The present study investigates the influence of compressibility, characterized by the rotational Mach number, on flow dynamics and heat transfer within a rotor–stator cavity with axial throughflow. Such configurations are relevant to high-speed generators and secondary air systems of gas turbines, where the tip Mach number can exceed 0.8 at high rotational speeds. Highly resolved large-eddy simulations of the compressible Navier–Stokes equations are performed for a fixed rotational Reynolds number of 3.8×104 and an axial throughflow-to-rotational speed ratio of 0.0333, while varying the Mach number from 0.293–0.889 to isolate compressibility effects. The results reveal an increase in radial and azimuthal velocity gradients with increasing Mach number, particularly within the rotor boundary layer, leading to enhanced turbulent kinetic energy production and dissipation rate. For the higher Mach number case, the mean and turbulent dissipation rates increase by approximately 26% and 28%, respectively, while the local viscous heating rate rises by nearly 30% compared to the lowest case. This increase in dissipation rate raises the wall temperature at higher Mach numbers and consequently increases the dynamic viscosity, thereby reducing the rotor Nusselt number by about 6%. The computed windage losses also exhibit a 22% increase between the lowest and highest Mach number cases. A thermodynamic feedback mechanism is identified, in which viscous heating elevates the local temperature and viscosity, reinforcing wall shear and dissipation. These findings demonstrate that even in subsonic regimes, compressibility induces significant thermo-viscous coupling that alters both momentum and energy transport within rotating enclosures. Hence, compressibility effects need to be accounted for in the design of efficient high-speed rotating machinery.
Saini et al. (Wed,) studied this question.