Session: 15-01-01: ASME International Undergraduate Research and Design Exposition

Paper Number: 100572

100572 - Pressure Measurement at the Surface of a Cylinder in Subsonic Wind Tunnel 

Wind tunnel testing is a critical component in the research and development of external flow applications and is practical in the design process for reliable and cost-effective prototyping. In certain instances, wind tunnel testing yields scalable experimental data that analytical models cannot reasonably produce. Coupled with numerical simulation methods, wind tunnel testing can provide invaluable insight into the behavior of scaled prototypes experiencing external flow conditions. External flow is found in aerospace, energy production, and structural applications. From flow around airplane wings and turbine fins to flow around bluff-body structures, this project applies incomplete similitude to the test samples that were created by a previous group during their design and development of a force balance and pressure data acquisition system. Upon completion of their system, significant boundary layer interference is assumed to be present due to an oversized sample. This project aims to acquire repeatable pressure measurements at the surface of a cylindrical test sample within a wind tunnel. The system and sample developed will be integrated into fluids laboratory curriculum to enhance the educational experience of undergraduate studies in Mechanical Engineering. This project also provides further information and reference on the effectiveness of similitude in laminar external flow conditions.

The ratio of test sample planform area to the wind tunnel cross sectional area is too large and suggests boundary layer interference. The application of similitude would require smaller pressure taps than what is currently in use. The new diameter was chosen by considering the constraints of the geometric relations of the pressure tap. The Reynold’s number of the old sample is held constant with the new sample, which decides the velocity that the two samples will be compared to confirm or deny the boundary layer interference. To validate the new pressure measurements, experimental data is compared to numerical simulations using Finite Element Analysis. During testing the following assumptions are made: the static pressure of the flow remains constant as it passes around the cylinder, the change in the hydrostatic pressure over the cylinder is negligible, and the internal flow field is uniform. Uncertainty calculations are done using Kline-McClintock method.

The diameter of the new sample was chosen to be 1.6 inches. To keep the aspect ratio of the previous sample constant, the length of the new sample was chosen to be 2.46 inches. The new velocity used for validation is 53 ft/s. The coefficient of pressure at the stagnation point should be one. This is due to the difference in stagnation pressure at the surface and the static pressure of the free stream which should equal the dynamic pressure. The experimental data yielded a value of 0.88. The first hypothesis for the inaccurate value was that the uncertainty of the acquisition equipment propagated enough through the calculation of the coefficient of pressure to offset the values. Uncertainty calculations of all pressure measurements averaged at a value of 0.051. Using an upper and lower bound from the uncertainty, a coefficient of pressure of one at the stagnation point does not lie within the bounds generated from the uncertainty; this indicates a systematic error. When plotting the individual pressures over time, there is a positive slope on all measurements. As the pressure at the cylinder surface creates a larger vacuum, the slope of the measurements increases; this indicates a leak in the system to atmospheric pressure. Given the preliminary results of the waveform, the similitude has been effective in reducing the error in pressures on the back half of the sample.

Presenting Author: Mirza Cirak Western Kentucky University

Presenting Author Biography: Current undergraduate student at Western Kentucky University perusing a degree of Bachelor of Science in Mechanical Engineering graduating December 2022. Current Tau Beta Pi Kentucky Gamma chapter Treasurer. Interests in Mechanical Engineering Thermofluid sciences. Presenting work with Matthew Clouse, Troy Steward, and Boston Wimmer under the guidance of Dr. Manohar Chidurala on wind tunnel data acquisition on pressure distribution of surface in external flow.

Authors:

Mirza Cirak Western Kentucky University
Matthew Clouse Western Kentucky University
Troy Steward Western Kentucky University
Boston Wimmer Western Kentucky University
Manohar Chidurala Western Kentucky University