Delta Winglet Vortex Generators Research Articles

Numerical Analysis of the Thermal-Hydraulic Performance on Circular Channel Using Vortex Generator

Vortex generators are often used in the industrial world because they can improve heat transfer well. Vortex generators make it possible to mix hot and cold fluids to be more optimal than not using them. Therefore, the current study aims to investigate the thermal-hydraulic of each case of a delta-winglet type vortex generator in a circular channel using numerical simulations. This modelling is carried out by varying the angle of the vortex generator type delta-winglet, namely, 90°, 105°, and 120°, which are arranged in a line, and the angle of attack in all cases is 30°. The Reynolds number is set from 4,000 to 12,000 with an interval of 2,000 and using the k-ω turbulent SST model. The working fluid used in this study is water. This fluid was chosen because it has better thermal conductivity than air, even though it has a higher viscosity and results in increased flow resistance. This study found that the highest heat transfer was a deltawinglet vortex generator at 90°, 105°, and 120°. But the delta-winglet, which has the highest heat transfer, will impact the increased flow resistance. Furthermore, the best thermal-hydraulic results were achieved in the case of the delta-winglet vortex generator at an angle of 120° of 2.47.

Heat Transfer Characteristic on Wing Pairs Vortex Generator using 3D Simulation of Computational Fluid Dynamic

Vortex generators are addition surface that can increase heat transfer area and change the fluid flow characteristics of the working fluid to increase heat transfer coefficient. The use of vortex generators produces longitudinal vortices that can increase the heat transfer performance because of the low pressure behind vortex generators. This investigation used delta winglet vortex generator that was combined with rectangular vortex generator to Reynold numbers ranging 6,000 to 10,000. The parameters of Nusselt number, friction factor, velocity vector and temperature distribution will be evaluated.

Comparison of Different Fin and Tube Compact Heat Exchanger with Longitudinal Vortex Generator in CFU-CFD Configurations

Over the last decades several studies have searched for improved Fin and Tube Heat Exchanger (FTHE) designs capable of providing the best thermo-hydraulic performance. The present study aims at quantifying and comparing the thermo-hydraulic performance of different FTHE configurations. Six different designs were analyzed. The first FTHE consisted of an in-line circular tube arrangement and the last one was a FTHE with staggered oval tube with two pairs of Delta Winglet Vortex Generators (DWVG) in common flow up–common flow down (CFU-CFD) configuration. The best performance was obtained using DWVG in CFU-CFD orientation. This configuration enabled a 90% increase of the thermal performance factor when compared with the first case, using only two pairs of vortex generator´s per tube.

Thermal and flow characteristics of a channel formed by aligned round tube bank fins stamped with curve delta-winglet vortex generators

The primary purpose of present study is to reveal the roles played by CDVGs in vectoring the airflow and breeding longitudinal vortices for enhancing heat transfer. The thermal-hydraulic characteristics of a finned aligned round tube heat exchanger with stamped CDVGs were numerically studied by using the custom code with SIMPLE algorithm in a nonorthogonal curvilinear coordinate system. Four geometric parameters including vortex generator height, radial position, peripheral position and fin pitch, were programmed to ascertain parametric effects on fin side thermal performance, and the regression formulas of Nusselt number and resistance coefficient in the fin side passage with Reynolds numbers and four geometric parameters were secured. The findings suggest that the mean Nusselt number, resistance coefficient and secondary flow strength for the novel fin with CDVGs are all prevail over that in the reference plain fin under a certain Reynolds number. The body fitted CDVGs are ideally situated for finned round tube exchanger in aligned arrangement. The action of CDVGs can not only efficiently lessen the size of recirculation area behind tube but also produce strong longitudinal vortices, accordingly heighten evidently the fin side heat transfer ability in the recirculation zone. Using the studied optimum geometric parameters can make the thermal property factor up to 1.35 under the same pumping power constraint in comparison with the reference plain fin geometry when Reynolds number equals to 3000. This study can be a real application in compact heat exchanger with finned round tubes when heat transfer augmentation is under consideration.

An experimental investigation on the thermal augmentation of internal endwall in a two-pass duct using an array of delta-winglet vortex generator pair

The present study experimentally demonstrates a novel design for an internal endwall in a two-pass duct heat exchanger. An array of delta-winglet vortex generator pairs with different aspect ratio, angle of attack, configuration are mounted on the internal endwall in a U duct. Liquid crystal thermalgraphy and static pressure measurements are utilized in this study to evaluate the heat transfer, thermal-hydraulic performance, and pressure drop penalty. The Reynolds number is varied from 10,000 to 20,000. A comparison between the current novel design and traditional enhanced heat transfer turbulators in the open literature is also included. The results show that the endwall heat transfer is enhanced greatly as the longitudinal vortex generator array is located on the endwall. The variation of the attack angle has great influence on the endwall heat transfer, The endwall fitted with turbulators with an aspect ratio (length/height) of 2 and attack angle of 45-deg provides the highest thermal-hydraulic performance with a relatively low pressure drop penalty as long lasting longitudinal vortices might be induced at this attack angle and the heat transfer is observed to be enhanced at the downstream part of the endwall. In addition, for the temperature uniformity on the endwall, the local heat transfer at the upstream part still has the potential to be further improved for all studied cases. The optimal thermalhydraulic performance is increased by more than 24% compared with that on the endwall in the smooth U duct. This novel design presents a rather high overall thermal performance compared with the traditional design in the open literature.

Numerical heat transfer in a solar air heater duct with punched delta-winglet vortex generators

The flow topology and thermohydraulic performance of a novel designed punched delta-winglet (P-DW) placed on the absorber of a solar air heater duct are numerically explored. The effects of geometrical parameters, namely, the relative winglet pitch, PR = 1–2 and the relative punched hole size, dR = 0–0.583 at a single value of blockage ratio, BR = 0.48 and attack angle, α = 30° on thermal characteristics are proposed for Reynolds number from 4000 to 24,000. Among several turbulence models, the simulation has shown that the realizable k–ε turbulence model is favorable with respect to measurements. For flow patterns, the P-DW produces several counter-spinning vortices helping induce the impinging jets onto the absorber surface whilst for thermal behaviors, the decline of PR and dR leads to the rise in the friction factor (f) and Nusselt number (Nu). The P-DW provides greater Nu and f than the plain flat plate by 17.1–78.21 and 3.92–5.9 times, respectively and gives the highest performance around 2.1. Further, the P-DW is modified by covering the punched hole partially with a circular flap, called the flapped delta-winglet (F-DW) and this F-DW yields the greatest performance around 2.16 higher than the P-DW about 2.9%.

Effect of perforated concave delta winglet vortex generators on heat transfer and flow resistance through the heated tubes in the channel

ABSTRACT This study focuses on improving heat transfer from the surface of heated tubes to airflow in the channel. Perforated concave delta winglet vortex generators, which have not been used in previous studies, were implemented in this study to increase the heat transfer rate. In this experimental study, the comparison of perforated concave delta winglet and perforated delta winglet was investigated in terms of increased heat transfer from a heated six-tube surface to the flow in a rectangular channel. The experimental results indicated that the use of perforated concave delta winglet vortex generators could increase the heat transfer rate of 46.3% toward the baseline. However, the optimal thermal-hydraulic performance was found in the use of the concave delta winglet at 1.37 with a staggered vortex generators arrangement. The results of this study indicated that the use of perforated vortex generators could reduce the pressure drop with a slight decrease in the heat transfer rate.

The optimal longitudinal location of curved winglets for better thermal performance of a finned-tube heat exchanger

The influence of longitudinal location of curved delta winglet vortex generator on the heat transfer of a finned-tube heat exchanger is numerically studied. The vertical right-angled side of the winglet vortex generator is arranged facing the main flow direction. Longitudinal vortex intensity and heat transfer are obviously affected by the longitudinal location of the vortex generator. There is an optimal longitudinal location of vortex generator for the largest heat transfer performance. At the optimal location, Nusselt number increases by 15.2%–43.9% and 5.4%–9.8%, while friction factor only increases by 12.2%–15.7% and 4.8%–12.2% compared with the plain fin and the original location, respectively. Thermal performance factor of the optimal longitudinal location increases by 8.1% compared with the original location and reaches up to 1.38. The pressure loss of the curved vortex generator is obviously smaller than that of the corresponding straight vortex generator. Good corresponding relationship exists between the Nusselt number and the intensity of longitudinal vortices, which means the intensity of the secondary flow determines the heat transfer. The results are of significance for the design and optimization of the studied finned-tube heat exchanger with curved delta winglet vortex generators.

On the solar air heater thermal enhancement and flow topology using differently shaped ribs combined with delta-winglet vortex generators

A numerical investigation has been conducted to study the convective heat transfer enhancement and friction loss behaviors for turbulent flow by using arrays of differently shaped ribs combined with delta-winglet vortex generators (DWVGs) pair on the absorber plate of a solar air heater. Four transverse vortex generators arrays, i.e., 90° continuous ribs, 90° truncated ribs, 60° V-shaped continuous ribs, and 60° V-shaped truncated ribs, are studied to investigate the mixing effect with the DWVGs pair. The aspect ratio (AR = Lv/Hv) of the DWVGs is 2:1 while the geometrical condition of the ribs is height of 0.003 m and pitch of 0.028 m. The Reynolds number ranges from 4000 to 20,000. Results of temperature, Nusselt number, vortical structure, topological portrait, turbulent kinetic energy (TKE), friction factor and thermal performance evaluation are included. The results show that the adoption of DWVGs and the shape type of the ribs have great impact on the heat transfer and flow structure in the solar air heater. It is found that the DWVGs combined with the 60° V-shaped continuous ribs contributes the best heat transfer performance, and the heat transfer is enhanced by 39.4% compared with the only DWVGs case.

Large eddy simulation of an inclined jet in crossflow with vortex generators

ABSTRACT Film cooling is one of the essential approaches to cool high-performance turbine blades. Film cooling with delta winglet vortex generator pair (DWVGP) placed upstream of the cooling hole is investigated by large eddy simulation (LES) at the blowing ratio of M=1.0. Film cooling effectiveness and vortical structures are evaluated in the flow field of a jet in crossflow (JICF). Results indicate that film cooling effectiveness increases significantly for the DWVGP case. As a dominant vortex structure, the ubiquitous counter-rotating vortex pair (CRVP) is recognized in the flow field. It has a detrimental effect that lifts the coolant off the cooling surface. The DWVGP evolved anticounter-rotating vortex pair (anti-CRVP) has the opposite sense of rotation to the jet introduced CRVP, which undertakes vorticity decay when developing downstream of the cooling hole. With the downwash effect of anti-CRVP, the reattachment of coolant is earlier, and a wide region of enhanced film cooling effectiveness in the spanwise direction is achieved. The coherent vortex structures including the classical vortices in the flow field and the vortex generator pair introduced vortices are analyzed. The genesis and evolution mechanism of CRVP with and without the vortex generators are discussed. It indicates that three branches of upstream spiral structures from the nozzle tube contribute to the CRVP. The merging of CRVP upstream branches is delayed by the vortex generators evolved anti-CRVP, which postpones the formation of downstream CRVP.

Review on Heat Transfer Enhancement by Louvered Fin

The heat transfer enhancement is recycled in many engineering uses such as heat exchangers, refrigeration and air conditioning structures, chemical apparatuses, and automobile radiators. Hence many enhancing extended fin patterns are developed and used. In multi louvered fin, in this segment for multi-row fin and tube heat exchanger, an increase in heat transfer enhancement is found 58% for ReH = 350. When the Reynolds number is 1075, the temperature gradient is more distinct for greater louver angle that is the higher heat transfer enhanced for large louver angle. For variable louver angle heat exchanger, the maximum heat transfer improvement achieved by 118% Reynolds number at 1075. In the vortex generator for the delta winglet vortex generator, the extreme enhancement of heat transfer increased to 16% compared to the baseline geometry (at ReDh = 600). For a compact louvered heat exchanger, the results showed that a regular arrangement of louvered fins gives a 9.3% heat transfer improvement. In multi-region louver fins and flat tubes heat exchanger, the louver fin with 4 regions and the louver fin with 6 regions are far better than the conventional fin in overall performance. At the same time, the louver fin with 6 regions is also better than the louver fin with 4-region. The available work is in experimental form as well as numerical form performed by computational fluid dynamics.

Development of hybrid thermal management techniques for battery packs

In this study, the thermal management issue of electric vehicle and hybrid electric vehicle battery pack is studied. Passive and hybrid techniques are developed and used in the battery pack. Multiple delta winglet vortex generators are introduced to enhance turbulence before the air flow interacts with the cells’ surface. Multiple jet inlets are introduced that enable the air flow to change its directions and pass through the dead air regions. A hybrid technique is also used in which a liquid jacket is added to each of the cells. The liquid within the jackets is in contact with the cells maximizing the contact surface area to improve heat transfer. Steady state computational fluid dynamic simulations are performed to study the effects of the passive and hybrid techniques added to the battery pack. The results indicate a substantial improvement in the temperature uniformity. The temperature difference of the hybrid battery pack reduces from 4.87 °C to 1.26 °C. Additionally, the temperature variance at the cell level reduces from 3.29 °C to 0.36 °C. This battery pack does not require moving parts and pumping power and it can achieve high levels of temperature uniformity.

THE AUGMENTATION OF INTERNAL TIP HEAT TRANSFER IN GAS TURBINE BLADES USING A PAIR OF DELTA-WINGLET VORTEX GENERATORS

A novel method to enhance the heat transfer on the internal tip surface of gas turbine blades was developed. Effects of delta-winglet vortex generators (DWVG) and their angle of attack on the vortical structures and mechanism of enhanced heat transfer were investigated. Seven different angles of attack were considered: 0°, 15°, 30°, 45°, 60°, 75°, and 90°. The Reynolds number varies from 10,000 to 50,000. Flow topology analysis was employed to better understand the evolution of vortices in the turn region. Results showed that a vortex was induced on the leeward side of the DWVG as the angle of attack was greater than 0°, which significantly enhanced the local heat transfer. Also, an extra saddle point was generated at the tip surface on the windward side of the DWVG as the angle of attack is greater than 45°, indicating that a vortex wass formed. The internal tip heat transfer increased as the angle of attack of the DWVG increased. The optimal design was reached when the angle of attack is greater than 60°. Compared with the smooth channel, the heat transfer and overall thermal performance are enhanced by up to 9.5% and 8.1%, respectively. (Less)

Efek vortex generators terhadap peningkatan perpindahan panas pada aliran melewati heated tubes

In this decade, improving the rate of heat transfer has become a big challenge. The high thermal resistance of the gas side of the heat exchanger has an impact on the low rate of heat transfer. Therefore, an experimental study was carried out aimed at looking at conditions of hot temperature and decreased air flow pressure through a heated tube in a rectangular channel using artificial surfaces, namely the concave delta winglet and delta winglet vortex generators. Concave delta winglet vortex generators (CDW VGs) are installed in-line and staggered with one, and two pairs are arranged in common-flow-down (CFD) in the direction of flow with an angle of attack of 15o. The experimental results show that the best thermal performance is observed in the use of two rows CDW VGs staggered, where the value of performance evaluation criteria (PEC) is 28.88% higher than the use of CDW VGs in-line, DW VGs staggered and DW VGs in-line at the same Reynolds number. At the same Reynolds number, the Nusselt number ratio and the friction factor ratio increased 45.25% and 152.05% respectively, occurring in two rows of CDW VGs staggered compared to other vortex generators.Keywords: vortex generators, heat transfer, Nusselt number, friction factor, PEC

On the topology of vortex structures and heat transfer of a gas turbine blade internal tip with different arrangement of delta-winglet vortex generators

This paper aims to provide a novel enhanced heat transfer method for the internal tip surface of a U bend channel of relevance for a gas turbine rotor blade. The DWVGs (delta-winglet vortex generators) pair is arranged at multiple locations on the tip surface. Two types of vortex generators are studied, including common-flow-up and common-flow-down configurations. The inlet channel Reynolds number varies from 10,000 to 50,000. The topological analysis method is used to determine the formation and evolution of the vortices and to better understand the mechanism of the heat transfer enhancement. Results of skin-friction lines, topological portrait, Nusselt number, friction factor, thermal performance are included. The results show that due to the interaction among the vortices surrounding the vortex generators, the DWVGs pair in common-flow-up configuration has a slight heat transfer improvement, and is not sensitive to the tip location. However, the DWVGs pair in common-flow-down configuration placed at the downstream of the tip surface improved the heat transfer significantly as the induced vortices between the turbulator pairs effectively reduce the thickness of the boundary layer. Compared with the smooth U bend channel, the optimal design shows that the heat transfer and overall thermal performance can be increased by up to 7.4% and 6.8%, respectively. This study elaborates the flow and heat transfer processes from the perspective of topology, which is helpful in the design of cooling procedures of turbine blades.

Experimental analysis and exergetic assessment of the solar air collector with delta winglet vortex generators and baffles

To increase the efficiency of solar air collectors (SACs), the combined effects of baffles and delta winglet vortex generator (DWLVG) on the performance of SAC have been investigated. An experimental setup has been made, and numerical simulation is carried out in Ansys Fluent. The numerical investigation is validated by the experimental study and focused on the number of baffles as well as the number and the height of DWLVG. The results show that the SAC with no baffles and DWLVG has the lowest efficiency with the maximum value of 13%, while for SAC with six baffles and three pairs of DWLVG, the efficiency reaches up to 20%. The exergy analysis of three cases, SAC without baffles and DWLVG, SAC with six baffles without DWLVG, and SAC with six baffles and three pairs of DWLVG, shows that the maximum exergy efficiency of the SAC is 30.44% and occurs when the height ratio and the number of DWLVG pairs are 0.5 and 3. The results show that for SAC with six baffles and three pairs of DWLVG, the energy and exergy efficiency improve 7.4% and 12% on an average basis compared to the typical flat plate SAC, respectively. This improvement in thermal and exergy efficiency is due to the implementation of DWLVG which produces more turbulence and eliminates the vortices generated at the corners of SAC.

Numerical optimization of a heat exchanger with slit fins and vortex generators using genetic algorithms

Abstract Heat exchangers are devices very commonly found in heating and air conditioning appliances. This work is about the optimization of compact heat exchangers with three rows of tubes and slit fins, using built-in longitudinal vortex generators on the fins. The Colburn factor and the friction factor were obtained out of numerical simulations from a universe of 32 geometries. Geometries were selected using the Latin hypercube design, and were numerically simulated. Two objective functions were employed as surrogate models for the Colburn and friction factor. The functions were determined by multiple regression with a level of R square higher than 99.5%. A multi-objective numerical optimization was made, to find the best location for delta winglet vortex generators and its angle of attack; searching for an increase of heat transfer and a low value in pressure penalty. Group of optimal geometries was obtained, because of the optimization process using genetic algorithms. The geometry, with the best performance was simulated, and the results were used to validate the optimization process. This geometry, when compared to the slit fin without vortex generators (smooth condition), increased by 8.74% the heat transferred and augmented by 14.77% the pressure drop. The angle of attack, module, and module angle of the optimized geometry were 49.86°, 5.08 mm and 22.51° respectively.

Numerical investigation of laminar flow and heat transfer in a channel using combined nanofluids and novel longitudinal vortex generators

Enhancement of heat transfer in plate-fin heat exchangers can be obtained using vortex generators (VG). The three-dimensional laminar flow of water/Al2O3 nanofluid with different nanoparticle volume fractions in a channel with longitudinal vortex generators is numerically simulated. Two novel forms of modified delta winglet VG pairs (MDWP1, MDWP2) are introduced by adding and subtracting a part of the quadrant profile to the delta winglet VG profile. Simulation is carried out for the classic delta winglet pair (DWP) and MDWPs. Performance of heat transfer and pressure drop is compared as well as the overall performance analysis of channel is conducted for all three forms of VGs and two flow arrangement types, common flow up (CFU) and common flow down (CFD). Analytical expressions from the literature are used to check the validity of the model. Governing equations of laminar fluid flow and heat transfer are solved based on the finite-element method. The range of Reynolds number is from 100 to 500. Results show that in the range of the present study, using nanofluid increases about 20% of the heat transfer coefficient and 18% of pressure drop compared to pure water. As results confirm in all of the cases, the heat transfer coefficient increases using VG. The MDWP2 leads to the highest pressure drop and heat transfer between the three VGs types. It can produce up to 9% higher heat transfer coefficient in Re = 100 and 20% of higher pressure drop for CFD flow arrangement. The overall performance of the CFD arrangement is higher than CFU for the studied cases relatively. And the values of performance in a channel with DWP are greater than MDWP1 and MDWP2, which is due to the lower pressure drop of DWP.

Analysis of flow characteristics downstream delta-winglet vortex generator using stereoscopic particle image velocimetry for laminar, transitional, and turbulent channel flow regimes

The evolution of flow structures downstream a single pair of delta-winglet vortex generators (VGs) is investigated experimentally using stereoscopic particle image velocimetry. In addition, the laser Doppler anemometer technique is performed to characterize the upstream flow. Experiments are conducted in a bounded channel flow (height H) for the Reynolds numbers (ReDH, based on the hydraulic diameter height) ranging from 400 to 12 000. The purpose of this study is to provide detail insight into the generation and the dissipation of longitudinal vortices over a wide flow regime range including the laminar–turbulent transition. With a focus on transverse sections, the flow field is detailed. For all flow regimes, the main flow topology shows that the two main counter-rotating vortices are generated at a certain streamwise distance downstream the VG and then are advected gradually toward the channel lateral-walls. A secondary vortex pair is induced closer to the wall. Our results show that close to the VGs, local regions (1 > z/H > −1) are strongly defined as the inception of the turbulence production. The intensity of this latter is shown to vanish beyond a certain distance far from the origin of the perturbation (when x/H is greater than 3). The instantaneous flow structure describes the mechanism of vortex generation, relying on the intermittence of the flow organization and the sweep and ejection event balance. Detailed analysis on the turbulence properties and wall shear stress has been assessed and revealed that the flow transition induced by the perturbation of the VG is achieved at a Reynolds number no greater than 1500.

Effects of Longitudinal Vortices on Turbulent Junction Flow Heat Transfer

Turbulent junction flow is a vortex system upstream of a blockage embedded in a turbulent boundary layer, which leads to augmented heat transfer near the blockage. Vortex legs wrap around the blockage and travel downstream as longitudinal vortices. In multistage axial turbines or multiple row tube heat exchangers, these longitudinal vortices can collide with junction flow vortices further downstream. Furthermore, these devices often augment mixing and increase heat transfer with high freestream turbulence. A comprehensive study on how longitudinal vortices affect junction flow heat transfer for different Reynolds numbers, freestream turbulence values, and longitudinal vortex configurations was performed. Longitudinal vortices were generated upstream of a symmetric airfoil using delta winglet vortex generators. Spatially resolved endwall heat transfer coefficients upstream and around the junction were measured using infrared thermography. Time-averaged flowfield measurements of the incoming longitudinal vortices were taken using stereo particle image velocimetry. Longitudinal vortices provided limited heat transfer augmentation around the junction and did not disrupt the time-averaged horseshoe vortex. These interactions were identical at high turbulence, but longitudinal vortices were less effective at augmenting heat transfer, likely due to an increase in vortex wandering. Vortex wandering also led to a broadening in lateral heat transfer profiles.