Mechanism of separation hysteresis in curved compression ramp

TL;DR

This paper investigates the mechanisms behind separation hysteresis in curved compression ramp flows, revealing parameter intervals for stable attachment and separation states, and analyzing the relationships between flow characteristics and shock wave configurations.

Contribution

It introduces a new spatial-related mechanism for understanding separation hysteresis in CCR flows and analyzes the effects of Mach number and wall temperature variations.

Findings

Existence of parameter intervals for stable attachment and separation.

Relationships between aerodynamic characteristics and shock configurations.

Estimation of adverse pressure gradients and boundary layer resistance.

Abstract

A new spatial-related mechanism is proposed to understand separation hysteresis processes in curved compression ramp (CCR) flows discovered recently (Hu et al. Phy. Fluid, 32(11): 113601, 2020). Two separation hystereses, induced by variations of Mach number and wall temperature, are investigated numerically. The two hystereses indicate that there must exist parameter intervals of Mach number and wall temperature, wherein both attachment and separation states can be established stably. The relationships between the aerodynamic characteristics (including wall friction, pressure and heat flux) and the shock wave configurations in this two hystereses are analyzed. Further, the adverse pressure gradient (APG) Isb(x) induced by the upstream separation process and APG Icw(x) induced by the downstream isentropic compression process are estimated by classic theories. The trend of boundary layer APG resistence Ib(x) is evaluated from the spatial distributions of the physical quantities such as the shape factor and the height of the sound velocity line. With the stable conditions of separation and attachment, a self-consistent mechanism is obtained when Isb, Icw and Ib have appropriate spatial distributions.