Instability Study of the Wake Behind a Discrete Roughness Element in a Hypersonic Boundary-Layer

2015 ◽  
pp. 91-96 ◽  
Author(s):  
P. Paredes ◽  
N. De Tullio ◽  
N. D. Sandham ◽  
V. Theofilis
Keyword(s):  
Boundary Layer ◽  
Roughness Element ◽  
Hypersonic Boundary Layer

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.

scholarly journals Response and receptivity of the hypersonic boundary layer past a wedge to free-stream acoustic, vortical and entropy disturbances

2016 ◽  
Vol 797 ◽  
pp. 874-915 ◽  
Author(s):  
Fufeng Qin ◽  
Xuesong Wu
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Roughness Element ◽  
Strong Shock ◽  
Neutral Position ◽  
Hypersonic Boundary Layer ◽  
Instability Mode ◽  
Coupling Coefficients ◽  
Strong Response ◽  
Acoustic Perturbation

This paper analyses the response and receptivity of the hypersonic boundary layer over a wedge to free-stream disturbances including acoustic, vortical and entropy fluctuations. Due to the presence of an attached oblique shock, the boundary layer is known to support viscous instability modes whose eigenfunctions are oscillatory in the far field. These modes acquire a triple-deck structure. Any of three elementary types of disturbance with frequency and wavelength on the triple-deck scales interacts with the shock to generate a slow acoustic perturbation, which is reflected between the shock and the wall. Through this induced acoustic perturbation, vortical and entropy free-stream disturbances drive significant velocity and temperature fluctuations within the boundary layer, which is impossible when the shock is absent. A quasi-resonance was identified, due to which the boundary layer exhibits a strong response to a continuum of high-frequency disturbances within a narrow band of streamwise wavenumbers. Most importantly, in the vicinity of the lower-branch neutral curve the slow acoustic perturbation induced by a disturbance of suitable frequency and wavenumbers is in exact resonance with a neutral eigenmode. As a result, the latter can be generated directly by each of three types of free-stream disturbance without involving any surface roughness element. The amplitude of the instability mode is determined by analysing the disturbance evolution through the resonant region. The fluctuation associated with the eigenmode turns out to be much stronger than the free-stream disturbances due to the resonant nature of excitation, and in the case of acoustic disturbances, to the well-known amplification effect of a strong shock. Moreover, excitation at the neutral position means that the instability mode grows immediately without undergoing any decay, or missing any portion of the unstable region. All these indicate that this new mechanism is particularly efficient. The boundary-layer response and coupling coefficients are calculated for typical values of parameters.

scholarly journals Effect of a Roughness Element on the Hypersonic Boundary Layer Receptivity Due to Different Types of Free-Stream Disturbance with a Single Frequency

Entropy ◽  
2019 ◽  
Vol 21 (3) ◽  
pp. 255 ◽  
Author(s):  
Mingfang Shi ◽  
Lidan Xu ◽  
Zhenqing Wang ◽  
Hongqing Lv
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Hypersonic Flow ◽  
Acoustic Waves ◽  
Fundamental Mode ◽  
Free Stream ◽  
Second Harmonic ◽  
Roughness Element ◽  
Hypersonic Boundary Layer ◽  
The Impact

The hypersonic flow field around a blunt cone was simulated using a high-order finite difference method. Fast acoustic waves, slow acoustic waves, entropy waves, and vortical waves were introduced into the free-stream to determine the influence of a free-stream with disturbances on the hypersonic flow field and boundary layer. The effect of disturbance type on the evolution of perturbations in the hypersonic boundary layer was analyzed. Fast Fourier Transform was adopted to analyze the effect of the disturbance type on the evolution of different modes in the boundary layer. A roughness element was introduced into the flow field to reveal the impact of the roughness element on hypersonic boundary layer receptivity. The results showed that a free-stream with disturbances affected the hypersonic flow field and boundary layer; acoustic waves had the greatest influence. The impact of slow acoustic waves on the flow field was mainly concentrated in the region between the shock and the boundary layer, whereas the influence of fast acoustic waves was mainly concentrated in the boundary layer. Multi-mode perturbations formed in the boundary layer were caused by the free-stream with disturbances, wherein the fundamental mode was the dominant mode of the perturbations in the boundary layer caused by fast acoustic waves, entropy waves, and vortical waves. The dominant modes of the perturbations in the boundary layer caused by slow acoustic waves were both the fundamental mode and the second harmonic mode. The roughness element changed the propagation process of different modes of perturbations in the boundary layer. In the downstream region of the roughness element, perturbations in the boundary layer caused by the slow acoustic waves had the greatest influence. The second harmonic mode in the boundary layer was significantly suppressed, and the fundamental mode became the dominant mode. The effects of fast acoustic waves and entropy waves on the boundary layer receptivity were similar, except the amplitude of the perturbations in the boundary layer caused by the fast acoustic waves was larger.

scholarly journals Effect of a Roughness Element on the Receptivity of a Hypersonic Boundary Layer over a Blunt Cone Due to Pulse Entropy Disturbance with a Single Frequency

Entropy ◽  
2018 ◽  
Vol 20 (6) ◽  
pp. 404 ◽  
Author(s):  
Zhenqing Wang ◽  
Mingfang Shi ◽  
Xiaojun Tang ◽  
Hongqing Lv ◽  
Lidan Xu
Keyword(s):  
Boundary Layer ◽  
Roughness Element ◽  
Single Frequency ◽  
Hypersonic Boundary Layer ◽  
Blunt Cone

Roughness-induced turbulent wedges in a hypersonic blunt-body boundary layer

2014 ◽  
Vol 754 ◽  
pp. 208-231 ◽  
Author(s):  
A. Fiala ◽  
R. Hillier ◽  
D. Estruch-Samper
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Laminar Flow ◽  
Boundary Layer Thickness ◽  
Blunt Body ◽  
Roughness Element ◽  
Surface Heat ◽  
Hypersonic Boundary Layer ◽  
Element Size ◽  
Body Boundary

AbstractThis paper uses measurements of surface heat transfer to study roughness-induced turbulent wedges in a hypersonic boundary layer on a blunt cylinder. A family of wedges was produced by changing the height of an isolated roughness element, providing conditions in the following range: fully effective tripping, for the largest element, with a turbulent wedge forming immediately downstream of the element; a long wake, in length several hundred times the boundary layer thickness, leading ultimately to transition; and retention of laminar flow, for the smallest element. With appropriate element size, a fully intermittent wedge formed, comprising a clear train of turbulent spots.

Effect of angle of attack on hypersonic boundary-layer stability

AIAA Journal ◽  
1997 ◽  
Vol 35 ◽  
pp. 464-470 ◽  
Author(s):  
Glen P. Doggett ◽  
Ndaona Chokani ◽  
Stephen P. Wilkinson
Keyword(s):  
Boundary Layer ◽  
Angle Of Attack ◽  
Boundary Layer Stability ◽  
Hypersonic Boundary Layer
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