scholarly journals Receptivity of a high-speed boundary layer to temperature spottiness

2013 ◽  
Vol 722 ◽  
pp. 533-553 ◽  
Author(s):  
A. V. Fedorov ◽  
A. A. Ryzhov ◽  
V. G. Soudakov ◽  
S. V. Utyuzhnikov
Keyword(s):  
Boundary Layer ◽  
Acoustic Waves ◽  
High Speed ◽  
Free Stream ◽  
Plate Boundary ◽  
Second Mode ◽  
Theoretical Predictions ◽  
Order Of Magnitude ◽  
Pass Through ◽  
Upper Boundary

AbstractTwo-dimensional direct numerical simulation (DNS) of the receptivity of a flat-plate boundary layer to temperature spottiness in the Mach 6 free stream is carried out. The influence of spottiness parameters on the receptivity process is studied. It is shown that the temperature spots propagating near the upper boundary-layer edge generate mode F inside the boundary layer. Further downstream mode F is synchronized with unstable mode S (Mack second mode) and excites the latter via the inter-modal exchange mechanism. Theoretical assessments of the mode F amplitude are made using the biorthogonal eigenfunction decomposition method. The DNS results agree with the theoretical predictions. If the temperature spots are initiated in the free stream and pass through the bow shock, the dominant receptivity mechanism is different. The spot–shock interaction leads to excitation of acoustic waves, which penetrate into the boundary layer and excite mode S. Numerical simulations show that this mechanism provides the instability amplitudes an order of magnitude higher than in the case of receptivity to the temperature spots themselves.

Spontaneous radiation of sound by instability of a highly cooled hypersonic boundary layer

2016 ◽  
Vol 805 ◽  
pp. 188-206 ◽  
Author(s):  
Pavel V. Chuvakhov ◽  
Alexander V. Fedorov
Keyword(s):  
Boundary Layer ◽  
Wave Packet ◽  
Acoustic Waves ◽  
Inviscid Flow ◽  
Spontaneous Radiation ◽  
Second Mode ◽  
Theoretical Predictions ◽  
Free Stream Mach Number ◽  
Wave Trains ◽  
Edge Temperature

The linear stability analysis predicts that the Mack second mode propagating in the boundary layer on a sufficiently cold plate can radiate acoustic waves into the outer inviscid flow. This effect, which is called as a spontaneous radiation (or emission) of sound, is associated with synchronization of the second mode with slow acoustic waves of the continuous spectrum. The theoretical predictions are confirmed by direct numerical simulations of wave trains and wave packets propagating in the boundary layer on a flat plate at free-stream Mach number 6 and wall-to-edge temperature ratio $T_{w}/T_{e}=0.5$. A non-uniform distribution of the wave packet components and the interference between the radiated acoustic waves result in an intricate pattern of the outer acoustic field. The spontaneous radiation of sound, in turn, strongly affects the wave packet in the boundary layer causing its elongation and modulation. This phenomenon may alter the downstream development of instability and delay the transition onset.

Transition of streamwise streaks in zero-pressure-gradient boundary layers

2002 ◽  
Vol 472 ◽  
pp. 229-261 ◽  
Author(s):  
LUCA BRANDT ◽  
DAN S. HENNINGSON
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
High Speed ◽  
Plate Boundary ◽  
Transition Process ◽  
Free Stream Turbulence ◽  
Tollmien Schlichting ◽  
Streamwise Streaks ◽  
The Stability ◽  
Optimal Disturbances

A transition scenario initiated by streamwise low- and high-speed streaks in a flat-plate boundary layer is studied. In many shear flows, the perturbations that show the highest potential for transient energy amplification consist of streamwise-aligned vortices. Due to the lift-up mechanism these optimal disturbances lead to elongated streamwise streaks downstream, with significant spanwise modulation. In a previous investigation (Andersson et al. 2001), the stability of these streaks in a zero-pressure-gradient boundary layer was studied by means of Floquet theory and numerical simulations. The sinuous instability mode was found to be the most dangerous disturbance. We present here the first simulation of the breakdown to turbulence originating from the sinuous instability of streamwise streaks. The main structures observed during the transition process consist of elongated quasi-streamwise vortices located on the flanks of the low-speed streak. Vortices of alternating sign are overlapping in the streamwise direction in a staggered pattern. The present scenario is compared with transition initiated by Tollmien–Schlichting waves and their secondary instability and by-pass transition initiated by a pair of oblique waves. The relevance of this scenario to transition induced by free-stream turbulence is also discussed.

scholarly journals A Theory for Wake-Induced Transition

1989 ◽  
Author(s):  
R. E. Mayle ◽  
K. Dullenkopf
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Flow ◽  
Flat Plate ◽  
Free Stream ◽  
Plate Boundary ◽  
Transition Model ◽  
Model Comparisons ◽  
Turbulent Wakes ◽  
Flat Plate Boundary Layer

A theory for transition from laminar to turbulent flow as the result of unsteady, periodic passing of turbulent wakes in the free stream is developed using Emmons’ transition model. Comparisons made to flat plate boundary layer measurements and airfoil heat transfer measurements confirm the theory.

scholarly journals On-Chip Thermal Insulation Using Porous GaN

Proceedings ◽  
2018 ◽  
Vol 2 (13) ◽  
pp. 776 ◽  
Author(s):  
Bogdan F. Spiridon ◽  
Peter H. Griffin ◽  
John C. Jarman ◽  
Yingjun Liu ◽  
Tongtong Zhu ◽  
...  
Keyword(s):  
Thermal Insulation ◽  
High Speed ◽  
Thermal Characterization ◽  
Semiconductor Materials ◽  
3Ω Method ◽  
Theoretical Predictions ◽  
Order Of Magnitude ◽  
On Chip ◽  
Fundamental Requirement

This study focuses on the thermal characterization of porous gallium nitride (GaN) usingan extended 3ω method. Porous semiconductor materials provide a solution to the need for on-chipthermal insulation, a fundamental requirement for low-power, high-speed and high-accuracythermal sensors. Thermal insulation is especially important in GaN devices, due to the intrinsicallyhigh thermal conductivity of the material. The results show one order of magnitude reduction inthermal conductivity, from 130 W/mK to 10 W/mK, in line with theoretical predictions for porousmaterials. This achievement is encouraging in the quest for integrating sensors with opto-, powerandRF-electronics on a single GaN chip.

scholarly journals NUMERICAL INVESTIGATION OF THE WAKE AFFECTED UNSTEADINESS ON FLAT PLATE BOUNDARY LAYER

2013 ◽  
Vol 43 (1) ◽  
pp. 15-22
Author(s):  
Sanchita Amin ◽  
Dipak Kanti Das
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Free Stream ◽  
Plate Boundary ◽  
Elliptic Cylinder ◽  
Stream Velocity ◽  
Element Formulation ◽  
Weighted Residual Method ◽  
Focal Distance ◽  
Coupled Equations

The present numerical simulation has been conducted with the aim to observe the unsteady boundarylayer characteristics on a flat plate induced by a von Karman vortex street wake. This flow situation is anidealization of that occurring on turbomachinery blades where unsteady wakes are generated by the precedingrow of blades. In this research, the boundary layer is developed under zero pressure gradients while the vortexstreet is generated by an elliptic cylinder positioned in the free stream. The minor-major axes ratio of theelliptic cylinder is taken as 0.6 with an angle of attack 00. The investigation has been performed for differentcylinder-to-plate relative position and a Reynolds number of 500 based on the focal distance of the ellipticcylinder and free stream velocity. The time dependent, two dimensional flow is simulated numerically. Theconsequent mathematical model is governed by the coupled equations of mass, and momentum and solved byemploying Galerkin weighted residual method of finite element formulation. The development of the flow fieldup to certain time period is considered. Instantaneous streamlines of the disturbed flow field, instantaneousvelocity field, boundary layer integral parameters, and skin friction on different streamwise locations on theplate are presented in this paper. The result shows that the wake vortices strongly affect the boundary layerover the flat plate.DOI: http://dx.doi.org/10.3329/jme.v43i1.15771

scholarly journals Flow in the exit of open pipes during acoustic resonance

1980 ◽  
Vol 99 (2) ◽  
pp. 293-319 ◽  
Author(s):  
J. H. M. Disselhorst ◽  
L. Van Wijngaarden
Keyword(s):  
Boundary Layer ◽  
Mathematical Model ◽  
Boundary Condition ◽  
Acoustic Wave ◽  
Acoustic Waves ◽  
Acoustic Radiation ◽  
Acoustic Resonance ◽  
The Other ◽  
Open Tube ◽  
Theoretical Predictions

The flow near the mouth of an open tube is examined, experimentally and theoretically, under conditions in which resonant acoustic waves are excited in the tube at the other end. If the edge of the tube is round, separation does not occur at high Strouhal numbers, which enables us to verify theoretical predictions for dissipation in the boundary layer and for acoustic radiation. Observation with the aid of schlieren pictures shows that in the case of a sharp edge vortices are formed during inflow. The vortices are shed from the pipe during outflow. Based on these observations a mathematical model is developed for the generation and shedding of vorticity. The main result of the analysis is a boundary condition for the pressure in the wave, to be applied near the mouth. The pressure amplitudes in the acoustic wave measured under resonance are compared with theoretical predictions made with the aid of the boundary condition obtained in the paper.

Leading-edge receptivity of a hypersonic boundary layer on a flat plate

2001 ◽  
Vol 426 ◽  
pp. 73-94 ◽  
Author(s):  
A. A. MASLOV ◽  
A. N. SHIPLYUK ◽  
A. A. SIDORENKO ◽  
D. ARNAL
Keyword(s):  
Boundary Layer ◽  
Acoustic Waves ◽  
Free Stream ◽  
Three Dimensional ◽  
Leading Edge ◽  
Experimental Investigations ◽  
Two Dimensional ◽  
Inclination Angles ◽  
Tollmien Schlichting ◽  
Radiation Conditions

Experimental investigations of the boundary layer receptivity, on the sharp leading edge of a at plate, to acoustic waves induced by two-dimensional and three- dimensional perturbers, have been performed for a free-stream Mach number M∞ = 5.92. The fields of controlled free-stream disturbances were studied. It was shown that two-dimensional and three-dimensional perturbers radiate acoustic waves and that these perturbers present a set of harmonic motionless sources and moving sources with constant amplitude. The disturbances excited in the boundary layer were measured. It was found that acoustic waves impinging on the leading edge generate Tollmien–Schlichting waves in the boundary layer. The receptivity coefficients were obtained for several radiation conditions and intensities. It was shown that there is a dependence of receptivity coefficients on the wave inclination angles.

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