Study, implementation and validation of a wall pressure-signature blockage correction method for the wind tunnel of the ESEIAAT Aerospace Laboratory
Document typeBachelor thesis
Rights accessRestricted access - author's decision
The purpose of this study is the development, implementation and validation of a blockage correction method based on wall pressure signatures. The work involves the design and construction of the required wind tunnel instrumentation and models, as well as the implementation of a computer program to process the wind tunnel data. The program is able to correct dynamic pressure and drag measurements, even for lifting models. In this work, the wall pressure signature is measured in a manual manner by means of a multi-tube manometer which has been designed and built for this purpose. Validation experiments have been also designed and performed using cylinders. A brief uncertainty study of the results is also presented. The program has been developed using MATLAB software. It is based on the iterative version of the wall pressure signature method originally developed by Hackett et al. The program is capable of obtaining a reconstruction of the wall pressure distribution along the wind tunnel walls. From this reconstruction, the required corrections for the dynamic pressure inside the tunnel, the measured aerodynamic resistance and the drag coefficient are obtained. The developed program has been validated experimentally. Experiments on cylinders of different diameter have been carried out to observe the change in corrections for different blockage ratios (relation between model frontal area and tunnel cross-sectional area). Velocity in each experiment has been adjusted in order to maintain a constant Reynolds number between different diameter cylinders. An uncertainty analysis of the results has been performed through the Monte Carlo method to obtain an approximate error for the corrections. The results obtained have been consistent for blockage ratios below 15% and coherent with the descriptions from Hackett. However, the measurements present some discrepancy with published data in the literature. For example, experimental force measures (before correction) obtained have been higher than predicted by other experiments (specially for low blockages). This can be due to some bias in the measurements (produced by misalignment) or simply due to the uncertainty observed in the experiment. Results of the uncertainty analysis have shown that the errors in drag coefficient are considerable for the magnitude of forces measured in the experiment, but reduce significantly as the measured force increases. It has also been observed that a large part of the uncertainty in the results is due to the uncertainty in the measurements of aerodynamic drag.
The main objective of this work is the development and application of a wall pressure-signature method for the correction of interference effects caused by body and wake blockage in closed test-sections. The method will be developed for application to the wind tunnel of the ESEIAAT Aerospace laboratory. In this work, the instrumentation required for pressure signature measurements will be designed and developed firstly, and a computer program for processing and correcting the measured data will be also implemented (with focus on aerodynamic forces corrections). Finally, experimental tests will be carried out to validate the proposed methodology.