Flow In Wavy Channel Research Articles

Numerical investigation of thermo-hydraulic features of viscoplastic flow in wavy channels

In the present work, the thermo- hydraulic characteristics are studied for a laminar viscoplastic flow through raccoon and serpentine type wavy channels. The results are presented by varying Bingham number (Bn), power-law index (n), Reynolds number (Re), dimensionless amplitude, and wave number in the physically justified ranges. It is found that the size of the recirculatory zone decreases with Bn and the zone disappears at the higher Bn values. The topology of the yielded-unyielded region highly depends on the geometry and the range of Bn. Moreover, the value of average Nusselt number decreases with n. With the increase in Bn, average Nusselt number gradually decreases up to a critical Bn value and then increases sharply at higher Bn values. Interestingly, the wavy channel is only advantageous at smaller Bn values up to a critical limit. The variation of performance factor (PF) strongly depends on the combined effect of rheological and geometrical parameters. Besides, results for raccoon and serpentine channels are highly dependent on the ranges of amplitude, wave number, Bn, and n.

Analysis of SWCNT-water nanofluid flow in wavy channel under turbulent pulsating conditions: Investigation of homogeneous and discrete phase models

Improving thermal performance in heated channels has received much attention from many researchers due to its presence in various thermal systems. The present research numerically illustrated the effect of turbulent pulsating flow and SWCNT-water nanofluids in sinusoidal wavy channel on hydrothermal characteristics and entropy production. This study aims to provide a new thermal management approach for compact heat exchangers. Two various models for describing the motion of nanoparticles in a base fluid are applied. These models are Homogeneous single-phase, SPM and Lagrangian-Eulerian model (or discrete phase model), DPM. Governing equations are computationally solved utilizing the finite volume technique. This simulation covers Reynolds number, pulsation frequency, phase shift and nanoparticles concentration in the range of (4000 ≤ Re ≤ 7000), (1 ≤ f ≤ 5), (0° ≤ θ ≤ 180°) and (0% ≤ φ ≤ 3%), respectively. CFD simulations show that the pulsation frequency, f and phase shift, θ have a significant role in improving the heat transfer ratio and controlling the entropy generation through the wavy channel. Finally, it is recommended to use SWCNT/water nanofluid with a high-volume fraction (φ = 3%) as a working fluid in the considered channel due to its high heat transfer ratio and low thermal irreversibility.

Numerical analysis on heat transfer performance of oscillating flow in wavy channel

This study focuses on the unsteady characteristics of heat transfer process and its augmentation in wavy channels working in an acoustic resonator with a standing wave imposing the oscillating flow. A two-dimensional numerical model is developed after a careful verification with the published experimental results. Forty cases, involving fifteen wavy channel structures along with a comparative parallel channel working in different driving ratios, were established considering the heating and cooling process in different heat exchangers. The dynamic characteristics of temperature and velocity field, redevelopment of boundary layer, spatial and time-spatial averaged Nusselt number are presented to depict the heat transfer performance in oscillating flow. The results show that the viscous boundary layer follows a procedure of generating, expanding, separating and merging in each acoustic cycle. Thermal boundary layer keeps a longer stability after experiencing the redevelopment, during which heat transfer augmentation occurs. However, heat transportation will be inhibited when thermal boundary layer separation happens. Besides, the heat transfer enhancement capacity of wavy channel compared with parallel channel can reach to 1.10 in both hot and cold side under driving ratio of 0.83 %. The optimal dimensional height of the wavy channel normalized by thermal penetration depth is also found to be located between 2–3. At last, the heat transfer performance is correlated with the change of amplitude height of wave, Reynolds and Prandtl number considering the heating and cooling processes. This study will provide numerical heat transfer data of oscillating flow using wavy channel and help the design of compact heat exchanger in thermoacoustic system.

Heat transfer characteristics of laminar and turbulent wavy channel flow in the presence of a stationary or rotating blade

Heat transfer characteristics of laminar and turbulent wavy channel flow in the presence of a stationary or rotating blade

Numerical investigation of turbulent flow in a wavy channel partially filled with a porous layer

In this paper, the effect of inserting a porous layer inside a wavy channel on the mean flow and turbulent characteristics in both developing and repeated flow regions have been investigated numerically. The modified Launder-Sharma low-Reynolds number k−ε turbulence model, which was used in a previous study [1] with two extensions model, has been utilised to represent the turbulence in the porous region. For validation, the flow in a clear channel with wavy bottom wall has been considered. The results of clear channel have been compared with the experimental data produced by [2], where the results computed were in a good agreement with the experimental data. In the porous wavy channel flow case, the same dimensions of the clear wavy channel have been adopted but with covering the bottom wavy wall with a porous layer formed of an open-cell metal foam. Three values for the wave amplitude of the wavy bottom wall and porous layer thickness have been considered, which are (0,0.1,0.2) and (0,0.15H,0.3H), respectively. Three samples of metal foams have been tested along with the effect of the wave amplitude of the wavy surface and the thickness of the wavy porous layer on the turbulent flow. These types are (ϕ=0.9486&ω=10PPI), (ϕ=0.952&ω=40PPI) and (ϕ=0.81&ω=13PPI). For all calculations, a Reynolds number equals to 20,600 has been considered. In the near fluid-porous interface region, damping functions have been used. The results show that the repeated flow pattern tends to occur in earlier region towards upstream than the flow over solid wavy surface when the permeability of the porous layer is decreased. Moreover, the repeated flow pattern also tends to occur in early region of the wavy part of the channel when the wave amplitude and porous layer thickness are increased, compared to the lower wave amplitude and low porous layer thickness. Decreasing the permeability increases the size of the recirculation cell in the repeated flow region and also increases the turbulent energy in the clear region. Increasing porous layer thickness, on the other hand, reduces the size of circulation cell and the turbulent energy.

Parametric Study of Turbulent Couette Flow over Wavy Surfaces Using RANS Simulation: Effects of Aspect-Ratio, Wave-Slope and Reynolds Number

A turbulent Couette flow over a wavy surface is subject to a detailed parametric study in which three parameters—Aspect Ratio, Wave Slope and Reynolds number—are independently varied over an order of magnitude to investigate their influence on the flow. Stdk−ε turbulence model with enhanced wall functions is used to simulate all cases in the study and the results are validated against experimental data as well as analytical theories pertaining to flow over wavy surfaces. Gross flow properties such as mean velocity profiles, mass flow rate, shear stress and pressure on the walls, as well as turbulent flow characteristics such as inner-wall coordinates, log-law fit, eddy viscosity profiles and turbulence kinetic energy across the domain, are presented and their corroboration with existing literature is discussed. The effect of the three parameters on the flow variables is investigated. It is observed that while all response flow variables scale monotonically with a progressive change in the parameters, there are certain flow characteristics that can be ascribed exclusively to one of the three parameters. The study also discusses the influence of the top plate, a much-needed discussion that seems to be absent in most literature pertaining to Couette flow in wavy channels.

Streamline segment statistics propagation in inhomogeneous turbulence

Streamline segment statistics are collected from tomographic particle image velocimetry and direct numerical simulation data of a turbulent wavy channel flow. The model equation for such statistics is adapted for inhomogeneous turbulence. The novel formulation is applied to explain the observations and identify the locally acting mechanisms.

Heat transfer in a triangular wavy channel with CuO-water nanofluids under pulsating flow

In this paper, heat transfer and pressure drop characteristics of CuO-water nanofluid flow in a isothermally heated triangular-wavy channel under pulsating inlet conditions are numerically investigated. A numerical simulation is conducted by solving the governing continuity, momentum, and energy equations for laminar flow using the finite volume approach. In the studies, the main parameters including the Reynolds number, pulsating amplitude and frequency, are changed while the nanoparticle volume fraction and the other parameters are kept constant for all cases. Numerical results are compared with the steady flow conditions, which showed that heat transfer performance significantly increases due to improve thermal conductivity and the use of nanoparticles in the pulsating flow conditions. The results indicate that there is a high potential for promoting the thermal performance enhancement by using nanoparticles under pulsating flow in wavy channels. It is found that the heat transfer enhancement increases with increasing pulsating amplitude and Reynolds number, and there is a slight increase in pressure drop. The obtained results are given as a function of dimensionless parameters.

Asymptotic solution to the viscous/inertial flow in wavy channels with permeable walls

Flow in a wavy channel immersed in the porous medium can be described neither as the flow in porous media nor as the flow in a regular pipe. The flow through the walls and the irregular wavy geometry of the walls result in non-negligible inertial and visco-inertial effects. The quadratic and cubic corrections to Darcy’s law proposed since Forchheimer have always been the subject of debate. In this paper, the complete set of Navier-Stokes equations is solved in a channel with wavy walls immersed in a porous medium. The asymptotic solution is obtained using the perturbation method considering the channel’s aspect ratio as the perturbation parameter. The two-scale homogenization technique is used to capture the effect of the wavy corrugations on the overall flow in the channel. The averaged pressure drop along the channel is represented as quadratic and cubic corrections to the linear law for a cylindrical and parallel-plate wavy channel.

Flow of a yield-stress fluid over a cavity: Experimental and numerical investigation of a viscoplastic boundary layer

The ability of viscoplastic fluids to self-select their flow geometry through the formation of unyielded dead zones has important consequences for flows in wavy channels, flows over obstacles, etc. Yet, the mechanisms controlling the formation and dimensions of the dead zones remain poorly understood. We present a detailed cross-comparison of experimental and numerical results concerning channel flows of a viscoplastic fluid over a rectangular cavity filled by the same material. In all the configurations studied, which correspond to moderate values of the Bingham number, a continuous dead zone forms inside the cavity. Both numerical and experimental data reveal that, unlike at high Bingham numbers, the shear-rate profiles above the dead zone display an asymmetric shape. Accordingly, two different flow zones can be distinguished: a Poiseuille-like zone, in which the velocity profile is similar to that over a rigid wall, and a boundary layer ensuring the transition with the dead zone below. It is shown that the effective boundary condition felt by the Poiseuille-like layer is essentially controlled by incoming flow characteristics, such that the thickness of this layer does not obey simple relations with cavity length. Interestingly, however, the thickness of the boundary layer appears to follow a generalized Oldroyd’s scaling with cavity length.

Numerical investigation of mixing enhancement for multi-species flows in wavy channels

The present study considers the mixing characteristics of gaseous species in a channel with wavy walls. Waviness imparted along the walls are uniquely defined by the wavelength (λ), amplitude (a) and phase difference (PD). A quasi-incompressible formulation in a three-dimensional collocated finite volume framework is employed for the numerical simulations. Results show that wavy channels lead to enhanced mixing, quantified by the mixing efficiency (M), compared to that of a plane channel. Moreover, the use of asymmetric channels (with 0° PD) shows better mixing capability than their symmetric counterparts (with 180° PD) for same wavelength and amplitude. We argue, based on numerical results that the enhanced mixing in the asymmetric channels is due to the generation of alternate recirculation patterns, leading to higher transverse velocities. These transverse convective currents combined with diffusion are observed to aid the mixing process. A complete set of parametric studies is subsequently carried out to investigate the effect of the geometric parameters of waves along with Reynolds number, Peclet number for the 0° PD wavy channel. It is observed that for a given length, there exists a critical wave number that maximizes the mixing efficiency.

Thermohydraulic transport characteristics in wavy microchannel under pulsating inlet flow condition

The numerical investigation on developing unsteady laminar fluid flow and heat transfer inside a 2D wavy microchannel, due to sinusoidal varying velocity component at inlet is done. The thermohydraulic flow was developing while the microchannel walls were kept at constant uniform temperature. The transient solution of 2DNavier-Stokes equation was attained using the SIMPLE algorithm with the momentum interpolation technique. The deionized water is used as working fluid and Reynolds number ranging from 0.1 to 100. The simulation results reports, mainly the heat transfer and pressure drop for wavy microchannel are compared with straight microchannelby keeping the cross sectional area same. By comparing with steady flow in wavy channel it was seen that imposed sinusoidal velocity at inlet can improved performance in terms of heat transfer at different amplitude (0.2, 0.5, 0.8) and frequency (1, 5, 10) while keeping the friction factor within tolerable limits.

Pulsating Flow and Heat Transfer in Wavy Channel with Zero Degree Phase Shift

In this study, heat transfer enhancement of laminar pulsating flow in wavy channel is investigated numerically . The wavy channel has constant wall temperature and its geometric parameters are fixed. Finite volume method based on SIMPLE technique is used to solve governing equations. Simulations performed for Reynolds numbers in the range of 200≤Re≤800. The effects of pulsation frequency is investigated for Strouhal numbers, (St) of 0.05, 0.15 and 0.25. The differences between flow structures of pulsating and steady flow are discussed. Results indicate that the pulsating flow significantly enhances heat transfer.

Numerical investigation of nanofluid turbulent flow in a wavy channel with different wavelengths, amplitudes & phase lag

Two dimensional incompressible turbulent nanofluid flow in a sinusoidal wavy channel is numerically investigated. Finite volume method and Rhie and Chow interpolation in a collocated grid arrangement are used for solving governing equations. The effects of the volume fraction of nanoparticles, Reynolds number, phase lag, frequency and amplitude of the wavy walls on the heat transfer rate are studied. The present work showed good agreement with existing experimental and numerical results. Increasing the frequency and amplitude of the wave and nanoparticles volume fraction has great effect on heat transfer rate.

Streamline segment scaling behavior in a turbulent wavy channel flow

A turbulent flow in a wavy channel was investigated by tomographic particle-image velocimetry measurements and direct numerical simulations. To analyze the turbulent structures and their scaling behavior in a flow undergoing favorable and adverse pressure gradients, the streamline segmentation method proposed by Wang (J Fluid Mech 648:183–203, 2010) was employed. This method yields joint statistical information about velocity fluctuations and length scale distributions of non-overlapping structures within the flow. In particular, the joint statistical properties are notably influenced by the pressure distribution. Previous findings from flat channel flows and synthetic turbulence simulations concerning the normalized segment length distribution could be reproduced and therefore appear to be largely universal. However, the mean streamline segment length of accelerating and decelerating segments varies within one wavelength typically elongating segments of the type which corresponds to the local mean flow. Furthermore, the local pressure gradient was found to significantly impact local joint streamline segmentation statistics as a main influence on their inherent asymmetry.

Using quasi-DNS to investigate the deposition of elongated aerosol particles in a wavy channel flow

In gas-cooled high temperature reactors, the diffusion of the fission products into the graphite matrix causes a radioactive contamination of the carbonaceous dust. The contaminated graphite aerosol particles often exhibit large aspect ratios and deposit in complex geometries, which hinders a detailed experimental investigation. The use of quasi Direct Numerical Simulation (quasi-DNS) to simulate the turbulent flow in nuclear reactors has seen an increased interest over the last few years. The capabilities of a quasi-DNS to simulate the transport and the deposition of elongated particles in a wavy channel flow are presently tested. It is shown that quasi-DNS effectively predicts deposition and that, unlike the deposition in a plane channel flow, the particle aspect ratio has no significant effect on the overall deposition rate in a wavy channel. It is suggested that in numerical studies of particle deposition on a significantly roughened channel, the particle can be assumed to be spherical without affecting the results of the deposition study.

The evaluation of a detached eddy simulation based on the k–ω–[formula omitted]–f model with three flow configurations

Detached Eddy Simulation (DES) based on the k–ω–υ2¯–f model, termed DES–k-ω–υ2¯-f, is developed and evaluated in the present study. In this model, the RANS–LES switching is achieved by an adaptation of the turbulent length scale between the LES and RANS regions. The SGS model coefficient is calibrated by the decaying homogeneous isotropic turbulence (DHIT). The capabilities of the proposed model are evaluated on various geometries, i.e. the plane channel flow, wavy channel flow and two side by side square cylinders. The DES results are compared with the URANS and LES results obtained in the present study and the available results obtained in other references. A good agreement is found between the results of the proposed DES model and the LES for three flow configurations employed. For the cases with flow separation, the DES model demonstrates accurate predictions in reproducing the resolved flow and turbulence quantities in comparison with full-resolved LES.

Application of the method of fundamental solutions and the radial basis functions for viscous laminar flow in wavy channel

This paper deals with the problem of viscous laminar flow in a wavy channel using the method of fundamental solutions and the radial basis functions. First approximation was obtained when the Reynolds number equals zero, in which the considered problem is homogeneous problem which can be easily solved using the method of fundamental solutions. In order to obtain subsequent approximations of the solution, the nonlinear problem was transformed into a sequence of inhomogeneous problems using the Picard iteration method. Applying the method of particular solutions on each iteration step the solution consists of the general solution and the particular solution. The right-hand side of the governing equation in subsequent iteration steps was interpolated using the radial basis functions. Simultaneously the particular solution was obtained and the general solution was obtained by means of the method of fundamental solutions. The unknown coefficients of the solution were obtained using the boundary collocation technique. The main advantage of the proposed procedure is its simplicity and analytical form of the approximate solution. Such meshless approach was never applied previously for the problem of viscous laminar flow in the wavy channel.

Behavior of particles in turbulence over a wavy boundary

Understanding the mechanism controlling the particle motion in flow over a complex boundary is of great importance for many engineering fields. It is well known that fluid flowing over a wavy boundary creates turbulence that is remarkably different from the flow over a flat wall. Previous studies have presented the role of vortical structures over a wavy boundary, which is associated with particle clustering near the boundary. In this study, behavior of particles in turbulence over a wavy wall is investigated by direct numerical simulation of a turbulent wavy channel flow with laden particles. Our investigation shows that particles interact selectively with vortical structures and accumulate in a specific region along the wavy wall. Active deposition and resuspension occur in the upslope region where streamwise vortices are concentrated. Depending on the particle Stokes number and waviness of the wall, a strip or streak pattern of particle clustering near the wall is observed due to the combined effect of the wavy wall and vortical structures. However, due to the particle inertia, particle velocity and its fluctuation do not change as much as fluid velocity along the wavy boundary. Statistics and relevant physical interpretations of particle motion are presented.

Numerical optimization of heat transfer enhancement in a wavy channel using nanofluids

In this study, a multi-parameter constrained optimization procedure integrating the design of experiments (DOE), full factorial experimental design (FFED), genetic algorithm (GA) and computational fluid dynamics (CFD) is proposed to design two-dimensional wavy channel with nanofluids (Cu/water, Al2O3/water and CuO/water). The elliptical, coupled, steady-state, two-dimensional governing partial differential equations for laminar forced convection of nanofluids are solved numerically using the finite volume approach. Some important parameters for the influences of heat transfer enhancement such as the Reynolds number (250≦Re≦1000), the particle volume concentration (0%≦ϕ≦5%), the wavy channel amplitude (0.1≦α≦0.3) and the wavy numbers (3≦β≦12) on the enhancement of nanofluid heat transfer have been investigated.The numerical results with a single-phase model are first validated with the available data in the literature. The maximum discrepancy is within 8%. Results of a further extension to a two phase model are also validated. The numerical results indicate that the thermal enhancement can achieve 15%, 24% in the wavy channel flow compared with pure fluid, with the particle volume concentration of ϕ=3% and ϕ=5% of Cu/water nanofluids. In addition, after the validation of the numerical results, the numerical optimization of this problem is also presented by using a full factorial experimental design and the genetic algorithm (GA) method. The objective function E which is defined as thermal performance factor has developed a correlation function with three design parameters. The predicting performance factor E (α=0.278, β=3, ϕ=5%) of regression function is closely agreed with those from the CFD computational results within 4.6% difference. The combination of parameters is considered as the optimal solution.