Experimental and Numerical Analysis of Pressure Pulsations and Mechanical Deformations in a Centrifugal Pump Impeller

2011 ◽  
Author(s):  
Stefan Berten ◽  
Sebastian Hentschel ◽  
Karin Kieselbach ◽  
Philippe Dupont
Keyword(s):  
Boundary Conditions ◽  
Flow Behavior ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Experimental Investigations ◽  
Pressure Waves ◽  
Centrifugal Pumps ◽  
Pressure Pulsations ◽  
Load Pressure ◽  
Part Load

Deformations, mechanical stresses and vibrations in centrifugal pumps are the result of pressure fluctuations, which are acting as excitation forces. When a pump operates at its optimum, the pressure pulsations are at minimum, but for a pump operating in part-load, pressure pulsations increase and subsequent vibration and deformation levels increase. In a recent experimental research, the pressure pulsations and the resulting structural stresses in the last stage impeller of a multistage pump have experimentally investigated for different operating conditions [1]. The experimental investigations have been complemented by transient numerical simulations using a commercial CFD code and structural analysis using the pressure pulsations resulting from the CFD code as boundary conditions. In the present study, a validation of these CFD and FEM simulations is presented. The analysis has been performed in three steps. In the first step, the transient CFD results for different load cases are analyzed and compared with the experimental results in order to evaluate the CFD simulations. In the second step the time domain pressure pulsation data are post-treated and decomposed into a series of rotating pressure waves. These pressure waves are then applied as boundary conditions to an FEM model and one full impeller revolution is simulated as steady calculations for 72 angular positions. The pressure pulsations in the best efficiency point are regularly distributed in space and time and dominated by rotor-stator-interaction. For part-load operation, the pressure distribution becomes more and more unsteady. The CFD results for part load exhibit stationary stall in the diffuser for a flow rate relative to best efficiency point of q* = 0.9 and unsteady stall behavior for a q* = 0.8. While the numerical CFD results agree well with experimental data for q* = 1 and q* = 0.9, at lower part load (q* = 0.8) the CFD didn’t reproduce the experimentally observed flow behavior, especially the rotating stall. The FEM results at design conditions show relatively low tangential stresses at the impeller outlet, which agree well with the measured deformations and stresses.

Rotating Instability in an Annular Cascade: Detailed Analysis of the Instationary Flow Phenomena

2013 ◽  
Vol 136 (6) ◽  
Author(s):  
Benjamin Pardowitz ◽  
Ulf Tapken ◽  
Robert Sorge ◽  
Paul Uwe Thamsen ◽  
Lars Enghardt
Keyword(s):  
Unsteady Flow ◽  
High Speed ◽  
Pressure Sensors ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Tip Vortex ◽  
Pressure Waves ◽  
Flow Profile ◽  
Rotating Instability ◽  
Annular Cascade

Rotating instability (RI) occurs at off-design conditions in compressors, predominantly in configurations with large tip or hub clearance ratios of s* ≥3%. RI is the source of the blade tip vortex noise and a potential indicator for critical operating conditions like rotating stall and surge. The objective of this paper is to give more physical insight into the RI phenomenon using the analysis results of combined near-field measurements with high-speed particle image velocimetry (PIV) and unsteady pressure sensors. The investigation was pursued on an annular cascade with hub clearance. Both the unsteady flow field next to the leading edge as well as the associated rotating pressure waves were captured. A special analysis method illustrates the characteristic pressure wave amplitude distribution, denoted as “modal events” of the RI. Moreover, the slightly adapted method reveals the unsteady flow structures corresponding to the RI. Correlations between the flow profile, the dominant vortex structures, and the rotating pressure waves were found. Results provide evidence to a new hypothesis, implying that shear layer instabilities constitute the basic mechanism of the RI.

Experimental investigations on instability evolution in a transonic compressor at different rotor speeds

2015 ◽  
Vol 229 (18) ◽  
pp. 3378-3391 ◽  
Author(s):  
Qiushi Li ◽  
Tianyu Pan ◽  
Tailu Sun ◽  
Zhiping Li ◽  
Yifang Gong
Keyword(s):  
Low Frequency ◽  
Axial Flow ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Experimental Investigations ◽  
Rotor Speed ◽  
Axial Flow Compressor ◽  
Transonic Compressor ◽  
New Type ◽  
Flow Compressor

Experimental investigations are conducted to study the instability evolution in a transonic axial flow compressor at four specific rotor speeds covering both subsonic and transonic operating conditions. Two routes of evolution to final instability are observed in the test compressor: at low rotor speeds, a disturbance in the rotor tip region occurs and then leads to rotating stall, while at high rotor speeds, a low-frequency disturbance in the hub region leads the compressor into instability. Different from stall and surge, this new type of compressor instability at high rotor speed is initiated through the development of a low-frequency axisymmetric disturbance at the hub, and we name it “partial surge”. The frequency of this low-frequency disturbance is approximately the Helmholtz frequency of the system and remains constant during instability inception. Finally, a possible mechanism for the occurrence of different instability evolutions and the formation of partial surge are also discussed.

A Study on Energetic and Hydraulic Interaction of Combined Journal and Thrust Bearings

2015 ◽  
Author(s):  
Thomas Hagemann ◽  
Hardwig Blumenthal ◽  
Christian Kraft ◽  
Hubert Schwarze
Keyword(s):  
Boundary Conditions ◽  
High Speed ◽  
Thrust Bearing ◽  
Journal Bearing ◽  
Measurement Data ◽  
Operating Conditions ◽  
Experimental Investigations ◽  
Minor Importance ◽  
Thrust Bearings ◽  
Side Flow

A theoretical algorithm for the analysis of bidirectional interaction of combined journal and thrust bearings is presented. While many theoretical and experimental investigations on the operating behavior of single journal and thrust bearings can be found only few results for combined bearings are available. However, combined bearings interact by exchanging lubricant and heat which can affect significant changes of boundary conditions compared to a single bearing application. Therefore, a novel procedure is developed to combine two separate codes for journal and thrust bearings in order to iteratively determine the coupling boundary conditions due to the special design of the entire bearing unit. The degree of interaction strongly depends on the type of lubrication. In a first step predictions are verified by measurement data for a combined bearing with a fixed-pad offset-halves journal bearing and a directed lubricated tilting-pad thrust bearing. Experiments were conducted on a high speed test rig up to sliding speeds of 107 m/s at the mean radius of the thrust bearing. As expected the interaction of the two oil films is comparably low in the investigated speed and load range for this bearing design because of the active lubrication of both bearings and the low hydraulic resistance of the thrust bearing. In order to theoretically investigate interaction of thrust and journal bearings in more details a combined bearing with fixed-pad thrust parts lubricated exclusively by the side flow of the journal bearing is studied. A variation of modeling level, pocket design of the journal part, thrust load and rotating frequency provides the following results: (i) hydraulic and energetic interaction have to be modelled in details, (ii) the axial flow resistance of the pockets strongly influences flow rates and the pressure level at the interfaces (iii) the level of interface pressure rises with increasing thrust loads and decreasing rotor speed, (iv) the axial bearing clearance is rather of minor importance for the investigated bearing. Finally, improvements in order to predict operating conditions more precisely are comprehensively discussed.

Numerical Simulation of Inner Flow in a Double Blades Pump Based on OpenFOAM and its PIV Verification

2012 ◽  
Author(s):  
Yun Ren ◽  
Houlin Liu ◽  
Kai Wang ◽  
Minggao Tan ◽  
Denghao Wu ◽  
...  
Keyword(s):  
Cfd Simulation ◽  
Flow Behavior ◽  
Energy Performance ◽  
Operating Conditions ◽  
Centrifugal Pumps ◽  
Complex Flow ◽  
Unstable Flow ◽  
Software Packages ◽  
Flow Phenomena ◽  
Particle Imaging

The presence of unstable flow phenomena may significantly alter the flow pattern and characteristics of centrifugal pumps; that is, the unstable flows may seriously deteriorate the pumps performance. In this paper, considering the high cost of running license fees and not available with all the computing resources, a high quality Open Source CFD simulation platform like OpenFOAM instead of commercial software packages is adopted. Furthermore, the required capability such as GGI is added and boundary conditions are specialized to better simulate complex flow behavior through rotor-stator components in a double blades pump, whose specific speed is 115.6. In order to disclose the characteristics completely, six research schemes are developed and are now presented in this paper. The ratios (Q/Qd) of the flow rate are 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, respectively. The task mainly focuses on the comparison of energy performance under different operating conditions between numerical calculations and experiments, the analysis of the inner flow in the impeller and the comparison of the velocity field in the impeller mid-height between simulation data and the Particle Imaging Velocimetry (PIV) experimental data. The results show that good agreements are found both in terms of the energy performance with experimental results and computed velocities with the PIV data, but improvements can be made.

FEM-DEM Dialogue for Tribological Understanding

2008 ◽  
Author(s):  
Aure´lien Saulot ◽  
Mathieu Renouf ◽  
Yves Berthier
Keyword(s):  
Boundary Conditions ◽  
Point Of View ◽  
Operating Conditions ◽  
Contact Dynamics ◽  
Experimental Investigations ◽  
Global Dynamics ◽  
Material Flows ◽  
Local Contact ◽  
Local Point ◽  
Two Bodies

In many mechanisms, global dynamics resulting from operating conditions act as external solicitations for bodies in contact. As a consequence, dynamic instabilities occur in the contact and lead to particle detachments, usually called 3rd body and wear flow. Obviously, once detached, these particles play an important role in the evolution of the local friction coefficient and thus the local contact dynamics. As the contact is a confined area, experimental investigations have mostly been unsuccessful to locally describe both contact dynamics and material flows. To balance this lack, two numerical methods can be used to solve independently each part of the problem. From a global point of view, local contact dynamics is considered as a local condition for the two 1st bodies described as continuous media. From a local point of view, the discontinuity of the interface should be taken into account to describe material flows, considering effect of two bodies as boundary conditions. To model continuous aspects, a semi-implicit dynamic Finite Element (FE) method is used taking into account the elasto-plastic behaviour of the two bodies in contact. To model discontinuous effects, a non conventional Discrete Element (DE) method is used, called the Non Smooth Contact Dynamic (NSCD) method coupled with Cohesive Zone Models (CZM) to describe the behaviour of the 3rd body particles. To give a reliable description of the behaviour of bodies in contact, a coupling of scales is required on both local conditions and boundary conditions which are respectively inputs coming from DE and FE methods. The aim of the present paper is to gather these two complementary approaches by creating a numerical dialogue between DE and FE methods acting respectively at the 3rd and 1st bodies scales. After a brief description of each numerical model, the dialogue methodology will be detailed and applied to a reference example where dynamic instabilities occur in the contact. A comparison between results obtained with “classical” FE simulation and “coupled” FE-DE simulations is presented. As a conclusion, this numerical dialogue is a first step toward a better taking into account of the 3rd body behaviour in continuum model and its consequences on local contact dynamics.

Unsteady Aerodynamic Blade Excitation at the Stability Limit and During Rotating Stall in an Axial Compressor

2006 ◽  
Author(s):  
Ronald Mailach ◽  
Konrad Vogeler
Keyword(s):  
Gas Turbines ◽  
Axial Compressor ◽  
Stability Limit ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Experimental Investigations ◽  
Momentum Exchange ◽  
Stall Inception ◽  
The Stability ◽  
Force Excitation

The stable operating range of axial compressors is limited by the onset of rotating stall and surge. These flow conditions endanger the reliability of operation and have definitely to be avoided in compressors of gas turbines. However, there is still a need to improve the physical understanding of these flow phenomena to prevent them while utilizing the maximum available working potential of the compressor. This paper discusses detailed experimental investigations of the rotating stall onset with the main emphasis on the aerodynamic blade excitation in the Dresden four-stage Low-Speed Research Compressor. The stall inception, which is triggered by modal waves, as well as the main flow features during rotating stall operation are discussed. To investigate the unsteady pressure distributions, both the rotor and the stator blades of the first stage were equipped with piezoresistive pressure transducers. Based on these measurements the unsteady blade pressure forces are calculated. Time-resolved results at the stability limit as well as during rotating stall are presented. For all operating conditions rotor-stator-interactions play an important role on the blade force excitation. Furthermore the role of the inertia driven momentum exchange at the stall cell boundaries on the aerodynamic blade force excitation is pointed out.

Numerical Investigations of Gas–Liquid Two-Phase Flow in a Pump Inducer

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Michael Mansour ◽  
Trupen Parikh ◽  
Sebastian Engel ◽  
Dominique Thévenin
Keyword(s):  
Two Phase Flow ◽  
Volume Fraction ◽  
Flow Behavior ◽  
Pressure Change ◽  
Positive Influence ◽  
Phase Flow ◽  
Centrifugal Pumps ◽  
Two Phase ◽  
Part Load ◽  
Gas Volume

Abstract Inducers show generally a positive influence on the performance of centrifugal pumps in the two-phase regime, since they produce more uniform mixtures and increase the pressure before the impeller. However, the effect is much more pronounced in part-load compared to overload conditions. In this study, the air–water two-phase flow behavior in a pump inducer was numerically investigated. The main objectives were to clarify the effect of the inducer, the effective operating range, and to examine flow mixing. Several flow conditions were studied, covering part-load, optimal, and overload pumping conditions, together with different relevant gas volume fractions (1%, 3%, and 5%). The simulations were performed using a transient setup and a moving-mesh approach. Two-phase air–water interactions were modeled by the volume of fluid (VOF) method. After checking the proper discretization in space and time, the model was validated against experimental results, revealing excellent agreement. The numerical analysis was able to explain different effects of inducers in part-load and overload conditions. Under overload conditions, the flow separates, leading to the generation of axial vortices and to a negative pressure change across the inducer; additionally, the residence time is reduced, hindering mixing. These vortices are intensified as the gas volume fraction increases, reducing further the pressure downstream of the inducer. This is the reason why inducers can mainly be used in part-load and near optimal conditions in order to improve pumping of two-phase flows.

Flow Phenomena in a Highly-Loaded Single-Stage Axial-Flow Pump: Comparison of Experimental and Numerical Results

2007 ◽  
Author(s):  
Friedrich-Karl Benra ◽  
Hans Josef Dohmen ◽  
Marina Schmidt
Keyword(s):  
Flow Structure ◽  
Flow Behavior ◽  
Axial Flow ◽  
Numerical Results ◽  
Operating Conditions ◽  
Flow Conditions ◽  
Part Load ◽  
Flow Phenomena ◽  
Operating Points ◽  
Highly Loaded

In highly loaded axial flow pumps considerable changes of the flow behavior were reported when altering the flow rate from design point operation to part load operation. The flow structure which is changing from stable operating conditions to stalled flow conditions has been investigated in detail by Kosyna and Stark with experimental methods. The present paper focuses on the application of numerical methods to simulate the flow behavior in the pump which has been investigated experimental. The obtained numerical results using a commercial solver for the unsteady Reynolds averaged Navier-Stokes equations (URANS) have been compared to the experimental results of Kosyna and Stark et al. The characteristic of the pump at different operating points is compared to the measurement. The change in the flow structure at part load conditions which gives a decrease of head is reproduced by the simulation results. The vortex structure induced by the tip leakage flow is a flow phenomenon which is well-known in external aerodynamics and in axial-flow compressors at flow conditions close to stall. The change of this vortex structure at different operating conditions is shown. Also the part load recirculation vortex dominating the rotor tip flow at deep stall conditions as well as the cross passage vortex is visualized from the numerical results. All addressed flow phenomena are shown in contrast to the findings of the experimental investigations. This comparison of the flow fields for appropriate operating points shows that the reported change in the flow structure can be detected by numerical simulation as well.

Rotating Instability in an Annular Cascade: Detailed Analysis of the Instationary Flow Phenomena

2013 ◽  
Author(s):  
Benjamin Pardowitz ◽  
Ulf Tapken ◽  
Robert Sorge ◽  
Paul Uwe Thamsen ◽  
Lars Enghardt
Keyword(s):  
Unsteady Flow ◽  
High Speed ◽  
Pressure Sensors ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Tip Vortex ◽  
Pressure Waves ◽  
Flow Profile ◽  
Rotating Instability ◽  
Annular Cascade

Rotating instability (RI) occurs at off-design conditions in compressors, predominantly in configurations with large tip or hub clearance ratios of s* ≥ 3% [1]. RI is the source of the blade tip vortex noise and a potential indicator for critical operating conditions like rotating stall and surge. The objective of this paper is to give more physical insight into the RI phenomenon using the analysis results of combined near-field measurements with High-Speed PIV and unsteady pressure sensors. The investigation was pursued on an annular cascade with hub clearance. Both the unsteady flow field next to the leading edge as well as the associated rotating pressure waves were captured. A special analysis method illustrates the characteristic pressure wave amplitude distribution, denoted as ‘Modal Events’ of the RI. Moreover, the slightly adapted method reveals the unsteady flow structures corresponding to the RI. Correlations between the flow profile, the dominant vortex structures and the rotating pressure waves were found. Results provide evidence to a new hypothesis, implying that shear layer instabilities constitute the basic mechanism of the RI.

Effect of Liquid Level on Gas Carry-Under in GLCC Compact Separators

2018 ◽  
Author(s):  
Srinivas Swaroop Kolla ◽  
Ram S. Mohan ◽  
Ovadia Shoham
Keyword(s):  
Swirling Flow ◽  
Flow Behavior ◽  
Operating Conditions ◽  
Liquid Level ◽  
Experimental Investigations ◽  
Level Control ◽  
Oil Flow ◽  
Control Configuration ◽  
Carry Over ◽  
The Stability

Gas Carry-Under (GCU) is one of the two undesirable phenomena that occurs in the GLCC©1 (Gas-Liquid Cylindrical Cyclone) separators. Initial studies have shown that maintaining liquid level below the inlet of the GLCC© under control configuration affects the GCU in GLCC©. Also, it has been hypothesized that effective formation of vortex that is formed in the lower part of the GLCC©, or a stable gas core enhances the separation of gas entrained in the liquid. However, there has not been a systematic study on the effect of liquid level and the stability of the vortex on the GCU. This detailed and extensive experimental study attempts to fill that gap, investigating the effect of different liquid levels maintained below the inlet on the GCU. These studies are performed under the NOC (Normal operating Conditions) below the OPEN for liquid carry-over using control configuration to maintain the liquid level in the GLCC©. This study focuses on measuring the cumulative GCU in the liquid leg of the GLCC© over a period of time. The experimental investigations for GCU are conducted in a state of the art experimental facility for air-water and air-oil flow incorporating pressure and level control configurations. The experiments were carried out using a 3″ diameter GLCC© equipped with gas trap sections to measure simultaneously the GCU in the liquid leg of the GLCC©. The equilibrium liquid level is controlled at 4 different settings starting at 6″ below the GLCC© inlet and increasing to 2 feet below the inlet. It has been observed that the liquid level has tremendous effect on the complex swirling flow behavior in the lower part of the GLCC© and vortex stability, which in turn affects the GCU in the liquid leg of the GLCC©. Also, it has been noted that the liquid level has a significant effect on the Gas Void-Fraction in the liquid leg of the GLCC©, which is a critical parameter for multiphase pump operations.

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