Thermal Aspects of a Novel Viscous Pump

1998 ◽  
Vol 120 (1) ◽  
pp. 99-107 ◽  
Author(s):  
M. C. Sharatchandra ◽  
M. Sen ◽  
M. Gad-el-Hak
Keyword(s):  
Viscous Dissipation ◽  
Temperature Rise ◽  
Channel Wall ◽  
Stokes Equations ◽  
Coupled System ◽  
Operating Conditions ◽  
Navier Stokes ◽  
Bulk Temperature ◽  
Temperature Dependent Viscosity ◽  
Pump Operation

We have previously introduced a novel method for pumping fluids via a viscous mechanism. The device essentially consists of a cylindrical rotor eccentrically placed in a channel, and it is suited for hauling highly viscous polymers in macroducts, or more common fluids in microducts. Under certain operating conditions, viscous dissipation can be important, and a significant attendant temperature rise can have adverse effects on the pump operation. For this reason, we have conducted a numerical experiment to characterize the associated phenomena. The coupled system of the two-dimensional Navier-Stokes equations, with temperature-dependent viscosity, and the energy equation, with viscous dissipation terms retained, are solved using a finite-volume method. Different types of thermal boundary conditions at the rotor-fluid interface are explored in the numerical scheme. An approximate theoretical model is also developed to analyze flow in the region between the rotor and the nearest plate (for small gaps). The results indicate that although the bulk temperature rise is minimal for typical microscale situations, significantly steep temperature gradients are observed in the region between the rotor and the nearest channel wall where the most intense shear stress occurs. For certain combinations of Re, Ec, and Pr, temperature rises along the channel wall of the order of 30 K were calculated. Moreover, for very small values of this gap, large errors in the computed flowrates and pumping power estimates can arise for large Brinkman numbers, if the effects of viscous dissipation are ignored. Furthermore, the existence of an optimum value of rotor position, such that the bulk velocity is a maximum, is demonstrated. These findings are significant, as they are indicative of trends associated with the flow of highly viscous polymeric liquids, where much larger temperature rises and their attendant degradation in performance are likely to occur.

scholarly journals Development of Hybrid Airlift-Jet Pump with Its Performance Analysis

2018 ◽  
Vol 8 (9) ◽  
pp. 1413 ◽  
Author(s):  
Dan Yao ◽  
Kwongi Lee ◽  
Minho Ha ◽  
Cheolung Cheong ◽  
Inhiug Lee
Keyword(s):  
Boundary Conditions ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Stokes Equations ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Navier Stokes ◽  
Jet Pump ◽  
Two Phase

A new pump, called the hybrid airlift-jet pump, is developed by reinforcing the advantages and minimizing the demerits of airlift and jet pumps. First, a basic design of the hybrid airlift-jet pump is schematically presented. Subsequently, its performance characteristics are numerically investigated by varying the operating conditions of the airlift and jet parts in the hybrid pump. The compressible unsteady Reynolds-averaged Navier-Stokes equations, combined with the homogeneous mixture model for multiphase flow, are used as the governing equations for the two-phase flow in the hybrid pump. The pressure-based methods combined with the Pressure-Implicit with Splitting of Operators (PISO) algorithm are used as the computational fluid dynamics techniques. The validity of the present numerical methods is confirmed by comparing the predicted mass flow rate with the measured ones. In total, 18 simulation cases that are designed to represent the various operating conditions of the hybrid pump are investigated: eight of these cases belong to the operating conditions of only the jet part with different air and water inlet boundary conditions, and the remaining ten cases belong to the operating conditions of both the airlift and jet parts with different air and water inlet boundary conditions. The mass flow rate and the efficiency are compared for each case. For further investigation into the detailed flow characteristics, the pressure and velocity distributions of the mixture in a primary pipe are compared. Furthermore, a periodic fluctuation of the water flow in the mass flow rate is found and analyzed. Our results show that the performance of the jet or airlift pump can be enhanced by combining the operating principles of two pumps into the hybrid airlift-jet pump, newly proposed in the present study.

scholarly journals Local Existence of Strong Solutions of a Fluid–Structure Interaction Model

2020 ◽  
Vol 22 (4) ◽  
Author(s):  
Sourav Mitra
Keyword(s):  
Stokes Equations ◽  
Local Existence ◽  
Interaction Model ◽  
Strong Solutions ◽  
Coupled System ◽  
Elastic Structure ◽  
Navier Stokes ◽  
Beam Equation ◽  
Navier Stokes Equations ◽  
System Coupling

AbstractWe are interested in studying a system coupling the compressible Navier–Stokes equations with an elastic structure located at the boundary of the fluid domain. Initially the fluid domain is rectangular and the beam is located on the upper side of the rectangle. The elastic structure is modeled by an Euler–Bernoulli damped beam equation. We prove the local in time existence of strong solutions for that coupled system.

scholarly journals Dynamic analysis of submerged microscale plates: the effects of acoustic radiation and viscous dissipation

2016 ◽  
Vol 472 (2187) ◽  
pp. 20150728 ◽  
Author(s):  
Zhangming Wu ◽  
Xianghong Ma
Keyword(s):  
Viscous Fluid ◽  
Boundary Conditions ◽  
Viscous Dissipation ◽  
Stokes Equations ◽  
Acoustic Radiation ◽  
Navier Stokes ◽  
Rectangular Plates ◽  
Fluid Loading ◽  
Navier Stokes Equations ◽  
Loading Impedance

The aim of this paper is to study the dynamic characteristics of micromechanical rectangular plates used as sensing elements in a viscous compressible fluid. A novel modelling procedure for the plate–fluid interaction problem is developed on the basis of linearized Navier–Stokes equations and no-slip conditions. Analytical expression for the fluid-loading impedance is obtained using a double Fourier transform approach. This modelling work provides us an analytical means to study the effects of inertial loading, acoustic radiation and viscous dissipation of the fluid acting on the vibration of microplates. The numerical simulation is conducted on microplates with different boundary conditions and fluids with different viscosities. The simulation results reveal that the acoustic radiation dominates the damping mechanism of the submerged microplates. It is also proved that microplates offer better sensitivities (Q-factors) than the conventional beam type microcantilevers being mass sensing platforms in a viscous fluid environment. The frequency response features of microplates under highly viscous fluid loading are studied using the present model. The dynamics of the microplates with all edges clamped are less influenced by the highly viscous dissipation of the fluid than the microplates with other types of boundary conditions.

Assessing the Dynamic Stability of an Offshore Supply Vessel

2011 ◽  
Author(s):  
Vladimir Shigunov ◽  
Ould el Moctar ◽  
Thomas E. Schellin ◽  
Jan Kaufmann ◽  
Rasmus Stute
Keyword(s):  
Dynamic Stability ◽  
Stokes Equations ◽  
Operating Conditions ◽  
Navier Stokes ◽  
Ship Motions ◽  
Navier Stokes Equations ◽  
Counter Measures ◽  
Seakeeping Analysis ◽  
Design Speed ◽  
Run Up

The dynamic stability was investigated of a typical offshore service vessel operating under stability critical operating conditions. Excessive roll motions and relative motions at the stern were studied for two loading conditions for ship speeds ranging from zero to the design speed. A linear frequency-domain seakeeping analysis was followed by nonlinear time-domain simulations of ship motions in waves. Based on results from these methods, critical scenarios were selected and simulated using finite-volume solvers of the Reynolds-averaged Navier-Stokes equations to understand the phenomena related to dynamically unstable ship motions as well as to confirm the results of the simpler analysis methods. Results revealed the possibility of excessive roll motions and water run-up on deck; counter measures such as a ship-specific operational guidance are discussed.

scholarly journals Tidal oscillations of rotating hot Jupiters

2020 ◽  
Vol 494 (3) ◽  
pp. 3141-3155 ◽  
Author(s):  
Umin Lee
Keyword(s):  
Viscous Dissipation ◽  
Stokes Equations ◽  
Rotation Frequency ◽  
Inertial Range ◽  
Navier Stokes ◽  
Ekman Number ◽  
Hot Jupiters ◽  
The Core ◽  
Convective Core ◽  
Tidal Torques

ABSTRACT We calculate small amplitude gravitational and thermal tides of uniformly rotating hot Jupiters composed of a nearly isentropic convective core and a geometrically thin radiative envelope. We treat the fluid in the convective core as a viscous fluid and solve linearized Navier–Stokes equations to obtain tidal responses of the core, assuming that the Ekman number, Ek, is a constant parameter. In the radiative envelope, we take account of the effects of radiative dissipations on the responses. The properties of tidal responses depend on thermal time-scales τ* in the envelope and Ekman number, Ek, in the core and on whether the forcing frequency ω is in the inertial range or not, where the inertial range is defined by |ω| ≤ 2Ω for the rotation frequency Ω. If Ek ≳ 10−7, the viscous dissipation in the core is dominating the thermal contributions in the envelope for τ* ≳ 1 d. If Ek ≲ 10−7, however, the viscous dissipation is comparable to or smaller than the thermal contributions and the envelope plays an important role to determine the tidal torques. If the forcing is in the inertial range, frequency resonance of the tidal forcing with core inertial modes significantly affects the tidal torques, producing numerous resonance peaks of the torque. Depending on the sign of the torque in the peaks, we suggest that there exist cases in which the resonance with core inertial modes hampers the process of synchronization between the spin and orbital motion of the planets.

Numerical Characterisation of Jet-Vane based Thrust Vector Control Systems

2015 ◽  
Vol 65 (4) ◽  
pp. 261 ◽  
Author(s):  
M.S.R. Chandra Murthy ◽  
Debasis Chakraborty
Keyword(s):  
Vector Control ◽  
Control Systems ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Static Tests ◽  
Thrust Vector Control ◽  
Thrust Vector

<p>Computational fluid dynamics methodology was used in characterising jet vane based thrust vector control systems of tactical missiles. Three-dimensional Reynolds Averaged Navier-Stokes equations were solved along with two-equation turbulence model for different operating conditions. Nonlinear regression analysis was applied to the detailed CFD database to evolve a mathematical model for the thrust vector control system. The developed model was validated with series of ground based 6-Component static tests. The proven methodology is applied toa new configuration.</p><p><strong>Defence Science Journal, Vol. 65, No. 4, July 2015, pp. 261-264, DOI: http://dx.doi.org/10.14429/dsj.65.7960</strong></p>

3-D Numerical Simulation for Fuel Cell Performance

2002 ◽  
Author(s):  
Tien-Chien Jen ◽  
S. H. Chan ◽  
T. Z. Yan
Keyword(s):  
Fluid Flow ◽  
Fuel Cell ◽  
Stokes Equations ◽  
Current Density Distribution ◽  
Mass Transfer Process ◽  
Operating Conditions ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Fuel Cell Performance ◽  
Gas Channel

A 3-D mathematical model for the PEM fuel cell including gas channel has been developed to simulate fluid flow, current density distribution, and multi-component transport. In order to understand the developing fluid flow and mass transfer process inside the fuel cell channels, the conventional Navier-Stokes equations for gas channel, and volume-averaged Navier-Stokes equations for porous gas diffusers and catalyst layer are adopted individually in this study. A set of conservation equations and species concentration equations are solved numerically in a coupled gas channel and porous media domain using the vorticity-velocity method with power law scheme. Detailed development axial velocity and secondary flow fields at various axial positions in the entrance region are presented. Polarization curves under various operating conditions are demonstrated by solving the equations for electrochemical reactions and the membrane phase potential. Compared with experimental data from published literatures, numerical results of this model agree closely with experimental results. Finally, mass transport equations are solved at a preset condition of electrochemical reaction, and oxygen and hydrogen mole fraction distribution fields are displayed.

scholarly journals An asymptotic expansion for the vortex-induced vibrations of a circular cylinder

2011 ◽  
Vol 671 ◽  
pp. 137-167 ◽  
Author(s):  
PHILIPPE MELIGA ◽  
JEAN-MARC CHOMAZ
Keyword(s):  
Circular Cylinder ◽  
Stokes Equations ◽  
Structural Parameters ◽  
Coupled System ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Fluid Equation ◽  
Wake Oscillator ◽  
Vortex Induced Vibrations ◽  
Lower Magnitude

This paper investigates the vortex-induced vibrations (VIV) of a spring-mounted circular cylinder. We compute analytically the leading-order equations describing the nonlinear interaction of the fluid and structure modes by carrying out an asymptotic analysis of the Navier–Stokes equations close to the threshold of instability of the fluid-only system. We show that vortex-shedding can occur at subcritical Reynolds numbers as a result of the coupled system being linearly unstable to the structure mode. We also show that resonance occurs when the frequency of the nonlinear limit cycle matches the natural frequency of the cylinder, the displacement being then in phase with the flow-induced lift fluctuations. Using an extension of this model meant to encompass the effect of the low-order added-mass and damping forces induced by the displaced fluid, we show that the amount of energy that can be extracted from the flow can be optimized by an appropriate choice of the structural parameters. Finally, we suggest a possible connection between the present ‘exact’ model and the empirical wake oscillator model used to study VIV at high Reynolds numbers. We show that for the low Reynolds numbers considered here, the effect of the structure on the fluid can be represented by a first coupling term proportional to the cylinder acceleration in the fluid equation, and by a second term of lower magnitude, which can stem either from an integral term or from a term proportional to the third derivative of the cylinder position.

A Multiscale Method Modeling Surface Texture Effects

2006 ◽  
Vol 129 (2) ◽  
pp. 221-230 ◽  
Author(s):  
Alex de Kraker ◽  
Ron A. J. van Ostayen ◽  
A. van Beek ◽  
Daniel J. Rixen
Keyword(s):  
Surface Texture ◽  
Reynolds Equation ◽  
Journal Bearing ◽  
Stokes Equations ◽  
Multiscale Method ◽  
Operating Conditions ◽  
Contact Load ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Inertia Effects

In this paper a multiscale method is presented that includes surface texture in a mixed lubrication journal bearing model. Recent publications have shown that the pressure generating effect of surface texture in bearings that operate in full film conditions may be the result of micro-cavitation and/or convective inertia. To include inertia effects, the Navier–Stokes equations have to be used instead of the Reynolds equation. It has been shown in earlier work (de Kraker et al., 2006, Tribol. Trans., in press) that the coupled two-dimensional (2D) Reynolds and 3D structure deformation problem with partial contact resulting from the soft EHL journal bearing model is not easy to solve due to the strong nonlinear coupling, especially for soft surfaces. Therefore, replacing the 2D Reynolds equation by the 3D Navier–Stokes equations in this coupled problem will need an enormous amount of computing power that is not readily available nowadays. In this paper, the development of a micro–macro multiscale method is described. The local (micro) flow effects for a single surface pocket are analyzed using the Navier–Stokes equations and compared to the Reynolds solution for a similar smooth piece of surface. It is shown how flow factors can be derived and added to the macroscopic smooth flow problem, that is modeled by the 2D Reynolds equation. The flow factors are a function of the operating conditions such as the ratio between the film height and the pocket dimensions, the surface velocity, and the pressure gradient over a surface texture unit cell. To account for an additional pressure buildup in the texture cell due to inertia effects, a pressure gain is introduced at macroscopic level. The method also allows for microcavitation. Microcavitation occurs when the pressure variation due to surface texture is larger than the average pressure level at that particular bearing location. In contrast with the work of Patir and Cheng (1978, J. Lubrication Technol., 78, pp. 1–10), where the microlevel is solved by the Reynolds equation, and the Navier–Stokes equations are used at the microlevel. Depending on the texture geometry and film height, the Reynolds equation may become invalid. A second pocket effect occurs when the pocket is located in the moving surface. In mixed lubrication, fluid can become trapped inside a pocket and squeezed out when the pocket is running into an area with higher contact load. To include this effect, an additional source term that represents the average fluid inflow due to the deformation of the surface around the pocket is added to the Reynolds equation at macrolevel. The additional inflow is computed at microlevel by numerical solution of the surface deformation for a single pocket that is subject to a contact load. The pocket volume is a function of the contact pressure. It must be emphasized that before ready-to-use results can be presented, a large number of simulations to determine the flow factors and pressure gain as a function of the texture parameters and operating conditions have yet to be done. Before conclusions can be drawn, regarding the dominanant mechanism(s), the flow factors and pressure gain have to be added to the macrobearing model. In this paper, only a limited number of preliminary illustrative simulation results, calculating the flow factors for a single 2D texture geometry, are shown to give insight into the method.

scholarly journals СНИЖЕНИЕ ВИБРОНАПРЯЖЕННОСТИ ПОПАРНО БАНДАЖИРОВАННЫХ РАБОЧИХ ЛОПАТОК ТУРБИНЫ

2020 ◽  
pp. 52-58
Author(s):  
Юрий Петрович Кухтин ◽  
Руслан Юрьевич Шакало
Keyword(s):  
Film Cooling ◽  
Gas Flow ◽  
Stokes Equations ◽  
Operating Conditions ◽  
Rotor Blades ◽  
Navier Stokes ◽  
Turbine Stage ◽  
Turbine Engine ◽  
Exciting Forces ◽  
Working Blades

To reduce the vibration stresses arising in the working blades of turbines during resonant excitations caused by the frequency of passage of the blades of the nozzle apparatus, it is necessary to control the level of aerodynamic exciting forces. One of the ways to reduce dynamic stresses in rotor blades under operating conditions close to resonant, in addition to structural damping, maybe to reduce external exciting forces. To weaken the intensity of the exciting forces, it is possible to use a nozzle apparatus with multi-step gratings, as well as with non-radially mounted blades of the nozzle apparatus.This article presents the results of numerical calculations of exciting aerodynamic forces, as well as the results of experimental measurements of stresses arising in pairwise bandaged working blades with a frequency zCA ⋅ fn, where fn – is the rotor speed, zCA – is the number of nozzle blades. The object of research was the high-pressure turbine stage of a gas turbine engine. Two variants of a turbine stage were investigated: with the initial geometry of the nozzle apparatus having the same geometric neck area in each interscapular channel and with the geometry of the nozzle apparatus obtained by alternating two types of sectors with a reduced and initial throat area.The presented results are obtained on the basis of numerical simulation of a viscous unsteady gas flow in a transonic turbine stage using the SUnFlow home code, which implements a numerical solution of the Reynolds-averaged Navier-Stokes equations. Discontinuity of a torrent running on rotor blades is aggravated with heat drops between an ardent flow core and cold jets from film cooling of a blade and escapes on clock surfaces. Therefore, at simulation have been allowed all blowngs cooling air and drain on junctions of shelves the impeller.As a result of the replacement of the nozzle apparatus with a constant passage area by a nozzle apparatus with a variable area, a decrease in aerodynamic driving force by 12.5 % was obtained. The experimentally measured stresses arising in a pairwise bandaged blade under the action of this force decreased on average by 26 %.

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