Radial Impeller Forces Using CFD: Part II — A Comparison Between Compressible and Incompressible Flows

2002 ◽  
Author(s):  
Daniel O. Baun ◽  
Ronald D. Flack
Keyword(s):  
Mach Number ◽  
Flow Rate ◽  
Incompressible Flows ◽  
Lateral Force ◽  
Magnetic Bearing ◽  
Flow Coefficient ◽  
Low Flow ◽  
Working Fluid ◽  
Centrifugal Impeller ◽  
Cfd Model

Lateral centrifugal impeller forces are calculated using the CFD model developed in Part I of this paper. The impeller forces are evaluated by integrating the pressure and momentum profiles at both the impeller inlet and exit planes. Direct impeller lateral force measurements were made using a magnetic bearing supported pump rotor. Comparisons between the simulated and measured forces are first made for both average and transient impeller forces with water as the working fluid. Air was then substituted as the working fluid in the validated CFD model and the effect of impeller Mach number and Reynolds number on the static impeller lateral forces was investigated. The non-dimensional lateral impeller force characteristics as a function of normalized flow coefficient are similar in character between the incompressible and compressible case. At the matching point flow coefficient the non-dimensional impeller force magnitude was the same for all compressible and incompressible simulations. For any normalized flow rate other than the matching point flow rate, the magnitude of the non-dimensional impeller force increased as the Mach number increased. As the choke condition was approached the magnitude of the impeller force increased exponentially. As the Mach number increased the transition of the force orientation vector from the low flow asymptote to the high flow asymptote occurred over a progressively smaller range of flows.

scholarly journals Compressible Flow Pressure Losses in Wye-Junctions

1992 ◽  
Author(s):  
N. I. Abou-Haidar ◽  
S. L. Dixon
Keyword(s):  
Mach Number ◽  
Compressible Flow ◽  
Incompressible Flows ◽  
Separate Flow ◽  
Working Fluid ◽  
Flow Visualisation ◽  
Vena Contracta ◽  
Pressure Losses ◽  
Flow Pressure ◽  
Limiting Condition

This paper considers the compressible flow pressure losses in sharp cornered wye-junctions with symmetrical branches under dividing and combining flow conditions. Determination of the additional total pressure losses occurring in flow through several three-leg junctions, using dry air as the working fluid, has been made experimentally. Results covering a wide speed range up to choking are presented for three different wye-junction geometries. Separate flow visualisation Schlieren tests detected the presence of normal shock waves, located at up to one duct diameter downstream of the junction, and therefore confirmed the choking of the flow at the vena contracta. The highest attainable Mach number (M3) of the averaged whole flow was 0.9 for one of the dividing flow geometries and 0.65 for several of the combining flow cases. These values of M3 were the maximum possible and hence represent a limiting condition dictated by choking. In general, the compressible flow loss coefficients, caused by the presence of the wye-junctions, can be expected to be higher for dividing flows and lower for combining flows than would be the case for incompressible flows because of the influence of Mach number (M3) on the magnitude of the denominator.

scholarly journals Comparison of Swing and Tilting Check Valves Flowing Compressible Fluids

Micromachines ◽  
2020 ◽  
Vol 11 (8) ◽  
pp. 758
Author(s):  
Zhi-xin Gao ◽  
Ping Liu ◽  
Yang Yue ◽  
Jun-ye Li ◽  
Hui Wu
Keyword(s):  
Mach Number ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Check Valve ◽  
Small Mass ◽  
Working Fluid ◽  
Valve Disc ◽  
Valve Opening ◽  
The Difference

Although check valves have attracted a lot of attention, work has rarely been completed done when there is a compressible working fluid. In this paper, the swing check valve and the tilting check valve flowing high-temperature compressible water vapor are compared. The maximum Mach number under small valve openings, the dynamic opening time, and the hydrodynamic moment acting on the valve disc are chosen to evaluate the difference between the two types of check valves. Results show that the maximum Mach number increases with the decrease in the valve opening and the increase in the mass flow rate, and the Mach number and the pressure difference in the tilting check valve are higher. In the swing check valve, the hydrodynamic moment is higher and the valve opening time is shorter. Furthermore, the valve disc is more stable for the swing check valve, and there is a periodical oscillation of the valve disc in the tilting check valve under a small mass flow rate.

Suppression of Self-Excited Flow Instability in a Radial Diffuser Using Rough Surfaces

2006 ◽  
Author(s):  
Saad A. Ahemd ◽  
Hayder Salem
Keyword(s):  
Flow Rate ◽  
Smooth Surface ◽  
Flow Instability ◽  
Rough Surfaces ◽  
Flow Coefficient ◽  
Flow Instabilities ◽  
Low Flow ◽  
Flow Rates ◽  
Flow Limit ◽  
Stable Operating

Flow instabilities in a compression system at low flow rates set the flow limit of the stable operating range. Experiments to investigate the feasibility of controlling the stall in the radial diffuser of a low speed centrifugal compressor were carried out. The technique was very simple and involved using rough surfaces (i.e., sand papers) attached to the diffuser shroud. The results showed that the flow instability in the diffuser (stall) was delayed to a lower flow coefficient (the mass flow rate could be reduced to 70% of its value with the smooth surface) when the rough surfaces were positioned on the diffuser shroud.

Measurement of Compressible Flow Pressure Losses in Wye-Junctions

1994 ◽  
Vol 116 (3) ◽  
pp. 535-541 ◽  
Author(s):  
N. I. Abou-Haidar ◽  
S. L. Dixon
Keyword(s):  
Mach Number ◽  
Compressible Flow ◽  
Incompressible Flows ◽  
Separate Flow ◽  
Working Fluid ◽  
Vena Contracta ◽  
Pressure Losses ◽  
Flow Loss ◽  
Flow Pressure ◽  
Limiting Condition

This paper considers the compressible flow pressure losses in sharp-cornered wye-junctions with symmetric branches under dividing and combining flow conditions. Determination of the additional total pressure losses occurring in flow through several three-leg junctions, using dry air as the working fluid, has been made experimentally. Results covering a wide speed range up to choking are presented for 30, 60, and 90 deg wye-junctions. Separate flow visualization schlieren tests detected the presence of normal shock waves, located at up to one duct diameter downstream of the junction, and therefore confirmed the choking of the flow at the vena contracta. The highest attainable Mach number (M3) of the averaged whole flow was 0.9 for one of the dividing flow geometries and 0.65 for several of the combining flow cases. These values of M3 were the maximum possible and hence represent a limiting condition dictated by choking. In general, the compressible flow loss coefficients, caused by the presence of the wye-junctions, can be expected to be higher for dividing flows and lower for combining flows than would be the case for incompressible flows because of the influence of Mach number, M3.

Design Parameters Exploration for Supercritical CO2 Centrifugal Compressors Under Multiple Constraints

2016 ◽  
Author(s):  
Wenyang Shao ◽  
Xiaofang Wang ◽  
Jinguang Yang ◽  
Huimin Liu ◽  
Zhenjun Huang
Keyword(s):  
Cfd Simulation ◽  
Velocity Ratio ◽  
Tangential Velocity ◽  
Flow Coefficient ◽  
Low Flow ◽  
Design Parameters ◽  
Working Fluid ◽  
Rotating Speed ◽  
Thermodynamic Conditions ◽  
Velocity Coefficient

The Supercritical Carbon Dioxide (SCO2) Brayton cycle has been getting more and more attentions all over the world in recent years for its high cycle efficiency and compact components. The compressor is one of the most important components in the cycle. Different from traditional working fluid, SCO2 has a risk of condensation at the impeller inlet because of the particular properties near the critical point. In order to determine the possibility of the condensation, a concept called “Condensation Margin (CM)” suited for SCO2 is introduced. It is associated with the total and saturated thermodynamic conditions. A design parameter called velocity ratio at the impeller inlet (IVR) is defined to control the state of working fluid at impeller inlet based on CM. In terms of different constraints and design requirements, such as impeller efficiency, operating range and processing technic, especially in small size cases, the design parameters at the impeller outlet are explored by establishing a function of outlet width, the number of blades, rotating speed, outlet tangential velocity coefficient and outlet meridional velocity coefficient. A preliminary design result of a low-flow-coefficient SCO2 centrifugal compressor is presented as an example of the application of the design parameters exploration results; then CFD simulation is performed, and consistent results are obtained compared with exploration results.

Flow at the Tip of a Forward Curved Centrifugal Fan

1984 ◽  
Author(s):  
A. Goulas ◽  
B. Mealing
Keyword(s):  
Flow Rate ◽  
Rotational Speed ◽  
Reverse Flow ◽  
Suction Side ◽  
Flow Coefficient ◽  
Low Flow ◽  
Centrifugal Fan ◽  
Single Vortex ◽  
Curvature Effects ◽  
Corner Vortex

The velocity profiles, radial and circumferential components, were measured at the tip of a forward curved centrifugal fan. Three sets of measurements are presented. Two at peak efficiency for different rotational speeds and a third at the lower rotational speed and for a reduced flow rate. A reverse flow region was formed near the hub, and almost in the middle, between pressure and suction sides of the blade. Near the shroud a high velocity region was observed and a low one near the suction side, picture similar to the jet-wake structure found in the literature. At the lower rotational speed and low flow rate the flow was affected mainly by the system rotation. A “wake” was formed along the suction side of the blade. Increasing the flow rate blade curvature effects became more dominant. Increasing the rotational speed and for the same flow coefficient the system of two vortices observed in the previous case disappears and a single vortex takes its place. In this case the wake is positioned on the hub. Corner vortices also affect the main flow by changing the turbulence intensities. A corner vortex observed on the pressure side reduced the turbulence intensities in the region and a wake was formed locally. However, another corner vortex on the suction side caused an increase to the local turbulence intensities and consequently a high local velocity.

Effect of rotor–stator axial spacing on the pressure-rise performance and flow field in an axial pump

2018 ◽  
Vol 233 (6) ◽  
pp. 727-737
Author(s):  
Han Xu ◽  
Donghai Jin ◽  
Dakun Sun ◽  
Lin Du ◽  
Xingmin Gui ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Rate ◽  
Particle Image ◽  
Incidence Angle ◽  
Pressure Rise ◽  
Low Flow ◽  
Working Fluid ◽  
Rate Condition ◽  
Axial Pump ◽  
Image Velocimetry

In this paper, the effect of the rotor–stator axial spacing is investigated in an axial pump with the working fluid of water. The pressure-rise performance was tested at a range of flow rates. Results indicate that decreased axial spacing generates improved hydraulic head, especially when the flow rate is low. Particle image velocimetry measurement was performed and flow fields for five rotor phases were obtained in a low flow rate condition. Particle image velocimetry results demonstrate that the stator inlet flow is both affected by the wake of the rotor and the existence of the stator. As the axial spacing gets close, the incidence angle of the stator decreases and the flow separation on the suction side is restrained, and therefore the pressure rise ability is improved.

An Off-Design Performance Prediction Model for Low-Speed Double-Discharge Centrifugal Fans

2013 ◽  
Author(s):  
Tristan Wolfe ◽  
Yu-Tai Lee ◽  
Michael E. Slipper
Keyword(s):  
Mach Number ◽  
Prediction Model ◽  
Test Data ◽  
Flow Coefficient ◽  
Low Flow ◽  
Centrifugal Fan ◽  
Input Coefficient ◽  
Low Speed ◽  
Work Input ◽  
Double Discharge

A generalized model for mapping the trend of the performance characteristics of a double-discharge centrifugal fan is developed based on the work by Casey and Robinson (C&R) which formulated compressor performance maps for tip-speed Mach numbers ranging from 0.4 to 2 using test data obtained from turbochargers with vaneless diffusers. The current paper focuses on low-speed applications for Mach number below 0.4. The C&R model uses four non-dimensional parameters at the design condition including the flow coefficient, the work input coefficient, the tip-speed Mach number and the polytropic efficiency, in developing a prediction model that requires limited geometrical knowledge of the centrifugal turbomachine. For the low-speed fan case, the C&R formulas are further modified to apply a low-speed, incompressible analysis. The effort described in this paper begins by comparing generalized results using efficiency data obtained from a series of fan measurements to that using the C&R model. For the efficiency map, the C&R model is found to heavily depend on the ratio of the flow coefficient at peak efficiency to that at the choke flow condition. Since choke flow is generally not applicable in the low-speed centrifugal fan operational environment, an alternate, but accurate estimation method based on fan free delivery derived from the fan test data is presented. Using this new estimation procedure, the modified C&R model predicts reasonably well using the double-discharge centrifugal fan data for high flow coefficients, but fails to correlate with the data for low flow coefficients. To address this undesirable characteristic, additional modifications to the C&R model are also presented for the fan application at low flow conditions. A Reynolds number correction is implemented in the work input prediction of the C&R model to account for low-speed test conditions. The new model provides reasonable prediction with the current fan data in both work input and pressure rise coefficients. Along with the developments for the efficiency and work input coefficient maps, the use of fan shut-off and free delivery conditions are also discussed for low-speed applications.

Numerical Investigation on the Labyrinth Seal Design for a Low Flow Coefficient Centrifugal Compressor

2010 ◽  
Author(s):  
Zhiheng Wang ◽  
Liqun Xu ◽  
Guang Xi
Keyword(s):  
Centrifugal Compressor ◽  
Labyrinth Seal ◽  
Flow Coefficient ◽  
Low Flow ◽  
Design Parameters ◽  
Centrifugal Impeller ◽  
Computational Domain ◽  
Cfd Simulations ◽  
Isentropic Efficiency ◽  
Low Flow Coefficient

The leakage flow across the shroud of a centrifugal compressor impeller has an important effect on the compressor’s performance, in particular, in the low flow coefficient compressor. This paper presents the three-dimensional CFD simulations and the Radial Basis Function (RBF) model to investigate the aerodynamic performance of the labyrinth seal as well as the low flow coefficient centrifugal impeller. The CFD simulations are performed on the computational domain consisting of the labyrinth seal and the impeller. The relationship between the leakage loss coefficient and the isentropic efficiency is indicated. With the application of the RBF model, the global sensitivity analysis to the seal geometric design parameters is carried out, and the geometry of the labyrinth seal is optimized. The leakage of the optimized labyrinth seal is reduced remarkably and the impeller’s isentropic efficiency improved by 2% in a wide operating range.

Automatic computational fluid dynamics-based procedure for the optimization of a centrifugal impeller

2005 ◽  
Vol 219 (7) ◽  
pp. 549-557 ◽  
Author(s):  
F Martelli ◽  
S Pazzi ◽  
V Michelassi
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
New Technologies ◽  
Geometric Constraints ◽  
Flow Coefficient ◽  
Low Flow ◽  
Centrifugal Impeller ◽  
Geometrical Parameters ◽  
Design Point ◽  
Blade Thickness

A typical centrifugal impeller characterized by a low flow coefficient and cylindrical blades is redesigned by means of an intelligent automatic search program. The procedure consists of a feasible sequential quadratic programming algorithm (Fletcher, R. Practical Methods of optimization, 2000 (Wiley)) coupled to a lazy learning (LL) interpolator 1 to speed-up the process. The program is able to handle geometric constraints to reduce the computational effort devoted to the analysis of non-physical configurations. The objective function evaluator is an in-house developed structured computational fluid dynamics (CFD) code. The LL approx-imator is called each time the stored database can provide a sufficiently accurate performance estimate for a given geometry, thus reducing the effective CFD computations. The impeller is represented by 25 geometric parameters describing the vane in the meridional and s-0 planes, the blade thickness, and the leading edge shape. The optimization is carried out on the impeller design point maximizing the polytropic efficiency with nearly constant flow coefficient and polytropic head. The optimization is accomplished by maintaining unaltered those geometrical parameters which have to be kept fixed in order to make the impeller fit the original stage. The optimization, carried out on a cluster of 16 PCs, is self-learning and leads to a geometry presenting an increased design point efficiency. The program is completely general and can be applied to any component which can be described by a finite number of geometrical parameters and computed by any numerical instrument to provide performance indices. The work presented in this paper was done under the METHOD EC funded project for the implementation of new technologies for optimization of centrifugal compressors.

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