SPractical impeller blades used to be designed for uniform upstream velocity distribution. Most of the problems seen at impeller blade's flow passage are caused at and near the tip radius of leading edge of impeller inlet. That is, separation of fluid particles from the blade surface is caused at and near the casing wall of leading edge of impeller inlet. It is well known that boundary layer is developed on the casing wall of conduit pipeline and axial component of velocity becomes small at and near the casing wall. Therefore, to improve the overall efficiency in practical operation of turbomachinery, improvement of fluids flow condition at casing wall, that is, boundary layer control just upstream of leading edge of impeller inlet is recommended. Some example grooves and notches are introduced.
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