Research Of Averaging Pitot Tube In Non-uniform Flow Field

Averaging Pitot tube(APT)is widely used in large diameter of the flow measurement because of its simple construction and small pressure loss.But its performances are badly affected by the length of the straight pipe up-and-down stream from the meter.There will be a terrible error in calculating averaged total-pressure with non-fully developed turbulence.In this paper,the flow measurement characteristics of APT were studied through CFD numerical simulation combined with experiments.First of all,it simulated the flow measurement characteristics of APT with different flow media,different velocity distribution model.It obtained the internal pressure distribution nephogram of APT and pressure value of each feature point.The internal pressure distribution of APT was analyzed.It was found that there would be a flow in high pressure chamber which made the velocity in detecting hole is no longer zero in non-uniform flow field.So the measured value was larger than the true value.It meant that high pressure chamber no longer had the ability to average the whole pressures.Namely dynamic pressure average method doesn’t fit for non-uniform flow field.Secondly,three different sizes of APT were used to measure fluid flow in four different places with non-uniform flow field.The experiment results validated simulation conclusion.Finally,orthogonal experiment with three factors and three levels was used to select nine typical experiments.The main effect factor of low measurement accuracy was determined by experiment results.It was found that flow medium and sizes of APT are not the cause of low measurement accuracy.Both influence on each measurement accuracy were within 1%.Velocity distribution influence on each measurement accuracy was 3.02% which was much larger than the two other factors.So it confirmed that non-uniform velocity distribution is the cause of low measurement accuracy.Through experiment,it obtained that the measurement accuracy of APT is high in symmetric velocity distribution flow field.It is necessary to set a rectifier before the installation of APT to improve measurement accuracy.