Wake Region Research Articles

Ship’s Wake on a Finite Water Depth in the Presence of a Shear Flow

The ship’s wake in the presence of a shear flow of constant vorticity at a finite water depth is investigated by expanding the Whitham-Lighthill kinematic theory. It has been established that the structure of a wave ship wake radically depends on Froude number Fr (in terms of water depth) and especially on the critical Froude number Frcr, which depends on the magnitude and direction of the shear flow. At its subcritical values Fr<Frcr two types of waves are presented: long transverse and short divergent waves inside the wedge area with an angle depending on Fr For the supercritical range Fr>Frcr only divergent waves are presented inside the wake region. Critical Froude number Frcr is variable and mostly depends on collinear with the ship path component of the shear flow: it decreases with the unidirectional shear flow and increases on the counter shear current. The wedge angle of the ship wake expands with an increase in the unidirectional shear flow and narrows in the oncoming flow in the subcritical mode of the ship’s motion Fr<Frcr. Wake angle decreased with Froude number for Fr>Frcr and only divergent waves with the crests almost collinear with ship path are finally presented in the narrow ship wake. For a critical value of the Froude number Fr=Frcr, the ship’s wake has a total wedge angle of 180° with waves directed parallel to the ship’s motion. The presence of a shear flow crossing the path of the ship gives a strong asymmetry to the wake. An increase in the perpendicular shear flow leads to an increase in the difference between the angles of the wake arms.

Investigations of Exterior Wind Flow and Aerodynamic Coefficient around Y-Plan Shape Tall Building

In recent years, the construction of skyscrapers is emerging in many countries and the study on the behaviour of wind around the building receives an additional interest among structural engineers and architects. Mostly, tall skyscrapers are planned in the shape of ‘Y’ in order to have a maximum exterior view and to support the central core of the structure. In the current scenario, it is important to study the actual wind load for irregular plan shape building. This paper presents the numerical wind flow simulation around ‘Y’ plan shape tall building using ANSYS Fluent software and validation is done using wind tunnel testing. The building model and wind velocity are scaled to the ratio 1:300 and 1:5 respectively. A wind velocity of 10 m/s is applied both for wind tunnel testing and for the numerical simulation. Error analysis is carried out in order to check the accuracy of the results obtained between wind tunnel and CFD. From the test results the mean Cp is investigated for various faces of the building for the wind angle 0˚, 45˚ and 90˚ from both using CFD and wind tunnel. The investigation of drag and lift coefficient is made on Y-plan shape building and it is observed that the maximum drag occurs at 45˚ wind angle, because of the less projected area when compared with the other wind angles 0˚ and 90˚ respectively. Further, this paper continues with the physics of wind flow behaviour around Y-plan shape building and flow character such as vortex formation, streamlines and identification of wake region for different wind angles.

곡면 델타 윙렛 와류발생기를 이용한 핀 휜의 열전달 및 유동 특성 개선

A numerical analysis was carried out to investigate the effects of curved delta winglet vortex generator on the heat transfer and flow characteristics of pin fin arrays. The steady RANS simulation has been performed with κ-ω SST turbulence model by using Fluent 18.0. The effects of the curved delta winglet vortex generators installed upstream of each pin of the staggered array 8 row pins were confirmed, and the cases where the curved delta winglet vortex generators were located on one endwall(Case 1) and on both endwalls(Case 2) were considered. The results showed that the curved delta winglet vortex generators induce the generation of mixed vortices that reduce the size of the wake region of the pin and improve the heat transfer of the pins. In addition, the pressure loss is reduced due to the effect of decreasing the size of wake occurring in the pin, and this tendency becomes stronger as the Reynolds number increases. As a result, the thermal performance factor(η) increases according to the Reynolds number, and when the Reynolds number is 30000, η of Case 1 and Case 2 increased by 11.3% and 12.2%, respectively, compared to the baseline.

Towards three dimensional aspects of plasticity-induced crack closure: A finite element simulation

The mutual interactions between intrinsic (damage) and extrinsic (shielding) mechanisms are essential for understanding fatigue crack growth in ductile materials. In the latter case, plasticity-induced crack closure is the dominating retardation mechanism in the Paris regime. The transition between plane strain and plane stress states leads to a locally different fracture surface contact, which is difficult to access during experiments. In this work, plasticity-induced crack closure under constant amplitude loading of an AlCu4Mg (AA2024) aluminium sheet material is studied from a three-dimensional perspective. An elastic–plastic 3D finite element model of an M(T)160 specimen with a bilinear isotropic hardening model is used to study the evolution of plasticity during fatigue crack growth. Cyclic crack propagation is simulated with the releasing-constraint method.In the results, plasticity-induced crack closure is present up to a load ratio R = 0.3. Detailed investigations of the contact pressure distributions indicate a strong dependence on the stress intensity factors and the sheet thicknesses. The contact pressure distributions on the fracture surface can be divided into three characteristic regions. Near the plastic zone, plastic energy is still induced during the unloading process after the crack is already closed. However, the crack surface contact does not affect the shape of the plastic zone. Additionally, further plastic energy accumulates in the plastic wake region during crack closure within subsequent load cycles, described here as cyclic plastic wake. In summary, the finite element model can reproduce the major features of fatigue crack closure like Kop or Kcl and the three-dimensional and load-dependent evolution of plasticity-induced crack closure.

Estimation of airflow distribution in cubic building group model using POD-LSE and limited sensors

Urban airflow has strong turbulence characteristics, and its distribution varies with time. Urban airflow distribution can be measured with sensors or simulated using Computational Fluid Dynamics (CFD). However, CFD is considered still expensive for the rapid calculation of unsteady airflow distribution and the measurement value of sensors is often inferior in terms of spatial resolution. In this study, the high spatial resolution airflow distribution in the cubic building group model was rapidly estimated from limited sensors by combining Proper Orthogonal Decomposition (POD) with Linear Stochastic Estimation (LSE). Validated airflow data simulated by Large-Eddy Simulation (LES) in a cubic building group model were selected as the airflow database. This study was conducted with two main objectives: 1) to verify the basic performance of the POD-LSE; and 2) to analyze the effects of changing the number of sensors and POD analysis regions on the estimation accuracy. By comparing the results of the POD-LSE estimations with the LES data as the true value in the reference region, the following conclusions were obtained: 1) The airflow distribution in the cubic building group model can be reconstructed and predicted by the POD-LSE; 2) nine sensors can provide acceptable estimation accuracy; 3) the velocity value of a point located in the wake region is difficult to estimate; 4) the accuracy does not increase as the POD region expands (without changing the number of sensors); and 5) with an increasing number of sensors, the accuracy of the velocity estimation is improved in reconstruction.

Pressure-sensitive paint measurements for microscale supersonic flow with wedge models

The pressure distribution around wedge models inside a submillimeter supersonic wind tunnel was experimentally investigated using pressure-sensitive paint (PSP) at a flow speed of Mach 1.6. The throat of the submillimeter supersonic wind tunnel was 500 μm. The two wedge models were isosceles triangles with a width of 50 μm and vertex angles of 20° and 30°, respectively. The pressure profiles and pressure distributions along the centerline inside the submillimeter supersonic wind tunnel with the wedge models agreed with the results of numerical simulation performed using ANSYS Fluent. The pressure distributions around the wedge models were examined, and a strong pressure rise at the front end of the wedge models was observed. A low-pressure region in the wake region downstream of the wedge models was identified. However, these results differed from the simulation data for the middle layer of the wind tunnel, which revealed bow shock and a shock wave interaction. This difference occurred because the PSP coating was located at the bottom of the wind tunnel, which was embedded inside a viscous layer. The pressure data measured with PSP were smeared, and it was consistent with the simulation data for the bottom layer. The PSP results reveal the overall pressure variation around the wedge models, and they will be useful for future designs of micro propulsion systems with supersonic nozzles.

Non-isothermal flow past a heated circular cylinder in subcritical regime: a numerical investigation based on large-eddy simulation

Compressible flow past a heated circular cylinder at subcritical Reynolds number of 3900 is numerically investigated by using the large-eddy simulation method. Rigorous validations of the numerical model are carefully performed under isothermal conditions on the basis of available experimental data. The calculated mean flow and Reynolds stresses show good agreement with the published experimental data. The effects of temperature difference between the cylinder surface and the freestream on the flow statistics and thermal characteristics are further studied in detail by setting two kinds of wall temperature boundary conditions. It is manifested that increasing the wall temperature leads to the augmentation of skin friction drag, suppression of turbulent intensity, enhancement of flow mixing and extension of recirculation zone. In addition, it is found that the variations of thermo-physical properties pose a slight effect on the wall heat flux before the boundary layer separates from the cylinder surface. It is worth noting that the recirculation bubble length can be used as a distance scaling parameter to weaken the temperature dependence of the flow and thermal statistics. These results provide a more detailed insight into the statistical difference in the wake region of cylinder when the temperature effect is taken into account.

Wake control of a bluff-body via distributed jets over its surface

The flow passing a circular cylinder can trigger flow-induced vibrations such as the vortex-induced vibration. In this paper, the authors investigated an active method to control the cylinder wake flow. The control scheme was achieved by active blowing through a structured porous surface that was manufactured by 3D printing precisely. The blowing momentum was changed by various mass flow rates so that it defined different values of a non-dimensional momentum coefficient Cμ. The experimental investigation was conducted in a wind tunnel. A 2D particle image velocimetry system was used to measure global flow fields. The Reynolds number based on D was 10 000 in the subcritical region, where D is the cylinder diameter. The proper orthogonal decomposition (POD) was utilized as a reduced-order model. Experimental results showed that transformations could be found in POD modal characteristics and vortex shedding frequencies. Fluctuations in the global wake were suppressed. Moreover, intensities of turbulence kinetic energy and elements of the Reynolds stress tensor T were decreased in the near wake region. It can be concluded that active blowing jets through the structured porous surface of the circular cylinder can be used to control the surrounding flow with effective Cμ values.

On the aerodynamic loads and flow statistics of airfoil with deformable vortex generators

The aerodynamic performances and flow statistics for a Delft University-91-W2-250 airfoil with deformable vortex generators (DVG) were experimentally studied in a wind tunnel across various angle of attacks and wind speeds. A high-resolution force sensor was used to measure the time-averaged lift force, while a planar particle image velocimetry system was applied to characterize the mean velocity and vortex shedding over airfoil surface. The results highlighted that, similar to conventional rigid vortex generators (RVG), DVG can effectively enhance lift coefficient after the stall angle of airfoil with clean surface under low incoming winds. However, the deformation of DVGs increased with the growth of wind speed; this suppressed the effectiveness of wake mixing where the aerodynamic performance of DVGs gradually converged to clean surface configurations. The flow measurements demonstrated that the deformation of DVG can lead to significant decrease in near-wall flow velocities close to the airfoil trailing edge and generate more dispersed vorticity distributions. To further investigate the linkage between DVG deformation and its wake mixing effectiveness, complementary tomographic particle image velocimetry measurements were conducted. The results indicated that the vorticity strength presented monotonic decay with the bending angle of DVG within both near and intermediate wake regions. The capability of DVGs passively adjusts their bending angle, and therefore, the airfoil lift coefficients provide a novel approach to reduce aerodynamic load fluctuations for aircraft within unsteady flows.

Large-eddy simulation of wind-turbine wakes over two-dimensional hills

Wind-turbine wakes over two-dimensional (2D) hills with different slope gradients are systematically investigated using large-eddy simulation with wind turbine parameterized as actuator disk model and hilly terrain modeled by immersed boundary method. The chosen hill models represent typical hilly terrains with and without flow recirculation in the wake of the hills. The flow characteristics of wind-turbine wakes [including mean velocity, wake-center trajectory, turbulence statistics, and mean kinetic energy (MKE) budgets] and the power performance are analyzed, and the related flow mechanisms are elucidated in our study. It is found that the velocity deficit in turbine wakes cannot be acceptably represented by the Gaussian model in the wake of the steep hill until at a further distance. It is also found that the assumption that the wake-center trajectory maintains a nearly constant elevation downwind of the hilltop proposed by Shamsoddin and Porté-Agel [“Wind turbine wakes over hills,” J. Fluid Mech. 855, 671–702 (2018)] may not be applicable in particular for the steep hill cases. Furthermore, the hilltop is the optimal location for turbine placement because the turbine harvests more wind energy due to the speed-up effect and suffers less fatigue loading due to the lower turbulence levels. Both the turbulence levels and the magnitude of vertical turbulent flux are found to drop below those of the flat ground case on the windward side of the hills, and they also decrease within the hill wake region compared with the no-turbine cases. A detailed analysis of MKE budgets reveals that the budgets of pressure transport and mean convection are mainly responsible for balancing the MKE in turbine wakes over hilly terrain.

Numerical Investigation of a Supersonic Flow in the Near Wake Region of a Cylindrical Afterbody

A computational study of a supersonic flow in the base region and the nearest wake of a cylindrical body moving at a supersonic speed have been carried out. A mathematical model of high-enthalpy flows is presented. In this case, the "prehistory" of the flow was taken into account, i.e., the configuration of the computational domain was as close as possible to the real one. The use of various turbulence models for calculating flow in the base region and the nearest wake was analyzed. The following turbulence models were considered: 1) the Spalart --- Allmaras model; 2) SST model; 3) standard k--ε model; 4) k--ε model with compressibility correction; 5) k--ε RNG (renormalized group) model; 6) k--ε Realizable model; 7) standard Reynolds Stress (RS) model; 8) RS BSL (Reynolds stress baseline) model. Based on a comparison of the calculation results with experimental data, it is shown that: 1) when calculating the flow in the base region and in the wake of the vehicle, it is very important to take into account the "prehistory" of the flow, i.e., to calculate the flow around the entire vehicle; 2) the best match was obtained using Reynolds Stress models and the k--ε RNG model

Effect of jet schemes of the double-nozzle strut injector on mixing efficiency of air and hydrogen for a scramjet combustor

This work presents the numerical analysis of the DLR scramjet combustor for different jet schemes of the double-nozzle injector, namely the various injection directions, injection angles, and nozzle spacings. After comparing various jet schemes, it is found that the optimal jet scheme for the double-nozzle strut is to set the angle of 60° for the inward injection direction and the nozzle spacing of 3 mm. Furthermore, the mixing efficiency of the optimal jet scheme is investigated at different Mach numbers. The current research focuses on the mixing mechanism of air and hydrogen by analyzing the flow structures in the strut's wake region. It is observed that the double-nozzle configuration increases the number of vortexes behind the strut and creates a recirculation zone between the two jet streams. The mixing efficiency of the scramjet combustor improves significantly with an increase in the injection angle, but the spacing and direction of the double-nozzle have little effect on the mixing efficiency. It is found that the additional total pressure loss generated by the double-nozzle configuration can be negligible. In addition, the results show that the mixing efficiency of the optimal jet scheme for the double-nozzle is improved more significantly at low Mach numbers (e.g., Ma = 2 and 3).

Heavy Ion Escape From Martian Wake Enhanced by Magnetic Reconnection

AbstractMars is a dry planet with a history of a warm and wet environment. Hydrogen and oxygen continuously escape from the unmagnetized planet. Although the heavy ion escape rate in the wake region is low due to Mars' obstruction, there are reports of events with bursty and enhanced ion escape. Here, we first find the evidence of the Alfvenic dayside‐produced plasma clouds accelerated by magnetic reconnection, which provides an explanation for the wake bursty mass escape by the observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. In the event reported by this study, two types of flux ropes were successively observed in the magnetic reconnection exhaust in the Martian wake. One is generated by the reconnection, while others are produced by dayside boundary instability. The ions convected from the dayside, as well as the local original ions, can both be accelerated to be Alfvenic and expelled in the Martian tail by reconnection. The oxygen escape rate in the reconnection exhaust is estimated to be a quarter of the previous statistical result in the entire wake region.

A study on the characteristic features of the lunar ionosphere using dual frequency radio science (DFRS) experiment onboard Chandrayaan-2 orbiter

ABSTRACT We present ‘first of its kind’ measurements of the enhanced integrated electron density profiles (iEDPs) at the lunar wake and trans-terminator regions using radio occultation (RO) experiments conducted with the dual frequency radio science (DFRS) payload onboard Chandrayaan-2 (CH2) spacecraft. DFRS uses one-way coherent signals at X and S-bands of radio frequencies for RO measurements. Detailed analysis of the results shows that the electron content is large (∼1.5 TECU, with 1 TECU = 1016 m−2) in the lunar wake region compared to the dayside. Large electron content is also seen near lunar polar regions during solar transition periods. These observations are unique in nature as they show post-sunset enhancements in the iEDPs compared to dayside, as reported by earlier missions. These results further confirm recent predictions from the theoretical model for the lunar ionosphere.

Characterization of wake interference between two tandem offshore floating vertical-axis wind turbines: Effect of platform pitch motion

The wake interference within the offshore wind farms, especially with the tandem arrangement scenario, affects the designed total power output. Also, the six degrees of freedom motions of the platforms not only can change the aerodynamics of the offshore floating wind turbines, but also may influence the wake interference between them. In the present study, the effect of the platform pitch motion on the wake interference between two tandem offshore floating vertical-axis wind turbines (VAWTs) is characterized using the improved delayed detached-eddy simulation (IDDES). First, the power performance of the downstream turbine (VAWT Ⅱ) at different separation distances, 2D ≤ LS ≤ 10D, and tip speed ratios, 0.4 ≤ TSRⅡ ≤ 1.5, are analyzed, assuming that the upstream turbine (VAWT Ⅰ) is bottom-fixed and operates at an optimal TSRⅠ of 1.2. Then, the effects of the pitch amplitude, 5° ≤ APⅠ ≤ 15°, and pitch period, 2TⅠ ≤ TPⅠ ≤ 8TⅠ, on the wake interference are characterized by assuming that the platform pitch motion of VAWT Ⅰ follows a prescribed simple harmonic law. The results show that locating VAWT Ⅱ in the medium wake region of VAWT Ⅰ, e.g., LS = 6D, can appropriately balance the power performance and space cost of the bottom-fixed turbine array. Also, the platform pitch motion can reduce the mean velocity deficit in the core wake region of VAWT Ⅰ. The mean wake deficit reduction increases the averaged power coefficient of VAWT Ⅱ, e.g., up to 22.67% when LS = 6D, TSRⅡ = 1.2, APⅠ = 15°, and TPⅠ = 4TⅠ. In addition, relatively larger pitch amplitudes and smaller pitch periods will further alleviate the negative effect of the wake interference. This study may serve as a reference for designing offshore floating wind farms.

Experimental study of flow and mass transport in the near-wake region of a rigid planar metal net panel

Aquaculture cages constructed from rigid material have become increasingly popular in recent years due in part to the continuous expansion of the aquaculture industry offshore, where cages need to withstand much harsher ocean conditions. Most previous studies of hydrodynamic interactions with aquaculture cages have explored the impacts of more traditional flexible cage net panels on wake flow fields and mass transport properties. In the current experimental study, Particle Image Velocimetry and Planar Laser Induced Fluorescence techniques were used to measure flow and concentration fields in the near wake region of a steady current through a rigid metal net panel to analyze both the flow patterns and mass transport processes. The results indicated that, similar to a flexible polyethylene net panel, the time-average velocities and turbulence characteristics in the near wake region were highly inhomogeneous and anisotropic, with the turbulent intensity following a short-range, power-law decay downstream of the panel. In direct comparison with a flexible net panel of similar net solidity, the rigid net panel was found to slightly enhance the lateral spreading of the plume, with cross-sectional profiles of the mean concentration and concentration fluctuation shown to exhibit self-similar Gaussian distributions. The rigid net panel also resulted in a lower flow blockage, as measured by a velocity reduction coefficient, with the corresponding turbulent intensity also reduced compared to the flexible panel due to an overall reduction in the drag force. In addition, the rigid panel tended to create larger wake eddies than the flexible panel, leading to enhanced scalar mixing and, hence, faster rates of concentration decay in the near-wake region. These experimental findings have potential implications for cage-based aquaculture operations, where rigid fish cages are comparatively more likely to generate favorable environments for fish growth, as well as helping to reduce negative impacts on the surrounding aquatic environment.

A numerical study of two-dimensional laminar flow of power-law fluids around three circular cylinders in side-by-side arrangement

PurposeThis study aims at investigating two-dimensional laminar flow of power-law fluids around three unconfined side-by-side cylinders.Design/methodology/approachThe numerical study is performed by solving the governing (continuity and momentum) equations using a finite volume-based code ANSYS Fluent. The numerical results have been presented for different combinations of the governing dimensionless parameters (dimensionless spacing, 1.2 = L = 4; Reynolds number, 0.1 = Re = 100; power-law index, 0.2 = n = 1.8). The dependence of the kinematic and macroscopic characteristics of the flow such as streamline patterns, distribution of the surface pressure coefficient, total drag coefficient with its components (pressure and friction) and total lift coefficient on these dimensionless parameters has been discussed in detail.FindingsIt is found that the separation of the flow and the apparition of the wake region accelerate as the dimensionless spacing decreases, the number of the cylinder increases and/or the fluid behavior moves from shear-thinning to Newtonian then to shear-thickening behavior. In addition, the distribution of the pressure coefficient on the surface of the cylinders presents a complex dependence on the fluid behavior index and Reynolds number when the dimensionless spacing between two adjacent cylinders is varied. At low Reynolds numbers, the drag coefficient of shear-thinning fluids is stronger than that of Newtonian fluids; this tendency decreases progressively with increasing of Re until a critical value; beyond the critical Re, the opposite trend is observed. The lift coefficient of the middle cylinder is null, whereas, the exterior cylinders experience opposite lift coefficients, which show a complex dependence on the dimensionless spacing, the Reynolds number and the power-law index.Originality/valueThe flow over bluff bodies is a practical engineering problem. In the literature, it can be seen that the previous studies on non-Newtonian fluids are limited to the flow over one or two cylinders (effect of an odd number of cylinders on each other). Besides that, the available results concerning the flow of Newtonian fluids over three cylinders are limited to the high Reynolds numbers region only. However, this work treats the flow of non-Newtonian power-law fluids past three circular cylinders in side-by-side arrangements under a wide range of Re. The outcome of the present study demonstrates that the augmentation of the geometry complexity to three cylinders (effect of pair surrounding cylinders on the surrounded ones in what concerns Von Karman Street phenomenon) causes a drastic change in the flow patterns and in the macroscopic characteristics. The present results may be used to predict the flow behavior around multiple side-by-side cylinders.

Convection of multi-scale motions in turbulent boundary layer by temporal resolution particle image velocimetry

Experiments of particle image velocimetry (PIV) in the turbulent boundary layer at have been conducted to investigate the convection characteristic of turbulent structure and the validity of Taylor’s hypothesis. Views of (, the boundary layer thickness) were captured by four streamwise-arranged cameras. Distributions of streamwise turbulent kinetic energy on a streamwise scale were investigated by continuous-wave transform, and scales were found where the portion of streamwise turbulent kinetic energy approaches maximum. Fluctuating velocities (instant velocity minus average velocity on time dimension) were divided into large-scale motion (LSM) and small-scale motion (SSM) portions, bounded by . Convection velocities of LSM and SSM are determined by the spatiotemporal correlation method, and they are larger than local average velocities in near-wall regions, but smaller than local average velocities in wake regions. Statistical characteristics between velocity fields reconstructed by Taylor’s hypothesis and original fields were compared by the autocorrelation method, and the reconstructed field’s patterns are longer than original field’s patterns, while their heights do not have clear distinction. The correlation of original velocity fields and reconstructed fields shows that LSM can hold on over and SSM over in streamwise convection separation for regions of , given a threshold value (correlation coefficient C = 0.6).

Numerical investigation on buoyancy-driven flow over a circular cylinder in a channel with nonparallel walls

The flow over a stationary cylinder is destabilized mainly in the separated shear layer (SSL) and wake regions and transverse shedding forms downstream of the cylinder. It has been revealed that aiding/opposing buoyancy or diverging/converging channel could stabilize/destabilize the separated and wake flows, while their joint effect has not been investigated. In this numerical investigation, the low-Re buoyancy-driven flow over a circular cylinder placed in a channel consists of diverging or converging walls is studied. We aim to reveal the effects of two parameters, i.e. Richardson number Ri representing buoyancy and channel angle α, on the flow dynamics and heat transfer. The cases of aiding (Ri > 0) and opposing (Ri < 0) buoyancy, and diverging (α > 0) and converging (α < 0) channels are considered in this work. The effects of Ri and α are presented in terms of the instantaneous flow field, global characteristic quantities, heat transfer between the fluid and cylinder surface, separation and shearing of wake flow, and temperature variations of the channel walls. We found that the flow transits to steady subjected to aiding buoyancy at a lower value of Ri where the fluctuations of force and heat transfer rate reduces to zero; however, the mean drag and Nusselt number do not exhibit monotonic variations with Ri. The convection heat transfer is prone to be notably affected by Ri rather than α on the leeward side of the cylinder, and its fluctuation is significant in the separation zone downstream of the separation point. Depending on the value of Ri, the steady and unsteady wake flow present different velocity profile as well as the shearing; the deficit wake flow recovers more rapidly for the steady flow cases.

Numerical investigation of turbulent flow and mixed convection around a wavy cylinder

The performance of different scale-resolving simulation (SRS) models in resolving the turbulent flow structures and forced convection around a wavy cylinder (TFWC) at subcritical Re = 3000 is compared firstly. The SRS models include the SST scale adaptive simulation (SAS), the SST delayed detached-eddy simulation (DDES), and the production-limited DDES (PL-DDES) models. The simulation results on a coarse grid resolution testify that the PL-DDES model is superior to the SAS and DDES models. Another primary purpose is exploring the turbulent flow and mixed convection around a wavy cylinder using the PL-DDES model. For the contra flow (Richardson number = −0.3), the Strouhal number, the drag coefficient, and the Root-Mean-Square (RMS) lift coefficient decrease, but the length of the recirculation zone increases. In contrast, it is inverse results in the parallel flow (Richardson number = 0.3). Due to the buoyancy effect, the region of the 3 d flow structures in the contra flow and the parallel flow are respectively larger and smaller than those in the non-buoyancy flow. The laminar mixed convection is dominant around the cylinder in the contra flow. The turbulent mixed convection plays an essential role in the wake region for the parallel flow. In the windward region, the laminar mixed convection is dominant for both flows. The Nusselt number decreases and increases in the contra flow and the parallel flow, respectively.