1. Compressible Vortex Rings in a Shock Tube with Helium Driver
R. Mariani
Prof. K. Kontis
The University of Manchester Aero-Physics Laboratory

2. The University of Manchester Aero-Physics Laboratory
Table of Contents
Project background
Experimental facility
Results and discussions
Conclusions
The University of Manchester Aero-Physics Laboratory

3. The University of Manchester Aero-Physics Laboratory
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
For point 2: we were trying to push the Mach number to higher values without having to go beyond the max allowable shock tube pressure ratio of 12. Helium increased the Mach value fr the three standard pressure ratios that we use (4/8/12)
The University of Manchester Aero-Physics Laboratory

4. Experimental Facility
Open end shock tube:
Driver gas: grade A helium
Driven gas: air at ambient conditions
Pressure ratios: 4/8/12
Constant cross-section
Fixed driven length
Variable driver length
Schlieren set up:
Shimadzu HPV-1 high-speed camera
Continuous xenon light
Particle image velocimetry:
TSI high-speed stereo PIV
The University of Manchester Aero-Physics Laboratory

5. Results and Discussion Effects 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
When using a constant gas, in our case air/air, the theoretical Mach number for the three pressure ratios is ~1.34, 1.43, 1.65
Ms: theoretical Mach number; Mse: experimental Mach number
P4: driver pressure
P1: driven pressure (atmospheric)
P4/P1 Ms
Mse 4
1.53
1.43 8
1.89
1.81 12
2.12
2.10
The University of Manchester Aero-Physics Laboratory

6. Results and Discussion Effects on Vortex Ring Structure
Pressure ratio ~4
Oblique shock system in the trailing jet
Embedded rearward facing shock
Presence of weak secondary vortex rings
Counter-rotating
Weaker compared to main ring
Formation threshold possibly lowered by non-homogeneous gas physical properties
Flow structure (above) and secondary VR (below)
Vortex ring caused by the adverse pressure gradient causing the flow to decelerate more near the central region, causing
a shear layer to be formed ahead of the main vortex ring due to the Kelvin-Helmholtz instability present
at the jet boundary
The presence of the secondary vortex rings is unexpected as they usually occur at M>~1.50. The theoretical Mach ~1.53, experimental ~1.43.
The University of Manchester Aero-Physics Laboratory

7. Results and Discussion Effects on Vortex Ring Structure
Pressure ratio ~8
Shape of jet becomes curvilinear
Oblique shock system transitions into a MR with a large Mach disk
Formation of a central jet
Formation of secondary vortex rings ahead of main vortex ring
Flow structure of the vortex ring at P4/P1 ~ 8
Shape becomes curvilinear to keep pressure ratio along the jet constant.
The University of Manchester Aero-Physics Laboratory

8. Results and Discussion Effects on Vortex Ring Structure
Pressure ratio ~12
Mach disk increases in size allowing a large central jet to be formed
Expanding central jet
Embedded rearward facing shock becomes straight
Flow structure of the vortex ring at P4/P1 ~ 8
The University of Manchester Aero-Physics Laboratory

9. Results and Discussion Effects on Vortex Ring Structure
Pressure ratio ~8
Secondary vortex rings formation
The University of Manchester Aero-Physics Laboratory

10. Results and Discussion Effects on Vortex Ring Structure
Figure on the right shows the central jet as well in between the two red-colored regions.
Pressure ratio ~12
Mach disk formation:
Formation of a lower velocity central jet
The University of Manchester Aero-Physics Laboratory

11. Results and Discussion Effects on Vortex Ring Structure
Pressure ratio ~12
Mach disk increases in size allowing a large central jet to be formed
Expanding central jet
Shear layer opposite to main ring circulation. Consistent with secondary vortex ring circulation
The University of Manchester Aero-Physics Laboratory

12. The University of Manchester Aero-Physics Laboratory
Conclusions
Lighter driver gas leads to an increase in Mach number for a given pressure ratio
Presence of secondary vortex rings below the expected threshold
Could be caused by the non-homogeneous physical gas properties.
Oblique shock system transitions from RR to MR
Formation of a lower velocity central jet
Formation of a central shear layer of opposite direction with main vortex ring. Consistent with circulation of secondary vortex ring
The University of Manchester Aero-Physics Laboratory