Thomas Gawehn

Application of Temperature and Pressure Sensitive Paints to DLR Hypersonic Facilities: “lessons learned”

PSP and TSP measurements have been carried out on the following DLR facilities: small test shock tube, High Enthalpy Shock Tunnel (both in Gottingen) and the Hypersonic Wind Tunnel (in Cologne). Based on the results from these measurements, various challenges and problem areas could be identified: the role played by these in hindering a quantitative application of PSP/TSP to the facilities is discussed, and ways and means are presented for either overcoming them or at least ameliorating their influence.

Numerical and Experimental Investigation of the Effect of Bypass Mass Flow Due to Small Gaps in a Transonic Channel Flow

Within the joint project PAK 75 (Deutsche Forschungsgesellschaft DFG), a novel process for the production of gas phase synthesized particles is developed. The key features of the process are shock induced precursor combustion, homogeneous particle growth at constant thermodynamic conditions and gas dynamic nozzle quenching within a double choked Laval nozzle system (fig. 1) [1] [2].

Pseudo-shock System Structure in Rectangular Laval Nozzles with Gaps

The acceleration of a fluid in a Laval nozzle to supersonic speed leads to a significant decrease of the static temperature in the flow, and deceleration via a normal shock results in a sudden reheating. Both effects are used within the joint project PAK 75 (Deutsche Forschungsgemeinschaft DFG) for the homogeneous ignition of a precursor and, hence, for the production of gas phase synthesized nanoparticles with narrow size distribution. However, the shock boundary layer interaction at the desired shock position leads to the formation of a so-called pseudo-shock system. Thereby, the heating rate across the shock system is reduced and the homogeneity of the particle growth is negatively affected by the inhomogeneous downstream conditions. Such pseudo-shock systems have been investigated by many research groups and a comprehensive overview is given by [1].

A planar Mie scattering visualization technique for turbo machinery application

A planar Mie scattering technique is described which allows for the systematical analysis of three-dimensional shock configurations without the need for velocity measurements. For that, small particles are added to the flow upstream of the shock and illuminated by a laser light sheet. The scattered light is captured by a CCD camera so that the position of the shock wave can be determined from the increase of the light intensity across the shock. To analyze the three-dimensional structure of a shock wave, the light sheet is moved perpendicular to the flow direction. The measurement technique is applied to both a supersonic wedge flow at Ma = 2.43 and a more complex shock wave configuration in a transonic cascade flow at Ma = 1.09. The gathered results are conclusive with Schlieren photographs, numerical simulations and surface pressure measurements. As the chosen setup allows the application to test sections with restricted optical access and a synchronization of the image capturing process with an external triggering signal, the three-dimensional shock configurations inside a transonic compressor rotor can also be visualized.