Shut-Off Head Prediction in Single Stage Centrifugal Pumps

Abstract

The prediction of the performance characteristic in centrifugal pumps at flow rates other than the design flow is of high relevance but relatively uncertain. In the present study, an evaluation of the existing shut-off head prediction methods and an assessment of both, the empirical approach and the numerical simulation are performed. For this purpose, after a review of existing methodologies, the empirical predictions are compared against available statistical data for single stage volute pumps. The CFD study, performed for 3 different single stage volute pumps with specific speeds between nq = 12 and nq = 54 is quantitatively compared against available model test data, which were obtained using precision manufactured hydraulic components. Several empirical methods from open literature have been reviewed for the shut-off head prediction. An overview of different prediction methods has been presented by Dyson [1], these and an empirical correlation proposed by Guelich have been compared against available data. The numerical study at shut-off condition requires a full-pump geometry, which also includes long suction and pressure pipes. Unlike several analyses present in the literature (Dyson & Texeira [2], Benigni et al. [3], Liu et al. [4]), which consider the internal leakage flow in the outlet boundary, the shut-off condition is obtained by imposing walls at inlet and outlet boundaries, but leakage flow through the gap between casing and impeller which is essential for the recirculation of the flow is numerically modeled. Because of the unsteady nature of the pressure in the pump volute, a transient simulation is performed and the predicted shut-off head is the average of the whole range of results for a minimum of 10 impeller revolutions.