• Energy Research
• FR close
• BE close
• Computers & Fluids close

Abstract This paper deals with numerical study of the coupled fluid flow and heat transfer within a scraped surface heat exchanger “SSHEs”. The finite volume Fluent™ 6.3 code was used to solve continuity, momentum and energy equations in a real SSHE geometry using multiple rotating reference frame formulation. The mesh of a real SSHE geometry was achieved with Gambit™ 2.2.3, in order to take into account geometry singularities and their effect on the heat transfer performance within SSHE. The steady laminar non-isothermal flow of pure Glycerin, 2% CMC solution and 0.2% Carbopol solution were investigated. The cooling process without phase change within SSHE was studied. The heat correlation was established numerically and validated with the given literature heat correlations. The obtained numerical results agree well with given heat correlations in the literature. The numerical model was then used to examine in more details the heat performance of SSHE. The effect of the rotating velocity on the SSHE heat performance was investigated. For pure Glycerin, the increases on the rotating velocity significantly reduced the cooling process due to viscous heating. In the case of considered non-Newtonian fluids, increases on the rotating velocity improved the thermal efficiency of SSHE. The temperature profile a long of tip of blade, have shown an important influence of blade fixation on the heat performance within SHHE. Viscous heating was investigated and occurred for Newtonian viscous fluids. The numerical results have shown, in the case of Glycerin when the rotating velocity was ω = 9 rev s −1 , that the total energy can reach 25% more than without viscous heating. Finally, the study of the mixing time have shown a best heat performance when mixing time was equal to t mix = 6.72 s.

Abstract In this paper unsteady RANS computations are used to study the inception of rotating stall in a transonic centrifugal compressor taking into account realistic installation effects on performance, as commonly found nowadays due to space limitations. To this end, the effect of an ideal uniform inlet conditions (normally found for long straight inlet) is compared with inlet distortions generated by a bent pipe installed just in front of the impeller. The numerical techniques that have to be applied to correctly represent the rotating stall are explained in detail: all simulations are done modeling the whole annulus of the radial machine, using high performance computing to represent the non-periodic phenomena leading to the stall inception. Moreover, stable boundary conditions are employed, with the aim to avoid the inception of large unphysical surge cycles. When an uniform inlet flow to the compressor is considered, the formation of 8 blockage cells rotating in the same direction of the compressor is pointed out. On the other hand, when the elbow is installed in front of the impeller, the distorted flow suppresses the formation of a rotating stall pattern.

In Computational Fluid Dynamics (CFD) studies for the prediction of room airflow the Reynolds-averaged Navier-Stokes (RANS) approach is often used, in which only the averaged quantities are computed, whereas the effect of turbulence is modeled. Since the RANS approach does not provide information on the velocity and concentration fluctuations, turbulent mass transport is often modeled using the standard gradient-diffusion hypothesis, which relates the turbulent mass flux to the mean concentration derivatives. This paper presents a CFD analysis of pollutant dispersion in an enclosure ventilated by a transitional wall jet (Re ˜ 2,500), using validated high-resolution RANS and Large Eddy Simulations (LES). The LES simulations show that a counter-gradient turbulent mass flux is present, indicating that the standard gradient-diffusion hypothesis used in RANS is not valid in the entire flow domain. However, it is shown that for this particular case, the convective mass fluxes dominate over the turbulent mass fluxes, and that the predicted pollutant concentrations by RANS will therefore not differ significantly from the results obtained with LES.

We are interested in optimal design of 3D complex geometries, such as radial turbomachines, in large control space. The calculation of the gradient of the cost function is a key point when a gradient based method is used. Finite difference method has a complexity proportional to the size of the control space and the adjoint method requires important extra coding. We propose to consider the incomplete sensitivities method for optimal design of radial turbomachinery blades. The central point of the paper is how to adapt some formulations in radial turbomachinery to the validity domain of incomplete sensitivities. Also, we discuss on how to improve the accuracy of incomplete sensitivities using reduced order models based on physical assumptions. Fine/Turbo flow solver is coupled with gradient based optimization algorithms based on CAD-connected frameworks. Newton methods together with incomplete expressions of gradients are used. The approach is validated through optimization of centrifugal pumps. Finally the results are considered and discussed.

Abstract The present document is a corrigendum to the article “Characteristic modal shock detection for discontinuous finite element methods”.

Abstract Aerodynamic instabilities that naturally occur in compression systems, such as surge and rotating stall, largely reduce the life duration and performance of system components. The prediction of the compressor operating range is thus a key parameter for the design of gas turbines. This paper investigates the ability of an unsteady flow solver to simulate the rotating stall phenomenon in the full annulus of an axial compressor stage. A comparison with experimental data indicates that the simulation correctly estimates the stability limit. However the rotating stall flow patterns are different. While measurements show only one full span rotating stall cell (40 Hz), the simulation shows first a part span stall with 10 cells (790 Hz) that evolves then towards a full span stall with three cells (170 Hz). A spectral analysis based on numerical results underlines the role of rotor–stator interactions in the development of rotating stall. The effects of downstream volumes and inlet distortions are also discussed, showing the necessity to consider the whole geometry to correctly predict the rotating stall frequency.

Abstract This paper presents a collection of experiments in which we investigate the question of grid adaption for flame propagation problems. Local refinement or mesh deformation procedures are applied to a sample of spatial approximations, including finite elements, finite differences and spectral methods. Comparisons are performed using the simplified thermo-diffusive model and a more realistic model involving compressible aerodynamics and combustion.

A robust optimization procedure based on a multi-objective genetic algorithm (MOGA) is used to generate airfoil profiles for transonic inviscid flows of dense gases, subject to uncertainties in the upstream thermodynamic conditions. The effect of the random variations on system response is evaluated using a non-intrusive polynomial chaos (PC) based method known as the probabilistic collocation method (PCM). After initial PCM simulations which showed that the dense gas system was highly sensitive to input parameter variation, a multi-objective genetic algorithm coupled to the PCM produced a Pareto front of optimized individual geometries which exhibited improvements in mean performance and/or stability over the baseline NACA0012 airfoil. This type of analysis is essential in improving the feasibility of organic Rankine cycle (ORC) turbines, which are typically designed to recover energy from variable sources such as waste heat from industrial processes.