scholarly journals Drag Reduction of Circular Cylinder using Square Disturbance Body at 600 Angle by 2D Numerical Simulation Unsteady-RANS

2017 ◽  
Author(s):  
Rina ◽  
Ruzita Sumiati
Keyword(s):  
Circular Cylinder ◽  
Drag Force ◽  
Flow Separation ◽  
Bluff Body ◽  
Aerodynamic Force ◽  
Narrow Channel ◽  
Main Body ◽  
Transition Flow ◽  
Rans Models ◽  
Force Reduction

Drag is an aerodynamic force that appears when the flow past the bluff body circular cylinder. Drag strongly influenced by the flow separation point. One of the ways reducing the drag force that is to control the flow by placing the disturbance body on the upstream side at a certain angle. Previous research has found at 60º angle of flow separation is faster than a single cylinder that produced greater drag. Therefore, this research was conducted to reduce the drag force on the corner with disturbance dimension variation. This research was carried out numerically using a FLUENT 6.3.26 CFD software in 2D unsteady viscous-RANS models Turbulence Model-Shear-Stress Transport (SST) k-ω in a narrow channel. The geometry is simulated in a circular cylinder as the main body and the square cylinder as a disturbance body being placed in front of the main body by s/D ratio. Dimensions of disturbance body varied at (s) 0,1; 0,2; 0,3; 0,4 dan 0,5 mm with a gap (δ=0,4mm). Reynolds number based on the diameter of the cylinder, ie ReD 2,32x104. The simulation results show that the transition flow on shifting 60º SDB angle for all SDB dimensional variations do not produce turbulent. The optimum condition for the drag force reduction is s/D = 0.008 about 48 %.

Reduction of Drag Force on a Circular Cylinder and Pressure Drop Using a Square Cylinder as Disturbance Body in a Narrow Channel

2014 ◽  
Vol 493 ◽  
pp. 192-197 ◽  
Author(s):  
Wawan Aries Widodo ◽  
Randi Purnama Putra
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Wind Tunnel ◽  
Circular Cylinder ◽  
Drag Force ◽  
Bluff Body ◽  
Flow Characteristics ◽  
Narrow Channel ◽  
Square Cylinder ◽  
Cross Sectional

Many studies related with characteristics of fluid flow acrossing in a bluff body have been conducted. The aim of this research paper was to reduce pressure drop occuring in narrow channels, in which there was a circular cylindrical configuration with square cylinder as disturbance body. Another goal of this research was to reduce the drag force occuring in circular cylinder. Experimentally research of flow characteristics of the wind tunnel had a narrow channel a square cross-section, with implemenred of Reynolds number based on the hydraulic diameter from 5.21x104 to 1.56x105. Wind tunnel that was used had a 125x125mm cross-sectional area and the blockage ratio 26.4% and 36.4%. Specimen was in the form of circular cylinder and square cylinder as disturbance body. Variation of angle position was the inlet disturbance body with α = 200, 300, 400, 500 and 600, respectively. The results was obtained from this study was Reynolds Number value was directly linear with pressure drop there, it was marked by increasing of Reynolds number, the value was also increasing pressure drop. Additional information was obtained by adding inlet disturbance body shaped of square cylinder on the upstream side of the circular cylinder that could reduce pressure drop in the duct and reduce drag happening on a circular cylinder. The position of the optimum angle to reduce pressure drop and drag force was found on the inlet disturbance body with angle α = 300.

Experimental Study of Drag Reduction on Circular Cylinder and Reduction of Pressure Drop in Narrow Channels by Using a Cylinder Disturbance Body

2014 ◽  
Vol 493 ◽  
pp. 198-203 ◽  
Author(s):  
Wawan Aries Widodo ◽  
Nuzul Hidayat
Keyword(s):  
Pressure Drop ◽  
Circular Cylinder ◽  
Drag Reduction ◽  
Drag Force ◽  
Bluff Body ◽  
Position Angle ◽  
Narrow Channel ◽  
Lower Side ◽  
Cross Sectional ◽  
Narrow Channels

This paper present the results of drag reduction on circular cylinder and reduction of pressure drop in narrow rectangular channels by using circular disturbance body. This study focused on the phenomenon when the flow through the arrangement of the circular cylinder, separation will occur at a specific point on a circular cylinder resulting drag force. When the separation can be delayed so that the resulting drag force will be smaller. This can be done in various ways, one of which is by using a cylinder disturbance body on the upper and lower side near the bluff body. This study will be conducted in a wind tunnel experiments which have narrow channels with a square cross-sectional area of 125 mm x 125 mm and a blockage ratio of 26.4% and 36.4%. Specimens used circular cylinder with 25 mm diameter (d/D= 0.16) and 37.5 mm (d/D= 0.107) as well as the circular disturbance body with a diameter of 4 mm. cylinder disturbance body placed on the upper and lower side with the position α=200 to 600 and spacing (δ=0.4 mm) to the main circular cylinder. Reynolds number based on the hydraulic diameter of 5.21×104 to 15.6×104. The results of this research show the effect of using circular disturbance body on circular cylinder and the characteristics of fluid flow on a narrow channel square cross section. At a certain position of the circular disturbance body provide value pressure drop reduction on narrow channels and drag reduction when compared to a single circular cylinder. From the experimental data presented in this paper it is observed that the position angle of circular disturbance body to reduce drag force on a circular cylinder and reducing the pressure drop in the channel are at angle 200 and 300 for D=25 mm, and 200, 300 and 400, respectively, for D= 37.5 mm then the best reduction for both cylinders are at an angle of 300.

scholarly journals Microfiber Coating for Drag Reduction by Flocking Technology

Coatings ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 464 ◽  
Author(s):  
Mitsugu Hasegawa ◽  
Hirotaka Sakaue
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Circular Cylinder ◽  
Drag Reduction ◽  
Flow Separation ◽  
Bluff Body ◽  
Rigid Surface ◽  
Smoke Flow ◽  
Flexible Fibers ◽  
Transition Delay

The biomimicry of using a hair-like structure is introduced as a drag reduction coating. The hair-like structure consists of an array of microfiber that is introduced as a passive drag reduction device. An effective flow control for a transition delay or a flow attachment is expected via an interaction or counteraction of flexible fibers, compared to the existing passive methods that use a solid or rigid surface device. The effect of the microfiber coating on drag reduction over a bluff-body was experimentally investigated using a circular cylinder in a wind tunnel at Reynolds number of 6.1 × 104. A drag reduction of 32% was obtained when the microfiber coating with a length of 0.012D was located at 40° from the stagnation point. Smoke flow visualization showed that flow separation delay was induced by the microfiber coating when the drag reduction occurred.

Drag Force Reduction of a Bluff-Body with an Underbody Slant and Rear Flaps

2008 ◽  
Vol 1 (1) ◽  
pp. 230-236 ◽  
Author(s):  
Shinsuke Kowata ◽  
Jongsoo Ha ◽  
Shuya Yoshioka ◽  
Takuma Kato ◽  
Yasuaki Kohama
Keyword(s):  
Drag Force ◽  
Bluff Body ◽  
Force Reduction

The Force and Pressure of a Diffuser-Equipped Bluff Body in Ground Effect

2000 ◽  
Vol 123 (1) ◽  
pp. 105-111 ◽  
Author(s):  
Andrea E. Senior ◽  
Xin Zhang
Keyword(s):  
Flow Separation ◽  
Bluff Body ◽  
Three Dimensional ◽  
Ground Effect ◽  
Surface Flow ◽  
Force Balance ◽  
Diffuser Flow ◽  
Subsequent Loss ◽  
Force Reduction ◽  
Low Speed Wind Tunnel

The force and pressure behavior of a generic diffuser in ground effect were investigated. The diffuser model is a bluff body with a rear diffuser at 17 deg to the horizontal, and side-plates. Measurements were conducted in a low speed wind tunnel equipped with a moving ground facility. Techniques employed were force balance, pressure taps, and surface flow visualization. The diffuser flow in ground effect was characterized by vortex flow and three-dimensional flow separation. Four types of force behavior were observed: (a) down-force enhancement at high ride heights characterized by an attached symmetric diffuser flow, (b) maximum down-force at moderate ride heights characterized by a symmetric diffuser flow and separation on the diffuser ramp surface, (c) down-force reduction at low ride heights characterized by an asymmetric diffuser flow and flow separation, and (d) low down-force at very low ride heights, also characterized by an asymmetric diffuser flow and flow separation. The down-force reduction near the ground is attributed to flow separation at the diffuser inlet and subsequent loss of suction in the first half of the diffuser.

scholarly journals Influence of Diffuser Angle on a Bluff Body in Ground Effect

2003 ◽  
Vol 125 (2) ◽  
pp. 332-338 ◽  
Author(s):  
Andreas Ruhrmann ◽  
Xin Zhang
Keyword(s):  
Flow Field ◽  
Flow Separation ◽  
Bluff Body ◽  
Vortex Breakdown ◽  
Three Dimensional ◽  
Ground Effect ◽  
Surface Flow ◽  
Ride Height ◽  
Force Reduction ◽  
Underbody Diffuser

The forces and pressures on a generic bluff body in ground effect were investigated. The bluff-body model was equipped with interchangeable underbody diffuser ramps and side plates. Five different diffuser angles were tested: 5, 10, 15, 17, and 20 deg to the horizontal. The experiments were undertaken in a low-speed wind tunnel equipped with a moving ground. Load cells, pressure taps, and surface flow visualization were the techniques used to evaluate the flow field. The flow field is characterized by vortex flow and three-dimensional flow separation. A region of hysteresis was found for the 15, 17, and 20 deg diffusers. As the ride height is varied, five different flow types can be identified with three subtypes within the region of hysteresis. The force reduction phenomenon was found to be caused by both vortex breakdown and flow separation.

The Numerical Simulation of Two-Degrees-of-Freedom Vortex-Induced Vibrations of Circular Cylinder with High Mass-Ratio

2013 ◽  
Vol 284-287 ◽  
pp. 557-561
Author(s):  
Jie Li Fan ◽  
Wei Ping Huang
Keyword(s):  
Circular Cylinder ◽  
Drag Force ◽  
Frequency Ratio ◽  
Lift Force ◽  
Degrees Of Freedom ◽  
Cross Flow ◽  
High Mass ◽  
Mass Ratio ◽  
Main Frequency ◽  
Line Amplitude

The two-degrees-of-freedom VIV of the circular cylinder with high mass-ratio is numerically simulated with the software ANSYS/CFX. The VIV characteristic is analyzed in the different conditions (Ur=3, 5, 6, 8, 10). When Ur is 5, 6, 8 and 10, the conclusion which is different from the cylinder with low mass-ratio can be obtained. When Ur is 3, the frequency of in-line VIV is twice of that of cross-flow VIV which is equal to the frequency ratio between drag force and lift force, and the in-line amplitude is much smaller than the cross-flow amplitude. The motion trace is the crescent. When Ur is 5 and 6, the frequency ratio between the drag force and lift force is still 2, but the main frequency of in-line VIV is mainly the same as that of cross-flow VIV and the secondary frequency of in-line VIV is equal to the frequency of the drag force. The in-line amplitude is still very small compared with the cross-flow amplitude. When Ur is up to 8 and 10, the frequency of in-line VIV is the same as the main frequency of cross-flow VIV which is close to the inherent frequency of the cylinder and is different from the frequency of drag force or lift force. But the secondary frequency of cross-flow VIV is equal to the frequency of the lift force. The amplitude ratio of the VIV between in-line and cross-flow direction is about 0.5. When Ur is 5, 6, 8 and 10, the motion trace is mainly the oval.

Lock-in regions of laminar flows over a streamwise oscillating circular cylinder

2018 ◽  
Vol 858 ◽  
pp. 315-351 ◽  
Author(s):  
Ki-Ha Kim ◽  
Jung-Il Choi
Keyword(s):  
Circular Cylinder ◽  
Aerodynamic Force ◽  
Lift Coefficient ◽  
Lower Boundary ◽  
Laminar Flows ◽  
Velocity Range ◽  
Frequency Range ◽  
Vortex Pattern ◽  
Moving Cylinder ◽  
Lock In

In this paper, flow over a streamwise oscillating circular cylinder is numerically simulated to examine the effects of the driving amplitude and frequency on the distribution of the lock-in regions in laminar flows. At $Re=100$, lock-in is categorized according to the spectral features of the lift coefficient as two different lock-in phenomena: harmonic and subharmonic lock-in. These lock-in phenomena are represented as maps on the driving amplitude–frequency plane, which have subharmonic lock-in regions and two harmonic lock-in regions. The frequency range of the subharmonic region is shifted to lower frequencies with increasing amplitude, and the lower boundary of this subharmonic region is successfully predicted. A symmetric harmonic region with a symmetric vortex pattern is observed in a certain velocity range for a moving cylinder. Aerodynamic features induced by different flow patterns in each region are presented on the driving amplitude–frequency plane. The lock-in region and aerodynamic features at $Re=200$ and $40$ are compared with the results for $Re=100$. A subharmonic region and two harmonic regions are observed at $Re=200$, and these show the same features as for $Re=100$ at a low driving amplitude. Lock-in at $Re=40$ also shows one subharmonic region and two harmonic regions. However, compared with the $Re=100$ case, the symmetric harmonic lock-in is dominant. The features of aerodynamic force at $Re=200$ and $40$ are represented on a force map, which shows similar characteristics in corresponding regions for the $Re=100$ case.

scholarly journals Dynamical effect of the total strain induced by the coherent motion on local isotropy in a wake

2013 ◽  
Vol 720 ◽  
pp. 393-423 ◽  
Author(s):  
F. Thiesset ◽  
L. Danaila ◽  
R. A. Antonia
Keyword(s):  
Circular Cylinder ◽  
Large Scale ◽  
Bluff Body ◽  
Initial Conditions ◽  
Scale Up ◽  
Wake Flow ◽  
Total Strain ◽  
Coherent Motion ◽  
Square Cylinder ◽  
Local Isotropy

AbstractWe assess the extent to which local isotropy (LI) holds in a wake flow for different initial conditions, which may be geometrical (the shape of the bluff body which creates the wake) and hydrodynamical (the Reynolds number), as a function of the dynamical effects of the large-scale forcing (the mean strain, $ \overline{S} $, combined with the strain induced by the coherent motion, $\tilde {S} $). LI is appraised through either classical kinematic tests or phenomenological approaches. In this respect, we reanalyse existing LI criteria and formulate a new isotropy criterion based on the ratio between the turbulence strain intensity and the total strain ($ \overline{S} + \tilde {S} $). These criteria involve either time-averaged or phase-averaged quantities, thus providing a deeper insight into the dynamical aspect of these flows. They are tested using hot wire data in the intermediate wake of five types of obstacles (a circular cylinder, a square cylinder, a screen cylinder, a normal plate and a screen strip). We show that in the presence of an organized motion, isotropy is not an adequate assumption for the large scales but may be satisfied over a range of scales extending from the smallest dissipative scale up to a scale which depends on the total strain rate that characterizes the flow. The local value of this scale depends on the particular nature of the wake and the phase of the coherent motion. The square cylinder wake is the closest to isotropy whereas the least locally isotropic flow is the screen strip wake. For locations away from the axis, the study is restricted to the circular cylinder only and reveals that LI holds at scales smaller than those that apply at the wake centreline. Arguments based on self-similarity show that in the far wake, the strength of the coherent motion decays at the same rate as that of the turbulent motion. This implies the persistence of the same degree of anisotropy far downstream, independently of the scale at which anisotropy is tested.

scholarly journals Control of flow separation over a circular cylinder using synthetic jet

2021 ◽  
Vol 2119 (1) ◽  
pp. 012025
Author(s):  
A. S. Lebedev ◽  
M. I. Sorokin ◽  
D. M. Markovich
Keyword(s):  
Circular Cylinder ◽  
Flow Control ◽  
Flow Separation ◽  
Gas Turbines ◽  
Acoustic Noise ◽  
Reverse Flow ◽  
Flow Region ◽  
Synthetic Jet ◽  
Separation Flow ◽  
Longitudinal Length

Abstract The development of methods of active separation flow control is of great applied importance for many technical and engineering applications. Understanding the conditions for the flow separation from the surface of a bluff body is essential for the design of aircrafts, cars, hydro and gas turbines, bridges and buildings. Drag, acoustic noise, vibrations and active flow mixing depend drastically on the parameters of the vortex separation process. We investigated the possibility of reducing the longitudinal length of a reverse-flow region using the method of «synthetic jet» active separation flow control. The experiment was carried out on a compact straight-through wind channel with a 1-m long test section of a cross-section of 125x125 mm. The jet was placed at the rear stagnation point of a circular cylinder. The Reynolds number, based on the cylinder diameter and the free-stream velocity, was 5000 and the von Kármán street shedding frequency without the synthetic jet was equal to 64.8 Hz. For the first time, for such a set of parameters, we applied high speed PIV to demonstrate that the injection of the synthetic jet into the cylinder wake region leads to a significant reduction in the longitudinal length of the reverse-flow region.

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