High Temperature SMA Actuators for Aeropropulsion Applications

    A variety of demonstration efforts have illustrated the capabilities of low temperature NiTi for effective actuation devices. Because of the high temperatures associated with aeropropulsion applications, identification and application of high temperature SMA alloys becomes highly desirable. In spite of the developmental nature of HTSMA materials, several promising laboratory demonstrations of devices incorporating Pt-doped NiTi have taken place in recent work at CDI under NASA/Glenn sponsorship.

    One example is the use of Ni30Ti50Pt20 alloy developed and supplied by NASA/Glenn researchers to study adaptive variants of conventional fixed geometry aircraft engine "chevrons" - structures mounted just outside in the exhaust path of jet aircraft) can be constructed to introduce disturbances in the high speed/high temperature flow that reduce noise over a limited range of flight conditions but also imposes a small but significant performance penalty in cruise. An adaptive geometry chevron could be used to mitigate noise during take-off (possibly even more so than current fixed designs because of greater immersion into the exhaust stream) and could then be retracted during cruise so as not to affect performance.

Figure 1: Schematic overview of recent CDI activity on development of adaptive chevrons using HTSMA alloy actuators.

    Figure 1 summarizes recent development of demonstrator-level device design for an active chevron; the initial demonstration shown here represents an ~8% (of stiffness) full scale test and the substantial deflection achieved during the test is a reflection of the high force generation capability of the HTSMA. CFD/FEM analysis accurately predicted successful performance of the subscale bench test demonstration and indicates that the concept is scalable to full-size (stiffness) components that could operate under realistic conditions using the NiTiPt alloy. While demonstrated for convenience in a room temperature environment the SMA has a transition temperature of approximately 275 °C (527 °F) and could be used in ambient environments up to about those temperatures.

    These activities complement other work on HTSMA applications are currently underway at CDI, including studies of the design of inlet actuators for supersonic aircraft. Tests of these actuators in a supersonic wind tunnel are anticipated before the end of 2006.

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