The Effect of Triangular Vortex Generators on Turbulent Flow and Heat Transfer in a Channel

Author(s):  
Hosseinali Soltanipour ◽  
Iraj Mirzaei ◽  
Parisa Choupani

In the present work heat transfer characteristics and flow structure in turbulent flow through a rectangular channel containing built-in triangular winglet-type vortex generators have been analyzed by means of solutions of the Navier-Stokes and energy equations using finite volume method. The geometrical configuration is representative of single element of plain-plate heat exchangers. Each winglet-pair induces longitudinal vortices behind it. Shear stress transport (SST) model is used in this study. The underlying physical phenomena have been described and the effects of Reynolds number and angle of attack, on the heat transfer, pressure drop and thermal performance have been presented.

2000 ◽  
Author(s):  
M. Singh ◽  
P. K. Panigrahi ◽  
G. Biswas

Abstract A numerical study of rib augmented cooling of turbine blades is reported in this paper. The time-dependent velocity field around a pair of symmetrically placed ribs on the walls of a three-dimensional rectangular channel was studied by use of a modified version of Marker-And-Cell algorithm to solve the unsteady incompressible Navier-Stokes and energy equations. The flow structures are presented with the help of instantaneous velocity vector and vorticity fields, FFT and time averaged and rms values of components of velocity. The spanwise averaged Nusselt number is found to increase at the locations of reattachment. The numerical results are compared with available numerical and experimental results. The presence of ribs leads to complex flow fields with regions of flow separation before and after the ribs. Each interruption in the flow field due to the surface mounted rib enables the velocity distribution to be more homogeneous and a new boundary layer starts developing downstream of the rib. The heat transfer is primarily enhanced due to the decrease in the thermal resistance owing to the thinner boundary layers on the interrupted surfaces. Another reason for heat transfer enhancement can be attributed to the mixing induced by large-scale structures present downstream of the separation point.


1994 ◽  
Vol 116 (3) ◽  
pp. 588-597 ◽  
Author(s):  
G. Biswas ◽  
P. Deb ◽  
S. Biswas

Laminar flow and heat transfer characteristics in a rectangular channel, containing built-in vortex generators of both the slender delta-wing and winglet-pair type, have been analyzed by means of solution of the full Navier–Stokes and energy equations. Each wing or winglet pair induces the creation of streamwise longitudinal vortices behind it. The spiraling flow of these vortices serves to entrain fluid from their outside into their core. These vortices also disrupt the growth of the thermal boundary layer and serve ultimately to bring about the enhancement of heat transfer between the fluid and the channel walls. The geometric configurations considered in the study are representative of single elements of either a compact gas-liquid fin-tube crossflow heat exchanger or a plate-fin crossflow heat exchanger. Physically, these vortex generators can be mounted on the flat surfaces of the above-mentioned heat exchangers by punching or embossing the flat surfaces. They can also act as spacers for the plate fins. Because of the favorable pressure gradient in the channel, the longitudinal vortices are stable and their influence persists over an area many times the area of the slender vortex generators. From a heat transfer point of view, the delta-wing generator is found to be more effective than the winglet-pair. However, most convective heat transfer processes encounter two types of loss, namely, losses due to fluid friction and those due to heat transfer across finite temperature gradient. Because these two phenomena are manifestations of irreversibility, an evaluation of the augmentation techniques is also made from a thermodynamic viewpoint. Conclusions that are drawn thus include discussion about the influence of vortex generators (wings/winglets) on irreversibility.


2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Abhishek G. Ramgadia ◽  
Arun K. Saha

Present study focuses on numerical investigation of fully developed flow and heat transfer through three channels having sine-shaped, triangle-shaped, and arc-shaped wall profiles. All computations are performed at Reynolds number of 600. Finite volume method on collocated grid is used to solve the time-dependent Navier–Stokes and energy equations in primitive variable form. For all the geometries considered in the study, the ratios Hmin/Hmax and L/a are kept fixed to 0.4 and 8.0, respectively. The thermal performances of all the three wall configurations are assessed using integral parameters as well as instantaneous, time-averaged and fluctuating flow fields. The geometry with the sinusoidal-shaped wall profile is found to produce the best thermal properties as compared to the triangle-shaped and the arc-shaped profiles though the obtained heat transfer is the highest for the arc-shaped geometry.


2001 ◽  
Vol 7 (3) ◽  
pp. 209-222
Author(s):  
Frank K. T. Lin ◽  
G. J. Hwang ◽  
S.-C. Wong ◽  
C. Y. Soong

This work is concerned with numerical computation of turbulent flow and heat transfer in experimental models of a radially rotating channel used for turbine blade cooling. Reynolds-averaged Navier-Stokes and energy equations with a two-layer turbulence model are employed as the computational model of the flow and temperature fields. The computations are carried out by the software package of “CFX-TASCflow”. Heat loss from the channel walls through heat conduction is considered. Results at various rotational conditions are obtained and compared with the baseline stationary cases. The influences of the channel rotation, through-flow, wall conduction and the channel extension on flow and heat transfer characteristics are explored. Comparisons of the present predictions and available experimental data are also presented.


2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Hooman Yarmand ◽  
Samira Gharehkhani ◽  
Salim Newaz Kazi ◽  
Emad Sadeghinezhad ◽  
Mohammad Reza Safaei

Thermal characteristics of turbulent nanofluid flow in a rectangular pipe have been investigated numerically. The continuity, momentum, and energy equations were solved by means of a finite volume method (FVM). The symmetrical rectangular channel is heated at the top and bottom at a constant heat flux while the sides walls are insulated. Four different types of nanoparticles Al2O3, ZnO, CuO, and SiO2at different volume fractions of nanofluids in the range of 1% to 5% are considered in the present investigation. In this paper, effect of different Reynolds numbers in the range of 5000 < Re < 25000 on heat transfer characteristics of nanofluids flowing through the channel is investigated. The numerical results indicate that SiO2-water has the highest Nusselt number compared to other nanofluids while it has the lowest heat transfer coefficient due to low thermal conductivity. The Nusselt number increases with the increase of the Reynolds number and the volume fraction of nanoparticles. The results of simulation show a good agreement with the existing experimental correlations.


2021 ◽  
Author(s):  
Muhammad Ibrahim ◽  
Tareq Saeed

Abstract This study examines the turbulent flow field and heat transfer rate (HTR) of the non-Newtonian H2O-Al2O3-carboxymethyl (CMC) in a channel with vortex generators. The finite volume method and SIMPLE algorithm were employed for solving the partial differential equations. The mean Nusselt numbers (Num) and pressure drops were studied at angles of 30-60°, vortex generator depths of 1-3 mm, Reynolds numbers (Re) of 3000-30000, and nanoparticles volume fractions (φ) of 0.5% and 1.5%. According to the numerical results, the use of triangular vortex generators significantly incremented the Nusselt number (Nu) of the non-Newtonian nanofluid (NF), while it had a lower effect on the enhancement of pressure drop (DP). It was also indicated that a change in the vortex generator depth in the range of a few millimeters had no significant effects on the Nu and pressure drop. Moreover, a rise in the Re (i.e., more turbulent flow) significantly incremented HTR. An increase in the Re raised pressure drop; however, the Num incremented more than the pressure drop. Also, the variations of the local Nu indicated that the local Nu significantly incremented around vortex generators due to the formation of vortex flows. An enhancement in the volume fraction of the base fluid’s nanoparticles (NPs) from 0.5% to 1.5% significantly incremented HTR and the Nu.


Author(s):  
Pankaj Saha ◽  
Gautam Biswas

Detailed flow structures in turbulent flow through a rectangular channel containing built-in winglet type vortex generators have been analyzed by means of solutions of the full Navier-Stokes equations using a Large-Eddy Simulation (LES) technique. The Reynolds numbers of investigation is 6000. The geometry of interest consists of a rectangular channel with a built-in winglet pair on the bottom wall with common-flow-down arrangement. The winglet pair induces streamwise longitudinal vortices behind it. The vortices swirl the flow around the axis parallel to the mainstream direction and disrupt the growth of thermal boundary layer entailing enhancement of heat transfer. The influence of the longitudinal vortices persists far downstream of the location of the winglet-pair. Since the structure of the turbulence is strongly affected by the streamline curvature, the flow of interest, despite the simplicity of its geometry, turns out to be extremely complex. Therefore it calls for more accurate calculation of the turbulence quantities. In the present study, flow structures are studied by using time-averaged quantities, such as the iso-contours of velocity components, vortices and turbulent stresses. The simulation shows that the secondary flow is stronger in the regions where the longitudinal vortices are more active. The wake like structures of streamwise velocity occurs due to strong distortion of the boundary layer by vortices. The spanwise distributions of turbulent kinetic energy and Reynolds stresses show the evidence of strong secondary flow. The computational results compare well with the experimental data qualitatively.


2021 ◽  
Vol 39 (4) ◽  
pp. 1305-1312
Author(s):  
Mohammad Mazidi Sharfabadi ◽  
Parham Mobadersani ◽  
Leila Nourpour

In this study, the effect of the vortex generators on the heat transfer and flow characteristics in a rectangular channel is investigated numerically by finite volume method. The governing equations are discretized using QUICK scheme. The numerical results are validated against published experimental data. In this paper, the effects of the winglet aspect ratio and the distance between the vertices of the winglets on the heat transfer and hydrodynamic characteristics of the flow are surveyed. In addition, to achieve the optimum amount of heat transfer, it is important to know the proper arrangement of the triangular winglet pairs as well as their suitable position. Therefore, the appropriate values of the longitudinal and transverse pitch are presented in this paper. The results show that the winglet with the aspect ratio of 1.75 has the best thermal and hydrodynamic performance. Furthermore, the transverse pitch of 1.24 causes 6.5% growth in the average Nusselt number.


2014 ◽  
Vol 13 (2) ◽  
pp. 96
Author(s):  
S. I. S. Souza ◽  
H. A. Martins ◽  
J. N. V. Goulart

Turbulent flow in channels with gap is still a challenge for engineering. The velocity fluctuations and the appearance of coherent structures have been playing a major role in forced convective heat transfer process between the warm tube walls and the cooling fluid. In this paper numerical simulation of non-isothermal turbulent flow in a rectangular channel containing only one tube was performed. Unsteady Reynolds Navier-Stokes along with the energy equation were applied to model the problem. In order to overcome the closure problem the turbulence was modeled applying SAS model. The simulated geometry consists of a heated cylindrical tube, placed 10 mm from the bottom wall of the rectangular duct. The fluid flows externally to the heated tube along the mainstream direction. The channel’s length was based on the tube diameter, yielding L/D equal 80.


2013 ◽  
Vol 388 ◽  
pp. 176-184
Author(s):  
Hussein A. Mohammed ◽  
Nur Irmawati Om ◽  
Mazlan A. Wahid

Combined convective nanofluids flow and heat transfer in an inclined rectangular duct is numerically investigated. Three dimensional, laminar Navier-Stokes and energy equations were solved using the finite volume method. Pure water and four types of nanofluids such as Au, CuO, SiO2 and TiO2with volume fractions range of 2% φ 7% are used. This investigation covers the following ranges: 2 × 106 Ra 2 × 107, 100 Re 1000 and 30° Θ 60°. The results revealed that the Nusselt number increased as Rayleigh number increased.SiO2nanofluid has the highest Nusselt number while Au nanofluid has the lowest Nusselt number. An increasing of the duct inclination angle decreases the heat transfer.


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