Turbulent boundary layer heat
Abstract
A Reynolds stress model for turbulent boundary layers is used to study surface roughness effects on skin friction and heat transfer. The issues of primary interest are the influence of roughness character (element shape and spacing) and the nature of roughness effects at high Mach numbers. Computations based on the model compare satisfactorily with measurements from experiments involving variations in roughness character, in low speed and modestly supersonic conditions. The more limited data base at hypersonic Mach numbers is also examined with reasonable success, although no quantitative explanation is offered for the reduction of heat transfer with increasing roughness observed by Holden at Me 9.4. The present calculations indicate that the mean velocity is approximately uniform over much of the height range below the tops of the elements, y less than or equal to k. With this constant (roughness velocity,) it is simple to estimate the form drag on the elements. This roughness velocity has been investigated by systematically exercising the present model over ranges of potential parameters. The roughness velocity is found to be primarily a function of the projected element frontal area per unit surface area, thus providing a new and simple method for predicting roughness character effects. The model further suggests that increased boundary layer temperatures should be generated by roughness at high edge Mach numbers, which would tend to reduce skin friction and heat transfer, perhaps below smooth wall levels.
 Publication:

Planetary Science Inst. Report
 Pub Date:
 January 1981
 Bibcode:
 1981psi..rept.....F
 Keywords:

 Aerodynamic Heating;
 Heat Transfer;
 Reentry Vehicles;
 Skin Friction;
 Surface Roughness Effects;
 Turbulent Boundary Layer;
 Coefficient Of Friction;
 Friction Drag;
 High Temperature;
 Mach Number;
 Mathematical Models;
 Reynolds Stress;
 Fluid Mechanics and Heat Transfer