An experimental investigation on the isoenergetic supersonic cooling films subjected to different ratios of static pressure

Abstract

Ratio of static pressure (RSP) is a critical factor affecting the development of supersonic cooling film flow field. To give a good account of flow characteristics and physical mechanisms on the influences of RSPs, experiments are conducted employing the nanoparticle planar laser scattering (NPLS) and particle-image velocimetry (PIV) techniques. A supersonic cooling film is tangentially injected at a Mach number of Maj=2 into a laminar boundary layer at a mainstream Mach number of Ma∞=3 with different RSP cases. The flow field is divided into four sections: the wake region, the potential core region, the wall-jet region, and the fully developed turbulent boundary layer region. The velocity profile extracted at the fully developed turbulent boundary layer region is proved to be consistent with the theoretical composite profile. Moreover, a new criterion that distinguishes the specific position of the impingement point where the mixing layer approaches the bottom boundary layer is proposed based on the distribution of principal strain rate of the mean velocity field. The analysis of turbulent structures finds that the K–H vortex structures are sensitive to RSPs, and more broken vortices generated when the two fluids mix. The intensity of wave structures is depicted in the synthetic schlieren images when subjected to different RSPs. In addition, the turbulent characteristics show a weaker mixing process with increased RSP, indicating a prolonging in the effective cooling length. Furthermore, the disturbance at the slot and variations of velocity gradient downstream are addressed and analyzed to reveal the physical mechanisms for the mixing process on RSP differences.