Flow Around Three Side-by-Side Square Cylinders and the Effect of the Cylinder Oscillation

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Bhupendra Singh More ◽  
Sushanta Dutta ◽  
Bhupendra Kumar Gandhi
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Drag Coefficient ◽  
Flow Structure ◽  
Power Spectra ◽  
Square Cylinders ◽  
Spacing Ratio ◽  
Hotwire Anemometry ◽  
Visualization Techniques ◽  
Flow Interference

Abstract In this study, the flow field over three square cylinders (SCs) arranged side by side is investigated in a low-speed wind tunnel. The experiments are performed with three similar SCs for Reynolds number (Re) 295. The influences of spacing ratio on the wake size, drag coefficient, and flow interference of the cylinders are reported with the hotwire anemometry, particle image velocimetry (PIV), and the flow visualization techniques. Special attention is paid to the oscillation given to the middle cylinder and its effect on flow structure and related forces. The spacing ratio (s/D) ranges from 1.5 to 3, whereas the forcing frequency ratio ranges from 0.5 to 2 with amplitude of 10% of the cylinder width. It is observed that the spacing influences the flow structure, and the vortex shedding mechanism strongly. A secondary frequency appears in the flow field for spacing ratio s/D = 2 and 3. Depending upon the spacing ratios, the flow pattern is seen to be asymmetric biased, symmetric biased, and weakly interactive. The wake interaction decreases with increase in spacing ratios. With the oscillations, the wake becomes more unstable and complex. Additional wake oscillation frequency appears in the power spectra. With an increase in spacing ratios, the drag coefficient decreases, whereas with oscillations, higher drag force is observed compared to a stationary cylinder. A correlation is developed between the time-averaged drag coefficient with cylinder spacing and Reynolds number.

scholarly journals Interactions between Two Deformable Droplets in Tandem Fixed in a Gas Flow Field of a Gas Well

2021 ◽  
Vol 11 (23) ◽  
pp. 11220
Author(s):  
Zhibin Wang ◽  
Tianli Sun ◽  
Zhongwei Yang ◽  
Guo Zhu ◽  
Hongyan Shi
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Drag Coefficient ◽  
Drag Force ◽  
High Reynolds Number ◽  
Droplet Breakup ◽  
Gas Well ◽  
Body Forces ◽  
Simulation Results ◽  
High Reynolds

Knowing the droplet-deformation conditions, the droplet-breakup conditions, and the drag force in the interaction between two droplets with a high Reynolds number is of importance for tracking droplet movement in the annular flow field of a gas well. The interactions between two droplets with a high Reynolds number in a tandem arrangement fixed in flowing gas was investigated. The volume of fluid (VOF) method was used to model the droplets’ surface structure. Two different body forces were exerted on both droplets to hold them suspended at a fixed location, which eliminated the effect of droplet acceleration or deceleration on the drag and decreased the amount of computation required. The exerted body forces were calculated using the Newton iteration procedure. The interactions between the two droplets were analyzed by comparison with the simulation results of a single isolated droplet. The effect of the separation distance on the drag force was investigated by changing the separation spacing. The simulation results showed that for droplets with a small separating space between them, the dynamics of the downstream droplet were influenced significantly by the upstream droplet. The drag coefficient of the downstream droplet decreased considerably to a small, even negative, value, especially for droplets with higher Weber numbers and smaller initial separating spaces between them, while the drag force of the upstream droplet was influenced only slightly. In addition, a formula for predicting the final drag coefficient of the downstream droplet was devised.

Passage Flow Structure and its Influence on Endwall Heat Transfer in a 90° Turning Duct: Turbulent Stresses and Turbulent Kinetic Energy Production

1996 ◽  
Author(s):  
Brian G. Wiedner ◽  
Cengiz Camci
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
High Resolution ◽  
Kinetic Energy ◽  
Flow Field ◽  
Turbulent Kinetic Energy ◽  
Flow Structure ◽  
Three Dimensional ◽  
Duct Flow ◽  
Turbulent Flow Field

The complex interaction between three-dimensional passage flow structure and endwall convective heat transfer in a square cross section, 90° turbulent duct flow has been experimentally investigated. Fine details of the momentum and heat transport process in a laboratory model that simulated a high Reynolds number three-dimensional passage flow are presented. The specific flow and heat transfer mechanisms are frequently encountered in the hot mainstream of axial flow turbines and internal coolant passages. Similar physical phenomena may also be observed in many other fluid machinery systems. The mean radius to duct width ratio was 2.3 and the Reynolds number based on inlet center line velocity, duct width, and ambient conditions was approximately 360,000. The complete Reynolds stress tensor was measured using a triple sensor hot wire. The turbulent normal and shear stresses, turbulent kinetic energy, and production of turbulent kinetic energy are presented. A steady state heat flux measurement technique and liquid crystal thermography were used to determine the character of the endwall heat transfer in the form of a high resolution heat transfer map. The flow field was dominated by strong counter rotating secondary flows characteristic of 90° turning ducts. The flow structure also included areas of strong streamwise accelerations and decelerations, high vorticity, local regions of significant total pressure loss, and a complex turbulent flow field structure. The development of the turbulent features of the 90° turning duct flow field and the influence of the turbulent flow field on the endwall convective heat transfer distribution are discussed. The multi-dimensional flow and high resolution heat transfer results are currently being incorporated in computational aerothermal models under development at Penn State University. The results are also available as a data base for future aerothermal model validation studies.

Drag Reduction of Ground Vehicles Using Air-Injected Wheel Deflectors

2019 ◽  
Author(s):  
Kaloki L. Nabutola ◽  
Sandra K. S. Boetcher
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Drag Coefficient ◽  
Parametric Study ◽  
Ground Vehicles ◽  
Ground Vehicle ◽  
Flow Modification ◽  
Air Jets ◽  
Air Jet ◽  
The Impact

Abstract Numerical simulations of flow modification devices on a simplified ground vehicle are conducted. A parametric study on the size and distance upstream of conventional wheel deflectors is conducted on a simplified body at a Reynolds number of 1.6 × 105 to observe the impact on drag coefficient. Results show that wheel drag is decreased as the height of the conventional wheel deflector is increased. Additionally, the further the conventional wheel deflector is from the wheelhouse, the more sensitive the wheel is to changes in drag coefficient. The conventional wheel deflectors are then replaced by air-jets which are used to manipulate the flow field in and near the wheelhouse to reduce the wheel drag of the simplified body. The air-jet successfully decreases the wheel drag and it is observed that the closer the air-jet is to the wheelhouse the less impact it has on the single wheel drag, but the greater the impact on the overall drag of the simplified body.

Measurements and Visualizations of the Unsteady Flow Field on a Freely Falling Plate

2013 ◽  
Vol 718-720 ◽  
pp. 1049-1054 ◽  
Author(s):  
Wen Tao Huang ◽  
Qi Zhou ◽  
Fu Xin Wang ◽  
Hong Liu ◽  
Jun Qi Wu
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Unsteady Flow ◽  
Flow Structure ◽  
Mode Switching ◽  
Stable Mode ◽  
The Past ◽  
Chaotic Mode ◽  
Unsteady Characteristics ◽  
Stable Flow

Freely falling of a plate contains very complicated unsteady characteristics. In the past decades, most of the studies focused on the mode and trajectoryofa freely falling plate. In this paper, we use PIV to study the instantaneous flow structure and analyze the force exerted on the plate and the influence of the flow on the motion of the plate. As the Reynolds number increases, the flow structure will be changed from the stable mode to the chaotic mode,and it accompanies with a mode switching of the freely falling plate. However, there is no necessarilycorresponding with the stable flow structure, even for the freely falling plate with a stable mode.

Experimental Investigation of Flow Over a Transversely Oscillating Square Cylinder at Intermediate Reynolds Number

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Manish Kumar Chauhan ◽  
Sushanta Dutta ◽  
Bhupendra Kumar Gandhi ◽  
Bhupendra Singh More
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Square Cylinder ◽  
Electromagnetic Actuators ◽  
Image Velocimetry ◽  
Oscillating Square Cylinder ◽  
Recirculation Length ◽  
Visualization Techniques

This paper presents an experimental study of flow over a square cylinder oscillating in transverse direction. The Reynolds number selected for present study is 485. Limited study has also been made for two other Reynolds numbers, namely, 295 and 775. The objective of the present study is to modify the near-wake flow structure using actuation of the cylinder for possible reduction in drag force. Transverse oscillations to the cylinder are provided using electromagnetic actuators. The flow field is investigated using two-dimensional (2D)-particle image velocimetry (PIV) system, hotwire anemometer (HWA), as well as flow visualization techniques. The effect of oscillation frequency and the amplitude on parameters like Strouhal number, drag coefficient, recirculation length, power spectrum, and Reynolds stress are studied. It is observed that the recirculation length is reduced significantly with increase in forcing frequency, and consequently drag coefficient is also reduced. For a constant forcing frequency, the vortex strength is reduced with the increase in the amplitude. Further, variation of instantaneous spanwise vorticity shows that separated shear length decreases with increase in forcing frequency. As a result, vortices are moved closer to the cylinder. These phenomena affect the forces acting on the cylinder. Lock-on is also observed at a frequency close to the vortex shedding frequency of the stationary cylinder.

Characteristic model-based adaptive control for cryogenic wind tunnels

2020 ◽  
pp. 014233122096065
Author(s):  
Chenhui Yu ◽  
Fei Liao ◽  
Haibo Ji ◽  
Wenhua Wu
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Flow Field ◽  
Control Problem ◽  
Mimo System ◽  
Adaptive Controller ◽  
Characteristic Model ◽  
Model Based ◽  
Field Control ◽  
Cryogenic Wind Tunnel

With the increasing requirement of Reynolds number simulation in wind tunnel tests, the cryogenic wind tunnel is considered as a feasible method to realize high Reynolds number. Characteristic model-based adaptive controller design method is introduced to flow field control problem of the cryogenic wind tunnel. A class of nonlinear multi-input multi-output (MIMO) system is given for theoretical research that is related to flow field control of the cryogenic wind tunnel. The characteristic model in the form of second-order time-varying difference equations is provided to represent the system. A characteristic model-based adaptive controller is also designed correspondingly. The stability analysis of the closed loop system composed of the characteristic model or the exact discrete-time model and the proposed controller is investigated respectively. Numerical simulation is presented to illustrate the effectiveness of this control method. The modeling and control problem based on characteristic model method for a class of MIMO system are studied and first applied to the cryogenic wind tunnel control field.

scholarly journals Simulation of Gas Flow Over a Micro Cylinder

2009 ◽  
Author(s):  
Yuan Hu ◽  
Quanhua Sun ◽  
Jing Fan
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Drag Coefficient ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Low Reynolds Number ◽  
Pressure Drag ◽  
Low Reynolds ◽  
Rarefied Gas Effect ◽  
Gas Effect

Gas flow over a micro cylinder is simulated using both a compressible Navier-Stokes solver and a hybrid continuum/particle approach. The micro cylinder flow has low Reynolds number because of the small length scale and the low speed, which also indicates that the rarefied gas effect exists in the flow. A cylinder having a diameter of 20 microns is simulated under several flow conditions where the Reynolds number ranges from 2 to 50 and the Mach number varies from 0.1 to 0.8. It is found that the low Reynolds number flow can be compressible even when the Mach number is less than 0.3, and the drag coefficient of the cylinder increases when the Reynolds number decreases. The compressible effect will increase the pressure drag coefficient although the friction coefficient remains nearly unchanged. The rarefied gas effect will reduce both the friction and pressure drag coefficients, and the vortex in the flow may be shrunk or even disappear.

scholarly journals Sensitivity analysis of FDA´s benchmark nozzle regarding in vitro imperfections - Do we need asymmetric CFD benchmarks?

2020 ◽  
Vol 6 (3) ◽  
pp. 78-81
Author(s):  
Michael Stiehm ◽  
Christoph Brandt-Wunderlich ◽  
Stefan Siewert ◽  
Klaus-Peter Schmitz ◽  
Niels Grabow ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
In Silico ◽  
Nozzle Geometry ◽  
Geometrical Imperfection ◽  
Custom Made ◽  
Inlet Conditions ◽  
Silicone Model ◽  
Bench Testing

AbstractModern technologies and methods such as computer simulation, so-called in silico methods, foster the development of medical devices. For accelerating the uptake of computer simulations and to increase credibility and reliability the U.S. Food and Drug Administration organized an inter-laboratory round robin study of a generic nozzle geometry. In preparation of own bench testing experiment using Particle Image Velocimetry, a custom made silicone nozzle was manufactured. By using in silico computational fluid dynamics method the influence of in vitro imperfections, such as inflow variations and geometrical deviations, on the flow field were evaluated. Based on literature the throat Reynolds number was varied Rethroat = 500 ± 50. It could be shown that the flow field errors resulted from variations of inlet conditions can be largely eliminated by normalizing if the Reynolds number is known. Furthermore, a symmetric imperfection of the silicone model within manufacturing tolerance does not affect the flow as much as an asymmetric failure such as an unintended curvature of the nozzle. In brief, we can conclude that geometrical imperfection of the reference experiment should be considered accordingly to in silico modelling. The question arises, if an asymmetric benchmark for biofluid analysis needs to be established. An eccentric nozzle benchmark could be a suitable case and will be further investigated.

Survey on the Indirect Methods of Potential Flow Used for the Optimization of Airships Profile

2014 ◽  
Vol 554 ◽  
pp. 717-723
Author(s):  
Reza Abbasabadi Hassanzadeh ◽  
Shahab Shariatmadari ◽  
Ali Chegeni ◽  
Seyed Alireza Ghazanfari ◽  
Mahdi Nakisa
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flow Field ◽  
Drag Coefficient ◽  
Body Surface ◽  
Potential Flow ◽  
The Body ◽  
Indirect Methods ◽  
Singularity Method ◽  
Singularity Distribution

The present study aims to investigate the optimized profile of the body through minimizing the Drag coefficient in certain Reynolds regime. For this purpose, effective aerodynamic computations are required to find the Drag coefficient. Then, the computations should be coupled thorough an optimization process to obtain the optimized profile. The aerodynamic computations include calculating the surrounding potential flow field of an object, calculating the laminar and turbulent boundary layer close to the object, and calculating the Drag coefficient of the object’s body surface. To optimize the profile, indirect methods are used to calculate the potential flow since the object profile is initially amorphous. In addition to the indirect methods, the present study has also used axial singularity method which is more precise and efficient compared to other methods. In this method, the body profile is not optimized directly. Instead, a sink-and-source singularity distribution is used on the axis to model the body profile and calculate the relevant viscose flow field.

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