科研之友
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摘要
Cold flow analysis is applied in a canonical scramjet combustor to obtain insights into key physics of the symmetric/asymmetric combustion modes under different equivalence ratios. Systematic experiments have been implemented in a single-expanding duct with backpressure produced by a cylinder at Mach 3. Fine structures of separated flow have been gained by the nanobased planar laser scattering system. High-frequency pressure signals are acquired to study the unsteady behaviors of separation shock. Velocity profiles obtained from particle image velocimetry are validated by numerical simulations. The results indicate that the symmetric backpressure itself can cause asymmetric separation. A steady symmetric separation mode forms when backpressure is relatively low. An unsteady asymmetric separation mode appears when backpressure is high enough. A large separated region always dominates at the expansion wall in the asymmetric separation mode. The asymmetric separation is formed by the increment of boundary-layer thickness and the reduction of turbulence intensity after expansion corner. An interlaced turbulence intensity distribution between the straight and expansion walls accounts for the transition of separation modes under different backpressure. A broadband oscillation of shock foot lies in the asymmetric separation mode, which is evolved from low-frequency unsteadiness in the shock-wave-boundary-layer interaction. Meanwhile, asymmetric backpressure is able to restrain the development of the separated region and forces the separation mode to stay symmetric and steady under high backpressure.
- 出版日期2017-4
- 单位中国人民解放军国防科学技术大学
