Influence of Marine Propeller Geometry on Turbulence Model Selection for CFD Simulations

2021 ◽  
Vol 55 (2) ◽  
pp. 150-164
Author(s):  
Mohamed R. Shouman ◽  
Mohamed M. Helal
Keyword(s):  
Turbulent Flows ◽  
Small Diameter ◽  
Turbulence Models ◽  
Dynamics Simulation ◽  
Geometrical Parameters ◽  
Test Case ◽  
Transition Model ◽  
Transient Flows ◽  
Marine Propellers ◽  
Numerical Predictions

Abstract One of the big challenges yet to be addressed in the numerical simulation of wetted flow over marine propellers is the influence of propellers' geometry on the selection of turbulence models. Since the Reynolds number is a function of the geometrical parameters of the blades, the flow type is controlled by these parameters. The majority of previous studies employed turbulence models that are only appropriate for fully turbulent flows, and consequently, they mostly caused high discrepancy between numerical predictions and corresponding experimental measurements specifically at geometrical parameters generating laminar and transient flows. The present article proposes a complete procedure of computational fluid dynamics simulation for wetted flows over marine propellers using ANSYS FLUENT 16 and employing both transition-sensitive and fully turbulent models for comparison. The K-Kl-ω transition model and the fully turbulent standard K-ε model are suggested for this purpose. The investigation is carried out for two different propellers in geometrical features: the INSEAN E779a model and the Potsdam Propeller Test Case (PPTC) model. The results demonstrate the effectiveness of the K-Kl-ω transition model for the INSEAN E779a propeller rather than the PPTC propeller. This can be interpreted as the narrow-bladed and small-diameter propellers have more likely laminar and transient flows over its blades.

On Turbulent Flows Dominated by Curvature Effects

1992 ◽  
Vol 114 (1) ◽  
pp. 52-57 ◽  
Author(s):  
G. C. Cheng ◽  
S. Farokhi
Keyword(s):  
Turbulent Flows ◽  
Turbulence Model ◽  
Dominant Role ◽  
Longitudinal Velocity ◽  
Turbulence Models ◽  
Separated Flows ◽  
Local Curvature ◽  
Streamline Curvature ◽  
Curvature Effects ◽  
Numerical Predictions

A technique for improving the numerical predictions of turbulent flows with the effect of streamline curvature is developed. Separated flows and the flow in a curved duct are examples of flow fields where streamline curvature plays a dominant role. New algebraic formulations for the eddy viscosity μt incorporating the k–ε turbulence model are proposed to account for various effects of streamline curvature. The loci of flow reversal (where axial velocities change signs) of the separated flows over various backward-facing steps are employed to test the capability of the proposed turbulence model in capturing the effect of local curvature. The inclusion of the effect of longitudinal curvature in the proposed turbulence model is validated by predicting the distributions of the longitudinal velocity and the static pressure in an S-bend duct and in 180 deg turn-around ducts. The numerical predictions of different curvature effects by the proposed turbulence models are also reported.

scholarly journals On the influence of turbulent kinetic energy level on accuracy of k − ε and LRR turbulence models

2018 ◽  
Vol 45 (2) ◽  
pp. 139-149
Author(s):  
Djordje Novkovic ◽  
Jela Burazer ◽  
Aleksandar Cocic ◽  
Milan Lecic
Keyword(s):  
Kinetic Energy ◽  
Theoretical Analysis ◽  
Turbulent Kinetic Energy ◽  
Turbulent Flows ◽  
Cross Sections ◽  
Turbulence Models ◽  
Velocity Profiles ◽  
Navier Stokes ◽  
Test Case ◽  
Reynolds Stresses

This paper presents research regarding the influence of turbulent kinetic energy (TKE) level on accuracy of Reynolds averaged Navier?Stokes (RANS) based turbulence models. A theoretical analysis of influence TKE level on accuracy of the RANS turbulence models has been performed according to the Boussinesq hypothesis definition. After that, this theoretical analysis has been investigated by comparison of numerically and experimentally obtained results on the test case of a steady-state incompressible swirl-free flow in a straight conical diffuser named Azad diffuser. Numerical calculations have been performed using the OpenFOAM CFD software and first and secondorder closure turbulence models. TKE level, velocity profiles and Reynolds stresses have been calculated downstream in four different cross sections of the diffuser. Certain conclusions about modeling turbulent flows by ?? ??? and LRR turbulence models have been made by comparing the velocity profiles, TKE distribution and Reynolds stresses on the selected cross sections.

Capabilities of Thermal Wall Functions to Predict Heat Transfer on the NGVs of a Gas Turbine With Multiple Can Combustors

2015 ◽  
Author(s):  
Cosimo Maria Mazzoni ◽  
Salvador Luque ◽  
Budimir Rosic
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Turbulence Models ◽  
Thermal Characterization ◽  
Test Case ◽  
Wall Region ◽  
Wall Functions ◽  
Numerical Predictions ◽  
Near Wall

Modern gas turbine combustion systems are characterised by enhanced air/fuel mixing and this results in more diffused and redistributed hot streaks leading to higher thermal loads established on the vane surface and endwalls. Thus, a detailed aero-thermal characterization of the near-wall region has become crucial both for the analysis of turbine performances and for the subsequent design of special features, such as the use of advanced materials and/or novel efficient cooling concepts. In order to investigate complex combustor-turbine flow interactions high fidelity experimental facilities and numerical tools are required. In particular, detailed prediction of heat transfer at the gas turbine hot walls is computationally very demanding since it requires fully resolved boundary layers and very fine computational meshes. The present work investigates the capabilities of computationally less demanding near wall treatments (thermal wall functions) to predict heat transfer in gas turbine first stage vanes. This paper first summarizes the recent progress in the implementation of heat transfer capabilities into the CFD solver TBLOCK, by describing the near-wall treatments for forced thermal convection adopted in combination with standard turbulence models and aerodynamic wall functions. In order to assess the capabilities of the flow solver TBLOCK to predict heat transfer under engine realistic conditions an experimental cascade is then modelled numerically. The test case is the new linear cascade built at Oxford’s Osney Thermofluids Laboratory to simulate combustor-vane interactions in gas turbines for power generation; it consists of four first stage vane passages downstream a contracting inlet duct divided in two by a transition splitter that acts as the wall between two can combustors. Both aerodynamic and heat transfer numerical results are compared with available experimental data. Numerical predictions show good agreement with experiments and well reproduce the aero-thermal influence of the combustor wall, showing the reliability of standard CFD tools in simulating these flow regimes without demanding CPU costs.

Numerical prediction of the performance of marine propellers using computational fluid dynamics simulation with transition-sensitive turbulence model

2018 ◽  
Vol 233 (2) ◽  
pp. 515-527 ◽  
Author(s):  
Mohamed M Helal ◽  
Tamer M Ahmed ◽  
Adel A Banawan ◽  
Mohamed A Kotb
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Turbulence Model ◽  
Numerical Models ◽  
Dynamics Simulation ◽  
Flow Transition ◽  
Transition Flow ◽  
Computational Fluid Dynamics Simulation ◽  
Marine Propellers ◽  
Numerical Predictions

Determining and understanding the performance characteristics of marine propellers by experiments is quite a complex and costly task. Numerical predictions using computational fluid dynamics simulations could be a valuable alternative provided that the laminar-to-turbulent transition flow effects are fundamentally understood with the suitable numerical models developed. Experience suggests that the use of classical turbulent flow models may lead to high discrepancies especially at low rotational speeds where the effects of fluid flow transition from the laminar to the turbulent state may influence the predicted propeller’s performance. This article proposes a complete and detailed procedure for the computational fluid dynamics simulation of non-cavitating flow over marine propellers using the “ k–kl–ω” transition-sensitive turbulence model. Results are evaluated by “ANSYS FLUENT 16” for the “INSEAN E779A” propeller. Comparisons against the fully turbulent standard “ k–ε” model and against experiments show improved agreement in way of flow transition zones at lower rotational speeds, that is, at low Reynolds numbers.

Predictions of the Laminarization Phenomena in an Axially Rotating Pipe Flow

1988 ◽  
Vol 110 (4) ◽  
pp. 424-430 ◽  
Author(s):  
Shuichiro Hirai ◽  
Toshimi Takagi ◽  
Masaharu Matsumoto
Keyword(s):  
Turbulent Flows ◽  
Pipe Flow ◽  
Pipe Wall ◽  
Turbulence Models ◽  
Stress Equation ◽  
Pipe Axis ◽  
Numerical Predictions ◽  
Axial Velocity Profile ◽  
Pipe Rotation ◽  
Rotating Pipe Flow

Numerical predictions are compared with the experiments of swirling turbulent flows in a pipe where the swirl is driven by the pipe wall rotating around the pipe axis. The laminarization phenomena, that is, the deformation of the axial velocity profile into a shape similar to the laminar one and the decrease of the friction factor, caused by the pipe rotation can be predicted by the calculations applying the stress equation turbulence model. However, calculations applying two types of the k-ε two-equation models with and without the modification by the Richardson number, cannot predict the laminarization phenomena and the characteristic behaviors due to the swirl. The interpretations of the laminarization phenomena and the applicability of the turbulence models are presented.

scholarly journals Turbulence model performance for ventilation components pressure losses

2021 ◽  
Author(s):  
Karsten Tawackolian ◽  
Martin Kriegel
Keyword(s):  
Reynolds Number ◽  
Turbulence Model ◽  
Pressure Loss ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Test Case ◽  
Pressure Losses ◽  
Loss Coefficients ◽  
Near Wall

AbstractThis study looks to find a suitable turbulence model for calculating pressure losses of ventilation components. In building ventilation, the most relevant Reynolds number range is between 3×104 and 6×105, depending on the duct dimensions and airflow rates. Pressure loss coefficients can increase considerably for some components at Reynolds numbers below 2×105. An initial survey of popular turbulence models was conducted for a selected test case of a bend with such a strong Reynolds number dependence. Most of the turbulence models failed in reproducing this dependence and predicted curve progressions that were too flat and only applicable for higher Reynolds numbers. Viscous effects near walls played an important role in the present simulations. In turbulence modelling, near-wall damping functions are used to account for this influence. A model that implements near-wall modelling is the lag elliptic blending k-ε model. This model gave reasonable predictions for pressure loss coefficients at lower Reynolds numbers. Another example is the low Reynolds number k-ε turbulence model of Wilcox (LRN). The modification uses damping functions and was initially developed for simulating profiles such as aircraft wings. It has not been widely used for internal flows such as air duct flows. Based on selected reference cases, the three closure coefficients of the LRN model were adapted in this work to simulate ventilation components. Improved predictions were obtained with new coefficients (LRNM model). This underlined that low Reynolds number effects are relevant in ventilation ductworks and give first insights for suitable turbulence models for this application. Both the lag elliptic blending model and the modified LRNM model predicted the pressure losses relatively well for the test case where the other tested models failed.

A numerical study on combined baffles quick-separation device

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Ehsan Dehdarinejad ◽  
Morteza Bayareh ◽  
Mahmud Ashrafizaadeh
Keyword(s):  
Turbulent Flows ◽  
Separation Efficiency ◽  
Numerical Study ◽  
Turbulence Models ◽  
Complete Separation ◽  
Solid Particles ◽  
Flow Rates ◽  
Separation Device ◽  
Coupling Technique ◽  
Laminar And Turbulent Flows

Abstract The transfer of particles in laminar and turbulent flows has many applications in combustion systems, biological, environmental, nanotechnology. In the present study, a Combined Baffles Quick-Separation Device (CBQSD) is simulated numerically using the Eulerian-Lagrangian method and different turbulence models of RNG k-ε, k-ω, and RSM for 1–140 μm particles. A two-way coupling technique is employed to solve the particles’ flow. The effect of inlet flow velocity, the diameter of the splitter plane, and solid particles’ flow rate on the separation efficiency of the device is examined. The results demonstrate that the RSM turbulence model provides more appropriate results compared to RNG k-ε and k-ω models. Four thousand two hundred particles with the size distribution of 1–140 µm enter the device and 3820 particles are trapped and 380 particles leave the device. The efficiency for particles with a diameter greater than 28 µm is 100%. The complete separation of 22–28 μm particles occurs for flow rates of 10–23.5 g/s, respectively. The results reveal that the separation efficiency increases by increasing the inlet velocity, the device diameter, and the diameter of the particles.

Numerical and Experimental Analysis of the Tensile and Bending Behaviour of CFRP Cables

2017 ◽  
Vol 25 (9) ◽  
pp. 643-650
Author(s):  
Eduardo Antonio Wink de Menezes ◽  
Laís Vasconcelos da Silva ◽  
Carlos Alberto Cimini Junior ◽  
Felipe Ferreira Luz ◽  
Sandro Campos Amico
Keyword(s):  
Analytical Model ◽  
Oil And Gas ◽  
Steel Wire ◽  
Small Diameter ◽  
Oil And Gas Industry ◽  
Small Radius ◽  
Tensile Behaviour ◽  
Specific Strength ◽  
Numerical Predictions ◽  
Bending Behaviour

Due to their high fatigue life, specific strength and specific stiffness in comparison with steel, carbon-fibre reinforced polymer (CFRP) cables have attracted the infrastructure industry interest in recent years, primarily for use as structural tendons. Particularly the oil and gas industry showed interest for application in offshore platform anchorage systems, because of their exceptional corrosion and creep/relaxation behaviour. In such applications, the cables need to be tensioned in service and to be bent around relatively small-diameter spools for transportation and maintenance. Therefore, their tensile and bending behaviour is a subject of great concern. The aim of this work was to perform a test program on 1 × 19 CFRP cables in two different situations: tensile loading and four-point bending loading. Finite element models were developed to simulate both conditions, including frictional contact between the cable wires. A simplified analytical model was also used to predict the cable behaviour in tension. Numerical predictions were compared to experimental data showing relatively good accuracy, unlike the verified analytical model. CFRP cables presented outstanding tensile behaviour, but bending over small radius spools could not reach the performance of steel wire ropes. Furthermore, simulation could only fairly predict bending below strains of μ1,000 μe for the external rods, beyond which the cable presented highly non-linear behaviour that could not be simulated by the numerical model.

Multiscale Partially Averaged Navier Stokes Approach for the Prediction of Flow in Linear Compressor Cascade With Moving Casing

2011 ◽  
Author(s):  
Domenico Borello ◽  
Giovanni Delibra ◽  
Franco Rispoli
Keyword(s):  
Turbulence Models ◽  
Navier Stokes ◽  
Test Case ◽  
Compressor Cascade ◽  
Preliminary Assessment ◽  
Linear Compressor ◽  
Tip Leakage ◽  
Experimental Campaign ◽  
Elliptic Relaxation ◽  
Linear Compressor Cascade

In this paper we present an innovative Partially Averaged Navier Stokes (PANS) approach for the simulation of turbomachinery flows. The elliptic relaxation k-ε-ζ-f model was used as baseline Unsteady Reynolds Averaged Navier Stokes (URANS) model for the derivation of the PANS formulation. The well established T-FlowS unstructured finite volume in-house code was used for the computations. A preliminary assessment of the developed formulation was carried out on a 2D hill flow that represents a very demanding test case for turbulence models. The turbomachinery flow here investigated reproduces the experimental campaign carried out at Virginia Tech on a linear compressor cascade with tip leakage. Their measurements were used for comparisons with numerical results. The predictive capabilities of the model were assessed through the analysis of the flow field. Then an investigation of the blade passage, where experiments were not available, was carried out to detect the main loss sources.

Numerical Prediction of Flow in a Nuclear Fuel Bundle With Various Turbulence Models

2002 ◽  
Author(s):  
Wang Kee In ◽  
Dong Seok Oh ◽  
Tae Hyun Chun
Keyword(s):  
Turbulent Flow ◽  
Nuclear Fuel ◽  
Turbulence Models ◽  
Convective Transport ◽  
Stress Model ◽  
Convergence Criteria ◽  
Mean Flow ◽  
Numerical Predictions ◽  
Viscosity Models ◽  
Fuel Bundle

The numerical predictions using the standard and RNG k–ε eddy viscosity models, differential stress model (DSM) and algebraic stress model (ASM) are examined for the turbulent flow in a nuclear fuel bundle with the mixing vane. The hybrid (first-order) and curvature-compensated convective transport (CCCT) schemes were used to examine the effect of the differencing scheme for the convection term. The CCCT scheme was found to more accurately predict the characteristics of turbulent flow in the fuel bundle. There is a negligible difference in the prediction performance between the standard and RNG k-ε models. The calculation using ASM failed in meeting the convergence criteria. DSM appeared to more accurately predict the mean flow velocities as well as the turbulence parameters.

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