Direct simulation Monte Carlo computations and experiments on leading-edge separation in rarefied hypersonic flow

Abstract

A comprehensive study of the fundamental characteristics of leading-edge separation in rarefied hypersonic flows is undertaken and its salient features are elucidated. Separation of a boundary layer undergoing strong expansion is typical in many practical hypersonic applications such as base flows of re-entry vehicles and flows over deflected control surfaces. Boundary layer growth under such conditions is influenced by effects of rarefaction and thermal non-equilibrium, thereby differing significantly from the conventional no-slip Blasius type. A leading-edge separation configuration presents a fundamental case for studying the characteristics of such a flow separation but with minimal influence from a pre-existing boundary layer. In this work, direct simulation Monte Carlo computations have been performed to investigate flow separation and reattachment in a low-density hypersonic flow over such a configuration. Distinct features of leading-edge flow, limited boundary layer growth, separation, shear layer, flow structure in the recirculation region and reattachment are all explained in detail. The fully numerical shear layer profile after separation is compared against a semi-theoretical profile, which is obtained using the numerical separation profile as the initial condition on existing theoretical concepts of shear layer analysis based on continuum flow separation. Experimental studies have been carried out to determine the surface heat flux using thin-film gauges and computations showed good agreement with the experimental data. Flow visualisation experiments using the non-intrusive planar laser-induced fluorescence technique have been performed to image the fluorescence of nitric oxide, from which velocity and rotational temperature distributions of the separated flow region are determined.

Shock-induced leading-edge separation in hypersonic flows

“…(2017) and Prakash et al. (2019) concern hypersonic separation for which the isentropic process at reattachment is not valid.…”

“…In recent years, advancements in experimental diagnostics and computations have significantly resolved the flow over the 'tick' configuration. Strong to moderate wall cooling effects, sharp and blunt leading-edge configurations, eddy structures within the primary recirculation flow and slightly downstream displacement of the separation location from the leading edge can be found in the works of Khraibut et al (2017) and Prakash et al (2019). Particularly, the works by Khraibut et al (2017) and Prakash et al (2019) concern hypersonic separation for which the isentropic process at reattachment is not valid.…”

An Exact Dynamic Analysis Method for Shallow Sagged Cables

“…When the flow is rarefied enough, the Monte Carlo method is very efficiency to describe the velocity distribution function, which makes stochastic particle methods suitable for simulating rarefied flows, and the most famous method of them is the Direct simulation Monte Carlo (DSMC) method [14]. It has been developed to maturity and used to simulate complex flows like thermochemical non-equilibrium flows in flow mechanism studies [15,16] and engineering applications [17,18]. However, the efficiency of stochastic particle methods reduces rapidly when the flow becomes nearcontinuum or low-speed.…”