Surface Roughness Effects on the Hypersonic Turbulent Boundary Layer

Surface Roughness Effects on the Hypersonic Turbulent Boundary Layer
Author:
Publisher:
Total Pages:
Release: 1977
Genre:
ISBN:

An experimental investigation of the response of a hypersonic turbulent boundary layer to a step change in surface roughness has been performed. The boundary layer on a flat nozzle wall of a Mach 6 wind tunnel was subjected to abrupt changes in surface roughness and its adjustment to the new surface conditions was examined. Both mean and fluctuating flow properties were acquired for smooth-to-rough and rough-to-smooth surface configurations. The boundary layer was found to respond gradually and to attain new equilibrium profiles, for both the mean and the fluctuating properties, some 10 to 25 delta downstream of the step change. Mean flow self-similarity was the first to establish itself, followed by the mass flux fluctuations, followed in turn by the total temperature fluctuations. Use of a modified Van Driest transformation resulted in good correlations of smooth and rough wall data in the form of the incompressible law of the wall. This is true even in the nonequilibrium vicinity of the step for small roughness heights. The present data are found to correlate well with previously published roughness effect data from low and high speed flows when the roughnesses are characterized by an equivalent sand grain roughness height.

Parametric Study of Hypersonic Turbulent Boundary Layers with Heat Transfer

Parametric Study of Hypersonic Turbulent Boundary Layers with Heat Transfer
Author: J. S. Shang
Publisher:
Total Pages: 48
Release: 1974
Genre: Turbulent boundary layer
ISBN:

Models of the Reynolds shear stress and the turbulent energy flux are modified to include the effect of fluctuating density for the hypersonic flow regime. The compressible turbulent boundary layer equations are solved by a finite difference scheme. The results, indicate a meaningful improvement in predicting the skin friction coefficient. The static pressure variation across a turbulent boundary layer is also investigated in the present analysis by including the normal momentum equation. A tentative model for the fluctuating velocity term is proposed and the resulting pressure variation across the boundary layer is confirmed by experimental measurements. (Modified author abstract).

DNS of Hypersonic Turbulent Boundary Layers

DNS of Hypersonic Turbulent Boundary Layers
Author: Junji Huang
Publisher:
Total Pages: 0
Release: 2022
Genre: Turbulence
ISBN:

Understanding the physics of the pressure fluctuations induced by high-speed turbulent boundary layers (TBLs) is of major practical importance. The fluctuating pressure on aerodynamic surfaces of flight vehicles determines the vibrational loading of the vehicles and often leads to damaging effects as fatigue and flutter. The freestream pressure fluctuations radiated from the tunnel-wall TBLs are responsible for the genesis of freestream acoustic noise in conventional (i.e., noisy) supersonic and hypersonic wind tunnels. In this manuscript, wall and freestream pressure fluctuations induced by high-speed TBLs were characterized by direct numerical simulations (DNS). The DNS database covered a broad range of flow conditions (Mach number of $M_\infty = 2.5-14$, wall-to-recovery temperature ratio of $T_w/T_r = 0.18-1.0$, Reynolds number of $Re_\tau=450-1172$) and geometric configurations (flat plate, sharp circular cone, two dimensional channel, realistic wind-tunnel nozzle). The DNS overcame multiple experimental difficulties and provided access to wall and freestream pressure statistics that were difficulty to obtain otherwise, including the root-mean-square fluctuations and higher order moments (skewness and flatness) , probability density function , two-point correlation, convection speed, and coherence function. The study yielded useful insights into the physics of the boundary-layer-induced pressure field and provided critical assessment to reduced-order models such as the Corcos theory for modeling the wall pressure and the eddy-Mach-wave radiation theory for predicting the freestream acoustic pressure.