Scarfing and Scalloping Effects on Lobed Forced Mixer at Low-Speed Conditions

Abstract

This paper presents the Ž ndings on two aspects of geometric modiŽ cation to a lobed forced mixer, namely scarŽ ng and scalloping. ScarŽ ng the lobes was achieved by alternately extending and cutting back the lobes at the trailing edge, and scalloping the lobeswas achievedby removinga certain percentage of the straight sidewall area in the penetration region.BothmodiŽ cationswere intended to enhance the strength of streamwise circulationwithout causing any undesirable consequences, such as  ow separation at the lobe troughs. Tests were conducted over a range of low-speed subsonic  ow conditions (maximumMach number of » 0:07) by using a three-hole pressure probe and a laser Doppler anemometer. The results showed that scarŽ ng the lobes would be more beneŽ cial than scalloping the lobes if the same level of enhancement for the streamwise circulation were to be achieved. Furthermore, for lobesat the samepenetrationangleandat the samepercentage of surface area change, streamwise circulation generated at the trailing edge was actually higher ( » 15%) for the scarfed lobes than for the 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 modiŽ cations on a lobed mixer, that is, a scarfed and scalloped mixer, however, did not promote any signiŽ cant streamwise-circulation enhancement.