scholarly journals INVESTIGATION OF HEAT DISTRIBUTION PROCESSES ON THE INNER SURFACE OF THE ENCLOSING STRUCTURE, TAKING INTO ACCOUNT THE MOVEMENT OF AIR IN THE BOUNDARY AREA BETWEEN THE DEVICE AND FENCING

2019 ◽  
Vol 16 (32) ◽  
pp. 345-361
Author(s):  
B. A. UNASPEKOV ◽  
Z. O. ZHUMADILOVA ◽  
S. S. AUELBEKOV ◽  
A. S. TAUBALDIEVA ◽  
G. B. ALDABERGENOVA
Keyword(s):  
Stokes Equations ◽  
Outer Wall ◽  
Conjugate Problem ◽  
Navier Stokes ◽  
Geometrical Parameters ◽  
Downward Flow ◽  
Navier Stokes Equations ◽  
Boundary Area ◽  
Air Mass ◽  
Hydrodynamic Motion

A study was made of the nature of the movement of air mass in the space between the device that warms the room and the confining outer wall of the room. The hydrodynamic motion of the air mass was simulated on the basis of the two-dimensional in space Navier-Stokes equations and the convective heat conduction equation to find out a detailed picture of the physical processes that occur. Also for some particular cases, analytical solutions were obtained for the conjugate problem, where the movement of air is caused by its thermal expansion and the action of gravity in areas with different densities (Archimedes' forces). The simulation of more complex types of air movement with the formation of vortex flows using numerical methods and the corresponding program codes written in C++. It was found that the movement of air mass in the space between the device and the fence strongly depends not only on the temperature of the device, the wall, and the outside air. It was revealed that hydrodynamics and heat transfer are significantly influenced by two geometrical parameters: the distance between the device and the wall, and the distance from the flooring to the bottom of the device. In particular, a thin layer of the downward flow of cold air along the fence and above the floor is possible. The condition for the occurrence of such a downward flow has been found, it is determined by the ratio of the temperature of the wall, the device, and the average temperature in the room.

scholarly journals Numerical simulation of supersquare patterns in Faraday waves

2015 ◽  
Vol 772 ◽  
Author(s):  
L. Kahouadji ◽  
N. Périnet ◽  
L. S. Tuckerman ◽  
S. Shin ◽  
J. Chergui ◽  
...  
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Outer Wall ◽  
Wave Pattern ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Critical Wavelength ◽  
Characteristic Wavelength ◽  
Cylindrical Domains ◽  
Lagrangian Tracking

We report the first simulations of the Faraday instability using the full three-dimensional Navier–Stokes equations in domains much larger than the characteristic wavelength of the pattern. We use a massively parallel code based on a hybrid front-tracking/level-set algorithm for Lagrangian tracking of arbitrarily deformable phase interfaces. Simulations performed in square and cylindrical domains yield complex patterns. In particular, a superlattice-like pattern similar to those of Douady & Fauve (Europhys. Lett., vol. 6, 1988, pp. 221–226) and Douady (J. Fluid Mech., vol. 221, 1990, pp. 383–409) is observed. The pattern consists of the superposition of two square superlattices. We conjecture that such patterns are widespread if the square container is large compared with the critical wavelength. In the cylinder, pentagonal cells near the outer wall allow a square-wave pattern to be accommodated in the centre.

Geometrical Effects on Fluid Mixing of Pulsatile Flow in Convergent-Divergent Micromixer

2015 ◽  
Author(s):  
Arshad Afzal ◽  
Kwang-Yong Kim
Keyword(s):  
Pulsatile Flow ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Geometrical Parameters ◽  
Navier Stokes Equations ◽  
Mixing Performance ◽  
Throat Width ◽  
Pulsatile Flows ◽  
Geometrical Effects ◽  
Diffusion Convection

Time-dependent pulsatile flows have been used by many researchers for fast and efficient mixing at micro-scale [1–2]. In a recent study, a convergent-divergent microchannel with sinusoidal walls showed a strong coupling with pulsatile flow for enhanced mixing performance over a short mixing length [3]. In the present study, effects of two geometrical parameters, i.e., the ratio of amplitude to wavelength and ratio of throat-width to depth on mixing performance, were analyzed with the Strouhal number and the ratio of pulsing amplitude to steady flow velocity at a fixed Reynolds number, Re = 0.5. The flow and mixing analyses were performed using unsteady Navier-Stokes equations and a diffusion-convection model for species concentration.

LES of Compressible Turbulent Annular Pipe Flow With a Rotating Wall

2003 ◽  
Author(s):  
Joon Sang Lee ◽  
Xiaofeng Xu ◽  
R. H. Pletcher
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Stokes Equations ◽  
Outer Wall ◽  
Navier Stokes ◽  
Subgrid Scale ◽  
Turbulent Structures ◽  
Navier Stokes Equations ◽  
Rotating Wall ◽  
Annular Pipe

Flow in an annular pipe with and without a wall rotating about its axis was investigated at moderate Reynolds numbers. The compressible filtered Navier-Stokes equations were solved using a second order accurate finite volume method. Low Mach number preconditioning was used to enable the compressible code to work efficiently at low Mach numbers. A dynamic subgrid-scale stress model accounted for the subgrid-scale turbulence. When the outer wall rotated, a significant reduction of turbulent kinetic energy was realized near the rotating wall and the intensity of bursting effects appeared to decrease. This modification of the turbulent structures was related to the vortical structure changes near the rotating wall. It has been observed that the wall vortices were pushed in the direction of rotation and their intensity increased near the non-rotating wall. The consequent effect was to enhance the turbulent kinetic energy and increased the intensity of the heat transfer rate there.

Viscous Flow Computations for Compressor/Combustor Diffuser Design to Allow Air Extraction for IGCC Systems

1991 ◽  
Author(s):  
Ajay K. Agrawal ◽  
Tah-Teh Yang
Keyword(s):  
Coal Gasification ◽  
Stokes Equations ◽  
Outer Wall ◽  
Computational Procedure ◽  
Navier Stokes ◽  
Structural Constraints ◽  
Navier Stokes Equations ◽  
Annular Diffuser ◽  
High Reynolds ◽  
Suction Slot

A computational procedure based on the solution of fully elliptic Navier-Stokes equations on a body-fitted non-orthogonal grid was used to obtain flow fields in annular diffusers with a suction slot at the inner and outer walls. The turbulence effects were simulated by high Reynolds number form of the k-ε model. The calculation method was used to modify an industrial gas turbine (GE MS · 7001F) compressor/combustor annular diffuser to allow extraction of compressed airflow for coal gasification in simplified IGCC Systems. The air for gasification was extracted through a suction slot on the outer wall of the diffuser which was curved to improve the overall performance and to avoid flow separation; both of these insured by providing accelerated flow through the suction slot and nearly constant wall pressure downstream of the slot. Suction slot and outer wall geometries to result in the above conditions were determined by a trial and error procedure. The diffuser’s performance was further improved by extracting 6% of the compressed air through a slot at the inner wall, kept straight due to structural constraints. The resulting diffuser arrangement was relatively insensitive to the upstream disturbances.

A Numerical Analysis of High-Temperature Heat Pipe Startup From the Frozen State

1993 ◽  
Vol 115 (1) ◽  
pp. 247-254 ◽  
Author(s):  
Y. Cao ◽  
A. Faghri
Keyword(s):  
Heat Pipe ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Conjugate Problem ◽  
Navier Stokes ◽  
Vapor Flow ◽  
Pipe Length ◽  
Navier Stokes Equations ◽  
Frozen State ◽  
Startup Period

Continuum and rarefied vapor flows-co-exist along the heat pipe length for most of the startup period. A two-region model is proposed in which the vapor flow in the continuum region is modeled by the compressible Navier-Stokes equations, and the vapor flow in the rarefied region is simulated by a self-diffusion model. The two vapor regions are linked with appropriate boundary conditions, and heat pipe wall, wick, and vapor flow are solved as a conjugate problem. The numerical solutions for the entire heat pipe startup process from the frozen state are compared with the corresponding experimental data with good agreement.

Bifurcation in steady laminar flow through curved tubes

1982 ◽  
Vol 119 ◽  
pp. 475-490 ◽  
Author(s):  
K. Nandakumar ◽  
Jacob H. Masliyah
Keyword(s):  
Stokes Equations ◽  
Outer Wall ◽  
Dual Solutions ◽  
Navier Stokes ◽  
Dean Number ◽  
Navier Stokes Equations ◽  
Vortex Solution ◽  
Duct Geometry ◽  
Flow Through ◽  
Curved Ducts

The occurrence of dual solutions in curved ducts is investigated through a numerical solution of the Navier-Stokes equations in a bipolar-toroidal co-ordinate system. With the shape of duct being the region formed by the natural co-ordinate surfaces, it was possible to alter the duct geometry gradually and preserve the prevailing form of the velocity field, in a manner suggested by Benjamin (1978).In addition to the Dean number Dn = Re/Rc½, a geometrical parameter that defines the shape of the duct was also varied systematically to study the bifurcation of a two-vortex solution into a two- and four-vortex solution. Dual solutions have been found for all geometrical shapes investigated here. Of particular interest are the shapes of a full circle and a semicircle with a curved outer wall.

Laminar flow in a square duct of strong curvature

1977 ◽  
Vol 83 (3) ◽  
pp. 509-527 ◽  
Author(s):  
J. A. C. Humphrey ◽  
A. M. K. Taylor ◽  
J. H. Whitelaw
Keyword(s):  
Stokes Equations ◽  
Laser Doppler Anemometry ◽  
Longitudinal Velocity ◽  
Flow Analysis ◽  
Maximum Velocity ◽  
Outer Wall ◽  
Navier Stokes ◽  
Upstream Region ◽  
Dean Number ◽  
Navier Stokes Equations

Calculated values of the three velocity components and measured values of the longitudinal component are reported for the flow of water in a 90° bend of 40 x 40mm cross-section; the bend had a mean radius of 92mm and was located downstream of a 1[sdot ]8m and upstream of a 1[sdot ]2m straight section. The experiments were carried out at a Reynolds number, based on the hydraulic diameter and bulk velocity, of 790 (corresponding to a Dean number of 368). Flow visualization was used to identify qualitatively the characteristics of the flow and laser-Doppler anemometry to quantify the velocity field. The results confirm and quantify that the location of maximum velocity moves from the centre of the duct towards the outer wall and, in the 90° plane, is located around 85% of the duct width from the inner wall. Secondary velocities up to 65% of the bulk longitudinal velocity were calculated and small regions of recirculation, close to the outer corners of the duct and in the upstream region, were also observed.The calculated results were obtained by solving the Navier–Stokes equations in cylindrical co-ordinates. They are shown to exhibit the same trends as the experiments and to be in reasonable quantitative agreement even though the number of node points used to discretize the flow for the finite-difference solution of the differential equations was limited by available computer time and storage. The region of recirculation observed experimentally is confirmed by the calculations. The magnitude of the various terms in the equations is examined to determine the extent to which the details of the flow can be represented by reduced forms of the Navier–Stokes equations. The implications of the use of so-called ‘partially parabolic’ equations and of potential- and rotational-flow analysis of an ideal fluid are quantified.

scholarly journals Numerical Analysis of a Vortex Controlled Diffuser

1995 ◽  
Vol 117 (1) ◽  
pp. 86-90 ◽  
Author(s):  
R. E. Spall
Keyword(s):  
Turbulence Model ◽  
Stokes Equations ◽  
Numerical Study ◽  
Outer Wall ◽  
Vortex Chamber ◽  
Area Ratio ◽  
Navier Stokes ◽  
Good Qualitative Agreement ◽  
Abrupt Increase ◽  
Navier Stokes Equations

A numerical study of a prototypical vortex controlled diffuser is performed. The basic diffuser geometry consists of a step expansion in a pipe of area ratio 2.25:1. The incompressible Reynolds averaged Navier-Stokes equations, employing the RNG based κ − ∈ turbulence model, are solved. Results are presented for bleed rates ranging from 1 to 7 percent. Diffuser efficiencies in excess of 80 percent were obtained. These results are in good qualitative agreement with previous experimental work. The results do not confirm previous suggestions that the increases in effectiveness of the VCD over a step expansion result from an inhibition of flow separation due to the generation and downstream convection of extremely high levels of turbulence generated in the region of the bleed gap. The results do indicate that the effectiveness of the diffuser is a consequence of the turning of the flow toward the outer wall due to the influence of the low pressure vortex chamber. Calculations employing the RNG based turbulence model were able to capture the abrupt increase in diffuser effectiveness that has been shown experimentally to occur at low bleed rates. Calculations employing the standard κ − ∈ model were unable to predict this occurrence.

Analysis of a Torsional Fluid Film Vibrator

2002 ◽  
Vol 124 (3) ◽  
pp. 480-485 ◽  
Author(s):  
C. V. Suciu ◽  
T. Iwatsubo ◽  
M. D. Pascovici
Keyword(s):  
Stokes Equations ◽  
Fluid Film ◽  
Navier Stokes ◽  
Viscous Drag ◽  
Thickness Variation ◽  
Geometrical Parameters ◽  
Navier Stokes Equations ◽  
Oscillatory Movement ◽  
Drilling Technology ◽  
Fluid Film Thickness

A novel hydrodynamic system, called torsional fluid film vibrator (TFFV) is proposed. This device is complementary to the Lanchester’s absorber and presents a classical response of a one-degree of freedom linear system with a periodical self-excitation. The fluid film thickness variation produces a variable viscous drag moment, which drives the elastically supported bush in a torsional oscillatory movement. The TFFV concept is connected with current research to improve the drilling technology of deep holes. The Navier-Stokes equations are solved on the particular geometry of this vibrator and the viscous drag moment is explicitly presented. The theoretical part is continued with the TFFV dynamic simulation and the analysis of the influence of the geometrical parameters on the amplitude of the viscous drag moment. Computed structural friction power and the amplitude of vibration agree reasonably well with the experimental measurements conducted on a TFFV test rig.

scholarly journals Performance Evaluation of an Air-Conditioning Compressor Part II: Volute Flow Predictions

1999 ◽  
Vol 5 (4) ◽  
pp. 241-250 ◽  
Author(s):  
Yu-Tai Lee ◽  
Thomas W. Bein
Keyword(s):  
Total Pressure ◽  
Air Conditioning ◽  
Stokes Equations ◽  
Outer Wall ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
High Loss ◽  
Pressure Distributions ◽  
Loss Component ◽  
Flow Stream

A numerical method that solves the Reynolds-averaged Navier-Stokes equations is used to study an inefficient component of a shipboard air-conditioning HCFC-124 compressor system. This high-loss component of the centrifugal compressor was identified as the volute through a series of measurements given in Part I of the paper. The predictions were made using three grid topologies. The first grid closes the connection between the cutwater and the discharge diffuser. The other two grids connect the cutwater area with the discharge diffuser. Experiments were performed to simulate both the cutwater conditions used in the predictions. Surface pressures along the outer wall and near the inlet of the volute were surveyed for comparisons with the predictions. Good agreements between the predicted results and the measurements validate the calculations. Total pressure distributions and flow stream traces from the prediction results support the loss distribution through the volute. A modified volute configuration is examined numerically for further loss comparison.

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