Pressure, temperature and velocity distributions behind an NGV cascade by filtered Rayleigh scattering measurements

The aero-thermal characterization of turbomachinery flows typically relies on well-proven conventional measurement technology such as pneumatic probes, hot-wire sensors or thermocouples. As these devices have to be introduced into the flow, they disturb the flow field at the actual measuring position. This is especially critical in the context of measurements in narrow flow channels typically found in turbomachinery applications. In this regard, both five-hole probe/temperature measurements as well as laser-optical filtered Rayleigh scattering measurements are carried out in order to characterize pressure, temperature and flow velocities downstream of a nozzle guide vane cascade with lean-burn combustion representative inflow distortions. By comparing the optical Doppler frequency-shifts measured with filtered Rayleigh scattering and calculated from five-hole probe velocity data, the study reveals a significant bias of the probe's velocity measurement caused by strong pressure gradients present in the airfoils' wake regions. In addition, passage flows are notably altered by the probe's intrusive impact on the flow. The study concludes that laser-optical filtered Rayleigh scattering diagnostics overcomes these shortcomings and is well suited to characterize aero-thermal flow properties in turbomachinery environments.