X Ray Measurements in a Cavitating Centrifugal Pump During Fast Start Ups

Abstract

The startup of rocket engine turbopumps is generally performed in a few seconds or even less. It implies that these pumps reach their nominal operating conditions after a few rotations only. During the startup, the flow evolution within the pump is governed by transient phenomena, based mainly on the flow rate and rotation speed increase. Significant pressure fluctuations, which may result in the development of cavitation, are observed. A centrifugal impeller whose transient behavior during startups has been detailed in a previous publication is considered. Three different cases of fast startups have been identified according the final operating point (Duplaa et al., 2010, “Experimental Study of a Cavitating Centrifugal Pump During Fast StartUps,â€‌ ASME J. Fluids Eng., 132(2), p. 021301). The aim of this paper is to analyze the evolution during the startups of the local amount of vapor in the blade to blade channels of the pump by fast Xray imaging. This technique has enabled to calculate the timeevolution of the fluid density within the pump, which appears to be correlated with pressure timeevolutions. For each investigated startup, Xray measurements have been performed at three different sections of the impeller height. For each investigated startup and section tested, measurements have been performed for several initial positions of the impeller, to estimate the measurement uncertainty, and to obtain records from different beam angles, like in tomography.