Generalized Roughness Effects on Turbulent Boundary Layer Heat Transfer. A Discrete Element Predictive Approach for Turbulent Flow Over Rough Surfaces

Abstract

UNCLASSIFIED tKCUNITV CLASSIFICATION Of TMIi »*0C fVlran Oaf« Kriar»« 20. ABSTRACT (CONCLUDED) equations which describe momentum and energy transport In turbulent flows. The model includes the necessary empirical information on the interaction between the roughness elements and the flow around and between the elements in a general way which does not require experimental data on each specific surface. This empirical information is input via algebraic models for the local element drag coefficient and Nusselt number. These models have been cslibrated by comparison with base data sets from surfaces with three-dimensional (distributed) roughness elements. Calculations using the present discrete element model are compared with experimental data from 118 separate experimental runs. The results of these comparisons range from gooc* tc excellent. The calculations are shown to compare equally well with both transitionally rough turbulent flow and fully rough turbulent flow without modification of the roughness model. In the course of the present work it was discovered that the definitive data set of Schlichting is flawed. Corrected values are presented for this data set.

Computational study of drag increase due to wall roughness for hypersonic flight

“…Equations (8) and (10) give y k r e Bκ = y + u u … (11) Using the approximation that u/y is infinitesimal of higher order, the dimensionless velocity shift can thus be expressed as…”

“…The idea of DEA is to modify the mean flow equations to account for blockage effects due to the presence of roughness elements as well as drag and heat flux on the roughness elements. This technique was introduced by Robertson 6 and further refined by Finson (7) , Coleman et al (8) and McClain et al (9,10) . However, it is difficult for DEA to be implemented into a general-purpose CFD (Computational Fluid Dynamics) code for they require altering the flow equations.…”