Highly separated transitional shock-wave/boundary-layer interactions: A spatial modal study

Physics of Fluids, vol. 36

Abstract

At cruise altitudes, the Reynolds number may become sufficiently low to allow a laminar boundary layer to persist on the suction side of a transonic fan blade up to the shock-wave/boundary-layer interaction (SBLI). In such a transitional SBLI with sufficiently large shock-induced separation, a shock oscillation mechanism occurs, with the source at the upstream growth (until a critical length) and natural suppression (through shear layer instabilities) of the separation bubble. The oscillation cycle is characterized by a temporarily vanishing upstream laminar part of the separation bubble. The suppression of this laminar part is accompanied by downstream advection of turbulence and subsequent entrainment into the bulk separation bubble, affecting the reflected shock movement. In order to study the spatial behavior of the mechanism, particle image velocimetry of a highly separated transitional oblique SBLI at Mach 2.3 is conducted in the high speed aerodynamics laboratory of Delft University of Technology. Statistical quantities, including root mean square velocity fluctuations, phase averages, and spatial modes from proper orthogonal decomposition, are investigated. The entrainment strength varies depending on the phase of the oscillation, and the turbulent shear layer is not fully developed. The main growth and shrinking mode of the separation bubble were extracted, which affects the slip line region size and shock position. Secondary modes that affect the shear layer undulation and upstream effects were also extracted. The study provides quantitative analyses of an important shock oscillation type, with the focus on capturing the separation bubble size variation and upstream effects.

Authors 5

1. Philipp L. Nel Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University 1 , Templergraben 55, Aachen 52062,

   RWTH Aachen University, Templergraben 55, Aachen 52062, Germany

2. Anne-Marie Schreyer Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University 1 , Templergraben 55, Aachen 52062,

   RWTH Aachen University, Templergraben 55, Aachen 52062, Germany

3. Ferry F. J. Schrijer

   Delft University of Technology

   Affiliation as printed

   Faculty of Aerospace Engineering, Delft University of Technology 2 , Kluyverweg 1, Delft 2629 HS,

   Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, Delft 2629 HS, the Netherlands

4. B.W. van Oudheusden

   Delft University of Technology

   Affiliation as printed

   Faculty of Aerospace Engineering, Delft University of Technology 2 , Kluyverweg 1, Delft 2629 HS,

   Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, Delft 2629 HS, the Netherlands

5. Marius Swoboda

   Rolls-Royce (Germany)

   Affiliation as printed

   Rolls-Royce Germany Ltd. & Co. KG 3 , Blankenfelde-Mahlow, Brandenburg 15827,

   Rolls-Royce Germany Ltd. & Co. KG, Blankenfelde-Mahlow, Brandenburg 15827, Germany