Pair Of Vortex Generators Research Articles

Heat Transfer Enhancement Simulation Employing Flat and Curved Winglet Vortex Generator Pairs with Punched Holes

Heat Transfer Enhancement Simulation Employing Flat and Curved Winglet Vortex Generator Pairs with Punched Holes

Experimental and numerical investigations of tube inserted with novel perforated rectangular V-shape vortex generators

The utilization of punched vortex generators has been established as an effective means to enhance heat transfer in heat exchangers. However, there are few studies on the use of perforated rectangular winglet pairs in heat exchange tubes and the study of perforation parameters based on this approach in the existing literature. In this paper, three parameters, including three height ratios, four perforation indices, and three pitch ratios, are considered experimentally and numerically. In the Reynolds number range of 7454–13,664, the effects of perforated rectangular vortex generator pairs on fluid flow and heat transfer are obtained by scaling parameters such as Nusselt number ratio, friction factor ratio, thermal enhancement factor, field synergy number, entropy generation, and exergy efficiency. The numerical results indicate that the perforation will lead to a reduction in turbulent kinetic energy in the local multi-longitudinal vortices on the rear side of the vortex generator, resulting in a decrease in local heat transfer as well as friction loss. Meanwhile, the pitch of perforated rectangular vortex generator pairs plays a crucial role in heat transfer and friction loss, enabling an increase in the Nusselt number of smooth tubes by 68–257%. Furthermore, the results are proved using the principle of entropy generation and exergy efficiency analysis. As Reynolds number increases, the thermal enhancement factor gradually decreases. Notably, the maximum thermal enhancement factor of 1.43 is achieved when the Reynolds number is equal to 7454, the height ratio is 0.08, the perforation index is 0.18, and the pitch ratio is 1.04.

Numerical analysis of microchannel heat sink performance using delta vortex generator

The design of unique microsinks arises from the desire to provide efficient cooling at low pressure drop for a more compact miniaturized electronic equipment. Three-dimensional numerical investigations of heat transfer and fluid flow have been carried out with delta vortex generator (DVG) structures in the rectangular microchannel. A pair of delta vortex generators (DVGs) are placed symmetrically about the horizontal mid plane in rectangular microchannels. Performance variances are assessed on the basis of the average Nusselt number (Nu), friction factor (f), and thermal performance (TP) along with the thermal resistance (RT) and hydraulic resistance (RH) for the Reynolds number in the range of 93 to 746. The parametric variation has been carried out by altering geometric parameters such as the angle of DVGs with centerline (θ), the number of pair of DVGs (n), the length of DVGs (l), the distance of DVGs from the centerline (B), the position of DVGs from the inlet for first pair (L1), and the distance between the vortex generators (S). The objective is kept to maximize the TP, to minimize the value of thermal resistance, and to decrease the increase in the hydraulic resistance for the same geometrical variation. The highest thermal performance equal to 1.256 has been achieved with the combination of θ, n, l, B, S, and L1 equal to 45°, 3, 0.6 mm, 0.1 mm, 4.5 mm, and 5.334 mm, respectively. For the same geometrical parameters, a minimum thermal resistance equal to 0.98 K/W and a hydraulic resistance equal to 3.234 kPa-min/ml have been attained at Re about 745.66. By minimizing the thermal and hydraulic resistance of the microchannel with DVGs, it becomes possible that heat can be more effectively transferred across the interface and the desired cooling can be achieved with less power input. The implementation of DVGs enhances intermixing through the generation of longitudinal and transverse vortices, leading to a more evenly distributed temperature across the channel. This enhancement in the heat transfer reduces the thermal resistance. Additionally, the vortices generated by DVGs modify the velocity profile, thereby decreasing the pressure drop and the hydraulic resistance. The specific impact of longitudinal vortices on the enhancement of the heat transfer through adjustments in geometric parameters is thoroughly elucidated.

Study of the Effect of Curve-Type Vortex Generator Pairs with Perforated and Flat Holes on Airfoil Performance

Study of the Effect of Curve-Type Vortex Generator Pairs with Perforated and Flat Holes on Airfoil Performance

Numerical investigation of model Francis turbine for performance enhancement with geometrical modification

Most of the hydropower plants in Nepal are run-of-river type and over 60% of them are operating with Francis turbines. There are huge fluctuations in flow during the dry and wet seasons, which force the power plant owner to operate the turbines at off-design conditions which can induce cavitation and fatigue loads on the turbines. This study focuses on numerical analysis of a model turbine designed for the Jhimruk hydropower plant in Nepal. A geometrical modification is made to the model turbine runner blades by attaching two pairs of vortex generators (VGs) to each blade surface on the pressure side at 0.5% span, at the leading edge. The flow on the blade breaks off and separates from the surface during the off-design conditions so VGs are introduced to mitigate swirls generated at the inlet of the turbine. VGs can help to reattach the flow and improve off-design performance of the turbine. The performance of model turbine is analyzed at different guide vane openings to simulate different operating conditions by keeping the operating head constant and varying the rotational speed of the turbine from 500 to 1500 rpm. Performance curves and hill diagrams of the turbine are generated for each case with and without VGs. The results show that VGs at off-design conditions show a maximum increment in efficiency by 12% and 1 to 5% on average. The power output is also boosted by 1 to 6 kW at off-design conditions. This objective has been achieved when compared to efficiency and power at low-discharge and high-speed regions. In conclusion, VGs are simple but effective tools to enhance the performance of hydraulic turbines as well.

Air Interactions of Magnetically Driven Plasma Discharges in Crossflow

Motivated by the use of magnetohydrodynamic devices in fluid dynamic flow control research, the current work experimentally studied the actuation mechanism and the resulting aerodynamic interactions of magnetically driven low-current arc-plasma discharges. The investigation was conducted in the context of boundary-layer interactions in low-speed crossflow conditions through the use of coaxial and v-shaped geometries. Time-averaged velocity field measurements showed that the toroidal region of vorticity induced by the coaxial geometry in quiescent air resulted in the formation of a horseshoe vortex in crossflow. Similarly, the v-shaped actuator resulted in the formation of streamwise vortices. The resulting boundary layers had s-shaped streamwise velocity profiles as measured in the wall-normal direction characteristic for the flow downstream of a conventional vortex generator pair, due to the three-dimensional mixing induced by coherent vortex structures. A simplified model based on intermolecular momentum transfer through collisions is proposed to explain the fundamental discharge–air interactions and the induced flowfields. These results inform the applications of various magnetically driven discharges in the field of aerodynamic flow control.

Analysis of the thermal improvement of plate fin-tube heat exchanger with straight and curved rectangular winglet vortex generators

A novel combination of curved and straight rectangular winglet vortex generator (RWVG) pairs was arranged in a common-flow-up (CFU) configuration on plate fins for enhancing the comprehensive performance of the fin-tube heat exchanger. The effects of RWVGs were compared with those of non-RWVGs for flow streamline, temperature distribution, and pressure field. Then the thermohydraulic performance and the comprehensive performance were numerically investigated among the cases with varied locations and sizes of RWVGs. The results revealed that j for all cases with RWVGs was higher than non-RWVGs and the values of JF were greater than 1.0 for all cases except for case 4. Especially, apparent improvements in heat transfer characteristics and comprehensive performance were observed with the novel combination. Furthermore, it was found that the appropriate location and size of RWVGs were able to influence the thermohydraulic characteristic positively. The curved RWVGs with a smaller offset showed better comprehensive performance, and the larger attack angle of the straight RWVGs was accompanied by a higher heat transfer intensity and a greater flowing drag force. Moreover, the curved RWVGs with a larger arc angle performed better in the comprehensive performance, and the length of the straight RWVGs was larger and JF smaller.

Enhanced performance of a microchannel with rectangular vortex generators

Microchannel heat sinks and heat exchangers are widely used in the cooling of electronic systems. However, it is still important to enhance the heat transfer in the microchannel so that the intense heat generated can be removed. Vortex generators (VGs) create secondary flow structures in the flow, increasing the fluid mixing, thinning the thermal boundary layer, and ultimately boosting heat transfer. Here, we have controlled the flow structure and improved the heat transfer with the lowest possible pressure loss by placing VGs of different sizes, numbers, and angles of attack in a microchannel. The improvement in heat transfer is accelerated as vortex intensity increases. The angle of attack has a significant impact on vortex formation lengths, which reach high dimensions around 90°. Furthermore, increasing the VG length significantly increases the vortex formation lengths. The number of VG pairs has a significant impact on heat transfer and pressure losses. As the number of VG pairs increases, so does the area occupied by the secondary flow regions in the microchannel, increasing the fluid mixture and boosting heat transfer. The highest enhancement in heat transfer using VGs is obtained at around 230%, while the corresponding increase in pressure loss is 950%. According to the JF factor which we consider a performance evaluation criteria, the best result is around 1.38. The Genetic Aggregation Response Surface Methodology has been applied to numerical results. The related method is realized to produce results that are consistent with the numerical results within a ±5% error interval. All the input parameters considered in the sensitivity analysis have an impact of at least 10% on the output parameters.

Prediction of heat transfer characteristics in a microchannel with vortex generators by machine learning

Abstract Because of the prompt improvements in Micro-Electro-Mechanical Systems, thermal management necessities have altered paying attention to the compactness and high energy consumption of actual electronic devices in industry. In this study, 625 data sets obtained numerically according to the change of five different geometric parameters and Reynolds numbers for delta winglet type vortex generator pairs placed in a microchannel were utilized. Four dissimilar artificial neural network models were established to predict the heat transfer characteristics in a microchannel with innovatively oriented vortex generators in the literature. Friction factor, Nusselt number, and performance evaluation criteria were considered to explore the heat transfer characteristics. Different neuron numbers were determined in the hidden layer of each of the models in which the Levethenberg–Marquardt training algorithm was benefited as the training algorithm. The predicted values were checked against the target data and empirical correlations. The coefficient of determination values calculated for each machine learning model were found to be above 0.99. According to obtained results, the designed artificial neural networks can provide high prediction performance for each data set and have higher prediction accuracy compared to empirical correlations. All data predicted by machine learning models were collected within the range of ±3% deviation bands, whereas the majority of the estimated data by empirical correlations dispersed within ±20% ones. For that reason, a full evaluation of the estimation performance of artificial neural networks versus empirical correlations data is enabled to fill a gap in the literature as one of the uncommon works.

Numerical simulation of heat transfer enhancement from tubes surface to airflow using concave delta winglet vortex generators

Improvement of the convection heat transfer coefficient of the airflow has become a concern nowadays to increase the rate of heat transfer. Therefore, the present study is focused on evaluating the improvement of heat transfer numerically from several heated tubes to the airflow in the channel using vortex generators. Airflow into the channel is varied in the range of Reynolds number of 2100–11,200. The vortex generators used in this study are delta winglet pairs and concave delta winglet pairs with in-line or staggered configurations for one to three pairs of vortex generators. The results of the study showed that the installation of three pairs of concave delta winglet vortex generators with a staggered arrangement resulted in the best convection heat transfer improvements with the highest increase in convection heat transfer coefficients up to 53.58% than those from the baseline (without vortex generators). However, the increase in the convection heat transfer coefficient is accompanied by an increase in pressure drop of up to 69.69% against the baseline.

Heat transfer enhancement by a pair of asymmetric flexible vortex generators and thermal performance prediction using machine learning algorithms

• Heat transfer enhancement system including two flexible vortex generators is analyzed by using an immersed boundary method. • Effects of the inclination angle, bending rigidity, and the gap distance on the thermal performance are analyzed in detail. • The thermal performance of the present heat transfer system is enhanced up to 122% as compared to baseline flow without flexible vortex generators. Heat transfer should be considered in the design process of various industrial fields such as electric-electronics, plants and refrigeration and air conditioning, etc. Many researchers have introduced vortex generators to promote mixing of fluids, thereby improving heat transfer performance. Convective heat transfer can be enhanced by using vortex generators where, however, the disadvantage of increased mechanical loss due to increased pressure drop is not avoidable. In order to compensate for the penalty, the present study utilizes the characteristics of self-sustained flapping motions of the flexible vortex generator to improve heat transfer without much increasing the pressure drop. The two flexible vortex generators (FVGs) fixed on the upper and lower channel walls, respectively, are introduced in the present study and they take the form of asymmetric configurations by adjusting the inclination angles. The heat transfer performance is observed to depend on the parametric conditions of FVGs such as the inclination angle, bending rigidity, and the gap distance between them. The present system including the asymmetric FVGs shows the improvement of thermal performance by 122% as compared to the baseline flow when the bending rigidity is 0.06, the initial inclination angle is 75°, and the gap distance is 2.4 times the length of FVGs. The attracting Lagrangian coherent structures (LCS) are visualized by calculating the finite-time Lyapunov exponent (FTLE) field to analyze the effects of the vortex structures near the heated channel walls on the fluid mixing. The net energy loss and average heat transfer are predicted by the three machine learning algorithms, i.e ., artificial neural network (ANN), support vector regression (SVR), and random forest (RF), where the inclination angle, bending rigidity, and gap distance of FVGs are selected as input data. The SVR and ANN algorithms show the best performance in predicting the mean energy loss and the heat transfer, respectively, with the R 2 value of above 0.99 and 0.95.

Effect of the Streamwise Orientation of a Pair of Vortex Generator on the Flow and Heat Transfer Characteristics in a Plain Channel

Abstract For a rectangular channel flow, a variant of delta winglet vortex generator (VG) in common flow up (CFU) orientation is presented to enhance the thermal performance factor by decreasing the friction losses. The new vortex generator is a simple reversal of a standard CFU orientation such that the leading edge and suction side of the conventional CFU orientation of the winglet become the trailing edge and pressure side for the reverse common flow up (RCFU) orientation of the winglet, respectively. Numerical simulations were carried out for a three-dimensional, steady, laminar, and incompressible rectangular channel flow with and without the two VG configurations. Performance analysis was done for global Nusselt number and friction factor for different inter-winglet spacings of the VG pair at a Reynolds number of 1478. An increase of 2.3% in the thermal enhancement factor was achieved in RCFU compared to CFU orientation at an inter-winglet spacing equal to 0.02 times the channel height. At the highest inter-winglet spacing equal to 0.6 times the channel height, the CFU orientation exhibited a gain of 3.2% in the enhancement factor over the RCFU orientation. Heat transfer downstream of the vortex generator was shown to be impacted in the reverse configuration (RCFU) due to stronger vortex formation compared to a standard CFU configuration at the least inter-winglet spacing.

Thermal-hydraulic characteristic of a novel wavy fin-and-circle tube heat exchanger with concave curved vortex generators

This paper proposes a novel configuration of two pairs of concave curved vortex generators located beside each tube in a wavy fin-and-circle tube heat exchanger. The effect of the concave curved vortex generator pairs with different transverse locations and attack angles on the thermal-hydraulic characteristics of the heat exchanger is numerically reported. The studied range of attack angle is 20° - 50° for five different transverse locations of vortex generators. The results show that the combination of concave curved vortex generators and wavy fins can significantly improve the heat transfer performance of the wavy fin-and-tube heat exchanger. Nu of the proposed fin configuration is enhanced by 30.6%, and the maximum thermal performance factor is increased by 24.0% compared with the wavy fin-and-tube heat exchanger without vortex generators. The multi-objective optimization and a neural network are adopted to optimize the vortex generator arrangements for the best heat transfer capacity. At the optimal Pareto front, the optimal heat transfer capacity is increased by 35.73% under the same pumping power. Correlations of Nu, f, JF and the optimal Qv and Pv are presented as a function of Re, transverse location, and attack angle of the vortex generator.

Cooling Effect of Water Channel with Vortex Generators on In-Wheel Driving Motors in Electric Vehicles

Designing an effective cooling system for high-power-density in-wheel motors of electric vehicles is required to avoid the irreversible demagnetization of the permanent magnet due to a rise in its temperature. In this study, a water-cooling channel was used between the stator and housing to evaluate the cooling performance of a 25 kW in-wheel motor utilizing the commercially available software Ansys Fluent 19.2. Initially, cooling channels with a single or pair of vortex generators have been used with varying heights for pressure drop evaluation considering the allowable pressure drop of 0.7 bar for a water pump. The results indicates that both a single and a pair of vortex generators satisfy the limit of a pressure drop at the height of 4 and 3 mm, respectively, and the cooling performances of two vortex generators were evaluated at these heights. It has been found that the cooling performance of a permanent magnet is enhanced by 4.1% and 6.5% using a single and a pair of vortex generators, respectively, compared to the cooling channel without a vortex generator. Furthermore, considering the ram air effect on water-cooling channels of in-wheel motors under high-speed conditions, the temperature of the permanent magnet is decreased by about 2.1 °C and was found to be 148.8 °C under the temperature limit of demagnetization of the permanent magnet.

Influence of spacing of a delta-winglet vortex generator pair on the flow behavior and heat transfer at the internal tip of gas turbine blades

The hot erosion of turbine tip and the maintenance of tip reliability and service times have always been great challenges for researchers. This work presents a novel design of a tip wall with the internal surface fitted with delta-winglet vortex generator pairs (DVGP). Various spacing of DVGP is considered to study the influence of spacing on the internal tip heat transfer and flow behavior in the turn region of a serpentine cooling channel inside a blade. A smooth internal cooling channel is regarded as the Baseline. Five spacings of the leading edge of the DVGP, i.e., 0.03Dh(hydraulic diameter), 0.07Dh, 0.13Dh, 0.2Dh, 0.27Dh, respectively, are considered. Topological analysis in the skin friction field is introduced to better illustrate the 3D fluid flow. The inlet Reynolds number is set in the range of 10,000 to 50,000. Results show that the variation of the spacing between the DVGPs has a remarkable influence on the thermal performance of the internal blade tip. The heat transfer on each side of the DVGP is weakened increaseing spacing, which is caused by the movement of the attachment line on the surface of the DVGP and the weakening of the vortex energy. The optimal thermal performance appears for the narrow spacing (0.03Dh) of the leading edge of the DVGP, and the heat transfer augmentation is approximately 7.90% compared with the two-pass channel with a smooth tip. The delta-winglet vortex generator arranged narrowly on the internal tip is aimed for enhancement of heat transfer. The analysis and results of this work are beneficial to the tip design of internal passages in gas turbine blades.

Heat Transfer Enhancement by a Pair of Asymmetric Flexible Vortex Generators and Thermal Performance Prediction Using Machine Learning Algorithms

Heat Transfer Enhancement by a Pair of Asymmetric Flexible Vortex Generators and Thermal Performance Prediction Using Machine Learning Algorithms

Heat transfer behind the backward-facing step in the presence of longitudinal vortex generators installed at an angle to each other

The paper presents the experimental results on the control of heat transfer enhancement behind the backward-facing step at Re = 4000. The flow is controlled by a pair of longitudinal vortex generators (LVGs) installed at the step edge. The pair of vortex generators (VG) consists of two plates positioned symmetrically relative to the flow. The influence of the height, the angle of VG installation relative to the flow, the distance between VG pairs and the shape of the plate on local and average heat transfer is investigated.

Influence of the punched holes on thermohydraulic performance and flow pattern of rectangular channels with a pair of perforated vortex generators

Vortex generators (VGs) are passive elements that contribute to enhance the heat transfer and produce a low pressure loss. Rectangular channels are the basic unit of many heat exchangers. Frequently, both are combined and therefore they are investigated intensively. Regardless, the influence of punched holes on the plate surface is often ignored when the thermohydraulic performance of rectangular channels has been studied. This work deals with a numerical study about the impact on the channel thermohydraulic performance of a delta winglet pair of perforated VGs punched on the channel surface. The VGs transversal pitch and the flow pattern in the common flow area were investigated for three configurations and sixteen different arrangements. The computational domain consisted of a plate centered in the middle of the rectangular channel. The numerical model was validated by comparison with published correlations for the entry region with isothermal walls as well as inside the laminar flow regime. Secondary flow was evaluated to explain the heat transfer enhancement. A performance evaluation criterion based on the similarity of pumping power was applied. All configurations studied enhanced the heat transfer and increased the pressure loss, with values up to 12.8% and 17.5% respectively. A reverse direction of rotation of vortices was found caused by the punched holes in two configurations, a result that was not found in the literature revised. A vortices inhibition caused by the punched holes was identified, which constitutes an important result and a novelty. For Reynolds numbers higher than 120, the application of VGs punched on the channel surface is advantageous. According to the performance evaluation criterion applied, the positive impact of VGs on the surface was increased with the Reynolds number, reaching values of 1.075 for the common flow up configuration with the punched holes behind and the highest VGs transversal pitch.

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.

Numerical Study on the Influence of Vortex Generator Arrangement on Heat Transfer Enhancement of Oil-Cooled Motor

At present, vortex generators have been extensively used in radiators to improve the overall heat transfer performance. However, there is no research on the effect of vortex generators on the ends of motor coils. Meanwhile, the current research mainly concentrates on the attack angle, shape and size, and lacks a detailed study on the transverse and longitudinal distance and arrangement of vortex generators. In this paper, the improved dimensionless number R is used as the key index to evaluate the overall performance of enhanced heat transfer. Firstly, the influence of the attack angle on heat transfer enhancement is discussed through a single pair of rectangular vortex generators, and the results demonstrate that the vortex generator with a 45° attack angle is superior. On this basis, we compare the effects of different longitudinal distances (2 h, 4 h, and 6 h, h meaning the height of vortex generator) on enhanced heat transfer under four distribution modes: Flow-Up (FU), Flow-Down (FU), Flow-Up-Down (FUD), Flow-Down-UP (FDU). Thereafter, the performances of different transverse distances (0.25 h, 0.5 h, and 0.75 h) of the vortex generators are numerically simulated. When comparing the longitudinal distances, FD with a longitudinal distance of 4 h (FD-4 h) performs well when the Reynolds number is less than 4000, and FU with a longitudinal distance of 4 h (FU-4 h) performs better when the Reynolds number is greater than 4000. Similarly, in the comparison of transverse distances, FD-4 h still performs well when the Reynolds number is less than 4000, and FU with a longitudinal distance of 4 h and transverse distance of 0.5 h (FU-4 h–0.5 h) is more prominent when the Reynolds number is greater than 4000.