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Kinematics of a Turbulent Vortex Ring

Samantha DamicoAdvanced Propulsion Research Laboratory

Advisor: Dr. Kenneth Yu

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Motivation

• Original interest was looking at entrained vortex in a combustor

• Large coherent vortices are a dominant feature in combustion instability. Want to study vortex dynamics and breakdown in a controlled environment

• Vortices are associated with pressure oscillations and heat release oscillations.

• If vortex formation, propagation, and breakdown can be better understood, perhaps vortices in combustion instability can be more accurately predicted and modeled

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Goal

• Investigate the motion of turbulent vortex ring structure found in combustors, develop a model to predict their behavior, and explore the feasibility of controlling their motion to actively suppress combustion instabilities

• Hope to see vorticity, watch vortex move out and break down, and look at distance with time

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Design

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Experiment Setup

• 3 orifice sizes (.5”, 1”, 1.5”)

• Push solenoid applied at range of voltages (14V, 16V, 18V, 20V, 22V, 24V) to hit membrane

• Solenoid applied at various stroke lengths (.1”, .2”, .35”, .5”)

• Used gasket for membrane

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Experiment

• Ran tests with argon then helium• Used schlieren visualization and a high speed

camera• Ran at 500Hz (or 2ms per frame)• Ran tests holding each of the parameters

constants while varying one of them

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Argon

20V, .5” Orifice, .35” Stroke, t=14ms 20V, 1” Orifice, .35” Stroke, t=20ms

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Helium – 20V, .5” Orifice, .35” Stroke

t=14mst=10ms

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Helium – 20V, 1” Orifice, .35” Stroke

t=14ms t=28ms

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Vortex Propagation

• Found that the density of the gas affects vortex formation and longevity– Used argon tests for analysis

• Using pixel measurements, estimated the distance traveled by the vortex each frame

• Using this raw data, calculated the steady-state velocity (Vss) for each test

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Vortex Propagation – Voltage Change

0 2 4 6 8 10 12 14 16 18 200

0.01

0.02

0.03

0.04

0.05

0.06

0.07

Vortex Propagation - .5" Orifice, .35" Stroke

16V20V24V

Time (ms)

Dist

ance

(m)

0 10 20 30 40 50 600

0.01

0.02

0.03

0.04

0.05

0.06

0.07

Vortex Propagation - 1" Orifice, .35" Stroke

16V20V24V

Time (ms)

Dist

ance

(m)

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Vortex Propagation – Orifice Change

0 5 10 15 20 25 30 350

0.01

0.02

0.03

0.04

0.05

0.06

0.07

Vortex Propagation - 20V, .35" Stroke

.5" Orifice1" Orifice

Time (ms)

Dist

ance

(m)

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Model Analysis• Modeling chamber as a cylinder, model the amount of gas

being pushed out same as volume of cone at complete stroke length

• Expect that as voltage increases, displacement time decreases– Amount of volume displacement related to stroke length– Time of volume displacement related to voltage applied

• (1/3)(CylinderArea)(StrokeLength) = displacement volume• VoltageRef is 16V• If model good, Displacement Time vs. VoltageRef/Voltage

should be roughly linear and with displacement time increasing as VoltageRef increases

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Model Analysis

0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.050

0.010.020.030.040.050.060.070.08

.5" Diameter Orifice

.1" Stroke

.2" Stroke

.35" Stroke

.5" Stroke

VoltageRef/Voltage

Disp

lace

men

t Tim

e (s

)

0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 1.050

0.02

0.04

0.06

0.08

0.1

1" Diameter Orifice

.2" Stroke

.35" Stroke

.5" Stroke

VoltageRef/Voltage

Disp

lace

men

t Tim

e (s

)

Threshold at about 20% of orifice diameter

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Independence Analysis

• Wanted to see if propagation independent of stroke and/or voltage

• Shown for .5” orifice• Vref - velocity of 1” orifice diameter tests• If independent, V/Vref should be about the

same as stroke length and voltage increase

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Independence Analysis

0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.550

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2

3

4

5

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Independent of Stroke Length

16V

20V

24V

Stroke (in)

V/Vr

ef

15 16 17 18 19 20 21 22 23 24 250

1

2

3

4

5

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Independent of Voltage

.2" Stroke

.35" Stroke

.5" Stroke

Voltage (V)

V/Vr

ef

Unclear dependence of vortex propagation on stroke length and voltageAverage V/Vref = 3.847Standard Deviation = 0.824

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Conclusions

• Type of gas affects vortex formation and propagation

• Orifice size greatly impacts vortex propagation• Good model of chamber as cylinder, with amount

of gas pushed out same as volume of cone at complete stroke length and expectation that as voltage increases, displacement time decreases

• There is some dependence on voltage and stroke length with further work needed

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Future Work

• Use the work here to create a model for predicting vortex propagation and velocity

• Use reacting gas to investigate heat release in a vortex (generate, propagate, burn, see where breaks up) – heat release usually spikes when vortex bursts

• Come up with rate at which displacement happens

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Acknowledgements

• Advisor: – Dr. Kenneth Yu

• Graduate Students: – Camilo Aguilera– Sammy Park– Jason Burr– Jonathan Geerts