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- Title
Study on Cooling Film and Aero-Optical Effect of Hypersonic Imaging Window.
- Authors
Mi, Q.; Yi, S. H.; Zhao, X. H.; Ding, H. L.; Zhang, B.
- Abstract
Aerodynamic heating on the optical window of hypersonic vehicles worsen its imaging quality. The cooling efficiency and the aero-optical effect of the supersonic cooling film on the optical window of a blunt cone model were studied in a Mach 8 hypersonic gun wind tunnel. The experiments were conducted under both the low enthalpy (Re∞ = 1.63 × 107 m–1) and the high enthalpy (Re∞ = 7.5 × 106 m–1) conditions. The centerline heat flux distribution on the window surface was measured by the platinum thin film gauges and the cooling length of the Mach 3 film was investigated for various pressure ratios of jet and various windward attack angles. Meanwhile, the nano-tracer-based planar laser scattering technique (NPLS) was applied to manifest the fine structures and the density field above the window, and the ray-tracing method based on NPLS density images was used to calculate the optical wavefront distortion across the external flow field. The results revealed that the far-end area of window cannot be completely cooled when the jet pressure was under the mainstream pressure, while the whole testing area (315 mm in length) can always be completely cooled in both the low and high enthalpy mainstream when the jet pressure matched the mainstream pressure. Besides, increase in the windward attack angle in a small range (0°–4°) would bring forward the reattachment position and promote the heat flux amplitude by 50% of the window surface when there was no cooling jet, but it had a little effect on the cooling length when the jet pressure matched. Under the same experimental conditions, the main factor affecting the cooling length is the mass flow rate of jet. Increase in the pressure ratio of jet can further reduce the heat flux, but the cooling efficiency of the unit mass coolant decreases. The maximum wavefront distortion of a collimated beam vertically incident through the non-cooling optical window would reach one wavelength (532 nm). Under the condition of jet pressure matched, the scale of the unstable vortex in the mixing layer decreases and the reattachment shockwave disappears. As a result, the distortion amplitude decreases obviously, ranging from –200 to 200 nm.
- Subjects
AERODYNAMICS; HYPERSONIC flow; ENTHALPY; SUPERSONIC aerodynamics; WAVEFRONTS (Optics)
- Publication
Fluid Dynamics, 2021, Vol 56, Issue 1, pS88
- ISSN
0015-4628
- Publication type
Article
- DOI
10.1134/S0015462822010086