanofluids) in laminar flow

The convective heat transfer coefficients of several nanoparticle-in-liquid dispersions (nanofluids) have been measured under laminar flow in a horizontal tube heat exchanger. The nanoparticles used in this research were graphitic in nature, with aspect ratios significantly different from one (l\\/d?0.02). The graphite nanoparticles increased the static thermal conductivities of the fluid significantly at low weight fraction loadings. However, the experimental

Ying Yang; Z. George Zhang; Eric A. Grulke; William B. Anderson; Gefei Wu

2005-01-01

421

The problem of unsteady laminar fully-developed flow and heat transfer of an electrically-conducting and heat-generating or absorbing fluid with variable properties through porous channels in the presence of uniform magnetic and electric fields is formulated. The general governing equations which include such effects as magnetic field, electric field, porous medium inertia and heat generation or absorption effects are non-dimensionalized and

Ali J. Chamkha

2001-01-01

422

A gas-phase process of single-walled carbon nanotube (SWCNT) formation, based on thermal decomposition of iron pentacarbonyl or ferrocene in the presence of carbon monoxide (CO), was investigated in ambient pressure laminar flow reactors in the temperature range of 600–1300°C. Ferrocene was found to be a better catalyst precursor in the studied conditions since iron pentacarbonyl decomposes at lower temperatures resulting

Anna Moisala; Albert G. Nasibulin; David P. Brown; Hua Jiang; Leonid Khriachtchev; Esko I. Kauppinen

2006-01-01

423

A numerical investigation of laminar and turbulent flow past a cube

Laminar and turbulent flow past a cube is investigated numerically. A vorticity-vector potential approach is used as the basis for a computational algorithm in which semi-implicit finite difference equations are solved iteratively by a vectorizable 8 color SOR algorithm. The calculations are performed on a CRAY X-MP/48 Supercomputers. The laminar calculations are done at a range of Reynolds numbers from 10 to 100. The predicted drag appear to be in good agreement with relevant data including that from a cube drop experiment performed specifically for the present study. An analysis of the flow structure is made which shows it to be in qualitative agreement with similar flows. The turbulent flow calculations are done at Reynolds numbers of 2,000, 14,000 and 170,000 using the Mean Vorticity and Covariance (MVC) closure. The turbulent flow field is computed down to the solid surface without the use of wall functions. The calculated drag is in good agreement with experimental results. A study of the three-dimensional flow structure is carried out with the help of computer graphics. The flow is observed to separate from the side surfaces of the cube. The calculated axial velocity distribution is shown to be in good agreement with that observed experimentally in similar bluff body flows.

Raul, R.

1989-01-01

424

Multifluid laminar flow in a microchannel (Kenis et al. 1999)

reactions, e.g., jet engine and power generation gas turbines, internal combustion engines, furnaces: Micro/biofluidics, multiphase flows, turbulent combustion, CFD. Softwares : We develop and use our in research, we specialize in fluid mechanics, combustion and scientific computing. We're primarily concerned

Muradoglu, Metin

425

F-111 natural laminar flow glove flight test data analysis and boundary layer stability analysis

NASA Technical Reports Server (NTRS)

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.

Runyan, L. J.; Navran, B. H.; Rozendaal, R. A.

1984-01-01

426

Transonic flight test of a laminar flow leading edge with surface excrescences

NASA Technical Reports Server (NTRS)

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.

Zuniga, Fanny A.; Drake, Aaron; Kennelly, Robert A., Jr.; Koga, Dennis J.; Westphal, Russell V.

1994-01-01

427

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

P. C. Jr. Arcara; D. W. Bartlett; L. A. Mccullers

1991-01-01

428

Active Control of Instabilities in Laminar BoundaryÂLayer Flow -- Part II: Use of Sensors the presumption of wave cancellaÂ tion. Joslin et al. 1 have definitively shown that flow control by wave automated control to external flow over an actual aircraft or to any flow which has instabilities

Erlebacher, Gordon

429

-rate, the considered material has the ability to capture shear-thinning or shear-thickening phenomena exhibited by manySlip boundary effects on unsteady flows of incompressible viscous heat conducting fluids with a non malek@karlin.mff.cuni.cz We consider unsteady flows of a homogeneous incompressible fluid-like material

Lisbon, University of

430

New Finite Difference Methods Based on IIM for Inextensible Interfaces in Incompressible Flows

In this paper, new finite difference methods based on the augmented immersed interface method (IIM) are proposed for simulating an inextensible moving interface in an incompressible two-dimensional flow. The mathematical models arise from studying the deformation of red blood cells in mathematical biology. The governing equations are incompressible Stokes or Navier-Stokes equations with an unknown surface tension, which should be determined in such a way that the surface divergence of the velocity is zero along the interface. Thus, the area enclosed by the interface and the total length of the interface should be conserved during the evolution process. Because of the nonlinear and coupling nature of the problem, direct discretization by applying the immersed boundary or immersed interface method yields complex nonlinear systems to be solved. In our new methods, we treat the unknown surface tension as an augmented variable so that the augmented IIM can be applied. Since finding the unknown surface tension is essentially an inverse problem that is sensitive to perturbations, our regularization strategy is to introduce a controlled tangential force along the interface, which leads to a least squares problem. For Stokes equations, the forward solver at one time level involves solving three Poisson equations with an interface. For Navier-Stokes equations, we propose a modified projection method that can enforce the pressure jump condition corresponding directly to the unknown surface tension. Several numerical experiments show good agreement with other results in the literature and reveal some interesting phenomena. PMID:23795308

Li, Zhilin; Lai, Ming-Chih

2012-01-01

431

We review and extend to the compressible regime an earlier parallelization of an implicit incompressible unstructured Euler code [9], and solve for flow over an M6 wing in subsonic, transonic, and supersonic regimes. While the parallelization philosophy of the compressible case is identical to the incompressible, we focus here on the nonlinear and linear convergence rates, which vary in different physical regimes, and on comparing the performance of currently important computational platforms. Multiple-scale problems should be marched out at desired accuracy limits, and not held hostage to often more stringent explicit stability limits. In the context of inviscid aerodynamics, this means evolving transient computations on the scale of the convective transit time, rather than the acoustic transit time, or solving steady-state problems with local CFL numbers approaching infinity. Whether time-accurate or steady, we employ Newton's method on each (pseudo-) timestep. The coupling of analysis with design in aerodynamic practice is another motivation for implicitness. Design processes that make use of sensitivity derivatives and the Hessian matrix require operations with the Jacobian matrix of the state constraints (i.e., of the governing PDE system); if the Jacobian is available for design, it may be employed with advantage in a nonlinearly implicit analysis, as well.

Kaushik, D. K.; Keyes, D. E.; Smith, B. F.

1999-02-24

432

Micropatterned biofilm formations by laminar flow-templating.

We present a microfluidic device capable of patterning linear biofilm formations using a flow templating approach. We describe the design considerations and fabrication methodology of a two level flow-templating micro-bioreactor (FT-?BR), which generates a biofilm growth stream surrounded on 3 sides by a growth inhibiting confinement stream. Through a combination of experiments and simulations we comprehensively evaluate and exploit control parameters to manipulate the biofilm growth template stream dimensions. The FT-?BR is then used to grow biofilm patterns with controllable dimensions. A proof-of-principle study using the device demonstrates its utility in conducting biofilm growth rate measurements under different shear stress environments. This opens the way for quantitative studies into the effects of the local shear environment on biofilm properties and for the synthesis of a new generation of functional biomaterials with controllable properties. PMID:24722812

Aznaveh, Nahid Babaei; Safdar, Muhammad; Wolfaardt, Gideon; Greener, Jesse

2014-08-01

433

Experimental study of “laminar” bubbly flows in a vertical pipe

Measurement of bubbly two-phase flow parameters in a vertical pipe were performed. To keep the pipe Reynolds number below that for single-phase turbulent transition, a water-glycerin solution was used as the test liquid. Local void fraction and liquid velocity profiles along with the wall shear stress were measured by an electrochemical method. Experiments were made with bubbles of two different

O. N. Kashinsky; L. S. Timkin; A. Cartellier

1993-01-01

434

NASA Technical Reports Server (NTRS)

Numerical solutions are presented for the flow over a spherically blunted cone and hyperboloid with massive surface blowing. Time-dependent viscous shock-layer equations are used to describe the flow field. The boundary conditions on the body surface include a prescribed blowing-rate distribution. The governing equations are solved by a time-asymptotic finite-difference method. Results presented here are only for a perfect gas-type flow at zero angle of attack. Both laminar and turbulent flow solutions are obtained. It is found that the effect of the surface blowing on the laminar flow field is to smooth out the curvature discontinuity at the sphere-cone juncture point, which results in a positive pressure gradient over the body. The shock slope increases on the downstream portion of the body as the surface blowing rate is increased. The turbulent flow with surface blowing is found to redevelop a boundary-layer-like region near the surface. The effects of this boundary-layer region on the flow field and heating rates are discussed.

Kumar, A.; Twari, S. N.

1979-01-01

435

Laminar flame and acoustic waves in two-dimensional flow

The complete system of fluid dynamics equations describing the development of instability of a reaction front in a two-dimensional flow in reversed time are reduced to a closed system of equations of front dynamics by using Lagrangian variables and integrals of motion. The system can be used to analyze processes behind the front without solving the complete system of fluid dynamics and chemical kinetics equations. It is demonstrated how the gas density disturbances induced by the moving front can be described in the adiabatic approximation.

Zaytsev, M. L., E-mail: mlzaytsev@gmail.com; Akkerman, V. B., E-mail: slava.akkerman@gmail.com [Russian Academy of Sciences, Nuclear Safety Institute (Russian Federation)

2011-03-15

436

Direct Numerical Simulation of Incompressible Pipe Flow Using a B-Spline Spectral Method

NASA Technical Reports Server (NTRS)

A numerical method based on b-spline polynomials was developed to study incompressible flows in cylindrical geometries. A b-spline method has the advantages of possessing spectral accuracy and the flexibility of standard finite element methods. Using this method it was possible to ensure regularity of the solution near the origin, i.e. smoothness and boundedness. Because b-splines have compact support, it is also possible to remove b-splines near the center to alleviate the constraint placed on the time step by an overly fine grid. Using the natural periodicity in the azimuthal direction and approximating the streamwise direction as periodic, so-called time evolving flow, greatly reduced the cost and complexity of the computations. A direct numerical simulation of pipe flow was carried out using the method described above at a Reynolds number of 5600 based on diameter and bulk velocity. General knowledge of pipe flow and the availability of experimental measurements make pipe flow the ideal test case with which to validate the numerical method. Results indicated that high flatness levels of the radial component of velocity in the near wall region are physical; regions of high radial velocity were detected and appear to be related to high speed streaks in the boundary layer. Budgets of Reynolds stress transport equations showed close similarity with those of channel flow. However contrary to channel flow, the log layer of pipe flow is not homogeneous for the present Reynolds number. A topological method based on a classification of the invariants of the velocity gradient tensor was used. Plotting iso-surfaces of the discriminant of the invariants proved to be a good method for identifying vortical eddies in the flow field.

Loulou, Patrick; Moser, Robert D.; Mansour, Nagi N.; Cantwell, Brian J.

1997-01-01

437

Demonstration of a plasma mirror based on a laminar flow water film

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.

Panasenko, Dmitriy; Shu, Anthony; Gonsalves, Anthony; Nakamura, Kei; Matlis, Nicholas; Toth, Csaba; Leemans, Wim

2011-07-22

438

Numerical Solution of Supersonic Laminar Flow Over an Inclined Body of Revolution

NASA Technical Reports Server (NTRS)

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.

Hung, C. M.

1980-01-01

439

Rearward-facing steps in laminar supersonic flows with and without suction.

NASA Technical Reports Server (NTRS)

It was found in the experimental study conducted that, for both suction and no-suction cases, an increase in the step height caused a sharp drop in the initial heating rates which then gradually recovered to less or near the attached-flow values. The height of the step controlled the heating rates at the step base. Mass suction from the separated area increased the local heating rates, the relative increase being most significant immediately behind the step. In general, however, the effect of mass suction on heat-transfer at all laminar flows was relatively weak.

Jakubowski, A. K.; Lewis, C. H.

1973-01-01

440

This briefing will describe and demonstrate fluidic-based sound reception, amplification, and pneumatic headphone presentation to the listener. Fluidics is non-electronic and uses laminar proportional amplifiers and fluid-flow technology to demonstrate a sensitive "microphone" due to its massless diaphragm (laminar jet of low-velocity air) and perfect impedance matching to the propagating medium (also air). Many years ago the U.S. Army developed a system called the Individual Soldier Operated Personal Acoustic Detection System (ISOPADS) that utilized this fluidic technology to enhance and extend the Soldier's listening range. This demonstration system will let people point a small parabolic dish and listen around the room using a pneumatic headset. It makes for a fun demo, especially when participants understand that they are listening to a non-electronic system that uses only air. PMID:25235428

Scanlon, Michael V

2014-04-01

441

Two experimental supercritical laminar-flow-control swept-wing airfoils

NASA Technical Reports Server (NTRS)

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.

Allison, Dennis O.; Dagenhart, J. Ray

1987-01-01

442

F-16XL Ship #2 during last flight showing titanium laminar flow glove on left wing

NASA Technical Reports Server (NTRS)

Dryden research pilot Dana Purifoy bends NASA F-16 XL #848 away from the tanker on the 44th flight in the Supersonic Laminar Flow Control program recently. The flight test portion of the program ended with the 45th and last data collection flight from NASA's Dryden Flight Research Center, Edwards, California, on Nov. 26, 1996. The project demonstrated that laminar--or smooth--airflow could be achieved over a major portion of a wing at supersonic speeds. The flight tests at Dryden involved use of a suction system which drew boundary-layer air through millions of tiny laser-drilled holes in a titanium 'glove' that was fitted to the upper surface of the F-16XL's left wing.

1996-01-01

443

F-16XL Ship #2 during last flight showing titanium laminar flow glove on left wing

NASA Technical Reports Server (NTRS)

The perforated titanium overlay mounted on the upper surface of the left wing is clearly evident on this view of NASA 848, a highly modified F-16XL aircraft flown by NASA's Dryden Flight Research Center in the Supersonic Laminar Flow Control (SLFC) research program. The two-seat, single-engine craft, one of only two 'XL' F-16s built, recently concluded the SLFC project with its 45th data collection mission. The project demonstrated that laminar--or smooth--airflow could be achieved over a major portion of a wing at supersonic speeds by use of a suction system. The system drew a small part of the boundary-layer air through millions of tiny laser-drilled holes in the 'glove' fitted to the upper left wing.

1996-01-01

444

Numerical simulation of laminar reacting flows with complex chemistry

We present an adaptive algorithm for low Mach number reacting flows with complex chemistry. Our approach uses a form of the low Mach number equations that discretely conserves both mass and energy. The discretization methodology is based on a robust projection formulation that accommodates large density contrasts. The algorithm uses an operator-split treatment of stiff reaction terms and includes effects of differential diffusion. The basic computational approach is embedded in an adaptive projection framework that uses structured hierarchical grids with subcycling in time that preserves the discrete conservation properties of the underlying single-grid algorithm. We present numerical examples illustrating the performance of the method on both premixed and non-premixed flames.

Day, Marcus S.; Bell, John B.

1999-12-01

445

NASA Astrophysics Data System (ADS)

To solve large scale 3-D non-stationary incompressible flow problems, an algorithm to perform an Incomplete Balancing Domain Decomposition (IBDD) is constructed in this work; as an improvement of the Balancing Domain Decomposition (BDD) method, it reduce the computation cost of the coarse problem by replacing the exact balancing procedure with an inexact balancing procedure; the nonlinear convection term of the Navier-Stokes equation is approximated by a characteristic-curve method, which is advantageous as it renders the matrix for linear equations symmetric, thus enabling the Conjugate Gradient (CG) method to be used together with the Schur complement system of Domain Decomposition Method (DDM); the algorithms are all implemented in parallel by the Hierarchical Domain Decomposition Method (HDDM) system, and the program provides solvability for models of over 10 million degrees of freedom (DOF).

Yao, Q. H.; Kanayama, H.; Ognio, M.; Notsu, H.

2010-06-01

446

We study a diffuse interface model for the flow of two viscous incompressible Newtonian fluids in a bounded domain. The fluids are assumed to be macroscopically immiscible, but a partial mixing in a small interfacial region is assumed in the model. Moreover, diffusion of both components is taken into account. In contrast to previous works, we study a model for

Helmut Abels

2011-01-01

447

A coupled volume-of-fluid and level set (VOSET) method for computing incompressible two-phase flows

2009 Available online 10 November 2009 Keywords: VOF method LS method VOSET method Volume fraction combines the advantages and overcomes the disadvantages of VOF and LS methods, is presented for computing incompressible two-phase flows. In this method VOF method is used to capture interfaces, which can conserve

Frey, Pascal

448

A fast pressure-correction method for incompressible two-fluid flows

NASA Astrophysics Data System (ADS)

We have developed a new pressure-correction method for simulating incompressible two-fluid flows with large density and viscosity ratios. The method's main advantage is that the variable coefficient Poisson equation that arises in solving the incompressible Navier-Stokes equations for two-fluid flows is reduced to a constant coefficient equation, which can be solved with an FFT-based, fast Poisson solver. This reduction is achieved by splitting the variable density pressure gradient term in the governing equations. The validity of this splitting is demonstrated from our numerical tests, and it is explained from a physical viewpoint. In this paper, the new pressure-correction method is coupled with a mass-conserving volume-of-fluid method to capture the motion of the interface between the two fluids but, in general, it could be coupled with other interface advection methods such as level-set, phase-field, or front-tracking. First, we verified the new pressure-correction method using the capillary wave test-case up to density and viscosity ratios of 10,000. Then, we validated the method by simulating the motion of a falling water droplet in air and comparing the droplet terminal velocity with an experimental value. Next, the method is shown to be second-order accurate in space and time independent of the VoF method, and it conserves mass, momentum, and kinetic energy in the inviscid limit. Also, we show that for solving the two-fluid Navier-Stokes equations, the method is 10-40 times faster than the standard pressure-correction method, which uses multigrid to solve the variable coefficient Poisson equation. Finally, we show that the method is capable of performing fully-resolved direct numerical simulation (DNS) of droplet-laden isotropic turbulence with thousands of droplets using a computational mesh of 10243 points.

Dodd, Michael S.; Ferrante, Antonino

2014-09-01

449

Stabilization of the Eulerian model for incompressible multiphase flow by artificial diffusion

NASA Astrophysics Data System (ADS)

The commonly used Eulerian or continuum model for incompressible multiphase flow is known to be unstable to perturbations for all wavenumbers, even if viscosity terms are used in the momentum equations. In the present work the model is stabilized by adding explicit artificial diffusion to the mass equations. The artificial diffusion terms lead to improved stability properties: uniform flow becomes linearly stable for large wavenumbers, and above an analytically derived threshold for the artificial diffusivity, stability for all wavenumbers is achieved. The artificial diffusivity reappears in the momentum equations, in such a way that fundamental properties of the standard equations remain valid: Galilean invariance is maintained, total mass and momentum are conserved, decay of total kinetic energy is ensured in the absence of external forces, and a flow initially at rest at hydrostatic pressure remains unchanged, even if the spatial distribution of volume fractions is nonuniform. A staggered finite volume pressure correction method using central differencing (leading to energy conserving discretization of convective and pressure terms) is presented. Application of the method to one-dimensional two-phase flow of falling particles particles confirms that the equations are stable with and unstable without artificial diffusion in the volume fraction equation.

Vreman, A. W.

2011-02-01

450

Wake Effects on Drift in Two-Dimensional Inviscid Incompressible Flows

This investigation analyzes the effect of vortex wakes on the Lagrangian displacement of particles induced by the passage of an obstacle in a two-dimensional incompressible and inviscid fluid. In addition to the trajectories of individual particles, we also study their drift and the corresponding total drift areas in the F\\"oppl and Kirchhoff potential flow models. Our findings, which are obtained numerically and in some regimes are also supported by asymptotic analysis, are compared to the wakeless potential flow which serves as a reference. We show that in the presence of the F\\"oppl vortex wake some of the particles follow more complicated trajectories featuring a second loop. The appearance of an additional stagnation point in the F\\"oppl flow is identified as a source of this effect. It is also demonstrated that, while the total drift area increases with the size of the wake for large vortex strengths, it is actually decreased for small circulation values. On the other hand, the Kirchhoff flow model is s...

Melkoumian, Sergei

2014-01-01

451

A sharp interface immersed boundary method for simulating incompressible viscous flow past three-dimensional immersed bodies is described. The method employs a multi-dimensional ghost-cell methodology to satisfy the boundary conditions on the immersed boundary and the method is designed to handle highly complex three-dimensional, stationary, moving and/or deforming bodies. The complex immersed surfaces are represented by grids consisting of unstructured triangular elements; while the flow is computed on non-uniform Cartesian grids. The paper describes the salient features of the methodology with special emphasis on the immersed boundary treatment for stationary and moving boundaries. Simulations of a number of canonical two- and three-dimensional flows are used to verify the accuracy and fidelity of the solver over a range of Reynolds numbers. Flow past suddenly accelerated bodies are used to validate the solver for moving boundary problems. Finally two cases inspired from biology with highly complex three-dimensional bodies are simulated in order to demonstrate the versatility of the method. PMID:20216919

Mittal, R.; Dong, H.; Bozkurttas, M.; Najjar, F.M.; Vargas, A.; von Loebbecke, A.

2010-01-01

452

NASA Astrophysics Data System (ADS)

In this paper the artificial compressibility flux Discontinuous Galerkin (DG) method for the solution of the incompressible Navier-Stokes equations has been extended to deal with the Reynolds-Averaged Navier-Stokes (RANS) equations coupled with the Spalart-Allmaras (SA) turbulence model. DG implementations of the RANS and SA equations for compressible flows have already been reported in the literature, including the description of limiting or stabilization techniques adopted in order to prevent the turbulent viscosity ?˜ from becoming negative. In this paper we introduce an SA model implementation that deals with negative ?˜ values by modifying the source and diffusion terms in the SA model equation only when the working variable or one of the model closure functions become negative. This results in an efficient high-order implementation where either stabilization terms or even additional equations are avoided. We remark that the proposed implementation is not DG specific and it is well suited for any numerical discretization of the RANS-SA governing equations. The reliability, robustness and accuracy of the proposed implementation have been assessed by computing several high Reynolds number turbulent test cases: the flow over a flat plate (Re=107), the flow past a backward-facing step (Re=37400) and the flow around a NACA 0012 airfoil at different angles of attack (?=0°, 10°, 15°) and Reynolds numbers (Re=2.88×106,6×106).

Crivellini, Andrea; D'Alessandro, Valerio; Bassi, Francesco

2013-05-01

453

Computational Analysis of a Laminar Jet in a Cross-Flow

NASA Technical Reports Server (NTRS)

A jet in cross-flow (JIFC) consists of a jet exhausting at a large angle into a freestream flow. It is a flow field which is relevant to a wide variety of technologies and applications. Despite the nearly 65 years of JIFC research there are few results available for laminar hypersonic flows, a combination which will be encountered by re-entry and high altitude vehicles over some portion of their flight path. This research consists of developing a numerical model to investigate the interaction of a normal sonic jet exhausting into a hypersonic cross-flow. The model was validated by comparing experimental measurements with corresponding numerical results generated by the model.

Jeffries, Damon K.; Krishnamurthy, R.; Chandra, S.

1998-01-01

454

Development of quiet-flow supersonic wind tunnels for laminar-turbulent transition research

NASA Technical Reports Server (NTRS)

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.

Schneider, Steven P.

1994-01-01

455

NASA Astrophysics Data System (ADS)

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 ?m 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.

Urban, O.; Jehli?ka, J.; Pokorný, J.; Rouzaud, J. N.

2003-08-01

456

Distinct large-scale turbulent-laminar states in transitional pipe flow

When fluid flows through a channel, pipe, or duct, there are two basic forms of motion: smooth laminar motion and complex turbulent motion. The discontinuous transition between these states is a fundamental problem that has been studied for more than 100 yr. What has received far less attention is the large-scale nature of the turbulent flows near transition once they are established. We have carried out extensive numerical computations in pipes of variable lengths up to 125 diameters to investigate the nature of transitional turbulence in pipe flow. We show the existence of three fundamentally different turbulent states separated by two distinct Reynolds numbers. Below Re 1 ? 2,300, turbulence takes the form of familiar equilibrium (or longtime transient) puffs that are spatially localized and keep their size independent of pipe length. At Re 1 the flow makes a striking transition to a spatio-temporally intermittent flow that fills the pipe. Irregular alternation of turbulent and laminar regions is inherent and does not result from random disturbances. The fraction of turbulence increases with Re until Re 2 ? 2,600 where there is a continuous transition to a state of uniform turbulence along the pipe. We relate these observations to directed percolation and argue that Re 1 marks the onset of infinite-lifetime turbulence. PMID:20404193

Moxey, David; Barkley, Dwight

2010-01-01

457

Distinct large-scale turbulent-laminar states in transitional pipe flow.

When fluid flows through a channel, pipe, or duct, there are two basic forms of motion: smooth laminar motion and complex turbulent motion. The discontinuous transition between these states is a fundamental problem that has been studied for more than 100 yr. What has received far less attention is the large-scale nature of the turbulent flows near transition once they are established. We have carried out extensive numerical computations in pipes of variable lengths up to 125 diameters to investigate the nature of transitional turbulence in pipe flow. We show the existence of three fundamentally different turbulent states separated by two distinct Reynolds numbers. Below Re (1) approximately equal 2,300, turbulence takes the form of familiar equilibrium (or longtime transient) puffs that are spatially localized and keep their size independent of pipe length. At Re (1) the flow makes a striking transition to a spatio-temporally intermittent flow that fills the pipe. Irregular alternation of turbulent and laminar regions is inherent and does not result from random disturbances. The fraction of turbulence increases with Re until Re (2) approximately equal 2,600 where there is a continuous transition to a state of uniform turbulence along the pipe. We relate these observations to directed percolation and argue that Re (1) marks the onset of infinite-lifetime turbulence. PMID:20404193

Moxey, David; Barkley, Dwight

2010-05-01

458

NASA Astrophysics Data System (ADS)

An experimental study on the efficiency of transpiration cooling in hypersonic laminar and turbulent flow regimes is carried out in the Hypersonic Windtunnel Cologne with a focus on the aerothermal problems downstream of the cooled model part. The model is made of a material of low thermal conductivity (PEEK) with an integrated probe of a porous material. The experimental setup allows the direct comparison of the thermal behavior of transpiration cooling to a well-defined and radiatively cooled reference surface. Experiments are performed at Mach number of 6 and two different Reynolds numbers. Air, argon and helium are used as coolants at various flow rates, in order to identify the influence of coolant medium on cooling efficiency. The cooling efficiency of air and argon is comparable. Helium provides significantly higher cooling efficiency at the same blowing ratio, i.e. same coolant mass flow rate. The experimental data shows that the efficiency of the transpiration cooling in turbulent flows is much lower than in laminar flow.

Gülhan, A.; Braun, S.

2011-03-01

459

Numerical approximation of laminar flows over rough walls with sharp asperities

NASA Astrophysics Data System (ADS)

We consider a viscous incompressible fluid filling an infinite horizontal domain bounded at the bottom by a plane wall and at the top by a rough wall. The latter is assumed to consist of a plane wall covered with periodically distributed asperities whose size depends on a small parameter [var epsilon]>0. The assumption of sharp asperities is made, that is the height of the asperities does not vanish as [var epsilon]-->0. The rough wall is at rest and the plane wall is moving at a constant horizontal velocity. We assume that the flow is governed by the stationary Stokes equations. We give an asymptotic approximation of the Stokes flow, under the rugose region, by a Couette flow, depending on the size [var epsilon] of the asperities. We then build a numerical approximation of the Couette flow based on a partial domain decomposition method.

Amirat, Youcef; Bodart, Olivier

2004-03-01

460

Nanofluids, because of their enhanced heat transfer capability as compared to normal water\\/glycol\\/oil based fluids, offer the engineer opportunities for development in areas where high heat transfer, low temperature tolerance and small component size are required. In this present paper, the hydrodynamic and thermal fields of a water–?Al2O3 nanofluid in a radial laminar flow cooling system are considered. Results indicate

Gilles Roy; Cong Tam Nguyen; Paul-René Lajoie

2004-01-01

461

A laminar flow unit for the care of critically ill newborn infants

Introduction Medical and nursing care of newborns is predicated on the delicate control and balance of several vital parameters. Closed incubators and open radiant warmers are the most widely used devices for the care of neonates in intensive care; however, several well-known limitations of these devises have not been resolved. The use of laminar flow is widely used in many fields of medicine, and may have applications in neonatal care. Objective To describe the neonatal laminar flow unit, a new equipment we designed for care of ill newborns. Methods The idea, design, and development of this device was completed in Sao Paulo, Brazil. The unit is an open mobile bed designed with the objective of maintaining the advantages of the incubator and radiant warmer, while overcoming some of their inherent shortcomings; these shortcomings include noise, magnetic fields and acrylic barriers in incubators, and lack of isolation and water loss through skin in radiant warmers. The unit has a pump that aspirates environmental air which is warmed by electrical resistance and decontaminated with High Efficiency Particulate Air Filter (HEPA) filters (laminar flow). The flow is directed by an air flow directioner. The unit has an embedded humidifier to increase humidity in the infant’s microenvironment and a servo control mechanism for regulation of skin temperature. Results The laminar flow unit is open and facilitates access of care providers and family, which is not the case in incubators. It provides warming by convection at an air velocity of 0.45 m/s, much faster than an incubator (0.1 m/s). The system provides isolation 1000 class (less than 1,000 particles higher than 0.3 micron per cubic feet at all times). This is much more protection than an incubator provides and more than radiant warmers, which have no isolation whatsoever. Additionally, it provides humidification of the newborn’s microenvironment (about 60% relative humidity), which is impossible with a radiant warmer, which produces high water body loss. It has no mechanical barriers like acrylic walls, its magnetic field is lower than an incubator (0.25 ?t versus 1.2 ?t), and the noise is minimal compared to incubators. The unit is also able to provide controlled total body hypothermia, which is not possible with either of the other two units. Conclusion The laminar flow unit for neonatal care is a novel device which we recently developed. The introduction of laminar flow technology represents a real innovation in the neonatal field. We have described the various components of the unit and the potential advantages for management of ill neonates. This will hopefully lead to improved clinical outcomes and more effective neonatal management and safety. PMID:24204178

Perez, Jose MR; Golombek, Sergio G; Fajardo, Carlos; Sola, Augusto

2013-01-01

462

We present a high-throughput continuous-flow C. elegans sorting device that works based on integrated optical fiber detection and laminar flow switching. Two types of genetically engineered nematodes are allowed to flow into the device and their genotypes are detected based on their fluorescence, without the need for immobilization, by integrated optical fibers. A novel dynamic fluidic switch sorts the nematodes to desired outlets. By changing input pressures of the control inlets, the laminar flow path is altered to steer the nematodes to appropriate outlets. Compared to previously reported microfluidic C. elegans sorting devices, sorting in this system is conducted in a continuous flow environment without any immobilization technique or need for multilayer mechanical valves to open and close the outlets. The continuous flow sorter not only increases the throughput but also avoids any kind of invasive or possibly damaging mechanical or chemical stimulus. We have characterized both the detection and the switching accuracy of the sorting device at different flow rates, and efficiencies approaching 100% can be achieved with a high throughput of about one nematode per second. To confirm that there was no significant damage to C. elegans following sorting, we recovered the sorted worms, finding no deaths and no differences in behavior and propagation compared to control. PMID:25140819

Yan, Yuanjun; Ng, Li Fang; Ng, Li Theng; Choi, Kwan Bum; Gruber, Jan; Bettiol, Andrew A; Thakor, Nitish V

2014-10-21

463

PIV experiments in rough-wall, laminar-to-turbulent, oscillatory boundary-layer flows

NASA Astrophysics Data System (ADS)

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.

Mujal-Colilles, Anna; Mier, Jose M.; Christensen, Kenneth T.; Bateman, Allen; Garcia, Marcelo H.

2014-01-01

464

An immersed boundary method for incompressible flows using volume of body function

NASA Astrophysics Data System (ADS)

A simple and effective immersed boundary method using volume of body (VOB) function is implemented on unstructured Cartesian meshes. The flow solver is a second-order accurate implicit pressure-correction method for the incompressible Navier-Stokes equations. The domain inside the immersed body is viewed as being occupied by the same fluid as outside with a prescribed divergence-free velocity field. Under this view a fluid-body interface is similar to a fluid-fluid interface encountered in the volume of fluid (VOF) method for the two-fluid flow problems. The body can thus be identified by the VOB function similar to the VOF function. In fluid-body interface cells the velocity is obtained by a volume-averaged mixture of body and fluid velocities. The pressure inside the immersed body satisfies the same pressure Poisson equation as outside. To enhance stability and convergence, multigrid methods are developed to solve the difference equations for both pressure and velocity. Various steady and unsteady flows with stationary and moving bodies are computed to validate and to demonstrate the capability of the current method.

Pan, Dartzi

2006-02-01

465

We consider unsteady flows of inhomogeneous, incompressible, shear-thickening and heat-conducting fluids where the viscosity depends on the density, the temperature and the shear rate, and the heat conductivity depends on the temperature and the density. For any values of initial total mass and initial total energy we establish the long-time existence of weak solution to internal flows inside an arbitrary

Jens Frehse; Josef Málek; Michael R?ži?ka

2010-01-01

466

\\u000a A ‘fictitious boundary method’ for computing incompressible flows with complicated small-scale and\\/or time-dependent geometric\\u000a details is presented. The underlying technique is based on a special treatment of Dirichlet boundary conditions, particularly\\u000a for FEM discretizations, together with so-called `iterative filtering techniques’ in the context of hierarchical multigrid\\u000a approaches such that the flow can be efficienctly computed on a fixed computational mesh

Stefan Turek; Decheng Wan; Liudmila S. Rivkind

467

A simple, stable, and accurate ghost cell method is developed to solve the incompressible flows over immersed bodies with heat transfer. A two-point stencil is used to build the flow reconstruction models for both Dirichlet and Neumann boundary conditions on the immersed surface. Tests show that the current scheme is second-order-accurate in all error norms for both types of boundary

Dartzi Pan

2010-01-01

468

Experimental Study of Saddle Point of Attachment in Laminar Juncture Flow

NASA Technical Reports Server (NTRS)

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.

Coon, Michael D.; Tobak, Murray

1995-01-01

469

An adaptive discretization of incompressible flow using a multitude of moving Cartesian grids

NASA Astrophysics Data System (ADS)

We present a novel method for discretizing the incompressible Navier-Stokes equations on a multitude of moving and overlapping Cartesian grids each with an independently chosen cell size to address adaptivity. Advection is handled with first and second order accurate semi-Lagrangian schemes in order to alleviate any time step restriction associated with small grid cell sizes. Likewise, an implicit temporal discretization is used for the parabolic terms including Navier-Stokes viscosity which we address separately through the development of a method for solving the heat diffusion equations. The most intricate aspect of any such discretization is the method used in order to solve the elliptic equation for the Navier-Stokes pressure or that resulting from the temporal discretization of parabolic terms. We address this by first removing any degrees of freedom which duplicately cover spatial regions due to overlapping grids, and then providing a discretization for the remaining degrees of freedom adjacent to these regions. We observe that a robust second order accurate symmetric positive definite readily preconditioned discretization can be obtained by constructing a local Voronoi region on the fly for each degree of freedom in question in order to obtain both its stencil (logically connected neighbors) and stencil weights. Internal curved boundaries such as at solid interfaces are handled using a simple immersed boundary approach which is directly applied to the Voronoi mesh in both the viscosity and pressure solves. We independently demonstrate each aspect of our approach on test problems in order to show efficacy and convergence before finally addressing a number of common test cases for incompressible flow with stationary and moving solid bodies.

English, R. Elliot; Qiu, Linhai; Yu, Yue; Fedkiw, Ronald

2013-12-01

470

NASA Technical Reports Server (NTRS)

A new formulation (including the choice of variables, their non-dimensionalization, and the form of the artificial viscosity) is proposed for the numerical solution of the full Navier-Stokes equations for compressible and incompressible flows with heat transfer. With the present approach, the same code can be used for constant as well as variable density flows. The changes of the density due to pressure and temperature variations are identified and it is shown that the low Mach number approximation is a special case. At zero Mach number, the density changes due to the temperature variation are accounted for, mainly through a body force term in the momentum equation. It is also shown that the Boussinesq approximation of the buoyancy effects in an incompressible flow is a special case. To demonstrate the new capability, three examples are tested. Flows in driven cavities with adiabatic and isothermal walls are simulated with the same code as well as incompressible and supersonic flows over a wall with and without a groove. Finally, viscous flow simulations of an oblique shock reflection from a flat plate are shown to be in good agreement with the solutions available in literature.

Hafez, M.; Soliman, M.; White, S.

1992-01-01

471

NASA Astrophysics Data System (ADS)

This study deals with a preliminary investigation of the effects of spin on the axisymmetric flow past a body of revolution. The study has its genesis larger problem of Magnus forces on spinning bodies at angle of attack. However, the fundamental behavior that arises when a spinning body is placed in a uniform stream is still not well understood; therefore, the problem of axisymmetric flow with spin was undertaken. The body consists of a 3-caliber cant-ogive blunted by a spherical nosecap, a 2-caliber cylindrical section, and a 1-caliber boattail. Numerical solutions of the compressible laminar Navier-Stokes equations are obtained using a modified version of the implicit-explicit method developed by MacCormack in 1981. The benchmark problem is the nonspinning body in uniform flow at a Reynolds number of 1.14. The results show that the modified method performs well and allows time steps that are in order of magnitude greater than those permitted by explicit stability criteria.

Weber, K. F.

1985-12-01

472

NASA Technical Reports Server (NTRS)

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.

Somers, D. M.

1981-01-01

473

The NASA Langley laminar-flow-control experiment on a swept, supercritical airfoil - Drag equations

NASA Technical Reports Server (NTRS)

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.

Brooks, Cuyler W., Jr.; Harris, Charles D.; Harvey, William D.

1989-01-01

474

NASA Technical Reports Server (NTRS)

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.

Pearce, W. E.

1982-01-01

475

Laminar boundary layer flow and heat transfer with favorable pressure gradient at constant K values

NASA Astrophysics Data System (ADS)

The Pohlhausen integral method has been used to analyze the fluid mechanics and heat transfer of a 2D laminar boundary layer with favorable pressure gradients at constant K values; this is relevant to wind tunnel experiments in which the flow is confined within the test walls, and the streamwise pressure gradients are generated through the manipulation of the wind-tunnel walls. Constant wall heat flux and constant wall temperature conditions are considered. The analytical solutions are in good agreement with numerical results from a parabolic boundary layer code.

Zhou, Dadong; Wang, Ting

1992-06-01

476

An Exploratory Investigation of a Slotted, Natural-Laminar-Flow Airfoil

NASA Technical Reports Server (NTRS)

A 15-percent-thick, slotted, natural-laminar-flow (SNLF) airfoil, the S103, for genera