Numerical Simulation of Stall Development Into Surge and Stall Control Using Air Injection in Centrifugal Compressors

2014 ◽  
Author(s):  
Taher Halawa ◽  
Mohamed Alqaradawi ◽  
Osama Badr ◽  
Mohamed S. Gadala
Keyword(s):  
Numerical Simulation ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Pressure Fluctuations ◽  
Air Injection ◽  
Good Effect ◽  
Sudden Increase ◽  
Centrifugal Compressors ◽  
Surge Margin

This study presents a numerical simulation of the formation of rotating stall and the initiation of surge in order to study the connection between stall and surge in centrifugal compressors. Also, the current paper introduces an optimization of the air injection method as a way to increase the surge margin. Results showed that during stall, the compressor is exposed to velocity and pressure fluctuations varying with time, and these fluctuations are increased suddenly and causing surge initiation. The major part which is responsible for the sudden increase in fluctuations is the vaneless region because it was found that the problem starts at the impeller exit near the shroud surface and then transfers to the impeller inlet. Results also showed that during surge, forces on the impeller blades increase to nearly double of its initial value and then decrease again. By using air injection at the vaneless region with different injection angles, it was found that injection with angle of 30° has a good effect on preventing surge and minimizing the pressure fluctuations comparing to other injection angles results. Results showed finally that the surge margin can be increased by using the injection with angle of 30° and with injection mass flow rate of 1% of the design inlet mass flow rate and this causes the surge limit to shift from 4 kg/s to 3.9 kg/s.

Optimization of the Efficiency of Stall Control Using Air Injection for Centrifugal Compressors—Additional Findings

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Taher Halawa
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Gas Turbines ◽  
Stable Condition ◽  
Tangential Direction ◽  
Air Injection ◽  
Centrifugal Compressors ◽  
Injection Angle ◽  
Stall Control

This study presents additional important findings to the results of the research paper; “Optimization of the efficiency of stall control using air injection for centrifugal compressors” published in the Journal of Engineering for Gas Turbines and Power in 2015 (Halawa, T., Gadala, M. S., Alqaradawi, M., and Badr, O., 2015, “Optimization of the Efficiency of Stall Control Using Air Injection for Centrifugal Compressors,” ASME J. Eng. Gas Turbines Power, 137(7), p. 072604). The aim of this study is to make a fine determination of the injection angle, which provides the best stable condition when the compressor operates close to stall condition. A relatively narrower range of injection angles with smaller intervals was selected comparing to the results of the referred published paper, which clarified that the best injection angle is 30 deg. External air was injected close to the diffuser entrance at the shroud surface. Injection was applied with mass flow rate equals 1.5% of the design compressor inlet mass flow rate with injection angles ranged from 16 deg to 34 deg measured from the tangential direction at the vaneless region. It was found that both of injection angles of 28 deg and 30 deg achieved the best results in terms of compressor stabilization but each one of them has a specific advantage comparing to the other one. Using injection angle of 28 deg provided the lowest kinetic energy losses while the best orientation of the fluid through diffuser resulted when using an injection angle of 30 deg.

Numerical Investigation of Rotating Stall Characteristics and Active Stall Control in Centrifugal Compressors

2014 ◽  
Author(s):  
Taher Halawa ◽  
Mohamed Alqaradawi ◽  
Osama Badr ◽  
Mohamed S. Gadala
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Rotating Stall ◽  
Air Injection ◽  
Tip Leakage Flow ◽  
Centrifugal Compressors ◽  
Flow Rates ◽  
Injection Angle ◽  
Mass Flow Rates

This paper focuses on providing better view for the understanding of rotating stall phenomenon in centrifugal compressors by using numerical simulations and presents a study of the role of air injection method in delaying stall inception by using different injection parameters aiming at increasing the efficiency of this method. Results showed that the formation of stall begins at the impeller inlet due to early flow separation at low mass flow rates and due to the increase of the turbulence level and the absence of fluid orientation guidance at the vaneless region. The flow weakness causes back flow that results in the formation of the tip leakage flow which causes stall development with time. Results also showed that using air injection at specified locations at the vaneless shroud surface at injection angle of 20° and with injection mass flow rate of 1.5% of the inlet design mass flow rate, can delay the stall onset to happen at lower mass flow rate about 3.8 kg/s comparing with using injection with angle of 10° with different injection mass flow rates and also comparing with the case of no injection.

Numerical Investigation of Steady Air Injection Flow to Control Rotating Stall in Centrifugal Compressors

2014 ◽  
Author(s):  
Taher Halawa ◽  
Mohamed Alqaradawi ◽  
Osama Badr ◽  
Mohamed S. Gadala
Keyword(s):  
Kinetic Energy ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Rotating Stall ◽  
Air Injection ◽  
Centrifugal Compressors ◽  
Injection Angle ◽  
Injection Method ◽  
Vane Angle

This paper concerns the role of air injection method in stabilization and stall control in centrifugal compressors. The main aim is to find the best arrangement of air injection parameters such as injection angle and injection mass flow rate in order to optimize the injection performance for stabilizing the compressor and increasing the surge margin. Numerical model was built to simulate high speed transonic centrifugal compressor working at an operating point close to surge. Air was injected at 12 locations at the vaneless region between the impeller and the diffuser at shroud surface with 5 different injection angles and 3 different injection mass flow rates. Results showed that the best injection method is when using an injection angle of 30° with injection mass flow rate of 1.5% of the design mass flow rate and the worst injection method is the injection at angle of 180° (reverse tangent injection). Results also indicated that by using air injection, the number of stalled diffuser passages is decreased compared to the case of no injection. The most significant result of this paper is that using an angle of injection around twice the value of the diffuser vane angle gives the best results and makes the ideal correction of the fluid kinetic energy and fluid angle at the diffuser inlet. It was found that injecting air at an angle less than the diffuser vane angle weakens the effect of injection and doesn’t increase kinetic energy of the fluid at diffuser inlet. It was also found that injecting air at an angle larger than the diffuser vane angle corrects the fluid direction but, at the same time, decreases the fluid kinetic energy at diffuser inlet.

Numerical Simulation of the Performance of an Axial Compressor Operating With Supercritical Carbon Dioxide

2018 ◽  
Author(s):  
Jinlan Gou ◽  
Wei Wang ◽  
Can Ma ◽  
Yong Li ◽  
Yuansheng Lin ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Numerical Simulation ◽  
Supercritical Carbon Dioxide ◽  
Critical Point ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Axial Compressor ◽  
Brayton Cycle ◽  
Supercritical Carbon

Using supercritical carbon dioxide (SCO2) as the working fluid of a closed Brayton cycle gas turbine is widely recognized nowadays, because of its compact layout and high efficiency for modest turbine inlet temperature. It is an attractive option for geothermal, nuclear and solar energy conversion. Compressor is one of the key components for the supercritical carbon dioxide Brayton cycle. With established or developing small power supercritical carbon dioxide test loop, centrifugal compressor with small mass flow rate is mainly investigated and manufactured in the literature; however, nuclear energy conversion contains more power, and axial compressor is preferred to provide SCO2 compression with larger mass flow rate which is less studied in the literature. The performance of the axial supercritical carbon dioxide compressor is investigated in the current work. An axial supercritical carbon dioxide compressor with mass flow rate of 1000kg/s is designed. The thermodynamic region of the carbon dioxide is slightly above the vapor-liquid critical point with inlet total temperature 310K and total pressure 9MPa. Numerical simulation is then conducted to assess this axial compressor with look-up table adopted to handle the nonlinear variation property of supercritical carbon dioxide near the critical point. The results show that the performance of the design point of the designed axial compressor matches the primary target. Small corner separation occurs near the hub, and the flow motion of the tip leakage fluid is similar with the well-studied air compressor. Violent property variation near the critical point creates troubles for convergence near the stall condition, and the stall mechanism predictions are more difficult for the axial supercritical carbon dioxide compressor.

Backward Traveling Rotating Stall Waves in Centrifugal Compressors

2002 ◽  
Author(s):  
Z. S. Spakovsky
Keyword(s):  
Mass Flow ◽  
Centrifugal Compressor ◽  
First Principles ◽  
Rotating Stall ◽  
Air Injection ◽  
System Stability ◽  
Centrifugal Compressors ◽  
Injection Scheme ◽  
Surge Margin ◽  
Low Order

Rotating stall waves that travel against the direction of rotor rotation are reported for the first time and a new, low-order analytical approach to model centrifugal compressor stability is introduced. The model is capable of dealing with unsteady radially swirling flows and the dynamic effects of impeller-diffuser component interaction as it occurs in centrifugal compression systems. A simple coupling criterion is developed from first principles to explain the interaction mechanism important for system stability. The model findings together with experimental data explain the mechanism for first-ever observed backward traveling rotating stall in centrifugal compressors with vaned diffusers. Based on the low-order model predictions, an air injection scheme between the impeller and the vaned diffuser is designed for the NASA Glenn CC3 high-speed centrifugal compressor. The steady air injection experiments show an increase of 25% in surge-margin with an injection mass flow of 0.5% of the compressor mass flow. In addition, it is experimentally demonstrated that this injection scheme is robust to impeller tip-clearance effects and that a reduced number of injectors can be applied for similar gains in surge-margin. The results presented in this paper firmly establish the connection between the experimentally observed dynamic phenomena in the NASA CC3 centrifugal compressor and a first principles based coupling criterion. In addition, guidelines are given for the design of centrifugal compressors with enhanced stability.

On the Dynamics of Compressor Surge

1976 ◽  
Vol 18 (5) ◽  
pp. 234-238 ◽  
Author(s):  
D. H. McQueen
Keyword(s):  
Mass Flow Rate ◽  
Limit Cycle ◽  
Mass Flow ◽  
Flow Rate ◽  
Pressure Head ◽  
Centrifugal Compressors ◽  
One Dimensional ◽  
Acoustical Properties ◽  
Compressor Surge ◽  
The One

The one-dimensional equations of surge in centrifugal compressors are solved graphically for the pressure head and mass flow rate as functions of time for a variety of situations, and the results are discussed in terms of the acoustical properties of the external piping. Two important parameters affecting the nature of the surge limit cycle are found to be simply related to the acoustic capacitance and acoustic inductance of the system.

Numerical Simulation of Steady Air Injection Flow Control Effects on a Transonic Axial Flow Compressor

2012 ◽  
Vol 224 ◽  
pp. 352-357
Author(s):  
Islem Benhegouga ◽  
Ce Yang
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Pressure Ratio ◽  
Axial Flow ◽  
Leading Edge ◽  
Air Injection ◽  
Axial Flow Compressor ◽  
Blade Tip ◽  
Flow Compressor

In this work, steady air injection upstream of the blade leading edge was used in a transonic axial flow compressor, NASA rotor 37. The injectors were placed at 27 % upstream of the axial chord length at blade tip, the injection mass flow rate is 3% of the chock mass flow rate, and 3 yaw angles were used, respectively -20°, -30°, and -40°. Negative yaw angles were measured relative to the compressor face in opposite direction of rotational speeds. To reveal the mechanism, steady numerical simulations were performed using FINE/TURBO software package. The results show that the stall mass flow can be decreased about 2.5 %, and an increase in the total pressure ratio up to 0.5%.

scholarly journals Numerical Investigation of the Hub-Seal Mass Flow Rate Effect on the Axial Turbine Stage Efficiency

2019 ◽  
Vol 213 ◽  
pp. 02080
Author(s):  
Petr Straka
Keyword(s):  
Numerical Simulation ◽  
Mass Flow Rate ◽  
Compressible Flow ◽  
Mass Flow ◽  
Flow Rate ◽  
Turbine Stage ◽  
Axial Turbine ◽  
Flow Through ◽  
Stage Efficiency ◽  
Flow Rate Effect

The contribution deals with numerical simulation of compressible flow through the axial turbine stage equipped with the hub-seal. The current flowing from the hub-seal has a major impact on the secondary flow in the hub-region of the blade span. The aim of this work is to found a dependency of the efficiency-drop on the hub-seal mass flow rate. Numerical simulation has been made for configuration of experimental axial single-stage reaction turbine.

Estimation of Leakage Mass Flow Rate through Labyrinth Seal Using CFD Techniques

2017 ◽  
Vol 3 (02) ◽  
Author(s):  
M Neeharika ◽  
Prabhat Kumar Hensh
Keyword(s):  
Numerical Simulation ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Flow Behavior ◽  
Labyrinth Seal ◽  
Empirical Correlation ◽  
Radial Clearance ◽  
Leakage Flow ◽  
Simulation Results

Seal design is an essential part for turbo machinery. Seal consisting of fins is placed in a gap between stationary and rotating component to minimize the leakage flow. Seal leakage flow has been considered as an inevitable loss factor that highly affects the efficiency of any machine. During operation of the equipment, thermal expansion/contraction of components take place, which causes variation of the gap between stationary and rotating component. Importance of the study is to understand the flow behavior due to variation of the gap. The variation of gap leads to change of radial clearance between fin to metal component and subsequent change of flow pattern. The main focus of the paper is to estimate the leakage flow through a labyrinth seal placed between rotor and casing of a typical steam turbine. Numerical techniques using 3D CFD tool are used for this purpose. Three different seal configurations are proposed in the study. The variables of the three seal configurations are radial clearance, number of fins in the flow passage and pressure drop across the seal passages. As an alternative methodology, an empirical correlation is formulated based on numerical simulation results for one set of radial clearance to estimate mass flow rate through the seal. In order to validate the formulated correlation, mass flow rate is determined for another set of radial clearance and compared with numerical simulation results. It is observed that flow rate estimated from 3D CFD study is around 20% lower compared to empirical correlation.

Numerical Simulation of Flow Field Dynamics Characteristics for One Novel Twin-Screw Kneader

2012 ◽  
Vol 271-272 ◽  
pp. 1049-1055
Author(s):  
Jing Wei ◽  
Xin Long Liang ◽  
Wei Sun ◽  
Li Cun Wang
Keyword(s):  
Numerical Simulation ◽  
Shear Stress ◽  
Flow Field ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Maximum Shear Stress ◽  
Twin Screw ◽  
Screw Rotors ◽  
Center Distance

The numerical simulation for dynamic characteristics of the flow field of a novel twin-screw kneader is carried out. The flow field model of the twin-screw kneader is established, and the three-dimensional, isothermal and steady numerical analysis of non-Newtonian fluid is presented based on computational fluid dynamics (CFD) theory, and the characteristics under the conditions of different speeds and center distances such as the distribution of pressure and velocity field, the maximum shear stress, the mass flow rate and so on, are studied. The research results show that: with increasing speed, the maximum flow pressure, the mass flow rate, the maximum shear stress will increase; the maximum shear stress increases first and then decreases with increasing of center distance of the screw rotors, while the mass flow rate increases with increasing of center distance; but when the center distance reaches a certain degree, the mass flow rate will be negative and the material will appear serious reflux which can lead the kneader to stopping working.

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