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This paper provides a detailed historical review of the cavity flow phenomena in fluid mechanics, from recorded studies in the late 19th century to more recent work. Research has been reviewed, independently and in culmination with other studies, to summarise the major and minor governing parameters of the flow. Outlined are influences of technology, regarding numerical models, experimental methods, analysis, and control techniques. All Mach regimes are assessed; low incompressible, sub-, trans-, super- and hypersonic where substantial research was available. A large variety of cavity geometry was presented, mostly rectangular, with more complex features akin to industry application, and where available, assessment of the boundary layer structure is also included. Conclusions on present understanding, and requirements for future work are given, with an aligned set of available data. Cavity flow-field initialisation and development is dependent on; upstream (U/S) flow conditions of; airspeed M ∞ , boundary layer (BL) disturbance (δ), displacement (δ ∗) and momentum (θ) thickness, either laminar or turbulent, and cavity geometry; length (L), depth (D) and width (W), with ratios L / D , L / W , δ / D and L / θ defining cavity response. I.e., a narrow cavity with a thin BL U/S tends toward a periodic 3D flow-field, with 3D effects and periodicity decreasing as W and δ increase. Control is achievable through SL stabilisation via spanwise disturbance from the leading edge (LE), or thickening the BL, thus shear layer (SL). Experiments are preferred over numerical models, due to the inefficiency and high cost of required models (Colonius, 2001; Rowley and Williams, 2006; Lawson and Barakos, 2011). We understand effects of L , D , L / D , and M ∞ , thus future work should focus on W , BL and how they impact mode switching and stream/spanwise flow propagation. Also introducing more complex geometry, realistic to application, to observe additional 3D effects and U/S momentum change, in contribution to a scaling parameter and determination of criteria for activation of material displacement. [ABSTRACT FROM AUTHOR]

We investigate and characterize the effect of compressibility and rarefaction on vortex structures in the benchmark lid-driven cavity flow. Direct numerical simulations are performed, employing the unified gas kinetic scheme to examine the changes in vortex generation mechanisms and the resulting flow structures at different Mach and Knudsen numbers. At high degrees of rarefaction, where inter-molecular interactions are minimal, the molecules mainly collide with the walls. Consequently, the dominant flow structure is a single vortex in the shape of the cavity. It is shown that increasing compressibility or decreasing rarefaction lead to higher molecular density in the cavity corners, due to more frequent inter-molecular collisions. This results in lower flow velocities, creating conditions conducive to the development of secondary and corner vortices. The physical processes underlying vortex formations at different Knudsen numbers, Mach numbers, and cavity shapes are explicated. A parametric map that classifies different regimes of vortex structures as a function of compressibility, rarefaction, and cavity shape is developed. [ABSTRACT FROM AUTHOR]

Deep cavity configurations are common in various industrial applications, including automotive windows, sunroofs, and many other applications in aerospace engineering. Flows over such a geometry can result in aeroacoustic coupling between the cavity shear layer oscillations and the surrounding acoustic modes. This phenomenon can result in a resonance that can lead to significant noise and may cause damage to mechanical structures. Flow control methods are usually used to reduce or eliminate the aeroacoustic resonance. An experimental set up was developed to study the effectiveness of both a cylinder and a profiled cylinder positioned upstream from the cavity in reducing the flow resonance. The cavity flow and the acoustic signals were obtained using particle image velocimetry (PIV) and unsteady pressure sensors, respectively. A decrease of up to 36 dB was obtained in the sound pressure levels (SPL) using the passive control methods. The profiled cylinder showed a similar efficacy in reducing the resonance despite the absence of a high-frequency forcing. Time-space cross-correlation maps along the cavity shear layer showed the suppression of the feedback mechanism for both control methods. A snapshot proper orthogonal decomposition (POD) showed interesting differences between the cylinder and profiled cylinder control methods in terms of kinetic energy content and the vortex dynamics behavior. Furthermore, the interaction of the wake of the control device with the cavity shear layer and its impact on the aeroacoustic coupling was investigated using the POD analysis. [ABSTRACT FROM AUTHOR]

The flow performance of a dual wall-mounted cavity in a strut-injector scramjet combustor in steady reacting flow conditions is computationally analyzed. A baseline configuration corresponding to DLR experiments and two proposed configurations with varying bottom wall cavity depth and fixed top wall ramp is considered. Steady-flow computations are performed using the 2-D Reynolds Averaged Navier–Stokes method with k-ω SST turbulence closure coupled and single-step reaction chemistry. The calculated flow patterns, density, pressure, and temperature fields are compared with shadowgraph and wall pressure measurements from DLR experiments. The cavity and strut are mounted downstream of the strut to analyze the shock patterns and their interference with the shear layer mixing features. The estimated flow patterns, density, pressure, and temperature fields are compared with shadowgraph and wall pressure measurements from DLR experiments. Incorporating cavity and ramp configuration provides earlier complete combustion compared to the baseline model, with a marginal rise in the total pressure caused by additional shock wave formation that emanates from the corners of the cavity and ramp. The combustion zone widens in the lateral direction as the cavity shifts the shock train downstream of the strut injector owing to intense shock shear layer interactions. [ABSTRACT FROM AUTHOR]

Alumina nanoparticles have been accumulating attention in recent years because of their unique physical characteristics and broad range of engineering and industrial applications. Scientists are paying close attention to analyzing the flow and heat transfer features of alumina-based nanofluids filled within a cavity due to their wide range of applications, such as heat exchangers, fuel cells, room ventilation, and cooling electronic systems. Motivated by the applications, the current study numerically analyzes the natural convective flow and heat transfer features of A l 2 O 3 - H 2 O and A l 2 O 3 / C 2 H 6 O 2 - H 2 O nanofluids in a rectangular porous cavity under the presence of thermal radiation and heat generation/absorption by using the non-Fourier heat flux model. The system of equations is numerically solved by utilizing the Marker and Cell technique. The comparative fluid flow and heat transfer features are performed by using different shapes of A l 2 O 3 nanoparticles (spherical, brick, cylindrical, platelet, and blade) dispersed in two different kinds of base fluids ( H 2 O and C 2 H 6 O 2 - H 2 O ). The flow domain is filled with an isotropic porous medium. Several pertinent parameters are considered in this investigation, such as the Darcy number, Rayleigh number, heat source/sink, radiation parameter, and nanoparticle volume fractions, which are analyzed in terms of streamlines, isotherms, and local and average Nusselt numbers. According to the findings, the average Nusselt number increases by augmenting the nanoparticle volume concentration and the heat source/sink parameters, while it decreases by improving the radiation influence. Thermal performance within the cavity is affected by varying radiation influences. By increasing the spherical-shaped A l 2 O 3 nanoparticle concentration from 0 to 5% in H 2 O and C 2 H 6 O 2 - H 2 O base fluids, the average heat transfer rate is augmented by 27.37% and 27.62%, respectively. The blade-shaped nanoparticles produce a better heat transfer rate than other-shaped nanoparticles. Finally, it was concluded that A l 2 O 3 - H 2 O nanofluid delivers better fluid flow and temperature distribution than A l 2 O 3 / C 2 H 6 O 2 - H 2 O nanofluid. [ABSTRACT FROM AUTHOR]

Cavity flows studied over the past few decades have led to an increased understanding of the flow physics and instability modes in a range of configurations. While a large number of these studies focus on two-dimensional and three-dimensional rectangular/cuboidal cavities, significant variations are seen with three-dimensional cylindrical cavities with a top bounding wall. The present work details the flow physics of such cavities with a compressible (air) flow past the cavity at two pressure drops of 3850 Pa and 2000 Pa. Results from detached eddy simulations (DES) reveal the presence of the wake mode and shear layer instabilities, respectively, with modified dynamics and oscillatory modes owing to the top wall. In the interest of preventing mode switching with changes in operating conditions, which could lead to large-scale flow disruptions, a passive flow control technique is tested. The modified cavity (with a downstream ramp scaled by the size of shed structures) is seen to maintain the same mode throughout the range of operation offering valuable insights into design modifications for such cavities in practical settings. [ABSTRACT FROM AUTHOR]

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This paper presents a numerical method for incompressible fluid flow. A difficulty in analyzing incompressible fluid flow is that the continuity equation has no time evolution term. In the marker and cell (MAC) method, Poisson's equation is solved iteratively, which takes most of the computation time, and in the artificial compressibility method (ACM), pseudo-time iteration is necessary to solve for unsteady solutions. Here, modal analysis that uses the velocity eigenvectors corresponding to zero eigenvalues is proposed for analyzing two-dimensional incompressible fluid flow. The proposed method involves only about one third of the number of variables needed in the MAC method and the ACM, and it does not require iterative calculation of Poisson's equation or pseudo-time iteration. Numerical results for a simple flow system and a cavity flow obtained using the proposed method are compared with those obtained using the ACM and the simplified MAC method. The results agree well, thereby validating the proposed modal analysis. [ABSTRACT FROM AUTHOR]

The use of nanofluids for convectional heat transfer has become a spry area of research in recent years with the aim of improving heat transfer efficiency. Hybrid nanofluids have attracted significant attention and are advancing research and industrial applications since they involve employing more than one type of nanoparticle(s) in a base fluid. They enhance heat transfer by combining the chemical and physical properties of several nanoparticles concurrently and providing the properties in a homogeneous state. However, few experimental studies have focused on natural convective heat transfer using hybrid nanofluids. In this study, the natural convection of alumina – multiwalled carbon nanotube/water hybrid nanofluids formulated using a two-step method at a percentage weight ratio of 10:90 Al2O3: MWCNT at various nanoparticles volume concentrations of 0.00, 0.05, 0.10, 0.15, and 0.20 vol% was studied inside a square cavity (AR = 1) with two vertical walls which are isothermal, aimed at the Rayleigh number (Ra) range of 2.81 × 108 to 8.58 × 108. The average Nusselt number (Nuav), heat transfer coefficient (hav), heat transfer (Qav), and Rayleigh number (Ra) were considered at varying temperature gradients of 20°C – 50°C. Al2O3-MWCNT/water hybrid nanofluid with 0.10 vol% volume concentration was discovered to have the maximum value for hav,Qav, and Nuav. However, it was also observed that a further increase in the hybrid nanoparticles' volume concentration led to their deterioration at various temperature gradients. The maximum enhancements of 44%, 49%, and 42% were noted for hav,Qav, and Nuav, respectively, at ∆T = 50 °C, in comparison with the base fluid. Al2O3-MWCNT/water hybrid nanofluids application in a square cavity demonstrated enhanced natural convection. This present study concluded that hybrid nanofluids as heat transfer fluid significantly improved heat transfer performance compared to the base fluid. [ABSTRACT FROM AUTHOR]

Combining the detached eddy simulation (DES) method and Ffowcs Williams-Hawkings (FW-H) equation, the effect of bogie cavity end wall inclination on the flow field and aerodynamic noise in the bogie region is numerically studied. First, the simulation is conducted based on a simplified cavity-bogie model, including five cases with different inclination angles of the front and rear walls of the cavity. By comparing and analyzing the flow field and acoustic results of the five cases, the influence of the regularity and mechanism of the bogie cavity end wall inclination on the flow field and the aerodynamic noise of the bogie region are revealed. Then, the noise reduction strategy determined by the results of the simplified cavity-bogie model is applied to a three-car marshaling train model to verify its effectiveness when applied to the real train. The results reveal that the forward inclination of the cavity front wall enlarges the influence area of shear vortex structures formed at the leading edge of the cavity and intensifies the interaction between the vortex structures and the front wheelset, front motor, and front gearbox, resulting in the increase of the aerodynamic noise generated by the bogie itself. The backward inclination of the cavity rear wall is conducive to guiding the vortex structures flow out of the cavity and weakening the interaction between the shear vortex structures and the cavity rear wall, leading to the reduction of the aerodynamic noise generated by the bogie cavity. Inclining the rear end wall of the foremost bogie cavity of the head car is a feasible aerodynamic noise reduction measure for high-speed trains. [ABSTRACT FROM AUTHOR]

In the high-temperature mainstream of gas turbines, there is a rim clearance between the rotor and the stator. A rim seal is to prevent the intrusion of high-temperature gas by spraying cool fluid from the inside of the rim clearance to the outside. In the past research on rim seals, the focus was on the overall performance of the sealing structure, and the flow in the disc cavity was studied more, but the high-radius flow was simplified. In recent years, additional research in the field has focused on more complex sealing structures and high-radius flows, such as the interface between the disk cavity and the mainstream. There is more work to be conducted in this area of research. In this paper, the unsteady numerical simulation of the flow in four different rim sealing geometries is carried out by the URANS method. The flow phenomena and the influence of geometry on the flow are studied. The numerical simulation results are validated with the experimental results. It is found that the fluid in the rim sealing obviously presents two distinct forms and confrontations according to the tangential velocity. The flow in the sealing structure presents obvious circumferential non-uniformity. Compared with the single-axial structure, in the single-radial structure, the mixing area is induced by the radial geometry, and more vortex structures are generated, the mixing process is more intense, and the sealing effect is better. In the double-sealing structure, the inner structure plays the role of a barrier, and the cavity geometry between the two layers has a major influence on the sealing performance. [ABSTRACT FROM AUTHOR]

When the nanoparticles are incorporated into the base fluid, the resultant fluid is known as nanofluid. Nanofluids have higher thermal efficiency as compared to base fluid. Some fluids have poor thermal conductivity like, water, air and ethylene glycol and oil. Thus, the thermal efficiency of the work can be increased by inserting the nanoparticles into base fluid. Furthermore, the nanoparticles can be used to enhanced the cooling rate of the system due to higher thermal conductivity. In this investigation, the magnetohydodynamics convective flow phenomenon under the consideration of different nanofluids inside a triangular porous conduit will investigated. For the better understanding of heat transfer characteristics, the thermal radiation and heat generation (or absorption) will also incorporated. We will impose constant and variable temperature on the left inclined wall to analyze the heat transfer mechanism. Furthermore, the heat transfer rate will also be analyzed by considering different nanoparticles. The robust numerical scheme namely the finite element method has been selected to simulate the nonlinear complex flow equations based on iterative scheme. In this technique, at the first stage the penalty method is employed for the purpose of the elimination of pressure from the equations of motion. After that the developed the system in the absence of pressure term is solved. To simulate the problem the value of penalty parameter is chosen 10−7. The contours of stream function and temperature distribution are displayed for several values of physical parameters. Furthermore, the variations of important quantity known as an average heat transfer rate are displayed through bar charts. For constant heating case the aluminum nano particles are the best choice to enhance the heat transfer rate in the system. Moreover, the magnitude of the stream function rises against the radiation and Rayleigh number. Furthermore, the conduction mode of heat transfer is achieved via thermal radiation parameter. The applications of the given study can be found in various industrial processes like, cooling of electronic devices, cooling of house and commercial buildings, cooling of microelectronics, cancer therapy, vehicle thermal management, and heat exchangers. [ABSTRACT FROM AUTHOR]

In this paper,a simplifiedtransonic weapon baywith a L/D=5 and Mach number 0.85 was considered using the large-eddy simulation(LES)with dynamic kinetic energy subgrid-scale (SGS)model. The M219 geometry has been analyzed using OpenFOAM for three different configurations based on the position of the covers. The obtained results have been validated against reference studies and presented in terms of mean streamwise velocity profile, overall sound pressure level, sound pressure level and band-integrated sound pressure level in both spatial and frequency domains. In order to mitigate the high computational cost associated with acoustic analysis, a Cartesian mesh topology has been employed as an alternative approach. The numerical findings have demonstrated a comparable level of accuracy to simulations conducted with high-cell count meshes. Based on these findings, a cavity analysis has been conducted for the configuration with covers positioned at a position of 45°.

Deep cavity configurations are common in various industrial applications, including automotive windows, sunroofs, and many other applications in aerospace engineering. Flows over such a geometry can result in aeroacoustic coupling between the cavity shear layer oscillations and the surrounding acoustic modes. This phenomenon can result in a resonance that can lead to significant noise and may cause damage to mechanical structures. Flow control methods are usually used to reduce or eliminate the aeroacoustic resonance. An experimental set up was developed to study the effectiveness of both a cylinder and a profiled cylinder positioned upstream from the cavity in reducing the flow resonance. The cavity flow and the acoustic signals were obtained using particle image velocimetry (PIV) and unsteady pressure sensors, respectively. A decrease of up to 36 dB was obtained in the sound pressure levels (SPL) using the passive control methods. The profiled cylinder showed a similar efficacy in reducing the resonance despite the absence of a high-frequency forcing. Time-space cross-correlation maps along the cavity shear layer showed the suppression of the feedback mechanism for both control methods. A snapshot proper orthogonal decomposition (POD) showed interesting differences between the cylinder and profiled cylinder control methods in terms of kinetic energy content and the vortex dynamics behavior. Furthermore, the interaction of the wake of the control device with the cavity shear layer and its impact on the aeroacoustic coupling was investigated using the POD analysis.

In recent years, the problem of low-frequency line spectrum noise generated by the flow-induced cavity oscillation of underwater vehicles has become increasingly prominent as it seriously threatens stealth performance. Focusing on practical engineering problems such as the flow-induced noise of underwater vehicles, this study analyzes the generation mechanism and characteristics of incompressible cavity flow-induced noise, and summarizes its flow characteristics and the development trend of noise control technology. First, the basic mechanisms and characteristics of cavity self-sustained oscillation are summarized, as well as research progress on the self-sustained oscillation feedback mechanism and three-dimensional instability characteristics. The generation mechanisms and basic characteristics of flow-induced cavity resonance are then introduced, including rectangular/cylindrical cavity acoustic modal resonance and flow-induced Helmholtz resonance. Second, the research progress of active and passive control methods is compared and analyzed. Finally, the future research direction of incompressible cavity flow is predicted. It is recommended to carry out research on the cavity self-sustaining oscillation feedback mechanism and three-dimensional instability, cavity flow-induced resonance mechanism and acoustic radiation characteristics, and incompressible cavity flow-induced noise control methods.

Bu çalışmada Mach sayısı 0.85 ve Reynolds sayısı 1.3x107 için zamana bağlı 3 boyutlu kavite akışı ve kavite boyunca anlık basınç salınımlarından kaynaklı oluşan gürültü açık kaynaklı Hesaplamalı Akışkanlar Dinamiği çözücüsü olan OpenFOAM kullanılarak incelenmiştir. Akış alanı modellemesinin gürültü oluşumuna etkisini gözlemlemek için iki farklı akış alanı modellemesi yapılmıştır. Akış alanı modelinin etkisine ek olarak duvar bölgesindeki ağ sıklığı ve ağdaki hücrelerin büyüme oranlarının aeroakustik bulgular üzerindeki etkisi incelenmiştir. Üç boyutlu akış alanının zamana bağlı incelemelerinde, Büyük Burgaç Benzetimi (LES) ve Ayrık Burgaç Benzetimi (DES) olmak üzere iki türbülans modeli kullanılmıştır. LES analizlerinde küçük girdap yapılarını çözmek için Smagorinsky ve WALE olmak üzere iki ağ-altı ölçek modeli kullanılmıştır. DES analizlerinde Spalart-Allmaras tabanlı DDES, IDDES ve SST k-ω tabanlı DES olmak üzere üç model kullanılmıştır. Transonik kavite için hesaplanan sayısal sonuçlar deneysel ve nümerik sonuçlarla hem konum hem frekans uzayında akustik sinyal verisi için karşılaştırılarak doğrulanmıştır. Analizler sonucu elde edilen konum uzayındaki Ortalama Ses Basınç Düzeyi verisi kavite gürültüsüne ait deneysel veri ile benzer davranışı gösterse de 8-10 desibellik bir sapma görülmüştür. Frekans uzayındaki Ses Basınç Düzeyi sonuçlarında ise Rossiter modları belirgin şekilde gözükmektedir ve hem deneysel hem nümerik çalışmaya yakın sonuçlar elde edilmiştir.

In this paper, a simplified transonic weapon bay with a L/D=5 and Mach number 0.85 was considered using the large-eddy simulation (LES) with dynamic kinetic energy subgrid-scale (SGS) model. The M219 geometry has been analyzed using OpenFOAM for three different configurations based on the position of the covers. The obtained results have been validated against reference studies and presented in terms of mean streamwise velocity profile, overall sound pressure level, sound pressure level and band-integrated sound pressure level in both spatial and frequency domains. In order to mitigate the high computational cost associated with acoustic analysis, a Cartesian mesh topology has been employed as an alternative approach. The numerical findings have demonstrated a comparable level of accuracy to simulations conducted with high-cell count meshes. Based on these findings, a cavity analysis has been conducted for the configuration with covers positioned at a position of 45°. [ABSTRACT FROM AUTHOR]

In this work, the ability of open-source CFD tools to conduct store separation simulations from cavities is evaluated and validated using a generic test case from the literature. Firstly, the ability and accuracy of these tools for solving cavity flows at high speeds are evaluated. Secondly, their competence in predicting the trajectory of a generic store from a generic deep cavity is checked. Finally, and in order to reduce the associated computational costs, a release-time dependability factor from the recent literature is studied and evaluated. The obtained results using the selected open-source CFD tools matched quite well with the wind tunnel results. Furthermore, the results show that predicting the release-time dependability using a quantified index/factor can be a potential remedy for reducing the computational cost for this type of CFD simulations. [ABSTRACT FROM AUTHOR]

Summary: Cavity flow research has been ongoing experimentally since the 1940s, especially for weapon bay use in fighter aircraft. Technology advancement has led to the beginning of simulations of experimental studies. The success of these simulations has increased with the emergence of High‐Performance Clusters, and simulation studies have started to take the role of experimental studies. In this paper, an open rectangular, unsteady transonic cavity with a length to depth ratio of 5, Mach number 0.85 and Reynolds number of approximately 6.5 × 106 is simulated using Computational Fluid Dynamics (CFD) on a High‐Performance Cluster. Likewise, cavity door is used to model a real weapon bay. Detached‐Eddy Simulation is used to resolve turbulent properties in the flow domain. Results compatible with experimental data are obtained with OpenFOAM, an open‐source CFD code based on the finite volume method. Additionally, computational costs are given in the clock‐time analysis section, and the necessity of high‐performance clusters for CFD and Computational Aeroacoustics studies is emphasized. [ABSTRACT FROM AUTHOR]

This study aims to understand the flow performance of a dual wall-mounted cavities in a strut-injector mounted scramjet combustor for steady-state and transient reacting conditions. Conventionally, two-dimensional Reynolds Averaged Navier-Stokes approach is adopted to compute the steady flow, whereas the current research employs Delayed Detached Eddy Simulation for predicting the unsteady flow characteristics as well. The calculated flow patterns, density, pressure, and temperature fields of dual cavities are compared with shadowgraph and wall pressure measurements from DLR experiments. The dual cavities position substantiates to explore the interplay between wave propagation and shear layer mixing characteristics. Employing a dual cavities arrangement accelerates toward the complete combustion relative to the baseline model. The combustion zone widens in the lateral direction as the dual cavities shift the shock train downstream of the strut injector owing to intense shock shear layer interactions. These cavities' existence significantly modifies the dominating frequencies and affects the strength of the diverging section's coherent flow structures. [Display omitted] • Computational study on a dual wall-mounted cavity in a strut-injector scramjet combustor. • Reynolds averaged Navier stokes equation adopted with SST k-ωturbulence model. • Dual cavity mounted at two locations to analyze shock waves, interactions of shear layer mixing. • Dual cavity shifts shock train downstream of injector due to shock shear layer interactions. • Cavity modifies the dominating frequencies and diverging section's turbulent structures. [ABSTRACT FROM AUTHOR]

Prevention and control measures of spontaneous combustion of coal and gas accumulation in a goaf require an accurate description of its gas flow state. However, the commonly used fluid dynamics in porous media is not suitable for the new-born goaf with fracture cavity combination, multi-scale, and large blocks. In this study, we propose a cavity flow algorithm to accurately describe the gas flow state in the new-born goaf. The genetic algorithm (GA) is used to randomly generate the binary matrix of a goaf caving shape. The difference between the gas flow state calculated by the lattice Boltzmann method (LBM) and the measured data at the boundary or internal measuring points of the real goaf is taken as the GA fitness value, and the real goaf caving shape and the gas flow state are quickly addressed by GA. The experimental model of new-born goaf is established, and the laser Doppler anemometry (LDA) experiment is carried out. The results show that the Jaccard similarity coefficient between the reconstructed caving shape and the real caving shape is 0.7473, the mean square error between the calculated wind speed and the LDA-measured value is 0.0244, and the R2 coefficient is 0.8986, which verify the feasibility of the algorithm.

In ureteroscopy, a common method for kidney stone removal, a ureteroscope is inserted into the patient’s kidney, through which working tools such as a laser are inserted. During the procedure, the renal space proximal to the scope tip is irrigated with fluid in order to clear stone particles and debris. However, even with continual fluid flow into and out of the kidney, stone dust may become trapped in vortical structures, significantly impairing the operating clinician’s field of view. Key to overcoming this challenge is a clear understanding of the flow patterns within an irrigated kidney calyx, and a modelling framework that enables to interrogate how different flow conditions impact on the wash-out time of debris. Previous theoretical studies have uncovered the interplay between fluid structure, in particular the presence of vortical regions, and dust washout, but only in a regime of steady inlet flow conditions. In this paper we model a kidney calyx in an idealised 2D cavity geometry, in which we investigate the presence and potential disturbance of vortical structures due to an oscillatory inlet condition, and the impact on dust washout, modelled as a passive tracer in the flow. By varying the flow amplitude and frequency at the inlet, we uncover a delicate relationship with vortex size and vortex disturbance, and we demonstrate the potential for significant decrease in wash-out time with low-frequency high-amplitude conditions. We then compare this result to the commonly used practice of flushing, a discrete and temporary increase in flow, and we also demonstrate the qualitative robustness of our findings to changes in cavity geometry.

The phenomena of unsteady magnetohydrodynamics (MHD) natural convection flow in an inclined square cavity filled with nanofluid and containing a heated circular obstacle at its center with heat generation/absorption impact are examined numerically. The cavity's right and left walls are maintained at low temperatures, while the remaining walls are adiabatic. The volumetric external force, MHD, is applied across the inclined cavity. A penalty formulation-based finite element method is used to solve the nonlinear set of governing equations iteratively. The numerical scheme and results are validated through a comparison with the benchmark results, and it shows that our solutions are in good agreement with them. The results are shown in terms of contours of streamlines, isotherms, and average Nusselt number. It is observed that MHD alters the streamlines, isotherms, and average Nusselt number and dominates the flow as compared to any other physical parameter. The average Nusselt number is found sensitive to the central obstacle's size, and it reduces sufficiently when the radius of the inner cylinder increases. For all the parameters, the streamlines' symmetric pattern holds, such that the anti-clockwise cells on the left side of the cavity have their symmetric clockwise cells on the right side. [ABSTRACT FROM AUTHOR]

The flow dynamics inside cavities associated with turbulent incoming flow and oscillations of the cavity shear layer is an important field of study that has attracted many researchers aiming to understand the complex flow features using both numerical and experimental techniques. Such a flow exists in many industries, such as in the automobile industry for flows over the sunroof of vehicles, and in the energy industry such as in finned heat-exchangers, combustion chambers, and turbines that utilizes wind energy harvesting in buildings. Most of those studies focused on the aero-acoustic mechanism and its control. Despite its wide industrial applications, heat transfer in cavity with oscillating shear layer remains less studied in the literature. The present paper presents a literature review of various studies that focuses on the heat transfer mechanism in those cavity configurations and how it is affected by the flow parameters.

Turbulent flow over open cavity has been investigated experimentally in water channel using Acoustic Doppler Velocimetry (ADV) and numerically using FLUENT. The mean velocity and turbulent kinetic energy distribution of the flow over cavity having an aspect ratio, l/d = 2 (where l and d is the length and depth of the cavity) obtained from FLUENT are validated by experimental results. Effects of different Reynolds numbers and aspect ratios of the cavity (i.e. l/d = 1, 2 and 4) on the flow are reported. The results show that there exists a critical Reynolds number at which the trend of variation of physical variables breaks in response to the change in Reynolds numbers. Recirculating zone inside the cavity for l/d = 1, interacts with downstream cavity flow whereas, for l/d = 2 and 4, the mass exchange between the cavity and upstream flow is noticed. As the aspect ratio is increased, the upstream flow becomes more attached and the instability near the trailing edge increases. [ABSTRACT FROM AUTHOR]

The enhancement of the heat transfer of fluids is a very important task in engineering and technology which can be accomplished through the hybrid nanoparticles. In this theoretical investigation, the natural convection flow of nanoliquid through a square container is examined under the impacts of thermal boundary conditions. The considered nanoliquid is a combination of titanium alloy Ti6Al4V (class of titanium) and aluminum alloy AA7075 (class of aluminum) nanoparticles and water as a base fluid. Aluminum alloys are commonly used in household wiring and manufacturing of wheels, etc. The titanium alloy Ti6Al4V is commonly acknowledged as the "workhorse" of titanium which is extensively used in aerospace and biomedical engineering. The mathematical model is developed in the form of nonlinear partial differential equations and later transformed into dimensionless form. The resultant dimensionless set of equations is simulated numerically by using the eminent finite element method (FEM). The iterative Newton's Raphson method is used to get the optimal solutions. The stream function and temperature contours are displayed against the Rayleigh number and nanoparticle volume friction. The variation of local and average Nusselt numbers is also plotted. The outcomes revealed that water-based titanium alloy is the best choice to enhance the heat transfer rate in the cavity. The results obtained in this investigation are very important in engineering research, academic, and discussion about the heat transfer analysis with these two types of alloy nanoparticles inside the cavity flows. [ABSTRACT FROM AUTHOR]

Flow over a cavity is one of the most intriguing problems in aeronautics. Although geometry is simple, the physics of cavity requires uttermost attention. In this study, various novel passive flow control techniques such as reshaping the aft wall as stair-stepped configuration or combinations of spoilers with reshaped aft wall are applied to cavity and effects of these techniques are investigated numerically. Combined configurations that are proposed in the present study are considered as a novelty to the literature. Analyses are performed with Detached Eddy Simulation method three-dimensionally in transonic regime (0.85 Mach) for a Reynolds number of ~107 based on the cavity length, 0.508 m, using open-source software OpenFOAM. Results are compared with both experimental data and each other, fundamentally in terms of Overall Average Sound Pressure Level. Further examinations are also performed for features such as Mach number, turbulent intensity and turbulent coherent structures. It is seen that combined passive flow control methods have reduced Overall Average Sound Pressure Level by ~10 dB. Newly proposed passive flow control methods have also reduced Overall Average Sound Pressure Level by ~6 dB. A high correlation between coherent turbulent structures and generated noise is observed.

Cost-effective wind energy harvesting by wind turbines in urban areas needs to strengthen the required flow field properties, such as mean velocity, turbulence, and its distribution. This paper conducts a series of CFD simulations to investigate the characteristics and related mechanisms of flow within the cavity, considering the force–turbulence interactions at the RANS scales. The pressure–velocity correlation term is formulated and solved by the elliptic relaxation equation to compensate for the Reynolds stress overestimation. Numerical simulations of flow over an open cavity with the proposed model are compared with corresponding PIV data. The results show that the mean velocity and the fluctuation velocity along the streamwise direction exist a slightly favorable pressure gradient. While the fluctuation velocity and fluctuation pressure show different correlation characteristics along the streamwise direction. Moreover, the pressure–velocity fluctuation correlation becomes obvious near the upper corner of the cavity due to the favorable pressure gradient. Hence, the leading and trailing locations of the cavity are both obvious favorable regions and further emphasis should be put on both high-accurate simulation methods and practical applications. [ABSTRACT FROM AUTHOR]

In this work, a numerical study of polymer flow behaviors in a lid-driven cavity, which is inspired by the coating process, at a broad range of Oldroyd numbers ( 0 ≤ Od ≤ 50 ), is carried out. The Reynolds number is height-based and kept at Re = 0.001 . The fluid investigated is of Carbopol gel possessing yield stress and shear-thinning properties. To express rheological characteristics, the Herschel–Bulkley model cooperated with Papanastasiou's regularization scheme is utilized. Results show that the polymer flow characteristics, i.e., velocity, viscosity, and vortex distributions, are considerably influenced by viscoplastic behaviors. Additionally, there exist solid-like regions which can be of either moving rigid or static dead types in the flow patterns; they become greater and tend to merge together to construct larger ones when Od increases. Furthermore, various polymer flow aspects in different cavity configurations are discussed and analyzed; the cavity width/aspect ratio and skewed angle are found to have significant impacts on the vortex structures and the formation of solid-like regions. Moreover, results for the critical aspect ratio at which the static dead zone is broken into two parts and the characteristic height of this zone are also reported in detail. [ABSTRACT FROM AUTHOR]

A numerical investigation of flow topology in open-type cavities with length-to-depth ratio L/h1 = 4 was performed in the Reynolds number range of 10–1000. Cavities with differently rounded corners were chosen for simulation. Three-dimensional numerical simulations were performed to analyse flow topology in different planes. A series of experiments was performed to ensure the validity of numerical simulations. Both numerical simulations and physical experiments were conducted with water as the working fluid. Since the results agreed acceptably, further simulations were performed. The main goal of this study was to investigate and highlight the influence of rounded cavity corners on the topology and stability of flow. Analysis revealed that fully rounded upper cavity corners decrease pressure loss compared to other investigated cases; therefore, the velocity of the main flow is increased. Additionally, fully rounded upper corners form a notably smaller recirculation zone compared to other investigated cases. Flow stability analysis showed that fully rounded cavity bottom corners negatively impact flow stability by increasing the intensity of turbulence. [ABSTRACT FROM AUTHOR]

It remains a challenge for ILES methods to provide physical consistent viscosity in real applications which comprise complex flow structures in both high and low Mach numbers regimes. For these, we analyze an Implicit Large Eddy Simulation (ILES) method based upon all-speed schemes in a framework of the finite volume method in this study. This method can accurately capture both compressible phenomena such as shock waves as well as small turbulent structures. With a detailed analysis of the numerical viscosity and effective eddy viscosities in physical and spectral spaces, the method is verified to be suitable for the simulation of compressible turbulent flows. After it, the derived ILES method is applied to the simulation of a cylinder flow and a transonic cavity flow. Both results are in good agreements with the previous LES or experimental data. These results indicate that it is promising to study the application of the all-speed scheme to the ILES of complex engineering flow problems. [ABSTRACT FROM AUTHOR]

This paper aims to study the effect of a pylon mounted cavity-based flameholder on the combustor flow ‎characteristics. Computational analysis of two different models of flameholder configurations is ‎performed. The novel cavity design 110_90 has a fore-wall ramp angle of 110 degrees and an aft-wall ‎ramp angle of 90 degrees and this design which shows a comparatively better combustor performance is ‎adopted and mounted with a pylon. The flow features over the high performance base cavity 110_90 is ‎compared with the flow features obtained by adding a pylon on the upstream of the base cavity. The two ‎cases are compared qualitatively as well as quantitatively based on the temperature distribution, pressure ‎distribution, recirculation zones and drag experienced by the model. These compared parameters helped ‎us to identify whether the mentioned combination is favorable and augments the flameholder ‎performance‎‎.

Abstract In order to validate a computational method for solving viscous fluid flows, experiments are carried out in an eccentric cylindrical cavity showing various flow formations over a range of Reynolds numbers. Especially, in numerical solution approaches for isothermal and incompressible flows, we search for simple experimental data for evaluating accuracy as well as performance of the computational method. Verification of different computational methods is arduous, and analytic solutions are only obtained for simple geometries like a channel flow. Clearly, a method is expected to predict different flow patterns within a cavity. Thus, we propose a configuration generating different flow formations depending on the Reynolds number and make the experimental results freely available in order to be used as an assessment criterion to demonstrate the reliability of a new computational approach.

Abstract The pantograph and its recess on the train roof are major aerodynamic noise sources on high-speed trains. Reducing this noise is particularly important because conventional noise barriers usually do not shield the pantograph. However, less attention has been paid to the pantograph recess compared with the pantograph. In this paper, the flow features and noise contribution of two types of noise reduction treatments rounded and chamfered edges are studied for a simplified high-speed train pantograph recess, which is represented as a rectangular cavity and numerically investigated at 1/10 scale. Improved delayed detached-eddy simulations are performed for the near-field turbulent flow simulation, and the Ffowcs Williams and Hawkings aeroacoustic analogy is used for far-field noise prediction. The highly unsteady flow over the cavity is significantly reduced by the cavity edge modifications, and consequently, the noise radiated from the cavity is reduced. Furthermore, effects of the rounded cavity edges on the flow and noise of the pantographs (one raised and one folded) are investigated by comparing the flow features and noise contributions from the cases with and without rounding of the cavity edges. Different train running directions are also considered. Flow analysis shows that the highly unsteady flow within the cavity is reduced by rounding the cavity edges and a slightly lower flow speed occurs around the upper parts of the raised pantograph, whereas the flow velocity in the cavity is slightly increased by the rounding. Higher pressure fluctuations occur on the folded pantograph and the lower parts of the raised pantograph, whereas weaker fluctuations are found on the panhead of the raised pantograph. This study shows that by rounding the cavity edges, a reduction in radiated noise at the side and the top receiver positions can be achieved. Noise reductions in the other directions can also be found.

Sedimentation of particle suspensions in a channel flow into a cavity is analysed numerically using a lattice Boltzmann method coupled with a discrete element method. The work focuses on the entrapment of particles inside a confined cavity and the particle dynamics after entrapment. A close examination of the particle motions reveals three distinct dynamic behaviours: i) resuspension, ii) circulation in the central vortex and iii) deposition to the rear edge of the cavity. The effects of fluid inertia, particle density and cavity size on the infiltration and resuspension behaviours are systematically investigated. The results show that decreasing the Reynolds number, and increasing the length and depth of the cavity all lead to an increase in the trap efficiency. Three distinctive regimes with respect to the trap efficiency were then identified by deriving an empirical dimensionless trap number T p : a resuspension regime when T p < 1, a continuous circulating regime when 1 ≤ T p ≤ 2.5, and a fully trapped regime when T p > 2.5. [Display omitted] • Sedimentation of particle suspensions in a cavity flow is numerically analysed. • The effects of the flow inertia and the configuration of the cavity are quantified. • A dimensionless trap number is proposed to well describe the trap efficiency. • Three distinctive regimes were identified based on the value of trap number. [ABSTRACT FROM AUTHOR]

The interaction of turbulent flows with the external structure of ground vehicles generates uncomfortable noise and a lot of attention is devoted to find new mechanisms for its suppression. The present work is concerned with open cavity flows, very often found in the automotive industry. A three-dimensional rectangular very wide open cavity with aspect ratio L / D = 4 at Reynolds number R e D = 5000 and Mach number M = 0.1 is considered. The passive control technique is based on eight different geometrical modifications: the length of the cavity, the radius of the trailing, leading and bottom edges and the difference in heights between the left and right wall of the cavity. Wall-resolved Large Eddy Simulations (LES) are used to obtain the flow fields and a post-process based on Curle's analogy is applied to evaluate the acoustic radiation and the effectiveness of the control mechanisms. The results show that the modifications on the trailing edge are the most effective to control the flow. They allow to reduce the pressure fluctuations produced by the recirculation confined inside the cavity and the abrupt ejection of the flow at the trailing edge. As a consequence, the overall sound pressure level can be decreased up to 9 dB. [ABSTRACT FROM AUTHOR]

The detailed mechanism of supersonic mixing enhancement by a novel device is investigated computationally based on the Navier-Stokes equations. The device is a wall-mounted three-dimensional cavity, several parts of the rear face of which are cut out, and the lower wall of the cut-out part has a slope directed toward the injector from which the injectant is discharged. The flow structures and behaviors observed in the computational results are confirmed in the experimental results. Experimental information about the high-frequency (several tens of kHz) pressure oscillation in the cut-out part is acquired in this study using a pressure-sensitive paint (PSP) responding to rapid change in pressure. The computational results reveal that a hairpin-like vortex is formed inside the cavity. The vortex works on the shear layer across the cavity to deflect it upward. The deflected shear layer shields the injectant from the primary flow, which causes the injectant to penetrate deep into the primary flow. The computational results also clarify that the expansion and compression waves produced in the rectangular part of the cavity are delivered effectively to the injector along the slope of the cut-out part, which is confirmed in the PSP measurement results. The delivered waves actuate the jet issuing from the injector to fluctuate up and down periodically with a large amplitude. • The mechanism of supersonic mixing enhancement by a three-dimensional cavity is investigated. • The hairpin-like vortex formed inside the cavity makes the injectant to penetrate deep into the primary flow. • The pressure waves contributing to mixing enhancement are captured computationally and experimentally. • The pressure waves actuate the jet issuing from the injector to fluctuate up and down. [ABSTRACT FROM AUTHOR]

This paper aims to study the effect of a pylon mounted cavity-based flameholder on the combustor flow characteristics. Computational analysis of two different models of flameholder configurations is performed. The novel cavity design 110_90 has a fore-wall ramp angle of 110 degrees and an aft-wall ramp angle of 90 degrees and this design which shows a comparatively better combustor performance is adopted and mounted with a pylon. The flow features over the high performance base cavity 110_90 is compared with the flow features obtained by adding a pylon on the upstream of the base cavity. The two cases are compared qualitatively as well as quantitatively based on the temperature distribution, pressure distribution, recirculation zones and drag experienced by the model. These compared parameters helped us to identify whether the mentioned combination is favorable and augments the flameholder performance. [ABSTRACT FROM AUTHOR]

The effects of elastic cavity walls on noise generation at transonic speed are investigated for the generic M219 cavity. The flow is simulated with the Spalart–Allmaras (SA) improved delayed detached-eddy simulation (IDDES) turbulence model in combination with a wall function. The structural analysis software uses a modal formulation. The first 50 structural normal mode shapes are included in the simulation, spanning frequencies of 468–2280 Hz. Results are compared with those from a reference simulation with rigid cavity walls. A spectral analysis of pressure fluctuations from a microphone array above the cavity evinces a distinct tone at 816 Hz, which is absent in the reference simulation. Furthermore, the power of the 4th Rossiter mode at 852 Hz is depleted, implying a significant energy transfer from the fluid to the structure. Spectral proper orthogonal decomposition (SPOD) is employed for analyses of cavity wall pressure fluctuations and wall displacements. The SPOD mode energy spectra show results consistent with the spectra of the microphone array with respect to the tone at 816 Hz and the depletion of the energy at the 4th Rossiter mode. Furthermore, the SPOD mode energy spectra show energy spikes at additional frequencies, which coincide with structural eigenfrequencies.

This paper involves a two-dimensional computational study of flow evolution patterns and the temperature distribution at evolved states of a fluid under compressible conditions contained within a driven rectangular cavity with two symmetrically placed circular cylinders, where one cylinder is heated and the other cooled. Conditions developed by varying the positions of the cylinders within the cavity, by varying the initial conditions of temperature distributions of the fluid as well as temperatures at which the cylinders are held to heat or cool the flow and by varying the orientation of the direction of rotation of the cylinders with respect to each other – either opposing or identical – are studied. The analyses are conducted by observing the temperature distributions over the streamline patterns, the velocity profiles over a line dividing the cavity length in half and the temperature distribution over a line dividing the cavity height in half. Best mixing conditions have been found to be for cavities with cylinders placed close to each other and rotating in identical directions.

This study experimentally investigated transonic cavity flows with different length-to-depth (L / h) ratios and yaw angles. Two rectangular models with L / h = 6.14 and 21.5 were examined with yaw angles of 10°, 30°, and 45° under a flow of Mach 0.83. The flow was visualized using pressure-sensitive paint (PSP) to obtain the detailed pressure distribution inside the cavity models. The acquired PSP data were compared with experimental data measured using Kulite transducers, and these data showed favorable agreement. Gradual pressure increases inside the cavity model with L / h = 6.14 were observed from the PSP measurements as open cavity flow. The flow impingement at the bottom of the cavity and the significant pressure rise inside the cavity model with L / h = 21.5 were observed as closed cavity flow. The present study quantitatively visualized the evolution of the pressure distribution from symmetric to asymmetric for different yaw angles using porous PSP sensors. [ABSTRACT FROM AUTHOR]

Strong wall pressure fluctuations are generated mostly by a high-speed flow passing over a cavity and should be accurately predicted and controlled for the structural design of aircraft. In this work, a spatiotemporal analysis was performed to estimate wall pressure fluctuations and reveal the mechanism of flow control by a sawtooth-like vortex generator installed on the leading edge or by the use of a rounded trailing edge in suppressing wall pressure fluctuations. Both the cavity tones and overall sound pressure level were analyzed under different flow speeds and flow control approaches. To investigate the power transfer in the temporal and spatial domains, power spectral density contours were drawn and discussed. For the mode separation, the phased array technique with an improved beamforming algorithm was adopted to calculate the wavenumber map and then to separate the acoustic modes from the convective modes by utilizing the spatial correlation of the wall pressure fluctuations. The mode separation results show that the convective modes contribute mainly to the low-frequency pressure fluctuations, while the acoustic modes contribute to both the low-frequency and high-frequency pressure fluctuations. Flow control by the rounded trailing edge approach is more effective than that by the serrated structure approach in reducing the cavity acoustic environment, which enables wall pressure fluctuations to transfer from the high-frequency range to the low-frequency range compared with the "no control" case. • Spatiotemporal analysis was performed to estimate wall pressure fluctuations and reveal the mechanism of flow control by a vortex generator or a rounded trailing edge on the cavity flow. • Phased array technique was adopted to separate the acoustic modes from the convective modes by utilizing the spatial correlation of wall pressure fluctuations. • Investigations addressed that convective modes contribute to the low-frequency fluctuations, while acoustic modes contribute to both the low-frequency and high-frequency fluctuations. [ABSTRACT FROM AUTHOR]

Thermal protection of hypersonic vehicles is of great concern during ascent and re-entry conditions due to higher aerothermal loads. The passive forward-facing cavity is exhibited a substantial reduction of aero heating effects. The experimental studies on unsteady aspects of the flow considering the cavity geometries and heat transfer effects within the cavity are not abundant. In the present study, we investigated the heat transfer variations and nature of shock around a blunt body with cylindrical and parabolic cavity geometries. Experiments are conducted in hypersonic shock tunnels using air as the test gas for flow enthalpy conditions of 3.2 and 5.4 MJ/kg for a free-stream Mach number of 10.9 and 10.2 respectively. The cavity flow is established by verifying the measured heat flux, pressure, and shock oscillation results. The unsteady heat flux measurements and high-speed schlieren imaging is performed to study the effects. The results reveal that the flow with the parabolic cavity geometry shows a significant increase in the mean shock standoff position of about 14% and 30% compared to the blunt-nosed body, and about 7%–18% compared to the cylindrical cavity geometry, with a reduction of bow shock oscillations. As a result, a substantial reduction of heat flux about 34%–59% on the nose surface is noticed and found it is effective for mitigating the aerodynamic heating at higher flow enthalpy conditions. The flow with a cylindrical cavity geometry indicated the substantial increase in the heat flux due to the shock interaction and the significant heat flux variation in the cavity region is recognized and observed that such effects were not prevalent with the parabolic cavity geometry. • Aero heating mitigation on blunt nosed surface is studied with different cavities. • The shock standoff distance is enhanced in parabolic cavity with lower heat flux. • The noticeable shock interaction effect is observed for cylindrical cavity case. • High frequency of oscillations and lower base pressure exists in parabolic cavity. • As flow enthalpy increases higher mitigation is observed in parabolic cavity case. [ABSTRACT FROM AUTHOR]

The present research focuses on flow oscillations in a planar rectangular cavity. The compressible URANS equations in combination with transition SST k−ω model are utilized to include the turbulence effects. The simulations are carried out for low Reynolds flow with Mach number ranging from 0.2 to 0.7. Flow features are investigated and the frequency analysis is discussed. Two flow oscillation modes, namely shear-layer mode and wake mode are thoroughly identified. The flow structure and oscillation frequencies compare well with LES and DNS results presented in the literature. Furthermore, the shear mode frequency is well aligned with that predicted by Rossiter. This research is aimed to evaluate the performance of URANS as an industrially attractive tool to capture flow phenomena, previously visualized by the aforementioned sophisticated methods.

Flow over a cavity is one of the most intriguing problems in aeronautics. Although geometry is simple, the physics of cavity requires uttermost attention. In this study, various novel passive flow control techniques such as reshaping the aft wall as stair-stepped configuration or combinations of spoilers with reshaped aft wall are applied to cavity and effects of these techniques are investigated numerically. Combined configurations that are proposed in the present study are considered as a novelty to the literature. Analyses are performed with Detached Eddy Simulation method three-dimensionally in transonic regime (0.85 Mach) for a Reynolds number of ~107 based on the cavity length, 0.508 m, using open-source software OpenFOAM. Results are compared with both experimental data and each other, fundamentally in terms of Overall Average Sound Pressure Level. Further examinations are also performed for features such as Mach number, turbulent intensity and turbulent coherent structures. It is seen that combined passive flow control methods have reduced Overall Average Sound Pressure Level by ~10 dB. Newly proposed passive flow control methods have also reduced Overall Average Sound Pressure Level by ~6 dB. A high correlation between coherent turbulent structures and generated noise is observed. [ABSTRACT FROM AUTHOR]

For high-speed trains, the aerodynamic noise becomes an essential consideration in the train design. The pantograph and pantograph recess are recognised as important sources of aerodynamic noise. This paper studies the flow characteristics and noise contributions of three typical high-speed train roof configurations, namely a cavity, a ramped cavity and a flat roof with side insulation plates. The Improved Delayed Detached-Eddy Simulation approach is used for the flow calculations and the Ffowcs Williams & Hawkings aeroacoustic analogy is used for far-field acoustic predictions. Simulations are presented for a simplified train body at 1/10 scale and 300 km/h with these three roof configurations. In each case, two simplified pantographs (one retracted and one raised) are located on the roof. Analysis of the flow fields obtained from numerical simulations clearly shows the influence of the train roof configuration on the flow behaviour, including flow separations, reattachment and vortex shedding, which are potential noise sources. A highly unsteady flow occurs downstream when the train roof has a cavity or ramped cavity due to flow separation at the cavity trailing edge, while vortical flow is generated by the side insulation plates. For the ramped cavity configuration, moderately large pressure fluctuations appear on the cavity outside walls in the upstream region due to unsteady flow from the upstream edge of the plate. The raised pantograph, roof cavity, and ramped cavity are identified as the dominant noise sources. When the retracted pantograph is located in the ramped roof cavity, its noise contribution is less important. Furthermore, the insulation plates also generate tonal components in the noise spectra. Of the three configurations considered, the roof cavity configuration radiates the least noise at the side receiver in terms of A-weighted level. [ABSTRACT FROM AUTHOR]