Kinematics of a Turbulent Vortex Ring

1. Kinematics of a Turbulent Vortex Ring Samantha Damico Advanced Propulsion Research Laboratory Advisor: Dr. Kenneth Yu

2. 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

3. 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

4. Design

5. 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

6. 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

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

8. Helium – 20V, .5” Orifice, .35” Stroke t=14ms t=10ms

9. Helium – 20V, 1” Orifice, .35” Stroke t=14ms t=28ms

10. 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

11. Vortex Propagation – Voltage Change

12. Vortex Propagation – Orifice Change

13. 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 VoltageRefincreases

14. Model Analysis Threshold at about 20% of orifice diameter

15. 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

16. Independence Analysis Unclear dependence of vortex propagation on stroke length and voltage Average V/Vref = 3.847 Standard Deviation = 0.824

17. 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

18. 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

19. Acknowledgements • Advisor: • Dr. Kenneth Yu • Graduate Students: • Camilo Aguilera • Sammy Park • Jason Burr • Jonathan Geerts