Author: University of Illinois Granger School of Engineering March 11, 2021

Griffith-type transonic airfoil in the test section of the wind tunnel. Image source: University of Illinois at Urbana-Champaign

Armando Collazo García III achieved more than expected results from the graduate program he took last spring. He gained a new understanding of the physics of transonic shock waves generated by laminar airfoils with boundary layer suction, and added a published paper to his resume.

"When I received an assignment for a research project, I realized that I had obtained a good data set from my master's thesis, and I could use it in a new way," Collazo Garcia Say. "I was able to apply linear algebra techniques to process flow field data and decompose the information into patterns. These patterns provide a snapshot of all aspects of flow and are ranked according to their energy contribution. The higher-ranked patterns show the most important aspects of flow. Features. The beauty of this technique is that it eliminates all random noise—all uncertainties associated with the data—and identifies the most important patterns so that we can study the process more effectively."

This paper was written for the course AE 598-Modal Analysis of Fluid Flow, taught by Assistant Professor Theresa Saxton-Fox, Department of Aerospace Engineering, University of Illinois at Urbana-Champaign.

It shows that the three modes established by the Mach wave lead to fully developed shock, oscillation and dissipation. Image source: University of Illinois at Urbana-Champaign

"In class, I learned how to use modal analysis techniques, especially proper orthogonal decomposition, and how this technique helps me understand the main patterns and main characteristics of the flow in question," said Collazo García . "During the analysis, I learned how to consider using the reduced-order model of the main mode so that I can understand the dynamics and important physical processes of the process without the instability and noise in the data."

In his master's thesis, Collazo Garcia evaluated the aerodynamic performance and related flow characteristics of a Griffith-type laminar airfoil in a transonic environment. Since the airfoil is designed to operate in the presence of active boundary layer suction to assist the pressure increase in the trailing edge region, the aerodynamic performance of the airfoil will be hindered when such suction is not applied. Due to the complex flow interaction process, a highly unstable shock oscillation process is also observed in the absence of suction. It has been observed that applying suction reduces this large variability in impact position and unstable motion. The work he started in the Saxton-Fox class allowed him to use modal analysis to expand his knowledge of this oscillating shock process.

Collazo Garcia said: "We obtained the relevant frequency of each mode and were able to reconstruct the process and capture important physics by removing all the relevant instability and noise in the data." "We observed the establishment of the Mach wave, which This resulted in a fully developed shock wave. After the oscillation, it dissipated, and then we saw the process take shape again."

Collazo Garcia said that the reconstruction assumes that each appropriate orthogonal decomposition mode has a single Fourier mode. It is a very simple technique that can be applied to other streams and other data sets for the purpose of understanding basic physics, which is unstable. the process of.

Reference: Armando R. Collazo Garcia III, Theresa Saxton-Fox and Phillip J. Ansell, "Modal Analysis of Griffith-type Laminar Airfoil Transonic Impact Process", January 4, 2021, AIAA Scitech 2021 Forum . DOI: 10.2514/6.2021-1646

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