Part4 - An Integrated Navier Stokes - Full Potential Free...

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An Integrated Navier Stokes - Full Potential - Free Wake Method for Rotor Flows Ph. D Work by Mert Enis Berkman Advisors: Prof. S. M. Ruffin & Prof. L. N. Sankar Georgia Institute of Technology School of Aerospace Engineering
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OUTLINE • Review of Rotorcraft CFD Techniques   Why is a hybrid approach more favorable ? • Hybrid Solver • Navier-Stokes Zone • Full Potential Zone • Boundary and Interface Conditions • Wake Model  • Results • Hover Analysis  Two-Bladed, UH-60A and Tapered Tip Rotors • Forward Flight Analysis  Two-Bladed, UH60A and H-34 Rotors • Conclusions
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     • Performance of rotary wings is limited by: transonic flow (on advancing blade)  stall (on retreating blade)  operation under its own wake. • The flow field is 3-D, unsteady, viscous and compressible. • Rotor wake is a distorted, skewed helix that stays in the  vicinity of the rotor and affects entire flow field. • The rotor wake structure determines performance, vibratory  airloads and acoustics. • Modeling the wake and its effects remains a very challenging  task. ROTARY WING AERODYNAMICS
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Lifting - Line (- Surface) Methods • Blades are modeled as a lifting-line (or -surface). • Wake is represented by a network of vortex filaments. • Routinely used in industry.  They need small CPU time, thus easily incorporated into comprehensive codes as aerodynamics  modules. • They require table look up for airfoil load data, and are often quasi-steady. • They are loaded with empirical corrections. ROTORCRAFT CFD
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     Finite-Difference Methods: (Potential, Euler and N-S) a) Finite-Difference Methods with External Wake Model: • The flow field is solved near the blade; the effects of the far wake is  modeled.                                                                            solved • They can handle compressible flows. • They require external coupling with a wake model to account for far wake.                 modeled ROTORCRAFT CFD
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 b) Wake Capturing Schemes • This class of methods attempt to capture the far wake as a  part of the solution. • They provide high quality detailed flow field solutions. • They require enormous computer time since they need to resolve the tip vortex adequately. • They diffuse the tip vortex too rapidly due to the dissipative nature of Euler/N.-S. schemes. • Higher order schemes, overset and/or unstructured grids were used to conserve vorticity without significant success.
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This note was uploaded on 01/05/2011 for the course DU 3 taught by Professor Frando during the Spring '10 term at University of Dundee.

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Part4 - An Integrated Navier Stokes - Full Potential Free...

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