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International audienceThe design of efficient structures for heat and mass transfer problems involves the implementation of an appropriate topology optimization strategy in order to fully take into account the bi-objective nature of the problem. This article couples the finite-volume method (FVM), for the direct solver, with the discrete adjoint approach, for the sensitivity analysis, in order to tackle both fluid dynamic and heat transfer optimization in the frame of laminar flows. Details are provided about the sparsity pattern of the discrete adjoint system, which requires special attention to select a suitable matrix iterative solver. Several examples underline the adequacy of topology optimization in conjunction with the FVM for the minimization of the power dissipated by the fluid. Then, a bi-objective problem aiming at minimizing the pressure drop while maximizing the recoverable thermal power is solved by the identification of its Pareto frontier, thanks to an aggregate objective function (AOF) method. The main conclusion deals with the possibility of finding an acceptable trade-off between both objectives and the potential of topology optimization for heat and mass transfer optimization

The results of an experimental investigation of the instability of variable-density plane jets issuing into ambient air are reported. When the jet to ambient fluid density ratio S(Sϭ j / ϱ ) is less than a critical value, an intense oscillating instability is observed. This instability is characterized by sharp peaks in the power spectral density measured in the near field of the jet. The effects of the control parameters S, Re, and H/ ͑jet width to exit momentum thickness͒ on the instability regime are determined. It is shown that Re is a better scaling parameter than H/. The Strouhal number of the dominant mode St H increases with S and Re up to a constant value of 0.25, which is in rather good agreement with the theory and the experiments of Yu and Monkewitz ͓Phys. Fluids A 2, 1175 ͑1990͒; J. Fluid Mech. 255, 323 ͑1993͔͒. In the present experiments the critical value S c above which the oscillating regime disappears is an increasing function of Re and S c seems to reach a limiting value in the neighborhood of 0.7, which does not agree well either with the theory or with the experiments of Yu and Monkewitz ͓Phys. Fluids A 2, 1175 ͑1990͒; J. Fluid Mech. 255, 323 ͑1993͔͒. This difference is in qualitative agreement with the results of linear stability computations, also reported in the paper, which take into account differences in shape and relative positions of the density and velocity profiles.