Analysis Of Flow Structures Research Articles

Effects of viscoelasticity on the onset of vortex shedding and forces applied on a cylinder in unsteady flow regime

The present paper aims to investigate the effect of viscoelasticity on the onset of vortex shedding of a high concentration polymer solution over a cylinder using the finite volume method for the first time. To describe the behavior of the viscoelastic fluid, mathematically, the Phan–Thien–Tanner (PTT) model is employed. The convergence problems are resolved using the rheoFoam solver developed by previous researchers based on the log-conformation method. The exact critical Reynolds number (Recr), which corresponds to the onset of vortex shedding, is estimated by implementing numerous unsteady simulations at each elasticity number (El). The Recr is also calculated at every retardation ratio (β) and elongational viscosity. The results revealed a significant impact of viscoelasticity on Recr so that the flow of a high viscosity ratio PTT becomes unstable at higher Re (at very low El) or lower Re (at higher El), compared to a Newtonian fluid. In addition, Recr decreases linearly with β according to Recr=−34.5β+46.525 and increases with extensional viscosity. It is also found that β plays a vital role in the effect of viscoelasticity on the flow parameters. The averaged drag coefficient (CD¯) and the amplitude of lift coefficient (CLmax) do not have similar behaviors for low and high β. Moreover, viscoelasticity enlarges the vortices and increases the shedding frequency. A comprehensive physical analysis of flow structures is carried out using the distribution of time-averaged stress components and pressure over the cylinder. The numerical results demonstrated the three regimes of drag reduction at El < 0.015, drag enhancement at 0.015 < E1 < 1, and a Newtonian behavior at El > 1 that is an opposite trend compared to a steady regime. The variations of CLmax with El are also similar to CD¯, but at different critical elasticity numbers (El = 0.005 and 2). It is found that the normal stress changes the drag force by the variation of pressure distribution over the cylinder, while the shear stress directly affects the drag and lift forces. In addition, the viscoelasticity decreases the size of the vortices behind the cylinder and increases their vorticity, and changes the position of maximum normal stress, which leads to drag variations. It was also concluded that the higher the elongational viscosities, the lower the shedding frequency.

Thermal convection in a tilted rectangular box

Thermal convection in a tilted three-dimensional rectangular box has been systematically investigated by direct numerical simulation. The Rayleigh number Ra varies from 107 to 109, the Prandtl number Pr is set to 0.7, and the tilted angle β ranges from 0° to 90°. The effects of tilting on large-scale circulation (LSC), Nusselt number (Nu), Reynolds number (Re), and boundary layers (BLs) and the Ra-dependency are investigated. For large β exceeding certain values, say 45°, the stable temperature stratification forms in the bulk, resulting in low Re and Nu. It is found that the tilting leads to a distinct trend for Nu and Re: Nu first increases to some extent for small β, then nearly stays unchanged for moderate β, and finally decreases for large β, while Re initially increases for small β and then directly declines with increasing β. Based on the analysis of flow structures, with increasing β, it is found that the volume of the high-velocity tube (HVT) initially increases for 107 ≤ Ra ≤ 108 but decreases for Ra = 109, which is responsible for the variation in Nu at small β. The probability density functions of instantaneous convective heat transport within the HVT show higher probabilities for large values when β increases, implying that LSC tends to be more coherent and causing different tilting behaviors between Nu and Re. Finally, we find that, except for β = 90°, the normalized profiles of viscous and thermal BLs tend to have universal profiles, deviating from the BL of the Prandtl–Blasius–Pohlhausen (PBP) type to some extent regardless of β. Only the thermal BL for β = 90° is found to be in good agreement with the classic PBP laminar BL profile.

Computational Assessment of Hemodynamics Vortices Within the Cerebral Vasculature Using Informational Entropy.

Propper assessment of hemodynamic swirling flow patterns, vortices, may help understand the influence of disturbed flow on arterial wall pathophysiology and remodeling. Studies have shown that vortices trigger pathologic cellular changes within the vasculature such as increased inflammation and cellular apoptosis, leading to weakening of the vessel wall indicative of aneurysm development and rupture. Yet many studies qualitatively assess the presence of vortices within the vasculature or assess only their centermost region (critical point analysis) which overlooks the broader characteristics of flow, leading to a narrow view of vortices. This chapter provides a protocol for utilizing commercially available computational fluid dynamic software (ANSYS-FLUENT) to simulate realistic hemodynamic flow patterns, fluid velocity, and wall shear stress in the complex geometry of the cerebral vasculature, as well as an innovative method for assessing flow vortices. This innovative analytic methodology can identify areas of flow vortices and quantify how the broader bulk-flow (opposed to critical point) characteristics change in space and time over the cardiac cycle. Analysis of such flow structures can be used to identify specific characteristics such as vortex stability and the portion of an aneurysmal sac that is dominated by swirling flow, which may be indicative of vascular pathologies.

Effects of baffle on cycle‐to‐cycle variation in stirred vessel driven by paddle turbine using quadruple proper orthogonal decomposition

AbstractThe flow of stirring process is complex and multiscale. To analyze the effects of baffle on the flow characteristics driven by paddle turbine, particle image velocimetry (PIV) experiments were performed for the unbaffled stirred vessel and the standard baffled stirred vessel stirred by the single paddle turbine. Under the baffle arrangement, the flow discharge was strengthened, and the range of high‐velocity region was obviously expanded, and the velocity significantly fluctuated near the blade. The swirling intensity behind the blade decreased significantly, and no significant wake structure was formed, thereby helping reduce the local velocity difference attributed to the wake structure and facilitate the uniform mixing of materials. The instantaneous velocity field was decomposed into four parts at different scales by employing quadruple Proper Orthogonal Decomposition method. The quantitative analysis of different scale flow structures in stirred process was realized. Under the baffle arrangement, the flow process was facilitated in the measurement plane. In addition, the fluctuation velocity increased significantly, and the mass transfer was enhanced by vortex motion of the fluid elements, which was conducive to the uniform mixing of materials.

3-D visualization of transparent fluid flows from snapshot light field data

This paper presents the use of light field data, recorded in a snapshot from a single plenoptic camera, for 3-D visualization of transparent fluid flows. We demonstrate the transfer of light field deconvolution, a method so far used only in microscopy, to macroscopic scales with a photographic setup. This technique is suitable for optically thin media without any additional particles or tracers and allows volumetric investigation of non-stationary flows with a simple single camera setup. An experimental technique for the determination of the shift-variant point spread functions is presented, which is a key for applications using a photographic optical system. The paper shows results from different test cases with increasing complexity. Reconstruction of the 3-D positions of randomly distributed light points demonstrates the achievable high accuracy of the technique. Gas flames and droplets of a fluorescent liquid show the feasibility of the proposed method for the visualization of transparent, luminous flows. The visualizations exhibit high quality and resolution in low-contrast flows, where standard plenoptic software based on computer vision fails. Axial resolution depends on the data and is about an order of magnitude lower than the lateral resolution for simple point objects. The technique also allows the time-resolved analysis of flow structures and the generation of 3D3C-velocity fields from a sequence of exposures.Graphical

Experience in creating a soil-reclamation map of the Zarafshan river valley based on the system analysis of lithodynamic flow structures

Analysis of lithodynamic flows and soil-reclamation studies, based on the plastic relief map, allowed for a systematic analysis of the main components of the natural environment. The ways of migration of chemical elements in the soil are established. For the first time, causal relationships of spatial differentiation of the degree and chemical composition of saline soils in the Zarafshan river valley were revealed. The Zarafshan river basin has a clearly defined border, as we can judge from the map of plastic relief made up in 1: 100 000 scale. Here three cascade systems are well distinguished, which is very important for the formation of the reclamation state of the territory. In this area, that is, the subsystem, on the proluvial-alluvial deposits is the main volume of groundwater, which is closely related to the surface. This subsystem is part of the catchment area of the Zarafshan river basin, which is the main source of removal from the territory of a huge mass of dissolved and solid substances.

Development of ecosystem‐based flood mitigation approach – investigations by experiments and numerical simulation

AbstractThe purpose of this research was to understand how to minimise the destructive effects of floods by establishing a bio‐shield of natural vegetation. Experiments were conducted in a water flume to determine the flow properties under different vegetation conditions whereas; volume of fluid (VOF) multiphase approach with a standard k‐ɛ turbulence model was developed for a simulation. The study involved comparative analysis of flow structures and loss of energy in a single patch of finite length, layered (single or double layer with gaps) and continuous (full width) vegetation models. The results showed that, for a single patch, the increase in vegetation density and aspect ratio increased the backwater rise in front of vegetation, reduced velocity and enhanced energy dissipation. Furthermore, in the case of horizontally layered vegetation models (single and double horizontal layers), the loss of energy was higher in double horizontally layered vegetation layouts. Gaps between vegetation patches of a single horizontally layered vegetation model possessed high flow velocity, which was countered by providing a second horizontal layer of vegetation with an alternate gap. The findings from this research are critical in designing optimum vegetation layouts for flood mitigation.

3D orthogonal multi-resolution analysis of flow structures around an improved vehicle external mirror

This paper proposes vehicle door mirrors with a tip shape and ditch to reduce the aerodynamic drag. The mean drag coefficients Cd of various mirror models were first measured using load cells within a 103–105 Reynolds number range in a wind tunnel. The Cd of controlled mirrors with different ditch widths remained constant at approximately 0.75 and was lower than that of conventional mirrors. Using a large eddy simulation (LES), the 3D flow structures around modified and conventional mirrors were numerically analyzed at a Reynolds number of 2.8 × 105. Based on a three-dimensional orthogonal wavelet multi-resolution technique, the instantaneous three-dimensional vorticity and velocity were decomposed into three wavelet levels or scales: large scale with a 62 mm central scale, intermediate scale with a 29 mm central scale, and small scale with a 16 mm central scale. This indicated that the length of the region of the vorticity iso-surfaces in an improved door mirror model as the tip ditch decreases. Because the tip ditch produced the more streamwise vortices, the large-scale spanwise vortices were suppressed. The streamwise vortices and spanwise vortices of the small- and intermediate-scale structures increased, which is mainly caused by the ditch in the tip.

Numerical analysis of the effects of circumferential groove casing suction in a counter-rotating axial flow compressor

To extend the current understanding of the circumferential groove casing suction applied to a counter-rotating axial flow compressor, the impact of different axial locations of the circumferential suction groove on the characteristics of the tip leakage flow (TLF) and the corresponding physical mechanisms producing the stability enhancement have been studied based on validated numerical simulations. The results show that the optimal location for the suction groove is at around 20% axial chord, which demonstrated a high potential for reducing additional stall mass flow coefficient with about 8.4% increment in the stall margin. After the casing suction groove was applied, the interface between the incoming main flow and TLF was pushed significantly downstream in the second rotor. The blade loading in the region below the groove, the tip leakage flow angle and the reversed axial momentum flux injected into main flow passage through the tip gap were all reduced, which contributed to the stall margin improvement. Detailed analysis of the tip leakage flow structures showed that the TLF originating from different chord locations played different roles in the stall inception process. It was found to be more effective to improve stall margin and adiabatic efficiency by controlling the front part of the TLF, which was most sensitive.

Development and Application of Bivariate 2D-EMD for the Analysis of Instantaneous Flow Structures and Cycle-to-Cycle Variations of In-cylinder Flow

The bivariate two dimensional empirical mode decomposition (Bivariate 2D-EMD) is extended to estimate the turbulent fluctuations and to identify cycle-to-cycle variations (CCV) of in-cylinder flow. The Bivariate 2D-EMD is an adaptive approach that is not restricted by statistical convergence criterion, hence it can be used for analyzing the nonlinear and non-stationary phenomena. The methodology is applied to a high-speed PIV dataset that measures the velocity field within the tumble symmetry plane of an optically accessible engine. The instantaneous velocity field is decomposed into a finite number of 2D spatial modes. Based on energy considerations, the in-cylinder flow large-scale organized motion is separated from turbulent fluctuations. This study is focused on the second half of the compression stroke. For most of the cycles, the maximum of turbulent fluctuations is located between 50 and 30 crank angle degrees before top dead center (TDC). In regards to the phase-averaged velocity field, the contribution of CCV to the fluctuating kinetic energy is approximately 55% near TDC.

Methodology for the large-eddy simulation and particle image velocimetry analysis of large-scale flow structures on TCC-III engine under motored condition

Large-eddy simulation has been increasingly applied to internal combustion engine flows because of their improved potential to capture the spatial and temporal evolution of turbulent flow structures compared with Reynolds-averaged Navier Stokes simulation. Furthermore, large-eddy simulation is universally recognized as capable of simulating highly unsteady and random phenomena, which drive cycle-to-cycle variability and cycle-resolved events such as knocks and misfires. To identify large-scale structure fluctuations, many methods have been proposed in the literature. This article describes the application of several analysis methods for the comparison between different datasets (experimental or numerical) and the identification of large-structure fluctuations. The reference engine is the well-known TCC-III single-cylinder optical unit from the University of Michigan and GM Global R&D center; the analyses were carried out under motored engine conditions. A deep analysis of in-cylinder gas dynamics and flow structure evolution was performed by comparing the experimental results (particle image velocimetry of the velocity fields) with a dataset of consecutive large-eddy simulation cycles on four different cutting planes at engine-relevant crank angle positions. Phase-dependent proper orthogonal decomposition was used to obtain further conclusions regarding the accuracy of the simulation results and to apply conditional averaging methods. A two-point correlation and an analysis of the tumble center are proposed. Finally, conclusions are drawn to be used as guidelines in future large-eddy simulation analyses of internal combustion engines.

Analysis of thermal-hydraulic performance and flow structures of nanofluids across various corrugated channels: An experimental and numerical study

The combination of nanofluid and corrugated surface is regarded as a very cost-efficient strategy for providing high heat transfer performance between the target surface and working fluid in different heating and cooling system applications. Herein a comparison study is reported on the thermal performance of different corrugated channels using nanofluids under turbulent flow and constant heat flux conditions. Three shapes, namely, semicircle corrugated channel (SCC), trapezoidal corrugated channel (TCC), and straight channel (SC) are fabricated and tested with 1% and 2% volume fraction of SiO2-water and Al2O3-water nanofluids. Nanoparticles with a size of 20 nm dispersed in water with specific volume fractions are used for comparison and evaluation. The numerical simulations present the flow structures of nanofluids in terms of velocity, isotherms, turbulent viscosity, vorticity and turbulent kinetic energy contours. The findings show that the heat transfer and pressure drop increase as volume fractions of nanofluids and Reynolds number increase. The experiments also revealed that the use of modified channels significantly increases the heat transfer ratio and the greatest enhancement ratio was achieved through the use of a trapezoidal corrugated channel with ϕ=2% of silica nanofluid. Over ranges of considered flow, silica nanofluid was better than alumina nanofluid and the best thermal performance of 1.94 was recorded using silica nanofluid at ϕ=2% and TCC at Reynolds number of 10000. Additionally, new empirical correlations were proposed and reported based on experimental data.

Analysis of turbulent flow structures in the straight rectangular open channel with floating vegetated islands.

Floating vegetated islands (FVIs) are extensively implemented in various river ecology restoration projects, given their capability of decontaminating pollutants. The fluid dynamical behaviors of turbulence through FVIs are studied in the flume by using the SonTek Acoustic Doppler Velocimetry. Through conventional spectral and quadrant analyses, flow characteristics, such as energy content and turbulent momentum exchange, are investigated as the flow encountered a series of root canopies. A shear layer with corresponding coherent vortex structures at the bottom of root canopies occurred, which is generated by Kelvin-Helmholtz instabilities. These instabilities are usually derived from velocity differences between root canopy and gap region. Shear- and stem-scale vortices are identified by using spectral analysis. The power spectral density function on measured vertical velocity fluctuations in the flow direction near the bottom of root canopies from the leading edge of FVIs is computed. Given the flow developing downstream, a series of the spectral curves has gradually showed one dominant dimensionless frequency at 0.046. The sweep and ejection events have contributed prominently to the Reynolds stress in whole vertical direction. Momentum flux carried by sweeps outweighs its counterpart carried by ejections inside root canopies. However, the situation is different outside root canopies. The sweep-ejection contributions are brief but crucial to the total turbulent momentum exchange, which is in good agreement with considerable studies on turbulent flow through canopies.

Unsteady behaviors of separated flow over a finite blunt plate at different inclination angles

This study comprises an extensive analysis of unsteady behaviors of a separated flow over a finite blunt plate at three different inclination angles, θ = 0°, 3°, and 6°. It was found that these three distinctly different flow patterns resulted from increasing inclination angles: reattachment, intermittent reattachment, and non-reattachment. The separated flow fields and wall-pressure fluctuations were experimentally measured with planar particle image velocimetry (PIV) operating at 1 Hz and a microphone array sampling at 5 kHz, respectively. Flow patterns were discussed in terms of the time-averaged flow fields and distributions of the statistical quantities (i.e., the reverse-flow intermittency, or velocity fluctuation intensity). A slender separation bubble formed in the front area of the plate (0 < x/D < 4.6) in the system where θ = 0° and then it enlarged to the whole surface of the plate in the system where θ = 3°. In contrast, in the system where θ = 6°, the plate surface was entirely engulfed by a large recirculation zone extending to the near-wake region. In the wall-pressure fluctuation analysis, two characteristic frequencies, St = 0.036 and 0.107, could be readily identified in all three systems; these corresponded to the flapping of separation bubble and the shedding of large-scale vortical structures, respectively. In addition, in the system where θ = 0°, wall-pressure fluctuations of the Karman vortex were detected at St = 0.154 but were suppressed in the systems where θ = 3° and 6° due to the extensive interaction between the shedding of large-scale vortical structures and the unsteady wake. Subsequently, a field-programmable gate array taking full advantage of dynamic mode decomposition (DMD) on the wall-pressure fluctuations was constructed, and a real-time conditional signal corresponding to individual unsteady behavior was generated to fire the phase-locking PIV measurement. High-resolution spatiotemporal evolutions of dominant flow behaviors (i.e., enlargement-and-shrinkage motion of the separation bubble and shedding motion of the large-scale vortical structures) were determined. In the system where θ = 6°, a separation bubble enlarged and shrank dramatically together with the shedding of large-scale vortical structures, leading to a large recirculation zone over the blunt plate, distinct from the behavior in the systems where θ = 0° and 3°. Finally, a joint dominant mode analysis of flow structures and wall-pressure fluctuations was further evaluated, which delineated the complex unsteady processes in separated flow clearly and provided more information and references for other studies on wind engineering, fluid-induced structure vibrations, and acoustic emissions.

Flow and heat transfer of couple stress nanofluid sandwiched between viscous fluids

PurposeThe purpose of this study is a numerical analysis of steady-state heat transfer behavior of couple-stress nanofluid sandwiched between viscous fluids. It should be noted that this research deals with the development of a cooling system for the electronic devices.Design/methodology/approachStokes model is used to define the couple-stress fluid and the single-phase nanofluid model is used to define the nanofluid transport processes. The fluids in all regions are assumed to be incompressible, immiscible and the transport properties in all the three layers are assumed to be constant. The governing coupled linear ordinary differential equations are made dimensionless by using appropriate fundamental quantities. The exact solutions obtained for the velocity and temperature fields are evaluated numerically for various model parameters.FindingsThe results are demonstrated using different types of nanoparticles such as copper, silver, silicon oxide (SiO2), titanium oxide (TiO2) and diamond. The investigations are carried out using copper–water nanofluid for different values of couple-stress parameter a with a range of 0 = a = 12, solid volume fraction ϕ with a range of 0.0 ≤ ϕ ≤ 0.05, Eckert number Ec with a range of 0.001 ≤ Ec ≤ 6 and Prandtl number Pr with a range of 0.001 ≤ Pr ≤ 6. It was found that the Nusselt number increases by increasing the couple stress parameter, Eckert number and Prandtl number and it decreases with a growth of the solid volume fraction parameter. It was also observed that using SiO2–water nanofluid, the optimal Nusselt number is obtained. Further, using copper, silver, diamond and TiO2, nanoparticles and water as a base fluid does not show any significant changes in the rate of heat transfer. The couple-stress parameter enhances the velocity and temperature fields whereas the solid volume fraction suppresses the flow field for both Newtonian and couple-stress fluid.Originality/valueThe originality of this work is to analyze the heat transfer behavior of couple-stress nanofluid sandwiched between viscous fluids. The results would benefit scientists and engineers to become familiar with the analysis of convective heat transfer and flow structures in nanofluids and the way to predict the heat transfer rate in advanced technical systems, in industrial sectors including transportation, power generation, chemical sectors, electronics, etc.

Statistical Analysis of Flow Structures around a Circular Cylinder

The turbulent flow characteristics around a partially submerged vertical circular cylinder mounted on a flat rigid surface have been studied experimentally in a laboratory flume to examine the turbulence characteristics, joint probability density function and the associated ejection-sweep cycles of Reynolds shear stresses. The results show the signatures of the recirculation zone and a thin shear layer between the recirculating flow behind the cylinder and the flow at the outer region. It is also noticed that at the upstream side of the cylinder, the correlation term $$ \overline{u^{\prime }w^{\prime }} $$ is prominent, whereas in the wake region behind the cylinder, the correlation term $$ \overline{u^{\prime }v^{\prime }} $$ is dominant. It is found that the contribution of stress fraction to total shear stress is more substantial at the upstream side of the cylinder compared to that at the reattachment region for uv-plane in the bottom wall region, signifying the reverse phenomenon observed for uw-plane at the same locations. Stratification of the intermittent nature of the energy dissipation within the entire flow depth at the upstream side of the cylinder is observed, while no distinct stratification of the intermittent nature of turbulence occurs at the wake region of the cylinder which creates a strong turbulent mixing. Results of the present study may be helpful for the better design of bridge pier and coastal structures.

Self-Suction-and-Jet Control in Flow Regime and Unsteady Force for a Single Box Girder

Self-suction-and-jet flow control is a passive flow control method involving self-organized suction at the leading edge and a wake jet at the trailing edge of a structure. In this study, it was used in a 1:125 physical model of the Great Belt East Bridge to decrease dynamic wind loads and modify the flow structure around the main girder. Experiments were performed in a wind tunnel at a wind speed of 12 m/s, yielding a Reynolds number of 2.8 × 104 for the height of the main girder model. The surface pressure (and therefore, the aerodynamic force) fluctuated less in the controlled models than in the uncontrolled model. The velocimetry data indicated that self-suction-and-jet flow control effectively changed the vortex shedding process in the wake of the model. The interactions between the self-organized jet flows and shear flows caused the trailing edge vortex shedding to transform from asymmetric to symmetric, eliminating the vortex shedding completely. Linear stability analysis of the mean wake flow structures indicated that self-suction-and-jet flow control pushed the unstable flow region farther downstream.

Leading-edge flow separation control over an airfoil using a symmetrical dielectric barrier discharge plasma actuator

In order to promote an in-depth understanding of the mechanism of leading-edge flow separation control over an airfoil using a symmetrical Dielectric Barrier Discharge (DBD) plasma actuator excited by a steady-mode excitation, an experimental investigation of an SC (2)-0714 supercritical airfoil with a symmetrical DBD plasma actuator was performed in a closed chamber and a low-speed wind tunnel. The plasma actuator was mounted at the leading edge of the airfoil. Time-resolved Particle Image Velocimetry (PIV) results of the near-wall region in quiescent air suggested that the symmetrical DBD plasma actuator could induce some coherent structures in the separated shear layer, and these structures were linked to a dominant frequency of f0 = 39 Hz when the peak-to-peak voltage of the plasma actuator was 9.8 kV. In addition, an analysis of flow structures without and with plasma actuation around the upper side of the airfoil at an angle of attack of 18° for a wind speed of 3 m/s (Reynolds number Re = 20000) indicated that the dynamic process of leading-edge flow separation control over an airfoil could be divided into three stages. Initially, this plasma actuator could reinforce the shedding vortices in the separated shear layer. Then, these vortical structures could deflect the separated flow towards the wall by promoting the mixing between the outside flow with a high kinetic energy and the flow near the surface. After that, the plasma actuator induced a series of rolling vortices in the vicinity of the suction side of the airfoil, and these vortical structures could transfer momentum from the leading edge of the airfoil to the separated region, resulting in a reattachment of the separated flow around the airfoil.

Numerical analysis of flow structures behind the bluff body at different aspect ratio

The present paper aimed for the numerical study on the flow structures behind the bluff body with different shapes. The variation of shapes like circular to elliptical was obtained by changing the major to minor axis ratio while keeping the Reynolds number constant. This numerical study was done with help of finite volume method using commercial software Ansys-Fluent at the lower subcritical Reynolds number, i.e., 5000and 10000 for comparison of different parameter variations separately. As the earlier studies reveals the significant effect of blockage ratio on flow features on circular cylinder, this work will be extended for different aspect ratio. The basic results, which are validated against the published results, shows the flow feature are highly sensitive to shape and blockage ratio even for different shapes. The mean pressure and turbulent kinetic energy for different blockage and aspect ratio is presented and found the strong interactions between them.

Visualization and analysis of flow structures in an open cavity

A numerical study is performed on the supersonic flow over an open cavity at Mach number of 1.5. A newly developed visualization method is employed to visualize the complicated flow structures, which provide an insight into major flow physics. Four types of shock/compressive waves which existed in experimental schlieren are observed in numerical visualization results. Furthermore, other flow structures such as multi-scale vortices are also obtained in the numerical results. And a new type of shocklet which is beneath large vortices is found. The shocklet beneath the vortex originates from leading edge, then, is strengthened by successive interactions between feedback compressive waves and its attached vortex. Finally, it collides against the trailing surface and generates a large number of feedback compressive waves and intensive pressure fluctuations. It is suggested that the shocklets beneath vortex play an important role of cavity self-sustained oscillation.