Hot-Wire Measurements of the Influence of Surface Steps on Transition in Favorable Pressure Gradient Boundary Layers

An examination of the effects of surface step excrescences on boundary layer transition was performed, using a unique experimental facility. The objective of the work was to characterize the variation of transition Reynolds numbers with measurable step size and boundary layer parameters, with the specific goal of specifying new tolerance criteria for laminar flow airfoils, alongside a fundamental investigation of boundary layer transition mechanisms. This paper focuses on interpretation of hot-wire measurements, including supporting stability calculations, undertaken as part of the study. The results for both forward and aft-facing steps indicated a substantial stabilizing effect of favorable pressure gradient on excrescence-induced boundary layer transition. These findings suggest that manufacturing tolerances for laminar flow aircraft could be loosened in areas where even mild favorable pressure gradients exist

The influence of the spatial frequency content of discrete roughness distributions on the development of the crossflow instability

An experimental investigation on the influence of the spatial frequency content of roughness distributions on the development of crossflow instabilities has been carried out. From previous research it is known that micro roughness elements can have a large influence on the crossflow development. When the spanwise spacing is chosen such that it is the most unstable wavelength (following linear stability analysis), stationary crossflow waves are amplified. While in earlier studies the focus was on the height or spanwise spacing of roughness elements, in the present study it is chosen to vary the shape of the elements. Through the modification of the shape the forcing at the critical wavelength is increased, while the forcing at the harmonics of the critical wavelength is damped. Experiments were carried in the low turbulence wind tunnel at City University London (Tu=0.006%) on a swept flat plate in combination with displacement bodies to create a sufficiently strong favourable pressure gradient. Hot wire measurements across the plate tracked the development of stationary and travelling crossflow waves. Initially, stronger crossflow waves were found for the elements with stronger forcing, while further downstream the effect of forcing diminished. Spatial frequency spectra showed that the stronger forcing at the critical wavelength (via the roughness shape) dominates the response of the flow while low forcing at the harmonics has no notable effect. Additionally, high resolution streamwise hot wire scans showed that the onset of secondary instability is not significantly influenced by the spatial frequency content of the roughness distribution

Verslag van een bezoek door Prof.dr.ir. H.J. van der Maas en ir. J.L. van Ingen gebracht aan het Engineering Laboratory van de Universiteit van Cambridge vanaf 30 april tot 2 mei 1959

Aerospace Engineerin

Een semi-empirische methode voor de bepaling van de ligging van het omslaggebied van de grenslaag bij onsamendrukbare tweedimensionale stromingen

Aerospace Engineerin

A method for calculating the transition region for two-dimensional boundary layers with distributed suction

Aerospace Engineerin

Theoretical and experimental investigations of incompressible laminar boundary layers with and without suction

Aerospace Engineerin

Theorie en experiment in de stromingsleer

Aerospace Engineerin

Phaseplane representation of the incompressible viscous flow between non-parallel plane walls

Aerospace Engineerin

A suggested semi-empirical method for the calculation of the boundary layer transition region

Aerospace Engineerin