scholarly journals CFD Modeling and evaluation of a bi-stable micro-diverter valve

2018 ◽  
Vol 8 (1) ◽  
pp. 77-84 ◽  
Author(s):  
Marco A Guevara L
Keyword(s):  
Steady State ◽  
Turbulence Models ◽  
Industrial Applications ◽  
Process Efficiency ◽  
Cfd Modeling ◽  
Time Step ◽  
Time Step Size ◽  
Operation Conditions ◽  
Low Reynolds ◽  
Transient And Steady State

Micro-diverter valves are innovative and efficient devices used to generate microbubbles that can significantly enhance process efficiency in industry. Micro-diverter valves have been experimentally tested and modeled using CFD in previous works. However, a detailed CFD modeling evaluation of these valves has not been performed employing detailed turbulence modeling at transient and steady state. This article presents a three-dimensional CFD simulation and performance evaluation of a bi-stable diverted valve for microbubble generation. In the model, transient and steady state approaches were used to quantify the behavior in the valve. The κ – ε standard and κ – ε RNG turbulence models were used and compared. Different mesh configurations, mesh generation methods, and both turbulence models were evaluated to find the best set-up to simulate this valve. A brief analysis of the time-step size using the Courant number approach was also performed. Operation conditions at low Reynolds (3800) and high frequency (200 Hz) were used to assess possible industrial applications, thus setting the base for further studies. The results of this work show that at low Reynolds numbers and high frequencies, the valve is able to divert the fluid and thus it may have wider industrial applications.

scholarly journals Feasibility Study of Rans in Predicting Propeller Cavitation in Behind-Hull Conditions

2020 ◽  
Vol 27 (4) ◽  
pp. 26-35
Author(s):  
Yuxin Zhang ◽  
Xiao-ping Wu ◽  
Ming-yan Lai ◽  
Guo-ping Zhou ◽  
Jie Zhang
Keyword(s):  
Model Test ◽  
Turbulence Models ◽  
Tip Vortex ◽  
Navier Stokes ◽  
Design Stage ◽  
Step Size ◽  
Time Step ◽  
Tip Vortex Cavitation ◽  
Time Step Size ◽  
Sheet Cavitation

AbstractThe propeller cavitation not only affects the propulsive efficiency of a ship but also can cause vibration and noise. Accurate predictions of propeller cavitation are crucial at the design stage. This paper investigates the feasibility of the Reynolds-averaged Navier–Stokes (RANS) method in predicting propeller cavitation in behind-hull conditions, focusing on four aspects: (i) grid sensitivity; (ii) the time step effect; (iii) the turbulence model effect; and (iv) ability to rank two slightly different propellers. The Schnerr-Sauer model is adopted as the cavitation model. A model test is conducted to validate the numerical results. Good agreement on the cavitation pattern is obtained between the model test and computational fluid dynamics. Two propellers are computed, which have similar geometry but slightly different pitch ratios. The results show that RANS is capable of correctly differentiating the cavitation patterns between the two propellers in terms of the occurrence of face cavitation and the extent of sheet cavitation; moreover, time step size is found to slightly affect sheet cavitation and has a significant impact on the survival of the tip vortex cavitation. It is also observed that grid refinement is crucial for capturing tip vortex cavitation and the two-equation turbulence models used – realizable k-ε and shear stress transport (SST) k-ω – yield similar cavitation results.

CFD Analysis of a Piping-Pressure Safety Valve System Working in Gas/Vapor Service

2020 ◽  
Author(s):  
Xue Guan Song ◽  
Chao Yong Zong ◽  
Feng Jie Zheng
Keyword(s):  
Safety Valve ◽  
Model Development ◽  
Turbulence Models ◽  
Experimental Tests ◽  
System Level ◽  
Cfd Model ◽  
Step Size ◽  
Time Step ◽  
Time Step Size ◽  
Transient Simulations

Abstract Configuration of piping-pressure safety valve (PPSV) is widely used but may sometimes show instabilities, which should be avoided or reduced. For exploring the cause of these instabilities, Computational Fluid Dynamics (CFD) provides a powerful tool that can be used not only to reproduce the system-level responses, but also to get the details of the local flows. However, the results of CFD simulations are usually sensitive to their model settings, thus, to ensure accuracy, effects of certain critical model settings (such as time-step size and turbulence model) on transient simulations should be determined. In this paper, a 2-D axisymmetric mesh model is developed first, which can be used to predict the dynamic responds of a PPSV system. With this model, three levels of time-steps are tested. The results indicate that the time-step of 1e−5 is a reasonable choice for transient simulations of the PPSV system. After that, a total of four two-equation turbulence models are used for transient simulations. The results indicate that the SST (Shear stress transport) k-omega model produce the closest results to the experiments. After that, the accuracy of the developed CFD model (with 1e−5s time-step and SST k-omega setting) is verified by experimental tests. The results indicate that the developed CFD model can accurately reproduce the dynamic responds of the PPSV system. Outcomes obtained in this paper can not only provide a reference for the transient CFD model development, but also verify the applicability and high accuracy of 2-D axisymmetric CFD models in PPSV dynamics prediction.

Thorough Verification and Validation of CFD Prediction of FPSO Current Load for Confident Applications

2019 ◽  
Author(s):  
Wei Xu ◽  
Zhenjia (Jerry) Huang ◽  
Hyunjoe Kim
Keyword(s):  
Mesh Refinement ◽  
Domain Size ◽  
Development Project ◽  
Transverse Load ◽  
Cfd Modeling ◽  
Current Load ◽  
Step Size ◽  
Time Step ◽  
Time Step Size ◽  
Rans Model

Abstract In this paper, a thorough verification of FPSO current load modeling and simulation using CFD was carried out and a modeling practice developed in a joint development project [1] was adopted. The towing test data obtained with thorough quality assurance process were used as benchmark data in the verification work. To have high confidence in the CFD modeling and simulations, both steady simulations with RANS model and unsteady simulations with IDDES model were carried out. For the steady simulations, sensitivity checks were carried out for the domain size, mesh refinement, turbulence models, boundary conditions and Reynolds effect. For unsteady simulations, the wake zone mesh refinement, time step size, number of inner iterations and different RANS model for boundary layers were considered during the sensitivity verification stage. It was found in this study that the transverse load (Fy) and yaw moment (Mz) of the FPSO can be predicted fairly well using RANS model, while the DES model needs to be adopted in order to accurately predict the longitudinal forces (Fx) at certain range of current directions. The wake grid for the DES needs to be fine enough in order to capture the details of vortices and the running time trace needs to be long enough to reduce the sensitivity on the mean current forces.

On Time-Averaged CFD Modeling of Circulating Fluidized Beds

2012 ◽  
Vol 13 (6) ◽  
Author(s):  
Veikko Taivassalo ◽  
Sirpa Kallio ◽  
Juho Peltola
Keyword(s):  
Steady State ◽  
Momentum Transfer ◽  
Fluidized Beds ◽  
Computing Time ◽  
Time Dependent ◽  
Cfd Modeling ◽  
Circulating Fluidized Beds ◽  
Time Step ◽  
Closure Models ◽  
Steady State Simulation

AbstractCFD simulations of single-phase flows are regularly performed as steady-state utilizing closure models of varying complexity. On the contrary, dense gas-solid flows are usually computed as time dependent. These simulations commonly require a small time step and a fine mesh resulting in costly and time-consuming computations. In case of large industrial circulating fluidized beds (CFB), the steady-state CFD modeling would be an attractive alternative for the transient simulations, if reliable closure models for the time-averaged transport equations were available. The multiphase closure models developed for time-dependent CFB computations are not as such applicable to the steady-state approach. For instance, the fraction of the momentum transfer expressed by the velocities is significantly smaller in the steady-state models than in the transient ones. Therefore, the steady-state simulations rely more on the closure relations and especially on the models for inter-phase momentum transfer and for the Reynolds stress terms.Several attempts to develop closure models for coarsemesh and steady-state simulations have been presented in the literature. In this paper, a novel steady-state simulation approach for a CFB process and a corresponding CFD model are introduced. A successful steady-state simulation for a test case is presented. Compared to the time-dependent simulations, the computing time is reduced by a factor of an order of 1000.

scholarly journals Numerical Investigation of the Performance, Hydrodynamics, and Free-Surface Effects in Unsteady Flow of a Horizontal Axis Hydrokinetic Turbine

Processes ◽  
2021 ◽  
Vol 10 (1) ◽  
pp. 69
Author(s):  
Aldo Benavides-Morán ◽  
Luis Rodríguez-Jaime ◽  
Santiago Laín
Keyword(s):  
Free Surface ◽  
Maximum Velocity ◽  
Turbulence Models ◽  
Horizontal Axis ◽  
Step Size ◽  
Time Step ◽  
Time Step Size ◽  
Power Extraction ◽  
Vof Model ◽  
Hydrokinetic Turbine

This paper presents computational fluid dynamics (CFD) simulations of the flow around a horizontal axis hydrokinetic turbine (HAHT) found in the literature. The volume of fluid (VOF) model implemented in a commercial CFD package (ANSYS-Fluent) is used to track the air-water interface. The URANS SST k-ω and the four-equation Transition SST turbulence models are employed to compute the unsteady three-dimensional flow field. The sliding mesh technique is used to rotate the subdomain that includes the turbine rotor. The effect of grid resolution, time-step size, and turbulence model on the computed performance coefficients is analyzed in detail, and the results are compared against experimental data at various tip speed ratios (TSRs). Simulation results at the analyzed rotor immersions confirm that the power and thrust coefficients decrease when the rotor is closer to the free surface. The combined effect of rotor and support structure on the free surface evolution and downstream velocities is also studied. The results show that a maximum velocity deficit is found in the near wake region above the rotor centerline. A slow wake recovery is also observed at the shallow rotor immersion due to the free-surface proximity, which in turn reduces the power extraction.

3D Coupled Fluid-Solid Thermal Simulation of a Turbine Disc Through a Transient Cycle

2012 ◽  
Author(s):  
Zixiang Sun ◽  
John W. Chew ◽  
Nicholas J. Hills ◽  
Christopher J. Barnes ◽  
Antonio Guijarro Valencia
Keyword(s):  
Test Data ◽  
Industrial Applications ◽  
Cfd Modeling ◽  
Test Case ◽  
Time Step ◽  
Element Analysis ◽  
Cooling Flow ◽  
Turbine Disc ◽  
Data Provision ◽  
Rapid Transients

Thermal analysis of a turbine disc through a transient test cycle is demonstrated using 3D computational fluid dynamics (CFD) modeling for the cooling flow and 3D finite element analysis (FEA) for the disc. The test case is a 3D angular sector of the high pressure (HP) turbine assembly of a civil jet engine and includes details of the coolant flow around the blade roots. Proprietary FEA and CFD solvers are used to simulate the metal and fluid domains, respectively. Coupling is achieved through an iterative loop with smooth exchange of information between the FEA and CFD simulations at each time step, ensuring consistency of temperature and heat flux on the coupled interfaces between the metal and fluid domains. The coupled simulation can be completed within a few weeks using a PC cluster with multiple parallel CFD executions. The FEA/CFD coupled result agrees well with corresponding rig test data and the baseline 3D and 2D FEA solutions, which have been calibrated using test data. Provision of upstream boundary conditions and modeling of rapid transients are identified as areas of uncertainty. Averaging of CFD solutions and relaxation is used to overcome difficulties caused by CFD oscillations associated with flow unsteadiness. The present work supports the continued use and development of the FEA/CFD coupling method for industrial applications.

Calibration 7" – Cutthroat Flume as New Size for Discharge Measurement at Free Flow Condition

2020 ◽  
Vol 38 (12A) ◽  
pp. 1783-1789
Author(s):  
Jaafar S. Matooq ◽  
Muna J. Ibraheem
Keyword(s):  
Steady State ◽  
Flow Condition ◽  
Laboratory Experiments ◽  
Free Flow ◽  
Experimental Program ◽  
Steady State Flow ◽  
Empirical Formulas ◽  
State Flow ◽  
Operation Conditions ◽  
Throat Width

 This paper aims to conduct a series of laboratory experiments in case of steady-state flow for the new size 7 ̋ throat width (not presented before) of the cutthroat flume. For this size, five different lengths were adopted 0.535, 0.46, 0.40, 0.325 and 0.27m these lengths were adopted based on the limitations of the available flume. The experimental program has been followed to investigate the hydraulic characteristic and introducing the calibrated formula for free flow application within the discharge ranged between 0.006 and 0.025 m3/s. The calibration result showed that, under suitable operation conditions, the suggested empirical formulas can accurately predict the values of discharge within an error ± 3%.

scholarly journals Prediction of Liner Metal Temperature of an Aeroengine Combustor with Multi-Physics Scale-Resolving CFD

Entropy ◽  
2021 ◽  
Vol 23 (7) ◽  
pp. 901
Author(s):  
Davide Bertini ◽  
Lorenzo Mazzei ◽  
Antonio Andreini
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Turbulence Models ◽  
Metal Temperature ◽  
Lean Burn ◽  
Turbulence Scale ◽  
Ansys Fluent ◽  
Multi Scale ◽  
Assessment Tests ◽  
Rans Turbulence Models

Computational Fluid Dynamics is a fundamental tool to simulate the flow field and the multi-physics nature of the phenomena involved in gas turbine combustors, supporting their design since the very preliminary phases. Standard steady state RANS turbulence models provide a reasonable prediction, despite some well-known limitations in reproducing the turbulent mixing in highly unsteady flows. Their affordable cost is ideal in the preliminary design steps, whereas, in the detailed phase of the design process, turbulence scale-resolving methods (such as LES or similar approaches) can be preferred to significantly improve the accuracy. Despite that, in dealing with multi-physics and multi-scale problems, as for Conjugate Heat Transfer (CHT) in presence of radiation, transient approaches are not always affordable and appropriate numerical treatments are necessary to properly account for the huge range of characteristics scales in space and time that occur when turbulence is resolved and heat conduction is simulated contextually. The present work describes an innovative methodology to perform CHT simulations accounting for multi-physics and multi-scale problems. Such methodology, named U-THERM3D, is applied for the metal temperature prediction of an annular aeroengine lean burn combustor. The theoretical formulations of the tool are described, together with its numerical implementation in the commercial CFD code ANSYS Fluent. The proposed approach is based on a time de-synchronization of the involved time dependent physics permitting to significantly speed up the calculation with respect to fully coupled strategy, preserving at the same time the effect of unsteady heat transfer on the final time averaged predicted metal temperature. The results of some preliminary assessment tests of its consistency and accuracy are reported before showing its exploitation on the real combustor. The results are compared against steady-state calculations and experimental data obtained by full annular tests at real scale conditions. The work confirms the importance of high-fidelity CFD approaches for the aerothermal prediction of liner metal temperature.

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