invertebrates and fluid dynamics : off the ground & movin’ around

INVERTEBRATES AND FLUID DYNAMICS:

OFF THE GROUND & MOVIN’ AROUND

FLIGHT

FLIGHT

Chord

Thickness

Angle of attack

Airfoil

FLIGHT

Standard airfoil

Area of relatively low pressure

Area of relatively high pressure

LIFT

FLIGHT

Lift

Drag

Resultant force

In flapping flight, need to compromise

1) lift

2) propulsion

3) Lowering of drag

As you increase angle of attack

generated

H.G. Magnus (1802 – 1870)

+

LIFT

=

translation circulation

MAGNUS EFFECT

Same principle is used in various sports

Curve ball

Overall flow

-

Translational flow

circulation

=

Circulation around wing

At the beginning of flight

Establish a counter vortex

Some coefficients of lift

Bird Re – 70002.0

Locust Re – 20001.3

Drosophila Re – 2000.9

Hovering Flight

Encarsia formosa

Wing – 0.6 mm

Mass - .000025 gm

Re - 15

Coefficient of lift (predicted) = 0.02

Coefficient of lift (actual) = 5.0

Clap-and Fling Mechanism

Hovering flight

Flip Mechanism - Dragonfly

Hovering flight

Translational Phase

A) upstroke

B) downstrokeHigh angle of attack

Rotational Phase

A) pronation

B) supinationWhen wing reverses direction

Hovering Flight

Hovering flight

Red arrows – total force and direction

1. Delayed Stall2. Rotational lift 3 Forward motion

Blue arrows – wing position

Hovering flight

Hovering flight

Vortices around a flying animal

Bound vortex Tip vortices

Tip vortices

Tip vortices

Propulsion at very low Re’s

Rowing a boat – propulsive stroke is in lower Re (water) than recovery stroke (air)

Propulsion at very low Re’s

What about smaller animals that have to do both in low Re?

Cladoceran

Dytiscid beetle

Thrips

Nepticulid moth

Mymarid wasp

Ptiliid beetle

Aquatic Aerial

Propulsion at very low Re’s

What about smaller animals that have to do both in low Re?

Relative sizes

Size difference and different viscosity of medium similar low Re’s

Fringed propelling mechanism

Power stroke (fringe expands)

Recovery stroke(fringe collapses)