scholarly journals Receptivity of the Boundary Layer over a Blunt Wedge with Distributed Roughness at Mach 6

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Zhenqing Wang ◽  
Mingfang Shi ◽  
Xiaojun Tang ◽  
Lidan Xu ◽  
Xiaokun Sun
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Hypersonic Flow ◽  
Fundamental Mode ◽  
Great Influence ◽  
Simulation Method ◽  
Dominant Mode ◽  
Mode Competition ◽  
Disturbance Waves ◽  
Cubic Polynomial

A hypersonic flow field over a blunt wedge with or without roughness is simulated by a direct numerical simulation method. The effect of isolated and distributed roughnesses on the steady and unsteady hypersonic flow field and boundary layer is analyzed. The shape of roughness is controlled by cubic polynomial. The evolution of disturbance waves caused by slow acoustic wave in the boundary layer is investigated by fast Fourier spectrum analysis. The results show that there is a great influence of roughness on the evolution of disturbance waves in the hypersonic boundary layer. The disturbance waves are promoted in the upstream-half region of roughness while suppressed in the downstream-half region of roughness. There is always a mode competition among different modes both in the temporal domain and in the frequency domain in the boundary layer, and mode competition is affected by roughness. The location of the dominant mode which is changed to a second-order harmonic mode from the fundamental mode moves upstream. The vortices caused by roughness also impact the evolution of disturbance waves in the boundary layer. The fundamental mode is suppressed in the vortex region while other harmonic modes are promoted.

scholarly journals Temporal and Spatial Evolution Characteristics of Disturbance Wave in a Hypersonic Boundary Layer due to Single-Frequency Entropy Disturbance

2014 ◽  
Vol 2014 ◽  
pp. 1-14 ◽  
Author(s):  
Zhenqing Wang ◽  
Xiaojun Tang ◽  
Hongqing Lv ◽  
Jianqiang Shi
Keyword(s):  
Boundary Layer ◽  
Nonlinear Evolution ◽  
Wedge Angle ◽  
Dominant Mode ◽  
Single Frequency ◽  
Mode Competition ◽  
Spatial Evolution ◽  
Frequency Range ◽  
Disturbance Waves ◽  
Temporal And Spatial

By using a high-order accurate finite difference scheme, direct numerical simulation of hypersonic flow over an 8° half-wedge-angle blunt wedge under freestream single-frequency entropy disturbance is conducted; the generation and the temporal and spatial nonlinear evolution of boundary layer disturbance waves are investigated. Results show that, under the freestream single-frequency entropy disturbance, the entropy state of boundary layer is changed sharply and the disturbance waves within a certain frequency range are induced in the boundary layer. Furthermore, the amplitudes of disturbance waves in the period phase are larger than that in the response phase and ablation phase and the frequency range in the boundary layer in the period phase is narrower than that in these two phases. In addition, the mode competition, dominant mode transformation, and disturbance energy transfer exist among different modes both in temporal and in spatial evolution. The mode competition changes the characteristics of nonlinear evolution of the unstable waves in the boundary layer. The development of the most unstable mode along streamwise relies more on the motivation of disturbance waves in the upstream than that of other modes on this motivation.

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.

Leading-edge receptivity to free-stream disturbance waves for hypersonic flow over a parabola

2001 ◽  
Vol 441 ◽  
pp. 315-367 ◽  
Author(s):  
XIAOLIN ZHONG
Keyword(s):  
Boundary Layer ◽  
Hypersonic Flow ◽  
Boundary Layers ◽  
Free Stream ◽  
Stokes Equations ◽  
Leading Edge ◽  
Bow Shock ◽  
Navier Stokes ◽  
Hypersonic Boundary Layer ◽  
Disturbance Waves

The receptivity of hypersonic boundary layers to free-stream disturbances, which is the process of environmental disturbances initially entering the boundary layers and generating disturbance waves, is altered considerably by the presence of bow shocks in hypersonic flow fields. This paper presents a numerical simulation study of the generation of boundary layer disturbance waves due to free-stream waves, for a two-dimensional Mach 15 viscous flow over a parabola. Both steady and unsteady flow solutions of the receptivity problem are obtained by computing the full Navier–Stokes equations using a high-order-accurate shock-fitting finite difference scheme. The effects of bow-shock/free-stream-sound interactions on the receptivity process are accurately taken into account by treating the shock as a discontinuity surface, governed by the Rankine-Hugoniot relations. The results show that the disturbance waves generated and developed in the hypersonic boundary layer contain both first-, second-, and third-mode waves. A parametric study is carried out on the receptivity characteristics for different free-stream waves, frequencies, nose bluntness characterized by Strouhal numbers, Reynolds numbers, Mach numbers, and wall cooling. In this paper, the hypersonic boundary-layer receptivity is characterized by a receptivity parameter defined as the ratio of the maximum induced wave amplitude in the first-mode-dominated region to the amplitude of the free-stream forcing wave. It is found that the receptivity parameter decreases when the forcing frequency or nose bluntness increase. The results also show that the generation of boundary layer waves is mainly due to the interaction of the boundary layer with the acoustic wave field behind the bow shock, rather than interactions with the entropy and vorticity wave fields.

Hypersonic viscous interaction on curved surfaces

1970 ◽  
Vol 43 (3) ◽  
pp. 497-511 ◽  
Author(s):  
J. L. Stollery
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Flow Field ◽  
Flat Plate ◽  
Hypersonic Flow ◽  
Curved Surfaces ◽  
Two Dimensional ◽  
Alternative Analysis ◽  
Viscous Interaction ◽  
Wedge Pressure

Cheng's analysis of strong viscous interaction between a laminar boundary layer growing over a flat plate and the external hypersonic flow field is extended to cover curved surfaces. It is demonstrated that the solutions for some concave surfaces are oscillatory and quantitatively unrealistic. The reason for this behaviour is that the Busemann term in the Newton–Busemann pressure law used in Cheng's analysis over-corrects for centrifugal effects. The removal of the Busemann term or the substitution of the tangent-wedge pressure law results in an alternative analysis which can cover both strong and weak viscous interaction over a wide variety of two-dimensional shapes. A number of examples are included together with comparative experimental data.

Stability characteristic of hypersonic flow over a blunt wedge under freestream pulse wave

Open Physics ◽  
2014 ◽  
Vol 12 (1) ◽  
Author(s):  
Xiaojun Tang ◽  
Hongqing Lv ◽  
Xiangnan Meng ◽  
Zhenqing Wang ◽  
Qin Lv
Keyword(s):  
Boundary Layer ◽  
Wall Temperature ◽  
Fundamental Mode ◽  
Pulse Wave ◽  
Continuous Wave ◽  
Second Harmonic ◽  
Dominant Mode ◽  
Stability Characteristic ◽  
Hypersonic Boundary Layer ◽  
The Stability

AbstractTo investigate the stability characteristic of hypersonic flow under the action of a freestream pulse wave, a high-order finite difference method was employed to do direction numerical simulation (DNS) of hypersonic unsteady flow over an 8° half-wedge-angle blunt wedge with freestream slow acoustic wave. The evolution of disturbance wave modes in the boundary layer under a pulse wave and a continuous wave are compared, and the wall temperature effect on the hypersonic boundary layer stability for a pulse wave disturbance is discussed. Results show that, both for a pulse wave and a continuous wave in freestream, the disturbance waves inside the nose boundary layer are mainly a fundamental mode; the Fourier amplitude of pressure disturbance mode in the boundary layer for a pulse wave is far less than that for a continuous wave, and the band frequency of the former is wider than that of the latter. All disturbance modes decay rapidly along the streamwise in the nose boundary layer. In the non-nose boundary layer, the dominant mode is transferred from fundamental mode into second harmonic. The transformation of dominant mode for a pulse wave appears much earlier than that for a continuous wave. Different frequency disturbance modes present different changes along streamline in the boundary layer, and the frequency band narrows around the second harmonic mode along the streamwise. Keen competition and the transformation of energy exist among different modes in the boundary layer. Wall temperature modifies the stability characteristic of the hypersonic boundary layer, which presents little effect on the development of fundamental modes and cooling wall could accelerates the growth of the high frequency mode as well as the dominant mode transformation.

INFLUENCE OF THE PLATE LEADING-EDGE SHAPE AND THICKNESS ON THE BOUNDARY LAYER LAMINAR-TURBULENT TRANSITION IN HYPERSONIC FLOW

2019 ◽  
Vol 50 (5) ◽  
pp. 461-481
Author(s):  
Sergei Vasilyevich Aleksandrov ◽  
Evgeniya Andreevna Aleksandrova ◽  
Volf Ya. Borovoy ◽  
Andrey Vyacheslavovich Gubernatenko ◽  
Vladimir Evguenyevich Mosharov ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Hypersonic Flow ◽  
Leading Edge ◽  
Turbulent Transition ◽  
Laminar Turbulent Transition

Experimental investigation on the three-dimensional flow field from a meltblowing slot die

e-Polymers ◽  
2020 ◽  
Vol 20 (1) ◽  
pp. 724-732
Author(s):  
Changchun Ji ◽  
Yudong Wang
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Great Influence ◽  
Distribution Characteristics ◽  
Air Velocity ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Airflow Distribution ◽  
Slot Die ◽  
Center Area

AbstractTo investigate the distribution characteristics of the three-dimensional flow field under the slot die, an online measurement of the airflow velocity was performed using a hot wire anemometer. The experimental results show that the air-slot end faces have a great influence on the airflow distribution in its vicinity. Compared with the air velocity in the center area, the velocity below the slot end face is much lower. The distribution characteristics of the three-dimensional flow field under the slot die would cause the fibers at different positions to bear inconsistent air force. The air velocity of the spinning centerline is higher than that around it, which is more conducive to fiber diameter attenuation. The violent fluctuation of the instantaneous velocity of the airflow could easily cause the meltblowing fiber to whip in the area close to the die.

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