DLR-Berlin has an extensive experience with the instantaneous hot-wire measurement technique. Several DNW wind tunnels have been tested by our department over the last 30 years. Since 2005 DLR have also qualified the hot wire technique for the investigation of turbo machinery application. The DLR hot-wire technique allows to measure airspeeds up to Ma=1. It is a point measurement with a high time resolution (up to 20 kHz).
With the DLR custom build hot wire anemometer the details of instantaneous flow structures can be measured under industrial environmental conditions. For example the wake flow of each individual blade of the fast rotating fan stage can be measured and analyzed in detail. In the last years the DLR- Berlin has measured and investigated in cooperation with the industrial partners the unsteady flow field at the inner stage section of two Counter Rotating Turbo Fans (CRTF), one Direct Driven Turbo Fan (DDTF) and one Geared Turbo Fan with an Ultra High Bypass Ration (UHBR) in different industry and DLR rigs. The averaged mean vectors as well as the fluctuation components of the velocity were determined. The calculated local turbulence distribution of the flow downstream of the rotating blades shows an increase of the turbulence intensity of 3-5 % in the wake.
These hot wire data offer valuable information for the validation of the numeric flow calculation code (CFD) to be applied. In addition, the results deliver a valuable data base for the development and future use of numerical acoustic simulation (CAA) tools, in particular to improve prediction models for coupling acoustics and aerodynamics. In future, this will enable an improved noise and efficiency prediction already in the early stage of the design process of fan modules.