Tip Vortex Back Flow Cavitation and Suppression in High Speed Pump Inducers

High speed and high performance inducers in turbo-machinery are critical components for the success of the overall system design. It is well known that cavitating flows can cause increased vibration and noise and create damage. The combination of high speed and low inlet pressures give rise to the possibility of the fluid's cavitating within the inducer flow field, especially at the inducer blade tip. At this location, fluid leaks around from the higher pressure side of the inducer blade to the lower pressure suction side, creating back flow and low pressure vortical structures. This type of cavitation can become unstable at certain operating conditions and be a source of high frequency pressure fluctuations that can stress the inducer or components in the flow field.;Experiments have been conducted on two inducers of different geometries to identify the frequency response cavitation signature and the operating conditions that promote the instability, which occurs at a frequency that is higher than the rotational frequency of the inducer. A new device called the tip vortex suppressor, TVS, was then tested with an operating inducer. The device injects high velocity flow at the leading edge where the back flow and tip vortex are being created, with the aim of reducing or eliminating the cavitation instabilities. To help in identifying the mechanism of the instability, high speed video was taken during operation at two different angles with and without the TVS installed. A computational fluid dynamics simulation of the inducer flow field was performed to explore and verify the experiment findings. In addition, a two-dimensional linear stability model was created to be able to predict cavitation signatures for designs without the need for costly experimental testing or computationally intensive simulations.;Analysis of the data shows that both inducers experience similar distinctive response signatures caused by the back flow cavitation. The signature is not present for any tested conditions with the TVS device installed and flowing, demonstrating it promise for practical systems. The numerical simulation and the 2D stability model both correctly predict the higher order cavitation responses, along with the ability of the TVS to suppress them.