Laser Doppler velocimeter measurements of boundary layer velocity and turbulent intensities in Mach 2.5 flow
In recent years, the interest in developing a high-speed civil transport has increased. This has led to an increase in research activity on compressible supersonic flows, in particular the boundary layer. The structure of subsonic boundary layers has been extensively documented using conditional sampling techniques which exploit the knowledge of both u and v velocities. Researchers using these techniques have been able to explore some of the complex three-dimensional motions which are responsible for Reynolds stress production and transport in the boundary layer. As interest in turbulent structure has grown to include supersonic flows, a need for simultaneous multicomponent velocity measurements in these flows has developed. The success of conditional analysis in determining the characteristics of coherent motions and structures in the boundary layer relies on accurate, simultaneous measurement of two instantaneous velocity components.
Prediction and control of transition in supersonic and hypersonic boundary layers
Computations for sharp cones, using the e N method with N=10, show that the first oblique Tollmien-Schlichting mode is responsible for transition at adiabatic wall conditions for freestream Mach numbers up to about 7. For cold walls, the two-dimensional second mode dominates the transition process at lower hypersonic Mach numbers due to the well-known destabilizing effect of cooling on the second mode
A hybrid explicit-implicit numerical algorithm for the three-dimensional compressible Navier-Stokes equations
A hybrid explicit-implicit numerical algorithm has been developed for the three-dimensional mean compressible Navier-Stokes equations. The algorithm combines the explicit finite difference algorithm of MacCormack and an implicit algorithm for the viscous sublayer and transition wall regions of the turbulent boundary layers. The algebraic turbulent eddy-viscosity model of Baldwin and Lomax is employed. A bodyoriented coordinate transformation is utilized to facilitate treatment of arbitrary flow regions. The hybrid algorithm has been vectorized on the CDC CYBER 203 computer using the SL/1 vector programming language developed at NASA Langley. The accuracy of the numerical algorithm, established previously for twodimensional flows with strong viscous-inviscid interaction (including flow separation), is validated for threedimensional flows. The algorithm is applied to the interaction of an oblique shock wave with a turbulent boundary layer in three dimensions. The computed results generally are found to be in close agreement with the experimental data. The hybrid algorithm is shown to provide a substantial improvement in computational efficiency compared to a vectorized MacCormack explicit algorithm alone.