Vibration Modeling and Experimental Results of Two Phase Flow Twin-Screw Pump

2015 ◽  
Author(s):  
Ameen R. A. Muhammed ◽  
Dara W. Childs
Keyword(s):  
Critical Speed ◽  
Dynamic Pressure ◽  
Excitation Frequency ◽  
Harmonic Excitation ◽  
Running Speed ◽  
Two Phase ◽  
Screw Pump ◽  
Positive Displacement ◽  
Twin Screw ◽  
Dynamic Pressure Measurements

In turbomachines, the transfer of energy between the rotor and the fluid does not — in theory — result in lateral forces on the rotor. In positive displacement machines, on the other hand, the transfer of energy between the moving and stationary components usually results in unbalanced pressure fields and forces. In [1] the authors developed a model to predict the dynamic forces in twin screw pumps, showing that the helical screw shape generates hydraulic forces that oscillate at multiples of running speed. The work presented here attempts to validate the model in [1] using a clear-casing twin screw pump. The pump runs in both single and multiphase conditions with exit pressure up to 300 KPa and a flow rate 0.6 liter per second. The pump was instrumented with dynamic pressure probes across the axial length of the screw in two perpendicular directions to validate the dynamic model. Two proximity probes measured the dynamic rotor displacement at the outlet to validate the rotordynamics model and the hydrodynamic cyclic forces predicted in [1]. The predictions were found in good agreement with the measurements. The amplitude of the dynamic pressure measurements in two perpendicular plans supported the main assumptions of the model (constant pressure inside the chambers and linear pressure drop across the screw lands). The predicted rotor orbits at the pump outlet in the middle of the rotor matched the experimental orbits closely. The spectrum of the response showed harmonics of the running speed as predicted by the model. The pump rotor’s calculated critical speed was at 24.8 krpm, roughly 14 times the rotor’s running speed of 1750 rpm. The measured and observed excitation frequencies extended out to nine times running speed, still well below the 1st critical speed. However, for longer twin-screw pumps running at higher speed, the coincidence of a higher-harmonic excitation frequency with the lightly damped 1st critical speed should be considered.

Vibration Modeling and Experimental Results of Two-Phase Twin-Screw Pump

2016 ◽  
Vol 138 (9) ◽  
Author(s):  
Ameen Muhammed ◽  
Dara W. Childs
Keyword(s):  
Gas Turbines ◽  
Critical Speed ◽  
Two Phase Flow ◽  
Dynamic Pressure ◽  
Working Fluid ◽  
Phase Flow ◽  
Running Speed ◽  
Two Phase ◽  
Screw Pump ◽  
Twin Screw

In turbomachines, the transfer of energy between the rotor and the fluid does not—in theory—result in lateral forces on the rotor. In positive displacement machines, on the other hand, the transfer of energy between the moving components and the working fluid usually results in unbalanced pressure fields and forces. Muhammed and Childs (2013, “Rotordynamics of a Two-Phase Flow Twin Screw Pump,” ASME J. Eng. Gas Turbines Power, 135(6), p. 062502) developed a model to predict the dynamic forces in twin-screw pumps, showing that the helical screw shape generates hydraulic forces that oscillate at multiples of running speed. The work presented here attempts to validate the model of Muhammed and Childs (2013, “Rotordynamics of a Two-Phase Flow Twin Screw Pump,” ASME J. Eng. Gas Turbines Power, 135(6), p. 062502) using a clear-casing twin-screw pump. The pump runs in both single and multiphase conditions with exit pressure up to 300 kPa and a flow rate 0.6 l/s. The pump was instrumented with dynamic pressure probes across the axial length of the screw in two perpendicular directions to validate the dynamic model. Two proximity probes measured the dynamic rotor displacement at the outlet to validate the rotordynamics model and the hydrodynamic cyclic forces predicted by Muhammed and Childs (2013, “Rotordynamics of a Two-Phase Flow Twin Screw Pump,” ASME J. Eng. Gas Turbines Power, 135(6), p. 062502). The predictions were found to be in good agreement with the measurements. The amplitude of the dynamic pressure measurements in two perpendicular plans supported the main assumptions of the model (constant pressure inside the chambers and linear pressure drop across the screw lands). The predicted rotor orbits at the pump outlet in the middle of the rotor matched the experimental orbits closely. The spectrum of the response showed harmonics of the running speed as predicted by the model. The pump rotor's calculated critical speed was at 24.8 krpm, roughly 14 times the rotor's running speed of 1750 rpm. The measured and observed excitation frequencies extended out to nine times running speed, still well below the first critical speed. However, for longer twin-screw pumps running at higher speed, the coincidence of a higher-harmonic excitation frequency with the lightly damped first critical speed should be considered.

Rotordynamics of a Two-Phase Flow Twin Screw Pump

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Ameen R. A. Muhammed ◽  
Dara W. Childs
Keyword(s):  
Steady State ◽  
Pressure Distribution ◽  
Two Phase Flow ◽  
Dynamic Pressure ◽  
Phase Flow ◽  
Two Phase ◽  
Screw Pump ◽  
Lateral Forces ◽  
Starting Point ◽  
Twin Screw

Twin screw pumps are positive displacement machines. Two meshing screws connected by timing gears push the fluid trapped in the screw cavities axially from suction to discharge. Available steady state hydraulic models predict pump performance and axial pressure distribution in the chambers in single- and two-phase flow conditions. However, no model is available for their rotordynamics behavior. Due to the helix angle of the screw, the pressure distribution around the rotor is not balanced, giving rise to both static and dynamic lateral forces. The work presented here introduces a starting point for rotordynamic analysis of twin screw pumps. First, we show that the screw rotor's geometry can be represented by axisymmetric beam elements. Second, we extend the steady state hydraulic model to predict both the static and dynamic lateral forces resulting from the unbalanced pressure field. Finally, hydraulic forces are applied to the rotor to predict static, synchronous, and nonsynchronous responses. Predictions of the dynamic pressure were compared to measurements from the literature and were found to be in good agreement.

Rotordynamics of a 2-Phase Flow Twin Screw Pump

2012 ◽  
Author(s):  
Ameen R. A. Muhammed ◽  
Dara W. Childs
Keyword(s):  
Steady State ◽  
Pressure Distribution ◽  
Dynamic Pressure ◽  
Phase Flow ◽  
Two Phase ◽  
Screw Pump ◽  
Lateral Forces ◽  
Starting Point ◽  
Twin Screw ◽  
Screw Rotors

Twin-screw pumps are positive displacement machines. Two meshing screws connected by timing gears push the fluid trapped in the screw cavities axially from suction to discharge. Available steady state hydraulic models predict pump performance and axial pressure distribution in the chambers in single and two phase flow conditions. However, no model is available for their rotordynamics. Due to the helix angle of the screw, the pressure distribution around the rotor is not balanced; giving rise to both static and dynamic lateral forces. The work presented here introduces a starting point for rotordynamic analysis of twin screw-pumps. We first show that the screw rotors geometry can be represented by axisymmetric beam elements. Second, we extend the steady state hydraulic model to predict both the static and dynamic lateral forces resulting from the unbalanced pressure field. Finally, hydraulic forces are applied to the rotor to predict static, synchronous and nonsynchronous responses. Predictions of the dynamic pressure were compared to measurements from the literature and were found to be in good agreement.

scholarly journals Air-Water Two-phase Characteristics of Twin-Screw Pump and Casing-Wall Pressure Measurements.

2002 ◽  
Vol 68 (674) ◽  
pp. 2788-2794
Author(s):  
Akinori FURUKAWA ◽  
Hidetsugu ODA ◽  
Hisasada TAKAHARA ◽  
Takashi EGUCHI
Keyword(s):  
Wall Pressure ◽  
Pressure Measurements ◽  
Two Phase ◽  
Screw Pump ◽  
Twin Screw

Predictions for Non-Contacting Mechanical Face Seal Vibration With External Excitation From Pump Vibration: Part II — Flexibly Mounted Rotor

2018 ◽  
Author(s):  
Clay S. Norrbin ◽  
Dara W. Childs
Keyword(s):  
Excitation Frequency ◽  
Harmonic Excitation ◽  
Fluid Film ◽  
Axial Distance ◽  
Mechanical Seal ◽  
Seal Ring ◽  
Mechanical Seals ◽  
Running Speed ◽  
Frequency Dependent ◽  
Frequency Independent

Stability and response predictions are presented for a Flexibly Mounted Rotor (FMR) mechanical seal ring using the model developed by Childs in 2018. The seal ring is excited by lateral/pitch vibration from the rotor/housing. The model includes a frequency dependent stiffness and damping model for the O-ring and a frequency independent model for the fluid film. The dynamic coefficients are speed and frequency dependent. The mechanical seal is modeled after a typical FMR mechanical seal. Parameters for radius, fluid film clearance, and O-Ring axial distances are varied. The axial distance between the O-Ring and seal ring inertia center doz is found to couple lateral rotor motion and seal ring pitch vibration. The predictions show a dependency on both excitation frequency and running speed. The analyzed FMR has a critical region with high transmissibility in a region around a speed and excitation frequency of 70 kRPM. Another region of high transmissibility is predicted to be with sub-harmonic excitation frequency. The FMR seal ring also has an unstable region that is sub-harmonic of 1% running speed. Running back on the HQ curve for a pump causes broadband sub-harmonic excitaiton, which can cause rub failures for FMR mechanical seals.

Numerical Analysis for Twin Screw Pump Internal Flow

2011 ◽  
Vol 130-134 ◽  
pp. 3658-3663
Author(s):  
Qian Tang ◽  
Abebe Misganaw ◽  
Xian Zhi Ye ◽  
Yuan Xun Zhang
Keyword(s):  
Control Volume ◽  
Flow Analysis ◽  
Internal Flow ◽  
Numerical Control ◽  
Screw Pump ◽  
Steady State Condition ◽  
Various Boundary Conditions ◽  
Positive Displacement ◽  
Twin Screw ◽  
Displacement Pump

Screw pump is a special type of rotary positive displacement pump in which the flow through the pumping elements is truly axial. The objective of this study is to develop a numerical solution method for flow analysis of a twin screw pump by using a Single Rotating Reference Frame method with various boundary conditions and rotational speeds of rotor on steady state condition. Flow variable contours and plots were obtained for fluid flow inside a pump subject to pressure inlet and pressure outlet conditions using the numerical control volume method in the commercial package of FLUENT. This work needs for the analysis of flow parameters inside a screw pump in order to achieve optimum design.

scholarly journals Numerical investigation of cavitation in twin-screw pumps

2017 ◽  
Vol 232 (20) ◽  
pp. 3733-3750 ◽  
Author(s):  
Di Yan ◽  
Ahmed Kovacevic ◽  
Qian Tang ◽  
Sham Rane
Keyword(s):  
Bubble Dynamics ◽  
Rotation Speed ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Distribution Area ◽  
Cavitation Model ◽  
Two Phase ◽  
Screw Pump ◽  
Twin Screw ◽  
Discharge Pressure

In order to investigate the flow characteristics and the formation process of cavitation in twin-screw pumps, three-dimensional computational fluid dynamics numerical analysis has been carried out. A conformal structured moving mesh generated by an in-house code SCORG was applied for the rotor domain. The volume of fluid method has been adopted for dealing with the liquid-gas two-phase flow, while the bubble dynamics was handled by a homogenous cavitation model. By changing the rotation speed and discharge pressure, the intensity, distribution area and variation of cavitation at different rotor angle were obtained. The effects of rotation speed and discharge pressure on cavitation characteristics have been analysed. Calculation results with cavitation model are compared with the results without cavitation and the experimentally obtained values. The influence of cavitation on the performance of a screw pump in terms of the mass flow rate, pressure distribution, rotor torque and the shaft power has been analysed and discussed. For analysis of cavitation in clearances, a 2D numerical model which includes radial and inter-lobe clearances was used. The relationship between volumetric efficiency and cavitation intensity was developed by variation of boundary conditions.

scholarly journals Numerical Modelling and Experimental Validation of Twin-Screw Expanders

Energies ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4700
Author(s):  
Kisorthman Vimalakanthan ◽  
Matthew Read ◽  
Ahmed Kovacevic
Keyword(s):  
Volume Ratio ◽  
Small Scale ◽  
Expansion Process ◽  
Two Phase ◽  
Experimental Conditions ◽  
Good Efficiency ◽  
Positive Displacement ◽  
Accurate Design ◽  
Twin Screw ◽  
Power Generation Systems

Positive displacement machines have been identified as appropriate expanders for small-scale power generation systems such as Organic Rankine Cycles (ORCs). Screw expanders can operate with good efficiency in working fluids under both dry and two-phase conditions. Detailed understanding of the fluid expansion process is required to optimise the machine design and operation for specific applications, and accurate design tools are therefore essential. Using experimental data for air expansion, both CFD and chamber models have been applied to investigate the influence of port flow and leakage on the expansion process. Both models are shown to predict pressure variation and power output with good accuracy. The validated chamber model is then used to identify the optimal volume ratio and rotational speed for experimental conditions.

scholarly journals Reproducibility of C. I. P.-compatible dynamic pressure measurements

2020 ◽  
Vol 87 (10) ◽  
pp. 630-636
Author(s):  
Oliver Slanina ◽  
Susanne Quabis ◽  
Robert Wynands
Keyword(s):  
Dynamic Pressure ◽  
Storage Conditions ◽  
Dynamic Measurement ◽  
Gas Pressure ◽  
Pressure Measurements ◽  
Small Arms ◽  
Minimum Pressure ◽  
Maximum Value ◽  
Preliminary Study ◽  
Dynamic Pressure Measurements

AbstractTo ensure the safety of users like hunters and sports shooters, the dynamic pressure inside an ammunition cartridge must not exceed a maximum value. We have investigated the reproducibility of the dynamic measurement of the gas pressure inside civilian ammunition cartridges during firing, when following the rules formulated by the Permanent International Commission for the Proof of Small Arms (C. I. P.). We find an in-house spread of 0.8 % between maximum and minimum pressure for runs with the same barrel and of 1.8 % among a set of three barrels. This sets a baseline for the expected agreement in measurement comparisons between different laboratories. Furthermore, a difference of more than 3 % is found in a preliminary study of the influence of ammunition storage conditions.

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