Engineering topics

Orszag, Steven A.

Publications and source records attributed to Orszag, Steven A..

5 records

NASA NTRS1992

Application of algebraic-RNG eddy viscosity model to simulation of transitional boundary layer flow

An algebraic eddy-viscosity model is derived from the renormalization group (RNG) theory of turbulence. A new length scale, based on boundary layer characteristics (displacement thickness, shape factor), is proposed. The model was applied to transitional boundary layer flow over a flat plate. Integral characteristics, such as the total skin friction coefficient, and mean velocity profile across the boundary layer, are found to be in good agreement with experimental data.

Yakhot, Alexander↗

NASA NTRS1990

Inhibition of mixing and self-focusing in high Mach number turbulence

It is shown that the hypothesis that eddy shocklets dissipate excess kinetic energy in compressible flow and thus limit the effective eddy Mach number to order 1 leads to the inhibition of mixing and self-focusing of turbulent jets at high Mach numbers, in agreement with experiment.

Orszag, Steven A.↗

NASA NTRS1990

Energy and spectral dynamics in forced compressible turbulence

Numerical simulations are used to study compressible turbulence with microscale Reynolds numbers up to 40 and rms Mach numbers M up to 0.9. The flows are randomly forced, with energy supplied to either the rotational or compressive components of kinetic energy, which is then transferred to internal energy through the pressure-dilatation interaction and viscous dissipation terms. Coupling between the two components of kinetic energy by the advection term is relatively weak, and most energy introduced to either component by the external force is transferred, without passing through the other component, to internal energy. A statistically quasi-equilibrium of kinetic energy is realized while internal energy increases steadily. The spectral form of the rotational component of velocity, which hardly depends on M, is very close to that for incompressible flow. On the other hand, the compressive component depends strongly on M, especially at large wave numbers.

Kida, Shigeo↗

NASA NTRS1990

Enstrophy budget in decaying compressible turbulence

The interaction of vorticity and shock waves in decaying compressible turbulence is investigated by direct numerical simulation of the Navier-Stokes equation using a spectral method with 64-cubed collocation points. The Taylor microscale Reynolds number decreases from 36 to 17 and the rms Mach number from 0.8 to 0.4 during the decay. It is observed that vorticity is created inside curved shocks through baroclinic interaction and intensified by the compression of fluid elements. Vortex stretching is, on the other hand, dominant outside shocks and is responsible for enhancing the strength of vorticity. A dipole of vorticity is typically created at the vertex of curved shocks, the structure of which is explained in terms of jump relations of velocity derivatives across a curved shock.

Kida, Shigeo↗

NASA NTRS1987

Linear stability analysis of three-dimensional compressible boundary layers

A compressible stability analysis computer code is developed. The code uses a matrix finite-difference method for local eigenvale solution when a good guess for the eigenvalue is available and is significantly more computationally efficient than the commonly used inital-value approach. The local eigenvalue search procedure also results in eigenfunctions and, at little extra work, group velocities. A globally convergent eigenvalue procedure is also developed that may be used when no guess for the eigenvalue is available. The global problem is formulated in such a way that no unstable spurious modes appear so that the method is suitable for use in a black-box stability code. Sample stability calculations are presented for the boundary layer profiles of an LFC swept wing.

Malik, Mujeeb R.↗