Simulation of the Piston Driven Flow Inside a Cylinder With an Eccentric Port

1998 ◽  
Vol 120 (2) ◽  
pp. 319-326 ◽  
Author(s):  
Adrin Gharakhani ◽  
Ahmed F. Ghoniem
Keyword(s):  
Unsteady Flow ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Vortex Method ◽  
Numerical Approach ◽  
Navier Stokes ◽  
Solid Boundary ◽  
Surface Boundary ◽  
Time Varying ◽  
Stroke Length

A grid-free Lagrangian approach is applied to simulate the high Reynolds number unsteady flow inside a three-dimensional domain with moving boundaries. For this purpose, the Navier-Stokes equations are expressed in terms of the vorticity transport formulation. The convection and stretch of vorticity are obtained using the Lagrangian vortex method, while diffusion is approximated by the random walk method. The boundary-element method is used to solve a potential flow problem formulated to impose the normal flux condition on the boundary of the domain. The no-slip condition is satisfied by a vortex tile generation mechanism at the solid boundary, which takes into account the time-varying boundary surfaces due to, e.g., a moving piston. The approach is entirely grid-free within the fluid domain, requiring only meshing of the surface boundary, and virtually free of numerical diffusion. The method is applied to study the evolution of the complex vortical structure forming inside the time-varying semi-confined geometry of a cylinder equipped with an eccentric inlet port and a harmonically driven piston. Results show that vortical structures resembling those observed experimentally in similar configurations dominate this unsteady flow. The roll-up of the incoming jet is responsible for the formation of eddies whose axes are nearly parallel to the cylinder axis. These eddies retain their coherence for most of the stroke length. Instabilities resembling conventional vortex ring azimuthal modes are found to be responsible for the breakup of these toroidal eddies near the end of the piston motion. The nondiffusive nature of the numerical approach allows the prediction of these essentially inviscid phenomena without resorting to a turbulence model or the need for extremely fine, adaptive volumetric meshes.

A 3D Unsteady Flow Analysis in a Doubly Constricted Tube

2000 ◽  
Author(s):  
B. V. Rathish Kumar ◽  
T. Yamaguchi ◽  
H. Liu ◽  
R. Himeno
Keyword(s):  
Pressure Drop ◽  
Unsteady Flow ◽  
Stokes Equations ◽  
Vortex Formation ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
In Series ◽  
3D Unsteady Flow

Abstract Unsteady flow dynamics in a doubly constricted vessel is analyzed by using a time accurate Finite Volume solution of three dimensional incompressible Navier-Stokes equations. Computational experiments are carried out for various values of Reynolds number in order to assess the criticality of multiple mild constrictions in series and also to bring out the subtle 3D features like vortex formation. Studies reveal that pressure drop across a series of mild constrictions can get physiologically critical. Further this pressure drop is found to be sensitive to the spacing between the constrictions and also to the oscillatory nature of the inflow profile.

Studies on natural convection-induced flow and thermal behaviour inside electronic equipment cabinet model

2003 ◽  
Vol 217 (3) ◽  
pp. 323-328 ◽  
Author(s):  
M Ishizuka ◽  
Y Kitamura
Keyword(s):  
Natural Convection ◽  
Thermal Behaviour ◽  
Stokes Equations ◽  
Three Dimensional ◽  
The Body ◽  
Electronic Equipment ◽  
Navier Stokes ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Induced Flow

In the present work, an important basic flow phenomenon, natural convection-induced flow, is studied numerically. Three-dimensional Navier-Stokes equations along with the energy equation are solved based on the finite difference method. A generalized coordinate system is used so that sufficient grid resolution could be achieved in the body surface boundary layer region. The results of calculation showed a satisfactory agreement with the measured data and led to a good understanding of the overall flow and thermal behaviour inside an electronic equipment cabinet model, which is very difficult, if not impossible, to gather by experiment.

scholarly journals Linear pulse structure and signalling in a film flow on an inclined plane

1999 ◽  
Vol 396 ◽  
pp. 37-71 ◽  
Author(s):  
LEONID BREVDO ◽  
PATRICE LAURE ◽  
FREDERIC DIAS ◽  
THOMAS J. BRIDGES
Keyword(s):  
Free Surface ◽  
Saddle Point ◽  
Convective Instability ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Numerical Results ◽  
Navier Stokes ◽  
Surface Boundary ◽  
Navier Stokes Equations ◽  
Surface Boundary Conditions

The film flow down an inclined plane has several features that make it an interesting prototype for studying transition in a shear flow: the basic parallel state is an exact explicit solution of the Navier–Stokes equations; the experimentally observed transition of this flow shows many properties in common with boundary-layer transition; and it has a free surface, leading to more than one class of modes. In this paper, unstable wavepackets – associated with the full Navier–Stokes equations with viscous free-surface boundary conditions – are analysed by using the formalism of absolute and convective instabilities based on the exact Briggs collision criterion for multiple k-roots of D(k, ω) = 0; where k is a wavenumber, ω is a frequency and D(k, ω) is the dispersion relation function.The main results of this paper are threefold. First, we work with the full Navier–Stokes equations with viscous free-surface boundary conditions, rather than a model partial differential equation, and, guided by experiments, explore a large region of the parameter space to see if absolute instability – as predicted by some model equations – is possible. Secondly, our numerical results find only convective instability, in complete agreement with experiments. Thirdly, we find a curious saddle-point bifurcation which affects dramatically the interpretation of the convective instability. This is the first finding of this type of bifurcation in a fluids problem and it may have implications for the analysis of wavepackets in other flows, in particular for three-dimensional instabilities. The numerical results of the wavepacket analysis compare well with the available experimental data, confirming the importance of convective instability for this problem.The numerical results on the position of a dominant saddle point obtained by using the exact collision criterion are also compared to the results based on a steepest-descent method coupled with a continuation procedure for tracking convective instability that until now was considered as reliable. While for two-dimensional instabilities a numerical implementation of the collision criterion is readily available, the only existing numerical procedure for studying three-dimensional wavepackets is based on the tracking technique. For the present flow, the comparison shows a failure of the tracking treatment to recover a subinterval of the interval of unstable ray velocities V whose length constitutes 29% of the length of the entire unstable interval of V. The failure occurs due to a bifurcation of the saddle point, where V is a bifurcation parameter. We argue that this bifurcation of unstable ray velocities should be observable in experiments because of the abrupt increase by a factor of about 5.3 of the wavelength across the wavepacket associated with the appearance of the bifurcating branch. Further implications for experiments including the effect on spatial amplification rate are also discussed.

scholarly journals Exploratory Simulation of Solar Granules: How Sharp is the Convection/Radiation Transition?

1998 ◽  
Vol 185 ◽  
pp. 217-218
Author(s):  
Kwing L. Chan ◽  
Y.C. Kim
Keyword(s):  
Stokes Equations ◽  
Fluid Layer ◽  
Three Dimensional ◽  
Thermal Relaxation ◽  
3D Models ◽  
Numerical Approach ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Space Resolution ◽  
Radiation Transition

Currently, the most successful direct simulation of the solar granules (and the convection/radiation transition layer) is the three-dimensional (3D) model computed by Stein and Nordlund (1989). So far, there is no other similar 3D models available for comparison [however, see Ludwig et al. (1997) for a recent 2D calculation]. We are developing an alternative numerical approach to simulate the 3D radiation hydrodynamics of this layer. In this approach, the Eddington approximation is used to handle the radiation rather than solving the radiative transfer equations along rays, and the ADISM method (Chan and Wolff 1982) which solves the Navier Stokes equations in conservative forms is used to speed up the thermal relaxation of the fluid layer. We are in the process of testing the numerical accuracy of the codes. This paper summarizes the results of a test that illustrate the effects of vertical space resolution on the mean profiles of some important quantities.

scholarly journals A Nonlinear Computational Model of Floating Wind Turbines

2013 ◽  
Vol 135 (12) ◽  
Author(s):  
Ali Nematbakhsh ◽  
David J. Olinger ◽  
Gretar Tryggvason
Keyword(s):  
Wind Turbines ◽  
Dynamic Models ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Numerical Approach ◽  
Navier Stokes ◽  
Immersed Boundary ◽  
Navier Stokes Equations ◽  
Structured Grid ◽  
Gyroscopic Effects

The dynamic motion of floating wind turbines is studied using numerical simulations. The full three-dimensional Navier–Stokes equations are solved on a regular structured grid using a level set method for the free surface and an immersed boundary method for the turbine platform. The tethers, the tower, the nacelle, and the rotor weight are included using reduced-order dynamic models, resulting in an efficient numerical approach that can handle nearly all the nonlinear hydrodynamic forces on the platform, while imposing no limitation on the platform motion. Wind speed is assumed constant, and rotor gyroscopic effects are accounted for. Other aerodynamic loadings and aeroelastic effects are not considered. Several tests, including comparison with other numerical, experimental, and grid study tests, have been done to validate and verify the numerical approach. The response of a tension leg platform (TLP) to different amplitude waves is examined, and for large waves, a nonlinear trend is seen. The nonlinearity limits the motion and shows that the linear assumption will lead to overprediction of the TLP response. Studying the flow field behind the TLP for moderate amplitude waves shows vortices during the transient response of the platform but not at the steady state, probably due to the small Keulegan–Carpenter number. The effects of changing the platform shape are considered, and finally, the nonlinear response of the platform to a large amplitude wave leading to slacking of the tethers is simulated.

Investigation of Periodically Unsteady Flow in a Radial Pump by CFD Simulations and LDV Measurements

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
Jianjun Feng ◽  
Friedrich-Karl Benra ◽  
Hans Josef Dohmen
Keyword(s):  
Unsteady Flow ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Measurement Data ◽  
Load Condition ◽  
Navier Stokes ◽  
Complex Flow ◽  
Data Set ◽  
Vaned Diffuser ◽  
Radial Pump

The periodically unsteady flow fields in a low specific speed radial diffuser pump have been investigated both numerically and experimentally for the design condition (Qdes) and also one part-load condition (0.5Qdes). Three-dimensional, unsteady Reynolds-averaged Navier–Stokes equations are solved on high-quality structured grids with the shear stress transport turbulence model by using the CFD (computational fluid dynamics) code CFX-10. Furthermore, two-dimensional laser Doppler velocimetry (LDV) measurements are successfully conducted in the interaction region between the impeller and the vaned diffuser, in order to capture the complex flow with abundant measurement data and to validate the CFD results. The analysis of the obtained results has been focused on the behavior of the periodic velocity field and the turbulence field, as well as the associated unsteady phenomena due to the unsteady interaction. In addition, the comparison between CFD and LDV results has also been addressed. The blade orientation effects caused by the impeller rotation are quantitatively examined and detailedly compared with the turbulence effect. This work offers a good data set to develop the comprehension of the impeller-diffuser interaction and how the flow varies with relative impeller position to the diffuser in radial diffuser pumps.

Numerical Study of the Pulsating Flow at the Tongue Region of a Centrifugal Pump for Several Flow Rates

2008 ◽  
Author(s):  
Rau´l Barrio ◽  
Jorge Parrondo ◽  
Eduardo Blanco ◽  
Joaqui´n Ferna´ndez
Keyword(s):  
Unsteady Flow ◽  
Centrifugal Pump ◽  
Stokes Equations ◽  
Numerical Study ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Numerical Predictions ◽  
Partial Load ◽  
Flow Through

A numerical study is presented on the unsteady flow at the tongue region of a single suction volute-type centrifugal pump with a specific speed of 0.46. The flow through the pump, available at laboratory, was simulated by means of a commercial CFD software that solved the Reynolds averaged Navier-Stokes equations for three-dimensional unsteady flow (3D-URANS). A sensitivity analysis of the numerical model was carried out and the numerical predictions were compared with previous experimental results of both global and unsteady variables. Once validated, the model was used to study the flow pulsations associated to the interaction between the impeller blades and the volute tongue as a function of the flow rate, from partial load to overload. The study allowed relating the passage of the impeller blades with the tangential and radial velocity pulsations at some reference positions and with the pressure pulsations at the tongue region.

Validation of a Navier-Stokes Solver for CFD Computations of Transonic Compressors

2006 ◽  
Author(s):  
Roberto Biollo ◽  
Ernesto Benini
Keyword(s):  
Numerical Model ◽  
Flow Field ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Numerical Approach ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Navier Stokes ◽  
Test Case ◽  
Complex Flow

The progress of numerical methods and computing facilities has led to using Computational Fluid Dynamics (CFD) as a current tool for designing components of gas turbine engines. It is known, however, that a sophisticated numerical model is required to well reproduce the many complex flow phenomena which characterize compression systems, such as shock waves and their interactions with boundary layers and tip clearance flows. In this work, the flow field inside the NASA Rotor 37, a well known test case representative of complex three-dimensional viscous flow structures in transonic bladings, was simulated using a commercial CFD code based on the 3-D Reynolds-averaged Navier-Stokes equations. In order to improve the accuracy of predictions, different aspects of the numerical model were analyzed; in particular, an attempt was made to understand the influence of grid topology, number of nodes and their distribution, turbulence model, and discretization scheme of numerical solution on the accuracy of computed results. Existing experimental data were used to assess the quality of the solutions. The obtainment of a good agreement between computed and measured performance maps and downstream profiles was clearly shown. Also, detailed comparisons with experimental results indicated that the overall features of the three-dimensional shock structure, the shock-boundary layer interaction, and the wake development can be calculated very well in the numerical approach for all the operating conditions. The possibility for a numerical model to better understand the aerodynamic behaviour of existing transonic compressors and to help the design of new configurations was demonstrated. It was also pointed out that the development of an accurate model requires the knowledge of both the physical phenomena place within the flow field and the features of the code which model them.

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