Influence of backward-facing steps on laminar-turbulent transition in two-dimensional boundary layers at subsonic Mach numbers
Year: 2025
Type: article
Abstract: Backward-facing steps (BFS) can have a detrimental impact on laminar flow lengths because of their strong effect on boundary layer transition. BFS with normalized step heights in the range of $$h/\delta _1 \approx$$ h / δ 1 ≈ 0.1 to 0.6 (corresponding to height-based Reynolds numbers of $$\hbox{Re}_h = (U_\infty h / \nu ) \approx$$ Re h = ( U ∞ h / ν ) ≈ 230 to 2430) were installed in a two-dimensional wind tunnel model and tested in the Cryogenic Ludwieg-Tube Göttingen, a blow-down wind tunnel with good flow quality. The influence of BFS on the location of laminar-turbulent transition was investigated over a wide range of unit Reynolds numbers from $$\hbox{Re}_1 = {17.5\times 10^{6}\,{\text {m}^{-1}}}$$ Re 1 = 17.5 × 10 6 m - 1 to $$80\times 10^{6}\,\hbox{m}^{-1}$$ 80 × 10 6 m - 1 , three Mach numbers, $$M= 0.35$$ M = 0.35 , 0.50 and 0.65, and various streamwise pressure gradients. The measurement of the transition locations was accomplished non-intrusively by means of temperature-sensitive paint. Transition Reynolds numbers, calculated with the flow length up to the location of laminar-turbulent transition $$x_{T}$$ x T , ranged from $$\hbox{Re}_{\rm tr}\approx$$ Re tr ≈ 1 × 106 to 11 × 106, and were measured as a function of step height, pressure gradient, Reynolds and Mach numbers. Incompressible linear stability analysis was used to calculate amplification rates of Tollmien–Schlichting waves; transition N-factors were determined by correlation with the measured transition locations. In parallel to earlier investigations with a similar setup, this systematic approach was used to identify functional relations between non-dimensional step parameters ( $$h/\delta _1$$ h / δ 1 and $$\hbox{Re}_h$$ Re h ) and the relative change of the transition location. Furthermore, the change of the transition N-factor $$\Delta N$$ Δ N due to the installation of the steps was investigated. It was found that the installation of backward-facing steps with $$h/\delta _1 \lesssim 0.15$$ h / δ 1 ≲ 0.15 and $$\hbox{Re}_h \lesssim 300$$ Re h ≲ 300 does not lead to a reduction of $$\hbox{Re}_{\rm tr}$$ Re tr
Source: Experiments in Fluids
Authors: Steffen Risius, Marco Costantini
Language: English
Subfield: Computational Mechanics
Field: Engineering
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $2,590
OpenAlex ID: W4409307221