Surface Temperature Effects on Boundary-Layer Transition at Various Subsonic Mach Numbers and Streamwise Pressure Gradients

Step-induced transition in compressible high Reynolds number flow

“…For the present experimental set-up in KRG, the average transition N-factor for the smooth configuration varies in the range N T ,0 = 5.3-7.6, depending on the free-stream Mach number. The scatter in the determined values of N T ,0 is within approximately ±25 % about the corresponding averages (Costantini et al, 2016a(Costantini et al, , 2020. These moderate values of transition N-factor are likely due to acoustic disturbances originating from the large separated flow region downstream of the model aft side (see figure 1a) and travelling upstream, as discussed in Costantini (2016) and Risius, Costantini, Koch, Hein, and Klein (2018).…”

“…The transition results have been thoroughly discussed in previous publications (Costantini, 2016;Costantini et al, 2015aCostantini et al, , 2016aCostantini et al, , 2016bCostantini et al, , 2018aCostantini et al, , 2020. A main focus of the present work is on the identification of functional relations that represent the effect of forward-facing steps on boundary-layer transition at various subsonic Mach numbers.…”

“…All other physics, receptivity and nonlinear breakdown included, are incorporated into the threshold N-factor, which is calibrated by means of experimental data. The free-stream parameters and the surface pressure distributions measured on the smooth configuration are used to conduct laminar boundary-layer computations by means of the boundary-layer solver COCO (Schrauf, 1998), with consideration of the examined non-adiabatic surface (Costantini, 2016;Costantini et al, 2016aCostantini et al, , 2020. The calculated wall-normal velocity and temperature profiles are analysed by means of the stability analysis tool LILO (Schrauf, 2006) to obtain the N-factors of TS waves with different frequencies, according to compressible, linear, local stability theory.…”

“…The wall temperature ratio increases at larger Mach numbers (see table 1) and cannot be set at a particular value with an accuracy comparable to that of the other parameters. This is due to the sensitivity of T w /T aw to even small variations of the temperatures of the model surface and/or of the gas in the KRG storage tube between the test runs (Costantini, 2016;Costantini et al, 2018aCostantini et al, , 2020. For this reason, a range of T w /T aw is reported in table 1 for each examined Mach number, i.e.…”

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

“…Previous research on thermal control of boundary layer instabilities focused on uniform wall-cooling and localized heating to stabilize TS-dominated transition scenarios. Several authors have previously demonstrated through experiments [7,8] and linear stability theory [9,10] that the spatial growth of Tollmien-Schlichting (TS) waves is significantly affected by the presence of a non-adiabatic wall. Leveraging the stabilizing effect of wall-cooling on TS waves, Dovgal et al [11] applied localized heating to achieve stabilization downstream of the heating strip, where the flow encounters a relatively cooler surface.…”