Christina Politz

Development of Particle Image Velocimetry for In-Flight Flow Measurement

Wind tunnel testing is widely used for the development and testing of numerous aerodynamic systems. Mature laser based optical methods such as particle image velocimetry (PIV) also now offer detailed flow diagnostics in the wind tunnel environment. The majority of wind tunnels, however, cannot correctly scale both Reynolds and Mach number simultaneously. In-flight testing from a full scale aircraft offers the potential to take correctly scaled data to validate both wind tunnel and computational models. Furthermore, PIV has the potential to take detailed, non-intrusive velocity data from a full scale flight test. The following chapter reports on what the authors believe is the seminal application of a modified PIV setup inside a DLR Dornier DO 228-101 research aircraft and the subsequent PIV flight tests. These tests were completed as part of a major European Framework 6 research program called Advanced In-flight Measurements (AIM). In particular, the chapter reports on the major challenges that were overcome by the German Aerospace Center (DLR) together with Cranfield University to complete the flight tests. These challenges included the laser safety considerations for the test, the certification of the aircraft and the requirement for suitable seeding during the tests. The latter issue was overcome by flight testing inside a suitable cloud formation and successful PIV data was recorded over a series of three flight tests in a region adjacent to the outside of the cabin. The PIV images obtained yield high data quality inside the turbulent boundary layer.

The Application of Background Oriented Schlieren Method to Aircraft Wake Vortex Investigations

Vortex wakes of conventional aircraft and their propagating nature close to the ground have a great impact on the safety and efficiency of the traffic flow on an airport. The development of a measurement technique which helps detecting e.g. the density gradients in the air due to the wake vortices and understanding the nature of such a flow structure in its natural environment can improve the predictability of this hazardous phenomenon. Therefore, the practical aspects of the implementation of an advanced Schlieren technique on an airport are described in this chapter. Two experiments based on slightly different setups and locations relatively to the runway were conducted in order to assess the feasibility of the Background Oriented Schlieren method (BOS) for the detection and investigation of aircraft wake vortices. The evaluation of the obtained data indicated a sufficient ability of this technique to detect strong density gradient but on the other hand, turned out to be less efficient when dealing with the peculiarities of a large scale outdoor experiment.

Ground Based Large Scale Wake Vortex Investigations by Means of Particle Image Velocimetry: A Feasibility Study

The investigation of aircraft wake vortices is a fundamental challenge in aerospace research. The enhanced safety and efficiency given by better prediction and detection of these complex vortex systems is significant. Within AIM several non-intrusive optical methods were considered to visualise and measure the wake vortex of a landing aircraft. The main objective of the herewith presented campaign was the application of the Particle Image Velocimetry (PIV) to the investigation of these vortex flows. This report describes the first steps and approaches for the implementation of a large scale PIV measurement system for the determination of wing wake vortices of a landing aircraft. Many issues have to be addressed before the flyover test could be carried out. During the realisation phase of this experiment several setups were considered and discarded, a prototype of a seeding generator based on helium filled soap bubbles was designed and preliminary studies have been carried out exclusively for the investigation of the laser light sheet behaviour when propagating over large distances. This report presents a summary of all the considerations and pretests for this particular application.