Implementation of Blade Element Theory in CFD Analysis of Edgewise Ducted Fan Vehicles

Open Access
Author:
Halwick, Jason Michael
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Dennis K Mclaughlin, Thesis Advisor
  • Jules Washington Lindau V, Thesis Advisor
Keywords:
  • Ducted Fan
  • CFD
  • Blade Element Theory
  • Aerodynamics
Abstract:
Ducted fans have received renewed interest in recent years for a variety of potential missions including both civil and military STOVL applications. The design of these vehicles includes many challenges related to the influence of the ducts. Considered in this work, is a dual ducted fan vehicle in edgewise forward flight. This class of vehicle has been shown to exhibit significant separation over the ducts, causing distortion of the rotor inflow and performance. Current methods of modeling the flow field around these vehicles and their performance have proven to be lacking in regards to a design environment. High fidelity, unsteady solution methods are far too computationally and time expensive while simplified actuator disk models fail to incorporate the necessary physics of the shrouded rotor. To alleviate these problems, a computational method which couples a momentum source CFD code to a blade element theory rotor performance prediction code has been developed and validated. The coupled method was shown to have adequately resolved the dominate flow field phenomena in and around the ducts of the model, in particular the recirculatory, separation region over the front duct. Good agreement with experiment was found in the characteristics of both the inflow and outflow of the front fan in forward flight. The aerodynamic force predictions demonstrated the ability to adequately predict performance at low forward speeds and hover. At the highest advance ratio of 0.24, however, the prediction under-predicted lift by 30%.While, the coupled method was able to outperform the simplified momentum source approach and converge to a solution faster than a fully resolved rotor solution, improvements can be made. A more precise rotor model is required to improve the accuracy of the performance prediction. This is supported by the sensitivity of the coupled method solution to the lift and drag coefficients of the airfoil section used. A strong correlation was found between sectional lift data utilized by blade element theory and the resulting coupled method lift predictions.