InflowModels - Classical Inflow Models Background In Part...

Info iconThis preview shows pages 1–7. Sign up to view the full content.

View Full Document Right Arrow Icon
Classical Inflow Models
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background In Part II and Part III of our lecture notes, we used Glauert’s inflow model to compute the induced velocity in forward flight. This model gives acceptable results for performance, but does not give good results for blade dynamics or vibratory loads. It fails miserably for Blade-Vortex- Interactions. ( 29 ( 29 2 2 v sin V cos V v 2 + + = α ρ A T
Background image of page 2
Why does the model fail in forward flight? Because most of the wake is the first and second quadrants. We can not expect the induced velocities to be uniform! Rotor Disk Tip Vortices Freestream
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Experiment by Harris Because most of the tip vortices are in the first and fourth quadrants, the induced velocity associated with these vorticies (i.e. the inflow) is very high in the first and fourth quadrants. The resultant reduced angle of attack leads to smaller lift forces in the aft region, compared to uniform inflow model. The blade responds to this reduced loads 90 degrees later. It flaps down (leading to a more negative β 1s ) more than expected. Harris experimentally observed this, in a paper published in 1972 in the Journal of the American Helicopter Society (See Wayne Johnson, page 274, figure 5-39).
Background image of page 4
Effects of Non-Uniform Inflow on Lateral Flapping Comparison of Lateral Flapping Using Two Induced Flow Models 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 Advance Ratio Lateral Flapping Angle (-Beta1s) degrees Uniform Inflow (Numerical Trim) Non-Uniform Inflow (Numerical Trim)
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Effects of Non-Uniform Inflow on Blade-Vortex-Interaction Loads During descent the tip vortices are pushed up against the rotor disk by the freestream, leading to a very close spacing between the blades and the vortices. According to Biot-Savart law, this leads to very high, and very rapidly varying, induced velocity. This affects the airloads dramatically.
Background image of page 6
Image of page 7
This is the end of the preview. Sign up to access the rest of the document.

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.

Page1 / 27

InflowModels - Classical Inflow Models Background In Part...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online