Experimental Investigation of Single Roughness Element Effects on Supersonic Boundary Layer Transition

2014 ◽  
Author(s):  
Henny Bottini ◽  
Bayindir H. Saracoglu ◽  
Guillermo Paniagua
Keyword(s):  
Boundary Layer ◽  
Wall Temperature ◽  
Roughness Element ◽  
Pressure Fluctuations ◽  
Supersonic Boundary Layer ◽  
Boundary Layer Transition ◽  
Adiabatic Wall ◽  
Layer Transition ◽  
Temperature And Pressure ◽  
Unsteady Effects

Predicting the characteristics of a transitional boundary layer remains an open challenge in supersonic flow fields. An experimental campaign to understand the effects of a single roughness element on a supersonic laminar boundary layer was designed. Two Mach numbers were tested, 1.6 and 2.3, including two roughness heights, 0.1 mm and 1 mm, over a flat plate. Steady and unsteady wall temperature and pressure levels were recorded to interpret the influence of the wake of the roughness. Heat flux and adiabatic wall temperature trends, temperature and pressure fluctuations RMS trends and time evolution of spectral content were reported. The initial wall temperature was varied during the wall temperature measurements and the resulting steady and unsteady effects on the roughness wake were investigated.

Infrared thermography of hypersonic boundary layer transition induced by isolated roughness elements

2021 ◽  
Author(s):  
Shicheng Liu ◽  
Meng Wang ◽  
Hao Dong ◽  
Tianyu Xia ◽  
Lin Chen ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Infrared Thermography ◽  
Roughness Element ◽  
Transition Process ◽  
Boundary Layer Transition ◽  
Hypersonic Boundary Layer ◽  
Layer Transition ◽  
Leading Role ◽  
Roughness Elements ◽  
Element Shape

Roughness element induced hypersonic boundary layer transition on a flat plate is investigated using infrared thermography at Ma = 5 and 6 flow condition. Surface Stanton number is acquired to analyze the effect of roughness element shape and height on the transition process. The correlation between the vortex structure induced by roughness element and the wall heat streaks is established. The results indicate that higher roughness element would induce stronger streamwise heat flux streaks, lead to transition advance in streamwise centerline and increase the width of spanwise wake. Moreover, for low roughness element, the effect of the shape is not obvious, and the height plays a leading role in the transition; for tall roughness element, the effect on accelerating transition for the diamond roughness element is the best, the square is the worst, and the shape plays a leading role in the transition.

Boundary-Layer Transition in Accelerating Flows With Intense Freestream Turbulence: Part 2—The Zone of Intermittent Turbulence

1992 ◽  
Vol 114 (3) ◽  
pp. 322-332 ◽  
Author(s):  
M. F. Blair
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Boundary Layer Transition ◽  
Transitional Region ◽  
Freestream Turbulence ◽  
Intermittent Turbulence ◽  
Adiabatic Wall ◽  
Layer Transition ◽  
Flow Acceleration ◽  
Boundary Layer Turbulence

Hot-wire anemometry was employed to examine the laminar-to-turbulent transition of low-speed, two-dimensional boundary layers for two (moderate) levels of flow acceleration and various levels of grid-generated freestream turbulence. Flows with an adiabatic wall and with uniform-flux heat transfer were explored. Conditional discrimination techniques were employed to examine the zones of flow within the transitional region. This analysis demonstrated that as much as one-half of the streamwise-component unsteadiness, and much of the apparent anisotropy, observed near the wall was produced, not by turbulence, but by the steps in velocity between the turbulent and inter-turbulent zones of flow. Within the turbulent zones u′/v′ ratios were about equal to those expected for equilibrium boundary-layer turbulence. Near transition onset, however, the turbulence kinetic energy within the turbulent zones exceeded fully turbulent boundary-layer levels. Turbulent-zone power-spectral-density measurements indicate that the ratio of dissipation to production increased through transition. This suggests that the generation of the full equilibrium turbulent boundary-layer energy cascade required some time (distance) and may explain the very high TKE levels near onset.

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