Modeling and numerical technique for investigating of turbulent transfer in a non-stationary boundary layer at impacts

2019 ◽  
Author(s):  
Vladislav N. Kovalnogov ◽  
Ruslan V. Fedorov ◽  
Larisa V. Khakhaleva ◽  
Andrei V. Chukalin ◽  
Yury A. Khakhalev
Keyword(s):  
Boundary Layer ◽  
Numerical Technique ◽  
Turbulent Transfer ◽  
Stationary Boundary

To calculation of a stationary boundary layer under conditions of strong thermochemical nonequilibrium

2020 ◽  
Author(s):  
Yurii N. Grigoryev ◽  
Aleksey G. Gorobchuk ◽  
Igor V. Ershov
Keyword(s):  
Boundary Layer ◽  
Stationary Boundary

Study of Heat Transfer Characteristics in the Boundary Layer of a Visco-Elastic Fluid Under Varying Influencing Parameters

2007 ◽  
Author(s):  
P. Anuradha ◽  
S. Krishnambal
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Numerical Study ◽  
Numerical Technique ◽  
Heat Transfer Characteristics ◽  
Elastic Fluid ◽  
Transfer Characteristics ◽  
Dimensional Parameters ◽  
Influencing Parameters ◽  
Sheet Stretching

The heat transfer characteristics of a visco-elastic fluid within the boundary layer formed by the passage of a sheet stretching at a uniform rate through it are studied under varying influencing parameters using a numerical technique. The influence of considering or ignoring elastic deformation in the thermal analysis is studied in the presence of chosen values of non-dimensional parameters like Prandtl number (Pr) and Eckert number (E). Two cases of sheet surface conditions are considered — (i) PST case involving prescribed surface temperature and (ii) PHF case involving prescribed heat flux at the surface. The results of this numerical study are diagrammatically represented with appropriate conclusions drawn on the influence of the above parameters considered in isolation or together. The trend of results is seen to agree well with those of other researchers who used other solution techniques. A judious choice of the above two principal non-dimensional parameters is suggested for application to a cooling process typical of a polymer extrusion industry.

scholarly journals Three-Dimensional Magnetic Fluid Boundary Layer Flow Over a Linearly Stretching Sheet

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
E. E. Tzirtzilakis ◽  
N. G. Kafoussias
Keyword(s):  
Magnetic Field ◽  
Boundary Layer ◽  
Magnetic Fluid ◽  
Boundary Layer Flow ◽  
Stretching Sheet ◽  
Numerical Technique ◽  
Three Dimensional ◽  
Magnetic Interaction ◽  
Layer Flow ◽  
The Magnetic Field

The three-dimensional laminar and steady boundary layer flow of an electrically nonconducting and incompressible magnetic fluid, with low Curie temperature and moderate saturation magnetization, over an elastic stretching sheet, is numerically studied. The fluid is subject to the magnetic field generated by an infinitely long, straight wire, carrying an electric current. The magnetic fluid far from the surface is at rest and at temperature greater of that of the sheet. It is also assumed that the magnetization of the fluid varies with the magnetic field strength H and the temperature T. The numerical solution of the coupled and nonlinear system of ordinary differential equations, resulting after the introduction of appropriate nondimensional variables, with its boundary conditions, describing the problem under consideration, is obtained by an efficient numerical technique based on the common finite difference method. Numerical calculations are carried out for the case of a representative water-based magnetic fluid and for specific values of the dimensionless parameters entering into the problem, and the obtained results are presented graphically for these values of the parameters. The analysis of these results showed that there is an interaction between the motions of the fluid, which are induced by the stretching surface and by the action of the magnetic field, and the flow field is noticeably affected by the variations in the magnetic interaction parameter β. The important results of the present analysis are summarized in Sec. 6.

Challenges in Linking Atmospheric CO2 Concentrations to Fluxes at Local and Regional Scales

1992 ◽  
Vol 40 (5) ◽  
pp. 697 ◽  
Author(s):  
MR Raupach ◽  
OT Denmead ◽  
FX Dunin
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Co2 Flux ◽  
Co2 Concentration ◽  
Atmospheric Co2 ◽  
Wheat Crop ◽  
Turbulent Transfer ◽  
Near Surface ◽  
Scalar Dispersion ◽  
Source Sink

We describe relationships between atmospheric CO2 concentration variations and CO2 source-sink distributions, at two important scales between the single plant and the whole earth: the vegetation canopy and the atmospheric planetary boundary layer. For both these scales, it is shown how knowledge of turbulence and scalar dispersion can be applied to infer CO2 source-sink distributions or fluxes from concentration measurements. At the canopy scale, the turbulent transfer of CO2 and other scalars is non-diffusive close to any point source or sink in the canopy, but diffusive at greater distances. This distinction leads to a physically tenable description of turbulent transfer, and thence to an 'inverse method' for finding the vertical profiles of sources and sinks in the canopy from measured concentration profiles. The method is tested with data from a wheat crop. At the scale of the planetary boundary layer, we consider the daily CO2 concentration drawdown (the depression of the near-surface CO2 concentration below the free-atmosphere value) of typically 20-40 ppm. This is determined by both the regionally averaged CO2 uptake at the surface and the growth of the daytime convective boundary layer (CBL). It is shown that, for a column of air which fills the CBL and is moved across the landscape by the mean wind, the net cumulative surface CO2 flux (in mol m-2) is given to a good approximation by h(t)[Cm(t) - C+]/V, where h(t) is CBL depth, Cm(t) the CO2 concentration in the CBL column in mol mol-1, C+ the concentration above the CBL, V the molar volume and time t is measured from the time at which Cm = C+ in the morning, typically about 0800 hours local time. The resulting CO2 flux estimates are regionally averaged over the trajectory followed by the column. This 'CBL budget method' for inferring surface fluxes is compared with direct measurements of CO2 fluxes, with satisfactory results. The technique has application to scalars other than CO2.

scholarly journals Observation and Parameterization of Ablation at the Base of Ronne Ice Shelf, Antarctica

2010 ◽  
Vol 40 (10) ◽  
pp. 2298-2312 ◽  
Author(s):  
Adrian Jenkins ◽  
Keith W. Nicholls ◽  
Hugh F. J. Corr
Keyword(s):  
Boundary Layer ◽  
Open Water ◽  
Ablation Rate ◽  
Ocean Currents ◽  
Turbulent Transfer ◽  
Transfer Coefficients ◽  
Ice Shelf ◽  
Direct Measurements ◽  
Oceanic Boundary Layer ◽  
The Impact

Abstract Parameterizations of turbulent transfer through the oceanic boundary layer beneath an ice shelf are tested using direct measurements of basal ablation. Observations were made in the southwestern part of Ronne Ice Shelf, about 500 km from open water. The mean basal ablation rate was measured over a month-long and a year-long period using phase-sensitive radar to record the thinning of the ice shelf. Ocean temperatures were observed within about 25 m of the ice shelf base over the period of the radar observations, while the tidally dominated ocean currents were estimated from tidal analysis of collocated current observations from an earlier period. Ablation rates derived using these ocean data and a number of bulk parameterizations of turbulent transfer within the boundary layer are compared with the direct measurements. The ablation rates derived using a parameterization that explicitly includes the impact of ocean currents on the turbulent transfer of heat and salt match the observations to within 40%; with suitable tuning of the drag coefficient, the mismatch can be reduced below the level of the observational errors. Equally good agreement can be obtained with two slightly simpler, current-dependent parameterizations that use constant turbulent transfer coefficients, and the optimal values for the coefficients at this particular location on Ronne Ice Shelf are given.

scholarly journals Mechanisms and models of control of turbulent transfer in boundary layer

2017 ◽  
Author(s):  
Vladislav N. Kovalnogov ◽  
Igor A. Maleshin ◽  
Ruslan V. Fedorov ◽  
Dmitry V. Suranov ◽  
Larisa V. Khakhaleva
Keyword(s):  
Boundary Layer ◽  
Turbulent Transfer

Numerical Modeling of Surface Wave Motion With a Bottom Turbulent Boundary Layer

2005 ◽  
Author(s):  
Mirmosadegh Jamali
Keyword(s):  
Boundary Layer ◽  
Surface Wave ◽  
Wave Motion ◽  
Turbulence Modeling ◽  
Numerical Technique ◽  
Equations Of Motion ◽  
Solid Surfaces ◽  
Bed Shear Stress ◽  
Finite Difference Technique ◽  
Mixing Length Theory

An effective numerical technique is presented to model turbulent motion of a standing surface wave in a tank. The equations of motion for turbulent boundary layers at the solid surfaces are coupled with the potential flow in the bulk of the fluid, and a mixed BEM-finite difference technique is used to obtain the wave and boundary layer characteristics such as bed shear stress. A mixing-length theory is used for turbulence modeling. Although the technique is presented for a standing surface wave, it can be easily applied to other free surface problems.

scholarly journals Diagnosing Coherent Structures in the Convective Boundary Layer by Optimizing Their Vertical Turbulent Scalar Transfer

2019 ◽  
Vol 174 (1) ◽  
pp. 119-144 ◽  
Author(s):  
Georgios A. Efstathiou ◽  
John Thuburn ◽  
Robert J. Beare
Keyword(s):  
Boundary Layer ◽  
Coherent Structures ◽  
Convective Boundary Layer ◽  
Thermodynamic Characteristics ◽  
Optimization Method ◽  
Area Fraction ◽  
Optimization Approach ◽  
Turbulent Transfer ◽  
Scalar Flux ◽  
Convective Boundary

Abstract A new method is introduced to identify coherent structures in the convective boundary layer, based on optimizing the vertical scalar flux in a two-fluid representation of turbulent motions as simulated by a large-eddy simulation. The new approach partitions the joint frequency distribution (JFD) of the vertical velocity and a transported scalar into coherent structures (fluid 2) and their environment (fluid 1) by maximizing that part of the scalar flux resolved by the mean properties in fluid 2 and fluid 1. The proposed method does not rely on any a priori criteria for the partitioning of the flow nor any pre-assumptions about the shape of the JFD. Different flavours of the optimization approach are examined based on maximizing either the total (fluid 1 $$+$$+ fluid 2) or the fluid-2 resolved scalar flux, and on whether all possible partitions or only a subset are considered. These options can result in different derived area fractions for the coherent structures. The properties of coherent structures diagnosed by the optimization method are compared to the conditional sampling of a surface-emitted decaying tracer, in which coherent structures are defined as having tracer perturbation greater than some height-dependent threshold. Results show that the optimization method is able to smoothly define coherent thermal structures in both the horizontal and the vertical. Moreover, optimizing the turbulent transfer by the fluid-2 resolved flux produces very similar coherent structures to the tracer threshold method, especially in terms of their area fraction and updraft velocities. Nonetheless, further analysis of the partitioning of the JFD reveals that, even though the area fraction of coherent structures might be similar, their definition can occupy different quadrants of the JFD, implying the contribution of different physical mechanisms to the turbulent transfer in the boundary layer. Finally, the kinematic and thermodynamic characteristics of the coherent structures are examined based on their definition criteria.

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