01 AERONAUTICS (GENERAL)

No abstracts in this category.

02 AERODYNAMICS

Includes aerodynamics of bodies, combinations, wings, rotors, and control surfaces; and internal flow in ducts and turbomachinery.

For related information see also 34 Fluid Mechanics and Heat Transfer.

N91-10839*# National Aeronautics and Space Administration.
Ames Research Center, Moffett Field, CA.

NASA COMPUTATIONAL FLUID DYNAMICS CONFERENCE.
VOLUME 1: SESSIONS 1-6
Sep. 1989 475 p

Conference held at Moffett Field, CA, 7-9 Mar. 1989 Original contains color illustrations (NASA-CP-10038-Vol-1; A-89160-Vol-1; NAS 1.55:10038-Vol-1) Avail: NTIS HC/MF A20; 25 functional color pages CSCL 01A Presentations given at the NASA Computational Fluid Dynamics (CFD) Conference held at the NASA Ames Research Center, Moffett Field, California, March 7-9, 1989 are given. Topics covered include research facility overviews of CFD research and applications, validation programs, direct simulation of compressible turbulence, turbulence modeling, advances in Runge-Kutta schemes for solving 3-D Navier-Stokes equations, grid generation and invicid flow computation around aircraft geometries, numerical simulation of rotorcraft, and viscous drag prediction for rotor blades. For individual titles, see N91-10840 through N91-10867.

N91-10840*#

National Aeronautics and Space Administration. Ames Research Center, Moffett Field, CA. COMPUTATIONAL FLUID DYNAMICS PROGRAM AT NASA AMES RESEARCH CENTER

Terry L. Holst In its NASA Computational Fluid Dynamics Conference. Volume 1: Sessions 1-6 Sep. 1989 p 3-34 (For primary document see N91-10839 02-02)

Avail: NTIS HC/MF A20; 25 functional color pages CSCL 01A

The Computational Fluid Dynamics (CFD) Program at NASA Ames Research Center is reviewed and discussed. The technical elements of the CFD Program are listed and briefly discussed. These elements include algorithm research, research and pilot code development, scientific visualization, advanced surface representation, volume grid generation, and numerical optimization. Next, the discipline of CFD is briefly discussed and related to other areas of research at NASA Ames including experimental fluid dynamics, computer science research, computational chemistry, and numerical aerodynamic simulation. These areas combine with CFD to form a larger area of research, which might collectively be called computational technology. The ultimate goal of computational technology research at NASA Ames is to increase the physical understanding of the world in which we live, solve problems of national importance, and increase the technical capabilities of the aerospace community. Next, the major programs

at NASA Ames that either use CFD technology or perform research in CFD are listed and discussed. Briefly, this list includes turbulent/transition physics and modeling, high-speed real gas flows, interdisciplinary research, turbomachinery demonstration computations, complete aircraft aerodynamics, rotorcraft applications, powered lift flows, high alpha flows, multiple body aerodynamics, and incompressible flow applications. Some of the individual problems actively being worked in each of these areas is listed to help define the breadth or extent of CFD involvement in each of these major programs. State-of-the-art examples of various CFD applications are presented to highlight most of these areas. The main emphasis of this portion of the presentation is on examples which will not otherwise be treated at this conference by the individual presentations. Finally, a list of principal current limitations and expected future directions is given. Author

N91-10841*# National Aeronautics and Space Administration. Langley Research Center, Hampton, VA.

COMPUTATIONAL FLUID DYNAMICS RESEARCH AND APPLICATIONS AT NASA LANGLEY RESEARCH CENTER Jerry C. South, Jr. In NASA, Ames Research Center, NASA Computational Fluid Dynamics Conference. Volume 1: Sessions 1-6 Sep. 1989 p 35-47 (For primary document see N91-10839 02-02)

Avail: NTIS HC/MF_A20; 25 functional color pages CSCL 01A

Information on computational fluid dynamics (CFD) research and applications carried out at the NASA Langley Research Center is given in viewgraph form. The Langley CFD strategy, the five-year plan in CFD and flow physics, 3-block grid topology, the effect of a patching algorithm, F-18 surface flow, entropy and vorticity effects that improve accuracy of unsteady transonic small disturbance theory, and the effects of reduced frequency on first harmonic components of unsteady pressures due to airfoil pitching are among the topics covered.

Author

N91-10842*# National Aeronautics and Space Administration.
Lewis Research Center, Cleveland, OH.

COMPUTATIONAL FLUID DYNAMICS AT THE LEWIS
RESEARCH CENTER: AN OVERVIEW

Robert M. Stubbs In NASA, Ames Research Center, NASA Computational Fluid Dynamics Conference. Volume 1: Sessions 1-6 Sep. 1989 p 49-61 (For primary document see N91-10839 02-02)

Avail: NTIS HC/MF A20; 25 functional color pages CSCL 01A Lewis is a multidisciplinary Center with strong research and development programs in aeronautical and space propulsion, power, space communications, space experiments and materials. Computational fluid dynamics (CFD) is playing an important and growing role in most of these areas. Described here is how CFD is integrated into these programs and highlights elements of the CFD activities. Examples are presented of codes developed to predict flow fields in advanced propulsion systems and several of the code validation experiments are described. The CFD effort at Lewis ranges from basic research on new and improved algorithms through code development to the application of these codes to specific engineering problems. Because of the substantial improvement in CFD's predictive capability, its use at Lewis is on a steep growth path, spreading rapidly into new areas which had not traditionally taken advantage of the techniques of numerical

simulation. Multidisciplinary codes and the future direction of CFD at Lewis are discussed. Author

N91-10843*#

National Aeronautics and Space Administration. Marshall Space Flight Center, Huntsville, AL.

MARSHALL SPACE FLIGHT CENTER CFD OVERVIEW Luke A. Schutzenhofer In NASA, Ames Research Center, NASA Computational Fluid Dynamics Conference. Volume 1: Sessions 1-6 Sep. 1989 p 65-94 (For primary document see N91-10839 02-02)

Avail: NTIS HC/MF A20; 25 functional color pages CSCL 01A

Computational Fluid Dynamics (CFD) activities at Marshall Space Flight Center (MSFC) have been focused on hardware specific and research applications with strong emphasis upon benchmark validation. The purpose here is to provide insight into the MSFC CFD related goals, objectives, current hardware related CFD activities, propulsion CFD research efforts and validation program, future near-term CFD hardware related programs, and CFD expectations. The current hardware programs where CFD has been successfully applied are the Space Shuttle Main Engines (SSME), Alternate Turbopump Development (ATD), and Aeroassist Flight Experiment (AFE). For the future near-term CFD hardware related activities, plans are being developed that address the implementation of CFD into the early design stages of the Space Transportation Main Engine (STME), Space Transportation Booster Engine (STBE), and the Environmental Control and Life Support System (ECLSS) for the Space Station. Finally, CFD expectations in the design environment will be delineated. Author

N91-10844*# National Aeronautics and Space Administration.
Lyndon B. Johnson Space Center, Houston, TX.
JOHNSON SPACE CENTER CFD OVERVIEW

Chien P. Li In NASA, Ames Research Center, NASA Computational Fluid Dynamics Conference. Volume 1: Sessions 1-6 Sep. 1989 p 95-121 (For primary document see N91-10839 02-02)

Avail: NTIS HC/MF_A20; 25 functional color pages CSCL 01A

Recent applications and development of CFD technology have focused on flow problems that are critically important to the operation and design of space flight vehicles. The main effort is spent on the Space Shuttle in order to provide an understanding of the cryogenic fluid in the duct connecting the External Tank and the Main Engines, the subsonic flow surrounding the Orbiter during crew egress maneuvers, the transonic aerodynamic forces on the Orbiter fuselage and wing, the high angle-of-attack abort flight, and the aerodynamic heating during entry. To provide in-depth analyses for such diverse problems within a timely schedule, matured panel codes and a state-of-the-art incompressible turbulent flow code were adapted. Collaboration with Ames Research Center has resulted in a Shuttle ascent aerodynamic code; and a viscous chemical nonequilibrium code is being developed for predicting Orbiter real-gas aerodynamics and finite-catalytic heating. The remaining activities are devoted to the prediction of the flow environment around the Aeroassist Flight Experiment vehicle at hypersonic speeds and high altitudes. A thermochemical nonequilibrium Navier-Stokes code has been developed on the basis of two- temperature and 11-species models for solving both the shock layer and near wake. After validating the code against wind-tunnel aerodynamic, pressure and heating data, the code is being used to supplement the ground test facilities in predicting a more realistic flight environment. CFD technology is being relied upon by other programs as well in the consideration of candidate configurations. Author

research and design tool, the requirement to validate CFD codes
has grown significantly. NASA had emphasized CFD validation
activities since 1986 when a separate work element was formed
to fund experimental activities related to validation. NASA's CFD
and CFD validation programs are closely coordinated to ensure
that experimental data bases are available as soon as possible
for validating codes. In response to industry and academic
requirements, four levels of experimental research have been
defined as part of CFD validation with NASA's Aeronautics Advisory
Committee (AAC) support although only the fourth level actually
has the detailed information necessary for validating codes. Critical
flow physics especially turbulence modeling are key to improved
CFD codes. NASA has focused additional resources on transition
and turbulence physics to meet these requirements. With improved
turbulence models, CFD codes will be more accurate, robust, and
efficient. However, with the level of detailed information available
from CFD codes, highly accurate and detailed experiments are
required to capture the critical information for validating codes.
Advanced instrumentation especially non-intrusive instrumentation
is required to acquire this information in validation experiments.
The CFD validation program is being coordinated and managed
to address these critical activities. A list of experiments which are
currently being supported at least partially are included. Author
N91-10846*# National Aeronautics and Space Administration.
Ames Research Center, Moffett Field, CA.
UNDERSTANDING TRANSITION AND TURBULENCE
THROUGH DIRECT SIMULATIONS

P. R. Spalart and J. J. Kim In its NASA Computational Fluid
Dynamics Conference. Volume 1: Sessions 1-6 Sep. 1989
p 137-149 (For primary document see N91-10839 02-02)
Avail: NTIS HC/MF A20; 25 functional color pages CSCL 01A

Direct simulations consist in solving the full Navier-Stokes equations, without any turbulence model, and describing all the detailed features of the flow. Usually the flows are three-dimensional and time-dependent and contain both coarse and fine structures, which makes the numerical task very challenging in terms of both the algorithm and the computational effort. Most of the work until now has involved spectral methods, which are highly accurate but not very flexible in terms of geometry or complex equations. For that reason, future work will also rely on high-order finite-difference or other methods. Direct simulations complement experimental work, and both contribute to the theory and the empirical knowledge of turbulence. Once such a simulation has been shown to be accurate, the flow field is completely known in three dimensions and time, including the pressure, the vorticity and any other quantity. On the other hand, most simulations to date solved the incompressible equations in rather simple geometries, and direct simulations will always be limited to moderate Reynolds numbers. Extensive simulations have been conducted in homogeneous turbulence, channel flows, boundary layers, and mixing layers. Much effort is devoted to addressing flows with compressibility and chemical reactions, and to new geometries such as a backward-facing step. Author

N91-10847*# National Aeronautics and Space Administration. Langley Research Center, Hampton, VA.

DIRECT SIMULATION OF COMPRESSIBLE TURBULENCE

T. A. Zang, Gordon Erlebacher, and M. Y. Hussaini (Institute for
Computer Applications in Science and Engineering, Hampton,
VA.) In NASA, Ames Research Center, NASA Computational
Fluid Dynamics Conference. Volume 1: Sessions 1-6 Sep. 1989
p 151-165 (For primary document see N91-10839 02-02)
Avail: NTIS HC/MF A20; 25 functional color pages CSCL 01A

Several direct simulations of 3-D homogeneous, compressible turbulence are presented with emphasis on the differences with incompressible turbulent simulations. A fully spectral collocation algorithm, periodic in all directions coupled with a 3rd order Runge-Kutta time discretization scheme is sufficient to produce well-resolved flows at Taylor Reynolds numbers below 40 on grids of 128x128x128. A Helmholtz decomposition of velocity is useful to differentiate between the purely compressible effects and those effects solely due to vorticity production. In the context of

homogeneous flows, this decomposition in unique. Time-dependent energy and dissipation spectra of the compressible and solenoidal velocity components indicate the presence of localized small scale structures. These structures are strongly a function of the initial conditions. Researchers concentrate on a regime characterized by very small fluctuating Mach numbers Ma (on the order of 0.03) and density and temperature fluctuations much greater than sq Ma. This leads to a state in which more than 70 percent of the kinetic energy is contained in the so-called compressible component of the velocity. Furthermore, these conditions lead to the formation of curved weak shocks (or shocklets) which travel at approximately the sound speed across the physical domain. Various terms in the vorticity and divergence of velocity production equations are plotted versus time to gain some understanding of how small scales are actually formed. Possible links with Burger turbulence are examined. To visualize better the dynamics of the flow, new graphic visualization techniques have been developed. The 3-D structure of the shocks are visualized with the help of volume rendering algorithms developed in-house. A combination of stereographic projection and animation greatly increase the number of visual cues necessary to properly interpret the complex flow. Author

N91-10848*#

National Aeronautics and Space Administration.
Langley Research Center, Hampton, VA.
NON LINEAR EVOLUTION OF A SECOND MODE WAVE IN
SUPERSONIC BOUNDARY LAYERS

Gordon Erlebacher and M. Y. Hussaini (Institute for Computer
Applications in Science and Engineering, Hampton, VA.) In NASA,
Ames Research Center, NASA Computational Fluid Dynamics
Conference. Volume 1: Sessions 1-6 Sep. 1989
p 167-181

(For primary document see N91-10839 02-02)
Avail: NTIS HC/MF A20; 25 functional color pages CSCL 01A
Presented here are several direct simulations of one 2-D
second mode perturbation wave, superimposed upon a prescribed
mean flow. Periodicity is assumed in the streamwise direction
(Fourier) and the variables are expanded in Chebyshev series in
the direction normal to the flat plate. The code is fully explicit and
is time advanced with a 3rd order Runge-Kutta scheme. The second
mode wave (R delta prime = 8000), interacts with itself to generate
higher streamwise harmonics. Physical parameters are chosen to
maximize the linear growth rate at the prescribed Reynolds number.
Initial results indicate that the nonlinear processes begin in the
critical layer region and are the result of the cubic interactions in
the momentum equations, rather than due to the higher streamwise
harmonics. Analysis of the various terms in the momentum
equations combined with numerical experiments in which various
modes are artificially suppressed, lead to the conclusion that
asymptotic methods will produce the saturated state in one or
two order of magnitude less computer time than that required by
the direct numerical simulations.
Author

N91-10849*# National Aeronautics and Space Administration.
Lewis Research Center, Cleveland, OH.

NUMERICAL SIMULATION OF NONLINEAR DEVELOPMENT
OF INSTABILITY WAVES

Reda R. Mankbadi (Cairo Univ., Egypt) In NASA, Ames Research Center, NASA Computational Fluid Dynamics Conference. Volume 1: Sessions 1-6 Sep. 1989 p 183-191 (For primary document see N91-10839 02-02)

(E-4658) Avail: NTIS HC/MF A20; 25 functional color pages CSCL 01A

The nonlinear interactions of high amplitude instability waves in turbulent jets are described. In plane shear layers Riley and Metcalf (1980) and Monkewitz (1987) have shown that these interactions are dependent, among other parameters, on the phase-difference between the two instability waves. Therefore, here researchers consider the nonlinear development of both the amplitudes and the phase of the instability waves. The development of these waves are also coupled with the development of the mean flow and the background turbulence. In formulating this model it is assumed that each of the flow components can be characterized by conservation equations supplemented by closure

models. Results for the interactions between the two instability waves under high-amplitude forcing at fundamental and subharmonic frequencies are presented here. Qualitative agreements are found between the present predictions and available experimental data. Author

N91-10850*# National Aeronautics and Space Administration.
Ames Research Center, Moffett Field, CA.

MORE ACCURATE PREDICTIONS WITH TRANSONIC
NAVIER-STOKES METHODS THROUGH IMPROVED
TURBULENCE MODELING

Dennis A. Johnson In its NASA Computational Fluid Dynamics
Conference. Volume 1: Sessions 1-6 Sep. 1989 p 193-204
(For primary document see N91-10839 02-02)
Avail: NTIS HC/MF_A20; 25 functional color pages CSCL 01A
Significant improvements in predictive accuracies for off-design
conditions are achievable through better turbulence modeling; and,
without necessarily adding any significant complication to the
numerics. One well established fact about turbulence is it is slow
to respond to changes in the mean strain field. With the 'equilibrium'
algebraic turbulence models no attempt is made to model this
characteristic and as a consequence these turbulence models
exaggerate the turbulent boundary layer's ability to produce
turbulent Reynolds shear stresses in regions of adverse pressure
gradient. As a consequence, too little momentum loss within the
boundary layer is predicted in the region of the shock wave and
along the aft part of the airfoil where the surface pressure
undergoes further increases. Recently, a 'nonequilibrium' algebraic
turbulence model was formulated which attempts to capture this
important characteristic of turbulence. This 'nonequilibrium'
algebraic model employs an ordinary differential equation to model
the slow response of the turbulence to changes in local flow
conditions. In its original form, there was some question as to
whether this 'nonequilibrium' model performed as well as the
'equilibrium' models for weak interaction cases. However, this
turbulence model has since been further improved wherein it now
appears that this turbulence model performs at least as well as
the 'equilibrium' models for weak interaction cases and for strong
interaction cases represents a very significant improvement. The
performance of this turbulence model relative to popular
'equilibrium' models is illustrated for three airfoil test cases of the
1987 AIAA Viscous Transonic Airfoil Workshop, Reno, Nevada. A
form of this 'nonequilibrium' turbulence model is currently being
applied to wing flows for which similar improvements in predictive
accuracy are being realized.
Author

N91-10851*# National Aeronautics and Space Administration.
Langley Research Center, Hampton, VA.

RECENT ADVANCES IN RUNGE-KUTTA SCHEMES FOR
SOLVING 3-D NAVIER-STOKES EQUATIONS

In NASA,

Veer N. Vatsa, Bruce W. Wedan, and Ridha Abid
Ames Research Center, NASA Computational Fluid Dynamics
Conference. Volume 1: Sessions 1-6 Sep. 1989 p 207-221
Original contains color illustrations (For primary document see
N91-10839 02-02)

Avail: NTIS HC/MF A20; 25 functional color pages CSCL 01A

A thin-layer Navier-Stokes has been developed for solving high Reynolds number, turbulent flows past aircraft components under transonic flow conditions. The computer code has been validated through data comparisons for flow past isolated wings, wing-body configurations, prolate spheroids and wings mounted inside wind-tunnels. The basic code employs an explicit Runge-Kutta time-stepping scheme to obtain steady state solution to the unsteady governing equations. Significant gain in the efficiency of the code has been obtained by implementing a multigrid acceleration technique to achieve steady-state solutions. The improved efficiency of the code has made it feasible to conduct grid-refinement and turbulence model studies in a reasonable amount of computer time. The non-equilibrium turbulence model of Johnson and King has been extended to three-dimensional flows and excellent agreement with pressure data has been obtained for transonic separated flow over a transport type of wing. Author