Effect of Reynolds number on boundary layer development behind an expansion fan

Relaminarization effects in hypersonic flow on a three-dimensional expansion–compression geometry

“…This recovery typically occurs within a few boundary-layer thicknesses (Dawson et al 1994). However, due to slower recovery of turbulent quantities and limited length of the test articles used in high-speed boundary-layer experiments, the recovery to equilibrium turbulence is typically not achieved (Goldfeld & Lisenkov 1991;Arnette et al 1998). For a minor expansion (Mach 2.7, ∼4 • corner), Sun et al (2017) found that that the near-wall velocity deficit was sustained even after approximately 15 boundary-layer thickness downstream of the corner, and the turbulent kinetic energy in the outer-layer was lower than that of a flat-plate boundary layer.…”

“…This explains the experimental findings of Zheltovodov et al (1993) and Huo et al (2022) on tandem expansion-compression geometries where larger separation regions were observed with stronger upstream expansions (larger K). As Re increases, the recovery (or the re-transition process) of the expanded boundary layer is expedited (Goldfeld & Lisenkov 1991), and the separation length decreases (Zheltovodov et al 1993;Xie et al 2022). It should be noted that while these studies do elucidate many important aspects of the expansion-compression flow field, these have been restricted to supersonic Mach numbers (Mach 2 to 4).…”

“…The two-layered boundary-layer structure, resulting from the relaminarization effects due to the expansion, typically recovers to a turbulent boundary layer further downstream. This recovery process takes longer at a lower Reynolds number (Goldfeld & Lisenkov 1991). Mean pressure recovery to inviscid values occurs over a distance that scales with the expansion strength that is quantified by a hypersonic similarity parameter , where is the corner angle (Stollery & Bates 1974; Lu & Chung 1992).…”

“…1994). However, due to slower recovery of turbulent quantities and limited length of the test articles used in high-speed boundary-layer experiments, the recovery to equilibrium turbulence is typically not achieved (Goldfeld & Lisenkov 1991; Arnette et al. 1998).…”

“…(2022) on tandem expansion–compression geometries where larger separation regions were observed with stronger upstream expansions (larger ). As Re increases, the recovery (or the re-transition process) of the expanded boundary layer is expedited (Goldfeld & Lisenkov 1991), and the separation length decreases (Zheltovodov et al. 1993; Xie et al.…”