Turbomachinery blade design is based on an axisymmetric model assuming identical blades in the circumferential direction. The blade manufacturing process, however, has a finite accuracy leading to surface imperfections and therefore non-identical blades. This leads to a variation in each passage cross area effecting the aerodynamic performance of the turbine.
The simulation of multiple 3D CFD blade passages, nevertheless, is still computational expensive. However, if the effect of nonaxisymmetric blades is small enough to be approximated as linear, the adjoint method is an inexpensive alternative, which can be used in an industrial context. A set of 102 turbine vanes is used to model the manufacturing variations and assess the aerodynamic impact of up to eight nonaxisymmetric blade passages of a transonic high pressure turbine stage.
It is shown that the modeled blade passage results superimpose linearly. Therefore, the aerodynamic impact of surface imperfections can be evaluated by superpositioning the singlepassage results, which are generated by an adjoint computation.