Momentum and heat transport in a three-dimensional transitional wake of a heated square cylinder

2009 ◽  
Vol 640 ◽  
pp. 109-129 ◽  
Author(s):  
L. DJENIDI ◽  
R. A. ANTONIA
Keyword(s):  
Spatial Organization ◽  
Transport Model ◽  
Order Approximation ◽  
Three Dimensional ◽  
Passive Scalar ◽  
Wake Flow ◽  
Square Cylinder ◽  
Reynolds Analogy ◽  
First Order Approximation ◽  
Boltzmann Method

The transport of momentum and a passive scalar (temperature) in a three-dimensional transitional wake of a heated square cylinder has been carried out through direct numerical simulations using the lattice Boltzmann method at a Reynolds number Rd = 200 (d is the cylinder diameter) and a Prandlt number of 0.7. The simulations shows that while momentum and heat are transported by vortical structures, heat is in general more effectively transported than momentum. It is argued that the nature of the structural flow is responsible for the longitudinal heat flux uθ being larger than the lateral one vθ in the wake region extending up to 45d. It was shown that a gradient transport model could, to a first-order approximation, be used to model uv but would be less accurate for modelling vθ. Also the Reynolds analogy between momentum and heat transports is not verified in this flow. The fluctuating temperature field presents thermal structures similar to the velocity structures with, however, a different spatial organization. In addition the analogy between fluctuating turbulent kinetic energy and the temperature variance is relatively well satisfied throughout the wake flow.

scholarly journals A linear CO chemistry parameterization in a chemistry-transport model: evaluation and application to data assimilation

2010 ◽  
Vol 10 (13) ◽  
pp. 6097-6115 ◽  
Author(s):  
M. Claeyman ◽  
J.-L. Attié ◽  
L. El Amraoui ◽  
D. Cariolle ◽  
V.-H. Peuch ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Large Scale ◽  
Lower Stratosphere ◽  
Transport Model ◽  
Order Approximation ◽  
Chemical Transport Model ◽  
Long Run ◽  
Linear Scheme ◽  
Mean Differences ◽  
First Order Approximation

Abstract. This paper presents an evaluation of a new linear parameterization valid for the troposphere and the stratosphere, based on a first order approximation of the carbon monoxide (CO) continuity equation. This linear scheme (hereinafter noted LINCO) has been implemented in the 3-D Chemical Transport Model (CTM) MOCAGE (MOdèle de Chimie Atmospherique Grande Echelle). First, a one and a half years of LINCO simulation has been compared to output obtained from a detailed chemical scheme output. The mean differences between both schemes are about ±25 ppbv (part per billion by volume) or 15% in the troposphere and ±10 ppbv or 100% in the stratosphere. Second, LINCO has been compared to diverse observations from satellite instruments covering the troposphere (Measurements Of Pollution In The Troposphere: MOPITT) and the stratosphere (Microwave Limb Sounder: MLS) and also from aircraft (Measurements of ozone and water vapour by Airbus in-service aircraft: MOZAIC programme) mostly flying in the upper troposphere and lower stratosphere (UTLS). In the troposphere, the LINCO seasonal variations as well as the vertical and horizontal distributions are quite close to MOPITT CO observations. However, a bias of ~−40 ppbv is observed at 700 Pa between LINCO and MOPITT. In the stratosphere, MLS and LINCO present similar large-scale patterns, except over the poles where the CO concentration is underestimated by the model. In the UTLS, LINCO presents small biases less than 2% compared to independent MOZAIC profiles. Third, we assimilated MOPITT CO using a variational 3D-FGAT (First Guess at Appropriate Time) method in conjunction with MOCAGE for a long run of one and a half years. The data assimilation greatly improves the vertical CO distribution in the troposphere from 700 to 350 hPa compared to independent MOZAIC profiles. At 146 hPa, the assimilated CO distribution is also improved compared to MLS observations by reducing the bias up to a factor of 2 in the tropics. This study confirms that the linear scheme is able to simulate reasonably well the CO distribution in the troposphere and in the lower stratosphere. Therefore, the low computing cost of the linear scheme opens new perspectives to make free runs and CO data assimilation runs at high resolution and over periods of several years.

scholarly journals Finite Time Correlations and Compressibility Effects in the Three-Dimensional Kraichnan Model

2020 ◽  
Vol 226 ◽  
pp. 02016
Author(s):  
Martin Menkyna
Keyword(s):  
Velocity Field ◽  
Finite Time ◽  
Order Approximation ◽  
Three Dimensional ◽  
Passive Scalar ◽  
Parametric Space ◽  
Kraichnan Model ◽  
Time Correlations ◽  
Spatial Dimensions ◽  
Compressibility Effects

Using the field theoretic renormalization group technique the simultaneous influence of the compressibility and finite time correlations of the non-solenoidal Gaussian velocity field on the advection of a passive scalar field is studied within the generalized Kraichnan model in three spatial dimensions up to the second-order approximation in the corresponding perturbative expansion. All possible infrared stable fixed points of the model, which drive the corresponding scaling regimes of the model, are identified and their regions of the infrared stability in the model parametric space are discussed. It is shown that, depending on the value of the parameter that drives the compressibility of the system, there exists a gap in the parametric space between the regions where the model with the frozen velocity field and the model with finite-time correlations of the velocity field are stable or there exists an overlap between them.

scholarly journals Deficit of sand in a sediment transport model favors coral reef development in Brazil

2008 ◽  
Vol 80 (1) ◽  
pp. 205-214 ◽  
Author(s):  
Abílio C.S.P. Bittencourt ◽  
Zelinda M.A.N. Leão ◽  
Ruy K.P. Kikuchi ◽  
José M.L. Dominguez
Keyword(s):  
Sediment Transport ◽  
Transport Model ◽  
Order Approximation ◽  
Regional Scale ◽  
Coastal System ◽  
Wave Refraction ◽  
First Order ◽  
Sediment Transport Model ◽  
Longshore Sediment Transport ◽  
First Order Approximation

This paper shows that the location of the shoreface bank reefs along the northeastern and eastern coasts of Brazil, in a first order approximation, seem to be controlled by the deficit of sediment in the coastal system. The sediment transport pattern defined by a numerical modeling of wave refraction diagrams, representing circa 2000 km of the northeastern and eastern coasts of Brazil, permitted the regional-scale reproduction of several drift cells of net longshore sediment transport. Those drift cells can reasonably explain the coastal sections that present sediment surplus or sediment deficit, which correspond, respectively, to regions where there is deposition and erosion or little/no deposition of sand. The sediment deficit allows the exposure and maintenance of rocky substrates to be free of sediment, a favorable condition for the fixation and development of coral larvae.

Modeling Three Dimensional Tolerance Zones Using Screw Parameters

1999 ◽  
Author(s):  
Alain Desrochers
Keyword(s):  
Order Approximation ◽  
Three Dimensional ◽  
Complex Surface ◽  
Mathematical Representation ◽  
Small Displacement ◽  
Dimensional Tolerance ◽  
Representation Model ◽  
Homogeneous Transformation Matrix ◽  
Tolerance Zones ◽  
First Order Approximation

Abstract This paper presents a mathematical representation of the three dimensional tolerance zones defined in the ANSI Y14.5 M standard. The tolerance zone models are based on the small displacement screw which is a screw parameter expressing first order approximation of traditional homogeneous transformation matrix. Modeling of datum system and complex surface association is also taken into account as well as modeling of multiple tolerance specifications and material modifiers. Application of the representation model is presented on a simple tolerance transfer case where emphasis is put on the translation components of the tolerance zones. The screw parameter representation is also compatible with the Technologically and Topologically Related Surfaces (TTRS) representation model.

Improved first-order approximation of eigenvalues and eigenvectors

AIAA Journal ◽  
1998 ◽  
Vol 36 ◽  
pp. 1721-1727
Author(s):  
Prasanth B. Nair ◽  
Andrew J. Keane ◽  
Robin S. Langley
Keyword(s):  
Order Approximation ◽  
Eigenvalues And Eigenvectors ◽  
First Order ◽  
First Order Approximation
Sign in / Sign up

Export Citation Format

Share Document