A system for time-fluctuating flow rate measurements in a single-blade pump circuit

Abstract

Commonly used flow rate measurement systems provide an accurate and stable output value of the quasi-stationary flow rate. In some pump types as e.g. single-blade pumps significant flow rate fluctuations may occur even in steady operation points due to rotor-stator interaction. For the analysis of the time-resolved flow rate a new measurement and evaluation method is presented based on an electromagnetic flow meter. Internal averaging of the flow meter is deactivated and the raw signal is evaluated directly with a sampling rate of 3 kHz. With ensemble-averaging in combination with an impeller position detection, interfering signals acting on the time-resolved measurement signal are filtered out. Accompanying numerical simulations of the pump flow circuit are carried out with a 1D method of characteristics and validated against well-established time-resolved pressure measurements of the pump flow. Experiment and simulation show a resembling trend of pressure as well as flow rate fluctuations over the entire operation range of the pump. Thus, by the combined utilisation of measurement and simulation technique, we assure the validity of the ensemble-averaged flow rate fluctuation results. We find that the flow rate fluctuations show a consistent phase shift to the pressure fluctuations that increases towards overload. The flow rate amplitude is an order of magnitude smaller than the amplitude of the pressure fluctuations.