scholarly journals IN-CYLINDER FLOW CHARACTERIZATION USING VORTICITY BASED PARAMETERS

2018 ◽  
Vol 18 (1) ◽  
pp. 11
Author(s):  
Petr Hatschbach ◽  
Oldřich Vítek ◽  
Radek Tichánek
Keyword(s):  
Angular Momentum ◽  
Momentum Flux ◽  
Cfd Simulation ◽  
Swirling Flow ◽  
Vortex Pair ◽  
Cylinder Wall ◽  
Dimensionless Numbers ◽  
Ic Engine ◽  
Flow Characterization ◽  
Cylinder Flow

The paper deals with intake swirling flow characterization in the cylinder of IC engine. The commonly used method based on the swirl resp. tumble number from angular momentum flux evaluation does not need to give the appropriate values in some cases. Typically, in the case of two intake ports, a counter-rotating swirl vortex pair is presented. However their summary angular momentum flux is zero a thus corresponding swirl number is zero too. In order to correctly quantify these cases, it is proposed to evaluate so called vorticity numbers, i.e. dimensionless numbers based on vorticity evaluation. Concrete results are evaluated from data obtained using 3-D CFD simulation in AVL FIRE code. Comparison of variously defined vorticity numbers with each other and with the vortex numbers is performed. A practical way of calculating the vorticity numbers was also suggested with regard to possible adverse effects of the velocity gradients at the cylinder wall.

Application of an Angular Momentum Balance Method for Investigating Numerical Accuracy in Swirling Flow

2003 ◽  
Vol 125 (4) ◽  
pp. 723-730
Author(s):  
H. Nilsson ◽  
L. Davidson
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Angular Momentum ◽  
Swirling Flow ◽  
Linear Momentum ◽  
Correct Solution ◽  
Momentum Balance ◽  
Numerical Accuracy ◽  
Water Turbine ◽  
Water Turbines

This work derives and applies a method for the investigation of numerical accuracy in computational fluid dynamics. The method is used to investigate discretization errors in computations of swirling flow in water turbines. The work focuses on the conservation of a subset of the angular momentum equations that is particularly important to swirling flow in water turbines. The method is based on the fact that the discretized angular momentum equations are not necessarily conserved when the discretized linear momentum equations are solved. However, the method can be used to investigate the effect of discretization on any equation that should be conserved in the correct solution, and the application is not limited to water turbines. Computations made for two Kaplan water turbine runners and a simplified geometry of one of the Kaplan runner ducts are investigated to highlight the general and simple applicability of the method.

scholarly journals Mechanisms of Jet Formation on the Giant Planets

2010 ◽  
Vol 67 (11) ◽  
pp. 3652-3672 ◽  
Author(s):  
Junjun Liu ◽  
Tapio Schneider
Keyword(s):  
Angular Momentum ◽  
Rossby Wave ◽  
Momentum Flux ◽  
Wave Generation ◽  
Heat Fluxes ◽  
Giant Planets ◽  
Radiative Heating ◽  
Flux Divergence ◽  
Low Latitude ◽  
Flow Configurations

Abstract The giant planet atmospheres exhibit alternating prograde (eastward) and retrograde (westward) jets of different speeds and widths, with an equatorial jet that is prograde on Jupiter and Saturn and retrograde on Uranus and Neptune. The jets are variously thought to be driven by differential radiative heating of the upper atmosphere or by intrinsic heat fluxes emanating from the deep interior. However, existing models cannot account for the different flow configurations on the giant planets in an energetically consistent manner. Here a three-dimensional general circulation model is used to show that the different flow configurations can be reproduced by mechanisms universal across the giant planets if differences in their radiative heating and intrinsic heat fluxes are taken into account. Whether the equatorial jet is prograde or retrograde depends on whether the deep intrinsic heat fluxes are strong enough that convection penetrates into the upper troposphere and generates strong equatorial Rossby waves there. Prograde equatorial jets result if convective Rossby wave generation is strong and low-latitude angular momentum flux divergence owing to baroclinic eddies generated off the equator is sufficiently weak (Jupiter and Saturn). Retrograde equatorial jets result if either convective Rossby wave generation is weak or absent (Uranus) or low-latitude angular momentum flux divergence owing to baroclinic eddies is sufficiently strong (Neptune). The different speeds and widths of the off-equatorial jets depend, among other factors, on the differential radiative heating of the atmosphere and the altitude of the jets, which are vertically sheared. The simulations have closed energy and angular momentum balances that are consistent with observations of the giant planets. They exhibit temperature structures closely resembling those observed and make predictions about as yet unobserved aspects of flow and temperature structures.

scholarly journals Characteristics of Size Change of Tropical Cyclones Traversing the Philippines

2018 ◽  
Vol 146 (9) ◽  
pp. 2891-2911 ◽  
Author(s):  
Shu-Jeng Lin ◽  
Kun-Hsuan Chou
Keyword(s):  
Angular Momentum ◽  
Relative Humidity ◽  
Tropical Cyclones ◽  
Momentum Flux ◽  
Vertical Wind Shear ◽  
The Philippines ◽  
Sea Surface ◽  
Japan Meteorological Agency ◽  
The South ◽  
Size Change

Abstract This study investigates the size changes of tropical cyclones (TCs) traversing the Philippines based on a 37-yr statistical analysis. TC size is defined by the radius of 30-kt (≈15.4 m s−1) wind speed (R30) from the best track data of the Japan Meteorological Agency. A total of 71 TCs passed the Philippines during 1979–2015. The numbers of size increase (SI; 36) and size decrease (SD; 34) cases are very similar; however, the last 15 years have seen more SI cases (17) than SD cases (11). SI and SD cases mostly occur along northerly and southerly paths, respectively, after TCs pass the Philippines. Before landfall, SI cases have small initial sizes and weak intensities, but SD cases have larger initial sizes and stronger intensities. After landfall, most SI cases are intensifying storms, and most SD cases are nonintensifying storms. Composite analyses of vertical wind shear, absolute angular momentum flux, relative humidity, and sea surface temperature between SI and SD cases are compared. All of these values are larger in SI cases than in SD cases. Furthermore, the interdecadal difference in the ratio of the numbers of SI to SD cases reveals an unusually high number of SI cases during 2001–15. The synoptic patterns between 1979–2000 and 2001–15 are analyzed. The high SI ratio in the latter period is related to strong southwesterly wind in the south of the South China Sea that raised relative humidity, warmed the sea surface, and increased import of angular momentum flux.

Boundary conditions for Maxwell fields in Kerr-AdS spacetimes

2016 ◽  
Vol 25 (09) ◽  
pp. 1641011 ◽  
Author(s):  
Mengjie Wang
Keyword(s):  
Black Holes ◽  
Angular Momentum ◽  
Boundary Conditions ◽  
Energy Flux ◽  
Momentum Flux ◽  
De Sitter ◽  
Perturbative Methods ◽  
Flux Boundary Conditions ◽  
Maxwell Fields ◽  
New Type

Perturbative methods are useful to study the interaction between black holes and test fields. The equation for a perturbation itself, however, is not complete to study such a composed system if we do not assign physically relevant boundary conditions. Recently we have proposed a new type of boundary conditions for Maxwell fields in Kerr-anti-de Sitter (Kerr-AdS) spacetimes, from the viewpoint that the AdS boundary may be regarded as a perfectly reflecting mirror, in the sense that energy flux vanishes asymptotically. In this paper, we prove explicitly that a vanishing energy flux leads to a vanishing angular momentum flux. Thus, these boundary conditions may be dubbed as vanishing flux boundary conditions.

scholarly journals Non-diffusive angular momentum transport in rotating -pinches

2019 ◽  
Vol 85 (6) ◽  
Author(s):  
G. Rüdiger ◽  
M. Schultz
Keyword(s):  
Angular Momentum ◽  
Momentum Flux ◽  
Eddy Viscosity ◽  
Rigid Rotation ◽  
Momentum Transport ◽  
Angular Momentum Transport ◽  
Magnetohydrodynamic Flows ◽  
The Stability ◽  
Background Fields ◽  
Axisymmetric Perturbations

The stability of conducting Taylor–Couette flows under the presence of toroidal magnetic background fields is considered. For strong enough magnetic amplitudes such magnetohydrodynamic flows are unstable against non-axisymmetric perturbations which may also transport angular momentum. In accordance with the often used diffusion approximation, one expects the angular momentum transport to be vanishing for rigid rotation. In the sense of a non-diffusive  $\unicode[STIX]{x1D6EC}$ effect, however, even for rigidly rotating $z$ -pinches, an axisymmetric angular momentum flux appears which is directed outward (inward) for large (small) magnetic Mach numbers. The internal rotation in a magnetized rotating tank can thus never be uniform. Those particular rotation laws are used to estimate the value of the instability-induced eddy viscosity for which the non-diffusive $\unicode[STIX]{x1D6EC}$ effect and the diffusive shear-induced transport compensate each other. The results provide the Shakura & Sunyaev viscosity ansatz leading to numerical values linearly growing with the applied magnetic field.

Optimal Design of IC Engine Cooling Fins by Using Genetic Algorithm

2014 ◽  
Author(s):  
Terry Yan ◽  
Jason Yobby ◽  
Ravindra Vundavilli
Keyword(s):  
Heat Transfer ◽  
Genetic Algorithms ◽  
Optimal Design ◽  
Degrees Of Freedom ◽  
Combustion Engine ◽  
Local Heat Transfer ◽  
System Component ◽  
Cylinder Wall ◽  
Ic Engine ◽  
Engine Cooling

The analysis for optimal design of an air-cooled internal combustion engine cooling fin array by using genetic algorithms (GA) is presented in this study. Genetic Algorithms are robust, stochastic search techniques which are also used for optimizing highly complex problems. In this study, the fin array is of the traditional circular fin type, which is subject to ambient convective heat transfer. The parameters (degrees of freedom) selected for the analysis include the cylinder wall thickness-to-radius ratio, fin thickness, fin length, the number of fins, and the local heat transfer coefficient. By using a single objective GA procedure, the heat transfer through the fin arrays is set as the objective function to be optimized with each parameter varied within the physical ranges. Proper population size is selected and the mutations, cross-over and selection are conducted in the GA procedure to arrive at the optimal set of parameters after a certain number of generations. The GA proves to be an effective optimization method in the thermal system component designs when the number of independent variables is large.

CFD simulation of swirling flow induced by twist vanes in a rod bundle

2018 ◽  
Vol 338 ◽  
pp. 52-62 ◽  
Author(s):  
Jinbiao Xiong ◽  
Ruiqi Cheng ◽  
Chuan Lu ◽  
Xiang Chai ◽  
Xiaojing Liu ◽  
...  
Keyword(s):  
Cfd Simulation ◽  
Swirling Flow ◽  
Rod Bundle

Determination of the solar wind angular momentum flux from the HELIOS data - an observational test of the Weber and Davis theory

1983 ◽  
Vol 271 ◽  
pp. 335 ◽  
Author(s):  
V. Pizzo ◽  
R. Schwenn ◽  
E. Marsch ◽  
H. Rosenbauer ◽  
K.-H. Muehlhaeuser ◽  
...  
Keyword(s):  
Solar Wind ◽  
Angular Momentum ◽  
Momentum Flux ◽  
Observational Test
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