Transpiration-Cooling Heat Transfer Experiments in Laminar and Turbulent Hypersonic Flows

Abstract

The design of a transpiration cooled system requires detailed local heat transfer information on and in the vicinity of the porous injector; however, limited spatially resolved experimental studies exist, particularly in hypersonic flows. In this work experiments were conducted in the Oxford High Density Tunnel at Mach 6.1 in both laminar and turbulent regimes. Spatially resolved 2D surface heat transfer measurements were acquired by imaging directly on and downstream of two micro-porous transpiration cooled injectors (METAPOR CE170 and Zirconia) using high-speed infra-thermography. Whilst injection in the laminar regime results in a steady, monotonic reduction in heat transfer from the start of the injector, a flatter profile is present for the turbulent cases where turbulent mixing inhibits surface heat transfer reduction.

Experimental Studies of Hypersonic Shock Impingement on a Transpiration-Cooled Flat Plate

“…This is likely due to a combination of the lower surface pressures (leading to a higher local blowing ratio) upstream of the interaction region (denoted approximately by the inviscid shock line) and the laminar nature of the flow before the strong separation caused by the shock. Downstream of the interaction region (𝑥 > 180 mm), the heat transfer reduction is very flat, characteristic of previous measurements of transpiration cooling in turbulent flows without SWBLI [10]. For helium injection, a blowing ratio of 0.214% essentially achieves a similar 𝑆𝑡 𝑠 /𝑆𝑡 0,𝑠 downstream of the shock interaction (𝑥 > 180 mm) as nitrogen with 1.711%; i.e.…”

“…Some of the values of 𝐹, especially for the laminar cases, are very high compared to previous experiments in a similar setup [10]. This is due to the higher free-stream mass flux post-recompression shock which then requires higher coolant mass fluxes to result in a significant heat transfer reduction.…”

“…With coolant injection, there are prominent 'cold' patches for the helium case downstream of impingement at approximately x = 195 mm. This may be attributed to non-uniformities in the coolant outflow for this porous injector [10]. These patches are not present for the nitrogen case likely due to the higher outflow velocity of helium for a given injected mass flux (due to its lower density) exacerbating local flow structures.…”

“…The experiments were conducted on a flat plate model at 0 • angle of attack as described in Naved et al [10]. Figure 1 shows a cross-section of the experimental model.…”

“…• 𝐵 ℎ,𝑠 6.75 turbulent (10) where the factor 4 in the denominator of the exponential has been changed to 4.75 and 6.75 respectively for the transitional and turbulent cases. It is difficult to isolate the exact reason for the differences between the Holden and Sweet correlation and the two conditions tested in this study.…”