Complete Computational Fluid Dynamics Model Research Articles

Dynamic Instability Analysis of a Spring-Loaded Pressure Safety Valve Connected to a Pipe by Using Computational Fluid Dynamics Methods

Abstract As the ultimate protection of a pressure system, pressure safety valves (PSV) can respond in an unstable manner in the form of flutter and chatter, which will affect service life, reliability, and performance. In order to study the dynamic instability caused by multisource forces including the flow force, the spring compression force, and the pressure wave forces, a high-fidelity computational fluid dynamics (CFD) model of the system is proposed. A complete CFD model, incorporating the PSV, connected pipes, and the pressure vessel, is developed, in which advanced techniques in Fluent using User Defined Function (UDF) and Dynamic Layering method are combined to allow the PSV to be coupled to the system dynamics. Based on this model, the valve's opening and reclosing process is monitored to examine the influence of design parameters on the dynamic instability of the PSV. Specifically, the propagation of pressure waves along the connecting pipes is successfully captured, helping to assess the instability mechanism and provide the ability to optimize the design and setup of pressure relief systems.

Thermal optimization of a totally enclosed forced ventilated permanentmagnet traction motor using lumped parameter and partial computational fluid dynamics modeling

In this study, we present a thermal optimization method using the overall lumped parameter (LP) and partial computational fluid dynamics (CFD) modeling for a 600-kW permanent magnet traction motor developed for high-speed trains. The motor is totally enclosed forced ventilated to achieve high power density, high efficiency, and low maintenance requirements. Considering the electro-magnetic performance, bogie space, and thermal capacity, we propose a ventilation structure with zigzag plates in sector cross-section. We focus particularly on the ventilation channels and propose an overall LP model for thermal optimization, in which the full consideration of the influence of turbulent flow is given by using a partial CFD model. Given the specific critical parameters from the optimization results, we present a complete 3D CFD model of the whole motor to obtain an accurate temperature distribution and the maximum temperature rises in local points. The benefit of zigzag plates is studied extensively using both the LP and the complete CFD models and the results are verified by equivalent thermal experiments under rated operations. Experimental results indicate that the ventilation structure fulfills the normal operational demands of high-speed trains by improving thermal performance by more than 15%. Additionally, we propose an engineering method to estimate iron loss constraint with the complete CFD model to guide the control system design.

Parametric Investigation Using Computational Fluid Dynamics of the HVAC Air Distribution in a Railway Vehicle for Representative Weather and Operating Conditions

A computational fluid dynamics (CFD) analysis of air distribution in a representative railway vehicle equipped with a heating, ventilation, air conditioning (HVAC) system is presented in this paper. Air distribution in the passenger’s compartment is a very important factor to regulate temperature and air velocity in order to achieve thermal comfort. A complete CFD model, including the car’s geometry in detail, the passengers, the luminaires, and other the important features related to the HVAC system (air supply inlets, exhaust outlets, convectors, etc.) are developed to investigate eight different typical scenarios for Northern Europe climate conditions. The results, analyzed and discussed in terms of temperature and velocity fields in different sections of the tram, and also in terms of volumetric parameters representative of the whole tram volume, show an adequate behavior from the passengers’ comfort point of view, especially for summer climate conditions.

Numerical Investigation of the Air Pumping Noise Generation Mechanism in Tire Grooves

Tire noise has been a topic of increased focus of research in industrial countries in the recent years, due to its contribution to traffic noise. However, knowledge about aerodynamic noise generation mechanisms, which are responsible for the high frequency noise in tires is lacking. This study focuses on the aerodynamic mechanism of small-scale air pumping in tire grooves, where computational fluid dynamics (CFD) is used to investigate the flow and noise features resulting from two different types of deformation in the process of a tire groove interacting with a smooth road surface. The two deformation types include (a) a commonly used piston-type motion of the bottom wall and (b) a more realistic bulging in/out of the side walls of a tire groove. The large eddy simulation (LES)-based approach consisting of the filtered Navier–Stokes equations is employed here along with the appropriate boundary conditions to accurately calculate the solution of the fluid flow resulting from the compression and expansion of air in the groove. Flow patterns are analyzed using velocity and pressure field data, whereas noise analysis is carried out using temporal pressure profiles and corresponding frequency spectra. The comparative study presented here provides a better understanding of the small-scale air pumping phenomenon in tire grooves and also demonstrates the significance of the choice of deformation type employed in such numerical simulations. The latter is critical in designing a more complete CFD model, which can further be used to optimize the tire acoustics.

Absorption and Clearance of Pharmaceutical Aerosols in the Human Nose: Development of a CFD Model.

The objective of this study was to develop a computational fluid dynamics (CFD) model to predict the deposition, dissolution, clearance, and absorption of pharmaceutical particles in the human nasal cavity. A three-dimensional nasal cavity geometry was converted to a surface-based model, providing an anatomically-accurate domain for the simulations. Particle deposition data from a commercial nasal spray product was mapped onto the surface model, and a mucus velocity field was calculated and validated with in vivo nasal clearance rates. A submodel for the dissolution of deposited particles was developed and validated based on comparisons to existing in vitro data for multiple pharmaceutical products. A parametric study was then performed to assess sensitivity of epithelial drug uptake to model conditions and assumptions. The particle displacement distance (depth) in the mucus layer had a modest effect on overall drug absorption, while the mucociliary clearance rate was found to be primarily responsible for drug uptake over the timescale of nasal clearance for the corticosteroid mometasone furoate (MF). The model revealed that drug deposition in the nasal vestibule (NV) could slowly be transported into the main passage (MP) and then absorbed through connection of the liquid layer in the NV and MP regions. As a result, high intersubject variability in cumulative uptake was predicted, depending on the length of time the NV dose was left undisturbed without blowing or wiping the nose. This study has developed, for the first time, a complete CFD model of nasal aerosol delivery from the point of spray formation through absorption at the respiratory epithelial surface. For the development and assessment of nasal aerosol products, this CFD-based in silico model provides a new option to complement existing in vitro nasal cast studies of deposition and in vivo imaging experiments of clearance.

CFD and comparative study on the dual-function solar collectors with and without tile-shaped covers in water heating mode

This paper presents a dedicated study of a novel tile-shaped dual-function solar collector in water heating mode by using computational fluid dynamics (CFD). This system employs a modular panel incorporating tile-shaped covers that is able to serve as part of building pitched roof, thus creating a building integrated, highly efficient and aesthetically appealing solar heating structure, particularly suitable for the Chinese traditional buildings. A complete 3D CFD model was developed. The numerical prediction was validated using experimental data. It was found that the established model is able to predict the operational performance of the system at reasonable accuracy. With the specified system structure, the efficiency of the solar system was found to be a function of its operational conditions. The results indicated that lower inlet water temperature, higher water flow rate, higher ambient air temperature and lower solar radiation led to enhanced thermal efficiency of the module. Further, the performance of the dual-function solar collector with and without tile-shaped covers was comparatively studied. It was found that the tile-shaped collector is able to achieve higher efficiency at higher temperature operation. This work outlines the impacts of the main operational conditions to the tile-shaped dual-function solar collector's efficiency.

Simulation of Flow and Chemical Reactions in a Claus Sulfur Converter

Three-dimensional computational fluid dynamics (CFD) models were developed to investigate the flow distribution and chemical reactions in a partially packed vessel similar to a catalytic sulfur converter used to sweeten sour gas, known as a Claus converter. A gas feed enters the vessel and reacts over the catalyst before leaving as products. Simulations of the flow in a Claus converter showed that the packed bed acts as a good flow distributor. However, some fluctuations of flow were observed in the packed bed, especially in the zones corresponding to the incoming feed jet impingement locations. Near the outlet of the bed, the flow becomes significantly better distributed. The chemical reactions were simulated using a finite rate model. Results of the complete CFD model (including flow, chemical reactions, and heat transfer) of each of two Claus converters placed in series showed good agreement with the available industrial data. The numerically predicted conversion matched the available value closely, and so did the detailed composition of the gas leaving each of the three converters. The predicted and measured values of the temperature also showed good agreement.

Computational and Mathematical Modeling of Turbine Rim Seal Ingestion

Abstract Understanding and modeling of main annulus gas ingestion through turbine rim seals is considered and advanced in this paper. Unsteady three-dimensional computational fluid dynamics (CFD) calculations and results from a more elementary model are presented and compared with experimental data previously published by Hills et al. (1997). The most complete CFD model presented includes both stator and rotor in the main annulus and the interdisk cavity. The k-ε model of turbulence with standard wall function approximations is assumed in the model which was constructed in a commercial CFD code employing a pressure correction solution algorithm. It is shown that considerable care is needed to ensure convergence of the CFD model to a periodic solution. Compared to previous models, results from the CFD model show encouraging agreement with pressure and gas concentration measurements. The annulus gas ingestion is shown to result from a combination of the stationary and rotating circumferential pressure asymmetries in the annulus. Inertial effects associated with the circumferential velocity component of the flow have an important effect on the degree of ingestion. The elementary model used is an extension of earlier models based on orifice theory applied locally around the rim seal circumference. The new model includes a term accounting for inertial effects. Some good qualitative and fair quantitative agreement with data is shown.