Pitot tubes, when used in conjunction with a differential pressure transducer can provide accurate velocity measurement of airflow. It does this by measuring the pressure difference between the static pressure and the dynamic pressure of the incoming flow. These devices are widely used in a number of fluid measurements, including wind tunnel experiments, and their small aerodynamic profiles are considered to have a negligible effect on the flow. However, past work have shown that even seemly ‘non-intrusive’ devices can cause flow disturbances downstream. This work aims to study the geometric effect of a Pitot tube in a wind tunnel. We utilize a TFI Series 100 Cobra Probe to measure wind speed downstream of a Pitot tube of 0.25 inches in diameter. In this work, the Pitot tube is placed in a closed return subsonic wind tunnel located in the Aerodynamics Laboratory located at the California State University, Los Angeles. This closed return wind tunnel is equipped with test section dimensions of 1.12 m by 0.71 m by 0.53 m. Wind tunnel testing were performed at wind speeds of 5, 7 and 9 m/s, with the Pitot placed at the center of the test section. Then velocity measurements were measured at increments of 4 times the diameters downstream of the Pitot tube, in the spanwise direction of half the original diameter. From the results gathered it is clear that the Pitot tube affects the velocity of the wind downstream even after a foot of distance. On the other hand the velocity in the spanwise direction recovers completely after 1 diameter of distance. Furthermore, we plan to perform computational fluid dynamics (CFD) simulations using Ansys Fluent which will be validated with experimental measurements. Once the simulations have been validated, they can provide detailed and valuable insights of the flow and the Pitot tube’s effect on the surrounding flow. Using a combination of experimental and numerical results, parametric studies will be performed to study the effects of freestream velocity and Pitot tube dimensions on flow velocity at various distances away from the Pitot tube. Then, dimensional analysis will be performed to reduce the parameters and variables to dimensionless numbers such as Reynolds number and normalized velocity deficit. The results will provide insights in developing guiding principles to size selection and placement of Pitot tubes, in order to provide the safest distances to place these measurement devices for minimal interference during wind tunnel testing, e.g. measuring flow in confined geometries.

 


The Impact of Pitot Tube Size on Velocity Field in a Closed Return Wind Tunnel

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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