Fluid Flow and Mixed Heat Transfer in a Horizontal Channel with an Open Cavity and Wavy Wall

Heat exchangers are utilized extensively in different industries and technologies.Consequently,optimizing heat exchangers has been a major concern among researchers.Although various studies have been conducted to improve the heat transfer rate,the use of a wavy wall in the presence of different types of heat transfer mechanisms has not been investigated.This study thus investigates the mixed heat transmission behavior of fluid in a horizontal channel with a cavity and a hot,wavy wall.The fluid flow in the channel is considered laminar,and the governing equations including continuity,momentum,and energy are all solved numerically.The numerical solution is stabilized by using a first-order multi-dimensional characteristic-based scheme in combination with a fifth-order Runge-Kutta method.The flow and heat transfer effects of varying Richardson numbers,Reynolds numbers,wave amplitude,wavelength,channel height,and cavity width are examined.The results indicate that the mean Nusselt number increases with an increase in Reynolds number,wave amplitude,and cavity width,while it decreases with an increase in Richardson number,wavelength,and channel height.The minimum Nusselt number is calculated to be 0.7,whereas the maximum Nusselt number is 27.09.The Nusselt number has only increased by 40%in the higher depths of the cavity,despite the Richardson number being 10,000 times larger.But this figure increases to 130%at lower depths.The mean Nusselt number is thus significantly influenced by channel height and cavity width.The influence of wave amplitude on the mean Nusselt number is twice that of wavelength.

Prediction of Hydrodynamic Noise of Open Cavity Flow

In this paper,the hydrodynamically generated noise by the flow over an open cavity is studied.First,aeroacoustic theories and computational aeroacoustic(CAA) methodologies are reviewed in light of hydrodynamic acoustics,based on which,a hybrid method is presented.In the coupling procedure,the unsteady cavity flow field is computed using large-eddy simulation(LES) ,while the radiated sound is calculated by the Ffowcs Williams-Hawkings(FW-H) acoustic analogy with acoustic source terms extracted from the time-dependent solutions of the unsteady flow.The hybrid LES-FW-H acoustic analogy method is tested with an open cavity flow at Mach number of 0.006 and Reynolds number of 105 .Following the reflection theorem of Powell,the contributions from different source terms are quantified,and the terms involving wall-pressure fluctuations are found to account for most of the radiated intensity.The radiation field is investigated in the frequency domain.For the longitudinal direction,the sound propagates with a dominant radiation downstream the cavity in the near-field and a flatter directivity in the far-field,while for the spanwise direction,the acoustic waves have a similar propagation along+z and-z directions,with no visible directivity.

A completely open cavity realized with photonic crystal wedges

A completely open cavity, which is formed by three 60-degree wedges of a photonic crystal with negative effective index, is introduced. Such a realizable design for a completely open cavity (i.e., without any reflective wall in the radial direction) is the first of its kind ever been reported. Due to the negative effective refraction index of the photonic crystal and the high transmission at the photonic crystal/air interfaces, a closed path with zero optical path is formed for the resonance. The present open cavity is very suitable for use as a biosensor as it has large air wedges into which a liquid measurand can flow easily.

Numerical Simulation of Flow over an Open Cavity with Self-Sustained Oscillation Mode Switching

Numerical simulations are used to investigate the self-sustained oscillating flows past an open cavity. The two-dimensional incompressible Navier-Stokes equations are solved directly by using the finite difference method for cavities with an upstream laminar boundary layer. A series of simulations are performed for a variety of cavity length-to-depth ratio. The results show the switching among some flow modes including non-oscillation mode, shear layer mode and wake mode. The variation of the Strouhal number is in favorable agreement with available experimental data. The results of flow fields in the cavity reveal the relationship between the cavity shear layer oscillation modes and recirculating vortices in the cavity.

Numerical investigation of entropy generation and heat transfer of pulsating flow in a horizontal channel with an open cavity

In this study, the entropy generation and the heat transfer of pulsating air flow in a horizontal channel with an open cavity heated from below with uniform temperature distribution are numerically investigated. A numerical method based on finite volume method is used to discretize the governing equations. At the inlet of the channel, pulsating velocity is imposed for a range of Strouhal numbers Stpfrom 0 to 1 and amplitude Apfrom 0 to 0.5. The effects of the governing parameters, such as frequency and amplitude of the pulsation, Richardson number, Ri, and aspect ratio of the cavity, L/H, on the flow field, temperature distribution, average Nusselt number and average entropy generation, are numerically analyzed. The results indicate that the heat transfer and entropy generation are strongly affected by the frequency and amplitude of the pulsation and this depends on the Richardson number and aspect ratio of the cavity. The pulsation is more effective with the aspect ratio of the cavity L/H= 1.5 in terms of heat transfer enhancement and entropy generation minimization.

Effects of Rayleigh Number on MHD Heat Transfer and Fluid Flow in Two-Dimensional Open Square Cavity with Heat Generation

The present work is devoted to investigating heat transfer and fluid flow in a two dimensional square open cavity containing a heated circular cylinder at the centre. A constant heat flux is set at the left sidewall;high and low temperatures are fixed at the bottom and top walls of the cavity respectively. The right side of the cavity is open. Galerkin Weighted Residual Finite Element Analysis is used to visualize the heat transfer and fluid flow solving two-dimensional governing mass, momentum and energy equations for steady state, heat transfer and fluid flow in presence of magnetic field in side an open square cavity. A uniformly heated circular cylinder is placed at the centre of the cavity as a heat source. To find the effects of Rayleigh number (Ra) on the thermal fields and fluid flow in presence of magnetic field and a heated circular cylinder as heat source by visualization and line graphs is the objective of this study. Numerical results are presented in graphical and tabular form. The study is conducted for different values of Rayleigh number, some fixed Hartmann numbers (Ha) and heat flux (q). In the conclusion it has been observed that the temperature field and fluid flow pattern are functions of the parameters Rayleigh number and Hartmann number.

Lattice Boltzmann simulation of natural convection in open end cavity with inclined hot wall

Natural convection in an open end cavity with a hot inclined wall is simulated based on the lattice Boltzmann method （LBM）. The physics of flow and energy transfer in open end cavities are addressed when the hot wall is inclined. The combination of the two topics （open cavity and inclined walls） is the main novelty of the present study. The effects of the angle of the hot inclined wall on the flow field and heat transfer are thoroughly investigated. The Prandtl number is fixed to 0.71 （air）. The Rayleigh number and the angle of the hot inclined wall are varied in the range of 10^4 to 10^6 and 60° to 85°, respectively. The results are presented for two different aspect ratios, i.e., A = 1 and 2. The results obtained with the LBM are also compared with those of the finite volume method （FVM）. The predicted results of the LBM conform to those of the FVM. The results show that by increasing the angle of the hot inclined wall and the aspect ratio of the cavity, the average Nusselt number decreases. The trend of the local Nusselt number on the inclined wall is also discussed.

Electronic transport through an open elliptic cavity

This paper computes the conductance of an open ellipse cavity and discusses the effect of finite leads on conductance. The lead introduces mode coupling with bound states in the cavity which contributes to Fano resonant line shapes in conductance. By examining the resonant states in the cavity, the effects of state mixing and annular probability distribution of wave function due to the presence of leads are found. The results have been compared with the transport properties of other systems. The finite leads result in two effects, i.e. the evanescent mode contribution and additional oscillations, to the conductance.

A hybrid method for inverse cavity scattering problem for shape

In this paper, we give a hybrid method to numerically solve the inverse open cavity scattering problem for cavity shape, given the scattered solution on the opening of the cavity. This method is a hybrid between an iterative method and an integral equations method for solving the Cauchy problem. The idea of this hybrid method is simple, the operation is easy, and the computation cost is small. Numerical experiments show the feasibility of this method, even for cases with noise.

Flow induced structural vibration and sound radiation of a hydrofoil with a cavity

The structural vibration and the sound radiation induced by the flow over a cavity on a hydrofoil are investigated experimentally and numerically. The large eddy simulation(LES) is adopted to calculate the flow field and the pressure fluctuation characteristics. A coupled finite element method/boundary element method approach is used to analyze the hydrofoil vibration and the structure-borne noise. The flow noise is calculated using an acoustic analogy by considering the surface pressure fluctuations as the dipole sources. A hollow hydrofoil with an orifice supported by four cylinder rods is constructed for the experiments. Modal tests are performed to obtain the natural frequencies of the hydrofoil in air and water. The vibro-acoustic experiments are carried out in the water tunnel at various free stream velocities with the orifice open and closed. A pressure transducer is used to measure the pressure fluctuations behind the downstream edge of the orifice. The triaxial accelerometers mounted on the side walls are used to measure the vibrational response of the hydrofoil. Furthermore, a hydrophone located in a box, filled with water is used to measure the sound radiation. The structure-borne noise and the flow noise are identified by their frequency properties. Reasonable agreements are observed between the numerical predictions and the experimental measurements.

Self-sustained oscillation for compressible cylindrical cavity flows

The presence of a cavity changes the mean and fluctuating pressure distributions. Similarities are observed between a cylindrical cavity and a rectangular cavity for a compressible flow.The type of cavity flow field depends on the diameter-to-depth ratio and the length-to-depth ratio.The feedback loop is responsible for the generation of discrete acoustic tones. In this study, the selfsustained oscillation for a compressible cylindrical cavity flow was investigated experimentally. For open-type cavities, the power spectra show that the strength of resonance depends on the diameterto-depth ratio（4.43–43.0） and the incoming boundary layer thickness-to-depth ratio（0.72–7.0）. The effective streamwise length is used as the characteristic length to estimate the Strouhal number. At higher modes, there is a large deviation from Rossiter＇s formula for rectangular cavities. The gradient-based searching method was used to evaluate the values of the empirical parameters. Less phase lag and a lower convection velocity are observed.

Turbulent Mixed Convection-Radiation Interactions in a Cavity

Two-dimensional turbulent mixed convection-surface radiation interaction phenomenon in a back-wall-heated open square cavity is numerically investigated. The flow medium is air, and the turbulence model used is the Low-Reynolds-Number κ-ε Scheme. Calculations have been performed for Grashof numbers Gr up to 10^(10). And the Richardson number Ri covers a range of 4×10^(-3)-45. It is shown that within a rather extensive range of Ri, the effects of radiation on the heat transfer and fluid flow in the cavity are significant, should not be neglected and become stronger with the increase of Ri and Gr.

Memory effects in scattering from accelerating bodies

Interaction of electromagnetic,acoustic,and even gravitational waves with accelerating bodies forms a class of nonstationary time-variant processes.Scattered waves contain intrinsic signatures of motion,which manifest in a broad range of phenomena,including Sagnac interference,and both Doppler and micro-Doppler frequency shifts.Although general relativity is often required to account for motion,instantaneous rest frame approaches are frequently used to describe interactions with slowly accelerating objects.We investigate theoretically and experimentally an interaction regime that is neither relativistic nor adiabatic.The test model considers an accelerating scatterer with a long-lasting relaxation memory.The slow decay rates violate the instantaneous reaction assumption of quasistationarity,introducing nonMarkovian contributions to the scattering process.Memory signatures in scattering from a rotating dipole are studied theoretically,showing symmetry breaking of micro-Doppler combs.A quasistationary numeric analysis of scattering in the short-memory limit is proposed and validated experimentally with an example of electromagnetic pulses interacting with a rotating wire.