Study of the Greitzer Model for Centrifugal Compressors: Variable Lc Parameter and Two Types of Surge

In this paper, the Greitzer surge model was systematically analysed with the model compressor duct length Lc as the tuning parameter. The surge phenomenon is known to induce a serious risk to centrifugal compressor operation. The two-dimensional Greitzer model is a well-established way of modelling this dangerous instability, but the determination and changes of the model parameters are still being discussed. In this paper an automated procedure determines the Lc value providing the best fit with the experimental data has been presented. The algorithm was tested on five valve positions and revealed that the best fit was obtained for different Lc values following a linear trend against the mass flow rate. The study has also shown that the Greitzer model has two solutions for a given pressure oscillation amplitude: one similar to the deep surge (low Lc) and one similar to the mild surge (low Lc). This suggests that this model can be used to simulate both types of the phenomenon known from the experimental analyses. The study proposes the dimensionless average pressure as the parameter allowing to distinguish which surge cycle was observed at a given instance. Past papers were analysed to observe the surge type that appeared in different experiments. It was found that most researchers obtained low Lc surge. The results show that both deep and mild surge could be simulated with the Greitzer model. It also revealed that the Lc should not be treated as a constant value for a given machine and that it changes with the mass flow rate.

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The Effects of Non-uniform Distribution of Oxidizer Flow on High-Frequency Combustion Instability

MATEC Web of Conferences ◽

10.1051/matecconf/201925701005 ◽

2019 ◽

Vol 257 ◽

pp. 01005

Author(s):

Peng Chen ◽

Wansheng Nie ◽

Kangkang Guo ◽

Xing Sun ◽

Yu Liu ◽

...

Keyword(s):

Heat Release ◽

Combustion Chamber ◽

Uniform Distribution ◽

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Rocket Engine ◽

Combustion Instability ◽

Oscillation Amplitude ◽

Pressure Oscillation

The numerical calculation of three-dimensional unsteady combustion for the combustion chamber of LOX/kerosene high pressure staged combustion rocket engine was carried out. By changing the offset ratio of oxygen mass flow rate in the edge area of the injector face, computational studies were conducted to investigate the effects of non-uniform distribution of oxidizer flow on combustion instability for a liquid-propellant rocket engine. The calculation results show that the offset ratio of oxygen mass flow rate changes the distribution of heat release in the combustion chamber. Within a certain range of offset ratio, the non-uniform distribution degree of oxidizer flow enhances the coupling between the pressure and heat release. As a result, it leads to an increase in the pressure oscillation amplitude in the combustion chamber. However, if the offset ratio is too large, the oxygen-fuel ratio will be too small in some regions, which will reduce coupling between the pressure and heat release and increase the damping of combustion instability.

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Investigations on the Effect of Blade Angle on Ventilated Brake Disc Using CFD

Heat Transfer, Part A ◽

10.1115/imece2005-79468 ◽

2005 ◽

Cited By ~ 2

Author(s):

Kannan M. Munisamy ◽

Hanan Mokhtar ◽

Hasril Hasini ◽

Mohd Zamri Yusof ◽

Mohd Azree Idris

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Linear Trend ◽

Brake Disc ◽

Blade Angle ◽

Flow And Heat Transfer

This paper presents the investigation on the effect of blade angle to the mass flow and heat transfer coefficient of a ventilated brake disc. Six different blade angle configurations are simulated using commercial computational fluid dynamics code, FLUENT. Important parameters such as mass flow rate of air through the ventilated blade and surface heat transfer coefficient are predicted and analyzed. Prediction shows reasonable estimation of mass flow rate and heat transfer coefficient on the disc brake. Linear trend is achieved on the mass flow and heat transfer coefficient as the vehicle speed increases. It is also concluded that the optimum mass flow and heat transfer coefficient are predicted at blade angle of 15°. The prediction provides an insight into the behavior of the air flow through the restricted passage of the brake disc design.

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Modeling and Simulation of Multistage Microcompressor With Passive Microvalves for Micro Coolers

ASME 2016 14th International Conference on Nanochannels, Microchannels, and Minichannels ◽

10.1115/icnmm2016-7934 ◽

2016 ◽

Author(s):

Shawn T. Le ◽

Hisham Hegab

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

High Frequency ◽

Pressure Ratio ◽

Model Parameters ◽

Negative Effect ◽

Frequency Threshold ◽

Gap Height ◽

Operation Frequency

A cascaded multistage (2-stage) micro gas compressor in series is investigated through a lump model simulation to determine its feasibility in increasing compressor performance. A dynamic model of the micro gas compressor which consists of a unimorph piezoelectric diaphragm and passive micro check valves is presented and simulated with a Matlab Simulink® tool. Simulation is implemented for a 1 and 2-stage microcompressor design. Finite element analysis (FEA) is used to determine the lump model parameters from the fluid-structure interaction (FSI) between the microvalve and gas flow dynamics. FSI model parameters are extracted and developed as a lump model equation for Simulink® numerical computation. Dynamic simulations confirm that there is an increase in pressure ratio for a multistage microcompressor when compared to a single stage, which is achievable with passive microvalves. However, there are negative effects of using passive microvalves at high frequency. Frequency response results gathered from simulation shows that mass flow rate through the microvalve decreases above the frequency threshold ∼1 kHz for our design. This is in two parts due to a smaller gap height opening of the microvalve plate at high frequency and the reverse flow leakage. Both losses in mass flow rate from the microvalves decrease the total flow rate of the microcompressor above ∼1 kHz. Increasing actuation frequency below the ∼1 kHz threshold increases the flow rate of the microcompressor in the design. Therefore, it is concluded that the maximum flow rate of the microcompressor increases with increasing operation frequency, but becomes limited by the negative effect of the microvalve at a high frequency threshold due to the attenuation of the microvalve gap height. Although flow rate is affected, maximum pressure ratio of the microcompressor is still achievable at various frequency range, assuming the stroke volume of the pump chamber is constant throughout all frequency ranges. Multistage simulations show that the operation frequency ratio between each stage can have some negative effect in achieving the maximum theoretical pressure ratio.

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A Reduced Complexity Model for the Compressor Power of an Automotive Turbocharger

Journal of Dynamic Systems Measurement and Control ◽

10.1115/1.4039285 ◽

2018 ◽

Vol 140 (6) ◽

Cited By ~ 2

Author(s):

Tao Zeng ◽

Devesh Upadhyay ◽

Guoming Zhu

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Power Transmission ◽

Bench Tests ◽

Operational Conditions ◽

Low Mass ◽

Model Compressor ◽

Compressor Power ◽

Operational Range

Control-oriented models for automotive turbocharger (TC) compressors typically describe the compressor power assuming an isentropic thermodynamic process with fixed isentropic and mechanical efficiencies for power transmission between the turbine and the compressor. Although these simplifications make the control-oriented model tractable, they also introduce additional errors due to unmodeled dynamics. This is especially true for map-based approaches since the manufacture-provided maps tend to be sparse and often incomplete at the operational boundaries, especially at operational conditions with low mass flow rate and low speed. Extrapolation scheme is often used when the compressor is operated outside the mapped regions, which introduces additional errors. Furthermore, the manufacture-provided compressor maps, based on steady-flow bench tests, could be quite different from those under pulsating engine flow. In this paper, a physics-based model of compressor power is developed using Euler equations for turbomachinery, where the mass flow rate and the compressor rotational speed are used as model inputs. Two new coefficients, speed and power coefficients, are defined. As a result, this makes it possible to directly estimate the compressor power over the entire compressor operational range based on a single analytic relationship. The proposed modeling approach is validated against test data from standard TC flow bench tests, standard supercharger tests, steady-state, and certain transient engine dynamometer tests. Model validation results show that the proposed model has acceptable accuracy for model-based control design and also reduces the dimension of the parameter space typically needed to model compressor dynamics.

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Performance Simulation of a 5 kW hall Thruster

Frontiers in Materials ◽

10.3389/fmats.2021.754479 ◽

2021 ◽

Vol 8 ◽

Author(s):

L. Yang ◽

P. Y. Wang ◽

T. Wang

Keyword(s):

Magnetic Field ◽

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Oscillation Amplitude ◽

Discharge Voltage ◽

Hall Thruster ◽

Total Efficiency ◽

Discharge Process ◽

Steady State Oscillation

Hall thruster is a kind of plasma optics device, which is used mainly in space propulsion. To simulate the discharge process of plasma and the performance of a 5 kW hall thruster, a two-dimensional PIC-MCC model in the R-Z plane is built. In the model, the anomalous diffusion of the electrons including Bohm diffusion and near-wall conduction is modeled. The Bohm diffusion is modeled by using a Brownian motion instead of the Bohm collision method and the near-wall conduction is modeled by a secondary electron emission model. In addition to the elastic, excitation, and ionization collisions between electrons and neutral atoms, the Coulomb collisions are included. The plasma discharge process including the transient oscillation and steady state oscillation is well reproduced. First, the influence of the discharge voltage and magnetic field on the steady state oscillation is simulated. The oscillation amplitude increases as the discharge voltage gets larger at first, and then decreases. While the oscillation amplitude decreases as the magnetic field gets stronger at first, and then increases. Later, the influence of the discharge voltage and mass flow rate on the performance of the thruster is simulated. When the mass flow rate is constant, the total efficiency initially increases with the discharge voltage, reaches the maximum at 600 V, and then declined. When the discharge voltage is constant, the total efficiency increases as the mass flow rate rises from 10 to 15 mg/s. Finally, a comparison between simulated and experimental performance reveals that the largest deviation is within 15%, thereby indirectly validating the accuracy of the model.

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Measurement and simulation validation of numerical model parameters of fresh concrete

Science and Engineering of Composite Materials ◽

10.1515/secm-2021-0042 ◽

2021 ◽

Vol 28 (1) ◽

pp. 437-452

Author(s):

Ke Zhang ◽

Wenda Yu ◽

Dong Li ◽

Defang Zou ◽

Shiying Zhang

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Particle Density ◽

Rolling Friction ◽

Screw Conveyor ◽

Physical Parameters ◽

Model Parameters ◽

Batch Production ◽

Shape Coefficient

Abstract In the numerical simulation of the macroscopic flow of the concrete, it can optimize the performance indicators of the screw conveyor and improve the uniformity of the material to be discharged in the batch production. The discrete element method is effective. The accuracy of physical parameters of this method is a key issue for the reliability of the simulation results of concrete. In this study, we measured the parameters describing the interaction between gravel, mortar, as well as between these two materials and the wall (steel). The experimentally determined parameters include the particle density, size, shape, coefficient of restitution, coefficients of static, and rolling friction. The cohesion coefficient of mortar particles for batch time was obtained by comparing the spread diameter and flow time in V-funnel experiments and simulation. After these calibration steps, the DEM parameters were validated by comparison of the mass flow rate and driving power by the batch production of screw conveying in simulations and experiments. The calculated results are proved to be close to the experimental data, which demonstrates that the measured DEM parameters are of sufficient accuracy to be used in the simulation of concrete flow performance (mass flow rate, energy consumption) in the screw conveyors.

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