Session: 5.2.1 - Novel Measurement Techniques in Fluid Engineering I

Paper Number: 158687

158687 - Method for Acquiring Forces and Pressure Distributions for Rotating Bluff Body Aerodynamics 

Abstract: 

The study of bluff body aerodynamics continues to be a challenging endeavor. Largely due to their blunt trailing edges, numerical simulations of flow characteristics often prove to be either inaccurate or expensive to compute, making them impractical in many cases. As a result, experimental approaches become the preferred alternative, driving the development of novel measurement techniques to capture the unique flow characteristics of arbitrary shapes. Among the vast array of bluff bodies, rotating bluff bodies pose unique experimental challenges, requiring specialized test setups to address their dynamic nature. This study explores the feasibility of using a tunable load cell and an array of integrated wireless MEMS pressure sensors to study flow physics on rotating bluff bodies.

Unlike traditional, aerodynamic bodies, bluff bodies can produce significant forces and moments in all directions. Multi-axis load cells are commonly used to capture these forces and moments in a convenient and robust manner. Commercial multi-axis load cells can be configured to meet specific load requirements at the time of purchase, but they cannot be altered afterwards. This limitation poses a challenge in studying bluff bodies, as different shapes can produce widely varying force ranges and oscillatory behaviors along each axis. The fixed characteristics of commercial multi-axis load cells come partially from their elastic structure. These structures are often made of a single piece of metal with chemically bonded strain-sensitive elements. For the load ranges of the sensor to change, the metal elastic portions need to be physically altered, making the modification infeasible. The ability to adapt the multi-axis load cell to the load requirements of various bluff bodies would enable high quality data with low uncertainty to be collected. This can be achieved by constructing a multi-axis load cell composed of single-axis load cells. These single-axis load cells can act as modular elastic portions, allowing the sensor to be customizable and tuned for different loading conditions. Additionally, by connecting each single axis load cell to an individual amplifier, the gain and filtering can be adjusted to maximize output signals and capture desired frequencies.

This coupled with the ability to measure pressure distribution on the surface of the bluff bodies offers a deeper understanding of their aerodynamics. Traditional direct measurement techniques involve pressure taps drilled directly into the skin of the model. Traditional approaches for measuring pressure at these taps involve either pneumatic lines or pressure transducers which are f lush mounted into the skin of the test articles. While pneumatic lines have a long history of reliability, their implementation presents challenges in certain applications. In wind tunnel testing, these lines must extend from the test article through the wind tunnel and connect to a central data acquisition system. While satisfactory for static test articles, pneumatic lines become problematic with a rotating test article because they will twist and compromise the system. The alternative is f lush mount the pressure transducers to the pressure taps, eliminating the pneumatic lines, but this leads to a similar issue. The wires required to power the sensors and transmit signals to an external data acquisition system also twist as the test article rotates, leading to system failure. To resolve this issue, a MEMS pressure sensor array with a fully wireless data acquisition system will be developed.

Research outcomes will show system characterization of the tunable load cell and the MEMS pressure sensor by providing linearity, sensitivity, time response, and other performance metrics. A rotating cylinder will serve as the test article to validate both sensors and the system as a whole in measuring rotating test articles.

Presenting Author: Bryan Hasselman California Polytechnic State University, San Luis Obispo

Presenting Author Biography: I'm passionate about aerodynamics and innovating on aerodynamic research. I am a graduate student at California Polytechnic State University, San Luis Obispo studying bluff body aerodynamics and direct pressure measurement methods for my thesis.