Experimental study on the aerodynamic performance of variable geometry low-pressure turbine adjustable guide vanes

An annular cascade testing rig of a variable-geometry low-pressure turbine with a large expansion angle was designed and built, combining a five-hole probe, a surface static pressure test system, and a PIV(Particle Image Velocimetry) measurement system. The effects of exit Mach numbers (0.2, 0.3, 0.4), turning angles (-1.5 degrees, 0 degrees, 3 degrees), and adjustable device diameters (30 mm, 40 mm) on turbine cascade aerodynamic performance were experimentally investigated. Numerical simulations were also carried out to gain more insight into the flow fundamentals. Results show that the endwall clearance and the adjustable device significantly influence the flow field, with leakage flows before, after, and around the disc. The leakage vortex and passage vortex formation resulted in two high-loss regions in the shroud and hub endwall regions. The aerodynamic loss structures at the exit section were similar at different Mach numbers and varied considerably at different turning angles. Besides, a larger area of the adjustable device (d = 40 mm) was found to reduce the leakage loss caused by upper and lower clearance leakage flows and inhibit the development of secondary flows, resulting in a more straightforward secondary flow structure and a smaller influence range. Quantitatively, the adjustable device with a diameter of 40 mm could decrease the average total pressure loss coefficients by 11.5%, 16.6%, and 6.3% at three turning angles (-1.5 degrees, 0 degrees, 3 degrees), respectively, compare to the adjustable device with a diameter of 30 mm.