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The impact angle of which a particle hits a wall is calculated by Fluent but not stored. To get access to this you will need to write a small UDF. In the UDF the angle can be accessed using the macro DEFINE_DPM_EROSION (called every time a particle hits a reflecting boundary) or be calculated inside the macro DEFINE_DPM_BC (called every time a particle hits a boundary (except symmetry or periodic boundary)). Inside one of these macros you can either directly write the information to a file or store in a particle user variable to be printed in another function. For an example on how to calculate the angle please take a look at the customization manual in section 2.5.1. DEFINE_DPM_BC. Alternatively the cosine of the angle is given by cos_a = NV_DOT(A,V)/(NV_MAG(A)*NV_MAG(V)) where A is the boundary face area and V the particle velocity vector. The angle is then alpha = acos(cos_a)