Influence of a Tip Blowing Casing Treatment on the Stator Flow

Abstract

In modern turbo machines, the stage loading in compressors is significantly increased to meet the power demand with enhanced efficiency. Casing treatments have proven to be effective in preventing stability issues that occur due to the high stage loading. Most numerical casing treatment studies cover only the rotor and neglect the stage behavior. However, the stage behavior is obviously impacted and the stator has to be redesigned if the rotor is treated.The present study investigates a 1.5 stage transonic and tip critical compressor. The stage was designed without a casing treatment. However, using a casing treatment now widely extend the operating range of the rotor, thus increasing its overall total pressure ratio. Therefore, the stator has also to cover a broader operating range. As the stator was not designed for this degree of throttling, surge is now triggered by the stator. In order to redesign the stator, the authors investigate the baseline stator to identify the reasons for failure and draw conclusions regarding the influence of the tip blowing casing treatment on the stator.The numerical investigation of the combined rotor and stator shows, on the one hand, the influence of the connecting interface on the compressor characteristic and the flow field. A model with a mixing plane interface is compared to a setup with a sliding plane interface. On the other hand, while using the circumferentially discrete interface, the influence of the tip blowing on the downstream stator is analyzed in depth. NomenclatureCT = casing treatment CTDI = CT duct inlet CTDO = CT duct outlet DP = design point operating condition MP = mixing plane NS = near stall operating condition PE = peak efficiency operating condition SC = smooth casing SM = stall margin SP = sliding plane TBCT = recirculating tip blowing casing treatment (U)RANS = (unsteady) Reynolds averaged Navier-Stokes (V)IGV = (variable) inlet guide vane [m 2 ] = flow area [J/(kgK)] = specific gas constant A.; Guinet, C.; Hupfer, A.; Schrapp, H.; Gümmer2 [K] = static temperature [m/s] = absolute flow velocity ̇ [kg/s] = mass flow ̇ [-] = corrected mass flow rate [Pa] = static pressure at stator inlet , [Pa] = total pressure at stator inlet , [Pa] = total pressure at stator exit , , [Pa] = total isentropic pressure at stator exit r [-] = radius, radial direction [m/s] = circumferential flow velocity [m/s] = velocity [m/s] = relative flow velocity x [-] = axial direction y + [-] = non-dimensional wall distance [°] = absolute flow angle [°] = absolute flow angle at stator leading edge − _ [°] = absolute flow angle of the SC-MP configuration at design point [°] = absolute flow angle at stator outlet [°] = relative flow angle [°] = relative flow angle at rotor inlet − _[°] = relative flow angle of the SC-MP configuration at design point [-] = circumferential direction [-] = total pressure ratio [-] = loss parameter − _[-] = loss of the SC-MP configuration at design point