Investigation of the Calmed Region Behind a Turbulent Spot

Abstract

Measurements are presented of the calmed region behind triggered wave packets and turbulent spots under a controlled diffusion adverse pressure gradient in a wind tunnel. Similar measurements are also presented from the stator blades of an axial flow compressor, where turbulent spots are induced by the passing of rotor wakes. The purpose is to gain an appreciation of turbulent spot behavior under a strong adverse pressure gradient as a foundation for the more accurate modeling of spots and their environment in predictions of transitional boundary layer flows. Under an adverse pressure gradient the calmed region behind the spot is extensive; its interaction with the surrounding boundary layer is complex and is dependent on whether the surrounding natural boundary layer is laminar or turbulent. Some insights are gleaned concerning the behavior of the calmed region, which will subsequently be used in attempts to model the calmed region. Although these fundamental investigations of the calmed region have been extensive, much remains to be understood.

The Influence of Wake-Wake Interactions on Loss Fluctuations of a Downstream Axial Compressor Blade Row

“…These values are low compared with those typical of aircraft gas turbine engine operation. as reported by Hourmouziadis (1989) and Mayle (1991); they are also generally lower than those in the experimental studies of Halstead et al (1995). The test compressor was nevertheless operating above the critical Reynolds number range where laminar separation stasis to cause a significant increase in blade losses (see Walker.…”

“…The recent experiments of Halstead et al (1995), Solomon and Walker (1995a,b) and Solomon (1996) have indicated that transitional flow may cover as much as 70% of compressor airfoil suction surfaces and 50% of turbine airfoil suction surfaces in the presence of periodic wake disturbances. The periodic transitional or turbulent flow strips generated by wake disturbances are followed by regions of relaxing laminar flow with a shear stress higher than steady laminar flow levels.…”

Streamwise Interfaces of an Isolated Turbulent Region in a Laminar Boundary Layer

“…In order to investigate the interface between the turbulent region and the laminar region, it is necessary to define the turbulent region. In the previous studies (Hedley et al (17) , Gad-el-hak et al (5) , Wygnanski et al (18) , Gostelow et al (11) , and Chong et al (19) ), many methods have been proposed. In this study, the random component of the streamwise velocity signal is used to define a turbulent region.…”

“…Further, the trailing or calmed region of the spot has been investigated by many researchers, and the presence of higher momentum fluid near the wall was revealed (e.g. Antonia et al (10) , Gostelow et al (11) , and Chong et al (12) ). In addition, this characteristic was captured by a theoretical model that was proposed by Brown et al (13) .…”

Boundary layer development in multi-stage low pressure turbines

“…A compilation of these findings are provided in Gostelow, Melwani, and Walker (1995). Also, comprehensive investigations have focused on the calmed region (Seifert, 1995, andGostelow et al, 1996).…”