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 STUDI NUMERIK PRESSURE DROP PADA SILINDER TANDEM DENGAN PENAMBAHAN SPLITTER PLATE DAN VORTEX GENERATOR DI PENAMPANG SEMPIT

Otopro ◽  
2021 ◽  
pp. 15-20
Author(s):  
Diastian Vinaya Wijanarko
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Circular Cylinder ◽  
Numerical Study ◽  
Vortex Generator ◽  
Splitter Plate ◽  
Blockage Ratio ◽  
Cross Sectional ◽  
The Cross

The numerical study of pressure drop on a tandem cylinder with the addition of a splitter plate and a vortex generator with the effect of a blockage ratio has been completed. The cross-sectional height and diameter of the cylinder in this study used H= 125 mm and D= 37.5 mm, respectively. The blockage ratio is 30%. The Reynolds number (Re) is 52100 ≤ Re ≤ 156000. The distance between cylinders is 5 to 8, where “s” is the distance from cylinder one to cylinder two. The dimensions of the splitter plate are L=D, L=1,5D, and L=2D where "L" is the length of the splitter plate, while the thickness in this study is 1, 75mm. The dimensions of the vortex generator in this study are used those of Hu, et al. [6]. The angle of the vortex generator is = 350 while the length of the vortex generator is H = 3 mm. All variations of this numerical study were carried out using the URANS (Unsteady Reynold Average Navier Stoke) method with a Reynolds number (Re) 52,100 Re 156,000. The smallest pressure drop value is obtained at the Reynolds number 52.100 for all variations, while the highest Reynolds number is obtained at Re 156.000. the addition of a splitter plate and a vortex generator, gives a higher pressure drop when compared to a circular cylinder.

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.

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 %.

scholarly journals Pengaruh Silinder Downstream terhadap Karakteristik Aliran Silinder Upstream Menggunakan Square Disturbance Body Tersusun Tandem

2018 ◽  
Vol 11 (2) ◽  
pp. 58
Author(s):  
Rina Rina ◽  
Sanny Ardhy
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Drag Force ◽  
Turbulence Model ◽  
Bluff Body ◽  
Pressure Coefficient ◽  
Model Parameters ◽  
Square Cylinder ◽  
Shear Stress Transport ◽  
Unsteady Rans

Fluida yang mengalir di sekitar bluff body silinder sirkular, akan menimbulkan gaya-gaya aerodinamika salah satunya gaya drag. Drag sangat tidak diinginkan untuk keselamatan struktur body. Reduksi gaya drag dilakukan dengan mengontrol medan aliran seperti meningkatkan kekasaran permukaan, mengiris silinder dengan sudut iris tertentu, dan menempatkan pengganggu di sisi upstream silinder. Penelitian ini bertujuan untuk melihat pengaruh silinder downstream terhadap karakteristik aliran silinder upstream menggunakan square disturbance body yang disusun tandem pada saluran sempit. Geometri yang digunakan adalah dua silinder sirkular yang disusun tandem berdiameter (D) 25 mm dengan variasi jarak antar silinder (L/D) 1,5; 2; 2,5; 3; 3,5; 4. Square Cylinder sebagai body pengganggu ditempatkan pada sisi upstream silinder utama berdiamensi 4 mm. Posisi sudut pengganggu (?) 30°, dan jarak gap (d=0.4mm). Reynolds number berdasarkan diameter silinder, yaitu ReD 2,32x104. Penelitian iini dilakukan secara numerik 2D Unsteady-RANS menggunakan CFD software FLUENT 6.3.26 dengan model viscous Turbulence Model Shear-Stress-Transport (SST) k-?. Parameter yang diamati adalah koefisien pressure (Cp), Koefisien drag pressure (Cdp) dan visualisasi aliran berupa velocity pathline. Hasilnya menunjukkan bahwa Penambahan silinder downstream memberikan kontribusi dalam pengurangan gaya drag pada silinder upstream menggunakan square disturbance body. Pengaruh wake silinder upstream terhadap silinder downstream berkurang dengan meningkatnya rasio L/D. Interaksi wake silinder upstream terhadap silinder downstream terjadi pada konfigurasi L/D 1,5 – 3. Pengurangan gaya drag optimum terjadi pada konfigurasi L/D 3. The fluid flows around the circular cylinder bluff body will produce aerodynamic forces, one of which is the drag force. Drag is very undesirable for the safety of the body structure. Reduction of drag force is carried out by controlling the flow field such as increasing the surface roughness, slicing the cylinder with a certain iris angle, and placing the disturbance on the upstream side of the cylinder. This purpose of the study is to see the effect of downstream cylinders on the flow characteristics of upstream cylinders using a square disturbance body arranged tandem in a narrow channel. The geometry used is two circular cylinders arranged in tandem diameter (D) 25 mm with a variation of distance between cylinders (L / D) 1.5; 2; 2.5; 3; 3.5; 4. Square Cylinder as a disturbing body is placed on the side of the main cylinder upstream with a diameter of 4 mm. The position of the disturbing angle (?) is 30 °, and the gap distance (d = 0.4mm). Reynolds number is based on cylinder diameter, ie ReD 2.32x104. This research was carried out numerical 2D Unsteady-RANS using a FLUENT 6.3.26 CFD software with viscous Turbulence model Shear-Stress-Transport (SST) k-? model. Parameters observed were pressure coefficient (Cp), drag pressure coefficient (Cdp) and flow visualization in the form of velocity pathline. The results show that the addition of a downstream cylinder contributes to the reduction of the drag force on the upstream cylinder using a square disturbance body. The wake influence of upstream cylinder to downstream cylinder decreasing with increasing the ratio of L/D. The interaction of wake cylinder upstream to downstream cylinder occurs at L/D 1.5 - 3. The optimum for the drag force reduction occurs at L/D 3.

scholarly journals Effects of Streamlining a Bluff Body in the Laminar Vortex Shedding Regime

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Ritvik Dobriyal ◽  
Maneesh Mishra ◽  
Markus Bölander ◽  
Martin Skote
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Shape Factor ◽  
Bluff Body ◽  
The Body ◽  
Cross Sectional ◽  
Shape Factors ◽  
Rear Part ◽  
Lift And Drag

Abstract Two-dimensional flow over bluff bodies is studied in the unsteady laminar flow regime using numerical simulations. In previous investigations, lift and drag forces have been studied over different cross-sectional shapes like circles, squares, and ellipses. We aim to extend the previous research by studying the variation of hydrodynamic forces as the shape of the body changes from a circular cylinder to a more streamlined or a bluffer body. The different body shapes are created by modifying the downstream circular arc of a circular cylinder into an ellipse, hence elongating or compressing the rear part of the body. The precise geometry of the body is quantified by defining a shape factor. Two distinct ranges of shape factors with fundamentally different behavior of lift and drag are identified. The geometry constituting the limit is where the rear part ellipse has a semi-minor axis of half the radius of the original circle, independent of the Reynolds number. On the other hand, the vortex shedding frequency decreases linearly over the whole range of shape factors. Furthermore, the variation of the forces and frequency with Reynolds number, and how the relations vary with the shape factor are reported.

scholarly journals Reduksi Gaya Drag Silinder Sirkular dengan Penambahan Square Disturbance Body Melalui Simulasi Numerik 2D Unsteady-RANS pada Reynold Number 34800

2017 ◽  
Author(s):  
Ruzita Sumiati ◽  
Rina
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Shear Stress ◽  
Circular Cylinder ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Bluff Body ◽  
Reynold Number ◽  
Square Cylinder ◽  
Unsteady Rans

Ketika fluida mengalir di sekitar Bluff body circular cylinder tunggal akan menghasilkan drag yang cukup besar, hal ini disebabkan karena ia memiliki kelengkungan kontur permukaan dengan karakteristik Andversse Pressure Gradient yang cukup kuat akibat tekanan aliran pada permukaan body. Untuk mengurangi drag tersebut, maka dilakukanlah kontrol aliran, salah satunya dengan menempatkan body pengganggu di depan circular cylinder. Penelitian ini bertujuan untuk membandingkan dan melengkapi penelitian eksperimen pengurangan gaya drag yang telah dilakukan sebelumnya. Penelitian ini dilakukan secara numerik 2D Unsteady-RANS menggunakan CFD software FLUENT 6.3.26 dengan model viscous Turbulence Model Shear-Stress-Transport (SST) k-ω pada saluran sempit. Geometri body yang disimulasikan adalah circular cylinder sebagai main bluff body dan square cylinder sebagai disturbance body yang ditempatkan di depan main bluff body dengan rasio s/D 0.107. Posisi disturbance body divariasikan pada (α) 20⁰, 30⁰, 40⁰, 50⁰ dan 60⁰ dengan jarak gap (δ=0,4mm). Reynolds number berdasarkan diameter silinder, yaitu ReD 3.48x104. Hasil simulasi ini menunjukkan bahwa interaksi fluida antara circular cylinder dengan dua body penganggu dapat meningkatkan transisi lapis batas dari laminer ke turbulent boundary layer sehingga menghasilkan drag yang kecil. Sudut optimum pengurangan gaya drag terjadi pada α = 30º yaitu sebesar 53%.

Experimental Investigation of Effect of Tip Coolant Ejection on Internal Flow Characteristics Within a Realistic Blade Coolant Channel

2013 ◽  
Author(s):  
Jian Pu ◽  
Zhaoqing Ke ◽  
Jianhua Wang ◽  
Lei Wang ◽  
Hongde You
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Turbine Blade ◽  
Flow Rate ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Flow Ratio ◽  
Lp Turbine ◽  
Mass Flow Ratio

This paper presents an experimental investigation on the characteristics of the fluid flow within an entire coolant channel of a low pressure (LP) turbine blade. The serpentine channel, which keeps realistic blade geometry, consists of three passes connected by a 180° sharp bend and a semi-round bend, 2 tip exits and 25 trailing edge exits. The mean velocity fields within several typical cross sections were captured using a particle image velocimetry (PIV) system. Pressure and flow rate at each exit were determined through the measurements of local static pressure and volume flow rate. To optimize the design of LP turbine blade coolant channels, the effect of tip ejection ratio (ER) from 180° sharp bend on the flow characteristics in the coolant channel were experimentally investigated at a series of inlet Reynolds numbers from 25,000 to 50,000. A complex flow pattern, which is different from the previous investigations conducted by a simplified square or rectangular two-pass U-channel, is exhibited from the PIV results. This experimental investigation indicated that: a) in the main flow direction, the regions of separation bubble and flow impingement increase in size with a decrease of the ER; b) the shape, intensity and position of the secondary vortices are changed by the ER; c) the mass flow ratio of each exit to inlet is not sensitive to the inlet Reynolds number; d) the increase of the ER reduces the mass flow ratio through each trailing edge exit to the extent of about 23–28% of the ER = 0 reference under the condition that the tip exit located at 180° bend is full open; e) the pressure drop through the entire coolant channel decreases with an increase in the ER and inlet Reynolds number, and a reduction about 35–40% of the non-dimensional pressure drop is observed at different inlet Reynolds numbers, under the condition that the tip exit located at 180° bend is full open.

Model reduction and mechanism for the vortex-induced vibrations of bluff bodies

2017 ◽  
Vol 827 ◽  
pp. 357-393 ◽  
Author(s):  
W. Yao ◽  
R. K. Jaiman
Keyword(s):  
Reynolds Number ◽  
Bluff Body ◽  
Low Reynolds Number ◽  
Smooth Curve ◽  
Bluff Bodies ◽  
Sharp Corner ◽  
Mass Ratio ◽  
Square Cylinder ◽  
Low Reynolds ◽  
Lock In

We present an effective reduced-order model (ROM) technique to couple an incompressible flow with a transversely vibrating bluff body in a state-space format. The ROM of the unsteady wake flow is based on the Navier–Stokes equations and is constructed by means of an eigensystem realization algorithm (ERA). We investigate the underlying mechanism of vortex-induced vibration (VIV) of a circular cylinder at low Reynolds number via linear stability analysis. To understand the frequency lock-in mechanism and self-sustained VIV phenomenon, a systematic analysis is performed by examining the eigenvalue trajectories of the ERA-based ROM for a range of reduced oscillation frequency $(F_{s})$, while maintaining fixed values of the Reynolds number ($Re$) and mass ratio ($m^{\ast }$). The effects of the Reynolds number $Re$, the mass ratio $m^{\ast }$ and the rounding of a square cylinder are examined to generalize the proposed ERA-based ROM for the VIV lock-in analysis. The considered cylinder configurations are a basic square with sharp corners, a circle and three intermediate rounded squares, which are created by varying a single rounding parameter. The results show that the two frequency lock-in regimes, the so-called resonance and flutter, only exist when certain conditions are satisfied, and the regimes have a strong dependence on the shape of the bluff body, the Reynolds number and the mass ratio. In addition, the frequency lock-in during VIV of a square cylinder is found to be dominated by the resonance regime, without any coupled-mode flutter at low Reynolds number. To further discern the influence of geometry on the VIV lock-in mechanism, we consider the smooth curve geometry of an ellipse and two sharp corner geometries of forward triangle and diamond-shaped bluff bodies. While the ellipse and diamond geometries exhibit the flutter and mixed resonance–flutter regimes, the forward triangle undergoes only the flutter-induced lock-in for $30\leqslant Re\leqslant 100$ at $m^{\ast }=10$. In the case of the forward triangle configuration, the ERA-based ROM accurately predicts the low-frequency galloping instability. We observe a kink in the amplitude response associated with 1:3 synchronization, whereby the forward triangular body oscillates at a single dominant frequency but the lift force has a frequency component at three times the body oscillation frequency. Finally, we present a stability phase diagram to summarize the VIV lock-in regimes of the five smooth-curve- and sharp-corner-based bluff bodies. These findings attempt to generalize our understanding of the VIV lock-in mechanism for bluff bodies at low Reynolds number. The proposed ERA-based ROM is found to be accurate, efficient and easy to use for the linear stability analysis of VIV, and it can have a profound impact on the development of control strategies for nonlinear vortex shedding and VIV.

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.

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