Pressure-Induced Separation of a Laminar Boundary Layer over a Partially-Slip Wall

TL;DR

This study uses direct numerical simulation to analyze how partial-slip walls influence pressure-induced laminar separation bubbles, revealing that increased slip length delays separation, reduces vortex shedding, and results in a less turbulent wake.

Contribution

It introduces a detailed comparison of laminar separation bubbles over partially-slip versus no-slip walls, highlighting the effects of slip length on flow separation and vortex dynamics.

Findings

Increased slip length delays flow separation and reattachment.

Higher slip reduces vortex shedding and turbulence.

Flow self-similarity is maintained despite slip effects.

Abstract

The characteristics of pressure-induced laminar separation bubbles (LSBs) over a partially-slip wall, compared with that over a canonical no-slip wall, are studied using direct numerical simulation. Three cases, two utilizing linear Robin-type slip boundary conditions of differing slip length ($\Lambda$), and one non-slip are compared. For the partial-slip cases, a streamwise distribution of slip profile is employed ensuring smooth transition between no-slip and partial-slip (transition from no-slip to a constant slip length takes 5$\delta$, where $\delta$ is the inflow boundary layer thickness). The constant target slip length is maintained for $20\delta$ upstream and during the onset of flow separation. The separation is induced by a wall-normal velocity profile applied at the top boundary. All cases are performed at $Re_\delta = U_{\infty}\delta/\nu = 455$. Initial results indicate that as slip length increases, separation and reattachment are delayed. Most notably, the formation and shedding of roller vortices is mitigated as slip length increases, resulting in a less turbulent wake, despite that self-similarity of the plane shear layer is maintained.