This application was performed in a double-staged combustion chamber consisting of two main and three pilot burners with simultaneous optical access from at least three sides (figure left). The chamber itself represents a segment of an annular combustion chamber for use in the engine of a transport aircraft. One of the principle aims here was to obtain a data base to validate CFD codes. Since the flow structure inside a combustion chamber is very complex it is desireable to acquire the entire three-dimensional volume data set - a task very tediously accomplished with single-point measurement techniques (e.g. LDA, L2F).
For the measurement the light sheets were introduced from either side as well as from the top or bottom of the chamber. A mirror was placed downstream of the combustion chamber exit such that the camera was not directly exposed to the flow. By mounting the entire DGV equipment, camera and light sheet devices, on a common translation stage, the interior of the chamber could by mapped in a tomographic manner (image of setup). Up to 50 adjacent places (Dx = 2 mm) were recorded in this manner resulting in tomographic data sets containing up to 120 × 60 × 50 distinct data points at a spacing of 1 × 1 × 2 mm3.
The following figures give an impression of the quality of the recovered data by showing various cross sections through the tomographic velocity data. The interaction between the swirling burner flows and the mixing jets of the secondary air can be easily recognized. Swirls within the mixing jets are also visible and are surprisingly similar to the CFD results (data not presented here). A comparison between DGV data and LDA data obtained for the swirler nozzle flow is presented in .
The above DGV measurements were restricted to the 'cold' (unfired) flow under atmospheric conditions. Measurements in the hot, burning flame were not possible due to the self-luminosity of the seeding particles as well as glowing soot which requires the use of intensifier-gated CCD cameras and pulsed, frequency-stabilized lasers, both of which were not available a the time. Current research efforts at DLR are directed at making such measurements possible in the future.