Computational Modelling of Fluid Flow in Radial Diffusers With Irregular Boundaries

2006 ◽  
Author(s):  
Viviana Cocco Mariani ◽  
Alvaro Toubes Prata
Keyword(s):  
Fluid Flow ◽  
Numerical Model ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Numerical Solutions ◽  
Computational Modelling ◽  
Reynolds Numbers ◽  
Valve Seat ◽  
Irregular Geometries

Radial diffusers are the basic geometry for the automatic valves in reciprocating hermetic compressors. In the present work numerical solutions for the laminar isocoric flow in radial diffusers are performed to investigate the influence of some geometry modifications on the mass flow, rate and on the resultant force on the valve. The numerical model was able to handle irregular geometries making use of a regular mesh, and was validated through comparisons with experiments. Results are presented in terms of the effective flow and force area of valves which are important efficiency parameters for the modelling and design of reciprocating hermetic compressors. The efficiency parameters are presented and explored in terms of small modification of the valve geometry, for Reynolds numbers varying from 1000 to 2500 and two values of the gap between valve reed and valve seat. The flow was significantly affected by the geometry modifications, indicating that with little effort the performance of automatic valves can be substantialy improved. For instance, with a small chamfer of 5° at the outlet of the valve feeding orifice, the effective force area was increased by 30 percent.

Predictions of Flow Separation at the Valve-Seat for Steady-State Port-Flow Simulation

2014 ◽  
Author(s):  
Tao Fang ◽  
Satbir Singh
Keyword(s):  
Steady State ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Flow Separation ◽  
Combustion Engine ◽  
Flow Simulation ◽  
Valve Lift ◽  
Valve Seat ◽  
Mesh Density

Steady-state port-flow simulations with static valve lift are often utilized to optimize the performance of intake system of an internal combustion engine. Generally, increase in valve lift results in higher mass flow rate through the valve. But in certain cases, mass flow rate can actually decrease with increased valve lift, caused by separation of turbulent flow at the valve-seat. Prediction of this phenomenon using computational fluid dynamics (CFD) models is not trivial. It is found that the computational mesh significantly influences the simulation results. A series of steady-state port flow simulation are carried out using a commercial CFD code. Several mesh topologies are applied for the simulations. The predicted results are compared with available experimental data from flow bench measurements. It is found that the flow separation and reduction in mass flow rate with increased valve lift can be predicted when high mesh density is used in the proximity of the valve seat and the walls of the intake port. Higher mesh density also gives better predictions of mass flow rate compared to the experiments, but only for high valve lifts. For low valve lifts, the error in predicted flow rate is close to 13%.

scholarly journals Quasi 3D Nacelle Design to Simulate Crosswind Flows: Merits and Challenges

2019 ◽  
Vol 4 (3) ◽  
pp. 25 ◽  
Author(s):  
Alex Yeung ◽  
Nagabhushana Rao Vadlamani ◽  
Tom Hynes ◽  
Sumit Sarvankar
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
High Speed ◽  
Computational Modelling ◽  
Flow Characteristics ◽  
Attached Flow ◽  
Set Up ◽  
Engine Nacelle ◽  
Shape Changes

This paper studies the computational modelling of the flow separation over the engine nacelle lips under the off-design condition of significant crosswind. A numerical framework is set up to reproduce the general flow characteristics under crosswinds with increasing engine mass flow rate, which include: low-speed separation, attached flow and high speed shock-induced separation. A quasi-3D (Q3D) duct extraction method from the full 3D (F3D) simulations has been developed. Results obtained from the Q3D simulations are shown to largely reproduce the trends observed (isentropic Mach number variations and high-speed separation behaviour) in the 3D intake, substantially reducing the simulation time by a factor of 50. The agreement between the F3D and Q3D simulations is encouraging when the flow either fully attached or with modest levels of separation but degrades when the flow fully detaches. Results are shown to deviate beyond this limit since the captured streamtube shape (and hence the corresponding Q3D duct shape) changes with the mass flow rate. Interestingly, the drooped intake investigated in the current study is prone to earlier separation under crosswinds when compared to an axisymmetric intake. Implications of these results on the industrial nacelle lip design are also discussed.

A Simple Numerical Model for the Prediction of Multiphase Mass Flow Rate through Chokes

2011 ◽  
Vol 29 (24) ◽  
pp. 2545-2553 ◽  
Author(s):  
W. Zhibin ◽  
L. Yingchuan ◽  
Z. Haiquan ◽  
L. Ximao ◽  
L. Yonghui
Keyword(s):  
Numerical Model ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Simple Numerical Model

Experimental and Numerical Study of Cavitation in Centrifugal Pumps

2010 ◽  
Author(s):  
Erfan Niazi ◽  
M. J. Mahjoob ◽  
Ardeshir Bangian
Keyword(s):  
Experimental Data ◽  
Numerical Model ◽  
Mass Flow Rate ◽  
Computer Simulations ◽  
Mass Flow ◽  
Flow Rate ◽  
Numerical Study ◽  
Numerical Results ◽  
Centrifugal Pumps ◽  
Cavitation Threshold

Cavitation in pumps is one of the most important causes of damage to pumps impellers/inducers. A numerical model is developed here to simulate the pump hydraulics in different conditions. Experiments are also conducted to validate the computer simulations. To verify the numerical model, the h–m˙ (head versus mass flow rate) of the model is compared with the experimental data. The system is then run under cavitation state. Two methods are applied to monitor the cavitation threshold: first by using stroboscope and observing cavitation bubbles through the transparent casing of the pump and second by checking the NPSHA value for cavitation based on ISO3555. The paper then compares the experimental and numerical results to find the strengths and weaknesses of the numerical model.

Predictions of Flow Separation at the Valve Seat for Steady-State Port-Flow Simulation

2015 ◽  
Vol 137 (11) ◽  
Author(s):  
Tao Fang ◽  
Satbir Singh
Keyword(s):  
Steady State ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Flow Separation ◽  
Combustion Engine ◽  
Valve Lift ◽  
Valve Seat ◽  
Flow Simulations ◽  
Mesh Density

Steady-state port-flow simulations with static valve lift are often utilized to optimize the performance of intake system of an internal combustion engine. Generally, increase in valve lift results in higher mass flow rate through the valve. But in certain cases, mass flow rate can actually decrease with increased valve lift, caused by separation of turbulent flow at the valve seat. Prediction of this phenomenon using computational fluid dynamics (CFD) models is not trivial. It is found that the computational mesh significantly influences the simulation results. A series of steady-state port-flow simulations are carried out using a commercial CFD code. Several mesh topologies are applied for the simulations. The predicted results are compared with available experimental data from flow bench measurements. It is found that the flow separation and reduction in mass flow rate with increased valve lift can be predicted when high mesh density is used in the proximity of the valve seat and the walls of the intake port. Higher mesh density also gives better predictions of mass flow rate compared to the experiments, but only for high valve lifts. For low valve lifts, the error in predicted flow rate is close to 13%.

DSMC Simulation: Validation and Application to Low Speed Gas Flows in Microchannels

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
T. Ewart ◽  
J. L. Firpo ◽  
I. A. Graur ◽  
P. Perrier ◽  
J. G. Méolans
Keyword(s):  
Flow Regime ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Streamwise Velocity ◽  
Accommodation Coefficient ◽  
Transitional Flow ◽  
Linearized Boltzmann Equation

A direct simulation Monte Carlo method (DSMC) solver, adapted to the subsonic microflow, is developed under the object-conception language (C++). Some technical details critical in these DSMC computations are provided. The numerical simulations of gas flow in a microchannel are carried out using the developed DSMC solver. Streamwise velocity distributions in the slip flow regime are compared with the analytical solution based on the Navier–Stokes equations with the velocity slip boundary condition. Satisfactory agreements have been achieved. Furthermore, the domain of the validity of this continuum approach is discussed. Simulations are then extended to the transitional flow regime. Streamwise velocity distributions are also compared with the results of the numerical solutions of the linearized Boltzmann equation. We emphasize the influence of the accommodation coefficient on the velocity profiles and on the mass flow rate. The simulation results on the mass flow rate are compared with the experimental data, which allow us to validate the “experimental” technique of the determination of the accommodation coefficient.

scholarly journals Exergetic Evaluation of Steel Coaxial Heat Exchangers

2021 ◽  
Author(s):  
Tobias Blanke ◽  
Markus Hagenkamp ◽  
Bernd Döring ◽  
Joachim Göttsche ◽  
Vitali Reger ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Reynolds Numbers ◽  
Circular Ring ◽  
High Mass ◽  
Flow Conditions ◽  
Hydraulic Losses ◽  
Pipe Radius

Abstract Background: A proven option to found buildings are geothermally activated steel pipes. Statics determine their dimensions. Energy improvement research focuses on the radius of inner pipe of such coaxial geothermal probes. Mass flow rate is often constant when optimizing inner pipe dimensions. In contrast, in this study flow conditions in outer pipe are constant (constant Reynolds number) to ensure that they not change during optimization. Aim is to maximize net exergy difference for the desired flow type by changing inner pipe radius (after deduction of hydraulic effort). System technology can be selected based on this optimal design and its associated boundary conditions for mass flow and temperatures.Methods: Thermal calculations based on Hellström are carried out to quantify an influence of changing inner pipe radius on thermal yield. A hydraulic optimization of inner pipe radius is performed. Increasing inner pipe radius results in decreasing hydraulic losses in inner pipe but increases hydraulic losses in outer circular ring. Net exergy difference is a key performance indicator to combine thermal and hydraulic effects. Optimization of net exergy difference is carried out for selected scenarios. All calculations are based on various, but fixed Reynolds numbers in the circular ring (Re = [4e3; 1e4; 1e5]), instead of fixed mass flow rates. This ensures fixed flow conditions and no unnecessary high mass flow rate.Results: Optimal inner radius is approximately as large as outer radius considering thermal results. Reynolds numbers are always bigger in inner pipe, due to the constant Reynolds number in circular ring. Both indicate that from a thermal point of view, a high mass flow rate and a high degree of turbulence are particularly important. Hydraulic optimal inner pipe radius is 54% of outer pipe radius for laminar flow scenarios and 60% for turbulent flow scenarios. Exergetic optimization shows a predominant influence of hydraulic losses, especially for small temperature gains.Conclusions: Design of coaxial geothermal probes should focus on the hydraulic optimum and take energetic optimum as a secondary criterion to maximize net exergy difference.

Impact Investigation on the Aerodynamic Performance for Seal Leakage at the Stator Root of Multistage Axial Compressor

2020 ◽  
Author(s):  
Qi Wang ◽  
Lanxue Ren ◽  
Zhou Zhang ◽  
Ting Wang ◽  
Mingcong Luo
Keyword(s):  
Numerical Model ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Axial Compressor ◽  
Flow Distribution ◽  
Numerical Approach ◽  
Aerodynamic Performance ◽  
The Impact ◽  
Multistage Axial Compressor

Abstract This paper presents a numerical model based on the mass flow rate of seal leakage. This numerical model is considered as a correct method for 3-D numerical simulation. It can be used to simulate the effect of seal leakage at the stator root of a multistage axial compressor. Implementation of the correct method is using a numerical model based on the flux conservation which can control the mass flow rate of seal leakage accurately at the seal cavity of compressor. The mass flow rate of seal leakage is chosen as the key research parameter on the aerodynamic performance effect of the seal engineering application in a multistage axial compressor. Combined with the 3-D numerical simulation methods, an engineering numerical approach is set up in this study. A nine-stage axial compressor is taken as the research object in this paper and its aerodynamic performance is tested for proving the applicability of the numerical model for seal leakage. In the cases of several operating rotation speeds, numerical results of the nine-stage axial compressor performance characteristic curves are in good agreement with the experimental data. It is considered that the numerical approach based on the simplified numerical model in this paper can predict the performance of multistage axial compressor accurately. Then, comparisons are made against different cases of seal leakage mass flow rate for analyzing the impact of seal leakage increasing on the aerodynamic performance of the nine-stage axial compressor. The main point of comparisons is focused on the changes of the overall performance and the flow distribution in the compressor with the seal leakage changing. The results indicate that performance of multistage axial compressor is degenerated faster and faster with seal leakage increasing in all operating working points. An overall decline is appeared in the flow capacity, working capacity, efficiency and surge margin of the compressor. For the impact investigation on the changes of flow distribution, the total pressure loss coefficient, the relative Mach number contours and the movement of streamlines are studied in different seal leakage cases under several operating working points. The result also shows that stators located in front stages of multistage axial compressor are affected more seriously with the increasing mass flow rate of seal leakage. Under the influence of seal leakage, degradation of flow condition in stators located in front stages is more severely than that in back stages, the total pressure loss coefficient and entropy are increased, and the flow separations at the root of stators in front stages are developed faster with seal leakage increasing. So it can be confirmed that relatively larger flow losses in front stages bring significant impact on the decay of aerodynamic performance for a multistage axial compressor.

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