An Investigation Of Initial Shock Cell Formation In Turbulent Coanda Wall Jets

Turbulent Coanda wall jets are present in a multitude of applications.(1) Their obvious advantages for flow deflection are often outweighed by disadvantages related to the increased noise levels associated with such jets. Better predictions of Coanda jet noise would allow the Coanda effect to be more widely applied, and its potential to be fully realized. This paper applies the method of characteristics to a steady two-dimensional axisymmetric supersonic flow in order to determine the location of the first shock cell downstream of the nozzle. This phenomenon has previously been found to be particularly important in determining both the OASPL and peak frequency of the broadband high-frequency Shock-Associated Noise (BBSAN) emitted by a given jet configuration.(10, 20) The current work has also illuminated the relationship between cell location and flow characteristics, and thus the effect of jet operating conditions on BBSAN can now be determined.(11) The relationship between cell location and jet breakaway is also under investigation. Predictions are compared with experimental results obtained using flow visualization techniques. This work is in the process of being extended so that the Rankine-Hugoniot conditions can be used to predict the shock cell structure (and thus the BBSAN) along the entire jet.(22)