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Research Papers

# Design and Manufacture of a Morphing Structure for a Shape-Adaptive Supersonic Wind Tunnel Nozzle

[+] Author and Article Information
Craig A. Steeves, Peter T. Maxwell

Department of Materials, University of California, Santa Barbara, Santa Barbara, CA 93106

Katherine H. Timpano, Luigi Martinelli, Richard B. Miles

Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544

J. Appl. Mech 76(3), 031012 (Mar 11, 2009) (6 pages) doi:10.1115/1.3005572 History: Received September 10, 2007; Revised April 29, 2008; Published March 11, 2009

## Abstract

Aerospace vehicles with fixed geometry are designed to operate at a predetermined flight condition. Variation of the aerodynamic environment, such as during acceleration, climbing, or turning, from the design condition reduces the efficiency of the vehicle. It would be advantageous to be able to adapt the vehicle geometry to maintain efficient flight over a range of aerodynamic conditions. Morphing sandwich structures offer sufficient strength and stiffness to serve as aerodynamic surfaces, while providing the shape-changing authority to attain a range of surface profiles without additional joints or seals. As a demonstration of the morphing concept in a supersonic environment, this paper describes the construction and testing of a morphing nozzle for a supersonic wind tunnel, which has been designed to operate isentropically over a Mach range from 2.5 to 3.8. The nozzle has been installed and operated in this Mach number range and the experimental results are presented.

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## Figures

Figure 1

A photograph of the morphing nozzle as installed in the in-draft wind tunnel. Visible are the curved morphing surface, the actuators, and the linear potentiometers used to control the system position.

Figure 2

The desired shapes for the morphing wind tunnel nozzle. The nozzle is manufactured to conform to the Mach 3 shape and must be morphed to attain the Mach 2.5 and 3.8 shapes. The antistreamwise distance is the length from the connection between the diffuser and the nozzle in the direction opposite the flow. The throat of the nozzle is found at x=445mm.

Figure 3

Isometric drawing of a morphing sandwich structure with actuators. The curved surface and the rigid back plate constitute the sandwich faces, while the oblique members and the vertical tie rods are the low-density sandwich core. The actuators are the rectangular elements of the vertical tie rods.

Figure 4

A flat cantilever beam with seven evenly spaced independently movable nodes. The shapes attainable by this configuration comprise the family of allowable shapes for the morphing wind tunnel surface.

Figure 5

A set of shape functions for a morphing aerodynamic surface with seven equally spaced actuators

Figure 6

The required shape changes, in black, to move between the Mach 3.0 shape and the Mach 2.5 shape (shown in negative here) and the Mach 3.8 shape. The quality of the approximated fit after the actuator locations are improved is given in red.

Figure 7

The progressive changes in the lengths of the intervals between the seven actuators during the optimization procedure for a change from the Mach 3.0 shape to the Mach 3.8 shape. Interval 1 is between the fixed end of the surface and the first actuator.

Figure 8

The differences between the desired shapes and the optimal shapes, in the least-squares sense, found by the shape fitting algorithm

Figure 9

A photograph of the morphing structure prior to its installation in the wind tunnel. The tunnel walls and flat non-morphing surface have been removed.

Figure 10

Gradual shock angle change from Mach 2.5 to Mach 3.0 read from left to right and top to bottom with the initial shock angle overlaid to show the change in shock angle as the surface deforms. Flow is left to right.

Figure 11

Oblique shock during the transition from the Mach 3.8 contour to the Mach 3 contour. The black tab in image shows the leading edge of the wedge.

Figure 12

Oblique shocks move rapidly downstream during the transition between various curve shapes. Flow is left to right. The black tab marks the curved morphing side of the nozzle.

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