Cylinder In Flow Research Articles

Effect of microfibres placed at the front stagnation point of a circular cylinder on aerodynamics and wake flow

We experimentally investigated the control effectiveness of circular cylinder flow and the mechanism of self-adaptive microfibres inspired by bird feathers. The nylon wires were placed at the front stagnation point of a circular cylinder at a Reynolds number of Re = 2.67×104. Surface pressure measurement was employed to analyse the unsteady aerodynamic forces around the circular cylinder, and a high-speed particle image velocimetry measurement system was used to visualise and analyse the wake flow structures. The results indicate that the nylon wires at a high length ratio L/D evidently suppress the Reynolds stress and turbulent kinetic energy, thus suppressing the fluctuating lift and mean drag forces of a circular cylinder. In addition, the nylon-induced vortex at high L/D values can inhibit the interaction of the original shear layers to moderate the von Kármán vortex street behind the cylinder. However, the control effect is limited at low L/D values because the nylon-induced vortex structures cannot reach the wake field and interact with the shear layer.

Novel Approach to Improve Stability and Convergence of Flowfield Solution Processes: Mode Multigrid

In the field of computational fluid dynamics, stability and convergence problems are often encountered when solving the governing equation. This paper studies the effect of the mode multigrid on the stability and convergence of iterative algorithms. By further analyzing the mechanism for accelerating the convergence of mode multigrid, a new adaptive mode multigrid (AMMG) is proposed, and an adaptive selection criterion is formulated for the parameters of dynamic modal decomposition, which can accurately identify and filter out the unstable modes in the flowfield, thus efficiently obtaining the accurate steady solution. In the cases of laminar flow past circular cylinder and turbulent flow past airfoil, the AMMG significantly improves the stability of the iterative algorithm; in the case of transonic flow past airfoil, the AMMG solves the problem of shock wave shaking during the iteration, and the convergence is significantly improved. In summary, the AMMG method significantly enhances the stability and convergence of the iterative algorithm, and can be used as an effective convergence-preserving computation strategy.

Self-adaptive turbulence eddy simulation of flow control for drag reduction around a square cylinder with an upstream rod

The use of an upstream circular rod to control the flow around a downstream square cylinder is found to efficiently reduce the drag of the square cylinder. The complex flow characteristics and mechanism of the rod-square system in tandem arrangement as a passive flow control method for various centre-to- centre gap ratios (L/D) are investigated by numerical simulation. Turbulence modelling of the rod-square cylinder system is challenging. To select a suitable turbulence modelling, the recently developed Self-Adaptive Turbulence Eddy Simulations (SATES), as well as IDDES (Improved Delayed Detached Eddy Simulation) and SBES (Stress Blended Eddy Simulation) are first assessed for single circular and single square cylinder flow test cases. The SATES method performs best among the three models for bluff body flow simulation and is thus used in the drag flow control study. For the rod-square flow control system, the Reynolds number is 34000 based on freestream velocity U0 and the edge length of the square cylinder D. The diameter of the control rod is kept constant at d/D = 0.18. The flow characteristics and mechanism are explored in detail, varying the rod and square cylinder distance of L/D = 1.5, 2.0, 2.5and 3.0. According to the absence or presence of vortex shedding from the upstream rod cylinder, two flow patterns (pattern I and pattern II) are observed. Large drag reduction is observed for all the simulation cases the maximum drag reduction is approximately 63% with L/D = 2.0, and the minimum drag reduction approximately 53% with L/D = 3.0. The secondary lock-frequency, which presents as pattern II, is caused by the excitation of upstream vortices. It is found that the side recirculation is associated with the wake recirculation length of the square cylinder, which is similar to the elongated cylinder in the flow pattern I. The flow mechanism of suppression of the vortices from the rod can be attributed to the effective diffusion of vorticity in the separating shear layer caused by the presence of the front wall of the square cylinder.

Passive control of wake flow behind a square cylinder using a flat plate

In this study, control over the wake flow of a single square cylinder exercised by a flat plate attached to the rear side of the cylinder is analyzed numerically via the lattice Boltzmann method. The Reynolds number (Re) is fixed at 150, and the length of the plate is varied from 0.1 to 8.5. Three distinct flow modes are observed in this study: unsteady, transient, and steady flow in the cases of plate lengths (L) in the ranges 0.1 ≤L≤ 6.5, 6.75 ≤L≤ 7.5, and 7.75 ≤L≤ 8.5, respectively. The streamlines exhibit different flow structures, termed hairpin-like, ellipse-like, and elongated bubble-like, at different values of L. Complete wake control is achieved at plate lengths beyond 7.75. This study reveals that the drag and lift coefficients exhibit unsteadiness at short plate lengths in early time steps, but as the plate length increases, unsteadiness slows down and eventually disappears, confirming the steady flow pattern. The mean drag coefficient (CDm), Strouhal number (St), and root-mean-square value of drag and lift coefficients (CDrms; CLrms) are reduced by maximums of 23.5%, 100%, 84.6%, and 99.5%, respectively, as a result of the presence of the plate.

Dairesel Silindir Çevresindeki Pasif Akış Kontrolünün Sayısal İncelenmesi

The effects of a perforated cylinder on the passive flow control around a circular cylinder mounted on a wall were investigated. The perforated cylinder was placed outside of the single circular cylinder concentrically. The large-eddy simulation was used to resolve the flow field. The study was aimed at both reducing the drag coefficient of the single cylinder and controlling the fluctuating forces acting on the single cylinder caused by vortex shedding in the downstream wake. The results showed that the structure of the downstream wake flow of the single cylinder changed significantly after placing the perforated cylinder. For example, von Karman vortices disappeared, and the maximum magnitude of turbulent kinetic energy, TKE, in the downstream wake was reduced. The time-averaged drag coefficient of the single cylinder was decreased by 69%. In addition, the maximum value of the lift coefficient of the single cylinder was reduced by eight times when the perforated cylinder was placed outside the single cylinder.

Coupling between vortex flow and whisker sensor in cylinder wakes with time-varying streamwise gaps

The flow-induced vibration of a whisker in the wake of a movable circular cylinder with time-varying streamwise gaps is experimentally investigated to understand how whiskers detect variations in the swimming status of an upstream target. The results show that whisker sensitivity to gap growth rates gradually decreases when such growth rates become sufficiently high, regardless of initial gaps. From the integrated experimental measurements and theoretical model, the reduction of whisker sensitivity under high gap growth rates can be attributed to sufficiently strong vortices initiated by fast movement of the upstream cylinder, which compensate vortex strength decay due to the gap growth.

Actuation of an electrohydraulic manipulator with a novel feedforward compensation scheme and PID feedback in servo-proportional valves

Achieving good tracking control beyond 0.1Hz by electrohydraulic manipulators still remains challenging due to the coupling of nonlinear actuation dynamics and multiple actuations. A novel order-separated feedforward, or FF, model has been proposed for estimating the major part of the commands of servo-proportional valves for metering their ports to monitor oil flow in the paired cylinders. Motion studies have been executed in serial manipulation mode by using such control to two valves and in serial–parallel mode to eight valves. Oil leakage and cylinder friction have been included as lower-order effects for the narrow radial clearance and near-zero lap in the valves each paired with a low-friction cylinder. Other assumptions of negligible inertia and suspended weight under the pistons have been validated by a numerical exercise. A PID feedback has been added during real-time tracking by an FFPID controller. Reciprocating and circular motion demands in the serial mode and heave tracking in serial–parallel mode, all in a vertical plane, have been executed. More precise and smoother tracking has been achieved up to 1Hz in the serial mode mostly with lower expense of energy than a conventional PID-alone controller. Results indicate FF guidance to mitigate oscillations occasionally apparent in PID-only case due to either hunting among multiple solutions or gain sensitivity of the nonlinear system. Good heave tracking has been obtained up to 0.2Hz. Substantial disturbance rejection capability of the controller has been demonstrated against tension arising from the connecting oil hoses. A potential use of the FF model in diagnosing emerging valve or cylinder fault with their aging has also been explained.

Research on the External Fluid Flow of a Round Cylinder with CFD

Fluid mechanics is a frequently applied discipline, and technology advancements have substantially improved how engineers’ approach and solve issues, and one of them is CFD. The purpose of the study was to evaluate how closely CFD adheres to accepted engineering principles. Selected CFD conducts computations to compare the magnitude and direction of drag coefficient changes under conditions of rising Reynolds number by simulating conditions in a wind tunnel to gather data on the object's reaction to fluid velocity. Within this range, the drag coefficient decreases with increasing Reynolds number. The simulated Reynolds number and drag coefficient do have a consistent relationship with the facts.

Square cylinder flow controlled by a synthetic jet at one leading edge

Shear layers separating from opposite sides of a bluff body are inherently connected with near wake flow structures; interfering one of the shear layers may lead to dramatic changes in the near wake flow and fluid forces on the bluff body. Being motivated by this, we investigate the square cylinder flow disturbed by a synthetic jet at one leading edge of the cylinder. Large-eddy simulations are conducted at a Reynolds number Re = 5.0 × 103. The synthetic jet is driven by a sine function with frequency fj = 0–1.65 fo and magnitude Vj,o = 0–1.0 Uo (corresponding to momentum coefficient Cμ = 0–1.01%), where Uo is the free stream velocity, and fo is the dominant vortex-shedding frequency of the uncontrolled flow. The results indicate a strong dependence of fluid forces and flow structures on Cμ and fj. Time-mean drag (C¯d) and fluctuating lift (Cl,rms) are significantly reduced at high fj (>1.21 fo) and Cμ (>0.25%), compared to those of the uncontrolled flow; the maximum reductions in C¯d and Cl,rms are up to 39% and 33%, respectively, at the highest fj = 1.65 fo and Cμ = 1.01% considered presently. Modifications of the near wake flows by the synthetic jet perturbations of different frequencies are discussed based on instantaneous, time-mean, and phased-averaged results. A high efficiency is attained by the present control strategy.

Hydraulic System Design and Simulation of the Lifting Device for the Hanging Barrel Campus Garbage Truck

According to the parameters of the Chengliwei CLW5165ZZZD5 garbage truck, the hydraulic system of the lifting device is designed and simulated. Firstly, the working pressure of the hydraulic system is calculated, and then the type of hydraulic components required is designed and selected; Secondly, the hydraulic system sketch is established through AMESim software and the parameter simulation is carried out; Finally, the variation law of pressure, flow, speed, displacement and other parameters of the hydraulic cylinder is analyzed. The results show that the lifting device can make the Chengliwei self-loading garbage truck work normally, and the design requirements meet the working requirements.

Experimental Study of Heat Transfer During Quenching of Steel Cylinders in Boiling Nanofluid

Current study was dedicated to explore cooling performance of TiO2 nanofluid. Preliminary tests have shown the possibility of significant improvement of emergency cooling performance by nanofluids in the case of overheated surfaces. Tests that were held during current investigation were performed with cylinders of stainless steel, which were used as an overheated surface. The temperature was recorded by a digital system of 3 type-K thermocouples. The object, preheated in a furnace to high temperatures (600–800 °C), was immersed into boiling distilled water. Usage of the set of thermocouples allows to determine heat flow in steel cylinder by its temperature distribution. The implementation of emergency cooling was to add a certain amount of nanofluid concentrate to the volume of boiling distilled water. The experiment was continued until the complete cooling of the object (up to 100 °C—the temperature of the surrounding liquid). Calculations confirmed increase of heat transfer coefficient for NF and, respectively, about 40% decrease in cooling time for NanoFluid compared to distilled water was observed. Three method of determination of heat transfer coefficient were compared.

On the cylinder noise and drag reductions in different Reynolds number ranges using surface pattern fabrics

This study experimentally investigates the potential of using surface pattern fabrics for the cylinder noise and drag control in different Reynolds number ranges. The aerodynamic and aeroacoustic effects were evaluated through the noise and force measurements in an anechoic wind tunnel. It was observed that the noise and drag reductions take place simultaneously but in different Reynolds number ranges, corresponding to the cylinder flow in different flow regimes, e.g., sub-critical, critical, and supercritical flow regimes. Microphone arc array measurements reveal that the suppression of the Aeolian tone in the critical regime is the major cause of noise reductions, and the noise directivity gradually loses dipole features in the critical and supercritical flow regimes, which is probably related to the reduced lift fluctuation coefficient and the spanwise segment of the sound sources. Further hotwire wake survey revealed significant changes in flow dynamics, which explain the variations of noise and drag in different flow regimes. We have shown for the first time that fabric with different surface patterns can effectively reduce cylinder drag and noise in different Reynolds number ranges. Since the Reynolds number is a key factor that determines the flow state in practical engineering applications, e.g., cycling aerodynamics, this study suggests that optimal drag and noise reductions can be realized by employing the combinations of different surface pattern fabrics to account for the Reynolds number effects.

Effects of flexible films on the aerodynamics of a 5:1 rectangular cylinder

The present study demonstrates the aerodynamics of a 5:1 rectangular cylinder with flexible films perpendicularly mounted on its upper surface at both the upstream and downstream ends in wind angle of attack (AOA) up to 20°. Flow and pressure fields around the cylinder are examined by smoke-wire visualizations and pressure measurements in a wind tunnel, respectively. Experimental results show that periodic flapping-induced vortices (FIVs) chiefly caused by the leading-edge flapping film play important roles in the cylinder flow and pressure field properties. The FIVs have a positive effect on the reattachment of the cylinder leading-edge shear layer. For the leading-edge film, the tip of the flapping film would touch down on the cylinder upper surface due to the large amplitude flapping of the film at fD/U∞ ≈ 0.811 (f is the film flapping frequency, D is the model characterized length, and U∞ is the free oncoming flow velocity). Meanwhile, the periodic FIVs dominate the cylinder flow and aerodynamic properties in the range of AoA = [0°, 8°), thus defined as the wall-flapped mode. With an increase in AoA = [8°, 20°], the tip of the flapping leading-edge film would not touch down owing to the small amplitude flapping of the film. Simultaneously, the periodic FIVs have limited effects on the cylinder flow and aerodynamic properties, thus named as the free-flapping mode. Compared to the without flexible films case, the scale of the FIVs is smaller than that of the impinging leading-edge vortices but in a higher frequency, resulting in a quick dissipation of the cylinder impinging shear layer instability, rapid recovery of the pressure on the cylinder upper surface, and reductions in the cylinder drag coefficient, lift coefficient, moment coefficient, and spanwise correlation. For the trailing-edge film, it flaps at fD/U∞ ≈ 0.650 and has a limited effect on the cylinder flow and aerodynamic properties. Finally, the flexible films can significantly mitigate the static stall of the rectangular cylinder, which may stabilize the elongated bluff bodies.

Free Convection Caputo-Fabrizio Casson Blood Flow in the Cylinder with Slip Velocity

Recently, fluid with fractional-order derivative model attracted many researchers to further study compared with the classical fluid mode since it is more precise and realistic. To imitate the applications of blood flow in narrow arteries, researchers focused on the fractional Casson fluid flow in the cylinder. However, most researchers solved the problems numerically and without considering the slip effect at the boundary. Thus, obtaining solutions analytically to the unsteady fractional Casson fluid flow in the slip cylinder with free convection is the goal of this study. The Caputo-Fabrizio fractional derivative approach is utilized to model this problem. By joining the approach of the Laplace transform and finite Hankel transform, the fractional governing equations are solved, and analytical solutions to the velocity and temperature profiles are gained. The fluid velocity rises as the slip velocity and Grashof number increase and it declines with the increment of the Casson parameter and Prandtl number. Increasing the fractional parameter will result in an increase in fluid velocity and temperature for a large time interval. The slip velocity effect influenced fluid flow, especially at the cylinder’s wall. These findings are beneficial to explore the more fractional-order derivative model and for studying the problems in biomedical engineering.

Image and video compression of fluid flow data

We study the compression of spatial and temporal features in fluid flow data using multimedia compression techniques. The efficacy of spatial compression techniques, including JPEG and JPEG2000 (JP2), and spatiotemporal video compression techniques, namely H.264, H.265, and AV1, in limiting the introduction of compression artifacts and preserving underlying flow physics are considered for laminar periodic wake around a cylinder, two-dimensional turbulence, and turbulent channel flow. These compression techniques significantly compress flow data while maintaining dominant flow features with negligible error. AV1 and H.265 compressions present the best performance across a variety of canonical flow regimes and outperform traditional techniques such as proper orthogonal decomposition in some cases. These image and video compression algorithms are flexible, scalable, and generalizable holding potential for a wide range of applications in fluid dynamics in the context of data storage and transfer.Graphic abstract

Time‐dependent pressure‐driven flow in a horizontal cylinder filled with a bidisperse porous material

AbstractSome properties of time‐dependent that modify Brinkman equations for fluid flow in a cylindrical tube filled with Bidisperse Porous Material are discussed in this article. The fluid velocities through the fracture and porous phases of the Bidisperse Porous Medium (BDPM) resulting from the application of pressure gradient are described by two coupled second‐order partial differential equations. Laplace transform technique, D'Alembert and Riemann‐Sum Approximation Methods are used to obtain a semianalytical solution for the model. The choice of the D'Alembert is made to systematically decouple the coupled governing equations without altering their initial orders. The role of the coupling parameter: The coefficient of momentum transfer in the flow formation is considered. Accordingly, three cases are analyzed: (a) weak coupling which described the fluid flow in the absence of the coupling parameter, (b) the strong coupling resulting from a large value of the coupling parameter , and (c) fluid momentum for any arbitrary value of . It is observed that fluid stability is attained when and are decreased; a finding that agrees with the findings of Nield and Kuznetsov and Magyari. Also, the maximum velocity in the fracture phase of the BDPM is attained when the coefficient of momentum transfer is neglected while an opposing flow formation is demonstrated in the fracture and porous phases of BDPM as is increased.

NUMERICAL INVESTIGATION OF FORCED CONVECTION HEAT TRANSFER AROUND AND THROUGH AN ELLIPTICAL POROUS CYLINDER

Convection heat transfer from a heated elliptical porous cylinder in the incompressible and laminar cross-flow is studied numerically. The effects of Darcy number (10<sup>-6</sup> ≤ Da ≤ 10<sup>-2</sup>), aspect ratio (0.2 ≤ AR ≤ 5), Prandtl number (0.7 ≤ Pr ≤ 70), Reynolds number (10 ≤ Re ≤ 40), on the average Nusselt number (Nu), as well as the lift and the drag coefficients are investigated. Two types of thermal boundary conditions for porous cylinder are investigated: uniformly distributed heat source and constant temperature. The fluid flow in the porous medium is numerically simulated by the superficial velocity model. Additionally, the energy equation in the porous medium is simplified by the local thermal equilibrium (LTE) hypothesis. It is concluded that the aspect ratio of the elliptical cylinder has a great influence on the heat transfer and fluid flow characteristics of this problem. Results show that increasing the Darcy number increases the Nusselt number and decreases the drag coefficient of the porous cylinder. Moreover, values of Da smaller than 10<sup>-4</sup> resemble the fluid flow and heat transfer characteristics of the impermeable solid cylinder.

"Study of Unsteady Fluid Flow of Co-Axial Cylinder through Porous Medium"

"Study of Unsteady Fluid Flow of Co-Axial Cylinder through Porous Medium"

Effect of Confinement of Flow by Side Walls on the Cross Flow

The effect of confinement of flow over the transversal coordinate on cross flow past a circular cylinder at the Reynolds numbers from 40 to 255 (based on the cylinder diameter and the undisturbed flow velocity) is studied numerically and experimentally. In the experiments, the cylinder was located in a rectangular channel and, in the case of numerical simulation, three types of the boundary conditions, namely, the periodic boundary conditions and the slip and no-slip conditions were imposed on the side walls confining the flow. Particular attention is concentrated on the vertical flow structure in the cylinder wake. It is shown that spiral vortices that travel in the plane of symmetry of the channel are formed only in the case of no-slip boundary conditions in the region of junction of the cylinder and the side walls. Under their interaction, vortex clusters are formed in the center of channel and some indications to flow turbulization can be observed in the wake. Under the periodic boundary conditions and the slip conditions on the side walls, there are no spiral vortices and, in the Re range from 200 to 250, the A and B modes of three-dimensional instability and turbulence transition are implemented in the cylinder wake. The effect of the channel width and the type of boundary conditions on the side walls on the vortex wake structure behind the cylinder and integral flow parameters is estimated.

Численное моделирование турбулентных потоков на основе двухжидкостной модели турбулентности

This paper discusses the capabilities of a two-fluid turbulence model for solving complex physical problems such as separated flow around a square cylinder and laminar-turbulent flow in a suddenly expanding channel. The numerical solution to the system of hydrodynamic equations is implemented using a finite-difference scheme. At each time step, the velocities are corrected through pressure calculations according to the SIMPLE algorithm. For verification purposes, the obtained numerical results are compared with available experimental data. A comparison of numerical results has shown that the two-fluid model is easy to implement, requires less computational resources and is capable of predicting laminar and turbulent flows with high accuracy.