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UBC Theses and Dissertations

Geometric error evaluation of pressure and suction sides of airfoil sections Bhadauria, Rashmi


This thesis presents geometric computing algorithms for the evaluation of geometric errors on the pressure and suction sides of an airfoil section. Airfoil blades such as those in an impeller have a complex freeform geometry which poses significant challenges to the geometric error evaluation tasks. Reliable error evaluation is critical to the impellers as wrongful rejections will lead to significant financial losses. In practice, touch-probe coordinate measuring machines are employed to acquire measurement data points on the impeller blade surface along pre-specified sections. The measurement data points are then used to evaluate against the specified geometric tolerances including the profile tolerance and airfoil thickness control. Profile tolerances can be defined in three ways: bilateral asymmetric, bilateral symmetric, and unilateral. Existing methods for profile error evaluation are not capable of evaluating all three possible types of profile tolerance. These methods are not adaptive with respect to the specified tolerance zone boundaries. This thesis proposes a novel Scaled Minimax Method which is able to address all types of profile tolerance. The proposed method builds on the conventional Minimax Method and utilizes a scaling constant to control the relative positioning of the evaluated profile error zone boundaries. Thickness control is a less-known tolerance specification for airfoil sections. It controls the overall shape deviation of an airfoil section between the pressure and suction sides. The proposed evaluation method is based on determining a minimum error zone via simultaneously shrinking the outer boundary and growing the inner boundary for the involved measurement data points. Numerous case studies have been performed to validate the effectiveness of the proposed geometric error evaluation methods.

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