Development and Validation of a Model for Centrifugal Compressors in Reversed Flow Regimes

2021 ◽  
pp. 1-30
Author(s):  
Katherine Powers ◽  
Ian Kennedy ◽  
Chris Brace ◽  
Paul Milewski ◽  
Colin Copeland
Keyword(s):  
Mass Flow ◽  
Reverse Flow ◽  
Characteristic Curve ◽  
Flow Region ◽  
Reverse Direction ◽  
Limiting Factor ◽  
Negative Mass ◽  
Stable Operating ◽  
Compressor Surge ◽  
Compressor Map

Abstract Turbochargers are widely used to help reduce the environmental impact of automotive engines. However, a limiting factor for turbochargers is compressor surge. Surge is an instability that induces pressure and flow oscillations that often damages the turbocharger and its installation. Most predictions of the surge limit are based on low-order models, such as the Moore-Greitzer model. These models tend to rely on a characteristic curve for the compressor created by extrapolating the constant speed lines of a steady-state compressor map into the negative mass flow region. However, there is little validation of these assumptions in the public literature. In this paper, we develop further the first-principles model for a compressor characteristic presented in Powers et al. [1], with a particular emphasis on reverse flow. We then perform experiments using a 58mm diameter centrifugal compressor provided by Cummins Turbo Technologies, where we feed air in the reverse direction though the compressor while the impeller is spinning in the forwards direction in order to obtain data in the negative mass flow region of the compressor map. This demonstrated experimentally that there is a stable operating region in the reverse flow regime. The recorded data showed a good match with the theoretical model developed in this paper. We also identified a change in characteristic behaviour as the impeller speed is increased which, to the authors knowledge, has not been observed in any previously published experimental work

Development and Validation of a Model for Centrifugal Compressors in Reversed Flow Regimes

2020 ◽  
Author(s):  
Katherine H. Powers ◽  
Ian J. Kennedy ◽  
Chris J. Brace ◽  
Paul A. Milewski ◽  
Colin D. Copeland
Keyword(s):  
Mass Flow ◽  
Reverse Flow ◽  
Characteristic Curve ◽  
Flow Region ◽  
Reverse Direction ◽  
Limiting Factor ◽  
Negative Mass ◽  
Stable Operating ◽  
Compressor Surge ◽  
Compressor Map

Abstract Turbochargers are widely used to help reduce the environmental impact of automotive engines. However, a limiting factor for turbochargers is compressor surge. Surge is an instability that induces pressure and flow oscillations that often damages the turbocharger and its installation. Most predictions of the surge limit are based on low-order models, such as the Moore-Greitzer model. These models tend to rely on a characteristic curve for the compressor created by extrapolating the constant speed lines of a steady-state compressor map into the negative mass flow region. However, there is little validation of these assumptions in the public literature. In this paper, we develop further the first-principles model for a compressor characteristic presented in Powers et al. [1], with a particular emphasis on reverse flow. We then perform experiments using a 58mm diameter centrifugal compressor provided by Cummins Turbo Technologies, where we feed air in the reverse direction though the compressor while the impeller is spinning in the forwards direction in order to obtain data in the negative mass flow region of the compressor map. This demonstrated experimentally that there is a stable operating region in the reverse flow regime. The recorded data showed a good match with the theoretical model developed in this paper We also identified a change in characteristic behaviour as the impeller speed is increased which, to the authors knowledge, has not been observed in any previously published experimental work.

Loss Mechanisms and Flow Control for Improved Efficiency of a Centrifugal Compressor at High Inlet Prewhirl

2016 ◽  
Vol 138 (10) ◽  
Author(s):  
Xinqian Zheng ◽  
Qiangqiang Huang ◽  
Anxiong Liu
Keyword(s):  
Flow Control ◽  
Mass Flow ◽  
Centrifugal Compressor ◽  
Flow Separation ◽  
Flow Instability ◽  
Reverse Flow ◽  
Leading Edge ◽  
Flow Region ◽  
Impeller Blade ◽  
Loss Mechanisms

Variable inlet prewhirl is an effective way to suppress compressor flow instability. Compressors usually employ a high degree of positive inlet prewhirl to shift the surge line in the performance map to a lower mass flow region. However, the efficiency of a compressor at high inlet prewhirl is far lower than that at zero or low prewhirl. This paper investigates the performances of a centrifugal compressor with different prewhirls, discusses the mechanisms which are responsible for the production of extra loss induced by high inlet prewhirl and develops flow control methods to improve efficiency at high inlet prewhirl. The approach combines steady three-dimensional Reynolds average Navier–Stokes (RANS) simulations with theoretical analysis and modeling. In order to make the study universal to various applications with inlet prewhirl, the inlet prewhirl was imposed by modifying the velocity direction of inlet boundary condition. Simulation results show that the peak efficiency at high inlet prewhirl is reduced by over 7.6% points compared with that at zero prewhirl. The extra loss occurs upstream and downstream of the impeller. Severe flow separation, which reduces efficiency by 2.3% points, was found near the inlet hub. High inlet prewhirl works like a centrifuge gathering low-kinetic-energy fluid to hub, which induces the separation. A dimensionless parameter C was defined to measure the centrifugal trend of gas and indicate the flow separation near the inlet hub. As for the extra loss which is produced downstream of the impeller, the flow mismatch of impeller and diffuser at high prewhirl causes a violent backflow near the diffuser vanes' leading edges. An analytical model was built to predict diffuser choking mass flow. It proves that the diffuser has already operated unstably at high prewhirl. Based on these two loss mechanisms, the hub curve and the diffuser stager angle were modified and adjusted, respectively, for higher efficiency at high prewhirl. The efficiency improvement benefited from the modification of the hub is 1.1% points, and that benefited from the combined optimization is 2.4% points. During optimizing, constant distribution of inlet prewhirl was found to be another factor for inducing reverse flow at the leading edge of the impeller blade root, which turned out being blamed on the misalignment of the swirl angle and the blade angle.

Loss Mechanisms and Flow Control for Improved Efficiency of a Centrifugal Compressor at High Inlet Prewhirl

2015 ◽  
Author(s):  
Zheng Xinqian ◽  
Huang Qiangqiang ◽  
Liu Anxiong
Keyword(s):  
Flow Control ◽  
Mass Flow ◽  
Centrifugal Compressor ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Leading Edge ◽  
Flow Region ◽  
Percentage Points ◽  
Stable Conditions ◽  
Loss Mechanisms

Variable inlet prewhirl is an effective way to suppress compressor instability. Compressors usually employ a high degree of positive inlet prewhirl to shift the surge line in the performance map to a lower mass flow region. However, the efficiency of a compressor at high inlet prewhirl is far lower than that at zero or low prewhirl. This paper investigates the performances of a centrifugal compressor with different prewhirl, discusses the mechanisms thought to be responsible for the production of extra loss induced by high inlet prewhirl and develops flow control methods to improve efficiency at high inlet prewhirl. The approach combines steady three-dimensional Reynolds average Navier-Stockes (RANS) simulations with theoretical analysis and modeling. In order to make the study universal to various applications with inlet prewhirl, the inlet prewhirl was modeled by modifying the velocity condition at the inlet boundary. Simulation results show that the peak efficiency at high inlet prewhirl is reduced compared to that at zero prewhirl by over 7.6 percentage points. The extra loss is produced upstream and downstream of the impeller. Severe flow separation was found near the inlet hub which reduces efficiency by 2.3 percentage points. High inlet prewhirl works like a centrifuge gathering low-kinetic-energy fluid to hub, inducing the separation. A dimensionless parameter C is defined to measure the centrifugal component of flow. As for the extra loss produced downstream of the impeller, the flow mismatch of impeller and diffuser at high prewhirl causes a violent backflow near the diffuser vanes’ leading edges. An analytical model is built to predict diffuser choking mass flow which proves that the diffuser flow operates outside of stable conditions. Based on the two loss mechanisms, hub curve and diffuser stager angle were modified and adjusted for seeking higher efficiency at high prewhirl. The efficiency improvement of a modification of the hub is 1.1 percentage points and that of the combined optimization is 2.4 percentage points. During optimizing, constant distribution of inlet prewhirl was found to induce reverse flow at the leading edge of the blade root, which turned out being uncorrelated with blade angle. By revealing loss mechanisms and proposing flow control ideas, this paper lays a theoretical basis for overcoming the efficiency drop induced by high inlet prewhirl and for developing compressors with high inlet prewhirl.

scholarly journals Laser-Doppler Velocimetry Measurements Inside a Backward Curved Centrifugal Fan

2001 ◽  
Vol 7 (3) ◽  
pp. 173-181
Author(s):  
Tong-Miin Liou ◽  
Meng-Yu Chen
Keyword(s):  
Flow Rate ◽  
Turbulence Intensity ◽  
Laser Doppler Velocimetry ◽  
Reverse Flow ◽  
Flow Region ◽  
Design Flow ◽  
Laser Doppler ◽  
Centrifugal Fan ◽  
Doppler Velocimetry ◽  
Flow Rates

Laser-Doppler velocimetry (LDV) measurements are presented of relative mean velocity and turbulence intensity components inside the impeller passage of a centrifugal fan with twelve backward curved blades at design, under-design, and over-design flow rates. Additional LDV measurements were also performed at the volute outlet to examine the uniformity of the outlet flow for the three selected flow rates. Complementary flow visualization results in the tongue region are further presented. It is found that the number of characteristic flow regions and the average turbulence level increase with decreasing air flow rate. For the case of under-design flow rate, there are a through-flow region on the suction side, a reverse flow region on the pressure side, and a shear layer region in between. The corresponding average turbulence intensity is as high as 9.1% of blade tip velocity.

Wind Tunnel Test on a Slowed Mach-Scaled Hingeless Rotor with Lift Compounding

2021 ◽  
Author(s):  
Shashank Maurya ◽  
Xing Wang ◽  
Inderjit Chopra
Keyword(s):  
Wind Tunnel ◽  
Reverse Flow ◽  
Wind Tunnel Test ◽  
Bending Moment ◽  
Flow Region ◽  
Dynamic Stall ◽  
Rolling Moment ◽  
Slowing Down ◽  
Slowed Rotor ◽  
Compressibility Effects

A single main rotor helicopter's maximum forward speed is limited due to the compressibility effects on the advancing side and reverse flow and dynamic stall on the retreating side. Compound helicopters can address these issues with a slowed rotor and lift compounding. There is a scarcity of test data on compound helicopters, and the present research focuses on a systematic wind tunnel test on lift compounding. Slowing down the rotor increases the advance ratio and, hence, the reverse flow region, which does not produce much lift. The lift is augmented with a wing on the retreating side. A hingeless rotor hub helps to balance the rolling moment with lift offset. Wind tunnel tests were carried out on this configuration up to advance ratios of 0.7 at two different wing incidence angles. Rotor performance, controls, blade structural loads, and hub vibratory loads were measured and compared with in-house comprehensive analysis, UMARC. A comparison between different wing incidences at constant total lift provided many insights into the lift compounding. It increased the vehicle efficiency and reduced peak-to-peak lag bending moment and in-plane 4/rev hub vibratory loads. The only trade-off was steady rotor hub loads and rolling moment at the wing root carried by the fuselage.

Compressor Performance 2D Modelling at Reverse Flow Conditions

2010 ◽  
Author(s):  
L. Gallar ◽  
I. Tzagarakis ◽  
V. Pachidis ◽  
R. Singh
Keyword(s):  
Experimental Data ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Engine Performance ◽  
Two Dimensional ◽  
Flow Conditions ◽  
Compressor Surge ◽  
Compressor Performance ◽  
Shaft Failure

After a shaft failure the compression system of a gas turbine is likely to surge due to the heavy vibrations induced on the engine after the breakage. Unlike at any other conditions of operation, compressor surge during a shaft over-speed event is regarded as desirable as it limits the air flow across the engine and hence the power available to accelerate the free turbine. It is for this reason that the proper prediction of the engine performance during a shaft over-speed event claims for an accurate modelling of the compressor operation at reverse flow conditions. The present study investigates the ability of the existent two dimensional algorithms to simulate the compressor performance in backflow conditions. Results for a three stage axial compressor at reverse flow were produced and compared against stage by stage experimental data published by Gamache. The research shows that due to the strong radial fluxes present over the blades, two dimensional approaches are inadequate to provide satisfactory results. Three dimensional effects and inaccuracies are accounted for by the introduction of a correction parameter that is a measure of the pressure loss across the blades. Such parameter is tailored for rotors and stators and enables the satisfactory agreement between calculations and experiments in a stage by stage basis. The paper concludes with the comparison of the numerical results with the experimental data supplied by Day on a four stage axial compressor.

Numerical Investigation of an Asymmetric Double Suction Centrifugal Compressor With Different Backswept Angle Matching for a Wide Operating Range

2017 ◽  
Author(s):  
Hanzhi Zhang ◽  
Dazhong Lao ◽  
Longyu Wei ◽  
Ce Yang ◽  
Mingxu Qi
Keyword(s):  
Mass Flow ◽  
Centrifugal Compressor ◽  
Flow Distribution ◽  
Operating Mode ◽  
Mode Transition ◽  
Distribution Characteristics ◽  
Operating Range ◽  
Stable Operating ◽  
Angle Difference ◽  
Matching Models

The work presented here investigates the characteristics of the different impeller backswept angle matchings for a wide stable operating range in an asymmetric double suction centrifugal compressor. The numerical simulation was employed to investigate the influence of different backswept angle matchings on the stable operating range. The aim is to propose a proper change of the backswept angle matching between two impeller sides to improve the impeller power capability and mass flow distribution, furthermore, to delay the operating mode transition and widen the stable operating range of the compressor. Firstly, the method to determine the optimum backswept angle matching obtained by the theory calculation. Then, three matching models were proposed and analyzed in detail. In three matching models, the backswept angle differences between the front and rear impeller side are 0°, 10° and 20°, respectively. The analysis mainly focused on the influence of the different backswept angle matchings on the compressor flow field characteristics and the mass flow distribution characteristics. The results show that the change of the impeller backswept angle matching can improve the mass flow distribution characteristics for two impeller sides and further reduce the stall mass flow rate of the double suction compressor. The model that the backswept angle difference is 10° can delay the operating mode transition and reduce the stall mass flow of the double suction compressor. The model that the backswept angle difference is 20° can also reduce the stall mass flow and finally enable the front impeller into the stall condition. Therefore, the proper change of the backswept angle matching can achieve the purpose of reducing the stall mass flow and widening the operating range for the double suction centrifugal compressor.

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.

Three-Dimensional Forced Convection in Plane Symmetric Sudden Expansion

2004 ◽  
Vol 126 (5) ◽  
pp. 836-839 ◽  
Author(s):  
J. H. Nie and ◽  
B. F. Armaly
Keyword(s):  
Nusselt Number ◽  
Forced Convection ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Flow Region ◽  
Outer Edge ◽  
Sudden Expansion ◽  
Recirculation Flow ◽  
Plane Symmetric ◽  
Laminar Forced Convection

Simulations of three-dimensional laminar forced convection in a plane symmetric sudden expansion are presented for Reynolds numbers where the flow is steady and symmetric. A swirling “jetlike” flow develops near the sidewalls in the separating shear layer, and its impingement on the stepped wall is responsible for the maximum that develops in the Nusselt number adjacent to the sidewalls and for the reverse flow that develops in that region. The maximum Nusselt number on the stepped wall is located inside the primary recirculation flow region and its location does not coincide with the jetlike flow impingement region. The results reveal that the location where the streamwise component of wall shear stress is zero on the stepped walls does not coincide with the outer edge of the primary recirculation flow region near the sidewalls.

scholarly journals Brain-wide mapping of water flow perception in zebrafish

2020 ◽  
Author(s):  
Gilles Vanwalleghem ◽  
Kevin Schuster ◽  
Michael A. Taylor ◽  
Itia A. Favre-Bulle ◽  
Ethan K. Scott
Keyword(s):  
Water Flow ◽  
Lateral Line ◽  
Reverse Flow ◽  
Forward Direction ◽  
Brain Regions ◽  
Reverse Direction ◽  
Departure Point ◽  
Forward Flow ◽  
Larval Zebrafish ◽  
The Brain

AbstractInformation about water flow, detected by lateral line organs, is critical to the behavior and survival of fish and amphibians. While certain specific aspects of water flow processing have been revealed through electrophysiology, we lack a comprehensive description of the neurons that respond to water flow and the network that they form. Here, we use brain-wide calcium imaging in combination with microfluidic stimulation to map out, at cellular resolution, all neurons involved in perceiving and processing water flow information in larval zebrafish. We find a diverse array of neurons responding to forward flow, reverse flow, or both. Early in this pathway, in the lateral line ganglia, these are almost exclusively neurons responding to the simple presence of forward or reverse flow, but later processing includes neurons responding specifically to flow onset, representing the accumulated volume of flow during a stimulus, or encoding the speed of the flow. The neurons reporting on these more nuanced details are located across numerous brain regions, including some not previously implicated in water flow processing. A graph theory-based analysis of the brain-wide water flow network shows that a majority of this processing is dedicated to forward flow detection, and this is reinforced by our finding that details like flow velocity and the total volume of accumulated flow are only encoded for the simulated forward direction. The results represent the first brain-wide description of processing for this important modality, and provide a departure point for more detailed studies of the flow of information through this network.Significance statementIn aquatic animals, the lateral line is important for detecting water flow stimuli, but the brain networks that interpret this information remain mysterious. Here, we have imaged the activity of individual neurons across the entire brains of larval zebrafish, revealing all response types and their brain locations as water flow processing occurs. We find some neurons that respond to the simple presence of water flow, and others that are attuned to the flow’s direction, speed, duration, or the accumulated volume of water that has passed during the stimulus. With this information, we modeled the underlying network, describing a system that is nuanced in its processing of water flow simulating forward motion but rudimentary in processing flow in the reverse direction.

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