Investigation of stationary-crossflow-instability induced transition with the temperature-sensitive paint method

Abstract

The Temperature-Sensitive Paint (TSP) method is used for surface-based flow visualizations on a swept-wing wind-tunnel model with a generic natural laminar-flow airfoil. Within the investigated parameter range the stationary crossflow instability is the dominating instability mechanism. Based on the TSP results the location of the laminar-turbulent transition and the most amplified wavenumber of the stationary crossflow instability are determined. The test is performed with three different conditions of the leading-edge surface: highly polished, unpolished, and highly polished with discrete roughness elements applied. The Temperature-Sensitive Paint method has proven to have sufficient spatial resolution and temperature sensitivity to resolve skin friction variations to detect the footprint of stationary crossflow vortices even inside of turbulent wedges. With the discrete roughness elements, i.e. cylindrical elements with micron-sized height, the transition could be delayed successfully for certain conditions. Local low-frequency movement of the beginning of turbulent wedges was detected for some data points with an unpolished leading edge.

Miniaturization and Model-Integration of the Optical Measurement System for Temperature-Sensitive Paint Investigations

“…The necessary temperature ratio for achieving satisfying visualization results can provide an indication of the sensitivity of the measurement setup. In a previous TSP measurement, cross-flow instabilities with scientific camera [ 31 ] temperature ratios of up to were investigated. In the current setup with the miniature camera, a lower temperature of was suitable for acquiring the TSP data.…”

“…In the current setup with the miniature camera, a lower temperature of was suitable for acquiring the TSP data. When comparing the current results with TSP visualizations acquired with scientific cameras of stationary cross-flow instability-induced transition [ 31 ], it is noticeable that the current results are more noisy. Nevertheless, the visualizations presented in this paper clearly demonstrate the suitability of qualitative, time-averaged TSP visualizations.…”

“…This temperature difference corresponds to a temperature ratio of between the surface and flow. In a previous investigation of cross-flow instability-induced transition with TSP [ 31 ], the influence of over-temperature on the transition location was negligible in the tested range of up to . Subsequently, the run phase started.…”

Stability of Swept Wing Boundary Layers under Non-Adiabatic Wall Conditions

“…Previous experimental studies on the effect of non-adiabatic walls on stationary CFI have been conducted as a secondary effect of Temperature Sensitive Paint (TSP) measurements. One example of this is the work of Lemarechal et al [18], where TSP is applied on a swept wing model and the effect of wall-temperature is investigated to determine a permissible wall-temperature ratio that does not affect laminar-to-turbulent transition, found to be 𝑇 w /𝑇 ∞ = 1.04. However, TSP measurements conducted in the European Transonic Wind Tunnel (ETW) by Fey et al [19] on a swept wing model under larger wall-temperature variations (𝑇 𝑤 /𝑇 ∞ ≤ 0.93) show a considerable influence on the transition behaviour.…”

Detection of Lambda- and Omega-vortices with the temperature-sensitive paint method in the late stage of controlled laminar–turbulent transition

“…The Temperature-Sensitive Paint (TSP) method is a surface-based flow visualization technique that can be used for transition measurements in a variety of applications, e.g. cryogenic facilities , rotating systems (Weiss et al, 2017), and low-speed atmospheric wind tunnels (Lemarechal et al, 2018a). It has also been used for visualizations on a cylinder in crossflow in water facilities at different Reynolds numbers (Fey et al, 2013;Capone et al, 2015).…”