Pre-stressed piezoelectric unimorphs are widely used in many engineering field due to their good actuation performances. They are manufactured by using stress mismatch of adjacent layers, which results in the domed shape and internal stress profile of the piezoelectric layer. The internal stress of the piezoelectric layer can affect the actuation performance of the pre-stressed piezoelectric unimorph significantly. This paper investigates the effect of mechanical pre-stress on the piezoelectric actuation characteristics, and evaluated the actuation performance of a new pre-stressed actuator developed by the present authors, PUMPS, considering the internal stress effects.

A three-dimensional numerical simulation was conducted to study an effect of the inlet boundary layer thickness on the rotating stall in an axial compressor. The inlet boundary layer thickness had significant effects on the hub-corner-separation in the junction of the hub and the suction surface. The hub-corner-separation grew significantly for the thick inlet boundary layer as the load was increased, while it was diminished to be indistinguishable from the rotor wake for the thin inlet boundary layer and a new corner-separation was originated near the casing. The difference in the internal flow at the near stall condition also had a large effect on characteristics of the rotating stall, especially the first asymmetric disturbance and the size of the stall cell. While a pre-stall disturbance arises firstly in the hub-corner-separation for the thick inlet boundary layer, an asymmetric disturbance was initially generated in the tip region because of the corner-separation for the thin inlet boundary layer. This disturbance was transferred to the tip leakage flow and grew to be an attached stall cell. When this attached stall cell reached a critical size, it moved along the blade row and became a short-length-scale rotating stall. The size of the stall cell for the thick inlet boundary layer was larger than that for the thin inlet boundary layer. The difference of the stall cell’s size affected the performance of the single rotor, causing large performance drop for the former case but a continuous performance change for the latter case.

This paper proposes a new fabrication method for a curved shape piezoelectric actuator. Instead of using thermal coefficient mismatch, which has been used for conventional processes for curved shape actuators, we used pre-stressed substrates and the room temperature adhesion process. First, a substrate material is strained in the longitudinal direction, and then a piezoelectric material is attached on the substrate. A difference of the mechanical strains between the substrate and the piezoelectric layer makes the final manufactured actuator get curved. Using this method, the curved shape actuator can be easily fabricated at room temperature. Several performance tests of the proposed unimorph actuators were accomplished and the test results showed the proposed actuator got comparable actuation capability compared with conventional curved shape actuators.