Effect of freestream turbulence on roughness-induced crossflow instability

Hosseini, Seyed Mohammd, 1985- (author): KTH,Stabilitet, Transition, Kontroll,Linné Flow Center, FLOW

Hanifi, Ardeshir (author): KTH,Stabilitet, Transition, Kontroll,Linné Flow Center, FLOW,FOI, Sweden

Henningson, Dan (author): KTH,Stabilitet, Transition, Kontroll,Linné Flow Center, FLOW

(creator_code:org_t)

Abstract Subject headings

The effect of freestream turbulence on generation and breakdown of crossflow disturbances over a swept wing is investigated through direct numerical simu- lations. The setup of simulations follows the experiments performed by Downs et al. which were conducted at a very low freestream turbulence level. The stationary cross flow vortices are generated by a row of uniformly distributed roughness elements. Here, the isotropic freestream turbulence are numerically generated through separate simulations. The generated freestream fields are then added to the inflow boundary condition for simulation of flow over the swept wing. Different levels of freestream turbulence and roughness heights are considered. It was observed that low freestream turbulence level could play a major role in triggering transition of the flow dominated by stationary cross- flow vortices. Similar to the observations in the experiment, increasing the turbulence level moved the transition location further upstream. Moreover, it was found that slight increment in the height of critically spaced roughness elements had an stabilizing effect and delayed transition to turbulence. The ob- servations made in the present study may explain the counter-intuitive results of the recent flight experiment by Saric et al. (2015), where transition occurred further downstream on the wing model with painted surface compared to the model with polished surface.

By the author/editor: Hosseini, Seyed ...; Hanifi, Ardeshir; Henningson, Dan

About the subject

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