Detonation Smoke Foil Page

Experimental and Numerical Smoke Foils

Experimental Results

Experimental results on detonations have largely been obtained using what are called "smoked foils". Smoked foils are routinely used as a diagnostic technique to measure the "cell size" of a detonation for a particular combustible (gaseous) mixture. These are generally obtained by placing a foil or mylar sheet that has been coated with soot the inside of the detonation tube. As the detonation propagates, the triple points of the leading shock front etch their tracks into the soot.

Some experimental smoked foils. The pictures were scanned from Fickett and Davis (1979). The experiments were performed by Strehlow (1969) which is where Fickett and Davis also obtained the pictures.

An extensive database of experimental results is maintained at by Joe Shepherd at Caltech.

Numerical Simulations

Fortunately, we can easily generate the same "smoked-foil" effect numerically. All this requires is to track the leading shock position and pressure as a function of time. Then we just plot this on a two-dimensional grid to give the results below.

Two-Dimensional Numerical Simulations

Overdrive 1.1, Activation Energy 20, Heat Release 2, Gamma 1.2

This case has fairly periodic cell structure The detonation starts out at the left hand side of the top picture, and propagates to the right. The second and third pictures are a direct continuation of the first. Out of the five complete cells in this series, the initial perturbation has the most effect on the first two. It finally merges with the main transverse waves about two thirds of the way through the second cell. By the third cell in the series, the detonation seems to be in its final state.

Click on small images to see larger ones

Overdrive 1.2, Activation Energy 10, Heat Release 50, Gamma 1.2

Since the heat release and overdrive is much higher in this case, the average shock pressures are much higher. The cell structure is also much more irregular than the previous case.

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Three-Dimensional Simulations

The following two pictures were generated for the same dimensionless paramaters as used in the two dimensional cases above. Two grid resolution were used, 16 and 32 mesh points per ZND half-reaction length. The major difference to note in the following numerical smoke foils is the presence of the slapping wave.

Overdrive 1.1, Activation Energy 20, Heat Release 2, Gamma 1.2

Click on small image to see larger one (jpeg, 43 KB)

16 mesh points per ZND half-reaction length (170x80x80)

32 mesh points per ZND half-reaction length (340x160x160)

Overdrive 1.2, Activation Energy 10, Heat Release 50, Gamma 1.2

Click on small image to see larger one (jpeg, 50 KB each)

16 mesh points per ZND half-reaction length (170x80x80)

32 mesh points per ZND half-reaction length (340x160x160)

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