scholarly journals Numerical models development for unidirectional air flow diffusers with lobed and circular orifices

2019 ◽  
Vol 111 ◽  
pp. 01049
Author(s):  
Laurentiu Tacutu ◽  
Ilinca Nastase ◽  
Florin Bode ◽  
Cristiana Croitoru ◽  
Catalin Lungu
Keyword(s):  
Numerical Simulation ◽  
Boundary Conditions ◽  
Numerical Study ◽  
Numerical Models ◽  
Ventilation System ◽  
Numerical Results ◽  
Airflow Distribution ◽  
Numerical Grid ◽  
Computational Resources ◽  
Real Scale

In order to achieve more realistic boundary conditions on the inlet of a ventilation system it is necessary to study the influences of the air diffuser orifices geometry on the airflow distribution in the enclosure. Integrating these orifices directly in a real scale air diffuser for a numerical study will result in a huge computational grid which will translate in huge computational resources and a much larger calculation time. The solution, in this case, was the numerical simulation of the airflow through small parts of the studied air diffuser. Later, the numerical results will be implemented as boundary conditions in the unidirectional diffuser of a numerical simulation that represents a real scale operating room (OR). In the current study two diffusers with different orifices were studied, one having circular („O”) and the other one lobbed („+”) orifices. The initial numerical model had 25 orifices on the diffuser, but because of the very large numerical grid resulted for the initial meshes (>35 million tetrahedral cells), a solution with only 4 orifices was chosen for this study. A mesh independency study was made for these two types of air diffusers. The numerical studies were made using RANS method, with SST k-ω turbulence model in steady state conditions. The numerical results obtained with the first step models showed very good agreement with the PIV stereoscopic experimental measurements.

scholarly journals Numerical study of the air distribution in the Crew Quarters on board of the International Space Station

2019 ◽  
Vol 85 ◽  
pp. 02015 ◽  
Author(s):  
Charles Berville ◽  
Matei-Răzvan Georgescu ◽  
Ilinca Năstase
Keyword(s):  
Numerical Simulations ◽  
International Space Station ◽  
Numerical Study ◽  
Ventilation System ◽  
Space Station ◽  
Air Distribution ◽  
Thermal Manikin ◽  
Airflow Rate ◽  
International Space ◽  
Airflow Distribution

The current concept of Crew Quarters on board of the International Space Station has several issues according to the crew member’s feedback. Major issues concern noise levels, the accumulation of CO2 and the quality of the air distribution. Our study targets the airflow distribution, to diagnose this issue, we realise a series of numerical simulations (CFD) based on a real scale replica of the Crew Quarters. Simulations were set with a zero-gravity mode and with the theoretical air parameters inside the SSI. The geometry includes a thermal manikin having the neutral posture of a body in the absence of gravity. Numerical simulations were run for the three different air flow rates provided by the current ventilation system. Results have shown that the air distribution inside the Crew Quarter is insufficient for low airflow rates but becomes acceptable for the higher airflow rate, however the higher airflow rate can potentially produce draught discomfort.

Numerical Simulation of Accident Scenario in High Temperature Gas Cooled (Pebble Bed) Nuclear Reactors

2012 ◽  
Author(s):  
Geoffrey J. Peter
Keyword(s):  
Numerical Simulation ◽  
High Temperature ◽  
Boundary Conditions ◽  
Nuclear Reactors ◽  
Numerical Study ◽  
Packed Bed ◽  
Pebble Bed ◽  
Accident Scenario ◽  
Set Up ◽  
High Temperature Gas

The accident scenario resulting from blockages due to the retention of dust in the coolant gas or from the rupture of one or more fuel particles used in the High Temperature Gas Cooled (Pebble Bed) Nuclear Reactors considered for the next generation of Advanced High Temperature Reactors (AHTR), for nuclear power production, and for high-temperature hydrogen production using nuclear reactors to reduce the carbon footprint is examined in this paper. Blockages can cause local variations in flow and heat transfer that may lead to hot spots within the bed that could compromise reactor safety. Therefore, it is important to know the void fraction distribution and the interstitial velocity field in the packed bed. The blockage for this numerical study simulated a region with significantly lower void than that in the rest of the bed. Finite difference technique solved the simplified continuity, momentum, and energy equations. Any meaningful outcome of the solution depended largely upon the validity of the boundary conditions. Among them, the inlet and outlet velocity profiles required special attention. Thus, a close approximation to these profiles obtained from an experimental set-up established the boundary conditions. This paper presents the development of the elliptic-partial differential equation for a bed of pebbles, and the solution procedure. The paper also discusses velocity and temperature profiles obtained from both numerical and experimental setup, with and without effect of blockage. In addition, the paper compares the results obtained from the experimental set-up with numerical simulation using a commercially available code that uses finite element techniques.

Natural Convection of Nanofluid in a Triangle Cavity with Different Angular Positions

2020 ◽  
Vol 12 (3) ◽  
pp. 325-329
Author(s):  
Mohsen Rostami ◽  
Mohammad Saleh Abadi
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Natural Convection ◽  
Flow Field ◽  
Boundary Conditions ◽  
Angular Position ◽  
Numerical Results ◽  
Heat Transfer Characteristics ◽  
Current Structure ◽  
Flow And Heat Transfer

The effects of the angular position on the flow and heat transfer of the nanofluid in a triangular cavity is investigated numerically. A triangular cavity is chosen with the same boundary conditions as the published results are available. The comparison between the current numerical results with the available data is made to show the accuracy of the numerical simulation. The current structure of triangular cavity is rotated to investigate the effects of various angular positions on the flow and heat transfer characteristics of nanofluid. For this purpose, the equations of continuity, momentum and energy are solved numerically. The results show that the hot fluid is more freely penetrated into the domain by increasing of the angular position. The velocity of fluid in the flow field becomes maximum for the angle of 120 . Also, the creation of vortices in the flow field depends on the value of angular position.

A 3D BOUNDARY ELEMENT METHOD FOR DETERMINATION OF ACOUSTIC EIGENFREQUENCIES CONSIDERING ADMITTANCE BOUNDARY CONDITIONS

1993 ◽  
Vol 01 (04) ◽  
pp. 455-468 ◽  
Author(s):  
Z. S. CHEN ◽  
G. HOFSTETTER ◽  
H. A. MANG
Keyword(s):  
Boundary Element Method ◽  
Boundary Conditions ◽  
Boundary Element ◽  
Large Scale ◽  
Numerical Study ◽  
Numerical Algorithms ◽  
Numerical Results ◽  
Simple Problem ◽  
Element Method

A 3D boundary element method for the determination of the acoustic eigenfrequencies of car compartments, characterized by a unified treatment of Robin, Dirichlet, and Neumann boundary conditions, is presented. The drawback of frequency-dependent matrices of the eigenvalue problem is overcome by means of the Particular Integral Method. Thus, the standard numerical algorithms for the extraction of eigenvalues can be applied. The numerical study contains both a comparison of numerical results with analytical solutions of a simple problem with different types of boundary conditions and a comparison of numerical results of a large-scale problem with respective numerical results, computed on the basis of the finite element method. In addition, for the latter example, different numerical algorithms for the eigenvalue extraction are examined.

Experimental and Numerical Study of the Response of an Axial Compressor to Distorted Inlet Flow

1988 ◽  
Vol 110 (4) ◽  
pp. 355-360 ◽  
Author(s):  
G. Billet ◽  
J. Huard ◽  
P. Chevalier ◽  
P. Laval
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Numerical Study ◽  
Axial Compressor ◽  
Numerical Approach ◽  
Compressor Blade ◽  
Numerical Results ◽  
Test Stand ◽  
Viscous Effects ◽  
Inlet Flow

A model representing the response of fixed or rotating axial compressor blade-rows is coupled to a 3-D numerical simulation of the flow outside the blade rows. The code can be used to study nonuniform compressible 3-D flows through turbomachines. The fluid is assumed to be inviscid in the space outside the rows, while the viscous effects are taken into account inside. Numerical results are compared with experimental data obtained on a test stand with steady distorted inflow. This comparison shows that this numerical approach is capable of predicting the response of the compressor. This work is part of a larger project aimed at predicting the response of a compressor to a nonuniform inlet flow that is periodic in time, or fully unsteady.

scholarly journals Numerical and Experimental Investigation into the Aerodynamic Benefits of Rotorcraft Formation Flight

2021 ◽  
Author(s):  
Ramon Duivenvoorden ◽  
Mark Voskuijl ◽  
Lars Morée ◽  
Jan de Vries ◽  
Finbar van der Veen
Keyword(s):  
Wind Tunnel ◽  
Numerical Study ◽  
Numerical Models ◽  
Wind Tunnel Experiment ◽  
Numerical Results ◽  
Formation Flight ◽  
Total Power ◽  
Small Scale ◽  
Main Rotor ◽  
Rotor Disk

The use of formation flight to achieve aerodynamic benefit applied to rotorcraft has, unlike its fixed-wing counterpart, received little attention in the literature. This document presents a proof-of-concept of rotorcraft formation flight from two independent investigations: a numerical study of a fully articulated helicopter influenced by an upstream helicopter wake and a wind-tunnel experiment featuring two small-scale helicopter models with fixed-pitch blades. Both cases feature a representation of two helicopters in a diagonal, staggered formation aligned on the advancing side of the main rotor, but do not simulate directly comparable flight conditions. The vertical and lateral alignment of the two helicopters is varied in order to observe the achievable reductions in main rotor power required during cruise flight. The wind-tunnel experiment data yield an estimated maximum total power reduction for the secondary aircraft of approximately 24%, while the numerical models yield reductions between 20% and 34% dependent on flight velocity. Both experiments predict a higher potential for aerodynamic benefit than generally observed for fixed-wing formations, which is attributed to the asymmetric velocity profile induced by the wake of the upstream rotor. Optimal lateral alignment of both experimental and numerical results is found to feature overlap of the rotor disk areas, rather than tip-to-tip alignment, as a result of the circular rotor disk area. Experimental data show an optimal vertical alignment of the secondary rotorcraft below the primary, due to the self-induced vertical displacement of the rotor wake, which is absent from the numerical results due to the application of a flat wake assumption. The results show a promising potential for rotorcraft formation flight, though due to the limited nature of the models used, conclusions cannot be generalized. The potential aerodynamic benefit indicated by the present study invites further research in the field of rotorcraft formation flight.

scholarly journals Combining H-Adaptivity with the Element Splitting Method for Crack Simulation in Large Structures

Materials ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 240
Author(s):  
Shi Song ◽  
Moritz Braun ◽  
Bjarne Wiegard ◽  
Hauke Herrnring ◽  
Sören Ehlers
Keyword(s):  
Numerical Simulation ◽  
Large Scale ◽  
Numerical Models ◽  
Mesh Refinement ◽  
Splitting Method ◽  
Ship Hulls ◽  
Large Structures ◽  
Loss Of Mass ◽  
Coarse Meshes ◽  
Computational Resources

H-adaptivity is an effective tool to introduce local mesh refinement in the FEM-based numerical simulation of crack propagation. The implementation of h-adaptivity could benefit the numerical simulation of fatigue or accidental load scenarios involving large structures, such as ship hulls. Meanwhile, in engineering applications, the element deletion method is frequently used to represent cracks. However, the element deletion method has some drawbacks, such as strong mesh dependency and loss of mass or energy. In order to mitigate this problem, the element splitting method could be applied. In this study, a numerical method called ‘h-adaptive element splitting’ (h-AES) is introduced. The h-AES method is applied in FEM programs by combining h-adaptivity with the element splitting method. Two examples using the h-AES method to simulate cracks in large structures under linear-elastic fracture mechanics scenario are presented. The numerical results are verified against analytical solutions. Based on the examples, the h-AES method is proven to be able to introduce mesh refinement in large-scale numerical models that mostly consist of structured coarse meshes, which is also beneficial to the reduction of computational resources. By employing the h-AES method, very small cracks are well represented in large structures without any deletions of elements.

scholarly journals Numerical Study on Crack Propagation by Using Softening Model under Blasting

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Rong Hu ◽  
Zheming Zhu ◽  
Jun Xie ◽  
Dingjun Xiao
Keyword(s):  
Numerical Simulation ◽  
Crack Propagation ◽  
Numerical Study ◽  
Numerical Models ◽  
Incident Angle ◽  
Damage Model ◽  
Maximum Principal Stress ◽  
Stress Criterion ◽  
Proposed Model ◽  
Simulation Results

A mixed failure criterion, which combined the modified maximum principal stress criterion with the damage model of tensile crack softening, was developed to simulate crack propagation of rock under blasting loads. In order to validate the proposed model, a set of blasting models with a crack and a borehole with different incident angles with the crack were established. By using this model, the property of crack propagation was investigated. The linear equation of state (EOS) was used for rock, and the JWL EOS was applied to the explosive. In order to validate the numerical simulation results, experiments by using PMMA (polymethyl methacrylate) with a crack and a borehole were carried out. The charge structure and incident angle of the blasting experimental model were the same as those in the numerical models. The experiment results agree with the numerical simulation results.

scholarly journals Numerical Study on Flow Characteristics in a Francis Turbine during Load Rejection

Energies ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 716 ◽  
Author(s):  
Daqing Zhou ◽  
Huixiang Chen ◽  
Jie Zhang ◽  
Shengwen Jiang ◽  
Jia Gui ◽  
...  
Keyword(s):  
Geometric Modeling ◽  
Numerical Study ◽  
Numerical Models ◽  
Experimental Testing ◽  
Pressure Fluctuations ◽  
Load Condition ◽  
Numerical Results ◽  
Francis Turbine ◽  
Labyrinth Seals ◽  
Load Rejection Process

Labyrinth seals are not usually included in the numerical models of hydraulic machinery to simplify the geometric modeling, and thereby reduce the calculation burden. However, this simplification affects the numerical results, especially in the load rejection process, because disc friction losses, volume losses, and pressure fluctuations in the seal ring (SR) clearance passage are neglected. This paper addresses the issue by considering all of the geometrical details of labyrinth seals when conducting multiscale flow simulations of a high head Francis turbine under a transient load rejection condition using the commercial software code. A comparison of the numerical results that were obtained with the experimental testing data indicates that the calculated values of both torque and mass discharge rate are 8.65% and 5% slightly less than the corresponding values that were obtained from experimental model testing, respectively. The obtained pressure fluctuations of the Francis turbine in the vaneless zone and the draft tube appear to more closely match with the experimental test data when including SR clearance. Moreover, the flow rates through SR clearance passages were very small, but the pressure fluctuations among them were significantly enhanced under the minimal load condition. The numerical model with SR clearance can more accurately reflect the fact that the water thrust on the runner only fluctuates from 800 N to 575 N during the load rejection process, even though the water thrust on the blades varies from −220 N to 1200 N. Therefore, multiscale flow study is of great significance in understanding the effect of clearance flow on the load rejection process in the Francis turbine.

Combined Experimental and Numerical Study for Multiple Microchannel Heat Transfer System

2010 ◽  
Author(s):  
Jingru Zhang ◽  
Yogesh Jaluria ◽  
Tiantian Zhang ◽  
Li Jia
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Steady State ◽  
Numerical Model ◽  
Initial Conditions ◽  
Numerical Study ◽  
Numerical Models ◽  
Three Dimensional ◽  
Variation Versus ◽  
Heat Transfer System

Multiple microchannel heat sinks for potential use for electronic chip cooling are studied experimentally and numerically to characterize their thermal performance. The numerical simulation is driven by experimental data, which are obtained concurrently, to obtain realistic, accurate and validated numerical models. The ultimate goal is to design and optimize thermal systems. The experimental setup was established and liquid flow in the multiple microchannels was studied under different flow rates and heat influx. The temperature variation versus time was recorded by thermocouples, from which the time needed to reach steady state was determined. Temperature variations under steady state conditions were compared with three-dimensional steady state numerical simulation for the same boundary and initial conditions. The experimental data served as input parameters for the validation of the numerical model. In case of discrepancy, the numerical model was improved. A fairly good agreement between the experimental and simulation results was obtained. The numerical model also served to provide input that could be employed to improve and modify the experimental arrangement.

Sign in / Sign up

Export Citation Format

Share Document