scholarly journals Optimization of Fluent Turbulence Models for Annular Diffuser

2020 ◽  
Vol 6 (6) ◽  
pp. 57-60
Author(s):  
Nagendra Kumar Sharma
Keyword(s):  
Kinetic Energy ◽  
Mathematical Models ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Cfd Analysis ◽  
Mechanical Device ◽  
Engineering Structures ◽  
Flowing Fluid ◽  
Characteristic Quantity ◽  
Annular Diffuser

A diffuser is a mechanical device used for converting the kinetic energy of flowing fluid into pressure energy. As the flow advances through the diffuser there is ongoing retardation of the flow resulting in conversion of kinetic energy into pressure energy. This is known as diffusion. Diffuser constitutes an essential part in turbo machinery and engineering structures. The present study aims at CFD analysis for the prediction of flow characteristics using various mathematical models. The annular diffuser considered in the present case has both the hub and casings are diverging with equal angles and hub angle keeping constant as 10°. The characteristic quantity such as velocity profiles at various sections and flow patterns have been presented for studying. Standard turbulence models are studied in the present study.

Recent Mathematical Models for Turbulent Flow in Saturated Rigid Porous Media

2001 ◽  
Vol 123 (4) ◽  
pp. 935-940 ◽  
Author(s):  
Marcelo J. S. de Lemos ◽  
Marcos H. J. Pedras
Keyword(s):  
Kinetic Energy ◽  
Mathematical Models ◽  
Time Integration ◽  
Turbulence Models ◽  
Volume Averaging ◽  
Turbulence Kinetic Energy ◽  
Time Space ◽  
Interfacial Surface ◽  
Flow Through ◽  
Double Decomposition

Turbulence models proposed for flow through permeable structures depend on the order of application of time and volume average operators. Two developed methodologies, following the two orders of integration, lead to different governing equations for the statistical quantities. The flow turbulence kinetic energy resulting in each case is different. This paper reviews recently published mathematical models developed for such flows. The concept of double decomposition is discussed and models are classified in terms of the order of application of time and volume averaging operators, among other peculiarities. A total of four major classes of models are identified and a general discussion on their main characteristics is carried out. Proposed equations for turbulence kinetic energy following time-space and space-time integration sequences are derived and similar terms are compared. Treatment of the drag coefficient and closure of the interfacial surface integrals are discussed.

Analysis of Impinging and Countercurrent Stagnating Flows by Reynolds Stress Model

2002 ◽  
Vol 124 (3) ◽  
pp. 706-718 ◽  
Author(s):  
Yong H. Im ◽  
Kang Y. Huh ◽  
Kwang-Yong Kim
Keyword(s):  
Numerical Simulation ◽  
Kinetic Energy ◽  
Turbulent Flows ◽  
Reynolds Stress ◽  
Dissipation Rate ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Stagnation Region

Numerical simulation is performed for stagnating turbulent flows of impinging and countercurrent jets by the Reynolds stress model (RSM). Results are compared with those of the k−ε model and available data to assess the flow characteristics and turbulence models. Three variants of the RSM tested are those of Gibson and Launder (GL), Craft and Launder (GL-CL) and Speziale, Sarkar and Gatski (SSG). As is well known, the k−ε model significantly overestimates turbulent kinetic energy near the wall. Although the RSM is superior to the k−ε model, it shows considerable difference according to how the redistributive pressure-strain term is modeled. Results of the RSM for countercurrent jets are improved with the modified coefficients for the dissipation rate, Cε1 and Cε2, suggested by Champion and Libby. Anisotropic states of the stress near the stagnation region are assessed in terms of an anisotropy invariant map (AIM).

scholarly journals Analysis of Flow Characteristics and Effects of Turbulence Models for the Butterfly Valve

2021 ◽  
Vol 11 (14) ◽  
pp. 6319
Author(s):  
Sung-Woong Choi ◽  
Hyoung-Seock Seo ◽  
Han-Sang Kim
Keyword(s):  
Turbulence Model ◽  
Dissipation Rate ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Flow Properties ◽  
Nominal Diameter ◽  
Large Pressure ◽  
Sst Model ◽  
Turbulence Effect ◽  
Valve Opening

In the present study, the flow characteristics of butterfly valves with different sizes DN 80 (nominal diameter: 76.2 mm), DN 262 (nominal diameter: 254 mm), DN 400 (nominal diameter: 406 mm) were numerically investigated under different valve opening percentages. Representative two-equation turbulence models of two-equation k-epsilon model of Launder and Sharma, two-equation k-omega model of Wilcox, and two-equation k-omega SST model of Menter were selected. Flow characteristics of butterfly valves were examined to determine turbulence model effects. It was determined that increasing turbulence effect could cause many discrepancies between turbulence models, especially in areas with large pressure drop and velocity increase. In addition, sensitivity analysis of flow properties was conducted to determine the effect of constants used in each turbulence model. It was observed that the most sensitive flow properties were turbulence dissipation rate (Epsilon) for the k-epsilon turbulence model and turbulence specific dissipation rate (Omega) for the k-omega turbulence model.

scholarly journals Mathematical models of supersonic and intersonic crack propagation in linear elastodynamics

2021 ◽  
Author(s):  
Javier Bonet ◽  
Antonio J. Gil
Keyword(s):  
Kinetic Energy ◽  
Crack Propagation ◽  
Mathematical Models ◽  
Linear Elasticity ◽  
Strain Energy ◽  
Equations Of Motion ◽  
Two Dimensions ◽  
Discontinuous Solutions ◽  
Linear Elasticity Theory ◽  
Intersonic Crack Propagation

AbstractThis paper presents mathematical models of supersonic and intersonic crack propagation exhibiting Mach type of shock wave patterns that closely resemble the growing body of experimental and computational evidence reported in recent years. The models are developed in the form of weak discontinuous solutions of the equations of motion for isotropic linear elasticity in two dimensions. Instead of the classical second order elastodynamics equations in terms of the displacement field, equivalent first order equations in terms of the evolution of velocity and displacement gradient fields are used together with their associated jump conditions across solution discontinuities. The paper postulates supersonic and intersonic steady-state crack propagation solutions consisting of regions of constant deformation and velocity separated by pressure and shear shock waves converging at the crack tip and obtains the necessary requirements for their existence. It shows that such mathematical solutions exist for significant ranges of material properties both in plane stress and plane strain. Both mode I and mode II fracture configurations are considered. In line with the linear elasticity theory used, the solutions obtained satisfy exact energy conservation, which implies that strain energy in the unfractured material is converted in its entirety into kinetic energy as the crack propagates. This neglects dissipation phenomena both in the material and in the creation of the new crack surface. This leads to the conclusion that fast crack propagation beyond the classical limit of the Rayleigh wave speed is a phenomenon dominated by the transfer of strain energy into kinetic energy rather than by the transfer into surface energy, which is the basis of Griffiths theory.

On Prediction and Unified Correlation for Decay of Vertical Buoyant Jets

1979 ◽  
Vol 101 (3) ◽  
pp. 532-537 ◽  
Author(s):  
C. J. Chen ◽  
C. H. Chen
Keyword(s):  
Kinetic Energy ◽  
Scaling Law ◽  
Flow Characteristics ◽  
Heat Fluxes ◽  
Buoyant Jets ◽  
Numerical Result ◽  
Plume Region ◽  
Unified Scaling Law ◽  
Rate Of Dissipation ◽  
Decay Behavior

A differential turbulence model is used to predict the decay behavior of turbulent buoyant jets in a uniform environment at rest. The turbulent stresses and heat fluxes are modeled by the algebraic expressions while the differential transport equations are solved for the kinetic energy of turbulence, k, the rate of dissipation of turbulence kinetic energy, ε, and the fluctuating temperature T′2. The numerical result correlated with a unified scaling law was shown to fall into a single curve for the flows beyond the zone of flow establishment. The flow characteristics are then classified into a non-buoyant region, an intermediate region and a plume region. The predicted results show that the buoyant jets is accelerated in the zone of flow establishment. Equations for decay of velocity, density, and turbulent quantities are given from the non-buoyant region to the plume region for both plane and round buoyant jets.

Analysis of an Airfoil Using a Transition and Turbulence Model

2016 ◽  
Vol 819 ◽  
pp. 356-360
Author(s):  
Mazharul Islam ◽  
Jiří Fürst ◽  
David Wood ◽  
Farid Nasir Ani
Keyword(s):  
Fluid Dynamics ◽  
Boundary Layer ◽  
Computational Fluid Dynamics ◽  
Kinetic Energy ◽  
Turbulence Model ◽  
Original Version ◽  
Transitional Region ◽  
Cfd Analysis ◽  
Computational Fluid Dynamics Cfd

In order to evaluate the performance of airfoils with computational fluid dynamics (CFD) tools, modelling of transitional region in the boundary layer is very critical. Currently, there are several classes of transition-based turbulence model which are based on different methods. Among these, the k-kL- ω, which is a three equation turbulence model, is one of the prominent ones which is based on the concept of laminar kinetic energy. This model is phenomenological and has several advantageous features. Over the years, different researchers have attempted to modify the original version which was proposed by Walter and Cokljat in 2008 to enrich the modelling capability. In this article, a modified form of k-kL-ω transitional turbulence model has been used with the help of OpenFOAM for an investigative CFD analysis of a NACA 4-digit airfoil at range of angles of attack.

scholarly journals Numerical and experimental study on turbulence statistics in a large fan-stirred combustion vessel

2021 ◽  
Vol 62 (5) ◽  
Author(s):  
M. E. Morsy ◽  
J. Yang
Keyword(s):  
Isotropic Turbulence ◽  
Burning Velocity ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Initial Pressure ◽  
Dynamics Modeling ◽  
Turbulence Statistics ◽  
Experimental Conditions ◽  
Measured Velocity

Abstract Particle image velocimetry (PIV) has become a popular non-intrusive tool for measuring various types of flows. However, when measuring three-dimensional flows with two-dimensional (2D) PIV, there are some uncertainties in the measured velocity field due to out-of-plane motion, which might alter turbulence statistics and distort the overall flow characteristics. In the present study, three different turbulence models are employed and compared. Mean and fluctuating fields obtained by three-dimensional computational fluid dynamics modeling are compared to experimental data. Turbulence statistics such as integral length scale, Taylor microscale, Kolmogorov scale, turbulence kinetic energy, dissipation rate, and velocity correlations are calculated at different experimental conditions (i.e., pressure, temperature, fan speed, etc.). A reasonably isotropic and homogeneous turbulence with large turbulence intensities is achieved in the central region extending to almost 45 mm radius. This radius decreases with increasing the initial pressure. The influence of the third dimension velocity component on the measured characteristics is negligible. This is a result of the axisymmetric features of the flow pattern in the current vessel. The results prove that the present vessel can be conveniently adopted for several turbulent combustion studies including mainly the determination of turbulent burning velocity for gaseous premixed flames in nearly homogeneous isotropic turbulence. Graphic abstract

Study of the Change of Performance of an Elastic Vertical Hydrofoil With Deformation

2014 ◽  
Author(s):  
Alexander Führing ◽  
Subha Kumpaty ◽  
Chris Stack
Keyword(s):  
Water Flow ◽  
Lift Coefficient ◽  
Flow Analysis ◽  
Turbulence Models ◽  
Flow Property ◽  
Performance Data ◽  
Cfd Analysis ◽  
Ansys Fluent ◽  
Drag Forces ◽  
Fluid Flow Analysis

In external and internal fluid flow analysis using numerical methods, most attention is paid to the properties of the flow assuming absolute rigidity of the solid bodies involved. However, this is often not the case for water flow or other fluids with high density. The pressure forces cause the geometry to deform which in turn changes the flow properties around it. Thus, a one-way and two-way Fluid-Structure Interaction (FSI) coupling is proposed and compared to a CFD analysis of a windsurfing fin in order to quantify the differences in performance data as well as the properties of the flow. This leads to information about the necessity of the use of FSI in comparison to regular CFD analysis and gives indication of the value of the enhanced results of the deformable analysis applied to water flow around an elastically deformable hydrofoil under different angles of attack. The performance data and flow property evaluation is done in ANSYS Fluent using the k-ω SST and k-ε model with a y+ of 1 and 35 respectively in order to be able to compare the behavior of both turbulence models. It is found that the overall lift coefficient in general is lower and that the flow is less turbulent because of softer transition due to the deformed geometry reducing drag forces. It is also found that the deformation of the tip of the hydrofoil leads to vertical lift forces. For the FSI analysis, one-way and two-way coupling were incorporated leading to the ability to compare results. It has been found that one-way coupling is sufficient as long as there is no stall present at any time.

Flow Characteristics of Transitional Boundary Layers on an Airfoil in Wakes

2000 ◽  
Vol 122 (3) ◽  
pp. 522-532 ◽  
Author(s):  
H. Lee ◽  
S.-H. Kang
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Skin Friction ◽  
Velocity Fluctuation ◽  
Plate Boundary ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Transitional Region ◽  
Mean Velocity ◽  
Measured Velocity

Transition characteristics of a boundary layer on a NACA0012 airfoil are investigated by measuring unsteady velocity using hot wire anemometry. The airfoil is installed in the incoming wake generated by an airfoil aligned in tandem with zero angle of attack. Reynolds number based on the airfoil chord varies from 2.0×105 to 6.0×105; distance between two airfoils varies from 0.25 to 1.0 of the chord length. To measure skin friction coefficient identifying the transition onset and completion, an extended wall law is devised to accommodate transitional flows with pressure gradient and nonuniform inflows. Variations of the skin friction are quite similar to that of the flat plate boundary layer in the uniform turbulent inflow of high intensity. Measured velocity profiles are coincident with families generated by the modified wall law in the range up to y+=40. Turbulence intensity of the incoming wake shifts the onset location of transition upstream. The transitional region becomes longer as the airfoils approach one another and the Reynolds number increases. The mean velocity profile gradually varies from a laminar to logarithmic one during the transition. The maximum values of rms velocity fluctuations are located near y+=15-20. A strong positive skewness of velocity fluctuation is observed at the onset of transition and the overall rms level of velocity fluctuation reaches 3.0–3.5 in wall units. The database obtained will be useful in developing and evaluating turbulence models and computational schemes for transitional boundary layer. [S0098-2202(00)01603-5]

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