On the lifespan of recirculating suspensions with pulsatile flow

2021 ◽  
Vol 928 ◽  
Author(s):  
Mark D. Jeronimo ◽  
David E. Rival
Keyword(s):  
Strouhal Number ◽  
Fluid Transport ◽  
Volume Fraction ◽  
Amplitude Ratio ◽  
Recirculation Region ◽  
Pure Liquid ◽  
Steady Flows ◽  
Lagrangian Analysis ◽  
Pulsatile Flows ◽  
Low Amplitude

A Lagrangian analysis is performed to measure the rate at which recirculating fluid is replaced (depleted) in pulsatile flows. Based on this approach, we then investigate how depletion is affected in dense suspensions. Experiments are conducted for pure liquid as well as suspensions with volume fractions of $\varPhi =5\,\%$ , 10 % and 20 %. Using Lagrangian tracking and pathline extension techniques, the depletion of the recirculation region is quantified via the trajectories of individual fluid parcels exiting the domain. Pulsatile flows with varying concentrations of hydrogel beads, up to a volume fraction of 20 %, are compared at mean Reynolds numbers of $Re=4800$ , 9600 and 14 400, while the Strouhal number ( $St=0.04$ , 0.08 and 0.15) and amplitude ratio ( $\lambda =0.25$ , 0.50 and 0.95) are systematically varied. A so-called ‘depletion efficiency’ is calculated for each test case, which is shown to increase with increasing Strouhal number and amplitude ratio. For most pulsatile cases, periodic vortex formation significantly increases depletion efficiency through enhanced entrainment of recirculating fluid. Conversely, low-amplitude pulsatile flows are dominated by Kelvin–Helmholtz instabilities, which do not penetrate into the recirculation region, and thus their depletion efficiency is markedly lower as a result. The efficiency trends and depletion mechanisms remain virtually unchanged between the pure liquid and each of the suspension concentrations under almost all flow conditions, which forms an unexpected conclusion. The only exception is for low-amplitude and steady flows, where increasing the suspension volume fraction is shown to suppress fluid transport across the shear layer, which in turn slows depletion and decreases the overall depletion efficiency.

Leakage, Drag Power and Rotordynamic Force Coefficients of an Air in Oil (Wet) Annular Seal

2017 ◽  
Author(s):  
Luis San Andrés ◽  
Xueliang Lu
Keyword(s):  
Test Data ◽  
Volume Fraction ◽  
Damping Coefficient ◽  
Liquid Volume ◽  
Pure Liquid ◽  
Test Results ◽  
Liquid Volume Fraction ◽  
Force Coefficients ◽  
Damping Coefficients ◽  
Annular Seal

Wet gas compression systems and multiphase pumps are enabling technologies for the deep sea oil and gas industry. This extreme environment determines both machine types have to handle mixtures with a gas in liquid volume fraction (GVF) varying over a wide range (0 to 1). The gas (or liquid) content affects the system pumping (or compression) efficiency and reliability, and places a penalty in leakage and rotordynamic performance in secondary flow components, namely seals. In 2015, tests were conducted with a short length smooth surface annular seal (L/D = 0.36, radial clearance = 0.127 mm) operating with an oil in air mixture whose liquid volume fraction (LVF) varied to 4%. The test results with a stationary journal show the dramatic effect of a few droplets of liquid on the production of large damping coefficients. This paper presents further measurements and predictions of leakage, drag power, and rotordynamic force coefficients conducted with the same test seal and a rotating journal. The seal is supplied with a mixture (air in ISO VG 10 oil), varying from a pure liquid to an inlet GVF = 0.9 (mostly gas), a typical range in multiphase pumps. For operation with a supply pressure (Ps) up to 3.5 bar (a), discharge pressure (Pa) = 1 bar (a), and various shaft speed (Ω) to 3.5 krpm (ΩR = 23.3 m/s), the flow is laminar with either a pure oil or a mixture. As the inlet GVF increases to 0.9 the mass flow rate and drag power decrease monotonically by 25% and 85% when compared to the pure liquid case, respectively. For operation with Ps = 2.5 bar (a) and Ω to 3.5 krpm, dynamic load tests with frequency 0 < ω < 110 Hz are conducted to procure rotordynamic force coefficients. A direct stiffness (K), an added mass (M) and a viscous damping coefficient (C) represent well the seal lubricated with a pure oil. For tests with a mixture (GVFmax = 0.9), the seal dynamic complex stiffness Re(H) increases with whirl frequency (ω); that is, Re(H) differs from (K-ω2M). Both the seal cross coupled stiffnesses (KXY and −KYX) and direct damping coefficients (CXX and CYY) decrease by approximately 75% as the inlet GVF increases to 0.9. The finding reveals that the frequency at which the effective damping coefficient (CXXeff = CXX-KXY/ω) changes from negative to positive (i.e., a crossover frequency) drops from 50% of the rotor speed (ω = 1/2 Ω) for a seal with pure oil to a lesser magnitude for operation with a mixture. Predictions for leakage and drag power based on a homogeneous bulk flow model match well the test data for operation with inlet GVF up to 0.9. Predicted force coefficients correlate well with the test data for mixtures with GVF up to 0.6. For a mixture with a larger GVF, the model under predicts the direct damping coefficients by as much as 40%. The tests also reveal the appearance of a self-excited seal motion with a low frequency; its amplitude and broad band frequency (centered at around ∼12 Hz) persist and increase as the gas content in the mixture increase. The test results show that an accurate quantification of wet seals dynamic force response is necessary for the design of robust subsea flow assurance systems.

scholarly journals Experimental and unsteady numerical research of a high-specific-speed pump for part-load cavitation instability

2019 ◽  
Vol 11 (3) ◽  
pp. 168781401982893 ◽  
Author(s):  
Hong Li ◽  
Zhenhua Shen ◽  
Nicholas Engen Pedersen ◽  
Christian Brix Jacobsen
Keyword(s):  
Volume Fraction ◽  
Suction Side ◽  
Recirculation Region ◽  
Cavitation Bubbles ◽  
Cavitation Region ◽  
Cavitation Instability ◽  
Numerical Research ◽  
Saddle Type ◽  
Specific Speed ◽  
Performance Results

Net positive suction head peak is a well-known cavitation instability phenomenon in high-specific-speed pumps. Both non-cavitating performance and cavitating performance of a high-specific-speed pump were investigated by experiments and numerical simulations. According to the cavitating performance results, net positive suction head peak is found at 80% of nominal flow. The head curves of non-cavitating performance also have saddle-type instabilities near 70%–80% of nominal flow. Water vapor volume fraction distributions show that cavitation region at net positive suction head peak flow only covers 3% of the blade length when head drops 6%. It proves that net positive suction head peak is not caused by huge amounts of cavitation bubbles, which indicates that net positive suction head peak does not represent excessive cavitation. The velocity vector and pressure distribution plots reveal that net positive suction head peak is related to recirculation near the trailing edge. With inlet pressure decreasing, the flow pattern is sensitive to the cavitation bubbles, and recirculation region from the pressure side to the suction side becomes larger and larger.

Influence of the Structure on the Strain-Controlled Fatigue of Nitinol

2013 ◽  
Vol 738-739 ◽  
pp. 316-320 ◽  
Author(s):  
Mikhail Kollerov ◽  
Elena Lukina ◽  
Dmitiy Gusev ◽  
Peter Mason ◽  
Paul Wagstaff
Keyword(s):  
Dislocation Density ◽  
Fatigue Resistance ◽  
High Cycle Fatigue ◽  
Volume Fraction ◽  
High Amplitude ◽  
Cycle Fatigue ◽  
Structure Parameter ◽  
High Dispersity ◽  
Low Amplitude

The influence of increased dislocation density; dispersity of Ni-rich (Ti3Ni4and Ti2Ni3) particles and volume fraction of Ti-rich (Ti2Ni) particles on the low-cycle (high amplitude) and high-cycle (low amplitude) fatigue resistance of nitinol has been considered in this paper. It was revealed that the fatigue resistance of nitinol in low-cycle conditions may be improved by increasing the part of deformation which is realized by martensitic mechanism. This part may be estimated by measuring εcr, which can reflect the influence of the structure parameter both on σMand σslip. It was found that in high-cycle fatigue conditions the substructure of nitinol predominantly determine its fatigue resistance, which is being the better in samples that had higher dislocation density or high dispersity of Ni-rich particles (up to 30 nm).

Flow Characterization in an ESP Pump Using Conductivity Measurements

2014 ◽  
Author(s):  
Sahand Pirouzpanah ◽  
Sujan Reddy Gudigopuram ◽  
Gerald L. Morrison
Keyword(s):  
Volume Fraction ◽  
Petroleum Industry ◽  
Pure Liquid ◽  
Two Phase ◽  
Fluid Mixture ◽  
Air Inlet ◽  
Flow Characterization ◽  
Electrical Submersible Pumps ◽  
Flow Medium ◽  
Gas Volume

Electrical Submersible Pumps (ESPs) are used in upstream petroleum industry for pumping liquid-gas mixtures. The presence of gas in the flow reduces the efficiency of ESPs. To investigate the effect of gas in the flow medium, Electrical Resistance Tomography (ERT) is performed on the two diffuser stages in a three-stage ESP which was manufactured by Baker Hughes Company. In an ERT system, the relative conductivity of the two-phase fluid mixture in comparison with the conductivity of pure liquid is measured which is used to obtain the Gas Volume Fraction (GVF) and mixture concentration. The measured GVF and concentration is used to characterize the flow for different flow rates of water and air, inlet pressures and rotating speeds.

scholarly journals Spatial model of convective solute transport in brain extracellular space does not support a “glymphatic” mechanism

2016 ◽  
Vol 148 (6) ◽  
pp. 489-501 ◽  
Author(s):  
Byung-Ju Jin ◽  
Alex J. Smith ◽  
Alan S. Verkman
Keyword(s):  
Solute Transport ◽  
Water Permeability ◽  
Extracellular Space ◽  
Fluid Transport ◽  
Volume Fraction ◽  
Convective Transport ◽  
Solute Diffusion ◽  
Model Parameters ◽  
Pulsatile Pressure ◽  
Brain Extracellular Space

A “glymphatic system,” which involves convective fluid transport from para-arterial to paravenous cerebrospinal fluid through brain extracellular space (ECS), has been proposed to account for solute clearance in brain, and aquaporin-4 water channels in astrocyte endfeet may have a role in this process. Here, we investigate the major predictions of the glymphatic mechanism by modeling diffusive and convective transport in brain ECS and by solving the Navier–Stokes and convection–diffusion equations, using realistic ECS geometry for short-range transport between para-arterial and paravenous spaces. Major model parameters include para-arterial and paravenous pressures, ECS volume fraction, solute diffusion coefficient, and astrocyte foot-process water permeability. The model predicts solute accumulation and clearance from the ECS after a step change in solute concentration in para-arterial fluid. The principal and robust conclusions of the model are as follows: (a) significant convective transport requires a sustained pressure difference of several mmHg between the para-arterial and paravenous fluid and is not affected by pulsatile pressure fluctuations; (b) astrocyte endfoot water permeability does not substantially alter the rate of convective transport in ECS as the resistance to flow across endfeet is far greater than in the gaps surrounding them; and (c) diffusion (without convection) in the ECS is adequate to account for experimental transport studies in brain parenchyma. Therefore, our modeling results do not support a physiologically important role for local parenchymal convective flow in solute transport through brain ECS.

On the Influence of Gas Content on the Rotordynamic Force Coefficients of a Three-Wave (Air in Oil) Annular Seal for Multiple Phase Pumps

2019 ◽  
Author(s):  
Luis San Andrés ◽  
Xueliang Lu ◽  
Tingcheng Wu
Keyword(s):  
Oil And Gas ◽  
Volume Fraction ◽  
Dynamic Stiffness ◽  
Excitation Frequency ◽  
Gas Content ◽  
Radial Clearance ◽  
Pure Liquid ◽  
Dynamic Force ◽  
Force Coefficients ◽  
Wet Gas

Abstract The subsea oil & gas industry efficiently uses multiphase pumps and wet gas compressors to eliminate upstream oil and gas separation stations, hence saving up to 30% in capital expenditures. Subsea multiphase process facilities must operate reliably for extended lengths of time while the wells, as they deplete, produce a process fluid varying from a pure liquid, to a mixture of gas and liquid, and to eventually just gas. The variation of gas volume fraction (GVF), by affecting the leakage and dynamic forced performance of sealing elements, alters turbomachinery performance to produce both an increase in synchronous speed rotor vibrations and a reduction in rotor dynamic stability. Prior laboratory work shows that plain cylindrical surface annular seals operating with a fluid flow in the laminar flow regime produce no direct (centering) stiffness and a large added mass, in particular for the liquid only condition. The early work also advanced a simple three-wave shape seal (akin to lobes) that generates a significant direct stiffness, impervious to GVF as large as 90%, and hence aids to increase the natural frequency of a vertical pump. Dynamic load tests for this wavy-seal configuration operating with a gas in liquid mixture [air in light ISO VG 10 oil] are the subject of this paper that presents dynamic force coefficients vs. excitation frequency (ω) while the shaft turns at a speed (Ω) equal to 3.5 krpm (23.3 m/s surface speed), a typical operating speed for multiphase pumps. The test seal has length L = 43 mm, diameter D = 127 mm, and a mean radial clearance cm = 0.191 mm. For operation with a pure liquid (GVF = 0), the seal force coefficients are frequency independent, thus a stiffness (K) - damping (C) − Mass (M) model fully characterizes the test article. On the other hand, for operation with an air in oil mixture, the test seal dynamic stiffness coefficients vary greatly with excitation frequency; the direct dynamic stiffness hardens while the cross coupled stiffness decreases as the frequency approaches running speed (ω &lt; Ω) and then increases for super synchronous frequency excitations (ω &gt; Ω). For operation with GVF from 0.1 to 0.8, the wavy seal produces a positive centering dynamic stiffness with large magnitude; a most desirable feature for a vertically installed pump. Notably, the seal direct damping coefficient (C) does not depend on the excitation frequency though reduces continuously as the inlet GVF increases from 0 to 1. For operation with either a pure liquid or a pure air conditions, a computational fluid dynamics (CFD) analysis accurately captures the seal leakage and force coefficients. The current research product adds relevant test data to better the design selection of seals in multiphase pumps.

Spatiotemporally-Resolved Dynamics of Dispersing Ferrofluid Aggregates

2008 ◽  
Author(s):  
Alicia M. Williams ◽  
Pavlos P. Vlachos
Keyword(s):  
Internal Flow ◽  
Bulk Flow ◽  
Experimental Techniques ◽  
Recirculation Region ◽  
Complex Flow ◽  
Time Resolved ◽  
Square Channel ◽  
Spatiotemporal Behavior ◽  
Pulsatile Flows ◽  
The Impact

Ferrohydrodynamics research has been approached predominantly from either numerical or basic experimental techniques. However, to date, these experimental techniques have been limited to ultrasonic point measurements or shadowgraphs due to the opacity of the ferrofluids. As a result, the complete dynamics of many ferrohydrodynamics flows have remained unexplored. In this work, Time Resolved Digital Particle Image Velocimetry (TRDPIV) is employed to fully resolve the dynamic interaction of ferrofluid aggregates with bulk nonmagnetic fluids. This topic is hydrodynamically rich, where shearing between the aggregate and bulk flow develop into the Kelvin-Helmholtz instability. Ferrofluid aggregates are mixed with fluorescent particles in order to enable visualization of the internal flow structure of the aggregate and generate quantitative velocity measurements. The TRDPIV measurements are made in a 15 mm square channel where ferrofluid retained by a 0.5 Tesla permanent magnet is studied as it disperses. The effects of both steady and pulsatile flows are quantified, as are the impact of varying the magnetic field gradients. In both steady and pulsatile flows, a recirculation region is observed within the ferrofluid, driven by the shear layer between the bulk flow and aggregate interface. The interaction of the aggregate with the flow is also governed by the aggregate height relative to that of the test section. Higher, larger aggregates are less stable, and therefore, more likely to be dispersed by the bulk flow. As the aggregate diminishes in size, it is both more stable and is less subject to shearing forces from the flow. Flow pulsatility enriches the dynamics of the flow and generates complex flow structures resulting from interaction between the aggregate and bulk flow. This work is the first to explore the rich spatiotemporal behavior of dispersing ferrofluid aggregates interacting with steady and unsteady bulk flows.

Numerical Simulation of Unsteady Laminar Flow Over Vibrating Bodies (Planar Flow)

1991 ◽  
Vol 35 (03) ◽  
pp. 230-249
Author(s):  
N. Kolluru Venkat ◽  
Malcolm Spaulding
Keyword(s):  
Steady State ◽  
Laminar Flow ◽  
Strouhal Number ◽  
Pressure Wave ◽  
Fourier Transforms ◽  
Amplitude Ratio ◽  
The Body ◽  
Series Data ◽  
Friction Coefficients ◽  
Highly Nonlinear

A model is developed to simulate two-dimensional laminar flow over an arbitrarily shaped body, a part of which is subjected to simple harmonic motion. The vibration amplitude ratio, Ho, and the Reynolds number, Re, are maintained at 0.1 and 1000, respectively. The Strouhal number, St, is varied in the range 0.0 ≤ St ≤ 1.0. The computer code is tested for the flow in a square cavity and also over a flat plate. The friction and pressure coefficients over the vibrating portion of the body are determined. Fast Fourier Transforms are performed on the time series data of these coefficients. For low-frequency vibrations (low Strouhal number) the pressure and friction coefficients match the steady-state results for flow over a sinusoidal bump. A small-amplitude pressure wave generated by the oscillating plate propagates downstream with the flow. For high-frequency vibrations (high Strouhal number) the pressure and friction coefficients over the vibrating portion of the body deviate from the steady-state results and a high-amplitude pressure wave propagates downstream. The pressure at one chord length upstream is also affected. As St increases, the flow becomes highly nonlinear and higher harmonics appear in the downstream flow. Subsequent analysis indicates that the nonlinearity is controlled by the term v(Əu/Əy).

The effects of non-Newtonian blood modeling and pulsatility on hemodynamics in the food and drug administration’s benchmark nozzle model

Biorheology ◽  
2021 ◽  
pp. 1-18
Author(s):  
Bryan C. Good
Keyword(s):  
Reynolds Numbers ◽  
Steady Flows ◽  
Modeling Framework ◽  
Cfd Simulations ◽  
Cardiovascular Devices ◽  
Recirculation Flow ◽  
Newtonian Model ◽  
Pulsatile Flows ◽  
Validation Procedure ◽  
Computational Fluid Dynamics Cfd

BACKGROUND: Computational fluid dynamics (CFD) is an important tool for predicting cardiovascular device performance. The FDA developed a benchmark nozzle model in which experimental and CFD data were compared, however, the studies were limited by steady flows and Newtonian models. OBJECTIVE: Newtonian and non-Newtonian blood models will be compared under steady and pulsatile flows to evaluate their influence on hemodynamics in the FDA nozzle. METHODS: CFD simulations were validated against the FDA data for steady flow with a Newtonian model. Further simulations were performed using Newtonian and non-Newtonian models under both steady and pulsatile flows. RESULTS: CFD results were within the experimental standard deviations at nearly all locations and Reynolds numbers. The model differences were most evident at Re = 500, in the recirculation regions, and during diastole. The non-Newtonian model predicted blunter upstream velocity profiles, higher velocities in the throat, and differences in the recirculation flow patterns. The non-Newtonian model also predicted a greater pressure drop at Re = 500 with minimal differences observed at higher Reynolds numbers. CONCLUSIONS: An improved modeling framework and validation procedure were used to further investigate hemodynamics in geometries relevant to cardiovascular devices and found that accounting for blood’s non-Newtonian and pulsatile behavior can lead to large differences in predictions in hemodynamic parameters.

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