scholarly journals Improvement of Grid Independence Test for Computational Fluid Dynamics Model of Building Based on Grid Resolution

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Minhyung Lee ◽  
Gwanyong Park ◽  
Changyoung Park ◽  
Changmin Kim
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Conventional Method ◽  
Characteristic Length ◽  
Grid Resolution ◽  
Test Method ◽  
Target Space ◽  
Independence Test ◽  
Grid Design ◽  
Grid Independence

Computational fluid dynamics (CFD) is being used in various research fields on the building environment. Target space of the CFD model is divided into a finite number of grids for numerical analysis. Therefore, an optimal grid design is required to obtain accurate results. The grid independence test is generally performed to design an optimal grid. However, given that there is no standardized procedure for gird independence test, most depend on the researcher’s experience and knowledge. In the conventional method, the subjective judgment of the researcher affected the selection of the grid conditions and the criteria for the optimal grid. It can lead to a decrease in the reliability of the simulation results by poor grid design. This study proposed a grid independence test method that applies the grid resolution to improve the conventional method. The grid resolution was calculated by applying the characteristic length. CV(RMSE) and R2 were applied as the criteria for optimal grid. A case study was conducted to evaluate the adequacy of the proposed method. As the characteristic length increased, the optimal grid resolution increased. In particular, for a characteristic length of 0.7 or more, the optimal grid resolution was evaluated as 24. The grid convergence index (GCI) was calculated to verify the suitability of the proposed method. As a result, all of the optimal grid resolution derived from the proposed method was evaluated as the optimal condition.

scholarly journals Numerical Investigation on Multiphase Flows in Various Configurations of Microchannels Using Computational Fluid Dynamics

2019 ◽  
Vol 17 (1) ◽  
pp. 82
Author(s):  
Mohd Fadhil Majnis ◽  
Mohamad Rawad Jalwan
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Fluid Flows ◽  
Chaotic Advection ◽  
Computational Domain ◽  
Mixing Performance ◽  
Vof Model ◽  
Computational Fluid Dynamics Cfd ◽  
Miscible Liquids ◽  
Grid Independence

A two-dimensional domain of multiphase flow analyses in this study using the Volume of Fluid (VOF) model was carried out in order to simulate and predict the fluid flows and mixing performance of two miscible liquids in various microchannel configurations. The various microchannels configurations were designed accordingly and the simulation was carried out based on the justified conditions, assumptions and considerations by using the commercial computational fluid dynamics (CFD) software, FLUENT. The grid type and size of the computational domain were verified in terms of stability by performing the grid independence analysis. The result showed that static mixing would be possible to achieve in various configurations of microchannels, however, the simulation results predicted that it appeared to be more efficient in complex and retrofitted microchannels. It showed the potential to promote and enhance chaotic advection, compositions distribution, and diffusivity as compared to basic microchannels that are mostly dependent only on the injection focus. Furthermore, the Reynolds number appeared to be a significant factor to enhance the mixing performance in microchannel beside the configurations.

Customized CFD for VIV: Advantages and Applications

2012 ◽  
Author(s):  
Oliver Heynes
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Conventional Method ◽  
General Purpose ◽  
Dynamics Modeling ◽  
Numerical Techniques ◽  
Computational Fluid Dynamics Modeling ◽  
Vortex Induced Vibrations ◽  
Simulation Time

A new concept is introduced in the field of Computational Fluid Dynamics modeling of vortex-induced-vibrations: a CFD code written specifically for modeling riser VIV. The concept of the “single-purpose” CFD code has numerous advantages over the conventional method of running a simulation within “general-purpose” CFD software. By virtue of choosing the most efficient numerical techniques for the type of flow encountered, accurate solutions can be obtained two orders of magnitude quicker than the equivalent simulation using general-purpose CFD software. This is demonstrated through several examples, where accurate run times are obtained within a few seconds of simulation time.

Modelling the effect of computation sampling on insight error in computational fluid dynamics scientific simulation

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Moeti Masiane ◽  
Eric Jacques ◽  
Wuchun Feng ◽  
Chris North
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Design Methodology ◽  
Cfd Simulation ◽  
Grid Resolution ◽  
Content Type ◽  
Computational Fluid Dynamics Cfd ◽  
Independent Variable ◽  
Cfd Applications ◽  
The Ideal

Purpose The purpose of this paper is to collect data from humans as they generate insights from the visualised results of computational fluid dynamics (CFD) scientific simulation. The authors hypothesise the behaviour of their insight errors (IEs) and proceed to quantify the IEs provided by the crowd participants. They then use the insight framework to model the behaviours of the errors. Using the crowd responses and models from the framework, they test the hypotheses and use the results to validate the framework for the speedup of CFD applications. Design/methodology/approach The authors use a randomised between-subjects experiment with blocking. CFD grid resolution is the independent variable while IE is the dependent variable. The experiment has one treatment factor with five levels. In case varying timestamps has an effect on insight variance levels, the authors block the responses by timestep. In total, 150 participants are randomly assigned to one of five groups and also randomly assigned to one of five blocks within a treatment. Participants are asked to complete a benchmark and open-ended task. Findings The authors find that the variances of insight and perception errors have a U-shaped relationship with grid resolution, that similar to the previously studied visualisation applications, the IE framework is valid for insights generated from CFD results and grid resolution can be used to predict the variance of IE resulting from observing CFD post-processing results. Originality/value To the best of the authors’ knowledge, no other work has measured IE variance to present it to simulation users so that they can use it as a feedback metric for selecting the ideal grid resolution when using grid resolution to speedup CFD simulation.

Effect of Valve Opening/Closing Setup on Computational Fluid Dynamics Prediction of Engine Flows

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Xiaofeng Yang ◽  
Seunghwan Keum ◽  
Tang-Wei Kuo
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Internal Combustion Engines ◽  
Flow Simulation ◽  
Grid Resolution ◽  
Valve Lift ◽  
Solid Boundary ◽  
Piv Measurement ◽  
Parametric Studies ◽  
Cylinder Flow

In computational fluid dynamics (CFD) simulations of internal combustion engines, one of the critical modeling parameters is the valve setup. A standard workaround is to keep the valve opens at a certain clearance (minimum valve lift), while imposing a solid boundary to mimic valve closure. This method would yield a step change in valve lift during opening and closing event, and different valve event timing than hardware. Two parametric studies were performed to examine (a) the effect of the minimum valve lift and (b) the effect of grid resolution at the minimum valve lift on predicted in-cylinder flow fields in Reynolds-averaged Navier–Stokes (RANS) simulations. The simulation results were compared with the state-of-the-art particle image velocimetry (PIV) measurement from a two-valve transparent combustion chamber (TCC-3) engine. The comparisons revealed that the accuracy of flow simulation is sensitive to the choice of minimum valve lift and grid resolution in the valve seat region. In particular, the predicted in-cylinder flow field during the intake process was found to be very sensitive to the valve setup. A best practice CFD valve setup strategy is proposed as a result of these parametric studies. The proposed CFD valve setup was applied to large eddy simulation (LES) of TCC-3 engine and preliminary results showed noticeable improvement already. Further evaluation of the valve setup strategy for LES simulations is ongoing and will be reported in a separate report.

scholarly journals Development and Verification of a Computational Fluid Dynamics Model of a Horizontal-Axis Tidal Current Turbine

2011 ◽  
Author(s):  
Michael J. Lawson ◽  
Ye Li ◽  
Danny C. Sale
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Tidal Current ◽  
Operating Conditions ◽  
Horizontal Axis ◽  
Grid Resolution ◽  
Computational Grids ◽  
Transient Simulations ◽  
Dependent Flow ◽  
Blade Element

This paper describes the development of a computational fluid dynamics (CFD) methodology to simulate the hydrodynamics of horizontal-axis tidal current turbines (HATTs). First, an HATT blade was designed using the blade element momentum method in conjunction with a genetic optimization algorithm. Several unstructured computational grids were generated using this blade geometry and steady CFD simulations were used to perform a grid resolution study. Transient simulations were then performed to determine the effect of time-dependent flow phenomena and the size of the computational timestep on the numerical solution. Qualitative measures of the CFD solutions were independent of the grid resolution. Conversely, quantitative comparisons of the results indicated that the use of coarse computational grids results in an under prediction of the hydrodynamic forces on the turbine blade in comparison to the forces predicted using more resolved grids. For the turbine operating conditions considered in this study, the effect of the computational timestep on the CFD solution was found to be minimal, and the results from steady and transient simulations were in good agreement. Additionally, the CFD results were compared to corresponding blade element momentum method calculations and reasonable agreement was shown. Nevertheless, we expect that for other turbine operating conditions, where the flow over the blade is separated, transient simulations will be required.

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