Experimental and numerical studies have been performed to investigate the performance of a vertical gust generator in a wind tunnel. Results from both experimental Particle Image Velocimetry (PIV) and those from numerical simulations of low-Mach-numberpreconditioned compressible Naiver-Stokes equations on unstructured grids using high-order spectral difference (SD) agreed reasonably well with each other. The gust was generated by ducting flow through the floor of the wind tunnel and at the wall of the numerical domain. The gust velocity profile bends downstream when interacting with freestream causing the incoming freestream flow to bend upward. The vertical gust changed the effective angle of attack over the airfoil when interacting with the freestream velocity. Due to the interaction of gust over the airfoil, the stationary airfoil at a nominal zero degree angle of attack undergo flow separation under stalled conditions. I. Nomenclature Re= Reynolds Number c = chord Δt = time step t* = convective time ∞ = freestream velocity = gust velocity

Note: This paper is part of the special topic, Tribute to Frank M. White on his 88th Anniversary.

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In this paper, a numerical study is conducted to understand the impact of nonuniform freestream on the aerodynamic performance of a flapping foil. Specifically, an unsteady flow environment is generated by stationary inline or staggered circular cylinder arrays upstream. A 2D NACA0012 airfoil is then placed at different locations downstream of the cylinder arrays, and oscillates in the nonuniform freestream. Unsteady flows over the flapping foil are numerically simulated by solving the 2D low-Mach-number-preconditioned compressible Naiver-Stokes equations on deformable unstructured grids using the high-order spectral difference method. The flow fields over a pitching airfoil in unsteady flow environments and the corresponding aerodynamic forces are analyzed and compared under different flow conditions. It is observed that the nonuniform freestream can significantly affect the unsteady vortex dynamics of a flapping foil, thus modifying the thrust and lift generation.

In this paper, both experimental and numerical studies have been performed on the convective boiling heat transfer of the Ethanol-in-Polyalphaolefin (PAO) Nanoemulsions inside a heat exchanger of twelve 1mm diameter mini-channels that was subjected to a uniform heat flux at its outer surface. The heat transfer characteristics and the pressure drop of the Ethanol/PAO nanoemulsion was studied experimentally, meanwhile, the volume of fraction (VOF) model with Pressure-Velocity coupling based Semi Implicit Method for Pressure Linked Equations (SIMPLE) iterative algorithm is employed to simulate the same experimental conditions numeircally. The results reveal that the convective boiling heat transfer coefficient of the nanoemulsion can be greatly enhanced upon the nucleation of ethanol nanodroplets inside, in which a maximum 50% enhancement compared to pure PAO base fluid can be achieved under current test conditions. However, the thermal conductivity and viscosity of the nanoemulsions has an insignificant effect on convective boiling heat transfer coefficient based on the experimental results. The ANSYS FLUENT simulation results also agree well with the experimental data. The Ethanol-in-PAO nanoemulsion could function as a good alternative conventional working fluid in two phase heat transfer applications.