Experimental and numerical calibration in a critical flow venturi of close to sonic flow

Abstract

This work introduces a new study in discharge coefficient performance in CFV when the throat flow is close to sonic regime Ma ≈ 1 and the throat strangulation is not fully developed. Thus, two CFV of 0,56 and 2,24 mm diameter were experimentally calibrated by applying the volume averaging method; experimental calibration allowed to estimate Cd and measure uncertainty, for 2,24 mm diameter Cd is 7,34% higher than for 0,56 mm diameter when Ma global is 7,30 % higher. Based on experimental calibration results and CFV geometries, numerical experiments were realized to explain how Ma ≈ 1 flow deviates Cd from the theoretical value, concluding compressibility affects thickness scrolling relation since it is 35,92% smaller for 2,24 mm diameter than 0,56 mm, giving a better approximation for Cd to the theoretical value for this throat diameter. Finally, numerical Cd models were obtained to evaluate the deviation these flow conditions produce in respect of empirical and numerical models, finding the numerical model's maximum error is 6,68% and the empirical model's maximum error is 1,64% under identical stagnation conditions.