Passive control of deep cavity shear layer flow at subsonic speed

2017 ◽  
Vol 95 (10) ◽  
pp. 894-899
Author(s):  
Mouhammad El Hassan ◽  
Laurent Keirsbulck
Keyword(s):  
Shear Layer ◽  
Passive Control ◽  
Control Method ◽  
Leading Edge ◽  
Layer Growth ◽  
Cavity Resonance ◽  
Passive Flow Control ◽  
Acoustic Coupling ◽  
Deep Cavity ◽  
Layer Flow

Passive control of the flow over a deep cavity at low subsonic velocity is considered in the present paper. The cavity length-to-depth aspect ratio is L/H = 0.2. particle image velocimetry (PIV) measurements characterized the flow over the cavity and show the influence of the control method on the cavity shear layer development. It is found that both the “cylinder” and the “shaped cylinder”, placed upstream from the cavity leading edge, result in the suppression of the aero-acoustic coupling and highly reduce the cavity noise. It should be noted that the vortical structures impinge at almost the same location near the cavity downstream corner with and without passive control. The present study allows to identify an innovative passive flow control method of cavity resonance. Indeed, the use of a “shaped cylinder” presents similar suppression of the cavity resonance as with the “cylinder” but with less impact on the cavity flow. The “shaped cylinder” results in a smaller shear layer growth than the cylinder. Velocity deficiency and turbulence levels are less pronounced using the “shaped cylinder”. The “cylinder” tends to diffuse the vorticity in the cavity shear layer and thus the location of the maximum vorticity is more affected as compared to the “shaped cylinder” control. The fact that the “shaped cylinder” is capable of suppressing the cavity resonance, despite the vortex shedding and the high frequency forcing being suppressed, is of high interest from fundamental and applied points of view.

scholarly journals Characterization of the aircraft bay/landing gear coupling noise at low subsonic speeds and its suppression using leading-edge chevron spoiler

2019 ◽  
Vol 11 (8) ◽  
pp. 168781401987143 ◽  
Author(s):  
Kun Zhao ◽  
Yong Liang ◽  
Tingrui Yue ◽  
Zhengwu Chen ◽  
Gareth J Bennett
Keyword(s):  
Shear Layer ◽  
Large Scale ◽  
Passive Control ◽  
Control Method ◽  
Leading Edge ◽  
Landing Gear ◽  
Pressure Transducers ◽  
Coupling Noise ◽  
Image Velocimetry

When the aircraft opens the bay door to let the landing gear either drop or retract, the incoming flow will result in a significant amount of coupling noise from the bay and the landing gear. Here, an experimental study was reported to characterise the acoustic performance and flow field at low subsonic speeds. Also, we examined a passive control method leading-edge chevron spoiler to suppress the noise. The experiment was performed in a low-speed aeroacoustic wind, the bay was simplified as a rectangular cavity and the spoiler was mounted to the leading edge. Both acoustic and aerodynamic measurements were performed through two microphone arrays, pressure transducers and particle image velocimetry. It was found that installation of the landing gear model can attenuate cavity oscillation noise to some extent by disturbing the shear layer of the cavity leading edge. Moreover, acoustic measurement confirmed the noise control when the spoiler was used. In addition, a parametric study on the effects of chevron topology was performed, and an optimised value was found for each parameter. From the aerodynamic measurement, the noise reduction was explained from the perspective of fluid dynamics. It was observed that installation of the chevron can raise the leading-edge shear layer and break up the large-scale vortices, thereby controlling the Rossiter mode noise and the landing gear model noise at certain frequencies.

Control effect on deep cavity noise by slanted walls at low Mach numbers

2020 ◽  
pp. 107754632093651
Author(s):  
Zhifei Guo ◽  
Peiqing Liu ◽  
Hao Guo
Keyword(s):  
Shear Layer ◽  
Passive Control ◽  
Control Method ◽  
Length Ratio ◽  
Front Wall ◽  
Rear Wall ◽  
Control Effect ◽  
Deep Cavity ◽  
Mach Numbers ◽  
Field Noise

Experimental and numerical studies on noise radiated by flow past a rectangular two-dimensional deep cavity with passive control are conducted to research the mechanism of cavity noise reduction at low Mach numbers. The clean cavity has a depth-to-length ratio of 1.5 and a width-to-length ratio of 3. The passive control method is used by slanting the front and rear walls. Using acoustic microphones, both the surface noise and far-field noise are tested in an aeroacoustic wind tunnel. It is observed that the slanted rear wall can suppress the noise effectively, but for the slanted front wall, the tones will be enhanced at some velocities. Numerical simulation is conducted to reveal the mechanism. The results reveal that the slanted rear wall can reflect the unsteadiness back to the shear layer and break up the vortices in it. These vortexes will diffuse after impacting the rear wall and prevent the perturbation from moving deeper, which brings a stable flow field into the cavity. As for the slanted front wall, the vortices will be enlarged and become accelerated in the shear layer, which makes the impingement of it to the rear wall more intense, thus leading to an increase in the noise level.

The flow over a backward-facing step under controlled perturbation: laminar separation

1992 ◽  
Vol 238 ◽  
pp. 73-96 ◽  
Author(s):  
M. A. Z. Hasan
Keyword(s):  
Shear Layer ◽  
Low Frequency ◽  
Layer Growth ◽  
Stream Velocity ◽  
Backward Facing Step ◽  
Laminar Separation ◽  
Vortex Merging ◽  
Layer Growth Rate ◽  
Merging Process ◽  
Layer Flow

The flow over a backward-facing step with laminar separation was investigated experimentally under controlled perturbation for a Reynolds number of 11000, based on a step height h and a free-stream velocity UO. The reattaching shear layer was found to have two distinct modes of instability: the ‘shear layer mode’ of instability at Stθ ≈ 0.012 (Stθ ≡ fθ/UO, θ being the momentum thickness at separation and f the natural roll-up frequency of the shear layer); and the ‘step mode’ of instability at Sth ≈ 0.185 (Sth ≡ fh/U0). The shear layer instability frequency reduced to the step mode one via one or more stages of a vortex merging process. The perturbation increased the shear layer growth rate and the turbulence intensity and decreased the reattachment length compared to the unperturbed flow. Cross-stream measurements of the amplitudes of the perturbed frequency and its harmonics suggested the splitting of the shear layer. Flow visualization confirmed the shear layer splitting and showed the existence of a low-frequency flapping of the shear layer.

Aero-Acoustic Coupling Inside Large Deep Cavities at Low-Subsonic Speeds

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Mouhammad El Hassan ◽  
Laurent Keirsbulck ◽  
Larbi Labraga
Keyword(s):  
Wind Tunnel ◽  
Shear Layer ◽  
Convection Velocity ◽  
Pressure Amplitude ◽  
Hydrodynamic Mode ◽  
Freestream Velocity ◽  
Acoustic Coupling ◽  
Deep Cavity ◽  
Cross Correlations ◽  
Deep Cavities

Aero-acoustic coupling inside a deep cavity is present in many industrial processes. This investigation focuses on the pressure amplitude response, within two deep cavities characterized by their length over depth ratios (L/H=0.2 and 0.41), as a function of freestream velocities of a 2×2m2 wind tunnel. Convection velocity of instabilities was measured along the shear layer, using velocity cross-correlations. Experiments have shown that in deep cavity for low Mach numbers, oscillations of discrete frequencies can be produced. These oscillations appear when the freestream velocity becomes higher than a minimum value. Oscillations start at L/θ0=10 and 21 for L/H=0.2 and 0.41, respectively. The highest sound pressure level inside a deep cavity is localized at the cavity floor. A quite different behavior of the convection velocity was observed between oscillating and nonoscillating shear-layer modes. The hydrodynamic mode of the cavity shear layer is well predicted by the Rossiter model (1964, “Wind Tunnel Experiments on the Flow Over Rectangular Cavities at Subsonic and Transonic Speeds,” Aeronautical Research Council Reports and Memo No. 3438) when measured convection velocity is used and the empirical time delay is neglected. For L/H=0.2, only the first Rossiter mode is present. For L/H=0.41, both the first and the second modes are detected with the second mode being the strongest.

A Numerical Study Into the Influence of Leading Edge Tubercles on the Aerodynamic Performance of a Highly Cambered High Lift Airfoil Wing at Different Reynolds Numbers

2020 ◽  
Author(s):  
Amr Abdelrahman ◽  
Amr Emam ◽  
Ihab Adam ◽  
Hamdy Hassan ◽  
Shinichi Ookawara ◽  
...  
Keyword(s):  
Control Method ◽  
Numerical Study ◽  
Leading Edge ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Passive Flow Control ◽  
Passive Flow ◽  
Stall Angle ◽  
Lifting Surfaces ◽  
Lift And Drag

Abstract Through the last two decades, many studies have demonstrated the ability of leading-edge protrusions (tubercles), inspired from the pectoral flippers of the humpback whale, to be an effective passive flow control method for the stall phase of an airfoil in some cases depending on the geometrical features and the flow regime. Nevertheless, there is a little work associated with revealing tubercles performance for the lifting surfaces with a highly cambered cross-section, used in numerous applications. The present work aims to investigate the effect of implementing leading edge tubercles on the performance of an infinite span rectangular wing with the highly cambered S1223 foil at different flow regimes. Two sets; baseline one and a modified with tubercles have been studied at Re = 0.1 × 106, 0.3 × 106 and 1.5 × 106 using computational fluid dynamics with a validated model. The numerical results demonstrated that Tubercles have the ability to entirely alter the flow structure over the airfoil, confining the separation to troughs, hence, softening the stall characteristics. However, the tubercle modification expedites the presence of the stalled flow over the suction side, lowering the stall angle for the three mentioned Reynolds numbers. While, no considerable difference occurs in lift and drag before the stall.

Control of cavity tones using a spanwise cylinder

2008 ◽  
Vol 86 (12) ◽  
pp. 1355-1365 ◽  
Author(s):  
L Keirsbulck ◽  
M El Hassan ◽  
M Lippert ◽  
L Labraga
Keyword(s):  
Experimental Study ◽  
Shear Layer ◽  
Layer Thickness ◽  
Axial Velocity ◽  
High Frequency ◽  
Sound Pressure ◽  
Leading Edge ◽  
Deep Cavity ◽  
Change In The Mean ◽  
The Mean

A detailed experimental study of flow over a deep cavity was conducted towards understanding the attenuation of tones using a spanwise cylinder. Two “no-control” cavities were compared with a similar configuration using a cylinder on the leading edge of the cavities. Parametric changes of the spanwise cylinder such as the distance from the wall are studied. Maximum control across the range of studied velocities occurs for a particular position of the spanwise cylinder for the two configurations. Reductions in sound pressure levels (SPL) of up to 36 dB were obtained. Moreover, a shaped cylinder was also studied and shows that the attenuation of tones is not due to high-frequency pulsing as suggested in the literature, but to an increase of the cavity-shear-layer thickness due to the change in the mean axial velocity profiles.PACS Nos.: 47.27.Rc, 47.27.Sd

Passive boundary layer control of oblique disturbances by finite-amplitude streaks

2014 ◽  
Vol 749 ◽  
pp. 1-36 ◽  
Author(s):  
Shahab Shahinfar ◽  
Sohrab S. Sattarzadeh ◽  
Jens H. M. Fransson
Keyword(s):  
High Speed ◽  
Passive Control ◽  
Control Method ◽  
Three Dimensional ◽  
Finite Amplitude ◽  
Transition To Turbulence ◽  
Spanwise Direction ◽  
Passive Flow Control ◽  
Tollmien Schlichting ◽  
Streamwise Streaks

AbstractRecent experimental results on the attenuation of two-dimensional Tollmien–Schlichting wave (TSW) disturbances by means of passive miniature vortex generators (MVGs) have shed new light on the possibility of delaying transition to turbulence and hence accomplishing skin-friction drag reduction. A recurrent concern has been whether this passive flow control strategy would work for other types of disturbances than plane TSWs in an experimental configuration where the incoming disturbance is allowed to fully interact with the MVG array. In the present experimental investigation we show that not only TSW disturbances are attenuated, but also three-dimensional single oblique wave (SOW) and pair of oblique waves (POW) disturbances are quenched in the presence of MVGs, and that transition delay can be obtained successfully. For the SOW disturbance an unusual interaction between the wave and the MVGs occurs, leading to a split of the wave with one part travelling with a ‘mirrored’ phase angle with respect to the spanwise direction on one side of the MVG centreline. This gives rise to $\Lambda $-vortices on the centreline, which force a low-speed streak on the centreline, strong enough to overcome the high-speed streak generated by the MVGs themselves. Both these streaky boundary layers seem to act stabilizing on unsteady perturbations. The challenge in a passive control method making use of a non-modal type of disturbances to attenuate modal disturbances lies in generating stable streamwise streaks which do not themselves break down to turbulence.

scholarly journals Effects of Active and Passive Control Techniques on Mach 1.5 Cavity Flow Dynamics

2017 ◽  
Vol 2017 ◽  
pp. 1-24
Author(s):  
Selin Aradag ◽  
Kubra Asena Gelisli ◽  
Elcin Ceren Yaldir
Keyword(s):  
Passive Control ◽  
Control Method ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Cavity Flow ◽  
Flow Dynamics ◽  
Cover Plate ◽  
Control Methods ◽  
Trailing Edge ◽  
Control Techniques

Supersonic flow over cavities has been of interest since 1960s because cavities represent the bomb bays of aircraft. The flow is transient, turbulent, and complicated. Pressure fluctuations inside the cavity can impede successful weapon release. The objective of this study is to use active and passive control methods on supersonic cavity flow numerically to decrease or eliminate pressure oscillations. Jet blowing at several locations on the front and aft walls of the cavity configuration is used as an active control method. Several techniques are used for passive control including using a cover plate to separate the flow dynamics inside and outside of the cavity, trailing edge wall modifications, such as inclination of the trailing edge, and providing curvature to the trailing edge wall. The results of active and passive control techniques are compared with the baseline case in terms of pressure fluctuations, sound pressure levels at the leading edge, trailing edge walls, and cavity floor and in terms of formation of the flow structures and the results are presented. It is observed from the results that modification of the trailing edge wall is the most effective of the control methods tested leading to up to 40 dB reductions in cavity tones.

scholarly journals Effects of Reynolds Number and Distribution on Passive Flow Control in Owl-Inspired Leading-Edge Serrations

2020 ◽  
Vol 60 (5) ◽  
pp. 1135-1146
Author(s):  
Chen Rao ◽  
Hao Liu
Keyword(s):  
Reynolds Number ◽  
Flow Control ◽  
Passive Control ◽  
Leading Edge ◽  
Aerodynamic Performance ◽  
Low Noise ◽  
Passive Flow Control ◽  
Turbulent Fluctuations ◽  
Passive Flow ◽  
Turbulent Transition

Synopsis As a sophisticated micro device for noise reduction, the owl-inspired leading-edge (LE) serrations have been confirmed capable of achieving passive control of laminar-turbulent transition while normally paying a cost of lowering the aerodynamic performance in low Reynolds number (Re∼O[103]) regime. In order to explore potential applications of the owl-inspired serrated airfoils or blades in developing low noise wind turbines or multi-copters normally operating at higher Res, we conducted a large-eddy simulation (LES)-based study of Re effects on the aerodynamic performance of 2D clean and serrated models. Our results show that the LE serrations keep working effectively in mitigating turbulent fluctuations over a broad range of Re (O[103] ∼ O[105]), capable of achieving marked improvement in lift-to-drag ratio with increasing Res. As the aeroacoustic fields are in close association with the propagation of the turbulence sources, it is observed that the tradeoff between passive mitigation of turbulent fluctuations (hence aeroacoustic noise suppression) and aerodynamic performance can be noticeably mitigated at large angles of attack (AoAs) and at high Res. This indicates that the LE serrations present an alternative passive flow control mechanism at high Res through a straightforward local excitation of the flow transition while capable of mitigating the turbulent intensity passively. We further developed a 3D LES model of clean and partially serrated rectangular wings to investigate the effects of the LE serrations’ distribution on aerodynamic features, on the basis of the observation that longer serrations are often distributed intensively in the mid-span of real owl’s feathers. We find that the mid-span distributed LE serrations can facilitate the break-up of LE vortices and the turbulent transition passively and effectively while achieving a low level of turbulence kinetic energy over the upper suction surface of the wing.

Direct simulation Monte Carlo computations and experiments on leading-edge separation in rarefied hypersonic flow

2019 ◽  
Vol 879 ◽  
pp. 633-681 ◽  
Author(s):  
R. Prakash ◽  
L. M. Le Page ◽  
L. P. McQuellin ◽  
S. L. Gai ◽  
S. O’Byrne
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Flow Separation ◽  
Direct Simulation Monte Carlo ◽  
Leading Edge ◽  
Layer Growth ◽  
Direct Simulation ◽  
Simulation Monte Carlo ◽  
Edge Separation ◽  
Boundary Layer Growth

A comprehensive study of the fundamental characteristics of leading-edge separation in rarefied hypersonic flows is undertaken and its salient features are elucidated. Separation of a boundary layer undergoing strong expansion is typical in many practical hypersonic applications such as base flows of re-entry vehicles and flows over deflected control surfaces. Boundary layer growth under such conditions is influenced by effects of rarefaction and thermal non-equilibrium, thereby differing significantly from the conventional no-slip Blasius type. A leading-edge separation configuration presents a fundamental case for studying the characteristics of such a flow separation but with minimal influence from a pre-existing boundary layer. In this work, direct simulation Monte Carlo computations have been performed to investigate flow separation and reattachment in a low-density hypersonic flow over such a configuration. Distinct features of leading-edge flow, limited boundary layer growth, separation, shear layer, flow structure in the recirculation region and reattachment are all explained in detail. The fully numerical shear layer profile after separation is compared against a semi-theoretical profile, which is obtained using the numerical separation profile as the initial condition on existing theoretical concepts of shear layer analysis based on continuum flow separation. Experimental studies have been carried out to determine the surface heat flux using thin-film gauges and computations showed good agreement with the experimental data. Flow visualisation experiments using the non-intrusive planar laser-induced fluorescence technique have been performed to image the fluorescence of nitric oxide, from which velocity and rotational temperature distributions of the separated flow region are determined.

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