Publications
60 results found
Prigent SL, Buxton ORH, Bruce PJK, 2017, Experimental investigation of the wake of a lifting wing with cut-in sinusoidal trailing edges, AIAA Journal, Vol: 55, Pages: 1590-1601, ISSN: 1533-385X
The wake behind a NACA0012 wing at incidence with cut-in sinusoidal trailing edges is experimentally investigated. A wing model with interchangeable trailing edges is used to study their impact on the wake properties. Both vertical and spanwise traverses of hot wires are done at different downstream positions to obtain the downstream evolution of statistical properties and to perform spectral analysis. Stereoscopic particle image velocimetry is used to study the flow structure in a spanwise/cross-stream plane. Spanwise inhomogeneity of the velocity deficit and of the wake width is observed and explained by the presence of a spanwise/cross-stream flow induced by the cut-in modifications. Spectral analysis shows a decrease of shedding intensity with a shorter trailing-edge wavelength, with a reduction of up to 57% when compared to a straight blunt wing. Blunt sinusoidal trailing edges exhibit a reduction of spanwise correlation compared to a blunt straight one. A sharp cut-in design is also studied, which exhibits a more broadband shedding spike at a lower frequency.
Rodríguez-López E, Bruce PJK, Buxton ORH, 2017, Experimental measurement of wall shear stress in strongly disrupted flows, Journal of Turbulence, Vol: 18, Pages: 271-290, ISSN: 1468-5248
Mean and fluctuating wall shear stress is measured in strongly disrupted cases generated by various low-porosity wall-mounted single- and multi-scale fences. These grids generate a highly turbulent wake which interacts with the wall-bounded flow modifying the wall shear stress properties. Measurement methods are validated first against a naturally growing zero pressure gradient turbulent boundary layer showing accuracies of 1% and 4% for extrapolation and direct measurement of the mean shear stress respectively. Uncertainty associated with the root mean square level of the fluctuations is better than 2% making it possible to measure small variations originating from the different fences. Additionally, probability density functions and spectra are also measured providing further insight into the flow physics. Measurement of shear stress in the disrupted cases (grid+TBL) suggest that the flow characteristics and turbulence mechanisms remain unaltered far from the grid even in the most disrupted cases. However, a different root mean square level of the fluctuations is found for different grids. Study of the probability density functions seem to imply that there are different degrees of interaction between the inner and outer regions of the flow.
Steiros K, Bruce PJK, Buxton ORH, et al., 2017, Power consumption and form drag of regular and fractal-shaped turbines in a stirred tank, AIChE Journal, Vol: 63, Pages: 843-843, ISSN: 0001-1541
Previous wind-tunnel measurements have shown that fractal-shaped plates have increased drag compared to square plates of the same area. In this study, the power consumption and drag of turbines with fractal and rectangular blades in a stirred tank are measured. Power number decreases from rectangular to fractal impellers by over 10%, increasingly so with fractal iteration number. Our results suggest that this decrease is not caused by the wake interaction of the blades, nor solely by the wake interaction with the walls either. Pressure measurements on the blades’ surface show that fractal blades have lower drag than the rectangular ones, opposite to the wind tunnel experiment results. All tested blades’ center of pressure radius increases with Re, while their drag coefficient decreases, a possible effect of the solid body rotation expansion with Re. Spectral analysis of the pressure signal reveals two peaks possibly connected to the blades’ roll vortices.
Rodriguez-Lopez E, Bruce P, Buxton O, 2016, Near field development of artificially generated high Reynolds number turbulent boundary layers, Physical Review Fluids, Vol: 1, Pages: 1-22, ISSN: 2469-990X
Particle image velocimetry is conducted in the near field of two distinct wall-mounted trips for the artificial generation of a high Reynolds number turbulent boundary layer. The first of these trips consists of high aspect ratio obstacles, which are supposed to minimize the influence of their wakes on the near-wall region, contrasting with low aspect ratio trips, which would enhance this influence. A comprehensive study involving flow description, turbulent-nonturbulent interface detection, a low-order model description of the flow and an exploration of the influence of the wake in the near-wall region is conducted and two different mechanisms are clearly identified and described. First, high aspect ratio trips generate a wall-driven mechanism whose characteristics are a thinner, sharper, and less tortuous turbulent-nonturbulent interface and a reduced influence of the trips' wake in the near-wall region. Second, low aspect ratio trips generate a wake-driven mechanisms in which their turbulent-nonturbulent interface is thicker, less sharply defined, and with a higher tortuosity and the detached wake of the obstacles presents a significant influence on the near-wall region. Study of the low-order modeling of the flow field suggests that these two mechanisms may not be exclusive to the particular geometries tested in the present study but, on the contrary, can be explained based on the predominant flow features. In particular, the distinction of these two mechanisms can explain some of the trends that have appeared in the literature in the past decades.
Melina G, Bruce PJK, Vassilicos C, 2016, Vortex shedding effects in grid-generated turbulence, Physical Review Fluids, Vol: 1, ISSN: 2469-990X
The flow on the centerline of grid-generated turbulence is characterized via hot-wire anemometry for three grids with different geometry: a regular grid (RG60), a fractal grid (FSG17), and a single-square grid (SSG). Due to a higher value of the thickness t0 of its bars, SSG produces greater values of turbulence intensity Tu than FSG17, despite SSG having a smaller blockage ratio. However, the higher Tu for SSG is mainly due to a more pronounced vortex shedding contribution. The effects of vortex shedding suppression along the streamwise direction x are studied by testing a three-dimensional configuration, formed by SSG and a set of four splitter plates detached from the grid (SSG+SP). When vortex shedding is damped, the centerline location of the peak of turbulence intensity xpeak moves downstream and Tu considerably decreases in the production region. For FSG17 the vortex shedding is less intense and it disappears more quickly, in terms of x/xpeak, when compared to all the other configurations. When vortex shedding is attenuated, the integral length scale Lu grows more slowly in the streamwise direction, this being verified both for FSG17 and for SSG+SP. In the production region, there is a correlation between the vortex shedding energy and the skewness and the flatness of the velocity fluctuations. When vortex shedding is not significant, the skewness is highly negative and the flatness is much larger than 3. On the opposite side, when vortex shedding is prominent, the non-Gaussian behavior of the velocity fluctuations becomes masked.
Melina G, Bruce PJK, Hewitt GF, et al., 2016, Heat transfer enhancement by grid-generated turbulence for a cylinder in crossflow, 5th International Conference on Jets, Wakes and Separated Flows (ICJWSF2015, Publisher: Springer, Pages: 125-132, ISSN: 0930-8989
The heat transfer coefficient is experimentally measured around a cylinder heated by ohmic effect. The heating technique approximates a uniform heat flux on the cylinder’s wall. The model is placed downstream of different perturbing grids in a wind tunnel. The Reynolds number based on the cylinder’s diameter varies between 10820 and 48830. At large distances from the grids, the heat transfer is significantly enhanced by using a fractal and a single square grid designed to increase turbulence intensity with a low blockage ratio. Significant differences exist between the heat transfer profiles measured in the production and in the decay region in positions where turbulence intensity is the same.
Steiros K, Bruce, Buxton O, et al., 2016, Flow Field Characteristics and Energy Injection in a Tank Stirred by Regular and Fractal Blade Impellers, Proceedings of the 5th International Conference on Jets, Wakes and Separated Flows (ICJWSF2015), Editors: Segalini, Publisher: Springer, Pages: 363-369, ISBN: 978-3-319-30602-5
Baj P, Bruce PJK, Buxton ORH, 2016, On a PLIF quantification methodology in a nonlinear dye response regime, Experiments in Fluids, Vol: 57, ISSN: 1432-1114
A new technique of planar laser-induced fluorescence calibration is presented in this work. It accounts for a nonlinear dye response at high concentrations, an illumination light attenuation and a secondary fluorescence’s influence in particular. An analytical approximation of a generic solution of the Beer–Lambert law is provided and utilized for effective concentration evaluation. These features make the technique particularly well suited for high concentration measurements, or those with a large range of concentration values, c, present (i.e. a high dynamic range of c). The method is applied to data gathered in a water flume experiment where a stream of a fluorescent dye (rhodamine 6G) was released into a grid-generated turbulent flow. Based on these results, it is shown that the illumination attenuation and the secondary fluorescence introduce a significant error into the data quantification (up to 15 and 80 %, respectively, for the case considered in this work) unless properly accounted for.
Rodríguez-López E, Bruce PJK, Buxton ORH, 2016, On the Formation Mechanisms of Artificially Generated High Reynolds Number Turbulent Boundary Layers, Boundary-Layer Meteorology, Vol: 160, Pages: 201-224, ISSN: 0006-8314
We investigate the evolution of an artificially thick turbulent boundary layer generatedby two families of small obstacles (divided into uniform and non-uniform wall normaldistributions of blockage). One- and two-point velocity measurements using constant temperatureanemometry show that the canonical behaviour of a boundary layer is recovered afteran adaptation region downstream of the trips presenting 150 % higher momentum thickness(or equivalently, Reynolds number) than the natural case for the same downstream distance(x ≈ 3 m). The effect of the degree of immersion of the trips for h/δ 1 is shown to play asecondary role. The one-point diagnostic quantities used to assess the degree of recovery ofthe canonical properties are the friction coefficient (representative of the inner motions), theshape factor and wake parameter (representative of the wake regions); they provide a severetest to be applied to artificially generated boundary layers. Simultaneous two-point velocitymeasurements of both spanwise and wall-normal correlations and the modulation of innervelocity by the outer structures show that there are two different formation mechanisms forthe boundary layer. The trips with high aspect ratio and uniform distributed blockage leavethe inner motions of the boundary layer relatively undisturbed, which subsequently drivethe mixing of the obstacles’ wake with the wall-bounded flow (wall-driven). In contrast, thelow aspect-ratio trips with non-uniform blockage destroy the inner structures, which are thenre-formed further downstream under the influence of the wake of the trips (wake-driven).
Bruce PJK, Buxton ORH, Rodriguez-Lopez E, 2016, Downstream evolution of perturbations in a zero pressure gradient turbulent boundary layer, Progress in Turbulence VI: Proceedings of the iTi Conference on Turbulence 2014, Vol: 165, Pages: 133-137, ISSN: 0930-8989
This paper examines the evolution of perturbations generated by various trips in a zero pressure gradient turbulent boundary layer. Measurements taken using hot-wire anemometry show that the evolution of the boundary layer towards the natural state is strongly dependent on the trip geometry. In particular the mechanisms creating the boundary layer appear to depend primarily on the wall normal distribution of blockage ratio, recovering the natural properties more rapidly for a uniform distribution of blockage (wall normal cylinders) than for non-uniform blockage (sawtooth fence). The relative size of the trip with respect to the boundary layer is shown to be a second order effect. Standard behaviour (characterized by the skin friction coefficient, CfCf, the wake component, ΠΠ, and the shape factor, H) is recovered successfully 500D∼75h500D∼75h downstream, presenting 175%175% higher momentum thickness, θθ, than the natural case for the same downstream distance.
Rodriguez-Lopez E, Bruce PJK, Buxton O, 2016, Downstream Evolution of Perturbations in a Zero Pressure Gradient Turbulent Boundary Layer, Progress in Turbulence VI, Editors: Peinke, Kampers, Oberlack, Waclawczyk, Talamelli, Publisher: Springer, ISBN: 978-3-319-29129-1
Jinks E, Santer M, bruce P, 2016, Aero-Structural Design Optimization of Adaptive Shock Control Bumps, 54th AIAA Aerospace Sciences Meeting, Publisher: American Institute of Aeronautics and Astronautics
Shock control bumps (SCB) are a transonic flow control device that aim to reduce theoverall drag due to a normal shock on a typical passenger jet at cruise. The concept of adaptiveSCB which can be deployed for best use are investigated through an aero-structuraldesign tool that produces optimal geometries. The optimizer uses a surface based performancemetric to highlight the importance of the flow quality around the SCB as wellas including a structural element that is required to provide the necessary flexibility todeform. The performance metric produces the target pressure distribution and successfullysmears the shock. It is found that the structural constraint does not inhibit bumpheight and global airfoil performance is not significantly a↵ected, L/D varies < 0.6%. Theaerodynamic pressure loading can be utilised to produce a new family of SCB geometriesthat are unachievable with mechanical actuation alone. The study shows that adaptiveSCB that exploit the naturally occurring pressure field around an airfoil in a passive wayare a feasible technology to mitigate the poor o↵-design performance of static SCB.
Jinks E, bruce P, Santer M, 2016, Wind Tunnel Experiments with Flexible Plates in Transonic Flows, 54th AIAA Aerospace Sciences Meeting, Publisher: AIAA
The evolution of adaptive shock control bump (SCB) design has seen the system flexibilityincrease to a point where the aerodynamic loading can affect the deformation of theplate. By studying the effects of a flexible plate subject to transonic flow the fluid structureinteraction can be investigated. In this study an array of thin plates (0.4 and 0.6 mm)with different aspect ratios (1 and 1.33) are exposed to a Mach 1.4 normal shockwave.PIV is used in combination with Schlieren imaging to provide a detailed view of the flowcurvature surrounding the plate as well as the global shock structure. A technique thatextracts the plate deformation from the PIV images is also presented which provides fluidand structural information for each test. The relationship between plate and flow angleis discussed as well as the effect of plate stiffness and free stream influence of each plateconfiguration.
Prigent SL, Buxton O, Bruce PJK, 2016, Experimental investigation of the wake of a lifting wing with cut-in sinusoidal trailing edges, 54th AIAA Aerospace Sciences Meeting, Publisher: American Institute of Aeronautics and Astronautics
The wake behind a NACA0012 wing at incidence with cut-in sinusoidal trailing edges(TE) is experimentally investigated. A wing model with interchangeable trailing edges isused to study their impact on the wake properties. Both vertical and span-wise traversesof hot-wires are done at different downstream positions, to obtain the downstream evolutionof statistical properties and to perform spectral analysis. Stereoscopic particle imagevelocimetry is used to study the flow structure in a span-wise/cross-stream plane.Span-wise inhomogeneity of the velocity deficit and of the wake width is observed andexplained by the presence of a span-wise/cross-stream flow induced by the cut-in modifications.Spectral analysis shows a decrease of shedding intensity with shorter TE wavelength,with up to 57% reduction when compared to a straight blunt wing. Blunt sinusoidal TEsoffer a reduction of span-wise correlation compared to the blunt straight one, which ismitigated when compared to an unmodified wing. A sharp cut-in design is also studied,that exhibits a more broad-band shedding spike at a lower frequency.
Melina G, Bruce PJK, Hewitt GF, et al., 2016, Heat transfer from a cylinder in the production and in the decay regions of grid-generated turbulence
Bruce PJK, Colliss SP, 2015, Review of research into shock control bumps, SHOCK WAVES, Vol: 25, Pages: 451-471, ISSN: 0938-1287
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- Citations: 62
Kahk JM, Villar-Garcia IJ, Grechy L, et al., 2015, A study of the pressure profiles near the first pumping aperture in a high pressure photoelectron spectrometer, Journal of Electron Spectroscopy and Related Phenomena, Vol: 205, Pages: 57-65, ISSN: 1873-2526
In a high-pressure photoelectron spectrometer, the sample is positioned close to a differential pumping aperture, behind which the pressure is several orders of magnitude lower than the pressure in the analysis chamber. To find the optimal sample position, where the path length of the photoelectrons through the high pressure region is minimized as far as possible without compromising knowledge of the actual pressure at the sample surface, an understanding of the pressure variations near the sample and the aperture is required. A computational fluid dynamics study has been carried out to examine the pressure profiles, and the results are compared against experimental spectra whose intensities are analyzed using the Beer–Lambert law. The resultant pressure profiles are broadly similar to the one previously derived from a simplistic molecular flow model, but indicate that as the pressure in the analysis chamber is raised, the region over which the pressure drop occurs becomes progressively narrower.
Baj P, Bruce PJK, Buxton ORH, 2015, The triple decomposition of a fluctuating velocity field in a multiscale flow, Physics of Fluids, Vol: 27, Pages: 075104-1-075104-24, ISSN: 1070-6631
A new method for the triple decomposition of a multiscale flow, which is based on the novel optimal mode decomposition (OMD) technique, is presented. OMD provides low order linear dynamics, which fits a given data set in an optimal way and is used to distinguish between a coherent (periodic) part of a flow and a stochastic fluctuation. The method needs no external phase indication since this information, separate for coherent structures associated with each length scale introduced into the flow, appears as the output. The proposed technique is compared against two traditional methods of the triple decomposition, i.e., bin averaging and proper orthogonal decomposition. This is done with particle image velocimetry data documenting the near wake of a multiscale bar array. It is shown that both traditional methods are unable to provide a reliable estimation for the coherent fluctuation while the proposed technique performs very well. The crucial result is that the coherence peaks are not observed within the spectral properties of the stochastic fluctuation derived with the proposed method; however, these properties remain unaltered at the residual frequencies. This proves the method’s capability of making a distinction between both types of fluctuations. The sensitivity to some prescribed parameters is checked revealing the technique’s robustness. Additionally, an example of the method application for analysis of a multiscale flow is given, i.e., the phase conditioned transverse integral length is investigated in the near wake region of the multiscale object array.
Rodriguez-Lopez E, Bruce PJK, Buxton ORH, 2015, A robust post-processing method to determine skin friction in turbulent boundary layers from the velocity profile, Experiments in Fluids: experimental methods and their applications to fluid flow, Vol: 56, Pages: 1-16, ISSN: 0723-4864
The present paper describes a method to extrapolate the mean wall shear stress, 𝜏𝑤𝑎𝑙𝑙, and the accurate relative position of a velocity probe with respect to the wall, Δ𝑦, from an experimentally measured mean velocity profile in a turbulent boundary layer. Validation is made between experimental and direct numerical simulation data of turbulent boundary layer flows with independent measurement of the shear stress. The set of parameters which minimize the residual error with respect to the canonical description of the boundary layer profile is taken as the solution. Several methods are compared, testing different descriptions of the canonical mean velocity profile (with and without overshoot over the logarithmic law) and different definitions of the residual function of the optimization. The von Kármán constant is used as a parameter of the fitting process in order to avoid any hypothesis regarding its value that may be affected by different initial or boundary conditions of the flow. Results show that the best method provides an accuracy of Δ𝑢𝜏≤0.6% for the estimation of the friction velocity and Δ𝑦+≤0.3 for the position of the wall. The robustness of the method is tested including unconverged near-wall measurements, pressure gradient, and reduced number of points; the importance of the location of the first point is also tested, and it is shown that the method presents a high robustness even in highly distorted flows, keeping the aforementioned accuracies if one acquires at least one data point in 𝑦+<10. The wake component and the thickness of the boundary layer are also simultaneously extrapolated from the mean velocity profile. This results in the first study, to the knowledge of the authors, where a five-parameter fitting is carried out without any assumption on the von Kármán constant and the limits of the logarithmic layer further from its existence.
Jinks E, Bruce P, Santer M, 2015, The use of actuated flexible plates for adaptive shock control bumps, 53rd AIAA Aerospace Sciences Meeting, Publisher: American Institute of Aeronautics and Astronautics
Rodríguez-López E, Bruce PJK, Buxton ORH, 2015, Downstream evolution of perturbations in a zero pressure gradient turbulent boundary layer
This abstract examines the evolution of perturbations generated by various trips in a turbulent boundary layer. Measurements taken using hot wire anemometry show that the evolution towards the natural state is strongly dependent on the formation mechanisms of the boundary layer, this being different for different wall normal distribution of the trips’ blockage. It is observed that standard boundary layer properties are recovered, after an adaptation region, with 175% higher momentum thickness than the natural case. Two-point measurements with time resolved velocity in the inner region are studied to explore the different formation mechanisms.
Baj P, Bruce PJK, Buxton ORH, 2015, Triple decomposition of a fluctuating velocity field in a multiscale flow
A method for the triple decomposition of fluctuating velocity in a multiscale flow, suitable for a spatiotemporal data set, is presented. It is applied to experimental data gathered by means of particle image velocimetry (PIV). The basic properties of the decomposed parts are shown. The presented method is then used to perform a conditional study on the residual transverse velocity fluctuations. It was found that phase locking occurs between the stochastic fluctuations embedded in the wakes of different bars, appearing after the wakes have merged.
Jinks E, Bruce P, Santer M, 2014, Adaptive Shock Control Bumps, 52nd Aerospace Sciences Meeting, Publisher: American Institute of Aeronautics and Astronautics
Bruce PJK, Babinsky H, 2012, Experimental study into the flow physics of three-dimensional shock control bumps, Journal of Aircraft: devoted to aeronautical science and technology
This paper describes a fundamental experimental study of the flow structure around a single three-dimensional (3-D) transonic shock control bump (SCB) mounted on a flat surface in a wind tunnel. Tests have been carried out with a Mach 1.3 normal shock wave located at a number of stream-wise positions relative to the SCB. A range of experimental techniques have been used to study details of the flow. The results of the work build on the findings of previous researchers and shed new light on the flow physics of 3-D SCBs. It is found that span-wise pressure gradients across the SCB ramp affect the magnitude and uniformity of flow-turning generated by the bump, which can impact on the span-wise propagation of the quasi-2-D shock structure produced by a 3-D SCB. At the bump crest, vortices can form if the pressure on the crest is significantly lower than at either side of the bump. The trajectories of these vortices, which are relatively weak, are strongly influenced by any span-wise pressure gradients across the bump tail. A significant difference between 2-D and 3-D SCBs highlighted by the study is the impact of span-wise pressure gradients on 3-D SCB performance. The magnitudeof these span-wise pressure gradients is determined largely by SCB geometry and shock position.
Bruce PJK, Babinsky H, Tartinville B, et al., 2011, Corner Effect and Asymmetry in Transonic Channel Flows, AIAA JOURNAL, Vol: 49, Pages: 2382-2392, ISSN: 0001-1452
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- Citations: 17
Bruce PJK, Babinsky H, Tartinville B, et al., 2011, Experimental and Numerical Study of Oscillating Transonic Shock Waves in Ducts, AIAA Journal, Vol: 49, Pages: 1710-1720
An experimental and computational study of a Mach 1.4 transonic shock wave in a parallel-walled duct subject to downstream pressure perturbations in the frequency range of 16–90 Hz has been conducted. The dynamics of unsteady shock motion and aspects of the unsteady transonic shock and turbulent tunnel-floor boundary-layer interaction have been investigated. The numerical computations were performed using an unsteady Reynoldsaveraged Navier–Stokes scheme. It is found that the (experimentally measured) shock dynamics are generally well replicated by the numerical scheme, especially at relatively low (40 Hz) frequencies. However, variations in shock/boundary-layer interaction structure during unsteady shock motion observed in experiments are not always well predicted by the simulation. Significantly, the computations predict variations in shock/boundary-layer interaction size due to shock motion that are much larger and in the opposite sense to the variations observed in experiments. Comparison of the unsteady results from the present study with steady (experimental) results from the literature suggests that unsteady Reynolds-averaged Navier–Stokes code used in the present study models the unsteady shock/boundary-layer interaction behavior as quasi-steady, whereas experiments suggest that it is more genuinely unsteady. Further work developing numerical methods that demonstrate a more realistic sensitivity of shock/ boundary-layer interaction structure to unsteady shock motion is required.
Bruce PJK, Burton DMF, Titchener NA, et al., 2011, Corner effect and separation in transonic channel flows, JOURNAL OF FLUID MECHANICS, Vol: 679, Pages: 247-262, ISSN: 0022-1120
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- Citations: 55
Bruce PJK, Babinsky H, 2010, An experimental study of transonic shock / boundary layer interactions subject to downstream pressure perturbations, Journal of Aerospace Science and Technology, Vol: 14, Pages: 134-142
An experimental study of the response to downstream pressure perturbations of transonic shocks in a parallel walled duct has been conducted. Tests have been carried out for normal shock strengths of M = 1.4 and 1.5 with pressure perturbation frequencies in the range 6–90 Hz. The measurement techniques of high speed schlieren photography, laser Doppler anemometry and high frequency pressure measurements have been used. In all test cases, the normal shock undergoes periodic oscillatory motion in the streamwise direction. The interaction structure between the oscillating shock and the tunnel wall turbulent boundary layer varies during oscillations, especially at M = 1.4, where the leading shock–leg of the lambda shock–foot structure gets significantly stronger during upstream shock motion and weaker during downstream motion. These changes are related to the relative strength of the shock (which varies due to the velocity of shock motion) and the effect that this has on the extent of boundary layer thickening and/or shock induced boundary layer separation. The dominant mechanism that governs the dynamics of shock motion in response to downstream pressure perturbations has also been identified and explains why the amplitude of shock motion decreases with increasing frequency.
Bruce PJK, Babinsky H, 2009, Dynamics of unsteady shock wave motion, 26th International Symposium on Shock Waves, Publisher: SPRINGER-VERLAG BERLIN, Pages: 1237-1242
Bruce PJK, Babinsky H, 2008, Unsteady shock wave dynamics, Journal of Fluid Mechanics, Vol: 603, Pages: 463-473
An experimental study of an oscillating normal shock wave subject to unsteady periodic forcing in a parallel-walled duct has been conducted. Measurements of the pressure rise across the shock have been taken and the dynamics of unsteady shock motion have been analysed from high-speed schlieren video (available with the online version of the paper). A simple analytical and computational study has also been completed. It was found that the shock motion caused by variations in back pressure can be predicted with a simple theoretical model. A non-dimensional relationship between the amplitude and frequency of shock motion in a diverging duct is outlined, based on the concept of a critical frequency relating the relative importance of geometry and disturbance frequency for shock dynamics. The effects of viscosity on the dynamics of unsteady shock motion were found to be small in the present study, but it is anticipated that the model will be less applicable in geometries where boundary layer separation is more severe. A movie is available with the online version of the paper.
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