Efficient upwind algorithms for solution of the Euler and Navier-stokes equations

An efficient three-dimensionasl tructured solver for the Euler and Navier-Stokese quations is developed based on a finite volume upwind algorithm using Roe fluxes. Multigrid and optimal smoothing multi-stage time stepping accelerate convergence. The accuracy of the new solver is demonstrated for inviscid flows in the range 0.675 :5M :5 25. A comparative grid convergence study for transonic turbulent flow about a wing is conducted with the present solver and a scalar dissipation central difference industrial design solver. The upwind solver demonstrates faster grid convergence than the central scheme, producing more consistent estimates of lift, drag and boundary layer parameters. In transonic viscous computations, the upwind scheme with convergence acceleration is over 20 times more efficient than without it. The ability of the upwind solver to compute viscous flows of comparable accuracy to scalar dissipation central schemes on grids of one-quarter the density make it a more accurate, cost effective alternative. In addition, an original convergencea cceleration method termed shock acceleration is proposed. The method is designed to reduce the errors caused by the shock wave singularity M -+ 1, based on a localized treatment of discontinuities. Acceleration models are formulated for an inhomogeneous PDE in one variable. Results for the Roe and Engquist-Osher schemes demonstrate an order of magnitude improvement in the rate of convergence. One of the acceleration models is extended to the quasi one-dimensiona Euler equations for duct flow. Results for this case d monstrate a marked increase in convergence with negligible loss in accuracy when the acceleration procedure is applied after the shock has settled in its final cell. Typically, the method saves up to 60% in computational expense. Significantly, the performance gain is entirely at the expense of the error modes associated with discrete shock structure. In view of the success achieved, further development of the method is proposed

Adjoint-based geometry optimisation with applications to automotive fuel injector nozzles

Methods of Computational Fluid Dynamics (CFD) have matured, over the last 30 years, to a stage where it is possible to gain substantial insight into fluid flow processes of engineering relevance. However, the motives of fluid dynamic engineers typically go well beyond the level of improved understanding, to the pragmatic aim of improving the performance of the engineering systems in consideration. It is in recognition of these circumstances that the present thesis investigates the use of automated design optimisation methodologies in order to extend the power of CFD as an engineering design tool. Optimum design problems require the merit or performance of designs to be measured explicitly in terms of an objective function. At the same time, it may be required that one or more constraints should be satisfied. To describe allowable variations in design, shape parameterisation using basic geometric entities such as straight lines and arcs is employed. Taking advantage of previous experience in the research group concerning cavitating flows, a fully automated method for nozzle design/optimisation was developed. The optimisation is performed by means of discharge coefficient (Cd) maximisation. The objective is to design nozzle hole shapes that maximise the nozzle Cd for a given basic nozzle geometry (i.e. needle and sac profile) and reduce or even eliminate the negative pressure region formed at the entry of the injection hole. The deterministic optimisation model was developed and implemented in the in-house RANS CFD code to provide nozzle shapes with pre-defined flow/performance characteristics. The required gradients are calculated using the continuous adjoint technique. A parameterisation scheme, suitable for nozzle design, was developed. The localised region around the hole inlet, where cavitation inception appears, is parameterised and modified during the optimisation procedure, while the rest of the nozzle remains unaffected. The parameters modifying the geometry are the radius of curvature and the diameter of the hole inlet or exit as well as the relative needle seat angle. The steepest descent method has been used to drive the calculated gradients to zero and update the design parameters. For the validation of the model two representative inverse design cases have been selected. Studies showing the behaviour of the model according to different numerical and optimisation parameters are also presented. For the purpose of optimising the geometries, a cost function intended to maximise the discharge coefficient was defined. At the same time it serves the purpose of restructuring geometries which have controlled or eliminated cavitation inception in the hole entrance. This is identified in the steady-state mode by reduction of the volume of negative relative pressure appearing in the hole entrance. Results of cavitation control on some representative nozzle geometries show significant benefits gained by the use of the developed method. This is mainly because the developed model performs optimisation on numerous parametric combinations automatically. Results showed that, by using the proposed method, geometries with larger Cd values can be achieved and the cavitation inception can, in some cases, be completely eliminated. Cases where all the parameters were combined for redesign the geometry required less modification to predict larger Cd values than cases where each parameter was modified individually. This is an important result since manufacturers are seeking improvement in the performance of products resulting from the least geometry modifications

Supercomputing in Aerospace

Topics addressed include: numerical aerodynamic simulation; computational mechanics; supercomputers; aerospace propulsion systems; computational modeling in ballistics; turbulence modeling; computational chemistry; computational fluid dynamics; and computational astrophysics

NASA Propulsion Engineering Research Center, volume 2

On 8-9 Sep. 1993, the Propulsion Engineering Research Center (PERC) at The Pennsylvania State University held its Fifth Annual Symposium. PERC was initiated in 1988 by a grant from the NASA Office of Aeronautics and Space Technology as a part of the University Space Engineering Research Center (USERC) program; the purpose of the USERC program is to replenish and enhance the capabilities of our Nation's engineering community to meet its future space technology needs. The Centers are designed to advance the state-of-the-art in key space-related engineering disciplines and to promote and support engineering education for the next generation of engineers for the national space program and related commercial space endeavors. Research on the following areas was initiated: liquid, solid, and hybrid chemical propulsion, nuclear propulsion, electrical propulsion, and advanced propulsion concepts

Aeronautical engineering: A continuing bibliography with indexes (supplement 245)

This bibliography lists 537 reports, articles, and other documents introduced into the NASA scientific and technical information system in October, 1989. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Transonic Symposium: Theory, Application, and Experiment, Volume 1, Part 1

Topics addressed include: wind tunnel and flight experiments; computational fluid dynamics (CFD) applications, industry overviews; and inviscid methods and grid generations

Third International Conference on Inverse Design Concepts and Optimization in Engineering Sciences (ICIDES-3)

Papers from the Third International Conference on Inverse Design Concepts and Optimization in Engineering Sciences (ICIDES) are presented. The papers discuss current research in the general field of inverse, semi-inverse, and direct design and optimization in engineering sciences. The rapid growth of this relatively new field is due to the availability of faster and larger computing machines

Aeronautical engineering: A continuing bibliography with indexes (supplement 268)

This bibliography lists 406 reports, articles, and other documents introduced into the NASA scientific and technical information system in July, 1991. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

A CFD investigation of wind tunnel interference on delta wing aerodynamics

To explore the influence of wind tunnel test facilities on delta wing aerodynamics, the interference has been separated into two distinct types, wall interference and support structure interference. The wall interference effects have been split into three further components, tunnel blockage, side wall interference, and roof and floor interference. Splitting the tunnel influence in this way allows us to determine the most detrimental interference effects, thus allowing the wind tunnel engineer to design experiments accordingly. Euler and more realistic RANS simulations of tunnel interference have been conducted. To reduce the question of grid dependence when comparing solutions, a common "farfield grid" was created and tunnel grids were extracted. Before doing RANS simulations an analysis of various turbulence models was conducted. It was found that turbulence models have difficulty in predicting turbulence levels in leading edge vortices. As such modifications have been applied to the models which improve predictions. Despite vortex breakdown being widely regarded as an inviscid phenomenon, dependence on turbulence modelling has been exhibited. This is due to the vortex properties being altered with turbulent diffusion of vorticity when turbulence levels are too high. Both 1- and 2-equation models were assessed and it was concluded that a modified 2-equation k-w model was the most suitable of the models available (when compared against experimental results), and was therefore used in all subsequent simulations. From both Euler and RANS simulations it has been concluded that the effect of sidewall proximity significantly promotes vortex breakdown. Side wall induced velocity components increase the mean effective incidence of the wing, the helix angle and the strength of the vortices. The combination of these effects promotes vortex breakdown. Roof and floor proximity has little effect on vortex breakdown as does the frontal area blockage. Pitching simulations have shown that the promotion of vortex breakdown is not consistent on both the upstroke and downstroke. Break-down was observed to be prompted furthest at the higher incidence of the upstroke and on the downstroke. This highlights the dependency of tunnel interference on vortex strength

Aeronautical engineering, a continuing bibliography with indexes (supplement 197)

This bibliography lists 488 reports, articles and other documents introduced into the NASA scientific and technical information system in January 1986