Downstream Flat Plate Research Articles

The influence of different downstream plate length towards the flow-induced vibration on a square cylinder

The investigations of flow-induced vibration have been around for decades to solve many engineering problems related to structural element. In a hindsight of advancing technology of microelectronics devices, the implementation of flow-induced vibration for energy harvesting is intrigued. The influence of downstream flat plate to flow-induced vibration experienced by a square cylinder is discussed in this study to surpass the limitation of wind energy due to geographical constraints and climate change. The mechanism of flow-induced vibration experienced by a square cylinder with downstream flat plate is numerically simulated based on the unsteady Reynolds Navier–Stokes (URANS) flow field. The Reynolds number, Re assigned in this study is ranging between 4.2 times 10^3–10.7 times 10^3 and the mass damping ratio designated for the square cylinder is m^*zeta = 2.48. The influence of three different flat plate lengths w/D = 0.5, 1 and 3 is examined. Each case of different flat plate is explored for gap separation between the square cylinder and the plate in the range 0.5 leqslant G/D leqslant 3. Based on the numerical findings, the configuration of cylinder-flat plate with length w/D = 1 has shown the highest potential to harvest high energy at comparatively low reduced velocity.

Interaction of free oscillating flat plate and VIV of a circular cylinder in laminar flow

The Flow-Induced vibration around bluff bodies is always of great interest in terms of control and suppressing the motion or amplifying and harvesting energy and the flat plates are known as useful means to make proper changes in flow structure. The objective of this paper is to investigate the effect of a downstream flat plate with one degree of freedom on the wake structure and FIV of an upstream circular cylinder in laminar flow. Numerical simulation is used to simulate the two-dimensional incompressible flow around two rigid objects with identical characteristic lengths and a variable horizontal spacing in a range of 0.5D≤G≤4D to focus on the near wake and interaction of two objects. The results show that a free to vibrate flat plate located in the wake of a rigid cylinder not necessarily plays the role of a splitter in the near wake and starts to vibrate in an even small spacing such as G =1.5D. The Recirculation zone structure and its length are found to be the main reasons for induced vibration in such close configurations. In the case of simultaneous free oscillation, reducing the horizontal gap amplifies the amplitude of both objects. The interaction of the oscillating plate and the shear layers results in vortices with more strength that affect both objects. This amplification in oscillation amplitude shows that the present concept has a considerable potential to be utilized in the design of an improved energy harvesting system by converting fluid dynamic energy into electric energy from independent objects in a small area.

Study on instability of lift force by longitudinal vortex in a circular cylinder with a downstream flat plate in cruciform arrangement

Study on instability of lift force by longitudinal vortex in a circular cylinder with a downstream flat plate in cruciform arrangement

A rational method for determining intermittency in the transitional boundary layer

A new rational procedure is proposed for determining the intermittency in the streamwise direction. One of the key parameters for the intermittency determination is the selection of a threshold value, which often involves a certain level of subjectivity. Here, a reliable way of choosing the threshold value in a more objective manner is proposed. The proposed approach involves a single threshold value, equal to the magnitude of the maximum laminar perturbation in the transitional flow. The results obtained are validated with the widely used dual-slope method. In this paper, the measurements are carried out on an experimental arrangement, involving the interaction of an upstream aerofoil wake with a downstream flat plate boundary layer. As a by-product of the study, a scaling parameter has been identified which captures the length of the transition zone as the proximity of the aerofoil in the wall-normal direction is varied.Graphic abstract

Flow-induced vibration of a square cylinder and downstream flat plate associated with micro-scale energy harvester

The phenomenon of flow-induced vibration (FIV) over a square cylinder at Reynolds numbers, Re = (3.6–12.5 × 103) is numerically studied. This current study provides a detailed explanation of the behaviour of transverse motion of square cylinder with the mass damping ratio, mζ* = 2.48. The computation of FIV is conducted by numerical simulation based on the Unsteady Reynolds Navier-Stokes (URANS) flow field using OpenFOAM software. The first part of the numerical simulation consists of an isolated square cylinder to validate the solution with previous studies. The computation of FIV with a total number of cells, N = 101,662 have shown a comparable pattern of amplitude curve. The coexistence of vortex-induced vibration (VIV) and galloping is observed for a single isolated cylinder. A downstream flat plate is introduced in the second part of the work. Different gaps separation between the cylinder and flat plate (0.1 ⩽G/D ⩽ 3) are simulated. Based on the amplitude curve against reduced velocities 4 ⩽UR⩽ 20, four regimes are identified. According to the power estimation, the optimum gap separation is G/D = 0.1. The harnessed power is higher than a single isolated square cylinder while preserving the robustness for the remote harvesting purpose.

Downstream flat plate as the flow-induced vibration enhancer for energy harvesting

The prospect of harvesting energy from flow-induced vibration using an elastic square cylinder with a detached flat plate is experimentally investigated. The feasibility of flow-induced vibration to supply an adequate base excitation for micro-scale electrical power generation is assessed through a series of wind tunnel tests. The current test model of a single square cylinder is verified through a comparable pattern of vibration amplitude response with previous experimental study and two-dimensional numerical simulations based on the unsteady Reynolds averaged Navier–Stokes (URANS). In addition, a downstream flat plate is included in the wake of the square cylinder to study the effects of wake interference upon flow-induced vibration. A downstream flat plate is introduced as the passive vibration control to enhance the magnitude of flow-induced vibration and simultaneously increases the prospect of harvesting energy from the airflow. The study is conducted by varying the gap separation between the square cylinder and flat plate for 0.1≤ G/D ≤3. The highest peak amplitude is observed for the gap G/D = 1.2 with yrms/D = 0.46 at UR = 17, which is expected to harvest ten times more energy than the single square cylinder. The high amplitude vibration response is sustained within a relatively broader range of lock-in synchronization. Meanwhile, for G/D = 2 the vibration is suppressed, which leads to a lower magnitude of harvested energy. Contrarily, the amplitude response pattern for G/D = 3 is in agreement with the single square cylinder. Hence, the flat plate has no significance to the wake interference of the square cylinder when the gap separation is beyond 3D.

Sound from high-Reynolds number flow over bluff bodies

Purpose – This paper aims to investigate the aerodynamic sound generated from flow over bluff bodies at a high Reynolds number. By taking circular and square cylinders as two representative geometries for the cross-section of bluff bodies, this study aims to clarify the difference in flow formation and sound generation between the two types of bluff bodies. Furthermore, the possibility for a downstream flat plate to be used as sound cancellation passive mechanism is also discussed in this study. Design/methodology/approach – Sound source from the near field is numerically solved by using the Unsteady Reynolds-Averaged Navier Stokes equations. While for the sound at far-field, the compact sound theory of Curle’s analogy is used. Findings – Magnitude of the generated sound is dominant by the aerodynamic forcer fluctuations, i.e. lift and drag, where the lift fluctuation gives the strongest influence on the sound generation. The square cylinder emits 4.7 dB higher than the sound emitted from flow over the ci...

Numerical simulations of non‐equilibrium turbulent boundary layer flowing over a bump

AbstractLarge‐eddy simulation (LES) and Reynolds‐averaged Navier–Stokes simulation (RANS) with different turbulence models (including the standard k−ε, the standard k−ω, the shear stress transport k−ω (SST k−ω), and Spalart–Allmaras (S–A) turbulence models) have been employed to compute the turbulent flow of a two‐dimensional turbulent boundary layer over an unswept bump. The predictions of the simulations were compared with available experimental measurements in the literature. The comparisons of the LES and the SST k−ω model including the mean flow and turbulence stresses are in satisfied agreements with the available measurements. Although the flow experiences a strong adverse pressure gradient along the rear surface, the boundary layer is unique in that intermittent detachment occurring near the wall. The numerical results indicate that the boundary layer is not followed by mean‐flow separation or incipient separation as shown from the numerical results. The resolved turbulent shear stress is in a reasonable agreement with the experimental data, though the computational result of LES shows that its peak is overpredicted near the trailing edge of the bump, while the other used turbulence models, except the standard k−ε, underpredicts it. Analysis of the numerical results from LES confirms the experimental data, in which the existence of internal layers over the bump surface upstream of the summit and along the downstream flat plate. It also demonstrates that the quasi‐step increase in skin friction is due to perturbations in pressure gradient. The surface curvature enhances the near‐wall shear production of turbulent stresses, and is responsible for the formation of the internal layers.The aim of the present work is to examine the response and prediction capability of LES with the dynamic eddy viscosity model as a sub‐grid scale to the complex turbulence structure with the presence of streamline curvature generated by a bumpy surface. Aiming to reduce the computational costs with focus on the mean behavior of the non‐equilibrium turbulent boundary layer of flow over the bump surface, the present investigation also explains the best capability of one of the used RANS turbulence models to capture the driving mechanism for the surprisingly rapid return to equilibrium over the trailing flat plate found in the measurements. Copyright © 2010 John Wiley & Sons, Ltd.

Turbulence development in a non-equilibrium turbulent boundary layer with mild adverse pressure gradient

High-resolution laser-Doppler anemometer measurements were acquired in a two-dimensional turbulent boundary layer over a ramp. The goals were to provide a detailed data set for an adverse pressure gradient boundary layer far from separation and to examine near-wall behaviour of the Reynolds stresses as compared to flat-plate boundary layers. The flow develops over a flat plate, reaching a momentum thickness Reynolds number of 3350 at an upstream reference location. The boundary layer is then subjected to a varying pressure gradient along the length of the ramp and partially redevelops on a downstream flat plate. Mean velocity measurements show a log law region in all velocity profiles, but the outer layer does not collapse in deficit coordinates indicating that the boundary layer is not in equilibrium. Measurements of non-dimensional stress ratios and quadrant analysis of the two-component data indicate relatively small changes to the turbulence structure. However, the streamwise normal stress has an extended outer layer plateau, and the shear stress and wall-normal stress have outer layer peaks. Near the wall, the streamwise normal stress and shear stress collapse with flat-plate data using standard scaling, but the wall normal stress is substantially larger than flat-plate cases.

Experimental study of a separating, reattaching, and redeveloping flow over a smoothly contoured ramp

Abstract A turbulent boundary layer that separates, reattaches, and redevelops over a smoothly contoured ramp and a downstream flat plate has been examined. In order to resolve the flow in the viscous sublayer, a custom-built, two-dimensional LDA with a very high resolution was used. A small separation bubble occurred over the trailing edge of the ramp. The v ′ v ′ and − u ′ v ′ Reynolds stress components increased rapidly in the adverse pressure gradient boundary layer, and developed large outer layer peaks aligned with the inflection point in the mean velocity profile. The high stress levels were nearly unchanged by the reattachment process, decaying only after the mean velocity profile recovered and outer-layer production dropped. A key feature is that the inner layer recovered relatively quickly to a typical turbulent boundary layer in the redeveloping region, while the outer layer recovery was retarded by the large eddies generated in the separation region.

Interference Drag of a Turbulent Junction Vortex

The interference drag identified with the junction of a streamlined cylindrical body and a flat plate was investigated. The junction drag was calculated from a set of detailed, self consistent, high quality data using a control volume approach. The drag for the isolated flat plate and streamlined cylinder making up the junction was calculated using boundary-layer solvers together with surface pressure measurements. For the particular and relatively thick body under consideration, the results show a significant increase in drag due to the junction. These and other available results indicate that the interference drag has a systematic dependence on the thickness to chord ratio. The junction vortex wake increases the downstream flat plate drag significantly. Because of this effect, a unique value for the drag force, drag coefficient, or induced drag coefficient for a junction vortex flow would require that the geometry be specified in detail. The induced drag and the total pressure losses identified with the junction are also reported.

The interference between two flat plates normal to a stream in staggered arrangement. 2nd report Vortex shedding.

The frequency of vortex shedding from two flat plates normal to a stream is experimentally investigated in various staggered arrangements at a Reynolds number of 2.60 ×104. The Strouhal number of vortex shedding varies widely from 0.067 to 0.343 for the upstream flat plate, and from 0.067 to 0.170 for the downstream flat plate. Four kinds of discontinuities in Strouhal number distributions are found. Flow visualizations suggest that wake widths behind the flat plates and path lines of shedding vortexes have an important influence on discontinuities of the Strouhal number. As long as distances between two centers of flat plates are larger than 2 chords, the wake Strouhal number, defined by the wake width, nearly equals that for a single flat plate, 0.156.