Synchronization of second-mode instability waves for high-enthalpy hypersonic boundary layers

2018 ◽  
Vol 838 ◽  
Author(s):  
Leonardo C. Salemi ◽  
Hermann F. Fasel
Keyword(s):  
Boundary Layer ◽  
Wave Packet ◽  
Acoustic Waves ◽  
Wave Train ◽  
Three Dimensional ◽  
Linear Wave ◽  
Surprising Result ◽  
Experimental Conditions ◽  
High Enthalpy ◽  
Second Mode

The stability of a hypersonic boundary layer for a $5^{\circ }$ half-angle cone at the Caltech T5 high-enthalpy flow conditions was investigated using direct numerical simulations. For the ‘linear’ stability investigations, the boundary layer was perturbed by small axisymmetric disturbances with very small amplitudes, and for the nonlinear regime, three-dimensional pulse disturbances with larger amplitudes were introduced. The surprising result from these investigations was that the 3D wave packet undergoes strong spatial modulations, which we have not observed for other experimental conditions (e.g. the Purdue BAM6QT). This modulation was found to be directly due to the synchronization between second-mode wave components and vorticity/entropy modes. Furthermore, it was found that a synchronization with slow acoustic waves leads to a sudden and strong emission of acoustic waves deep into the free stream, which was observed for both a linear wave train and a 3D nonlinear wave packet. Therefore, it can be concluded that this is a linear mechanism that is not suppressed by nonlinear effects.

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.

Role of Freestream Slow Acoustic Waves in a Hypersonic Three-Dimensional Boundary Layer

AIAA Journal ◽  
2018 ◽  
Vol 56 (9) ◽  
pp. 3570-3584 ◽  
Author(s):  
Guoliang Xu ◽  
Gang Liu ◽  
Jianqiang Chen ◽  
Song Fu
Keyword(s):  
Boundary Layer ◽  
Acoustic Waves ◽  
Three Dimensional ◽  
Dimensional Boundary

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.

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.

scholarly journals Optimal wave packets in a boundary layer and initial phases of a turbulent spot

2010 ◽  
Vol 656 ◽  
pp. 231-259 ◽  
Author(s):  
S. CHERUBINI ◽  
J.-C. ROBINET ◽  
A. BOTTARO ◽  
P. DE PALMA
Keyword(s):  
Boundary Layer ◽  
Wave Packet ◽  
Scaling Law ◽  
Initial Perturbation ◽  
Three Dimensional ◽  
Plate Boundary ◽  
Optimal Time ◽  
Spanwise Direction ◽  
Turbulent Spot ◽  
Hairpin Vortices

The three-dimensional global optimal dynamics of a flat-plate boundary layer is studied by means of an adjoint-based optimization in a spatial domain of long – but finite – streamwise dimension. The localized optimal initial perturbation is characterized by a pair of streamwise-modulated counter-rotating vortices, tilted upstream, yielding at the optimal time elongated streaks of alternating sign in the streamwise direction. This indicates that perturbations with non-zero streamwise wavenumber have a role in the transient dynamics of a boundary layer. A scaling law is provided, describing the variation of the streamwise modulation of the optimal initial perturbation with respect to the streamwise domain length and to the Reynolds number. For spanwise-extended domains, a near-optimal three-dimensional perturbation is extracted during the optimization process; it is localized also in the spanwise direction, resulting in a wave packet of elongated disturbances modulated in the spanwise and streamwise directions. The nonlinear evolution of the optimal and near-optimal perturbations is investigated by means of direct numerical simulations. Both perturbations are found to induce transition at lower levels of the initial energy than local optimal and suboptimal perturbations. Moreover, it is observed that transition occurs in a well-defined region of the convected wave packet, close to its centre, via a mechanism including at the same time oscillations of the streaks of both quasi-sinuous and quasi-varicose nature. Hairpin vortices are observed before transition; they have an active role in the breakdown of the streaks and result in a turbulent spot which spreads out in the boundary layer.

scholarly journals Second-mode attenuation and cancellation by porous coatings in a high-speed boundary layer

2013 ◽  
Vol 726 ◽  
pp. 312-337 ◽  
Author(s):  
Guillaume A. Brès ◽  
Matthew Inkman ◽  
Tim Colonius ◽  
Alexander V. Fedorov
Keyword(s):  
Boundary Layer ◽  
Numerical Simulations ◽  
Boundary Layers ◽  
Acoustic Waves ◽  
Porous Coating ◽  
Small Scale ◽  
High Porosity ◽  
Worst Case ◽  
Porous Coatings ◽  
Second Mode

AbstractNumerical simulations of the linear and nonlinear two-dimensional Navier–Stokes equations, and linear stability theory are used to parametrically investigate hypersonic boundary layers over ultrasonic absorptive coatings. The porous coatings consist of a uniform array of rectangular pores (slots) with a range of porosities and pore aspect ratios. For the numerical simulations, temporally (rather than spatially) evolving boundary layers are considered and we provide evidence that this approximation is appropriate for slowly growing second-mode instabilities. We consider coatings operating in the typical regime where the pores are relatively deep and acoustic waves and second-mode instabilities are attenuated by viscous effects inside the pores, as well as regimes with phase cancellation or reinforcement associated with reflection of acoustic waves from the bottom of the pores. These conditions are defined as attenuative and cancellation/reinforcement regimes, respectively. The focus of the present study is on the cases which have not been systematically studied in the past, namely the reinforcement regime (which represents a worst-case scenario, i.e. minimal second-mode damping) and the cancellation regime (which corresponds to the configuration with the most potential improvement). For all but one of the cases considered, the linear simulations show good agreement with the results of linear instability theory that employs an approximate porous-wall boundary condition, and confirm that the porous coating stabilizing performance is directly related to their acoustic scattering performance. A particular case with relatively shallow pores and very high porosity showed the existence of a shorter-wavelength instability that was not initially predicted by theory. Our analysis shows that this new mode is associated with acoustic resonances in the pores and can be more unstable than the second mode. Modifications to the theoretical model are suggested to account for the new mode and to provide estimates of the porous coating parameters that avoid this detrimental instability. Finally, nonlinear simulations confirm the conclusions of the linear analysis; in particular, we did not observe any tripping of the boundary layer by small-scale disturbances associated with individual pores.

scholarly journals Stability of highly cooled hypervelocity boundary layers

2015 ◽  
Vol 778 ◽  
pp. 586-620 ◽  
Author(s):  
N. P. Bitter ◽  
J. E. Shepherd
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Wall Temperature ◽  
Free Stream ◽  
Boundary Layer Stability ◽  
High Enthalpy ◽  
Wide Range ◽  
Second Mode ◽  
High Mach ◽  
The Stability

The influence of high levels of wall cooling on the stability of hypervelocity boundary layers is investigated. Such conditions are relevant to experiments in high-enthalpy impulse facilities, where the wall temperature is much smaller than the free-stream temperature, as well as to some real flight scenarios. Some effects of wall cooling are well known, for instance, the stabilization of the first mode and destabilization of the second mode. In this paper, several new instability phenomena are investigated that arise only for high Mach numbers and high levels of wall cooling. In particular, certain unstable modes can travel supersonically with respect to the free stream, which changes the nature of the dispersion curve and leads to instability over a much wider band of frequencies. The cause of this phenomenon, the range of parameters for which it occurs and its implications for boundary layer stability are examined. Additionally, growth rates are systematically reported for a wide range of conditions relevant to high-enthalpy impulse facilities, and the stability trends in terms of Mach number and wall temperature are mapped out. Thermal non-equilibrium is included in the analysis and its influence on the stability characteristics of flows in impulse facilities is assessed.

Sign in / Sign up

Export Citation Format

Share Document