Effects of jet installation on screeching tone generation

This study investigates how a flat plate affects the generation of axisymmetric A1 and A2 screech modes in an under-expanded supersonic jet. The plate, positioned parallel to the nozzle axis, is large enough to disregard edge effects. By conducting acoustic measurements in the jet’s far field under various flow conditions, it was found that when the plate distance (H) is equal to or less than one nozzle diameter (D), it significantly alters the modes’ typical behavior. Specifically, it reduces the range of jet Mach numbers supporting A2 mode. Additionally, when the distance between the jet and plate is less than 0.85 diameter, mode A2 disappears and mode A1 extends into flow conditions where A2 is usually dominant. To investigate this, schlieren measurements are used to assess whether changes in the structure of the shock-cells are related to the different behavior of A1 and A2 screech modes. To get a more complete view of the physical phenomenon, RANS simulations are carried out to assess whether what is found experimentally also occurs numerically.