Transonic Dimples

An experimental study of the flow structures formed at transonic speeds over dimpled surfaces

Master thesis (2021)

Authors

E. Claro Dittrich Aerospace Engineering

Contributors

B.W. van Oudheusden Aerodynamics - Aerospace Engineering (supervisor 1)
F.F.J. Schrijer Aerodynamics - Aerospace Engineering (supervisor 2)
O.W.G. van Campenhout Aerodynamics - Aerospace Engineering (coach)
Faculty
Aerospace Engineering
Copyright: © 2021 Eric Claro Dittrich
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Published Date

08-02-2021

Language

English

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Faculty

Aerospace Engineering

Abstract

Dimples are shallow surface indentations that have been recently considered as a passive viscous drag reducing technique for turbulent boundary layers. Studies so far were limited to incompressible low-Re flows and display little consensus on whether dimples can actually produce net improvements in total drag. Conversely, dimple geometry can be regarded as the inverse of transonic bumps, a matured wave drag reduction. In light of this, this thesis sets off to analyse the flow structures that arise over dimples at transonic speeds provide, serving as an initial assessment of their wave drag reducing potential.

A transonic flow was reproduced experimentally using an asymmetric nozzle. Then, the performance of five dimple designs was evaluated against the criteria adopted for transonic bumps. Measurements included Schlieren, surface pressure and PIV. Results reveal that small spherical dents seem to produce spanwise excitations that subdue the detrimental effects of expansion fans formed at their edges, and ultimately allow for a higher momentum retention across the interaction.