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Chapman, D. R.

Publications and source records attributed to Chapman, D. R..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Simulation and modeling of homogeneous, compressed turbulence

Low Reynolds number homogeneous turbulence undergoing low Mach number isotropic and one-dimensional compression was simulated by numerically solving the Navier-Stokes equations. The numerical simulations were performed on a CYBER 205 computer using a 64 x 64 x 64 mesh. A spectral method was used for spatial differencing and the second-order Runge-Kutta method for time advancement. A variety of statistical information was extracted from the computed flow fields. These include three-dimensional energy and dissipation spectra, two-point velocity correlations, one-dimensional energy spectra, turbulent kinetic energy and its dissipation rate, integral length scales, Taylor microscales, and Kolmogorov length scale. Results from the simulated flow fields were used to test one-point closure, two-equation models. A new one-point-closure, three-equation turbulence model which accounts for the effect of compression is proposed. The new model accurately calculates four types of flows (isotropic decay, isotropic compression, one-dimensional compression, and axisymmetric expansion flows) for a wide range of strain rates.

Wu, C. T.↗
NASA NTRS1984

Navier-Stokes Simulation of Homogeneous Turbulence on the CYBER 205

A computer code which solves the Navier-Stokes equations for three dimensional, time-dependent, homogenous turbulence has been written for the CYBER 205. The code has options for both 64-bit and 32-bit arithmetic. With 32-bit computation, mesh sizes up to 64 (3) are contained within core of a 2 million 64-bit word memory. Computer speed timing runs were made for various vector lengths up to 6144. With this code, speeds a little over 100 Mflops have been achieved on a 2-pipe CYBER 205. Several problems encountered in the coding are discussed.

Wu, C. T.↗
NASA NTRS1981

Two-component Navier-Stokes computational model of viscous sublayer turbulence

A new computational method is presented for developing a quantitative model of viscous sublayer turbulence in incompressible flow. Appropriate space- and time-dependent boundary conditions are constructed for the three fluctuating velocity components at the outer edge of the viscous sublayer. This construction is formulated so as to model essential coherent structures observed in experiments. Time dependent Navier-Stokes equations are used to compute the characteristics of turbulence in the viscous sublayer.

Chapman, D. R.↗
NASA NTRS1981

Trends and pacing items in computational aerodynamics

A perspective is presented of trends in computational aerodynamics, and of important technology development items that pace future advanced applications. From a survey of AIAA Journal papers published during the past two decades, the growth trends and the progressively increasing emphasis on code development for viscous, compressible, turbulent flow are illustrated. These trends are reflected in the chronology of introduction by the aerospace industry of new computational methods in aircraft design. Key pacing items outlined are: automatic grid generation for nonlinear inviscid computations; advanced computers, improved efficiency of numerical methods, and improved turbulence models for Reynolds-averaged Navier-Stokes computations; advanced computers, time-dependent three-dimensional law-of-the-wall, code development, improved efficiency of numerical methods, and improved subgrid-scale turbulence modeling for large eddy simulations.

Chapman, D. R.↗
NASA NTRS1979

Computational aerodynamics development and outlook /Dryden Lecture in Research for 1979/

Some past developments and current examples of computational aerodynamics are briefly reviewed. An assessment is made of the requirements on future computer memory and speed imposed by advanced numerical simulations, giving emphasis to the Reynolds averaged Navier-Stokes equations and to turbulent eddy simulations. Experimental scales of turbulence structure are used to determine the mesh spacings required to adequately resolve turbulent energy and shear. Assessment also is made of the changing market environment for developing future large computers, and of the projections of micro-electronics memory and logic technology that affect future computer capability. From the two assessments, estimates are formed of the future time scale in which various advanced types of aerodynamic flow simulations could become feasible. Areas of research judged especially relevant to future developments are noted.

Chapman, D. R.↗
NASA NTRS1976

Status and prospects of computational fluid dynamics

The use and limitations on using computational aerodynamics in approximating inviscid linear, inviscid nonlinear, vicous time averaged, and viscous time dependent flow past airfoils, wings, and aircraft is reviewed. The current status of two- and three-dimensional time averaged Navier-Stokes equation is discussed and possible applications for the 1980 and 1985 to 1990 period is projected for three-dimensional applications.

Chapman, D. R.↗
NASA NTRS1975

Computers vs. wind tunnels for aerodynamic flow simulations

It is pointed out that in other fields of computational physics, such as ballistics, celestial mechanics, and neutronics, computations have already displaced experiments as the principal means of obtaining dynamic simulations. In the case of aerodynamic investigations, the complexity of the computational work involved in solving the Navier-Stokes equations is the reason that such investigations rely currently mainly on wind-tunnel testing. However, because of inherent limitations of the wind-tunnel approach and economic considerations, it appears that at some time in the future aerodynamic studies will chiefly rely on computational flow data provided by the computer. Taking into account projected development trends, it is estimated that computers with the required capabilities for a solution of the complete viscous, time-dependent Navier-Stokes equations will be available in the mid-1980s.

Chapman, D. R.↗
NASA NTRS1975

Computational aerodynamics

The application of computer techniques for solving Navier-Stokes equations in support of wind tunnel tests is discussed. The ILLIAC IV computer is considered for this purpose and its limitations are analyzed. The author states that improved computers will make it possible to solve many aerodynamic problems and reduce the amount of wind tunnel testing required for adequate data processing.

Chapman, D. R.↗
NASA NTRS1975

Impact survival conditions for very large meteorites, with special reference to the legendary Chinguetti meteorite

Contrary to popular belief, very large meteorites can be sufficiently slowed by aerodynamic drag to survive impact with the earth's surface provided that they enter the atmosphere at very low angles. This is a stringent requirement and survival probabilities for large, unguided objects are low; but they are not zero. Based on high-velocity impact experiments and published tabulations of the parameters of shallow angle entry trajectories, we estimate the probability of survival for an iron meteorite approximately the size and shape of the legendary Chinguetti meteorite (100 x 40 x 20-40 m) to be between 0.1 and 1 percent. Together with a limiting estimate of the flux of such bodies encountering the earth, this leads to an expected survival rate of one per (0.1-1.0) billion years on the earth's land surface.

Fudali, R. F.↗