Hotwire turbulence signal - Iowa State Universityhuhui/teaching/2015Fx/class-notes/AerE344... ·...

Copyright © by Dr. Hui Hu @ Iowa State University. All Rights Reserved!

Hotwire turbulence signal

Fig. 1. Time trace of hw signal

and velocity Fig. 2. Spectrum of fluctuations

• Sample voltages, v → use calibration fit to find velocity u

•Fluctuating component ~ u-mean(u)

•Compute spectrum of fluctuations

•E.g., >> Y = fft(u-mean(u)); •Better: >> pwelch(u,[],[],[], Fs);

>> set(gca, ‘Xscale’, ‘Log’);


Dr. Hui Hu

Dr. Rye M Waldman

Department of Aerospace Engineering

Iowa State University

Ames, Iowa 50011, U.S.A

Lecture # 08: Boundary Layer Flows and Controls

AerE 344 Lecture Notes

Sources/ Further reading: Schlichting, “Boundary Layer Theory,” any ed

White, “Viscous Fluid Flow,” 3rd ed.

Kundu & Cohen, “Fluid Mechanics,” 3rd ed.


Flow Separation on an Airfoil


Quantification of Boundary Layer Flow

y

Uu 99.0

, yat

Displacement thickness:

Momentum thickness:


Boundary Layer Theory

X

X

X

X

f

X

X

X

X

C

XU

Re

664.0

Re

72.1*

Re

0.5

Re

328.1

Re

0

y

p

X

Y Blasius solution for laminar

boundary layer:

wall

wy

U


Boundary Layer Theory

5/1

5/1

)(Re

37.0

)(Re

074.0

Re

X

X

f

X

X

C

XU

0

y

p

X

Y

Turbulent boundary layer:

wall

wy

U


Boundary Layer Flows

wall

wy

U

X

Y

Which one will induce more

drag?

Laminar boundary layer?

Turbulent boundary layer?


Flow Around A Sphere with laminar and Turbulence

Boundary Layer


Boundary Layer Flows

wall

wy

U

Which one will induce more drag?

Laminar boundary layer? Turbulent boundary layer?


Conventional vs Laminar Airfoils

• Laminar flow airfoils are usually thinner than the

conventional airfoil.

• The leading edge is more pointed and its upper

and lower surfaces are nearly symmetrical.

• The major and most important difference

between the two types of airfoil is this, the

thickest part of a laminar wing occurs at 50%

chord while in the conventional design the

thickest part is at 25% chord.

• Drag is considerably reduced since the laminar

airfoil takes less energy to slide through the air.

• Extensive laminar flow is usually only

experienced over a very small range of angles-of-

attack, on the order of 4 to 6 degrees.

• Once you break out of that optimal angle range,

the drag increases by as much as 40%

depending on the airfoil


Active flow control: Plasma actuators

Corke et al, Annu. Rev. Fluid Mech.

2010. 42:505–529

Use methods to actively control boundary

layer separation:

•Suction

•Blowing

•Plasma actuators: Applies a body force

acting on weakly ionized air to couple

momentum into the flow

•Synthetic Jets


Active flow control: Synthetic jets

Synthetic jets: zero mass flux

actuators that inject momentum into

the flow

Glezer & Amitay, Annu. Rev. Fluid Mech.

2002. 34:503–29


Passive flow control: Shark Skin

Dean & Bhushan, Phil. Trans. R.

Soc. A (2010) 368, 4775–4806


Vortex Structure over Riblets


Shark Skin


Shark Skin Swimming Suits


Micro Air Vehicles (MAVs)

• Micro Air Vehicles (MAVs) are commonly defined as an air vehicle with wingspan less

than 15 cm (~ 6 in.) and capable of operating at speeds of about 10 m/s (~ 20 mph).

• There is a wide range of applications to motivate development of MAVs.

– Militaristic Applications

– Surveillance

– Chemical/Radiation Detection

– Communication Links

– Rescue and Life Detection

– Visual Inspections

– Toys

Fixed-Wing MAV design Rotary-Wing MAV design Flapping-Wing MAV design


Rec < 5,000

Rec ≈ 100,000 Rec ≈ 10,000, 000

Rec ≈ 50, 000 Rec ≈ 5,000,000

MAV Operating Envelope vs All Fliers

MAVs


Micro-Air-Vehicles (MAVs)

The airfoil and planform designs for most of

the existing MAVs rely on “scaled-down” of

those used by convectional, macro-scale

aircraft.

– “macro-scale” aircraft: ReC = 106 ~108

– MAVs: ReC = 104 ~105

“Scale-down” of conventional airfoils could not

provide sufficient aerodynamic performance

for MAV applications.

It is very necessary and important to establish

novel airfoil shape and wing planform design

paradigms for MAVs in order to achieve

superb aerodynamic performances to improve

their flight agility and versatility.

(from McMaster and Henderson, 1980)

interest for

MAV

applications

310 610410 510

010

110

210

310

710

CURe

MAXD

L

C

C

Streamlined airfoil

rough

surface

airfoil


Insects: Biological Micro-Air-Vehicles

Cicada Dragonfly Bee

Locust Damselfly Chrysomya megacephala

(fly)


Close views of dragonfly wings

Vein network

Membranes Corrugated wing cross section!

1 2 3

1

2

3

Profiles taken from Kesel, A. B., Journal of

Experimental Biology, Vol. 203, 2000, pp.

3125-3135


Bio-Inspired Corrugated Wings

a. Flat plate

b. Bio-inspired corrugated

airfoil

• A simple flat plate

• The flat plate has a rectangular cross section

without any rounded treatment at the leading edge

and trailing edge.

• A bio-inspired corrugated airfoil

• The shape of the bio-inspired corrugated airfoil

corresponds to the forewing of a dragonfly acquired

at the mid section of the wing, which was digitally

extracted from the profiles given in Kesel (Journal of

Experimental Biology, 2000).

• A profiled airfoil

• The profiled airfoil was formed by tautly wrapping a

thin film around the bio-inspired corrugated airfoil in

order to produce a smooth surfaced airfoil. C. Profiled airfoil


Aerodynamic Force Measurement Results

Re=58,000

0

0.2

0.4

0.6

0.8

1.0

0 2 4 6 8 10 12 14 16 18 20

Flat Plate

Profiled Airfoil

Corrugated Airfoil

Angle of Attack (Deg.)

CL

0

0.1

0.2

0.3

0.4

0 2 4 6 8 10 12 14 16 18 20

Flat Plate

Profile Airfoil

Corrugated Airfoil


CD

Re=125,000

0

0.2

0.4

0.6

0.8

1.0

1.2

0 2 4 6 8 10 12 14 16 18 20

Flat Plate

Profiled Airfoil

Corrugated Airfoil


CL

0

0.1

0.2

0.3

0.4

0 2 4 6 8 10 12 14 16 18 20

Flat Plate

Profiled Airfoil

Corrugated Airfoil


CD


PIV Measurement Results

( AOA = 6.0 deg. , Re=58,000)

A. instantaneous results

B. ensemble-averaged results

X/C*100

Y/C

*10

0

0 20 40 60 80 100 120 140

-20

0

20

40

60

80

-1.60 -1.20 -0.80 -0.40 0.00 0.40 0.80

Shadow Region

Spanwise vorticity(1000*1/s)

10.0 m/s

X/C*100

Y/C

*10

0

0 20 40 60 80 100 120 140

-20

0

20

40

60

80

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Shadow Region

Velocity(m/s)

10.0 m/s

X/C*100Y

/C*1

00

-40 -20 0 20 40 60 80 100 120

-40

-20

0

20

40

60

80

-1.6 -1.2 -0.8 -0.4 0.0 0.4 0.8

Shadow Region

Spanwise vorticity(1000 *1/s)

10.0 m/s

X/C*100

Y/C

*10

0

-40 -20 0 20 40 60 80 100 120

-40

-20

0

20

40

60

800.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Shadow Region

Velocity(m/s)

10.0 m/s

X/C*100

Y/C

*10

0

-40 -20 0 20 40 60 80 100 120

-40

-20

0

20

40

60

80-1.60 -1.20 -0.80 -0.40 0.00 0.40 0.80

Shadow Region

spanwise vorticity(1000*1/s)

10.0 m/s

X/C*100

Y/C

*10

0

-40 -20 0 20 40 60 80 100 120

-40

-20

0

20

40

60

800.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Shadow Region

Velocity(m/s)

10.0 m/s



( AOA = 12.0 deg. , Re=58,000)

A. instantaneous results

B. ensemble-averaged results

X/C*100

Y/C

*10

0

0 20 40 60 80 100 120 140

-40

-20

0

20

40

60 -1.60 -1.20 -0.80 -0.40 0.00 0.40 0.80

Shadow Region

Spanwise vorticity(1000*1/s)

10.0 m/s

X/C*100

Y/C

*10

0

0 20 40 60 80 100 120 140

-40

-20

0

20

40

60 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Shadow Region

Velocity(m/s)

10.0 m/s

X/C*100Y

/C*1

00

-40 -20 0 20 40 60 80 100 120-60

-40

-20

0

20

40

60

80

-1.60 -1.20 -0.80 -0.40 0.00 0.40 0.80

Shadow Region


10.0 m/s

X/C*100

Y/C

*10

0

-40 -20 0 20 40 60 80 100 120

-40

-20

0

20

40

60

80

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Shadow Region

Velocity(m/s)

10.0 m/s

X/C*100

Y/C

*10

0

-40 -20 0 20 40 60 80 100 120

-40

-20

0

20

40

60

80

-1.60 -1.20 -0.80 -0.40 0.00 0.40 0.80

Shadow Region


10.0 m/s

X/C*100Y

/C*1

00

-40 -20 0 20 40 60 80 100 120

-40

-20

0

20

40

60

80

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Shadow Region

Velocity(m/s)

10.0 m/s



( AOA = 6.0 deg. , Re=58,000)

X/C*100

Y/C

*10

0

0 10 20 30 40 50-5

0

5

10

15

10.0

8.0

6.0

4.0

2.0

0.0

Velocity(m/s)

X/C*100

Y/C

*10

0

0 10 20 30 40 50-5

0

5

10

15

0.50

-0.50

-1.50

-2.50

-3.50

-4.50

-5.50

Spanwisevorticity(1000*1/s)

X/C*100

Y/C

*10

0

0 10 20 30 40 50-5

0

5

10

15

0.085

0.075

0.065

0.055

0.045

0.035

0.025

0.015

0.005

T.K.E

X/C*100

Y/C

*10

0

0 10 20 30 40 50-5

0

5

10

15

0.085

0.075

0.065

0.055

0.045

0.035

0.025

0.015

0.005

T.K.E.

X/C*100

Y/C

*10

0

0 10 20 30 40 50-5

0

5

10

15

0.50

-0.50

-1.50

-2.50

-3.50

-4.50

-5.50


X/C*100

Y/C

*10

0

0 10 20 30 40 50-5

0

5

10

15

10.0

8.0

6.0

4.0

2.0

0.0

Velocity(m/s)


X/C*100

Y/C

*10

0

0 10 20 30 40 50

-5

0

5

10

15

0.50

-0.50

-1.50

-2.50

-3.50

-4.50

-5.50


X/C*100

Y/C

*10

0

0 10 20 30 40 50

-5

0

5

10

15

0.085

0.075

0.065

0.055

0.045

0.035

0.025

0.015

0.005

T.K.E

X/C*100

Y/C

*10

0

0 10 20 30 40 50

-5

0

5

10

15

0.085

0.075

0.065

0.055

0.045

0.035

0.025

0.015

0.005

T.K.E.


( AOA = 12.0 deg. , Re=58,000)

X/C*100Y

/C*1

00

0 10 20 30 40 50

-5

0

5

10

15

10.0

8.0

6.0

4.0

2.0

0.0

Velocity(m/s)

X/C*100

Y/C

*10

0

0 10 20 30 40 50

-5

0

5

10

15

0.50

-0.50

-1.50

-2.50

-3.50

-4.50

-5.50


X/C*100

Y/C

*10

0

0 10 20 30 40 50

-5

0

5

10

15

10.0

8.0

6.0

4.0

2.0

0.0

Velocity(m/s)


AerE344 Lab7: Hot wire measurements in the wake of an airfoil y

x

80

mm

Pressure rake

Hotwire probe

Test conditions:

Velocity: V=15 m/s

Angle of attack: AOA=0, and 12 deg.

Data sampling rate: f=5000Hz

Number of samples: 50,000 (10s in time)

No. of points: 20~25 points

Gap between points: ~0.2

inches

Lab#6

Lab#7


AerE344 Lab: Hot wire measurements in the wake of an airfoil

Hotwire

probe Lab#4

FFT 0

4

8

12

16

20

0 1000 2000 3000 4000

time sequence with data sampling rate of 1000 HzF

orc

e -

Z c

om

ponent

(N)

0

500

1000

1500

2000

2500

3000

5 10 15 20 25 30

Freqency (Hz)

arb

ita

ry s

ca

le

X/C *100

Y/C

*10

0

-40 -20 0 20 40 60 80 100 120 140

-60

-40

-20

0

20

40

60

vort: -4.5 -3.5 -2.5 -1.5 -0.5 0.5 1.5 2.5 3.5 4.5

shadow region

GA(W)-1 airfoil

25 m/s


AerE344 Lab: Hot wire measurements in the wake of an airfoil

Hotwire

probe Lab

Required data for the lab report:

1. Wake velocity profiles at AOA =0 and 12 deg

2. Wake turbulence intensity profiles at AOA =0 and 12 deg.

3. Estimated drag coefficients at AOA=0, and 12 deg.

4. FFT transformation to find vortex shedding frequency in the wake of the airfoil

5. Discussions based on the measurement results

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