Longitudinal Vortices Research Articles

Experimental Investigation on Vortex Generator's Distance From Film Cooling Hole

Abstract The effects of vortex generator distance from film cooling hole on increasing gas turbine blade film cooling efficiency have been studied experimentally. The technique of infrared (IR) thermography has been implemented to study the temperature field. The diameter of the film cooling hole and the cross-flow velocity define the Reynolds number, which is fixed at 2369. There are now three different jet to cross-flow blowing ratio adjustments: 0.5, 1.0, and 1.5. Three different vortex generator distance from film cooling hole have been studied experimentally to increase the gas turbine blade film cooling efficiency. It has been shown that lowest distance among vortex generator distance and film cooling hole, yields better film cooling efficiency. Overall, the delta winglet pair with lowest distance between vortex generator distance and film cooling hole outperforms the higher distance because of the generation of secondary longitudinal vortices that completely destroy counter rotating vortex structures because their rotational tendency is opposite to that of the counter rotating vortex pair (CRVP).

Analysis of hydrodynamics and thermal–hydraulic performance of twisted angle fins within an annular conduit

AbstractThis paper investigated the influence of various twisted angles of fin inserts integrated on the inner heated pipe wall of a double-pipe heat exchanger by analysing the thermal–hydraulic performance through numerical simulations. Results showed twisted angle fin (TAF) induced turbulent fluid flow phenomena, generating transverse and longitudinal vortices, along with swirling flow. This collaboration between the vortices and swirling flow effectively prevents heat trapping and enhances heat transfer from the inner pipe wall through the intensive fluid mixing. Despite longitudinal swirling vortices and turbulence significantly enhance local and global heat transfer performance, they led to increased pressure drop. However, TAF twisting reduces pressure drop by streamlining flow. The performance evaluation criterion (PEC) value is a dimensionless quantity that facilitates the comprehensive evaluation of optimal configurations by comparing the increment in Nusselt number and the increment in friction factor. PEC values greater than 1 indicate that the increase in Nusselt number exceeded the increase in friction factor. Among tested configurations, the twisted fin angles of 60° (TAF60) exhibited the highest improvement in Nusselt number and friction factor, also achieving the highest PEC of 1.59712 at Reynolds number of 1194.71. TAF40 and TAF50 were identified as optimal configurations for enhancing the thermal–hydraulic efficiency, with average PEC values of 1.26893 and 1.27030, respectively. Overall, the study indicated a consistent enhancement trend with increasing twisted angles and emphasizes the significant thermal performance improvement of TAF configurations compared to the smooth conduit. Furthermore, the results showed a converging tendency across all TAF configurations in the percentage improvement in Nusselt number and friction factor, as well as PEC compared to the baseline No fin configuration with increasing Reynolds number, suggesting that future improvements in thermal–hydraulic performance are more dependent on geometric angles than fluid flow velocity.

Numerical investigation on the impact of aerodynamic braking plates positioned at streamlined sections on the slipstream and wake flow of the high-speed train based on train-fixed reference frame

This paper studies the aerodynamic characteristics of high-speed trains (HSTs) featuring aerodynamic braking plates installed on the streamlined sections, employing the improved delayed detached eddy simulation (IDDES) method at Re = 5.0 × 105. The precision of the numerical simulation methodology has been validated through reduced-scale wind tunnel experiments. A comparative analysis has been conducted on the characteristics of slipstream, wake flow, and upper flow between the original configuration (OC) and the braking configuration (BC) of the HSTs. The findings reveal that the application of braking plates promotes significant separation phenomena around the HSTs, enhancing the slipstream velocity distribution. In the BC, compared to the OC, the maximum value of the time-averaged slipstream velocity has increased by approximately 134.9% and 76.8% at the trackside and platform positions, respectively. Additionally, the TSI value of the slipstream velocity shows increases of around 100.4% and 210.4% at the trackside and platform positions, respectively. Meanwhile, the turbulence fluctuations within the wake region have been enhanced, with the formation of a longitudinal vortex alongside the railway subgrade, whose core nearly covers the TSI positions. Notably, obvious shifts occur within the upper flow field, which significantly strengthens both flow turbulence and slipstream velocity, potentially influencing components on the upper surface of HSTs, such as the pantograph. The deployment of braking plates contributes to a significant increase in overall vehicle pressure drag, thereby enhancing the train's aerodynamic drag. Relative to the OC, the aerodynamic drag of the HST has increased by approximately 235.4% in the BC.

Investigating Enhanced Convection Heat Transfer in 3D Micro-Ribbed Tubes Using Inverse Problem Techniques

The improved heat dissipation observed in 3D micro-ribbed tubes is primarily influenced by the intricate interplay of multiple structural parameters. Nevertheless, research into the coupling mechanisms of these multi-structural parameters remains constrained by the absence of effective methodology in numerical solutions. In the present work, a new 3D micro-rib structure based on discrete adjoint method is established. Firstly, the research examines the interplay of different parameters (such as arrangement, relative roughness height, angle of attack, and circumferential rows) on the thermo-hydraulic performance. It is noted that the heat transfer efficiency is notably impacted by the relative roughness height. And the arrangement methodology dictates the optimal positioning for heat transfer efficiency. An increase in the number of circumferential rows enhances fluid mixing, while the angle of attack plays a crucial role in the formation of longitudinal vortices. Secondly, the coupling optimization technique is employed to obtain the optimal structure featuring non-uniform relative roughness height by the developed numerical solution. Overall, in comparison to the smooth tube, the optimized ribbed tube exhibits a remarkable 64.9% enhancement in performance evaluation criteria. Finally, a notable enhancement of 10.65–22.78% is observed when comparing with the prevailing micro-rib structures.

Enhancing heat transfer with a hybrid vortex generator combining delta wing and winglet designs: A numerical study using the GEKO turbulence model

This paper presents a numerical study on the enhancement of heat transfer in a solar air heater (SAH) duct with Hybrid Vortex Generators (HVG) placed periodically along the flow direction on its heated wall (absorber plate) for fluid flow and convection heat transfer at Reynolds numbers between 4121 and 25,365. HVGs consist of a trapezoidal winglet (TWL) for HVG-winglet-base-angles θ = 45° and 30°, or a combination of a delta winglet (DWL) with a delta wing (DWG) for angles θ = 26°, 18° and 12°. The angle of attack for the winglet (TWL or DWL) in the HVG is set at 30°, while the merging angle with the DWG is 45°, and the relative height BR = e/H = 0.48 remains constant. Initially, the effects on heat transfer and friction factor of Trapezoidal Winglet Vortex Generator (TWVG) and HVG45 (θ = 45°) obtained by basic modification on TWVG are investigated under the same flow conditions for PR = 1.5 and Re = 11,205. Subsequently, parametric studies are performed for five different HVG-winglet-base-angles (θ = 45°, 30°, 26°, 18° and 12°) and three different longitudinal pitch ratios (PR = PL/H = 1.0, 1.5 and 2.0). The calculations are performed with ANSYS Fluent 2021R2 based on the finite volume method. In order to model turbulent flow, the GEKO (GEneralized K-Omega) turbulence model recently developed by ANSYS and based on the k-ω formulation is used. HVG45, obtained by basic modification on TWVG, produces slightly stronger and more effective longitudinal vortices compared to TWVG, showing a 3.87 % decrease in friction factor and a 4.11 % increase in Nusselt number and thus a 5.43 % increase in Thermal Enhancement Factor (TEF). Parametric investigations are conducted across a range of values for both θ and PR. The highest rise in friction factor is attained at the lowest Reynolds number, reaching a value of f/f0 = 54.52, while the most significant enhancement in heat transfer rate is noted at the highest Reynolds number, with Nu/Nu0 = 5.86 for θ = 45° and PR = 1.0. The TEF reaches 2.42 at the lowest Reynolds number for the HVG18 with a winglet-base-angle of 18° and a longitudinal pitch ratio of 1.5. The resulting findings not only offers a new approach to improve the thermal performance of solar air heaters but also hints at the potential success of the GEKO model in predicting turbulent flow and heat transfer analysis.

Orbit–Orbit Interaction in Spatiotemporal Optical Vortex

While spin-orbit interaction has been extensively studied, few investigations have reported on the interaction between orbital angular momenta (OAMs). In this work, we study a new type of orbit–orbit coupling between the longitudinal OAM and the transverse OAM carried by a three-dimensional (3D) spatiotemporal optical vortex (STOV) in the process of tight focusing. The 3D STOV possesses orthogonal OAMs in the x–y, t–x, and y–t planes, and is preconditioned to overcome the spatiotemporal astigmatism effect. x, y, and t are the axes in the spatiotemporal domain. The corresponding focused wavepacket is calculated by employing the Debye diffraction theory, showing that a phase singularity ring is generated by the interactions among the transverse and longitudinal vortices in the highly confined STOV. The Fourier-transform decomposition of the Debye integral is employed to analyze the mechanism of the orbit–orbit interaction. This is the first revelation of coupling between the longitudinal OAM and the transverse OAM, paving the way for potential applications in optical trapping, laser machining, nonlinear light-matter interactions, and more.

Investigation of mechanisms on leading edge vortex generation and suppression in vaned diffuser of a centrifugal compressor

This study numerically investigates the mechanisms for generating and suppressing the leading edge vortex (LEV) in a vaned diffuser of a centrifugal compressor, aiming to enhance the compressor's stable operating range. Detailed analyses focus on the mechanisms of the rotating stall and the initiation process of the LEV. Notably, the end wall contouring method is applied to vaned diffuser to suppress the LEV and improve diffuser stability. The suppression mechanisms of the LEV are examined to deepen the understanding of stability enhancement mechanisms. Results demonstrate that, under stall conditions, the vaned diffuser experiences two-cell rotating stalls moving opposite to the impeller rotation direction, each rotating at approximately 12% of impeller rotation speed. The formation of diffuser stall is attributed to a longitudinal vortex developing from the LEV and causing the passage blockage. The increasing spanwise distortion of leading edge (LE) incidence angles and circumferential distortion of static pressures at the diffuser inlet promote the evolution of the longitudinal vortex from LEV. The end wall contouring of vaned diffuser effectively enhances the compressor's stable operating range by 15.10% and 8.90% toward lower flow rate conditions for machine Mach numbers 1.3 and 1.2, respectively. At near-stall points, the end wall contoured diffuser reduces spanwise distortion of LE incidence angles and circumferential distortion of static pressures at the diffuser inlet, mitigates the LE flow separation and corner separation, suppresses the generation and development of the LEV, delays the onset of rotating stall in vaned diffuser, and thereby improves the stable operating range of centrifugal compressor stage.

Dual coaxial electric field components in tightly focused circularly polarized Pearcey beams

The optical vortex, with its capacity to carry orbital angular momentum per photon, has garnered significant attention among researchers. Our study showcases the emergence of dual coaxial longitudinal electric field vortices during the non-paraxial propagation of tightly focused circularly polarized Pearcey beams. Our research indicates that combining the self-focusing characteristics of Pearcey beams with the tight focusing effect results in the formation of four focal points. We have achieved controllable adjustment of four distinct focal points. This study also encompasses a detailed numerical analysis of the application in optical trapping, and we investigate and elucidate the trapping strength and corresponding potential energies.

Performance analysis and optimization of the Gyroid-type triply periodic minimal surface heat sink incorporated with fin structures

The Triply Periodic Minimal Surface (TPMS) structures demonstrate substantial value and development potential in applications and research concerning heat sinks and heat exchangers. To further enhance the convective heat transfer performance of TPMS, this study proposes a novel method of incorporating fin structures into TPMS. This method is applicable to various types of TPMS, and the new structure constructed using this method is termed “TPMS with Fin Structures (TFS).” Subsequently, a TFS-Gyroid heat sink based on the Gyroid-type TPMS was constructed. This study presents a calculation method for the fin height in TFS-Gyroid (HTFS-Gyroid). Numerical simulation methods were employed to investigate the influence and mechanism of HTFS-Gyroid on the convective heat transfer performance and flow resistance of the TFS-Gyroid heat sink model, with air as the working fluid and under constant wall temperature (100 °C) conditions. The results indicate that within the flow range of 24–120 L/min, as HTFS-Gyroid increases from 0 to 1.6 mm, the average surface convective heat transfer coefficient (h̅) of the TFS-Gyroid heat sink model increases by 27.4 %-34.6 %, and the inlet–outlet pressure drop (ΔP) increases by 42.5–632.8 Pa. As HTFS-Gyroid increases, the PEC of the TFS-Gyroid heat sink model gradually decreases, whereas j/f gradually increases. The primary mechanisms by which the fin structures enhance the convective heat transfer performance of the TFS-Gyroid heat sink are: 1) increased heat exchange area, 2) the fin structures induce a large number of longitudinal vortices and secondary flows within the flow channels, and 3) the formation of “Fins Occupying the Perforated Structure (FOPS)” within the flow channels.

Angle-of-attack characteristics of opposing jet for improving drag and heat reduction

While the opposing jet technique has the potential to achieve efficient drag and heat reduction, it can be severely affected by the incoming angle of attack. To analyze the angle-of-attack characteristics of opposing jet for improving drag and heat reduction, a three-dimensional blunt model was studied under various jet stagnation pressure ratios and angles of attack using the verified numerical method. The results showed that the enhanced reattachment shock on the windward side resulted in a higher pressure and temperature rise, which led to the deterioration of drag and heat reduction. Under the influence of the incoming angle of attack, the recirculation vortex transformed into a longitudinal vortex, resulting in a slanted U-shaped distribution of the surface pressure coefficient and Stanton number. Increasing the jet stagnation pressure ratio widened the coverage of the recirculation vortex on both the windward and leeward sides, which brought an improvement in drag and heat reduction. The interaction between the incoming angle of attack and the opposing jet caused a double-peak distribution of Stanton number due to the recirculation vortex reattachment and the compression of the incoming flow. The inclined opposing jet could reduce the peak values of pressure coefficient and Stanton number when subjected to the incoming flow with an angle of attack by spreading the recirculation vortex along the windward side. There should exist an optimal inclination angle that can effectively reduce the peak caused by the compression of the incoming flow without generating an excessive peak due to the recirculation vortex reattachment.

The heat transfer enhancement mechanism of W-shaped micro-ribs on impingement cooling

In order to improve the performance of impingement cooling in turbine blades, W-shaped micro-ribs are arranged on the target surface to weaken the influence of cross-flow and generate longitudinal vortexes. The k-ω SST turbulence model is used for numerical simulation, and the mechanism of W-ribs on the enhancement of air impingement cooling performance and the influence of W-ribs geometry are studied. Under the condition of jet flow Reynolds number 4000 to 10000, based on the W-ribs with an angle α = 120°, width W = 0.1 mm and height H = 0.3 mm, the effects of angle (α = 90°, 120°, 150°, 180°), width (W = 0.05, 0.1, 0.2, 0.4 mm) and height (H = 1, 3, 4, 8 mm) on flow and heat transfer are investigated respectively. The results show that the W-ribs can separate the flow to both sides while generating longitudinal vortexes, which can reduce the influence of crossflow and enhance the sweep of the target surface to achieve the effect of enhancing heat transfer. α is the key factor affecting the generation of longitudinal vortex. W has little effect on the flow structure, but mainly affects the vorticity. H mainly affects the distribution of mass flow rate, which has a direct impact on the uniformity of upstream and downstream heat transfer. The W-ribs with α = 120°, W = 0.1 mm and H = 0.4 mm is recommended because of its excellent heat transfer performance and high comprehensive heat transfer performance, which are 39.7–48.9 % and 1.5–9.7 % higher than the smooth target surface, respectively.

Influence of Coherent Vortex Rolls on Particle Dynamics in Unstably Stratified Turbulent Channel Flows

This work investigates the dynamics of heavy particles dispersed in turbulent channel flows under unstable thermal stratification conditions using point-particle direct numerical simulations (PP-DNS), to quantify the influence of large-scale coherent vortex rolls, arising from the combined effects of shear and buoyancy, on the spatial distribution and preferential sampling behavior of inertial particles. We examined three particle Stokes numbers (St+=0.6,60,120) and two friction Richardson numbers, Riτ=0.272 and Riτ=27.2, which exemplify the regimes below and above the critical condition for vortex roll formation, respectively. The results indicate that the flow reorganization into large-scale longitudinal vortices significantly alters the topological features of small scales in the near-wall region impinged by the thermal plumes, resulting in a prevalence of vorticity-dominated topologies. The interplay between this phenomenon and the tendency of particles to preferentially sample strain-dominated topologies leads to a distinctive asymmetric particle distribution in the near-wall planes. Inertial particles markedly accumulate in the strain-dominated regions where the coherent thermal plumes emerge from the walls, while avoiding the vorticity-dominated impingement zones. This peculiar particle response to the vortex rolls is most pronounced when the particle response time matches the characteristic timescale of the large-scale coherent motions in the cross-stream planes.

Thermal-hydraulic performance investigation of the cooling passage featuring the ridged V-shaped dimple

The ridged V-shaped dimple (RVD) is proposed to improve the thermal-hydraulic performance of the dimpled cooling passage by generating a ridge at the junction of the spherical dimple and V-shaped dimple. The impacts of arrangements (staggered, inline), geometric parameters (the length l/D of RVD leg, the angle α between two legs, the spacing s/D between the spherical dimple and V-shaped dimple in RVD, the depth-to-diameter ratio of dimple), and Reynolds number (Re = 8,500-50,000) on the thermal-hydraulic performance of RVD are investigated through numerical simulations. Results demonstrate that RVD significantly improves thermal-hydraulic performance by forming larger and stronger longitudinal vortexes and disrupting the boundary layer. The inline RVD has a higher thermal-hydraulic performance compared to the staggered RVD due to the stronger disturbance. Moreover, the RVD is appropriate for enhancing the thermal-hydraulic performance of deeper dimples, case 0.3-0.1 has the largest PEC (1.38-1.50) compared to other dimpled cases, and it achieves a 10.50%-18.18% increase over the corresponding typical VD. Finally, the correlations for Nu/Nu 0 and f/f 0 of inline RVD are proposed based on the numerical results, and the deviations between the predicted results and the simulated results are 10% for Nu/Nu 0 and f/f 0.

Heat transfer enhancement of a Stirling engine heating tube with three-pronged slant rods under oscillatory flow

Heaters are crucial components in Stirling engines, where the working medium adsorbed heat from an external heat source. Enhancing heat transfer within the heater is essential for boosting the operational efficiency of the Stirling engine. In this study, a tube equipped with three-pronged slant rods was employed to improve the heat transfer within the heater under conditions of oscillatory flow. Three pairs of dynamic longitudinal vortices were generated and exhibited regular movement patterns with distinct phase angles. In comparison to the smooth tube configuration, the enhanced tube outlet exhibited a notable increase in the average working-medium temperature by 62 K and 46 K during the entry and return stages, respectively. The degree of heat transfer enhancement was found to be contingent upon the pitch, height, and inclination angle of the slant rod. Optimal heat transfer enhancement was achieved with slant rods featuring a pitch of 26 mm, a height of 3.5 mm, and an inclination angle of 45°. The performance evaluation criterion ranged from 1.29 to 1.81 of enhanced tube compared to smooth tube. These findings underscore the effective enhancement of heat transfer facilitated by the three-pronged slant rods within the Stirling engine's heater.

Effects of airflow direction on the thermal-hydraulic performance of louvered fin-common flow up vortex generator

To improve the thermal-hydraulic performance of the louvered fin and flat tube heat exchangers (LFHEs), this paper innovatively proposes the louvered fin-common flow up vortex generator (LF-CFUVG). Then, numerical simulations are conducted to study the effects of airflow direction γ on the thermal-hydraulic performance of the LF-CFUVG. The corresponding results indicate that the flow resistance of the LF-CFUVG is always greater than the Baseline (the LFHE without CFUVGs), as the CFUVGs reduce the minimum free flow area while forming low-speed wake zones behind them. The heat transfer capacity of the LF-CFUVG exceeds the Baseline as well, this is attributed to the longitudinal vortices induced by the CFUVGs, which is helpful to homogenize the temperature field and transport the high-speed and low-temperature airflow. And the thermal-hydraulic performance of LF-CFUVG also outperforms the Baseline. In comparison to the working condition of γ is 0°, the pressure drop Δp for the LF-CFUVG declines with increase of γ from 0° to 30°, thus a larger angle helps to reduce flow resistance. However, the heat transfer coefficients hLF and performance evaluation criteria (PEC) of the LF-CFUVG deteriorate with the increasing γ, so a smaller angle is recommended to obtain an intenser heat transfer and better PEC.

Thermohydraulic performance augmentation of triangular duct solar air heater using semi‐conical vortex generators: Numerical and experimental study

AbstractThermohydraulic performance augmentation using turbulence promotors is a commonly adopted technique in solar air heater (SAH) applications. This article presents the thermohydraulic performance augmentation of triangular duct SAH using semi‐conical vortex generators (SCVG) using computational fluid dynamics and experimental methodology for various flow Reynolds numbers ranging from 6000 to 21,000. An in‐depth parametric analysis is undertaken to establish the influence of flow attack angle, relative longitudinal pitch, relative transverse pitch and cone diameter of SCVG on the thermohydraulic performance as indicated by the thermohydraulic performance parameter (THPP). The results reveal that the SCVG generates longitudinal vortices and introduces flow impingement zones which significantly affects the flow and heat transfer characteristics of air heaters. Correlations for Nusselt number and friction factor are established, which predicts the performance outcomes with an average error of 6.74% and 4.46%, respectively. The optimal THPP is determined to be 1.74 using artificial neural network model and Bonobo Optimization algorithm. The SCVG produces THPP values well above unity for the entire flow Reynolds number range of 6000–21,000.

Heat transfer mechanism of different vortex generators arrangements embedded in heat exchange tubes

Heat exchange is widely used in many fields to improve heat transfer efficiency and save energy, while longitudinal vortex generator (VG) is widely used in many heat transfer heat exchangers. In this work, the effect of VGs with different numbers and different pitch ratios (PR) on the heat transfer characteristics in the tube was studied numerically. The results show that when the fluid flows through the VG, the reflux region will be generated, and the fluid velocity in the reflux region will be inhibited, resulting in uneven temperature distribution and increased Nu. When multiple VGs are arranged in a row, the number of vortices is increased, and the area affected is increased. This improves the overall heat transfer performance. With the decrease of PR, the number of VG rows increases, and the heat transfer performance increases first and then decreases with the decrease of PR.

Characterization and low-order representation of the vortex meandering motion in upswept afterbody wakes

Vortex meandering is often characterized by seemingly stochastic motions of the vortex core. An elucidation of the underlying mechanisms of core movement aids not only in characterizing the meandering phenomenon but also forms a starting point to guide flow control techniques. This paper investigates the complex motion of longitudinal vortices behind an abstracted cargo aircraft fuselage. In contrast to wingtip vortices that arise in relative isolation, in this case the large aft region upsweep generates a meandering counter-rotating vortex pair that retains its coherence for long distances downstream. High-resolution spatio-temporal datasets obtained from large-eddy simulation of a cylindrical fuselage with longitudinally aligned axis and a sharp-edged base are used for this purpose. The circulation of each vortex in the pair initially increases immediately after formation and asymptotes to a near constant value downstream. Although the time-mean form of the vortices becomes nearly axisymmetric, the transient disorganized motions include time-local regions of opposite vorticity. The complicated meandering motion is decomposed using proper-orthogonal decomposition (POD) modes as primary building blocks. The first two modes constitute a mutually orthogonal |m|=1 elliptic pair, accounting for about 35% of the total energy; individually these modes account for the displacement of vortex cores along straight lines whose slopes coincide with their respective dipole axes. The wake outside of the immediate vicinity of the base displays low-rank behavior, in that the number of modes required to reproduce the flow to a given degree of accuracy diminishes rapidly. Beyond two fuselage (cylinder) diameters downstream, the two leading POD modes can reconstruct the dominant meandering motion and spatial structure in the LES data with less than 15% error using a suitable loss measure.

Experimental and numerical study on configuration, shape, distance and angle of attack in film cooling implementing vortex generator

The impact of vortex generator configuration, shape, angle of attack and distance between vortex generator and film cooling hole has been studied using both experimental and numerical methods for enhancing the gas turbine blade’s film cooling efficiency. Infrared (IR) thermography technique has been used for investigating the temperature field. In order to obtain the velocity field ANSYS FLUENT has been implemented. The diameter of the film cooling hole and the cross-flow velocity are used to calculate the Reynolds number, which is set at 2369. The blowing ratio of the jet to the cross-flow has been changed to 0.5, 1.0, and 1.5. Effect of CFU and common flow down configuration has been investigated. The angle of attack has been varied as 35° and 45°. It is observed that common flow down configuration of vortex generator performs better than Common Flow Up configuration. Common flow down configuration as well as lower distance between vortex generator and film cooling hole enhance the film cooling effectiveness due to generation of secondary longitudinal vortices which decrease the strength of the counter rotating vortex structures. Among all the shape (triangular, rectangular and trapezoidal) rectangular vortex generator performs better. Growths of shear layer vortices are modified due to the inclusion of vortex generator. Overall, Vortex Generator with common flow down configuration and 35° angle of attack performs better than Common Flow Up configuration due to generation of secondary longitudinal vortices which annihilates the counter rotating vortex structures due to having rotational tendency opposite to Counter rotating vortex pair.

Temperature uniformity analysis and multi-objective optimization of the microchannel heat sink with cavities under longitudinal vortex flow

With the development of electronic devices toward a more centralized direction, there is an urgent need to introduce new technologies in the microchannel heat sink to address thermal deformation or failure caused by uneven temperature distribution. Therefore, microchannels with longitudinal vortex generators (LVGs) and different shapes of cavity structures combination are designed innovatively to address this issue. The laminar flow solver solves for single-phase, steady, and fully developed liquid flows through microchannels in the inlet Reynolds number range of 168–793. Study finds that the longitudinal vortex flow not only mixes the fluid in the mainstream region but also effectively weakens the retention effect in the cavities. Among all microchannels, the microchannel with LVGs and triangular cavities combination (MC-LTC) shows the best performance. Subsequently, multi-objective optimization of the MC-LTC is carried out using Non-dominated Sorting Genetic II Algorithm with the pumping power (Pp) and the temperature uniformity factor (E) as objective functions, and the relative heights (α, β, γ) of the three pairs of LVGs as the three design variables. The optimal solutions set for Pp and E range from 0.706 mW to 1.018 mW and 0.547 to 0.716, respectively. Among the five selected Pareto optimal solution parameters, MC-LTC (α = 0.6001, β = 1.3528, γ = 1.3707) and MC-LTC (α = 0.6001, β = 1.0725, γ = 1.3017) show the best temperature uniformity performance.