Experimental and numerical study of squealer tip flow field considering relative casing motion

The tip leakage flow is an important factor that causes the internal loss of the aeroengine turbine. The squealer tip can effectively control the tip leakage flow. Accurate understanding of the tip leakage flow structures in the cavity contributes to the understanding of the flow characteristics of the leakage flow and the physical mechanism of the leakage loss. In order to study the change of flow structures in the tip cavity when considering the relative casing motion and the effect on the leakage flow, a low-speed turbine cascade testing facility is built that can model the relative casing motion. The test facility can study factors such as blade profiles, different tip structures, and different incidence angles. A visual testing method of Particle Image Velocimetry (PIV) is proposed to obtain the complex flow structures within the tip cavity. The measurement method developed can obtain the complex flow field and successfully capture the scraping vortex in the tip cavity. In addition, the evolution of the flow structures in the tip cavity is analyzed with the help of numerical results under different casing motion conditions. An aero-labyrinth like sealing effect is formed by the scraping vortex. This sealing effect reduces the equivalent flow area at the gap outlet and diminishes the discharge coefficient of the squealer tip, therefore finally achieving the purpose of controlling the leakage flow. Choosing the appropriate blade load distribution and cavity geometry can improve the clogging effect and expand the control range of the scraping vortex. Mid-loaded blades have a more obvious effect on controlling the leakage flow when using the cavity tip. The tip gap height affects the generation and evolution of the flow structure in the tip cavity by which changes the effect of controlling the leakage flow.