The main objective of this study is to examine the noise produced by an orifice jet when it impacts various corrugated geometries at different nozzle pressure ratios. A comparison is made between the corrugated geometries and a flat plate. The study considers a standoff distance of 3.5 times the jet diameter. The analysis focuses on identifying different tones and their harmonics that result from the feedback loops between the orifice exit and the plates. To gain insights into the feedback processes responsible for mode generation and their behavior, statistical post processing and modal decomposition of schlieren images are employed. The study also investigates the locations of dominant modes using amplitude and phase plots obtained through dynamic mode decomposition. The flow field within the semi-circular corrugations is analyzed using large eddy simulation techniques. Directivity studies are conducted across different nozzle pressure ratios (NPR) of 1.2, 1.8, 3, 4, and 4.8 for all the plates. The impact of corrugations on crackle noise is assessed by analyzing the skewness value of acoustic pressure data. Furthermore, the study addresses an optimization problem using the response surface methodology. The goal is to determine the flow and geometric parameters that minimize the overall sound pressure level. Initially, the two-factor central composite method is utilized to find the optimal nozzle pressure ratio and standoff distance for minimizing the sound pressure level. Subsequently, the three-factor central composite method is employed, incorporating the pitch length of the impinging plate as a design variable along with standoff distance and nozzle pressure ratio, to further minimize the sound pressure level. Experimental tests are conducted based on the designed matrix, and the sound pressure level is calculated using the obtained acoustic pressure data. The results are then optimized, and a second-order quadratic model is developed to predict the response for different input parameters.
Other Information: A part of this work is published in the Journal of Vibration and Acoustics, ASME. DOI is :http://dx.doi.org/10.1115/1.4054254. The work related to the crackle noise is published in the Internoiseconference, Glasgow.
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