scholarly journals Identification of 1-D cavitation model parameters by means of computational fluid dynamics

2021 ◽  
pp. 1-12
Author(s):  
Jean Decaix ◽  
Sebastien Alligne ◽  
Andres Müller ◽  
Christophe Nicolet ◽  
Cecile Münch ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Model Parameters ◽  
Cavitation Model

scholarly journals Journal Bearing: An Integrated CFD-Analytical Approach for the Estimation of the Trajectory and Equilibrium Position

2020 ◽  
Vol 10 (23) ◽  
pp. 8573
Author(s):  
Franco Concli
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Pressure Distribution ◽  
Equilibrium Position ◽  
Analytical Approach ◽  
Journal Bearing ◽  
Cfd Model ◽  
Cavitation Model ◽  
Computational Fluid Dynamics Cfd ◽  
The Mathematical Model

For decades, journal bearings have been designed based on the half-Sommerfeld equations. The semi-analytical solution of the conservation equations for mass and momentum leads to the pressure distribution along the journal. However, this approach admits negative values for the pressure, phenomenon without experimental evidence. To overcome this, negative values of the pressure are artificially substituted with the vaporization pressure. This hypothesis leads to reasonable results, even if for a deeper understanding of the physics behind the lubrication and the supporting effects, cavitation should be considered and included in the mathematical model. In a previous paper, the author has already shown the capability of computational fluid dynamics to accurately reproduce the experimental evidences including the Kunz cavitation model in the calculations. The computational fluid dynamics (CFD) results were compared in terms of pressure distribution with experimental data coming from different configurations. The CFD model was coupled with an analytical approach in order to calculate the equilibrium position and the trajectory of the journal. Specifically, the approach was used to study a bearing that was designed to operate within tight tolerances and speeds up to almost 30,000 rpm for operation in a gearbox.

An Improved Computational Fluid Dynamics (CFD) Model for Erosion Prediction in Oil and Gas Industry Applications

2014 ◽  
Author(s):  
Deval Pandya ◽  
Brian Dennis ◽  
Ronnie Russell
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Surface Velocity ◽  
Particle Model ◽  
Model Parameters ◽  
Cfd Model ◽  
Erosion Model ◽  
Erosion Prediction ◽  
Erosion Models ◽  
Computational Fluid Dynamics Cfd

In recent years, the study of flow-induced erosion phenomena has gained interest as erosion has a direct influence on the life, reliability and safety of equipment. Particularly significant erosion can occur inside the drilling tool components caused by the low particle loading (<10%) in the drilling fluid. Due to the difficulty and cost of conducting experiments, significant efforts have been invested in numerical predictive tools to understand and mitigate erosion within drilling tools. Computational fluid dynamics (CFD) is becoming a powerful tool to predict complex flow-erosion and a cost-effective method to re-design drilling equipment for mitigating erosion. Existing CFD-based erosion models predict erosion regions fairly accurately, but these models have poor reliability when it comes to quantitative predictions. In many cases, the error can be greater than an order of magnitude. The present study focuses on development of an improved CFD-erosion model for predicting the qualitative as well as the quantitative aspects of erosion. A finite-volume based CFD-erosion model was developed using a commercially available CFD code. The CFD model involves fluid flow and turbulence modeling, particle tracking, and application of existing empirical erosion models. All parameters like surface velocity, particle concentration, particle volume fraction, etc., used in empirical erosion equations are obtained through CFD analysis. CFD modeling parameters like numerical schemes, turbulence models, near-wall treatments, grid strategy and discrete particle model parameters were investigated in detail to develop guidelines for erosion prediction. As part of this effort, the effect of computed results showed good qualitative and quantitative agreement for the benchmark case of flow through an elbow at different flow rates and particle sizes. This paper proposes a new/modified erosion model. The combination of an improved CFD methodology and a new erosion model provides a novel computational approach that accurately predicts the location and magnitude of erosion. Reliable predictive methodology can help improve designs of downhole equipment to mitigate erosion risk as well as provide guidance on repair and maintenance intervals. This will eventually lead to improvement in the reliability and safety of downhole tool operation.

An Assessment of Computational Fluid Dynamics Cavitation Models Using Bubble Growth Theory and Bubble Transport Modeling

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Michael P. Kinzel ◽  
Jules W. Lindau ◽  
Robert F. Kunz
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Analytic Solutions ◽  
Cfd Modeling ◽  
Computational Time ◽  
Cavitation Model ◽  
Modeling Framework ◽  
Homogeneous Models ◽  
Bubble Transport ◽  
Computational Fluid Dynamics Cfd

This effort investigates advancing cavitation modeling relevant to computational fluid dynamics (CFD) through two strategies. The first aims to reformulate the cavitation models and the second explores adding liquid–vapor slippage effects. The first aspect of the paper revisits cavitation model formulations with respect to the Rayleigh–Plesset equation (RPE). The present approach reformulates the cavitation model using analytic solutions to the RPE. The benefit of this reformulation is displayed by maintaining model sensitivities similar to RPE, whereas the standard models fail these tests. In addition, the model approach is extended beyond standard homogeneous models, to a two-fluid modeling framework that explicitly models the slippage between cavitation bubbles and the liquid. The results indicate a significant impact of slip on the predicted cavitation solution, suggesting that the inclusion of such modeling can potentially improve CFD cavitation models. Overall, the results of this effort point to various aspects that may be considered in future CFD-modeling efforts with the goal of improving the model accuracy and reducing computational time.

Computational fluid dynamics modelling of the visible light photocatalytic oxidation process of toluene for indoor building materials with locally doped titanium dioxide

2019 ◽  
Vol 29 (2) ◽  
pp. 163-179 ◽  
Author(s):  
Koki Nakahara ◽  
Mahbubul Muttakin ◽  
Kiyoshi Yamamoto ◽  
Kazuhide Ito
Keyword(s):  
Fluid Dynamics ◽  
Mathematical Model ◽  
Computational Fluid Dynamics ◽  
Titanium Dioxide ◽  
Gas Phase ◽  
Photocatalytic Oxidation ◽  
Building Materials ◽  
Model Parameters ◽  
Surface Boundary ◽  
Cfd Analysis

Computational fluid dynamics (CFD) is one of the promising methods that can precisely predict non-uniform air flow and contaminant distribution in indoor environments. The overarching objective of this study was to develop a mathematical model for describing the photocatalytic oxidation (PCO) reaction mechanism of gas phase toluene with titanium dioxide (TiO2)-bound indoor building materials. This mathematical model was developed based on Langmuir-Hinshelwood type kinetics and for the integration with CFD simulations as a wall surface boundary condition. The effects of gas phase toluene concentration, illuminance and humidity on the toluene oxidation reaction were considered with locally TiO2-doped building materials. Especially, humidity dependence was explicitly integrated as a competitive adsorption model between toluene and water vapour. Moreover, surface compositions of TiO2 and the substrate (ceramic tile in this study), and the physical adsorption properties of those materials, were modelled and integrated into the mathematical model. A 0.02 m3 chamber experiment and adsorption isotherm measurements were conducted to identify the model parameters. CFD analysis was carried out according to experimental scenarios, and an optimization procedure for the model parameters was proposed for their application as the boundary conditions in the CFD analysis.

Investigation of the cavitation model in an inducer for water and liquid nitrogen

2019 ◽  
Vol 233 (19-20) ◽  
pp. 6939-6952
Author(s):  
Yuqiao Zhang ◽  
Xiaodong Ren ◽  
Yan Wang ◽  
Xuesong Li ◽  
Yu Ito ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Liquid Nitrogen ◽  
Cavitation Number ◽  
Tip Vortex ◽  
Dynamics Simulation ◽  
Computational Fluid Dynamics Simulation ◽  
Cavitation Model ◽  
Model Features ◽  
Empirical Constants

Cavitation commonly occurs in the hydraulic machineries like inducers. Cavitation happening in the cryogens is sophisticated due to their complicated thermodynamic properties. Computational fluid dynamics could provide relatively precise prediction for water. However, existing computational fluid dynamics methods may fail to simulate the cryogens cavitation precisely. This study presents a computational fluid dynamics simulation of four major cavitation models in both the liquid nitrogen and the water in an inducer. Four different cavitation models analyzed in this work are full cavitation model, Kunz model, Zwart–Gerber–Belamri, and Schnerr & Sauer. And the computational fluid dynamics simulation results are verified by the experiment to ensure the cavitation model's applicability in both liquid. Comparison of cavitation in water and liquid nitrogen is conducted and analyzed. The four cavitation models can predict cavitation in water, but the Zwart–Gerber–Belamri model and Schnerr & Sauer model also feature high capability to predict tip vortex cavitation. The results show that the full cavitation model is suitable for simulating the liquid nitrogen cavitation without changing of the model constants. The empirical constants of the other models should be adjusted in the liquid nitrogen cavitation simulation. Full cavitation model features high robustness in various liquids. The Schnerr & Sauer model can achieve the best results by adopting different empirical constants. In addition, the inducer performs better in the liquid nitrogen than water at low cavitation number regime as the head coefficient drops smoothly in liquid nitrogen with decreasing cavitation number.

Analysis of Steam Turbine Blade Tip Excitation Forces by Means of Computational Fluid Dynamics and Experimental Cascade Results

2018 ◽  
Author(s):  
Stefan aus der Wiesche ◽  
Maximilian Passmann
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Large Scale ◽  
Analytical Relation ◽  
Model Parameters ◽  
Force Model ◽  
Local Pressure ◽  
Effective Discharge ◽  
Blade Tip ◽  
Gap Width

A semi-empirical steam excitation force model is presented for freestanding unshrouded blades. The model is resting on a superposition of the classical Thomas-Alford cross forces and additional fluid derived forces. The additional fluid derived forces are caused by static pressure modifications in the blade tip region and large-scale redistributions of the inflow velocity caused by the varying tip gap width due to eccentricity. The empirical model parameters are obtained by means of computational fluid dynamics (CFD) and experimental turbine cascade results. The Thomas-Alford cross force contribution is formulated by means of an analytical relation for the effective discharge coefficient. It is found, that the Thomas-Alford coefficient for the excitation cross-force increases if the blade tip gap decreases. That effect is caused by taking viscous flow effects into account, and it is in good agreement with available literature data. The direct force contribution results mainly from local pressure variation in the blade tip region, and it depends also on the mean tip gap width. A further effect is caused by an upstream redistribution of the velocity due to the varying tip gap width. This effect was discovered by Song and Martinez-Sanchez first, and it is confirmed experimentally by cascade measurements in the present paper.

scholarly journals Uncertainty analysis of rising sewer models with respect to input parameters and model structure using Monte Carlo simulations and computational fluid dynamics

2021 ◽  
Author(s):  
Ahmed Khalil ◽  
Domenico Santoro ◽  
Damien J. Batstone ◽  
Christopher T. DeGroot
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Model Parameters ◽  
Model Structure ◽  
Mathematical Form ◽  
Homogeneous Surface ◽  
Simple Flows ◽  
D Model

Abstract Modelling conversion processes in sewers can help minimize odour and pipe corrosion issues, but model uncertainties and errors must be understood. In this study, the Wastewater Aerobic/Anaerobic Transformation in Sewers (WATS) model is implemented in two different frameworks; 1-D (CSTR-in-series) and computational fluid dynamics (CFD) to study the uncertainties due to model parameters and its mathematical form. The 1-D model is used to conduct uncertainty/sensitivity analysis using Monte Carlo simulations. Time-averaged outputs were represented using a general linearized model to quantify the importance of specific parameters. The sulfide formation rate per unit area of the biofilm is the most influential parameter. Parameters controlling anaerobic hydrolysis and fermentation are also significant. Uncertainty due to model structure is studied using CFD to explore the influences of non-homogeneous surface reactions and solids settling. These showed that the 1-D model provides a reasonable characterisation of the process for simple flows in pressure mains.

Computational Fluid Dynamics As a Tool for Deriving Subchannel Model Parameters: The PSBT Case Study

2018 ◽  
Author(s):  
R. Puragliesi ◽  
R. Mukin ◽  
I. Clifford ◽  
H. Ferroukhi ◽  
M. Seidl
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Pressure Loss ◽  
Numerical Models ◽  
Flow Distribution ◽  
Loss Coefficient ◽  
Wall Friction ◽  
Model Parameters ◽  
Pressure Loss Coefficient ◽  
Loss Coefficients

The development of subchannel models for fuel assemblies and reactor cores requires accurate information on flow distribution, wall friction and loss coefficients in order to accurately predict the pressure, temperature and flow distribution on a subchannel level. This paper discusses the use of Computational Fluid Dynamics (CFD) simulations as a practical tool for characterising inlet velocity boundary conditions, an approximation of wall friction factor and spacer grid pressure loss coefficient, which are of fundamental importance to correctly generate a consistent subchannel model of a given assembly system. The geometry of the simplified PWR assembly presented here is based on the NUPEC PWR subchannel and bundle tests. Comparison of the derived friction factors and grid pressure loss coefficient with published and recommended values are reported. Discrepancies are also explained using additional calculations. A comparison of the overall system pressure drop, by comparing_numerical and analytical solutions, and the local axial pressure distribution at subchannel level are presented. To make a one-to-one comparison between CFD and subchannel solutions, volume-averaging is applied to the CFD results according to the chosen subchannel nodalization. The obtained results show a perfect agreement between the two codes. This outcome reflects the correct approach employed to build two consistent numerical models by properly carrying important information from the high-resolution models (CFD) to the low-resolution models (subchannel code). Furthermore, it has been found that the large discrepancies recorded in the CFD prediction of the grid pressure loss coefficients suggested in the benchmark specifications are mainly because the suggested benchmark values do not take into account the presence of the bounding channel that was present in the experimental facility.

Sign in / Sign up

Export Citation Format

Share Document