scholarly journals Studi Numerik Steady RANS Aliran Fluida di Dalam Asymmetric Diffuser

2017 ◽  
Vol 4 (1) ◽  
pp. 20 ◽  
Author(s):  
Yiyin Klistafani
Keyword(s):  
Fluid Flow ◽  
Pressure Gradient ◽  
Numerical Study ◽  
Maximum Velocity ◽  
Turbulence Models ◽  
Adverse Pressure Gradient ◽  
Positive Pressure ◽  
Front Wall ◽  
Human Beings ◽  
Vertical Side

Research on fluid flow becomes a necessity to develop technology and for the welfare of human beings on earth. One of them is study of fluid flow in the diffuser. The example of diffuser application is used as a flue gas duct in the car or motorcycle. In addition, diffuser is also applied in air conditioning systems. Diffuser is a construction that able to control the behavior of the fluid. The increasing of cross section area in the diffuser will generate a positive pressure gradient or also called adverse pressure gradient (APG). The greater APG that happens, the greater energy required by the fluid to fight it, because APG will lead to separation. This study aimed to evaluate the numerical fluid flow in the asymmetric diffuser with divergence angle (θ) = 10 ° (upper wall) and widening one vertical side (α) of 20 ° (front wall). The Reynolds number is 8.7 x 104 by high inlet diffuser and the maximum velocity at the inlet diffuser. Turbulence models used are standard k-ɛ, realizable k-ε, and shear stress transport (SST) k-ω. Numerical study of steady RANS used Fluent 6.3.26 software. Results of numerical visualizations show that huge vortex established in diffuser, that’s why performance of diffuser is not optimal. In addition the location of separation point shown by SST k-ω is earlier than other turbulence models (standard k-ε and realizable k-ε).

scholarly journals Simulasi Numerik pada Rectangular Cylinder dekat Dinding yang mengunakan Diffuser dan tanpa Diffuser dengan Mengunakan K Model

2016 ◽  
Vol 11 (2) ◽  
pp. 64
Author(s):  
Nuzul Hidayat
Keyword(s):  
Pressure Gradient ◽  
Rectangular Cross Section ◽  
Lift Coefficient ◽  
Turbulence Models ◽  
Internal Flow ◽  
Adverse Pressure Gradient ◽  
Positive Pressure ◽  
Rectangular Cylinder ◽  
Architectural Features ◽  
Flow Geometry

Rectangular Cylinder with a rectangular cross section is also used as a building, the architectural features of the building, the internal flow geometry, and beam. In addition, flow around Rectangular Cylinder can produce local instability and can lead to global instability. Diffuser can work for both conditions by reducing the drag force and increase down force. Diffuser is designed to change the fluid kinetic energy into potential energy in the form of pressure. The increase in pressure that occurs in the diffuser will generate a positive pressure gradient or also called adverse pressure gradient (APG). In this case Rectangular Cylinder that use Diffuser And Without Diffuser at Re 1 x 106 obtained graphs of: (a) Drag Coefficient (Cd) (b) Lift Coefficient (Cl) and (c) Velocity contour in the area of mid span numerically using the software Fluent 6.3.26 with k ε- turbulence models that Standard are two-dimensional (2D). On the Cylinder Rectangular diffuser values obtained using 1:36 Cd and Cl -0.81 and Rectangular Cylinder without diffuser obtained value Cd Cl 0:47 and 1:53, clearly visible on the use Rectangular Cylinder diffuser turns diffuser provides greater Cd and Cl negative or increase down force. The treatment is to eliminate the other side upper corner on the front of a quarter circle with r = 0.1, this produces a different contour velocity when compared experiment this treatment capable of eliminating reattached flow on the upper side area.

Numerical Simulations of Heat Transfer and Fluid Flow for a Rotating High-Pressure Turbine

2006 ◽  
Author(s):  
F. Mumic ◽  
L. Ljungkruna ◽  
B. Sunden
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Fluid Flow ◽  
Numerical Study ◽  
Three Dimensional ◽  
Turbulence Models ◽  
High Pressure Turbine ◽  
Experimental Heat ◽  
Commercial Code ◽  
Stator Vane

In this work, a numerical study has been performed to simulate the heat transfer and fluid flow in a transonic high-pressure turbine stator vane passage. Four turbulence models (the Spalart-Allmaras model, the low-Reynolds-number realizable k-ε model, the shear-stress transport (SST) k-ω model and the v2-f model) are used in order to assess the capability of the models to predict the heat transfer and pressure distributions. The simulations are performed using the FLUENT commercial software package, but also two other codes, the in-house code VolSol and the commercial code CFX are used for comparison with FLUENT results. The results of the three-dimensional simulations are compared with experimental heat transfer and aerodynamic results available for the so-called MT1 turbine stage. It is observed that the predictions of the vane pressure field agree well with experimental data, and that the pressure distribution along the profile is not strongly affected by choice of turbulence model. It is also shown that the v2-f model yields the best agreement with the measurements. None of the tested models are able to predict transition correctly.

scholarly journals Similarity Solutions of the MHD Boundary Layer Flow Past a Constant Wedge within Porous Media

2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Ramesh B. Kudenatti ◽  
Shreenivas R. Kirsur ◽  
Achala L. Nargund ◽  
N. M. Bujurke
Keyword(s):  
Boundary Layer ◽  
Porous Medium ◽  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Velocity Profiles ◽  
Similarity Solutions ◽  
Positive Pressure ◽  
Boundary Layer Equations ◽  
Similarity Transformations ◽  
Wide Range

The two-dimensional magnetohydrodynamic flow of a viscous fluid over a constant wedge immersed in a porous medium is studied. The flow is induced by suction/injection and also by the mainstream flow that is assumed to vary in a power-law manner with coordinate distance along the boundary. The governing nonlinear boundary layer equations have been transformed into a third-order nonlinear Falkner-Skan equation through similarity transformations. This equation has been solved analytically for a wide range of parameters involved in the study. Various results for the dimensionless velocity profiles and skin frictions are discussed for the pressure gradient parameter, Hartmann number, permeability parameter, and suction/injection. A far-field asymptotic solution is also obtained which has revealed oscillatory velocity profiles when the flow has an adverse pressure gradient. The results show that, for the positive pressure gradient and mass transfer parameters, the thickness of the boundary layer becomes thin and the flow is directed entirely towards the wedge surface whereas for negative values the solutions have very different characters. Also it is found that MHD effects on the boundary layer are exactly the same as the porous medium in which both reduce the boundary layer thickness.

Numerical Performance of Transition Models in Different Turbomachinery Flow Conditions: A Comparative Study

2000 ◽  
Author(s):  
Jiasen Hu ◽  
Torsten H. Fransson
Keyword(s):  
Reynolds Number ◽  
Pressure Gradient ◽  
Numerical Study ◽  
Adverse Pressure Gradient ◽  
Navier Stokes ◽  
Test Cases ◽  
Pressure Gradients ◽  
Flow Conditions ◽  
Transition Models ◽  
High Reynolds

A numerical study has been performed to compare the overall performance of three transition models when used with an industrial Navier-Stokes solver. The three models investigated include two experimental correlations and an integrated eN method. Twelve test cases in realistic turbomachinery flow conditions have been calculated. The study reveals that all the three models can work numerically well with an industrial Navier-Stokes code, but the prediction accuracy of the models depends on flow conditions. In general, all the three models perform comparably well to predict the transition in weak or moderate adverse pressure-gradient regions. The two correlations have the merit if the transition starts in strong favorable pressure-gradient region under high Reynolds number condition. But only the eN method works well to predict the transition controlled by strong adverse pressure gradients. The three models also demonstrate different capabilities to model the effects of turbulence intensity and Reynolds number.

Assessment of Various Turbulence Models in a High Pressure Ratio Centrifugal Compressor With an Object Oriented CFD Code

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Luca Mangani ◽  
Ernesto Casartelli ◽  
Sebastiano Mauri
Keyword(s):  
Boundary Layer ◽  
High Pressure ◽  
Pressure Gradient ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Turbulence Models ◽  
Object Oriented ◽  
Adverse Pressure Gradient ◽  
High Mass ◽  
High Pressure Ratio

The flow field in a high pressure ratio centrifugal compressor with a vaneless diffuser has been investigated numerically. The main goal is to assess the influence of various turbulence models suitable for internal flows with an adverse pressure gradient. The numerical analysis is performed with a 3D RANS in-house modified solver based on an object-oriented open-source library. According to previous studies from varying authors, the turbulence model is believed to be the key parameter for the discrepancy between experimental and numerical results, especially at high pressure ratios and high mass-flow. Particular care has been taken at the wall, where a detailed integration of the boundary layer has been applied. The results present different comparisons between the models and experimental data, showing the influence of using advanced turbulence models. This is done in order to capture the boundary layer behavior, especially in large adverse pressure gradient single stage machinery.

Direct Simulations of Wake-Perturbed Separated Boundary Layers

2011 ◽  
Author(s):  
Ayse G. Gungor ◽  
Mark P. Simens ◽  
Javier Jime´nez
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Separation Bubble ◽  
Turbine Blades ◽  
Plate Boundary ◽  
Maximum Velocity ◽  
Adverse Pressure Gradient ◽  
Suction Side ◽  
Single Experiment ◽  
The Stability

A wake-perturbed flat plate boundary layer with a stream-wise pressure distribution similar to those encountered on the suction side of typical low-pressure turbine blades is investigated by direct numerical simulation. The laminar boundary layer separates due to a strong adverse pressure gradient induced by suction along the upper simulation boundary, transitions and reattaches while still subject to the adverse pressure gradient. Various simulations are performed with different wake passing frequencies, corresponding to the Strouhal number 0.0043 < fθb/ΔU < 0.0496 and wake profiles. The wake profile is changed by varying its maximum velocity defect and its symmetry. Results indicate that the separation and reattachment points, as well as the subsequent boundary layer development, are mainly affected by the frequency, but that the wake shape and intensity have little effect. Moreover, the effect of the different frequencies can be predicted from a single experiment in which the separation bubble is allowed to reform after having been reduced by wake perturbations. The stability characteristics of the mean flows resulting from the forcing at different frequencies are evaluated in terms of local linear stability analysis based on the Orr-Sommerfeld equation.

Turbulence in a separated boundary layer

1991 ◽  
Vol 226 ◽  
pp. 91-123 ◽  
Author(s):  
M. Dianat ◽  
Ian P. Castro
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Low Frequency ◽  
Turbulence Models ◽  
Adverse Pressure Gradient ◽  
Spanwise Direction ◽  
Wall Region ◽  
Thin Wall ◽  
Wall Boundary Layer ◽  
Stress Ratios

This paper presents and discusses the results of an extensive experimental investigation of a flat-plate turbulent boundary subjected to an adverse pressure gradient sufficiently strong to lead to the formation of a large separated region. The pressure gradient was produced by applying strong suction through a porous cylinder fitted with a rear flap and mounted above the boundary layer and with its axis in the spanwise direction. Attention is concentrated on the structure of the turbulent flow within the separated region and it is shown that many features are similar to those that occur in separated regions produced in a very dissimilar manner. These include the fact that structure parameters, like Reynolds stress ratios, respond markedly to the re-entrainment of turbulent fluid transported upstream from the reattachment region, the absence of any logarithmic region in the thin wall boundary layer beneath the recirculation zone and the lack of any effective viscous scaling in this wall region, and the presence of a significant low-frequency motion having timescales much longer than those of the large-eddy structures around reattachment.Similarities with boundary layers separating under the action of much weaker pressure gradients are also found, despite the fact that the nature of the flow around separation is quite different. These similarities and also some noticeable differences are discussed in the paper, which concludes with some inferences concerning the application of turbulence models to separated flows.

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