Open Rectangular Cavity Research Articles

Conjugate Heat Transfer During Viscous Incompressible Liquid Movement in the Cavity Considering its Cooling Through Outer Boundary

The paper presents the numerical simulations of the motion of a viscous incompressible non-isothermal fluid in an open rectangular cavity under conditions of conjugate heat transfer. The hydrodynamic flow pattern of a viscous fluid in the cavity obtained. The temperature profiles for the two phases - solid and liquid obtained. The influence of model parameters on the nature of motion and heat transfer conditions studied. Shows the effect of external cooling from the lateral surface on hydrodynamics and heat transfer of liquid in the cavity.

Unconstrained melting and solidification inside rectangular enclosure

The present study concerns with the numerical study of unconstrained solidification and melting of phase change material (PCM) inside a two dimensional open rectangular cavity. The Cavity is filled by RT-27 as phase change material and air. Numerical study is carried out for different cavity aspect ratios. Result indicates that the conduction heat transfer is dominant at initial time of melting process where the layer of liquid PCM near hot surface is so thin. Solid PCM sinks to bottom of cavity due to higher density in respect to liquid PCM. Melting rate does not experience significant change by increasing cavity aspect ratio. The time of full solidification is much more than melting. It is due to the absence of natural convection with respect to melting process. By increasing the cavity aspect ratio, the solidification rates enhances significantly and its total time therefore reduces.

Visualization of wave propagation within a supersonic two-dimensional cavity by digital streak schlieren

Optical measurements were carried out in planar two-dimensional open shallow cavities in order to determine how the flow field inside the cavity changes if the length-to-depth ratio of the cavity and the conditions of the boundary layer at the cavity leading edge are varied. The main challenge in this configuration, namely the fact that there are often no clearly identifiable wave fronts in the flow within the cavity, was overcome by applying a digital streak schlieren technique in combination with time-resolved high-speed flow visualizations. Using this approach, one can identify the propagation of waves within the cavity which allows one to determine the frequencies of flow oscillations inside the cavity entirely by optical means. The results from these measurements showed excellent agreement with independently conducted pressure measurements, simulations and analytical predictions. The applied technique also provides a measurement for the convective flow velocity within the cavity, for which different values can be found in the literature. The paper presents the results obtained for a Mach 2 supersonic flow over shallow rectangular open cavities with length-to-depth ratios of 3, 5, 6 and 8.

English

Heat transfer inside a semi porous two-dimensional rectangular open cavity was numerically investigated. The open cavity comprises two vertical walls closed to the bottom by an adiabatic horizontal wall. One vertical wall is a porous and an inflow of fluid occurs normal to it. The other wall transfers a uniform heat flux to the cavity. It shows how natural convection effects may enhance the forced convection inside the open cavity. The main motivation for the work is its application for electronic equipment where frequently the devices used for the electronic equipment cooling are based on natural and forced convection. Governing equations are expressed in Cartesian coordinates and numerically handled by a finite volume method. Results are presented for both local and average Nusselt numbers at the heated wall and for the isotherms and streamlines of the fluid flowing inside the open cavity as a function of Reynolds number ranging from 1 to 100, Grashof number ranging from 0 to 10+7 and the aspect ratio number of the open cavity equal 2, 4 and 8. The results obtained show that the forced convection inside the semi-porous open cavity studied may be greatly enhanced by natural convection effects. Key words: Computational simulation, electronic equipment cooling, finite volume, natural convection, open cavity; porous media.

Control of Transonic Shock Wave Oscillation over a Supercritical Airfoil

In the present study, a numerical investigation is carried out on the aerodynamic performance of a supercritical airfoil RAE 2822. Transonic flow fields are considered where self-excited shock wave oscillation prevails. To control the shock oscillation, a passive technique in the form of an open rectangular cavity is introduced on the upper surface of the airfoil where the shock wave oscillates. Reynolds Averaged Navier-Stokes (RANS) equations have been used to predict the aerodynamic behavior of the baseline airfoil and airfoil with cavity at Mach number of 0.729 and at angle of attack of 5°. The aerodynamic characteristics of the baseline airfoil are well validated with the available experimental data. It is observed that the introduction of a cavity around the airfoil upper surface can completely stop the self-excited shock wave oscillation and successively improve the aerodynamic characteristics.

Noise control of subsonic cavity flows using plasma actuated receptive channels

We introduce a passive receptive rectangular channel at the trailing edge of an open rectangular cavity to reduce the acoustic tones generated due to coherent shear layer impingement. The channel is numerically tested at Mach 0.3 using an unsteady three-dimensional large eddy simulation. Results show reduction in pressure fluctuations in the cavity due to which sound pressure levels are suppressed. Two linear dielectric barrier discharge plasma actuators are placed inside the channel to enhance the flow through it. Specifically, acoustic suppression of 7 dB was obtained for Mach 0.3 flow with the plasma actuated channel. Also, the drag coefficient for the cavity reduced by over three folds for the channel and over eight folds for the plasma actuated channel. Such a channel can be useful in noise and drag reduction for various applications, including weapons bay, landing gear and branched piping systems.

Effects of dual jets distance on mixing characteristics and flow path within a cavity in supersonic crossflow

A rectangular open cavity with upstream dual injectors at a freestream Mach number of 1.9 was investigated experimentally. To evaluate the effect of the distance between the jets, the flow characteristics were investigated using the high-speed schlieren photography, particle image velocimetry, and surface oil flow techniques. The dual jet distances of 18 and 54mm were used. Unstable flow occurs over the cavity in all cases and is not improved by changing the distance between the dual jets. Although the distance between the dual jets does not influence the flow stability, the flow field varies decidedly depending on the dual jets distance. The enhancement of air mixing depends on the distance between the jets. A long dual jets distance was found to yield better mixing characteristics within the cavity than a short one. When the jets are further apart, the mainstream between two counter-rotating vortex pairs behind the jets flows strongly into the cavity because of the increased blow-down occurring between the vortex pairs. Additionally, a counterflow with a low velocity magnitude occurs behind the jets. Hence, mixing is enhanced within the cavity by effects of the opposed flow. When the jet pairs are closer to each other, the counter-rotating vortex pairs are in contact; as a result, the blow-down effect does not occur between them. The flow drawn into the cavity from the mainstream is supplied from the sides of the test section into the cavity.

On linear instability mechanisms in incompressible open cavity flow

AbstractA theoretical study of linear global instability of incompressible flow over a rectangular spanwise-periodic open cavity in an unconfined domain is presented. Comparisons with the limited number of results available in the literature are shown. Subsequently, the parameter space is scanned in a systematic manner, varying Reynolds number, incoming boundary-layer thickness and length-to-depth aspect ratio. This permits documenting the neutral curves and leading eigenmode characteristics of this flow. Correlations constructed using the results obtained collapse all available theoretical data on the three-dimensional instabilities.

Three-dimensional instabilities over a rectangular open cavity: from linear stability analysis to experimentation – ERRATUM

Three-dimensional instabilities over a rectangular open cavity: from linear stability analysis to experimentation – ERRATUM

The efficiency of an open-cavity tubular solar receiver for a small-scale solar thermal Brayton cycle

The first law and second law efficiencies are determined for a stainless steel closed-tube open rectangular cavity solar receiver. It is to be used in a small-scale solar thermal Brayton cycle using a micro-turbine with low compressor pressure ratios. There are many different variables at play to model the air temperature increase of the air running through such a receiver. These variables include concentrator shape, concentrator diameter, concentrator rim angle, concentrator reflectivity, concentrator optical error, solar tracking error, receiver aperture area, receiver material, effect of wind, receiver tube diameter, inlet temperature and mass flow rate through the receiver. All these variables are considered in this paper. The Brayton cycle requires very high receiver surface temperatures in order to be successful. These high temperatures, however, have many disadvantages in terms of heat loss from the receiver, especially radiation heat loss. With the help of ray-tracing software, SolTrace, and receiver modelling techniques, an optimum receiver-to-concentrator-area ratio of A′≈0.0035 was found for a concentrator with 45° rim angle, 10mrad optical error and 1° tracking error. A method to determine the temperature profile and net heat transfer rate along the length of the receiver tube is presented. Receiver efficiencies are shown in terms of mass flow rate, receiver tube diameter, pressure drop, maximum receiver surface temperature and inlet temperature of the working fluid. For a 4.8m diameter parabolic dish, the larger the receiver tube diameter and the smaller the mass flow rate through the receiver, the higher the receiver surface temperature and the less efficient the collector becomes. However, the smaller the receiver tube diameter, the higher the pressure drop through the tube and the smaller the second law efficiency. It was found that the receiver with larger tube diameter would perform better in a solar thermal Brayton cycle. An overall solar-to-heat efficiency of between 45% and 70% is attainable for the solar collector using the open-cavity receiver.

Three-dimensional instabilities over a rectangular open cavity: from linear stability analysis to experimentation

AbstractThree-dimensional instabilities arising in open cavity flows are responsible for complex broad-banded dynamics. Existing studies either focus on theoretical properties of ideal simplified flows or observe the final state of experimental flows. This paper aims to establish a connection between the onset of the centrifugal instabilities and their final expression within the fully saturated flow. To that end, a linear three-dimensional modal instability analysis of steady two-dimensional states developing in an open cavity of aspect ratio $L/D=2$ (length over depth) is conducted. This analysis is performed together with an experimental study in the same geometry adding spanwise endwalls. Two different Reynolds numbers are investigated through spectral analyses and modal decomposition. The physics of the flow is thoroughly described exploiting the strengths of each methodology. The main flow structures are identified and salient space and time scales are characterised. Results indicate that the structures obtained from linear analysis are mainly consistent with the fully saturated experimental flow. The analysis also brings to light the selection and alteration of certain wave properties, which could be caused by nonlinearities or the change of spanwise boundary conditions.

Conjugate heat transfer during viscous liquid movement in the open cavity, considering its cooling through outer boundary of back surface

Numerical simulation was carried out for nonisothermal incompressible viscous liquid in the open rectangular cavity, considering the heat loss through the channel bottom outer boundary. Liquid flow pattern and temperature profiles were obtained for solid and liquid phases. Influence of model parameters on heat carrier motion pattern and cavity cooling mode has been investigated. The interest in studies of convective flow in different heat transfer conditions and for various cavities is caused by a wide applied value of the problem. Large amount of heating devices is being used in power plants and energy systems, production processes of a various complexity level. The necessity of studying these processes is determined by development of such energy-intensive indistries as power engineering, metallurgy, chemical industry and many other (1-5). Experimental development of technologies always assumes a high probability of selecting not the best process conditions both for productivity and quality, and for implementation costs. Therefore, there arises a necessity to study theoretical hydrodynamic regularities and heat transfer during heat carrier motion in limited space. This article considers nonsteady interaction of liquid with the open cavity (Fig. 1). Process of molten metal movement in the channel is being investigated with consideration to heat exchange with its walls. Thermal and physical characteristics of the molten metal and cavity walls are identical. The purpose of this work is to investigate the hydrodynamics and conjugate heat transfer during movement of nonisothermal incompressible viscous liquid in the rectangular-type cavity in conditions of the channel's outer boundary cooling. Similar problems have been solved before (6-8) for thermal insulation conditions of the cavity outer boundaries. Study of the described process was done using a mathematical model based on the Navier-Stokes equations in the variables vortex-stream function, the energy equation, and the heat-conduction equation for the cavity material with corresponding initial and boundary conditions + U X + V Y = 1

Three-dimensional flow within shallow, narrow cavities

AbstractThe three-dimensional structure of incompressible flow in a narrow, open rectangular cavity in a flat plate was investigated with a focus on the flow topology of the time-averaged flow. The ratio of cavity length (in the direction of the flow) to width to depth was $l{: }w{: }d= 6{: }2{: }1$. Experimental surface pressure data (in air) and particle image velocimetry data (in water) were obtained at low speed with free-stream Reynolds numbers of ${\mathit{Re}}_{l} = 3. 4\times 1{0}^{5} $ in air and ${\mathit{Re}}_{l} = 4. 3\times 1{0}^{4} $ in water. The experimental results show that the three-dimensional cavity flow is of the ‘open’ type, with an overall flow structure that bears some similarity to the structure observed in nominally two-dimensional cavities, but with a high degree of three-dimensionality both in the flow near the walls and in the unsteady behaviour. The defining features of an open-type cavity flow include a shear layer that traverses the entire cavity opening ultimately impinging on the back surface of the cavity, and a large recirculation zone within the cavity itself. Other flow features that have been identified in the current study include two vortices at the back of the cavity, of which one is barely visible, a weak vortex at the front of the cavity, and a pair of counter-rotating streamwise vortices along the sides of the cavity near the cavity opening. These vortices are generally symmetric about the cavity centre-plane. However, the discovery of a single tornado vortex, located near the cavity centreline at the front of the cavity, indicated that the flow within the cavity is asymmetric. It is postulated that the observed asymmetry in the time-averaged flow field is due to the asymmetry in the instantaneous flow field, which switches between two extremes at large time scales.

Effectiveness of jet location on mixing characteristics inside a cavity in supersonic flow

The incorporation of cavities within supersonic combustion chambers is an effective means of slowing down the flow for fuel injection and consequent stable combustion. Understanding the flow physics associated with such flows, especially with the injection of a gas to replicate fuel injection, are essential for the optimum design of supersonic propulsion mechanisms. An experimental investigation was performed on a rectangular open cavity with upstream injection model in a Mach number of 1.9 using a trisonic indraft wind tunnel. A rectangular open cavity of dimensions L/D=5, 100mm in length (L) and 20mm deep (D), was adopted, and it was embedded into the lower wall of the test section. An air jet with a jet-to-freestream momentum flux ratio of J=1.2, 2.7 and 5.3 was injected upstream of the cavity. To evaluate the effect on mixing and flow stability the jet position, measured from the front edge of the cavity, was varied between 0.1L and 1L. The flow field was visualized using schlieren photography, particle image velocimetry, and oil flow measurements. It is found that the mixing characteristic within the cavity when the jet is positioned 0.1L is enhanced independent on the J value because the turbulence intensity of the flow velocity within the cavity is strongly influenced by the jet interaction which lifted the flow from the floor of the cavity compared to the other jet positions. However, the flow over the cavity is unstable at all jet positions. The separation shock formed at the front edge of the cavity oscillates significantly for the case where the jet is located at 0.1L because the separation shock location coincides with the compression shock behind the jet.

A sixth-order fast algorithm for the electromagnetic scattering from large open cavities

In this paper, a sixth-order fast algorithm is presented for solving the electromagnetic scattering problem from a rectangular open cavity embedded in an infinite ground plane. Firstly, a sixth-order compact finite difference scheme is employed to discretize the scattering problem described by the Helmholtz equation with a nonlocal boundary condition. Then, exploiting the discrete Fourier transformation in the horizontal and a Gaussian elimination in the vertical direction presented by [2], the discrete system reduces to a much smaller interface system. An effective preconditioner is developed for the Krylov subspace iterative solver to solve this interface system. Numerical results show the remarkable efficiency and accuracy of the new algorithm.

Efficient modeling and experimental validation of acoustic resonances in three-dimensional rectangular open cavities

The goal of this paper is to investigate the acoustic resonances of a three-dimensional open cavity by a fast and efficient method in the time domain. This method models the time response in any point as the convolution of the source waveform with the impulse response of the cavity, which, in turn, is obtained as a sequence of attenuated and delayed impulses coming, the first from the real, and the subsequent from the mirror imaged sources (Image Source Model). This method, which main advantages with respect to others that work in the frequency domain are that the results for all frequencies can be calculated at once, the time domain data is recovered directly, and the computational cost does not increase with frequency, can easily provide the frequency response at each point of the cavity by Fourier transform. From these frequency responses, the relevant resonances of the cavity can simply be obtained. Illustration and experimental validation of the proposed method is presented by its application to a rectangular open cavity.

Investigation of the Effects of Length to Depth Ratio on Open Supersonic Cavities Using CFD and Proper Orthogonal Decomposition

Simulations of supersonic turbulent flow over an open rectangular cavity are performed to observe the effects of length to depth ratio (L/D) of the cavity on the flow structure. Two-dimensional compressible time-dependent Reynolds-averaged Navier-Stokes equations with k-ω turbulence model are solved. A reduced order modeling approach, Proper Orthogonal Decomposition (POD) method, is used to further analyze the flow. Results are obtained for cavities with several L/D ratios at a Mach number of 1.5. Mostly, sound pressure levels (SPL) are used for comparison. After a reduced order modeling approach, the number of modes necessary to represent the systems is observed for each case. The necessary minimum number of modes to define the system increases as the flow becomes more complex with the increase in the L/D ratio. This study provides a basis for the control of flow over supersonic open cavities by providing a reduced order model for flow control, and it also gives an insight to cavity flow physics by comparing several simulation results with different length to depth ratios.

Constructal design of conducting body cooled by open cavity

AbstractThis paper investigates the constructal design of a body where a rectangular open cavity intruded into a trapezoidal solid by taking the maximum dimensionless thermal resistance minimisation as the optimisation objective in the most fundamental sense. Two cases, i.e. body with heat generation and body heated externally, are considered. The numerical results indicate that for the two cases, the more slender the cavity, the safer the thermal system. In addition, in thermal design and management, the effect of heat origin on the system safety should be taken into account sufficiently. The triple optimisation results show that the optimum ratio of left body height to right body height for the two cases approach each other relatively; the double optimum ratios of right body height to body length for body with heat generation are smaller than those for body heated externally when the ratio of cavity height to cavity length is from 0·01 to 2, while the former are equal or similar to the latter when the r...

Field Distribution of Environment and Vibration Chamber

Environment and vibration test system can test equipment such as radars in full load condition. Environment and vibration chamber is an opening rectangular cavity. In order to study the field distribution of environment and vibration chamber, the open rectangular cavity field distribution and parabolic antenna are analyzed by using the Dyadic Green’s functions. According to the Dyadic Green’s functions, the field distribution of environment and vibration chamber is concluded by MATLAB. The simulation result of FEKO proves that the method by using Dyadic Green’s functions is available. The innovation of this article is using the Dyadic Green’s functions to analyzed open cavity field and parabolic antenna.

Field Distribution of Environment and Vibration Chamber

Environment and vibration test system can test equipment such as radars in full load condition. Environment and vibration chamber is an opening rectangular cavity. In order to study the field distribution of environment and vibration chamber, the open rectangular cavity field distribution and parabolic antenna are analyzed by using the Dyadic Green’s functions. According to the Dyadic Green’s functions, the field distribution of environment and vibration chamber is concluded by MATLAB. The simulation result of FEKO proves that the method by using Dyadic Green’s functions is available. The innovation of this article is using the Dyadic Green’s functions to analyzed open cavity field and parabolic antenna. DOI: http://dx.doi.org/10.11591/telkomnika.v10i3.620