Periodic Vortex Shedding Research Articles

Numerical investigation of three-dimensional flow over dual particles during settling

This study investigates three-dimensional flow over dual particles at various separation distances and Re, mainly focusing on the particle's lift behavior in close proximity. Minimal changes in separation distance can result in various unique flow patterns and a non-linear augmentation in lift coefficient. Additionally, quantifying flow blockage between two particles suggests that repulsion behavior and blockage phenomenon are not mutually inclusive. Transient simulations suggest that periodic vortex shedding is not only a function of Re and separation distance, but they also suggest the existence of multiple combinations of separation distance and Re at which the shedding mechanism is triggered. Evident periodic vortex shedding was quantified at 0.25D and Re = 250, while miniature periodic instabilities at the same Re but for a larger separation distance (0.5D). An observable inverse relationship between lift and separation distance exists, while different patterns were quantified for the variation of lift at different Re.

Applying reinforcement learning to mitigate wake-induced lift fluctuation of a wall-confined circular cylinder in tandem configuration

The flow around two tandem circular cylinders leads to significant lift fluctuation in the downstream cylinder owing to periodic vortex shedding. To address such research issues, we present herein a numerical study that uses deep reinforcement learning to perform active flow control (AFC) on two tandem cylinders with a low Reynolds number of 100, where the actuator causes the rotation of the downstream cylinder. First, the cylinder center spacing ratio L* varies from 1.5 to 9.0, and the variation of L* leads to the quasi-steady reattachment regime (L*≤3.5) and the co-shedding regime (L*≥4.0). The fluctuating lift of the downstream cylinder is maximum when L*=4.5. Next, we train an optimal AFC strategy that suppresses 75% of the lift fluctuation in the downstream cylinder. This approach differs from using direct-opposition control to change the vortex-shedding frequency or strength, as reported in previous studies. This strategy modifies the phase difference between the lift fluctuations of the two cylinders by delaying the merging with the upstream cylinder wake and accelerating the formation of recirculating bubbles after the vortex merging. With the new phase difference, the effect of the additional lift from the upstream cylinder is significantly mitigated. The results of the dynamic mode decomposition show that the vortices surrounding the downstream cylinder in mode 1 that contribute to the lift fluctuation are weakened. To the best of our knowledge, this investigation can provide new ideas and physical insights into the problem of AFC under disturbed incoming flow.

Flow Control Around a Cylinder With a Perforated Cylinder

AbstractIn this work, periodic vortex shedding at both sides of a circular cylinder is aimed to be suppressed using a concentrically located perforated cylinder under laminar flow conditions at Re = 200. A code is developed in comsolmultiphysics, 5.3a, and validated using the outcomes of ansysfluent, and previous studies in the open literature, which exhibit a good agreement. In this study, the porosity, β is varied within 0.5 ≤ β ≤ 0.9, and the gap ratio, D/d is varied within 1.5 ≤ D/d ≤ 3.5. The results of the present numerical investigation are evaluated using instantaneous and time-averaged vorticity, streamwise, and transverse components of the velocity and pressure. The drag, CD and lift, CL coefficients are calculated. The Strouhal number, St from the pointwise spectral analysis of the streamwise velocity component is plotted for various cases. It is observed that porosity, β has a dominant effect rather than the gap ratio, D/d on the flow past a solid cylinder. The low-velocity and low-pressure regions are getting large in the transverse direction as the porosity, β increases. The separated layers from solid and perforated cylinders merge for low gap ratios, D/d. However, individual movement of these layers is evident for larger gap ratios, D/d with low porosity, β values. A perfect suppression of the periodicity of vortex shedding is obtained for the cases of D/d = 3.5 with β = 0.5, 0.6, and D/d = 3 with β = 0.5.

On the crown formation and cavity dynamics of free-falling thick disks

The water entry, crown formation, and cavity dynamics of gravity-driven thick solid and annular disks were studied by conducting a series of detailed laboratory experiments. Three different release conditions were examined to study the fully guarded and partially guarded release conditions on the cavity dynamics. The effects of aspect ratio, geometry, and density of disks on crown formation, interface impact, seal development, and air entrainment were investigated. Four crown shapes were identified, and the crown structure was classified based on the dimensionless moment of inertia, I*, and the impact Froude number, Fro. The effects of controlling parameters on variations of crown dimensions were investigated. It was found that the normalized crown diameter decreased with I* and crown geometries were found to be smaller in annular disks. Experimental observations have shown that high-density disks have larger pinch-off depth and form a deep seal in the ambient water. The normalized pinch-off depth increased with Fro and the normalized pinch-off depth in cylindrical thick disks were smaller than thin disks and spherical objects. The temporal variations of cavity indicated a non-linear correlation between the growth rate of normalized pinch-off depth and time. The disk's velocities in three different stages were measured, it was found that the settling velocities followed a linear relationship with I*, and it was affected by the release conditions. The velocity and vortex fields were extracted from the particle image velocimetry data. The velocity fields showed that the solid disks affected a greater surrounding ambient in comparison to the annular disks due to their higher initial momentum. Periodic vortex shedding was formed in the wake of annular disks, and the frequency of the vortex field was found to be proportional to the disk density.

Numerical simulations of the flow around a finite-height circular cylinder under turbulent

To investigate the 3-D characteristics of the flow around a finite-height circular cylinder, this study was based on the CFD technology. The flow was numerically simulated between Re = 1000 and 10000 using the large eddy simulation method to verify and analyze the results. Comparing the instantaneous contours of vorticity for different heights at the same Reynolds number, it can be seen that the free end influences vortex shedding. The instantaneous contours of vorticity for a complete period of vortex shedding were analyzed to explain the causes of lift force generation. Analysis of the effect of Reynolds numbers on the Strohal number was done. The analysis focused on the wake structure of the column at Re = 1000 and Re = 10000, and a significant difference was found between the two cases.

Unsteady flow past slotted circular cylinders in laminar regime: Effect of slit shapes and Reynolds number

A numerical study of incompressible and unsteady flow past a slotted circular cylinder was carried out in a laminar regime. Three different-shaped slits (converging, diverging, and parallel) were installed symmetrically about the cylinder's horizontal axis. A finite volume-based open-source computational toolbox, OpenFOAM, was used to compute the flow field in the Reynolds number (Re) range of 60–180. The results showed the presence of the periodic vortex shedding for all Re ranges and the slotted cylinders were effectively able to suppress it. The surface vorticity over the slotted cylinder surface increased by 16%–23% as compared to the normal cylinder. The momentum injection to the cylinder base reduced the strength of vortex shedding and shedding frequency for the slotted cylinders. Pressure recovery was improved due to an increase in the pressure coefficient which further led to a decrease in the pressure drag. The total drag coefficient for the slotted cylinders was lower than the normal cylinders for Re > 70. Also, a comparatively lower Strouhal number was observed for the slotted cylinders.

Near wake flow and forced convection heat transfer of sinusoidal wavy cylinder based on flow decomposition

Based on flow decomposition we investigate the near wake flow and forced convection heat transfer around sinusoidal wavy cylinders, with an attempt to deepen our understanding of inherent correlations between near wake flow and heat transfer/transport. Large eddy simulations (LES) are conducted at a Prandtl number Pr = 0.7 and a subcritical Reynolds number Re = 3.0 × 103 for the unsteady flow of the sinusoidal wavy cylinder of different wavelengths λ (= 1.89, 3.79 and 6.06Dm) and a fixed wave amplitude a (= 0.152Dm), where Dm is the mean diameter of the cylinder. The near wake flow of the wavy cylinder, together with heat transport, is decomposed via the traditional triple decomposition and a newly-proposed quadruple decomposition, taking into account dominant periodic vortex shedding and/or spanwise heterogeneity of the flow. While heat transfer from the surface of the wavy cylinder to the surrounding flow is distinctly different from that of the smooth cylinder, results from the flow decomposition reveal intrinsic characteristics of the near wake flow and heat transport for the wavy cylinder with different wavelengths. It is observed that heat transport in the near wake of the wavy cylinder is predominantly associated with the coherent spanwise vortices of dominant shedding frequency as well as the spanwise time-invariant components of the mean flow. It is also found that the major contributor to Reynolds stresses (heat flux) is the temporal random stresses (temporal random heat flux) in the near wake of the wavy cylinder. Furthermore, results from the quadruple decomposition show that the spanwise-averaged heat flux in the near wake of the smooth cylinder and the wavy cylinder with λ = 1.89Dm encompasses both spatiotemporal random and temporal dispersive heat fluxes outside the recirculation bubble and only the former heat flux inside the recirculation bubble. However, the spanwise-averaged heat flux in the near wake of the wavy cylinder with λ = 3.79 or 6.06Dm is profoundly and exclusively contributed by the spatial dispersive heat flux outside the recirculation bubble.

Gust effect factors for regions of separated flow around rigid low-, mid-, and high-rise buildings

This paper examines the gust effect factor model for regions of separated flow on rigid buildings. Boundary layer wind tunnel data for a total of 58 buildings, with heights ranging from low-rise to high-rise were analyzed. The results show that the characteristics of separated flow determine the statistical distribution of surface pressures. It was found that the reattachment of separated flows onto building surfaces reduces the skewness and kurtosis of area-averaged surface pressures, causing them to follow the Gaussian distribution more closely. However, the pressures tend to have non-Gaussian distributions for surfaces without flow reattachment. Strong Karman-like vortex shedding increases aerodynamic admittance functions around the Strouhal number, along with the peak factors and gust effect factors of area-averaged side wall pressures. For surfaces with flow reattachment, Solari's (1993a) model predicts the gust effect factors with reasonable accuracy, particularly for uplift on low-rise buildings, mid-rise buildings with height-to-width ratios, H/W = 1 and high-rise buildings with height-to-width ratios, H/W > 4, and length-to-breadth ratios, L/B > 2. For separated flows without reattachment on the building, particularly for H/W > 4 and L/B < 2, periodic Karman-like vortex shedding tends to cause inaccuracies in the gust effect factor model, as might be expected.

Numerical Investigation of Vortex Shedding from a 5:1 Rectangular Cylinder at Different Angles of Attack

Although flow around a 5:1 rectangular cylinder at small angles of attack (AoA) has been extensively studied, when the AoA becomes larger, the research is rare. Therefore, this study performs Unsteady Reynolds-Averaged Navier-Stokes simulations (URANS) using the k-ω SST turbulence model for unsteady flow around a two-dimensional 5:1 rectangular cylinder at different AoAs up to 45°. A strong dependence of the flow characteristics on AoA is observed through the analysis of the time-averaged lift coefficient, drag coefficient, and Strouhal number. The peak of lift and drag coefficient is observed to be correlated, respectively, to the leading- and trailing-edge vortex based on the analysis of the flow. The x′-directional length of the main recirculation bubble on the top side and the distance from the bubble center to the leading edge of the cylinder both reach the maximum when α = 15°. In addition, the standard deviation σx′ of the time-averaged velocity U¯x′ along the cylinder shows a trend of increasing at first and then decreasing, and that σy′ also shows the same trend at α = 20°~45°; it fluctuates within a range of 0.05~0.2 at α = 0°~20°. Finally, two principal modes of vortex shedding are observed with α = 15° being their turning point, (i) “1 + 1” mode: in one vortex shedding period, two major vortices shed off from the top and bottom sides of the cylinder at α ≤ 15°; (ii) “2 + 2” mode, four vortices shed off from the top and bottom sides of the cylinder at α &gt; 15° in one vortex shedding period.

Experimental verification and numerical simulation of a vortex flowmeter at low Reynolds numbers

This study presents experimental verification and numerical simulations of a vortex flow meter in the Reynolds number range between 8300 and 50,000. A custom-designed bluff body with a wedge back shape was used in the flowmeter. A shedding frequency of the flowmeter was measured in an air duct using a hot-film probe. To evaluate the accuracy of the flowmeter, a measurement uncertainty analysis was performed. Numerical simulations of the vortex flowmeter were performed with the open source code OpenFOAM. Transient simulations of periodic vortex shedding behind the bluff body were performed using different simulation methods depending on the pipe Reynolds number, such as Direct Numerical Simulation (DNS), Large Eddy Simulation (LES) and Unsteady Reynolds Averaged Navier Stokes (URANS) method. The simulated vortex shedding frequencies matched the experimental data very well. Experiments and simulations demonstrated a clear linear dependence of the shedding frequency on the volumetric flow rate over the entire range of Reynolds numbers. In addition, numerical simulations were used to study the main mechanisms of vortex formation and shedding behind the considered bluff body.

LES and PIV Investigation of the Flow Past a Cactus-Shaped Cylinder with Four Ribs

The flow past a cactus-shaped cylinder with four ribs is investigated numerically using large eddy simulations (LES) at Reynolds number of 20,000 and experimentally using particle image velocimetry (PIV) at Reynolds number of 50,000. In both approaches, the full range of angle of attack is covered. LES results show a good qualitative and quantitative match of the aerodynamic properties to previous experimental data, although the value of the critical angle of attack is slightly lower. The results confirm that there is no Reynolds number dependency within the investigated range allowing a comparison of the flow fields from the present LES and PIV. Significant variations of the flow patterns with the angle of attack are found and quantified using the recirculation length and wake width. Overall, the observed angle of attack dependence resembles the behaviour of the square cylinder. However, the studied cylinder has a narrower wake at all angular orientations. Proper orthogonal decomposition is used to identify large coherent structures in the flow. At all angles of attack the first two modes remain dominant making it possible to reconstruct the periodic vortex shedding process using a low-order model.

Experimental and theoretical study on the association between entrainment vortex evolution and pressure oscillation of steam jet condensation

Condensation pressure oscillation of steam jet has great influence on direct contact condensation (DCC) equipment. Therefore, it is essential to reveal the microscopic mechanism of pressure oscillation of steam jet condensation. In this study, the association between entrainment vortex evolution and pressure oscillation of steam jet condensation is investigated. Firstly, the periodic variation of characteristic parameters of jet oscillation caused by periodic vortex shedding is obtained based on the image processing techniques. Secondly, by synchronous comparison between the pressure oscillation cycles and the jet parameters oscillation cycles, it is found that the periodic evolution and shedding of two-phase entrainment vortexes formed in the upper and lower mixing layers is the microscopic mechanism which causes condensation pressure oscillation. Specifically, the high-frequency pressure oscillation near the steam jet results from the high-frequency transverse oscillation of the steam jet which is caused by the periodic vortex evolution in the mixing layer and the periodic shedding of the vortex blob at the tail of the jet; the low-frequency pressure oscillation near the steam jet results from the low frequency oscillation of the whole steam jet caused by periodic shedding of the paired vortex blobs; the pressure oscillation in the downstream of the steam jet is caused by the condensation oscillation of periodic shedding vortex blobs. Finally, the dominant frequency distribution of condensation pressure oscillation under various test conditions is analysed. Combined with the vortex shedding model, a prediction equation of the dimensionless characteristic frequency St of the shedding vortexes is established. The predicted values had good agreement with the experimental results.

Global stability analysis and direct numerical simulation of boundary layers with an isolated roughness element

Global stability analysis and direct numerical simulation (DNS) are used to study boundary layer flows with an isolated roughness element. The aspect ratio of the element ( $\eta$ ) is small, while the ratio of element height to displacement boundary layer thickness ( $h/\delta ^{*}$ ) is large. Both steady base flows and time-averaged mean flows are able to capture the frequencies of the primary vortical structures and mode shapes. Global stability results highlight that although the varicose instability is dominant for large $h/\delta ^{*}$ , sinuous instability becomes more pronounced as $Re_h$ increases for the thin geometry ( $\eta =0.5$ ), due to increased spanwise shear in the near-wake region. Wavemaker results indicate that $\eta$ affects the convective nature of the shear layer more than the type of instability. DNS results show that different instability mechanisms lead to different development and evolution of vortical structures in the transition process. For $\eta =1$ , the varicose instability is associated with the periodic shedding of hairpin vortices, and its stronger spatial transient growth indicated by wavemaker results aids the formation of hairpin vortices farther downstream. In contrast, for $\eta =0.5$ , the interplay between varicose and sinuous instabilities results in a broader-banded energy spectrum and leads to the sinuous wiggling of hairpin vortices in the near wake when $Re_h$ is sufficiently high. A sinuous mode with a lower frequency captured by dynamic mode decomposition analysis, and associated with the ‘wiggling’ of streaks, persists far downstream and promotes transition to turbulence. A new regime map is developed to classify and predict instability mechanisms based on $Re_{hh}^{1/2}$ and $d/\delta ^{*}$ using a logistic regression model. Although the mean skin friction demonstrates different evolutions for the two geometries, both of them efficiently trip the flow to turbulence at $Re_h=1100$ . An earlier location of a fully-developed turbulent state is established for $\eta =1$ at $x \approx 110h$ .

Wind Energy Potential Ranking of Meteorological Stations of Iran and Its Energy Extraction by Piezoelectric Element

Piezoelectrics have been used in several recent works to extract energy from the environment. This study examines the average wind speed across Iran and evaluates the amount of extracted voltage from vortex-induced vibrations with the piezoelectric cantilever beam (Euler–Bernoulli beam). This study aims to compute the maximum extracted voltage from polyvinylidene fluoride piezoelectric cantilever beam at the resonance from vortex-induced vibration to supply wireless network sensors, self-powered systems, and actuators. This simulation is proposed for the first-ranked meteorological station at its mean velocity over six years (2015–2020), and the finite element method is used for this numerical computation. The wind data of 76 meteorological stations in Iran over the mentioned period at the elevation of 10 m are collected every three hours and analyzed. Based on the statistical data, it is indicated that Zabol, Siri Island, and Aligudarz stations had recorded the maximum mean wind speed over the period at 6.42, 4.73, and 4.42 m/s, respectively, and then energy harvesting at the mean wind speed of top-ranked station (Zabol) is simulated. The prevailing wind directions are also studied with WRPLOT view software, and the wind vector field of 15 top-ranked stations is plotted. For energy harvesting simulation, periodic vortex shedding behind the bluff body, known as vortex-induced vibration, is considered numerically (finite element method). The piezoelectric cantilever beam is at a millimeter-scale and has a natural frequency of 630 Hz in its mode shapes to experience resonance phenomenon, which leads to maximum extracted voltage. The maximum extracted voltages for three piezoelectric cantilever beams with the natural frequency of 630 Hz with the wind speed of 6 m/s are 1.17, 1.52, and 0.043 mV, which are suitable for remote sensing, supplying self-power electronic devices, wireless networks, actuators, charging batteries, and setting up smart homes or cities. To achieve this, several energy harvesters with various dimensions should be placed in different orientations to utilize most of the blown wind.

Aeroacoustic Optimization Design of the Middle and Upper Part of Pantograph

The pantograph is the main noise source of high-speed trains, of which the middle and upper parts of the pantograph account for about 50% of the whole noise energy. Taking CRH380BL pantograph as the basic prototype, three aerodynamic noise reduction measures of opening, slotting, and airfoil are introduced to build a new pantograph, and their aeroacoustic performances are comprehensively investigated through large eddy simulation (LES) and Ffowcs Williams–Hawkings (FW-H) equation method. The research results show that the open upper and lower arms (ULA) can reduce the downstream vorticity intensity and vortex structure scale, which in turn reduces the noise source intensity, thus reducing their radiated noise by approximately 1.1 dBA. The slotted ULA reduce the size of the rear vortex structure but increase the vorticity intensity, so it is difficult to effectively control their radiated noise. The airfoil bow head reduces the vorticity intensity and vortex structure scale behind it, and avoids periodic vortex shedding, thereby reducing its noise source intensity, thus reducing its radiated noise by about 1.2 dBA.

Lagrangian coherent structures in flow past a backward-facing step

This paper investigates flow past a backward-facing step (BFS) in a duct at Reynolds number $Re = 5080$ based on step height, mean inflow velocity and fluid kinematic viscosity. The flow configuration matches a combustion experiment conducted by Pitz and Daily in 1983. High-resolution velocity fields are obtained in OpenFOAM by direct numerical simulation, and the flow field analysed by Lagrangian approaches. Trajectories of fluid particles in areas of interest are obtained by high-order numerical integration, and used to compute finite-time Lyapunov exponents (FTLEs) and polar rotation angles. Lagrangian coherent structures (LCSs) are extracted using geodesic theory, including hyperbolic LCSs and elliptic LCSs. We use complementary qualitative and quantitative LCS analyses to uncover the underlying flow structures. Notably, we find that a flow pathway in which fluid particles rarely diverge from adjacent particles is opened and closed by FTLE ridges determined by the periodic shedding of vortices from the BFS. Two dominant vortices with significant Lagrangian coherence, generated respectively by the separated boundary layer and shear layer, are self-sustaining and of comparable strength. Hyperbolic repelling LCSs act as transport barriers between the pathway and cores of the coherent vortices, thus playing a major part in the fluid entrainment process. Interactions between these different geometric regions partitioned by LCSs lead to intrinsic complexity in the BFS flow.

Numerical investigation of flow around two cylinders in tandem above a scoured bed

Flow mechanisms around two cylinders in tandem arrangement above a scoured bed have been investigated using the three-dimensional unsteady Navier–Stokes equations with the Spalart–Allmaras improved delayed detached-eddy simulation model. A turbulent inlet boundary layer generation method is adopted to obtain more realistic inlet boundary conditions. First, uniform flow over a single cylinder at Re = 3900 and flow over a single cylinder above scoured beds at Re = 6000 were simulated to validate the numerical model, boundary layer generation method, and mesh density effect. Second, two cylinders in the tandem arrangement above scoured beds with six different pitch ratios L/D are investigated numerically in terms of instantaneous vortex characteristics, the hydrodynamic force, and time-averaged flow fields. The simulation results in scoured beds are compared with simulations under the near flat wall and wall-free conditions. The major findings can be summarized as follows. (1) When L/D≤2.0, the wake of two tandem cylinders is dominated by the intermittent shedding, and the downstream sand dune in the scoured bed hinders the Kármán vortex formation at the rear of the downstream cylinder. Lift force fluctuations of the two cylinders have small amplitudes, and their spectra show a multi-peak distribution and no dominant peak frequency in the spectrum of the upstream cylinder. A squarish cavity-like recirculation zone is formed between two cylinders at L/D=2.0. (2) When L/D≥3.0, the periodic vortex shedding is evident in the wake of the upstream cylinder, and the small sand berm between two cylinders has an impact on the bottom shear layer of the upstream cylinder. The downstream cylinder is periodically impacted by the vortices shed from the upstream cylinder. Lift force spectra of the upstream and downstream cylinders have the same peak frequency. (3) Due to the influence of scoured bed and the inlet boundary layer, the time-averaged lift coefficient of the upstream cylinder remains negative when L/D≥1.5, and the critical spacing for drag inversion is relatively smaller compared with under wall-free conditions. The negative pressure coefficient values of the upstream cylinder are smaller than the values in near flat wall and wall-free conditions.

Vortex shedding frequency of a moving obstacle in a Bose–Einstein condensate

We experimentally investigate the periodic vortex shedding dynamics in a highly oblate Bose–Einstein condensate using a moving penetrable Gaussian obstacle. The shedding frequency f v is measured as a function of the obstacle velocity v and characterized by a linear relationship of f v = a(v − v c) with v c being the critical velocity. The proportionality constant a is linearly decreased with a decrease in the obstacle strength, whereas v c approaches the speed of sound. When the obstacle size increases, both a and v c are decreased. We discuss a possible association of a with the Strouhal number in the context of universal shedding dynamics of a superfluid. The critical vortex shedding is further investigated for an oscillating obstacle and found to be consistent with the measured f v. When the obstacle’s maximum velocity exceeds v c but its oscillation amplitude is not large enough to create a vortex dipole, we observe that vortices are generated in the low-density boundary region of the trapped condensate, which is attributed to the phonon emission from the oscillating obstacle.

The flow past a sphere with centric cylindrical bore of different diameter and orientation

Motivated by the potential safety hazard of cracks in flow past bluff bodies in ocean engineering applications, incompressible viscous flow past a sphere with a centric, cylindrical bore at Reynolds number of 300 is investigated by a finite volume method with adaptive mesh. The influence of bore with different Rd (the diameter ratio of the bore to the sphere, is ranged from 0 to 0.3) and orientation on the vortex shedding, flow separation and drag coefficients are analyzed. The results show that the streamwise-orientated bore has significant influence on vortex shedding (it becomes to the double-line vortex, instead of hairpin vortex at Rd≥0.25) and drag coefficients. Due to the interruption of fluid flows through the bore, it disturbs the periodicity of vortex shedding and pushes the separation bubble back away from the sphere. The crosswise-orientated bore has little effect on vortex shedding and drag coefficients, but the flow separation and the transition to the unsteady regime are delayed due to the bore closed to the separation points in (x,y)-plane. Due to the jet-like flow, the instability of the flow past a sphere is magnified when the diameter of borehole is sufficiently small (Rd=0.05), whether it is streamwise-orientated or crosswise-orientated bore.

Transient flow and thermal transport characteristics of wall-bounded turbulent dual jet with heated undulated wall

The present computational study aims to investigate and improve the turbulent dual jet cooling performance on an undulated surface with varying profiles. This study also aims to highlight the flow and thermal features arising owing to an undulated surface having amplitude (UA) between 0.0 and 0.7. The transient RANS equations are considered to simulate the complex behaviour of turbulent dual jet. Four Reynolds-Averaged Navier-Stokes (RANS) turbulence models, namely, standard k-ω, shear-stress transport (SST) k-ω, renormalization group (RNG) k-ϵ, and realizable k-ϵ models, are used to predict the thermal performance and flow field of a turbulent dual jet for a fixed Reynolds number (Re) of 10,000 and offset ratio of 2. A constant wall temperature and constant wall heat flux boundary conditions are used. For the amplitude between 0.0 and 0.1, a periodic vortex shedding phenomenon near the jet exit is observed. However, two stable counter-rotating vortices are observed with no periodic vortex shedding for higher values of UA ≥ 0.3. The axial position of the merge point reduces with a rise in the amplitude. It is also observed that the velocity profile becomes self-similar and the inflection point in the velocity profile rises near the wall region with amplitude. The time series of U and V velocity signals unveil sinusoidal oscillations and display almost the same peak to peak amplitude for UA ≤ 0.1 at various times. The FFT of U velocity signals displays a solo peak dominant frequency which is the same as shown by V velocity in the FFT plot corresponding to the Strouhal number of the vortex shedding phenomenon. The average Nusselt number is increased up to 63.89% and 65.03% for higher amplitude for the constant heat flux and constant temperature boundary conditions. Correlations have been also proposed for the average Nusselt number, the average heat flux and the merge point. The outcomes of the present research can be implemented for better design in automobile industries and utilization of cooling or heating jets in electronics, metal, and material processing.