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\Large
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		      Department of Mathematics\\
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                           University of Houston\\

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{{\Large\bf                Scientific Computing Seminar}}

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Prof.  M. S. Ivanov\\
Khristianovich Institute of Theoretical and Applied Mechanics\\
Siberian Branch of the Russian Academy of Sciences\\
Novosibirsk, Russia\\

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\Large

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{\bf New numerical and experimental results \\
on transition between regular and Mach reflection \\
of strong shock waves }

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                         Monday, June 29, 2009 \\
                               2 PM - 3 PM\\
%                           Room 127  \  \  \  S\&R1 \\
                           Room 646  \   \  PGH \\
%                         Room 634  \  \  \  S\&R1 \\
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\noindent {\bf Abstract:} 
An overview of our recent numerical and experimental studies on transition 
between steady regular and Mach reflections of strong shock waves will be 
presented. The existence of the dual solution domain at high Mach numbers 
implies that, depending on the initial conditions, both regular and Mach 
reflections may be observed at the same flow parameters.

 	The numerical simulations confirm the hypothesis of the existence 
of a hysteresis of regular and Mach reflections with variation of the 
incident shock wave angle. Regular reflection (RR) is maintained until 
the shock wave angle exceeds the upper limit of its existence, where a 
sudden transition to Mach reflection (MR) occurs. When the shock wave angle 
is decreased back, the Mach reflection is maintained until the lower limit 
of its existence is reached. 

 However, the experimental data are ambiguous. In some wind tunnels the 
transition from RR to MR occurs at any angle inside the dual solution domain. 
This is usually explained by the influence of the flow disturbances, which 
promote the transition. However, the mechanisms of such forced transition are 
still not understood. 

 Our recent experiments performed in a "quiet" supersonic wind tunnel have 
shown a prominent hysteresis loop: the transition between regular and Mach 
reflections occurs in close agreement with theoretical predictions. The 
conclusion is that the interpretation of wind tunnel experiments in this 
problem must take into account the level of free-stream disturbances in 
the wind tunnel flow.


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%\noindent {\bf Future talks in Scientific Computing Seminar}

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\noindent This seminar is easily accessible to persons with disabilities.
For more information or for assistance, please contact the Mathematics
Department at 743-3500.





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