| 1. |
- Eliasson, Veronica, et al.
(author)
-
Controlling the form of strong converging shocks by means of disturbances.
- 2007
-
In: Shock Waves. - : Springer Science and Business Media LLC. - 0938-1287 .- 1432-2153. ; 17:1-2, s. 29-42
-
Journal article (peer-reviewed)abstract
- The influence of artificial disturbances on the behavior of strong converging cylindrical shocks is investigated experimentally and numerically. Ring-shaped shocks, generated in an annular cross sectional shock tube are transformed to converging cylindrical shocks in a thin cylindrical test section, mounted at the rear end of the shock tube. The converging cylindrical shocks are perturbed by small cylinders placed at different locations and in various patterns in the test section. Their influence on the shock convergence and reflection process is investigated. It is found that disturbances arranged in a symmetrical pattern will produce a symmetrical deformation of the converging shockfront. For example, a square formation produces a square-like shock and an octagon formation a shock with an octagonal front. This introduces an alternative way of tailoring the form of a converging shock, instead of using a specific form of a reflector boundary. The influence of disturbances arranged in non-symmetric patterns on the shape of the shockfront is also investigated.
|
|
| 2. |
- Eliasson, Veronica, et al.
(author)
-
Focusing of strong shocks in an annular shock tube
- 2007
-
In: Shock Waves. - : Springer Science and Business Media LLC. - 0938-1287 .- 1432-2153. ; 15:3-4, s. 205-217
-
Journal article (peer-reviewed)abstract
- Focusing of strong shock waves in a gas-filled thin convergence chamber with various forms of the reflector boundary is investigated experimentally and numerically. The convergence chamber is mounted at the end of the horizontal co-axial shock tube. The construction of the convergence chamber allows the assembly of the outer chamber boundaries of various shapes. Boundaries with three different shapes have been used in the present investigation-a circle, an octagon and a smooth pentagon. The shock tube in the current study was able to produce annular shocks with the initial Mach number in the range M-s = 2.3-3.6. The influence of the shape of the boundary on the shape and properties of the converging and reflected shock waves in the chamber has then been investigated both experimentally and numerically. It was found that the form of the converging shock is initially governed by the shape of the reflector and the nonlinear interaction between the shape of the shock and velocity of shock propagation. Very close to the center of convergence the shock obtains a square-like form in case of a circular and octagonal reflector boundary. This is believed to stem from the instability of the converging shock front triggered by the disturbances in the flow field. The outgoing, reflected shocks were also observed to be influenced by the shape of the boundary through the flow ahead as created by the converging shocks.
|
|
| 3. |
- Eliasson, Veronica, et al.
(author)
-
Light emission during shock wave focusing in air and argon
- 2007
-
In: Physics of fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 19:10, s. 106106-1-106106-17
-
Journal article (peer-reviewed)abstract
- The light emission from a converging shock wave was investigated experimentally. Results show that the shape of the shock wave close to the center of convergence has a large influence on the amount of emitted light. It was found that a symmetrical polygonal shock front produced more light than an asymmetrical shape. The light emission appears as the shock wave collapses. The full width at half maximum of the light pulse is about 200 ns for all geometrical shapes. It was also found that argon as a test gas produces more light than air. Numerical simulations showed good agreement with experimental results regarding the shape of the shock and the flow field behind the shock. The temperature field from the numerical simulations was investigated and shows that the triple points behind the shock front are hot spots that increase the temperature at the center as they arrive there.
|
|
| 4. |
- Eliasson, Veronica, et al.
(author)
-
On cylindrically converging shock waves shaped by obstacles
- 2008
-
In: Physica D. - : Elsevier BV. - 0167-2789 .- 1872-8022. ; 237:14-17, s. 2203-2209
-
Journal article (peer-reviewed)abstract
- Motivated by recent experiments, numerical simulations of cylindrically converging shock waves were performed. The converging shocks impinged upon a set of 0-16 regularly space obstacles. For more than two obstacles the resulting diffracted shock fronts formed polygonal shaped patterns near the point of focus. The maximum pressure and temperature as a function of the number of obstacles were studied. The self-similar behavior of cylindrical, triangular and square-shaped shocks was also investigated.
|
|
| 5. |
- Eliasson, Veronica, 1978-
(author)
-
On focusing of shock waves
- 2007
-
Doctoral thesis (other academic/artistic)abstract
- Both experimental and numerical investigations of converging shock waves have been performed. In the experiments, a shock tube was used to create and study converging shock waves of various geometrical shapes. Two methods were used to create polygonally shaped shocks. In the first method, the geometry of the outer boundary of the test section of the shock tube was varied. Four different exchangeable shapes of the outer boundary were considered: a circle, a smooth pentagon, a heptagon, and an octagon. In the second method, an initially cylindrical shock wave was perturbed by metal cylinders placed in various patterns and positions inside the test section. For three or more regularly spaced cylinders, the resulting diffracted shock fronts formed polygonal shaped patterns near the point of focus. Regular reflection was observed for the case with three cylinders and Mach refection was observed for cases with four or more cylinders. When the shock wave is close to the center of convergence, light emission is observed. An experimental investigation of the light emission was conducted and results show that the shape of the shock wave close to the center of convergence has a large influence on the amount of emitted light. It was found that a symmetrical polygonal shock front produced more light than an asymmetrical shape. The shock wave focusing was also studied numerically using the Euler equations for a gas obeying the ideal gas law with constant specific heats. Two problems were analyzed; an axisymmetric model of the shock tube used in the experiments and a cylindrical shock wave diffracted by cylinders in a two dimensional test section. The results showed good agreement with the experiments. The temperature field from the numerical simulations was investigated and shows that the triple points behind the shock front are hot spots that increase the temperature at the center as they arrive there. As a practical example of shock wave focusing, converging shocks in an electrohydraulic lithotripter were simulated. The maximum radius of a gas bubble subjected to the pressure field obtained from the lithotripter was calculated and compared for various geometrical shapes and materials of the reflector. Results showed that the shape had a large impact while the material did not influence the maximum radius of the gas bubble.
|
|
| 6. |
- Eliasson, Veronica, 1978-
(author)
-
On focusing of strong shock waves
- 2005
-
Licentiate thesis (other academic/artistic)abstract
- Focusing of strong shock waves in a gas-filled thin test section with various forms of the reflector boundary is investigated. The test section is mounted at the end of the horizontal co-axial shock tube. Two different methods to produce shock waves of various forms are implemented. In the first method the reflector boundary of the test section is exchangeable and four different reflectors are used: a circle, a smooth pentagon, a heptagon and an octagon. It is shown that the form of the converging shock wave is influenced both by the shape of the reflector boundary and by the nonlinear dynamic interaction between the shape of the shock and the propagation velocity of the shock front. Further, the reflected outgoing shock wave is affected by the shape of the reflector through the flow ahead of the shock front. In the second method cylindrical obstacles are placed in the test section at various positions and in various patterns, to create disturbances in the flow that will shape the shock wave. It is shown that it is possible to shape the shock wave in a desired way by means of obstacles. The influence of the supports of the inner body of the co-axial shock tube on the form of the shock is also investigated. A square shaped shock wave is observed close to the center of convergence for the circular and octagonal reflector boundaries but not in any other setups. This square-like shape is believed to be caused by the supports for the inner body. The production of light, as a result of shock convergence, has been preliminary investigated. Flashes of light have been observed during the focusing and reflection process.
|
|
| 7. |
- Eliasson, Veronica, et al.
(author)
-
Regular versus Mach reflection for converging polygonal shocks
- 2007
-
In: Shock Waves. - : Springer Science and Business Media LLC. - 0938-1287 .- 1432-2153. ; 17:1-2, s. 43-50
-
Journal article (peer-reviewed)abstract
- The onset of Mach reflection or regular reflection at the vertices of a converging polygonal shock wave was investigated experimentally in a horizontal annular shock tube. The converging shock waves were visualized by schlieren optics. Two different types of polygonal shock convergence patterns were observed. We compared the behavior during the focusing process for triangular and square-shaped shocks. It is shown that once a triangular shaped shock is formed, the corners in the converging shock will undergo regular reflection and consequently the shape will remain unaltered during the focusing process. A square-shaped shock suffers Mach reflections at the corners and hence a reconfiguring process takes place; the converging shock wave alternates between a square and an octagon formation during the focusing process.
|
|
| 8. |
- Eliasson, Veronica
(author)
-
The Production of Converging Polygonal Shock Waves by Means of Reflectors and Cylindrical Obstacles
- 2006
-
In: Flow Dynamics. - : AIP. - 0735403244 ; , s. 445-449
-
Conference paper (peer-reviewed)abstract
- Converging and reflecting strong shock waves are investigated experimentally in a horizontal co-axial shock tube. The shock tube has a test section mounted at the end of the tube. Two different methods to produce various geometrical shapes of shock waves are tested. In the first method the reflector boundary of the test section is exchangeable and four different reflectors are used: a circle, a smooth pentagon, a heptagon and an octagon. It is shown that the form of the converging shock wave is influenced both by the shape of the reflector boundary and by the nonlinear dynamics between the shape of the shock and the velocity of the shock front. Further, the reflected outgoing shock wave is affected by the shape of the reflector through the flow ahead of the shock front. In the second method we use cylindrical obstacles, placed in the test section at various positions and patterns, to create disturbances in the flow that will shape the shock wave. It is shown that it is possible to shape the shock wave in a desired way with these obstacles. The influence of the supports of the inner body of the co-axial shock tube is also investigated. A square shaped shock wave is observed close to the center of convergence for the circular and octagonal reflectors but not in any other setups. This square-like shape is believed to be caused by the supports for the inner body.
|
|
