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Rongfei Yang,Hao Wang,Dongdong Zhong,Ning Ge 한국항공우주학회 2023 International Journal of Aeronautical and Space Sc Vol.24 No.3
Dynamic hump is an active control method, which has been proved to be able to suppress laminar flow separation on the suction surface of high-loaded low-pressure turbine (LPT) blades at low Reynolds number (Re). This paper further discusses the effectiveness of dynamic hump with different parameters for flow separation control. The Pak-B cascade working at Re = 25,000 was selected as the research object, and a small-sized two-dimensional dynamic hump designed in a half-sinusoidal configuration was placed just upstream of the peak velocity point on the suction surface. At inlet free-stream turbulence intensity (FSTI or Tu) of 1.5%, the controlled cascade loss and flow mechanism under different hump-oscillating frequency and amplitude was numerically analyzed in detail. The results show that the development characteristics of vortices/separation bubbles attached to the suction surface of the blade were significantly changed under the influence of the dynamic hump, which contributed to the variations of cascade loss accordingly. When the separation bubble at the trailing edge of the hump was forced to form shedding vortices, the large-sized separation bubble on suction surface of uncontrolled cascade was replaced by small-sized vortices with a certain spacing, thus inhibited the flow separation. The increase in amplitude and frequency of hump promote the formation of shedding vortices at the trailing edge of the hump. The optimal amplitude should be slightly less than the local boundary layer thickness at the position of hump on the uncontrolled cascade. Under the optimal hump amplitude, the effective hump-oscillating frequency is 50–250 Hz, which is approximately 0.5–2.7 times of the characteristic frequency defined by blade exit velocity and the distance between the hump trailing edge and the blade trailing edge. When inlet FSTI of the controlled cascade is reduced from 1.5 to 0.08%, the profile loss is approximately unchanged due to the same characteristics of the boundary layer in the hump region and upstream.
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