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The wake behind a sphere, rotating about an axis aligned with the streamwise direction, has been experimentally investigated in a low-velocity water tunnel using LIF visualizations and PIV measurements. The measurements focused on the evolution of the flow regimes that appear depending on two control parameters, namely the Reynolds number Re and the dimensionless rotation or swirl rate Ω, which is the ratio of the maximum azimuthal velocity of the body to the free stream velocity. In the present investigation, we cover the range of Re smaller than 400 and Ω from 0 and 4. Different wakes regimes such as an axisymmetric flow, a low helical state and a high helical mode are represented in the (Re, Ω) parameter plane.

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INTRODUCTIONPredicting and controlling the motion of rainwater over the exterior of road vehicles, EWM, is an important consideration for vehicle designers. Phenomena such as A-pillar overflow can obscure a driver's vision and droplets or rivulets falling on passengers or their belongings can be a significant source of customer dissatisfaction.There are a wide range of engineering applications involving the flow of liquid films, rivulets and droplets over solid surfaces. For example, water or ice on an airplane wing can significantly interfere with its overall performance [1,2]. Rivulets are also observed in coating flows in the chemical industry [3]. In the automotive sector examples of EWM simulations can be found in [4] and [5] that both use Lagrangian particle tracking for the airborne droplets and a simple 2D film model for the surface flow. While the approach to the dispersed phase (airborne) may be satisfactory, the assumption that the surface flow can be modelled using a 2D film has limitations. These 2D film models, details of which can be found in [6] for example, solve transport equations for the film thickness but make no attempt to resolve the 3D shape of the surface water. Using such film methods behaviour such as film-stripping and breakup can only be modelled empirically, with the results being valid within certain flow regimes. More fundamentally the two-way interaction between the aerodynamic drag on the water and the shape of the water feature cannot be predicted using such methods.The objective here is to develop and demonstrate a computational method that can capture the underlying physics and predict the motion of various liquid flow features on the exterior surface of vehicles. By predicting the resolved 3D shape of the droplet it is hoped that this will be more general than existing thin film models. By resolving water features fully in 3D it is possible to predict droplet breakup or coalescence without the need for empirical modelling as is the case for film models. ABSTRACTThe motivation for this paper is to predict the flow of water over exterior surfaces of road vehicles. We present simulations of liquid flows on solid surfaces under the influence of gravity with and without the addition of aerodynamic forces on the liquid. This is done using an implementation of a Coupled Level Set Volume of Fluid method (CLSVOF) multiphase approach implemented in the open source OpenFOAM CFD code. This is a high fidelity interface-resolving method that solves for the velocity field in both phases without restrictions on the flow regime. In the current paper the suitability of the approach to Exterior Water Management (EWM) is demonstrated using the representative test cases of a continuous liquid rivulet flowing along an inclined surface with a channel located downstream perpendicular to the oncoming flow. Experimental work has been carried out to record the motion of the rivulet in this case and also to measure the contact angle of the liquid with the solid surface. The measurements of the liquid/...