Integrating pressure in CFD simulations to compute force

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Hi! I am working on a vertical-axis wind turbine and I'd like to compute the forces exerted on its blades by the wind. In order to do so, I am performing CFD simulations on my wind turbine in the following manner: I Import my 3D geometry from SolidWorks, then I build a block to simulate wind tunel, I set up acrylic plastic and air as materials for the wind turbine and wind tunel respectively. Finally, I add laminar flow physics and set up its boundary conditions with an inlet wind speed of 2.04 m/s. No turbulence model is used. Then, to compute forces, I am integrating the pressure magnitude (p) along to the normal of the surface of each of the blades of the wind turbine. From doing this, I expect to get positive pressure, and therefore, positive force on the surfaces labeled as 1,2 and 3 (see Figures attached), which are the blades surfaces where the wind impacts directly (1 and 2) and where part of the wind flow is deviated (3). But I am actually getting negative values of pressure and force in the blade 3. Does anyone know why I am getting negative values of pressure and force on the sides of the blades that are "behind" the wind flow? I'd appreciate any help, thanks.


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