For determining the model shape and model deformation in wind tunnels or wing deformation in flight tests, Image Pattern Correlation Technique (IPCT) is applied. This technique utilizes photogrammetry together with evaluation algorithms developed for PIV (Particle Image Velocimetry) such as cross-correlation and additional scaling algorithms. With a multi-camera system complex shapes can be fully sampled in their 3D-geometry.
For deformation analysis areas on the test object which are suspected to suffer deformation are covered with a random dot pattern. By means of stereoscopic pattern correlation the deformation of the object surface relative to a reference surface can be measured with high accuracy. For this method being fully 3D it allows for the determination of the absolute surface shape of a test object. A random dot pattern applied to a model-propeller blade is shown in the image. The evaluation algorithm yields a quasi continuous sampling of the object shape. Its accuracy is estimated to be of the order of 0.01% (0.1mm per meter) of the field of view.
By comparison of the model shape in its reference condition and its deflected state the deformation of a model surface under e.g wind load is determined. A comparison of the propeller blade at different speeds of revolution is given in the image. The higher load (right drawing) yields a small deflection of the propeller tip.
Shape of a model propeller blade at revolution speeds of 15 Hz (left) and 95 Hz (right)
Application of optical non-contact measurement techniques allows for the determination of object deformations during rapid movement, like a spinning propeller, which is hardly achieved otherwise.
