  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.
