Scale Effects in the Dynamic Transfer Functions for Cavitating Inducers

Abstract

Dynamic transfer functions for two cavitating inducers of the same geometry but different size are presented, compared, and discussed. The transfer functions for each inducer indicate similar trends as the cavitation number is decreased. The nondimensional results for the two sizes are compared with themselves and with theoretical calculations based on the Bubbly Flow Model (reference [2]). All three sets of results compare well and lend further credance to the theoretical model. The best values of the two parameters in the model (K and M) are evaluated and recommended for use in applications.

Numerical Evaluation of Dynamic Transfer Matrix and Unsteady Cavitation Characteristics of an Inducer

“…The velocity vectors show that the flow gets into/out from the cavitating region, typical for bubbly flow cavitation. Figure 10 compares the transfer matrix elements obtained in the present calculations with the original experimental results by Brennen [5] and the correlation given by Rubin [8] based on the same experimental data. Open symbols show the results based on the calculations on the same domain geometry shown in Fig.…”

“…To the author's knowledge, the first introduction of transfer function as well as mass flow gain factor and cavitation compliance was made by Brennen and Acosta [3] in which they were evaluated by quasisteady calculation of blade surface cavitation. They further carried out experiments and the results are reported in [4] and [5]. Since then, several attempts [6], [7] were made to measure the unsteady cavitation characteristics.…”

“…Since then, several attempts [6], [7] were made to measure the unsteady cavitation characteristics. Recently, Rubin [8] re-examined the data of [4] and [5].to obtain better correlation, since the data available is limited perhaps because of the difficulty in the precise measurements of flow rate fluctuation. In addition to the use in POGO analysis, the mass flow gain factor and the cavitation compliance are important in the understanding the flow instabilities such as cavitation surge and rotating cavitation [9].…”

Experimental method for the evaluation of the dynamic transfer matrix using pressure transducers

“…Brennen & Acosta (1976) evaluated the transfer matrix of a cavitating inducer using a quasi-steady calculation of the blade surface cavitation. The first reliable experimental data were obtained by Ng & Brennen (1978) and Brennen, Meissner, Lo, & Hoffman (1982). They initially used Laser Doppler Velocimetry (LDV) for measuring the fluctuating discharge to compute the transfer matrix, and later an electromagnetic flow meter as a supplementary tool.…”

“…They initially used Laser Doppler Velocimetry (LDV) for measuring the fluctuating discharge to compute the transfer matrix, and later an electromagnetic flow meter as a supplementary tool. Rubin (2004) re-examined the data given by Brennen et al (1982) to obtain a better correlation. Stirnemann et al (1987) investigated the transfer matrices of a pump by using a pressure transfer function and admittance to avoid the fluctuating discharge measurement.…”