Matched pressure injections through diamond-shaped injectors were applied to a Mach 2.5 supersonic crossflow, and penetration and mixing characteristics of the injected plume were experimentally investigated. In determining injection conditions, the effective backpressure to the injectant plume was assumed to be equal to pressure on a solid-wedge surface with the identical wedge angle to the injector orifice at a designed flow rate. Both subsonic and supersonic injections were introduced to attain the required low plume pressure at a high supply pressure, ensuring a stable injectant flow rate in reacting flows with high backpressures. The matched pressure injections through the diamond-shaped orifices resulted in little jet-airflow interaction. With the supersonic injection, the plume floated from the injection wall, and the best penetration height was attained, whereas the benefit of matched pressure supersonic injection over the matched pressure sonic injection was not as remarkable as the circular injector case. The penetration height increased at an overexpanded condition, while the maximum mass fraction decay was insensitive to the injection pressure. In the case with the subsonic injection, the plume shape was similar to a pillar, and a certain fraction of the injectant was left within the boundary layer region. The penetration height as well as the maximum mass fraction decay was found to be insensitive to the injection pressure.
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