Aerodynamic Interaction Between an Incoming Vortex and Tip Leakage Flow in a Turbine Cascade

Abstract

In turbines, secondary vortices and tip leakage vortices form in the blade passage and interact with each other. In order to understand the flow physics of this vortices interaction, the effects of incoming vortex on the downstream tip leakage flow are investigated by experimental, numerical, and analytical methods. In the experiment, a swirl generator was used upstream of a linear turbine cascade to generate the incoming vortex, which could interact with the downstream tip leakage vortex (TLV). The swirl generator was located at ten different pitchwise locations to simulate the quasi-steady effects. In the numerical study, a Rankine-like vortex was defined at the inlet of the computational domain to simulate the incoming swirling vortex (SV). The effects of the directions of the incoming vortices were investigated. In the case of a positive incoming SV, which has a large vorticity vector in the same direction as that of the TLV, the vortex mixes with the TLV to form one major vortex near the casing as it transports downstream. This vortices interaction reduces the loss by increasing the streamwise momentum within the TLV core. However, the negative incoming SV has little effects on the TLV and the loss. As the negative incoming SV transports downstream, it travels away from the TLV and two vortices can be identified near the casing. A triple-vortices-interaction kinetic model is used to explain the flow physics of vortex interaction, and a one-dimensional mixing analytical model are proposed to explain the loss mechanism.