Measurement methods in turbulent flows

Abstract

In this Master Thesis, the performance of a cobra probe in turbulent flows is investigated. For this purpose, cobra probe was used in two experiments that were done in the Fluid Mechanics building at NTNU.First experiment was done for the fully developed pipe flow to test out cobra probe and estimate the errors. Measuring instruments cobra probe and pitot probe were used in this experiment. The obtained results for the mean flow velocity were compared. Also, results of turbulence intensity and Reynolds stress from the previous studies were used as a reference in cobra s probe performance analyses. This experiment was used as an initial test for better comprehension of a cobra probe s performance in complex flows with increased free stream turbulence levels. The main goal was to test out cobra probe for such flows, so that the second experiment took place in the recirculating wind tunnel with a grid placed at the entrance of its test section. The measurements were done simultaneously by cobra probe and LDV that were set 12 diameters downstream the wind turbine model. The discrepancy between the results of measurements that these two measuring instruments had provided was studied in this thesis. The cobra probe showed to be able to measure with quantified errors which are within the values for the measurement uncertainty of ±0.5 m/s that is set in the manufacturer s specifications.