Instrumentation

The instrumentation for high speed measurements is conceptually the same as that used for low speed testing. This instrumentation is described by Ban – ieghbal et. al, (1995). The differences between the acquisition of data in low speed and high speed ft>ws are due to the different scales of the values to be measured. This influences the quality of the measurements by influencing the resolution of the output of the signal and the resolution of the characteristic time.

The response frequency of conventional hot films and hot wires is of the order of 25 to 50kHz. The scale of the boundary layers and the freestream velocity indicates that the lowest turbulent frequencies are expected to be of the order of 3kHz and 100kHz for the low speed and high speed blades respec­tively. Therefore, the lowest turbulent frequencies can be characterized only for low speed fbws. Additionally, Table 1 presents the typical value of the bar passing frequency in high speed cascade testing. This is of the order of 3kHz. Thus, for a given the response frequency of the anemometers, a poorer resolution of the bar passing period is obtained for high speed cascades.

2. Results