Time-averaged surrogate modeling for small scale propellers based on high-fidelity CFD simulations

• Main Author: Carroll, Joseph Ray
• Other Authors: D. Keith Walters
• Format: Others
• Language: en
• Published: MSSTATE 2013
• Subjects: Mechanical Engineering
• Online Access: http://sun.library.msstate.edu/ETD-db/theses/available/etd-10312013-094500/

<p>Many Small Unmanned Aerial Vehicles (SUAV) are driven by small scale, fixed blade propellers. The flow produced by the propeller, known as the propeller slipstream, can have significant impact on SUAV aerodynamics. In the design and analysis process for SUAVs, numerous Computational Fluid Dynamic (CFD) simulations of the coupled aircraft and propeller are often conducted which require a time-averaged, steady-state approximation of the propeller for computational efficiency. Most steady-state propeller models apply an actuator disk of momentum sources to model the thrust and swirl imparted to the flow field by a propeller. These momentum source models are based on simplified theories which lack accuracy. Currently, the most common momentum source models are based on blade element theory. Blade element theory discretizes the propeller blade into airfoil sections and assumes them to behave as two-dimensional (2D) airfoils. Blade element theory neglects many 3D flow effects that can greatly affect propeller performance limiting its accuracy and range of application.</p> <p>The research work in this dissertation uses a surrogate modeling method to develop a more accurate momentum source propeller model. Surrogate models for the time averaged thrust and swirl produced by each blade element are trained from a database of time-accurate, high-fidelity 3D CFD propeller simulations. Since the surrogate models are trained from these high-fidelity CFD simulations, various 3D effects on propellers are inherently accounted for such as tip loss, hub loss, post stall effect, and element interaction. These efficient polynomial response surface surrogate models are functions of local flow properties at the blade elements and are embedded into 3D CFD simulations as locally adaptive momentum source terms. Results of the radial distribution of thrust and swirl for the steady-state surrogate propeller model are compared to that of time-dependent, high-fidelity 3D CFD propeller simulations for various aircraft-propeller coupled situations. This surrogate propeller model which is dependent on local flow field properties simulates the time-averaged flow field produced by the propeller at a momentum source term level of detail. Due to the nature of the training cases, it also captures the accuracy of time-dependent 3D CFD propeller simulations but at a much lower cost.</p>