CFD Simulation of Large Dust Collection Cyclones Positioned Vertically in Staggered Downward Cascade Arrangement

Three dimensional, time dependent Euler-Euler simulation approach for numerical calculation of multiphase strongly swirling turbulent gas-heavy laden particulate flow in large industrial collection cyclones, positioned vertically, in staggered downward cascade arrangement has been performed. The multiphase flow was featured high mass loading. This paper specifically addresses a CFD modeling of a “suspension preheater”, typical equipment for dry process cement kiln. Big sized cyclone separator is a key component of this device. The simulation case study was developed in the frame of the commercial general-purpose code ANSYS-Fluent R13. In cyclone separators the swirling gas motion induces a centrifugal force on the solid particulate phase which is the driving force behind the separation process. The turbulence disperses the solid particulates and enhances the probability that particles are discharged, as reject. Both phenomena are related to solid phase particle size distribution (PSD) and flow pattern into the collection cyclones. The multiphase turbulence was modeled using the RSM Mixture Turbulence Model. The simulation results were validated against industrial measurements carried out on an industrial suspension preheater, in the frame of heat and mass balance of cement kiln energy audit. The numerical simulation results were found in reasonable agreement with the collected industrial measurements. This CFD simulation represents a powerful engineering tool on behalf of the cement process engineer either for new cutting-edge design or for performance verification of an existing plant.

Implications of Using Dual Number Derivatives With a Numerical Solution

Dual number arithmetic is a well-known strategy for automatic differentiation of computer codes which gives exact derivatives, to the machine accuracy, of the computed quantities with respect to any of the involved variables. A common application of this concept in Computational Fluid Dynamics, or numerical modeling in general, is to assess the sensitivity of mathematical models to the model parameters. However, dual number arithmetic, in theory, finds the derivatives of the actual mathematical expressions evaluated by the computer code. Thus the sensitivity to a model parameter found by dual number automatic differentiation is essentially that of the combination of the actual mathematical equations, the numerical scheme and the grid used to solve the equations not just that of the model equations alone as implied by some studies. This aspect of the sensitivity analysis of numerical simulations using dual number auto derivation is explored in the current study. A simple one-dimensional advection diffusion equation is discretized using different schemes of finite volume method and the resulting systems of equations are solved numerically. Derivatives of the numerical solutions with respect to parameters are evaluated automatically using dual number automatic differentiation. In addition the derivatives are also estimated using finite differencing for comparison. The analytical solution was also found for the original PDE and derivatives of this solution are also computed analytically. It is shown that a mathematical model could potentially show different sensitivity to a model parameter depending on the numerical method employed to solve the equations and the grid resolution used. This distinction is important since such inter-dependence needs to be carefully addressed to avoid confusion when reporting the sensitivity of predictions to a model parameter using a computer code. A systematic assessment of numerical uncertainty in the sensitivities computed using automatic differentiation is presented.

Effect of Rotor-Stator Configuration in the Generation of Vortical Scales and Wake Mixing in Single Stage Axial Fans: Part II — Assessment of Vortex Sound Sources

This second part is devoted to the identification of vortex sound sources in low-speed turbomachinery. As a starting point, the time-resolved evolution of the vortical motions associated to the wake shear layers (reported in the first part of the present study) is employed to obtain vorticity distributions in both blade-to-blade and traverse locations throughout the axial fan stage. Following, the Powell analogy for generation of vortex sound is revisited to obtain the noise sources in the nearfield region of the fan. Both numerical and experimental databases presented previously are now post-processed to achieve a deep understanding of the aeroacoustic behavior of the vortical scales present in the flow. A LES simulation at midspan, using a 2.5D scheme, allows an accurate description of the turn-out time of the shedding vortices, within high-density meshes in the blades and vanes passages, and a correct modeling of the dynamics of turbulence. Besides, thermal anemometry has been employed with a two-wire probe to measure the planar flow in the midspan sections of the fan. Statistical procedures and signal conditioning of velocity traces have confirmed experimentally the unsteady flow patterns devised in the numerical model. The comparison of the rotor-stator and the stator-rotor configurations provides the influence of the wake mixing and the nucleation of turbulent spots in the distribution of the Powell source terms. Moreover, the relation between the turbomachine configuration and the generation of vortex sound can be established, including the impact of the operating conditions and the contributions of the interaction mechanisms.

Calculation of Aerodynamic Noise for Centrifugal Fan of Air-Conditioner

Flow fields in a centrifugal fan for an indoor unit of an air-conditioner were calculated with finite element method-based large eddy simulation (LES) with the aim of predicting fan performance and aerodynamic noise in this study. The numerical simulation code employed throughout the LES was called FrontFlow/blue (FFB). We compared 10M grid [coarse grid] and 60M grid [fine grid] calculation results for investigation of influence of grid resolution. In the fine grid, the number of grid elements in blade-to-blade direction, and of region between the shroud and the bell mouth increased in particular. By calculating with the fine grid, calculated distributions of absolute velocities at blade exit reasonably agreed with experimental results. Because of this, maximum absolute velocity by fine grid near hub decreased as compared to those by coarse grid. Calculated sound pressure level by fine grid was therefore smaller than that by coarse grid, and the overestimation of sound pressure was suppressed by calculating with fine grid. This decrease of the absolute velocity was a first factor for the improvement of calculation accuracy. Moreover, number of captured streaks on the blade, hub, and shroud surfaces by fine grid increased as compared to those by coarse grid. As a result, size of streak by fine grid became smaller than that by coarse grid. Static pressure fluctuations by fine grid on the blade, hub, and shroud surfaces therefore reduced as compared to those by coarse grid. Aerodynamic noise was related to static pressure fluctuations according to Curle’s equation. This reduction of static pressure fluctuations was therefore a second factor for improvement of calculation accuracy.

Particle Transport in a Turbulent Square Duct Flow With an Imposed Magnetic Field

In this paper we study the particle transport and deposition in a turbulent square duct flow with an imposed magnetic field using Direct Numerical Simulations (DNS) of the continuous flow. A magnetic field induces a current and the interaction of this current with the magnetic field generates a Lorentz force which brakes the flow and modifies the flow structure. A second-order accurate finite volume method in time and space is used and implemented on a GPU. Particles are injected at the entrance to the duct continuously and their rates of deposition on the duct walls are computed for different magnetic field strengths. Because of the changes to the flow due to the magnetic field, the deposition rates are different on the top and bottom walls compared to the side walls. This is different than in a non-MHD square duct flow, where quadrant (and octant) symmetry is obtained.

An Approach on Fluid-Structure Interaction for the Prediction of Blood Flow in Aneurysms With Various Shapes

Recently, the rapid evolution of numerical methodologies for CFD and structural analyses has made it possible to predict the arterial hemodynamics closely related to vascular disease. In the present study, a framework for fluid-structure interaction (FSI) analysis was developed to accurately predict the arterial hemodynamics. The numerical results from the FSI analysis of the hemodynamics inside aneurysms of various shapes were compared to the results without FSI analysis. The results showed that FSI analysis needs to be performed in order to accurately predict the blood flow affected by the wall motion of compliant arteries. FSI analysis is essential to predict the hemodynamics in a saccular aneurysm because the arterial wall’s movement, which is a result of the variation of blood pressure in the aneurysmal sac, mainly produces the blood flow to a saccular aneurysm.

Development of High-Order Scheme in Unstructured Mesh for Direct Numerical Simulations

There has been a growing interest in higher-order spatial discretization methods due to their potential for delivering high accuracy at reasonable computational overhead for the Direct Numerical Simulation (DNS) of vortex-dominated flows. Many of the existing high-order schemes for unstructured grids use more degrees-of-freedom (DOF) in each cell to achieve high-order accuracy. This paper formulates and demonstrates a high-order correction method for unstructured grids. Using this approach, there is no increase in DOF within each cell. By adding higher order correction terms, higher order accuracy can be achieved. The present technique is innovative in that it can be readily added to existing lower order solvers, it can achieve very high-order accuracy, it is stable, and it can make use of either central or upwind schemes. Many examples are presented and used to demonstrate the high-order accuracy.

Reynolds Averaged Navier Stokes Models Compared to Direct Numerical Simulations in an Adverse Pressure Gradient Boundary Layer Over a Flat Plate

In Reynolds-Averaged Navier Stokes (RANS) models simplifying assumptions breakdown in near wall regions. Wall functions/treatments become inaccurate and the homogeneity and isotropy models may not hold. To see the effect that these assumptions have on the validity of boundary layer results in a commercially available RANS code, key boundary layer parameters are compared from laminar, transitional, and fully turbulent RANS results to an existing direct numerical simulation (DNS) simulation for flow over a flat plate with an adverse pressure gradient (APG). Parameters compared include velocity profiles in the free stream, boundary layer thicknesses, skin friction coefficient and the pressure gradient parameter. Results show comparable momentum thickness and pressure gradient parameters between the transition RANS model and the DNS simulation. Differences in the onset of transition between the RANS transition model and DNS are compared as well. These simulations help evaluate the models used in the RANS code. Of most interest is the transition model, a transition shear-stress transport (SST) k–omega model. The RANS code is being used in conjunction with an APG boundary layer experiment being undertaken at the Idaho National Laboratory (INL).

Computing Profiles of Porosity and Surface/Volume Ratio in a Packed Bed Using Monte Carlo Method

Porosity and surface/volume ratio are two important parameters for a packed bed. In cylindrical packed beds at low tube-to-particle diameter ratio, they vary greatly in the radial direction. In the existing literature, radial profiles of porosity and surface/volume ratio have been computed using some analytical equations which involve elliptic integrals. In this paper, a Monte Carlo method is used to compute those profiles. To the authors’ knowledge, the method has never been employed in this context. The procedure of using this novel method is explained in detail. Through a rigorous error analysis based on statistics, the accuracy of the simulation result can be controlled. Before any simulation, the number of sampling points needed in the Monte Carlo simulation can be determined given an accuracy requirement. The method is completely general and can be used to compute profiles of porosity and surface/volume ratio in any packed bed with any shape of packing elements.