Computation of pressure pulsations in the outlet devise of screw-centrifugal pump with acoustic-vortex method

Studies in the problem of the liquid rocket engine reliability and service life increasing have a great importance. In this paper the key objective is to reduce the hydrodynamic vibration of screw-centrifugal pump, which is caused by pressure pulsations in the pump flow path. Due to the uneven impeller outlet flow pressure pulsations occur at a blade passing frequency and its harmonics. These oscillations cause dynamic loads on the pump housing, causing it to vibrate, so the calculation of the amplitudes of pressure pulsations in a screw-centrifugal pump at an early development stage is an urgent task. In determining the pressure pulsation generated by three-dimensional vortex flow in the screw-centrifugal pump one must take account of their dual nature. Inhomogeneous distribution of the flow at the outlet of the impeller generates acoustic disturbances that spread with the speed of sound in the working fluid. At the same time there are eddy disturbances that convert with the main flow. Vortex fluctuations in the parameters of the main flow is called “pseudosound” or vortex mode. The oscillation amplitude of the vortex mode can be determined with the unsteady flow computation using the incompressible fluid model. However, this model is not applicable for acoustic fluctuations spreading in the pressure pipe. In this article a three-dimensional acoustic-vortex method is developing for calculation the pressure pulsations, which provides the possibility of determining the acoustic mode amplitude. There is outlined derivation of acoustic vortex equations and example of calculation the amplitude of the pressure pulsations at the screw-centrifugal pump outlet of liquid rocket engine. The amplitude of pressure pulsations at the first harmonic of blade passing frequency varies depending on the flow rate through the pump. Application boundary condition in the form of acoustic impedance for the long outlet pipe leads to an underestimation of the amplitude in comparison with known experimental values.