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Compressible Vortex Rings in a Shock Tube with Helium Driver

R. Mariani

Prof. K. Kontis

2The University of Manchester Aero-Physics Laboratory

Table of Contents

Project background Experimental facility Results and discussions Conclusions

Project Background

Aim: to evaluate the characteristics of compressible vortex loops where the physical properties of the driver and driven gas differ

Variation of the theoretical Mach number while keeping max pressure ratio constant

Real life applications where gas properties are not constant

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Experimental Facility

Open end shock tube:Driver gas: grade A heliumDriven gas: air at ambient conditions

Pressure ratios: 4/8/12Constant cross-section

Fixed driven lengthVariable driver length

Schlieren set up:Shimadzu HPV-1 high-speed cameraContinuous xenon light

Particle image velocimetry:TSI high-speed stereo PIV

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Results and DiscussionEffects on Shock Strength Non-homogeneous gases in the shock tube:

Mixture of gases affect propagation velocity or flow structure only negligibly(C.G. Miller)

A light driver gas increases shock wave strength for a given pressure ratio:Higher Mach number compared to air/air gas

combination

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P4/P1 Ms Mse

4 1.53 1.43

8 1.89 1.81

12 2.12 2.10

Results and DiscussionEffects on Vortex Ring Structure Pressure ratio ~4

Oblique shock system in the trailing jet

Embedded rearward facing shock

Presence of weak secondary vortex ringsCounter-rotatingWeaker compared to

main ringFormation threshold

possibly lowered by non-homogeneous gas physical properties

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Flow structure (above) and secondary VR (below)

Results and DiscussionEffects on Vortex Ring Structure Pressure ratio ~8

Shape of jet becomes curvilinear

Oblique shock system transitions into a MR with a large Mach diskFormation of a central

jetFormation of

secondary vortex rings ahead of main vortex ring

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Flow structure of the vortex ring at P4/P1 ~ 8

Results and DiscussionEffects on Vortex Ring Structure Pressure ratio ~12

Mach disk increases in size allowing a large central jet to be formedExpanding central

jet

Embedded rearward facing shock becomes straight

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Flow structure of the vortex ring at P4/P1 ~ 8

Results and DiscussionEffects on Vortex Ring Structure

Pressure ratio ~8Secondary vortex

rings formation

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Results and DiscussionEffects on Vortex Ring Structure

Pressure ratio ~12Mach disk formation:

Formation of a lower velocity central jet

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Results and DiscussionEffects on Vortex Ring Structure

Pressure ratio ~12Mach disk increases in size allowing a large central jet to

be formedExpanding central jetShear layer opposite to main ring circulation. Consistent with

secondary vortex ring circulation

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Conclusions

Lighter driver gas leads to an increase in Mach number for a given pressure ratio

Presence of secondary vortex rings below the expected thresholdCould be caused by the non-homogeneous physical gas

properties. Oblique shock system transitions from RR to MR

Formation of a lower velocity central jetFormation of a central shear layer of opposite direction

with main vortex ring. Consistent with circulation of secondary vortex ring

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