Scarfing and scalloping effects on lobed forced mixer at low-speed conditions

This paper presents the findings on two aspects of geometric modification t o a lobed forced miser namely scarfing and scalloping Scarfing the lobes wa s achieved by alternately extending and cutting back the lobes at the trail ing edge, and scalloping the lobes was achieved by removing a certain perce ntage of the straight sidewall area in the penetration region. Both modific ations were intended to enhance the strength of streamwise circulation with out causing any undesirable consequences, such as flow separation at the lo be troughs. Tests were conducted over a range of low-speed subsonic how con ditions (maximum Mach number of similar to 0.07) by using a three-hole pres sure probe and a laser Doppler anemometer, The results showed that scarfing the lobes would be more beneficial than scalloping the lobes if the same l evel of enhancement for the streamwise circulation were to be achieved. Fur thermore, for lobes at the same penetration angle and at the same percentag e of surface area change, streamwise circulation generated at the trailing edge was actually higher (similar to 15%) for the scarfed lobes than for th e scalloped lobes. However, the associated mixing and boundary-layer losses incurred by the scarfed lobes would be higher than those of the scalloped lobes. Finally, the combined effects of the two modifications on a lobed mi ser, that is, a scarfed and scalloped miser, however, did not promote ally significant streamwise-circulation enhancement.