Stability of the Rotating-Disk Boundary Layer: Roughness Effects and Beyond P. J. Thomas, A. J. Cooper, M. Özkan, S.J. Garrett
Fluid Dynamics Research Centre, School of Engineering, University of Warwick, Coventry CV4 7AL, UK
Department of Engineering, University of Leicester, University Road, Leicester LE1 7RH, UK Department of Mechanical Engineering, Bilecik Seyh Edebali University Bilecik, Bilecik, Turkey
Abstract:
Results of our computations [1-3] investigating the effects of surface roughness on the stability of the boundary-layer flow over a rotating disk will be summarized. The results reveal stabilising, that is energetically beneficial, effects on the dominant instability mode responsible for transition over rotating disks. This result is qualitatively consistent with the measurements in Ref. [4] which show drag reduction of up to 15% for disks with roughness patterns similar to those studied computationally in Refs. [1-2]. The agreement suggests that, in the long-term, our computational methods may enable the design of energetically optimized surface roughness for laminar-flow control in the applied context of new drag-reduction techniques in, for instance, aeronautics. Our results [1-3] for rough disks will be briefly compared to corresponding computational data by other authors who studied transition over rotating speed-modulated disks, rotating disks with compliant surfaces and rigid disks spinning in non-Newtonian liquids. The goal of this comparison is to highlight some qualitative similarities of the results for all these different scenarios.
References:
[1] Cooper et al. 2015 Phys. Fluids. 27, 014107. [2] Garrtett, S.J. et al. 2016 Phys. Fluids. 28, 014104.
[3] Özkan, M., J. et al. 2017, Eng. Appl. Comp. Fluid Mech. 11, 142-158. [4] Watanabe et al. Journal of Environment and Engineering, 2, 97-107.
[1] Cooper, A.J., Harris, J.H., Garrett, S.J., Özkan, M. & Thomas, P.J. 2015 The effects of anisotropic and isotropic roughness on the convective stability of the rotating-disk boundary layer, Phys. Fluids. 27, 014107.
[2] Garrtett, S.J., Cooper, A.J., Harris, J.H., Özkan, M., Segalini, A. & Thomas, P.J. 2016 On the stability of von Kármán rotating-disk boundary layers with radial anisotropic surface roughness, Phys. Fluids. 28, 014104.
[3] Özkan, M., J., Thomas, P.J., Cooper, A.J., Garrett, S.J. 2017 Comparison of the Effects of Surface Roughness and Confinement on Rotor-Stator Cavity Flow, Eng. Appl. Comp. Fluid Mech. 11, 142-158.
[4] Watanabe K., Budiarso, ?, Ogata, S., Uemura, K. 2007, Drag reduction of an enclosed disk with fine spiral grooves, Journal of Environment and Engineering, 2, 97-107.
