Hypersonic flow and heat transfer of a micro-rough plate in the near-continuum regime

Hypersonic near-continuum flow over a flat plate with micro-scale roughness is studied using the kinetic direct simulation Monte Carlo method on roughness module configurations with different relative roughness (h) values and roughness densities (RN) under a matrix of freestream parameters (Mach number Ma∞, Reynolds number Re∞, temperature T∞, and Knudsen number Kn∞). An open-source Stochastic PArallel Rarefied-gas Time-accurate Analyzer code, which enables Cartesian grid adaption and efficient parallelization, is utilized for the rough-plate flow simulations. Flowfield analysis reveals that the local patterns inside the roughness modules evolve starting from closed (two vortices) via transitional ultimately to open (one vortex) by an increase in h, with co-existing shrinkage of high-density zones and attenuation of density peaks. The surface quantities are significantly influenced by the flowfield characteristics, and a local association between the peak heat flux and the peak pressure is identified. Non-dimensional peak heating and pressure correlation laws for the local peak heat flux and pressure coefficients in terms of two length-scale transformations are proposed, enabling the capture of local heating and pressure extrema on rough plates with varying h and RN conditions under different Ma∞, Re∞, and T∞ parameter values. The peak heat flux and pressure coefficients can be described by analogous correlating equations expressed by first-order-polynomial or power functions. An increase in the rarefaction degree (Kn∞) deviating from the near-continuum regime causes the correlation laws to fail.