Flow Simulation

Objective: Reduction of NOx at Calciner outlet by primary measures through CFD fluid flow analysis study

1. Actual Process data (Boundary conditions for implementation of CFD consulting services, Coal analysis, Particle size, NOx emissions, Temperatures, flow etc) collection from plant

2. 3D Geometry preparation: Drawings collection, the study of drawings and 3D Geometry created using Ansys DM. Confirmation of Geometry by comparing it with photos received from plant

3. Meshing: Using ICEM for the airflow modeling, the whole geometry is divided into several million small volume elements (mesh/grid) to facilitate the multiphysics modeling.

In this fluid dynamic simulation case, the whole geometry is divided into more than 4 million volume elements. Prism, Tetra, and Hex meshing done

4. Fixing of solver parameters

To solve the complex mathematical equations for the fluid flow simulation, like Navier-Stokes equation and turbulence models, CFD simulation solver parameters need to be given for a convergent solution during the steady-state thermal analysis. These parameters when given correctly facilitate the problem solving of the multiphysics simulation.

5. Preparation of Case file

Once all the physics and model parameters are identified for the fluid dynamic analysis, all the above ingredients are combined to prepare a case file for the CFD modeling simulation.

6. Case file simulation

Case files prepared in the Ansys Fluent CFD simulation software are solved on the 128 processor cluster as mentioned above.

During the post-processing or analyzing fluid-structure interaction results, the results file generated by the fluid simulation software is analyzed using the post-processing tool provided by the ANSYS Fluent software.

– The Existing NOx emissions at the plant was found through CFD computational fluid analysis study

– Coal firing nozzle changed to CombEff FD nozzle and followed above procedure from a to h points. Estimated NOx after firing nozzle changed

– NOx reduction – 10%

This is a parametric CFD consulting study using Vortex Generators VGs, fitted internally into a pipe, to generate longitudinal vortices which enhance the heat transfer performance of heat exchangers.

The enhancement during the transient thermal analysis was assessed based on the Nusselt number, friction coefficient, and thermal performance enhancement.  The dimensional parameters of the thermodynamics simulation included several attack angles and blockage ratios for a Reynolds number varying in the range 6000 to 33000.

The thermal performance enhancement (TPE) during the CFD thermal analysis is equal to the heat transfer coefficient with vortex generators over heat transfer coefficient without vortex generators.

The geometrical configuration of the FEM thermal analysis consisted of four VGs, fitted in a circular pattern inside a smooth pipe.  The different sets of delta winglets were characterized by four attack angles β (0°, 15°, 30° and 45°) and three blockage ratios B (0.1, 0.2 and 0.3). As part of the FSI simulation, the flow was assumed 3D, turbulent and steady during the CFD flow analysis.  The turbulent flow was numerically simulated using the Shear Stress Transport SST k-omega model.  The smooth-pipe flow was validated with empirical formula during the turbulent flow simulation.

A no-slip condition was applied to the walls of the VGs and the inner surface of the pipe as part of the CFD design setup.  A constant heat flux of 694 W/m2 was imposed at the pipe inner surface while a zero heat flux was assumed on the FSI analysis of the VGs. Grid independence test was conducted to eliminate any undesirable effects of the mesh. The Nusselt number and friction factor were validated with empirical correlations for smooth pipes.

The combination β45-B0.3 generates the highest heat transfer increase and the highest frictional effect as well. However, the thermal simulation configuration β30-B0.1 generated the highest thermal performance enhancement (TPE) due to the low friction it generates.  The corresponding flow structure of each thermal analysis configuration was explored in detail to explain the causes of heat transfer enhancement or deterioration.

In the past half of a century, the lid-driven cavity flow has been served as a classical benchmark problem to validate the numerical methods for incompressible fluid flow. The turbulence modeling for CFD exhibits almost all phenomena that possibly exist in incompressible flow: eddies, secondary flows, instabilities, chaotic particle motions, transition, and turbulence.

Most of existing CAE services are focused on the square cavity. But in our nature, the cavity may have complex geometries, such as rectangular, triangular and semi-elliptical cavities. In this project work, the lid-driven flows of 2D semi-elliptical cavity are simulated. Furthermore, the effect of aspect ratio on the oscillatory instability is presented. When the Reynolds number is larger than the steady-oscillatory transition value, which is an important criterion for keeping the steady state, the fluid flow in the semi-elliptical cavity would become turbulent.

The multi-relaxation time lattice Boltzmann method (MRT-LBM) is applied to simulate the lid-driven flows in the semi-elliptical cavity with different aspect ratio, which resides in the range of 1.0-3.0. In recent years, the LBM has been developed into a promising and successful alternative to the conventional computational fluid dynamics simulation method. It models the fluid to fictive particles by using discrete distribution functions, these particles would perform consecutive collision and streaming processes over a discrete lattice mesh. Due to its particulate nature and local dynamics, LBM owns several advantages over traditional CFD methods, especially the intrinsic parallelism of algorithm and data structure. Then in this study, the parallelization of LBM code is realized by using the Graphical Processing Unit (GPU) through the Compute Unified Device Architecture (CUDA).

In this computational fluid dynamics analysis study, a novel efficient CUDA implementation of MRT-LBM has been developed to investigate the vortex structure and oscillatory instability in the lid-driven flows of a semi-elliptical cavity. The computational platform is NVIDIA Tesla K40c GPU. The simulation results indicate that the parallel efficiency of CUDA program is strongly dependent on the grid size. In the current study, the maximum speedup of GPU implementation is 47.6 times faster than the same LBM simulation on Intel Xeon E5 CPU for the grid size 1024×1024. Regarding the oscillatory instability, for aspect ratios K= 1.0, 2.0, 3.0, the simulation results indicate that the steady-oscillatory transition Reynolds numbers reside in the ranges of 7250-7300, 5650-5700 and 5200-5250, respectively. They correlate negatively with the aspect ratio. Moreover, these transition Reynolds numbers are smaller than those of rectangular cavity at the same aspect ratio. In addition, within one period, it is found that the main changes of vortex structure reside in the left top vortices, which would split and merge periodically.

In terms of aerodynamics simulation problems, our CFD engineers simulated the flow around smooth and rough domes using Large Eddy Simulation Proceedings of the Institution of Mechanical Engineers. The objective was to investigate the possibility of generating an artificially roughened surface which can exist in practical applications.

Large eddy airflow Simulation, in conjunction with the dynamic Smagorinsky–Lilly SGS model, was used to simulate the flow around both smooth and rough external surfaces of domes.  The dome was roughened by creating alternate small squares on the surface and extruding them according to the appropriate roughness required for the study. The approach was adopted to overcome the lack of appropriate near-wall models for hydraulically non-smooth walls in the framework of LES. The domes were submerged in a boundary layer. A multi-block hybrid mesh of hexahedral and tetrahedral cells was generated.  The computational domain was divided into about 9 million computational cells.  The governing equations used for the air dispersion modeling were solved using ANSYS FLUENT 12.0. The integration time step was 10-4 s to ensure a cell Courant number in the domain less than 2 as recommended in the literature.

It was found during the CFD analysis that the approach of roughening the surface of the dome could yield relatively good results in terms of quantifying the wake characteristic dimensions.  The pressure coefficient distribution along the centerline of the dome was predicted with very good accuracy. The LES model provided useful information through the visualization of interesting features of the flow which are difficult to observe experimentally at such high Reynolds numbers.  A flattened horseshoe vortex developed around the rough dome shifting away from the dome compared to the smooth dome. A larger wake, with higher vorticity content, was observed for the rough dome.

The objective was to improve the efficiency of Cyclone through CFD study. This is achieved by optimizing the k-epsilon turbulence model for shock-turbulence interaction in our in-house compressible solver.

Conservative form of the k-epsilon equation which is conserved across the discontinuities in the flow was formulated.

a. Actual Process data (Boundary conditions for CFD study, cyclone inlet velocity, Particle size, temperatures etc) collection from plant

b. 3D Geometry preparation: Drawings collection, the study of drawings and 3D Geometry created using Ansys DM. Confirmation of Geometry by comparing it with photos received from plant

c. Meshing: Using ICEM the whole geometry is divided into several million small volume elements (mesh/grid).

In this case, the whole geometry is divided into more than 3 million volume elements. Prism, Tetra, and Hex meshing done

Conservative form of the k-epsilon equation, predicted the TKE jump across the shock accurately without any numerical errors, as the Mach number tends to the high supersonic regime and hypersonic regime.