Daniel Bougeard

Topology Optimization Using the SIMP Method for Multiobjective Conductive Problems

The efficient cooling of a finite-size volume generating heat, including adiabatic boundary conditions with the exception of a small heat sink, poses the problem of optimal allocation of high-conductivity material. Among the structural optimization methods, this article couples solid isotropic material with penalization parametrization (SIMP) with an aggregated objective function approach (AOF) to tackle this topology optimization problem through a multiobjective strategy. Both average and variance temperature-reduction problems is solved by the identification of Pareto fronts, which are highly dependent on the quantity of the high-conductivity material. This study also underlines the link between the sensitivity analysis of both objective functions, which is required by the method of moving asymptotes (MMA). Furthermore, additional calculations have been done to include variations in heat-generation rate between two conductive materials by means of an additional penalization strategy. The main conclusion deals with the possibility of finding an acceptable trade-off between average and variance objective functions thanks to the convex shape of Pareto frontiers.

Numerical analysis of the fin spacing effect on the horseshoe vortex system evolution in a two-rows finned-tube heat exchanger

Purpose – In finned-tube heat exchangers, the array of tubes generates three-dimensional vortices at fin-tube junctions. Theses vortices known as horseshoe vortex (HSV) system are responsible of flow mixing and heat transfer increase. The purpose of this paper is to focus on the effect of the fin spacing on the formation, the spatial evolution and dissipation of the HSV system at fin-tube junctions in a two-rows finned-tube heat exchanger. The global characterisation of the heat exchanger performance is also presented. Design/methodology/approach – The flow structure is numerically analysed through the use of computational fluid dynamics tools. The different vortices of the HSV system are highlighted and quantitatively analysed at each fin-tube junction with vorticity, wall shear stress analysis and two-dimensional streamline plots around tubes. Findings – The results show that the primary and secondary vortices of the HSV system have antagonistic behaviors with respect to the azimuthal angle variation. T...

Wall temperature fluctuations measurements downstream of a pipe junction using infrared thermography

Thermal fatigue issue is of concern when two flows with large temperature differences are mixing. In this study, a hot cylindrical pipe flow comes out in a cold main straight channel flow through an orthogonal junction to experimentally reproduce thermal stresses. This work aims to investigate temperature fields at the wall of two turbulent water flows mixing at a low velocity ratio (i.e. secondary pipe flow velocity to main flow velocity ratio). As infrared measurements are difficult to perform because of the semi-transparent properties of liquid water, we focus on the development of a specific infrared thermography procedure to get wall temperature fields downstream of the mixing region.

Infrared thermography for local Nusselt number estimation of an elliptical fin with a transient method

In this paper, a transient method involving an infrared (IR) set-up is used to investigate local heat transfer distribution over the fin of a staggered elliptical finned tube heat exchanger assembly. An experimental test bench was designed to record data during the fin cooling. The procedure of data preprocessing including IR camera calibration is presented. It allows extracting the temperature field evolution of the fin. These temperatures feed a numerical model that works with thermally thin material and takes into account lateral heat conduction and radiation with the surrounding. The heat transfer coefficient field is determined by integrating the model over time intervals that depend on space. Distributions of Nusselt number over the fin and their uncertainties are presented for several Reynolds numbers. The high resolution of the whole method and set-up allows detecting thermal imprints of developing horseshoe vortices.

Numerical simulation of the interaction between fluid flow and elastic flaps oscillations

Several numerical methods have been developed recently to solve problems including the interaction between viscous fluid flow and elastic solid structures. In this work, an in-house partitioned numerical solver is developed by using the open source C++ library OpenFOAM. Finite volume method is used to discretize the fluid flow problem on a moving mesh in an Arbitrary Lagrangian-Eulerian formulation and by using an adaptive time step. The structural elastic deformation is analyzed in a Lagrangian formulation using the St. Venant-Kirchhoff constitutive law. The solid structure is discretized by the finite volume method in an iterative segregated approach. The automatic mesh motion solver is based on Laplace smoothing equation with variable mesh diffusion. The strong coupling between the segregated solvers and the equilibrium on the fluid-structure interface are achieved by using an iterative implicit fixed-point algorithm with dynamic Aitken’s relaxation method. The solver is first validated on a benchmark largely used in the open literature. Then, a more complex case is studied including two elastic flaps immersed in a pulsatile fluid flow. The present solver predicts accurately the interaction between the complex flow structures generated by the flaps and the effect of the flaps oscillations on each other.Copyright