Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
5
1
2013
LARGE-EDDY SIMULATION OF A BUOYANT PLUME PAST A BLUFF BODY: EFFECTS OF FLOW STRUCTURES ON ENTRAINMENT CHARACTERISTICS
1-10
Hitoshi
Suto
Fluid Dynamics Sector, Civil Engineering Research Laboratory, Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko-city, Chiba, 270-1194, Japan
Yasuo
Hattori
Fluid Dynamics Sector, Civil Engineering Research Laboratory, Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko-shi,
Chiba, 270-1194, Japan
A large-eddy simulation of a buoyant plume past a bluff body (BB) is performed. The modified Rayleigh number based on the total heat input and the diameter of a BB is set at 1.2×1010. Distributions of basic statistics showed that the existence of a BB greatly varies the spatial structures of momentum and energy transport, although they gradually approached distributions corresponding to the similarity law for a fully developed plume when z/D > 2.5 (z: vertical position from a heat source, D: BB diameter) since the influence of a BB becomes weaker there. Then, the relationship between entrainment and flow structures was investigated and the entrainment coefficient was found to be locally large right above a BB owing to stationary horizontal flows and azimuthal vortices. Moreover, in the case of an insulated BB, some azimuthal vortices were formed in the process of developing a plume, 1.0 < z/D < 2.0, owing to both weak buoyancy and BB effects, and it is suggested that they are linked to the increase of entrainment there.
NUMERICAL ANALYSIS OF CONJUGATE NATURAL CONVECTION AND SURFACE RADIATION IN AN ENCLOSURE WITH LOCAL HEAT SOURCE
11-25
Semen G.
Martyushev
Faculty of Mechanics and Mathematics, Tomsk State University, Tomsk, 634050, Russia
Mikhail A.
Sheremet
Department of Theoretical Mechanics, Tomsk State University, 634050, Tomsk, Russia; Institute of Power Engineering, Tomsk Polytechnic University, 634050, Tomsk, Russia
Mathematical simulation of natural convection and surface radiation in a square cavity having heat-conducting walls of finite thickness with a heat source located at the bottom of the cavity in convective heat exchange with an environment has been carried out. Numerical analysis has been based on a solution of the two-dimensional Boussinesq equations in the dimensionless variables such as stream function, vorticity, and temperature. Main attention was paid to the effects of Rayleigh number 104 ≤ Ra ≤ 106, an emissivity of internal surfaces of walls 0 ≤ ε < 1, a thermal conductivity ratio 1 ≤ k1,2 ≤ 15, a thickness of walls 0.1 ≤ l/L ≤ 0.3, and a dimensionless time 0 ≤ τ ≤ 100 on the velocity and temperature fields. The effect scales of the key parameters on the average Nusselt numbers have been determined.
NUMERICAL SIMULATION OF MIXED CONVECTION FLOW OVER HEAT SOURCE MODULES MOUNTED ON A HORIZONTAL PLATE
27-41
K.
Venkatasubbaiah
Department of Mechanical Engineering, Indian Institute of Technology Hyderabad, Hyderabad, 502205, India
Abhishek
Anand
Department of Mechanical Engineering, Indian Institute of Technology Hyderabad, Hyderabad 502205, India
Mixed convection flow over heat source modules mounted on a horizontal plate has been studied numerically. The present analysis is valid when the buoyancy force effects are small compared to forced convection effects. The mixed convection flow problem is formulated by two-dimensional incompressible flow with the buoyancy term represented by the Boussinesq approximation. The governing equations are solved in the stream function and vorticity formulation using high accuracy finite difference schemes. Results are reported for single and two heat source modules mounted on a horizontal plate with and without thickness. The effects of induced velocity, heat input, thickness, and location of heat source modules on heat transfer rate and thermal field in the vicinity of heat sources are reported. Results have shown that there is a decrease of maximum temperature on heat source modules with increase in free-stream velocity of the fluid. Results show that the change of location and thickness of heat source modules has a significant effect on thermal flow field characteristics. The maximum temperature and average Nusselt number on heat source modules are reported at different parameters. The reported results agreed well with experimental results available in the literature.
ON THE STEADY AND UNSTEADY ASPECTS OF COMBINED SORET EFFECT AND DOUBLE-DIFFUSIVE CONVECTION IN A BENARD SQUARE CAVITY SUBMITTED TO A HORIZONTAL GRADIENT OF CONCENTRATION
43-61
Mohamed
Lamsaadi
Sultan Moulay Slimane university, Faculty of Sciences and Technologies, Physics Department, UFR of Sciences and Engineering of Materials, Team of Flows and Transfers Modelling (EMET), B.P. 523, Béni-Mellal, Morocco
Mohamed
Naimi
Faculty of Sciences and Technologies, Physics Department, Laboratory of Flows and Transfers Modeling (LAMET), Sultan Moulay Slimane University, B.P. 523, Beni-Mellal, Morocco
H.
El Harfi
Faculty of Sciences and Technologies, Physics Department, Laboratory of Flows and Transfers Modeling (LAMET), Sultan Moulay Slimane University, B.P. 523, Beni-Mellal, Morocco
Abdelghani
Raji
Sultan Moulay Slimane university, Faculty of Sciences and Technologies, Physics Department, UFR of Sciences and Engineering of Materials, Team of Flows and Transfers Modelling (EMET), B.P. 523, Béni-Mellal, Morocco
Mohammed
Hasnaoui
Cadi Ayyad University, Faculty of Sciences Semlalia, Physics Department, UFR TMF, Laboratory of Fluid Mechanics and Energetics (LMFE), B.P. 2390, Marrakech, Morocco
In this paper, a numerical study of the incidence of Soret effect on double-diffusive convection in a Benard square cavity submitted to a horizontal gradient of concentration is presented. The computations, which are limited to water-based solutions, are carried out for governing parameters; namely, the Lewis number, Le; Soret parameter, M; buoyancy ratio, N; Prandtl number, Pr; and thermal Rayleigh number, RaΤ; such that Le = 10, −111 ≤ M ≤ 122, −0.1 ≤ N ≤ 0.1, Pr = 7, and 5 × 104 ≤ RaΤ ≤ 5 × 105. In such a situation it is possible to discover a wide variety of steady-state solutions that are stable up to a threshold value of M. The effect of M on the flow, temperature, and concentration fields and the resulting heat and mass transfers are analysed for given values of N and RaΤ. It is demonstrated that the heat and mass transfers could change significantly from one solution to another, depending on M. Moreover, particular attention is paid to the oscillatory behavior of the convection that appears for M in the ranges M < −50.2 (for vertical bicellular flow) and M < −23.8 (for horizontal bicellular flow) and at specific values of N and RaΤ.
EFFECTS OF DIFFERENT TURBULENT DISPERSION AND SPRAY BREAKUP MODELS ON THREE-DIMENSIONAL MODELING OF IN-CYLINDER FUEL SPRAY
63-72
Reza
Kamali
Department of Mechanical Engineering, Shiraz University, Shiraz, Iran
M.
Mofarrahi
Department of Mechanical Engineering, Shiraz University, Shiraz, Iran
Spray and mixture formation processes are known to play a pivotal role in determining combustion and emissions in diesel engines. The purpose of this study is to numerically investigate the effects of various spray breakup and turbulent dispersion models on fuel spray characteristics as well as on in-cylinder pressure in Caterpillar heavy duty diesel engines by using the computational fluid dynamics (CFD) simulation. The domain considers only one-sixth of the combustion chamber because the chamber geometry is symmetric and a six-hole injector is used. Furthermore, the simulation is performed from intake valve closing (IVC) to exhaust valve opening (EVO) when the engine works at steady conditions. In the present study, these models are numerically investigated and compared and some possible reasons for the differences between their related results are discussed. The simulation results show the significant influence of different spray breakup and turbulent dispersion models on fuel spray penetration. Experimental data have been used to validate the numerical results.
ANALYTICAL SOLUTION FOR NATURAL CONVECTION HEAT TRANSFER ABOUT A VERTICAL CONE IN POROUS MEDIA FILLED WITH A NON-NEWTONIAN Al2O3-WATER NANOFLUID
73-82
Alireza
Rasekh
Department of Flow, Heat and Combustion Mechanics, Faculty of Engineering and Architecture, Ghent University, Ghent, Belgium
Davood
Ganji (D.D. Ganji)
Babol University
S.
Tavakoli
Department of Mechanical Engineering, Babol University of Technology, Babol, Iran
This work deals with the problem of a steady free convection boundary layer flow over a downward pointing vertical cone in a porous medium saturated with a non-Newtonian Al2O3-water nanofluid under various prescribed surface temperature thermal boundary conditions. The governing partial differential equations are transformed into ordinary differential equations, employing a similarity approach and are then solved through the optimal homotopy analysis method (optimal HAM). The effects of the parameters involved, such as nanoparticle volume fraction and prescribed temperature parameter on temperature distribution on the surface of the cone and heat transfer characteristics for a non-Newtonian power-law nanofluid with different values of the power-law viscosity index have been studied. Results show that the rate of natural convection heat transfer deteriorates in the presence of Al2O3 nanoparticles, in particular under constant surface temperature conditions (m = 0). Furthermore, the rate of heat flux is highest in the case of dilatant nanofluid, i.e., when the power-law index is equal to 2 (n = 2).
INFLUENCE OF THREE-DIMENSIONAL PERTURBATIONS ON HEAT TRANSFER IN HYPERSONIC FLOW
83-95
Ivan Vladimirovich
Egorov
Central Aerohydrodynamic Institute (TsAGI), 1, Zhukovsky Str., Zhukovsky,
Moscow Region, 140180, Russian Federation
Natalia
Palchekovskaya
Moscow Institute of Physics and Technology, Institutsky pereulok 9, Dolgoprudny, Moscow
Region, 141700, Russia
Vladimir Viktorovich
Shvedchenko
Central Aerohydrodynamic Institute (TsAGI) , Zhukovsky, Moscow region, Russia
The present paper deals with the three-dimensional flow in a shock layer at supersonic transverse flow conditions over the front surface of a cylinder and a sphere under small, spatially periodic perturbations along the transverse coordinate. Based on the numerical solution of the unsteady three-dimensional Navier−Stokes equations, it is shown that small imposed perturbations of the free-stream velocity (0.5−3 %) along the transverse coordinate lead to the shock curvature and cause the formation of vortex structures in the shock layer and significant perturbations of the heat flux on the surface.