A Fundamental Viscous Flow Study to Understand a Separation Control Mechanism

Abstract Computational analyses aimed at the viscous sublayer (VSL) separation-hindering nature of boundary-layer embedded flow control ridges (FCRs), such as sharkskin denticles, are absent. Parametrically quantifying the effects of a single FCR geometry on local mass flow recovery is a key building block for eventual broader studies. Pursuant to this, a single one-dimensional (1D) FCR was placed in a Couette flow, rendering the study applicable to both laminar flows and the VSL of a turbulent flow. Various degrees of separation were simulated by controlling upper wall velocity relative to the adverse pressure gradient (APG) to achieve a range of positive and negative initial mass flow rates. Many 1D FCR geometries were studied with angles from 15 deg to 85 deg and flow blockage ratios from 0.05 to 0.85. It was shown that the antiflow-reversal abilities of the FCR in a viscous flow are independent of Reynolds number and Euler number. However, the effectiveness of the FCR and its optimal design are strongly dependent on a new dimensionless parameter, the Strasser number. The outcome is that we have markedly reduced the geometric permutational space necessary to be addressed by future, more geometrically rigorous studies.