Hi all,

I have a low density gas (1 mbar), in which a shock is present. Based on the Reynolds number (100), the flow is laminar. My question is if it is physically correct to assume that the flow around a shock is laminar. Isn't it always turbulent......

Kind Regards, Pascale.

At such a low Reynolds number do you actually have a shock?

Strictly speaking a shock can only form in a inviscid fluid (where it is termed a weak solution). At high Reynolds number the discontinuity is smoothed out through a viscous transition layer which results a smooth (or strong) solution. As the Reynolds number decreases the thickness of the transition layer grows and eventually becomes a meaningless concept. This is similar to the concept of a boundary layer - it's impossible to talk about boundary layers at low Reynolds numbers.

At a Reynolds number of 100 the flow will be laminar,

Tom.

Hi Tom,

The software I use, calculates a speed of sound based as a function of the molecular mass (100-300 kg/kmol). Then, when velocity becomes larger than this speed of sound, Mach exceeds 1,2,3 or whatsoever, and will fall down at a certain position. All simulations I have seen so far are not really influenced by the density.

Pascale

Hi Pascale,

I have run inviscid and laminar simulations of shock diffraction over objects such as cylinders and half diamonds at ambient pressures of 10Pa. I have found the results to match to shock tunnel experiments extremley well using a laminar assumption.

Hi Michael,

Thank you for responding. Do you have any references in open literature, or can you recommend open literature in general regarding this subject?

Pascale

Hi Pascale,

I have not yet published any papers as I am concentrating on completing my thesis. However, if you want to see papers on shock diffraction try this journal:

"Shock Waves" - springer verlag

Also, I think there are some simulations on this web page which might be of interest to you:

http://www.mech.uq.edu.au/staff/jacobs/cfcfd/index.html