Effect of optimal slot location on the performance of cascades of blades

Abstract

Overloaded blades and lower solidities are two main characteristics of modern gas engines to reach lower specific fuel consumption and weight to thrust ratio. Hence, flow optimization methods are employed to maximize the performance. Slot treatment on blades is considered as a potential method to stand against the boundary layer separation for this issue. In the present study, the different locations of passive flow control with the slot along the compressor blade chord are simulated at four angles of attack (α), ranging from 10.93° to 28.93°. The purpose of this study is to discover the underlying reason in obtaining the best slot location, regarding the blade turning angle and total loss coefficient, in every tested inflow angle. Based on the results, the slot jet shows its utmost performance in eliminating the trailing edge separation when it is located upstream of the separation lines in the mid-span. The best slot location is able to improve the turning angle and the total loss coefficient up to 16.41% and 16.47% at 26.93°, respectively. The synthetic slot jet confines the growth of corner vortices and increases the turning angle near end walls up to 4°. In addition, the slot treatment pushes the backflow region over the suction surface up to 10% of the span toward the side walls. The importance of choosing the slot location decreases with an increase in inflow angle. However, the effect of slot locations on the performance in low angles is still considerable. With the tested blade geometry, the slotted profile in locations between 0.5 and 0.8 of axial chord length indicates a promising blade performance either in low or high angles. The slot treatment weakens the flow upstream of its location which is in contradiction with previous investigations. Two separation bubbles near the leading edge in the baseline profile have a greater size of about 2% of the blade chord for the slotted case.