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

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.

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

10.31227/osf.io/fk8du ◽

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%.

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Sensitivity Studies of Shear Stress Transport Turbulence Model Parameters on the Prediction of Seven-Rod Bundle Benchmark Experiments

Journal of Nuclear Engineering and Radiation Science ◽

10.1115/1.4031035 ◽

2015 ◽

Vol 2 (1) ◽

Cited By ~ 2

Author(s):

Cale Bergmann ◽

S. Ormiston ◽

V. Chatoorgoon

Keyword(s):

Shear Stress ◽

Turbulence Model ◽

Turbulence Modeling ◽

Sensitivity Study ◽

Model Parameters ◽

Rod Bundle ◽

Shear Stress Transport ◽

Sst Turbulence Model ◽

Sensitivity Studies ◽

Two Parameters

This paper reports the findings of a sensitivity study of parameters in the shear stress transport (SST) turbulence model in a commercial computational fluid dynamics (CFD) code to predict an experiment from the Generation IV International Forum Supercritical-Water-Cooled Reactor (GIF SCWR) 2013–2014 seven-rod subchannel benchmark exercise. This study was motivated by the result of the benchmark exercise that all the CFD codes gave similar results to a subchannel code, which does not possess any sophisticated turbulence modeling. Initial findings were that the CFD codes generally underpredicted the wall temperatures on the B2 case in the region where the flow was supercritical. Therefore, it was decided to examine the effect of various turbulence model parameters to determine if a CFD code using the SST turbulence model could do a better job overall in predicting the wall temperatures of the benchmark experiments. A sensitivity study of seven parameters was done, and changes to two parameters were found to make an improvement.

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

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.493.192 ◽

2014 ◽

Vol 493 ◽

pp. 192-197 ◽

Cited By ~ 1

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.

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Evaluation of the Shear-Stress Transport Turbulence Model for Heat Transfer Applications

41st Aerospace Sciences Meeting and Exhibit ◽

10.2514/6.2003-769 ◽

2003 ◽

Cited By ~ 3

Author(s):

Xiao-Ling Tong ◽

Edward Luke ◽

Lin Tang

Keyword(s):

Heat Transfer ◽

Shear Stress ◽

Turbulence Model ◽

Shear Stress Transport

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

Journal of Fluid Mechanics ◽

10.1017/jfm.2017.525 ◽

2017 ◽

Vol 827 ◽

pp. 357-393 ◽

Cited By ~ 19

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.

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Modification of Shear Stress Transport Turbulence Model Using Helicity for Predicting Corner Separation Flow in a Linear Compressor Cascade

Journal of Turbomachinery ◽

10.1115/1.4045658 ◽

2020 ◽

Vol 142 (2) ◽

Cited By ~ 1

Author(s):

Yangwei Liu ◽

Yumeng Tang ◽

Ashley D. Scillitoe ◽

Paul G. Tucker

Keyword(s):

Shear Stress ◽

Turbulence Model ◽

Incidence Angle ◽

Computational Cost ◽

Separation Flow ◽

Compressor Cascade ◽

Production Term ◽

Corner Separation ◽

Shear Stress Transport ◽

Sst Model

Abstract Three-dimensional corner separation significantly affects compressor performance, but turbulence models struggle to predict it accurately. This paper assesses the capability of the original shear stress transport (SST) turbulence model to predict the corner separation in a linear highly loaded prescribed velocity distribution (PVD) compressor cascade. Modifications for streamline curvature, Menter’s production limiter, and the Kato-Launder production term are examined. Comparisons with experimental data show that the original SST model and the SST model with different modifications can predict the corner flow well at an incidence angle of −7 deg, where the corner separation is small. However, all the models overpredict the extent of the flow separation when the corner separation is larger, at an incidence angle of 0 deg. The SST model is then modified using the helicity to take account of the energy backscatter, which previous studies have shown to be important in the corner separation regions of compressors. A Reynolds stress model (RSM) is also used for comparison. By comparing the numerical results with experiments and RSM results, it can be concluded that sensitizing the SST model to helicity can greatly improve the predictive accuracy for simulating the corner separation flow. The accuracy is quite competitive with the RSM, whereas in terms of computational cost and robustness it is superior to the RSM.

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Wake Interaction of a Square Cylinder With a Splitter Plate Boundary Layer at a Low Reynolds Number

Volume 1A: Symposia, Part 2 ◽

10.1115/ajkfluids2015-01793 ◽

2015 ◽

Author(s):

Smriti Srivastava ◽

Sudipto Sarkar

Keyword(s):

Boundary Layer ◽

Reynolds Number ◽

Bluff Body ◽

Acoustic Noise ◽

Vortex Formation ◽

Plate Boundary ◽

Wake Flow ◽

Stream Velocity ◽

Square Cylinder ◽

Plate Length

One of the most important researches in bluff body aerodynamics is to control the shear layer evolution leading to vortex formation. This kind of research is closely associated with reduction of aerodynamics forces and acoustic noise. Passive and active control of wake-flow from bluff bodies have received a great deal of attention in the last few decades [1–4]. Keeping this in mind, authors investigate the interaction of a square cylinder (side of the square = a) wake with a flat plate (length L = a, width w = 0.1a) boundary layer positioned at various downstream locations close to the cylinder. The gap-to-side ratios are maintained at G/a = 0, 0.5, 1 and 2 (where G is the gap between square cylinder and plate), and the simulation is performed at a Reynolds number, Re = 100 (Re = U∞a/v, where U∞ is free stream velocity and v is kinematic viscosity). Instantaneous flow visualization, aerodynamic forces and vortex shedding frequencies for all cases are described to gain insight about the changes associated with wake of the cylinder when a short plate is kept in its downstream.

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