Heat Transfer in Reacting Cooling Films: Part II — Modelling Near-Wall Effects in Non-Premixed Combustion With OpenFOAM

2014 ◽  
Author(s):  
Gabriele Frank ◽  
Stephanie Pohl ◽  
Michael Pfitzner
Keyword(s):  
Heat Losses ◽  
Premixed Combustion ◽  
Rate Data ◽  
Laminar Cooling ◽  
Finite Rate ◽  
Ansys Fluent ◽  
Defect Parameter ◽  
Flamelet Model ◽  
Definition Of ◽  
Near Wall

To account for heat losses near cooled walls an extension of the flamelet model is proposed based on an enthalpy defect parameter. A definition of the enthalpy defect and its transport equation is introduced. The inclusion of the enthalpy defect into the flamelet generation and the integration in terms of a probability density function for this parameter is discussed. The near wall extension is implemented into the OpenFOAM architecture and compared to ANSYS Fluent finite rate data for a testcase of a reacting laminar cooling film over a cooled flat plate. The near wall extension seems to improve the predicted heat flux compared to the original flamelet model, but profound validation was not possible due to a lack of suitable experimental or DNS data so far.

Large-Eddy Simulation of Combustion Oscillation in Premixed Combustor

1999 ◽  
Author(s):  
Tomoya Murota ◽  
Masaya Ohtsuka
Keyword(s):  
Large Eddy Simulation ◽  
Present Method ◽  
Premixed Combustion ◽  
Compressible Turbulence ◽  
Flamelet Model ◽  
Turbulent Premixed Flame ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Combustion Oscillation ◽  
Combustion Flow

To analyze combustion oscillation in the premixed combustor, a large-eddy simulation program for premixed combustion flow was developed. The subgrid scale (SGS) model of eddy viscosity type for compressible turbulence (Speziale et al., 1988) was adopted to treat the SGS fluxes. The fractal flamelet model, which utilizes the fractal properties of the turbulent premixed flame to obtain the reaction rate, was developed. Premixed combustion without oscillation was analyzed to verify the present method. The computational results showed good accordance with experimental data (Rydén et al., 1993). The combustion oscillation of an “established buzz” type in the premixed combustor (Langhorne, 1988) was also analyzed. The present method succeeded in capturing the oscillation accurately. The detailed mechanism was investigated. The appearance of the non-heat release region, which is generated because the supply of the unburnt gas into the combustion zone stagnates, and its disappearance play an important role.

scholarly journals METHODS OF CFD MODELLING OF TWIN-SCREW PUMPS FOR NON-NEWTONIAN MATERIALS

2021 ◽  
Vol 2021 (6) ◽  
pp. 5366-5372
Author(s):  
MARIAN BOJKO ◽  
◽  
LUKAS HERTL ◽  
SYLVA DRABKOVA ◽  
◽  
...  
Keyword(s):  
Power Law ◽  
Food Industry ◽  
3D Model ◽  
Design Parameters ◽  
Cfd Modelling ◽  
Ansys Fluent ◽  
Screw Pump ◽  
Twin Screw ◽  
Definition Of ◽  
Power Law Parameters

The twin-screw pump is designed for pumping highly viscous materials in the food industry. Rheological characteristics of materials are important in the specification of design parameters of screw pumps. Analysis of flow in the twin-screw pumps with definition of non-newtonian materials can be made by numerical modelling. CFD generally oriented software ANSYS Fluent and ANSYS Polyflow has been used for modelling. In this study those software’s (ANSYS Fluent and ANSYS Polyflow) were defined for solution of flow in the twin-screw pumps. Results were compared for the same boundary conditions on the inlet and outlet of the 3D model. For definition of the viscosity were used the Nonnewtonian power law. Parameters as consistency coefficient and flow exponent for Nonnewtonian power law were analysed by software ANSYS Fluent and ANSYS Polyflow. Postprocessing form ANSYS Fluent and ANSYS Polyflow were made by contours of field and by graphs.

scholarly journals Recycling Heat Losses of an Oil-Immersed Transformer: Feasibility Study

2021 ◽  
Vol 21 (1) ◽  
pp. 48-54
Keyword(s):  
High Efficiency ◽  
Power Transformer ◽  
Heat Losses ◽  
Power Transformers ◽  
Passive Mode ◽  
Active Mode ◽  
Short Circuits ◽  
Definition Of ◽  
The Relationship ◽  
Novel Design

The paper investigates the feasibility of adding a liquid heater to an oil-immersed transformer. It proves that design the high efficiency of power transformers, losses due to idling and short circuits are substantial and are scattered in the environment as heat. The paper proposes a novel design that implements a liquid (coolant) heater to enable the unit not only to convert electricity, but also to generate heat. In order to analyze the feasibility of such heat recycling, the authors have developed an equivalent thermal circuit and a mathematical model thereof. Said heater can operate in two modes. In the passive mode, the coolant it contains only absorbs the heat emitted (lost) by the power transformer. In the active mode, it also receives the heat emitted due to the passage of electric current through the pipes of the heater. The paper further introduces the definition of heater efficiency. Studies have shown that up to 50 % of transformer heat losses can be recycled by heating the coolant in the heater. The paper presents the relationship between utilized heat and transformer losses, as well as heater efficiency as a function of coolant flow rate. The heater efficiency exceeds 90 % in the active mode.

An Investigation of Methane Combustion in a Rectangular Shaped Meso Chamber

2014 ◽  
Author(s):  
Mahbub Ahmed ◽  
Cheng Zhang ◽  
Scott McKay ◽  
Vivek Shirsat ◽  
Jobaidur Khan
Keyword(s):  
Cfd Simulation ◽  
Methane Combustion ◽  
Ansys Fluent ◽  
Flamelet Model ◽  
Power Generators ◽  
Rich Condition ◽  
Higher Power ◽  
Fluent Software ◽  
Finite Volume Approach ◽  
Power Densities

Hydrocarbon-based miniature power generators are promising any many application since hydrocarbon based fuels have higher power densities compared to conventional lithium batteries. A 40mm long meso-combustor of two different configurations, two-inlet and three-inlet, were used to investigate the combustion of methane in the meso-chamber. A non-premixed combustion of methane and oxygen was simulated numerically using a steady laminar flamelet model. The mesh generation and the CFD simulation were performed using ANSYS FLUENT software. A a finite volume approach was used for the simulation. The fuel-oxidizer mixing, thermal behavior and fuel burning efficiency were studied. An adequate mixing that supports the combustion was observed in certain locations. The exhaust gas was analyzed experimentally. The temperature distributions were also observed to predict the flame locations. According to the numerical analysis it was apparent that the flame would be anchored in the well mixed regions of the chamber the flames were found to be attached in two distinct locations. One in the upstream zone and the other one in the downstream zone. Another important finding was that the fuel lean condition produced higher efficiency than the fuel rich condition.

Study of the Gas Combustion LP in an Atmospheric Burner

2008 ◽  
Author(s):  
Armando Gallegos-Mun˜oz ◽  
Armando Balderas-Bernal ◽  
Alejandro Rami´rez-Barro´n ◽  
J. C. Prince-Avelino
Keyword(s):  
Fluid Dynamic ◽  
Premixed Combustion ◽  
Experimental Results ◽  
Experimental Measurements ◽  
Finite Rate ◽  
Gas Combustion ◽  
Finite Speed ◽  
Computational Fluids Dynamics ◽  
Computational Fluids ◽  
Laminar Flamelet

The study of the gas combustion LP in an atmospheric burner to bake ceramics is presented. The study includes different models from combustion and turbulence to find the best interaction chemistry-turbulence, applying Computational Fluids Dynamics (CFD) through FLUENT®. For the study different models of combustion were considered, where the finite speed of the reaction is important by means of kinetic chemistry from Arrhenius. The different models of combustion were; a generalized model of speed of Finite Rate/Eddy dissipation, non-premixed combustion Laminar Flamelet and Eddy dissipation. Each one of these models represents the combustion non-premixed of gas LP, to simulate the combustion of turbulent diffusive flames. For the study of the turbulence the model k-epsilon was applied. The results obtained for each combination turbulence-chemistry were compared with experimental measurements of temperature within the furnace. This comparison allowed making adjustments in the modeling of the process of combustion, identifying the best interaction between combustion and turbulence. According to the obtained results, the k-epsilon model represents adequately the fluid-dynamic development of the flame within the furnace. The models of combustion Finite Rate/Eddy dissipation and Laminar Flamelet show the best approach to the experimental results, where the k-epsilon model is applied to modeling the turbulence-chemistry interaction.

Applying the Representative Interactive Flamelet Model to Evaluate the Potential Effect of Wall Heat Transfer on Soot Emissions in a Small-Bore DI Diesel Engine

2001 ◽  
Author(s):  
Carl Hergart ◽  
Norbert Peters
Keyword(s):  
Heat Transfer ◽  
Diesel Engine ◽  
Wide Spectrum ◽  
Turbulent Flame ◽  
Combustion Process ◽  
Heat Losses ◽  
Wall Heat Transfer ◽  
Two Phase ◽  
Flamelet Model ◽  
Di Diesel Engine

Abstract Due to the wide spectrum of turbulent and chemical length- and time scales occurring in a HSDI diesel engine, capturing the correct physics and chemistry underlying combustion poses a tremendous modeling challenge. The processes related to the two-phase flow in a DI diesel engine add even more complexity to the total modeling effort. The Representative Interactive Flamelet (RIF) model has gained widespread attention owing to its ability of correctly describing ignition, combustion and pollutant formation phenomena. This is achieved by incorporating very detailed chemistry for the gas phase as well as the soot particle growth and oxidation, without imposing any significant computational penalty. The model, which is based on the laminar flamelet concept, treats a turbulent flame as an ensemble of thin, locally one-dimensional flame structures, whose chemistry is fast. A potential explanation for the significant underprediction of part load soot observed in previous studies applying the model is the neglect of wall heat losses in the flamelet chemistry model. By introducing an additional source term in the flamelet temperature equation, directly coupled to the wall heat transfer predicted by the CFD-code, flamelets exposed to walls are assigned heat losses of various magnitudes. Results using the model in three-dimensional simulations of the combustion process in a small-bore direct injection diesel engine indicate that the experimentally observed emissions of soot may have their origin in flame quenching at the relatively cold combustion chamber walls.

Analysis and modelling of subgrid-scale motions in near-wall turbulence

1998 ◽  
Vol 356 ◽  
pp. 327-352 ◽  
Author(s):  
CARLOS HÄRTEL ◽  
LEONHARD KLEISER
Keyword(s):  
Eddy Viscosity ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Large Eddy Simulations ◽  
Inverse Cascade ◽  
Large Eddy ◽  
Wall Flow ◽  
Definition Of ◽  
Subgrid Stress ◽  
Near Wall

A numerical study of turbulent channel flow at various Reynolds numbers (Reτ=115, 210, 300) is conducted in order to examine the requirements for a reliable subgrid modelling in large-eddy simulations of wall-bounded flows. Using direct numerical simulation data, the interactions between large and small scales in the near-wall flow are analysed in detail which sheds light on the origin of the inverse cascade of turbulent kinetic energy observed in the buffer layer. It is shown that the correlation of the wall-normal subgrid stress and the wall-normal derivative of the streamwise grid-scale velocity plays the key role in the occurrence of the inverse cascade. A brief a priori test of several subgrid models shows that currently applied models are not capable of accounting properly for the complex interactions in the near-wall flow. A series of large-eddy simulations gives evidence that this deficiency may cause significant errors in important global quantities of the flow such as the mean wall shear stress. A study of the eddy-viscosity ansatz is conducted which reveals that the characteristic scales usually employed for the definition of the eddy viscosity are inappropriate in the vicinity of a wall. Therefore, a novel definition of the eddy viscosity is derived from the analysis of the near-wall energy budget. This new definition, which employs the wall-normal subgrid stress as a characteristic scale, is more consistent with the near-wall physics. No significant Reynolds-number effects are encountered in the present analysis which suggests that the findings may be generalized to flows at higher Reynolds numbers.

Sign in / Sign up

Export Citation Format

Share Document