Hydrogen combustion pressures and interactions with the structure in an enclosure.
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Transcript of Hydrogen combustion pressures and interactions with the structure in an enclosure.
Hydrogen combustion pressures and
interactions with the structure in an enclosure
Outline of the presentation
• Interaction of pressure waves with the structure
• Hydrogen combustion with emphasis on detonation
• A random choice method ( LES) for solving the compressible equations
• Conclusions
Relevant recent references
• S.B.Dorofeev ( and Russian Kuchatov institute)
• W. Breitung et.al. (Karlsruhe Forschungscentrum, OECD report)
• CFD codes: B02, DET3D, TONUS and others
Interaction with the structure
• The response of the walls is decoupled from the fluid dynamics because the characteristic times are vastly different
• The structure was Reinforced Concrete• Approximate single degree of freedom
system (SDOF) for the system represented by an infinite cylinder is not conservative. Therefore a complete FE solution is needed
Table 1. Peak detonation pressures and impulses on the containment wall
Initiation at mid-height Location on wall Initiation at the base Q/RTo=17 a/RT=17 Q/RTo=23
(sec)Impulse
oP (sec)
Impulse
oP (sec)
Impulse
oP
Radius (m)
Elevation (m)
oP
Pmax At 85
msec*
At 140
msec*
oP
Pmax At 85
msec*
At 140
msec*
oP
Pmax At 85
msec*
At 140
msec* 20.6 20.6 20.6 20.6 20.6 20.6 20.6 20.6 20.5 14.7 17.5 13.1 9.3 5.3
0
0.0 6.0
12.0 18.0 94.0 30.0 36.0 42.0 47.0 51.0 56.0 61.0 63.5 65.0 65.7
77.0 72.0 51.0 48.0 37.0 30.0 48.0 42.0 43.0 42.0 71.0 65.0 71.0 68.0 65.0
0.56 0.82 0.74 0.72 0.65 0.62 0.63 0.52 0.37 0.90 0.58 0.64 0.49 0.50 0.76
1.18 1.35 1.24 0.97 0.85 0.88 0.81 0.73 0.56 1.24 0.75 0.79 0.63 0.66 1.11
72.0 75.0 51.0 55.0 70.0 58.0 49.0 21.0 34.0 27.0 41.0 25.0 59.0 23.0 69.0
0.75 0.70 0.67 0.61 0.37 0.39 0.35 0.25 0.25 0.22 0.19 0.26 0.40 0.42 0.46
0.81 0.78 0.73 0.68 0.46 0.45 0.40 0.25 0.25 0.22 0.19 0.26 0.41 0.44 0.55
76.0 78.0 80.0 46.0 66.0 68.0 48.0 26.0 41.0 30.0 48.0 34.0 71.0 32.0 53.0
0.63 0.51 0.59 0.40 0.51 0.50 0.41 0.38 0.35 0.31 0.19 0.21 0.33 0.31 0.44
0.63 0.51 0.59 0.40 0.51 0.50 0.41 0.38 0.38 0.33 0.19 0.22 0.33 0.31 0.46
17oRT
q17
oRT
q
17oRT
q
Dome apex
Stress histories
Approximate solution is not conservative
The numerical method of solution
• Use the Riemann solution to solve the Euler equations i.e. viscosity and very small scale motions are neglected = LES (MILES)
• This solution is defined as if a dividing wall ( left and right side) separates two neighbouring uniform states
• Sharp discontinuities are reproduced
The Riemann problem:right and left states define states at the next time step through
a simple algebraic relation
DETONATION STRUCTURE
• The ZND model applies i.e. a shock (Neumann conditions) is followed by expanding deflagration at CJ conditions
• Both the shock and reaction zones are thin so that the detonation is represented by a sharp discontinuity
Detonation wave
u2/1
cjcjbbuucj /))/p(u(U
Advancing the solution to the next time step
• The dividing wall is assumed to be located at a random location between two neighbouring sates
• The solution is then advanced in time by sampling the exact solution at the mid-point (GLIMM-CHORIN)
Simple procedure for Glimm’s method
Sequence of Riemann Problems on Grid
Two dimensional case is handled by operator
splitting in space
Numerical conditions
• No numerical diffusion i.e. sharp discontinuities are reproduced
• CFL conditions must be satisfied
• Error is proportional to grid spacing
Error bound
• If h is the grid spacing, Dt is the time step , T is the final time of calculation , and uo the initial value the error is given by
o2/12/1N u))hT()
t
h(
3
2h()T(.,u)T(.,u
One dimensional spherical
Two dimensional axisymmetric
Pressure profile evolution Planar geometry
Pressure at the wall Planar geometry
Pressure profile evolution Spherical geometry (2m radius)
Pressure at the wall Spherical geometry
rtCo /
rtCo /
Discussion and Conclusions
• The RCM-Godunov method is an accurate LES and has been extended to 3-D calculations including reactions
• It can be used also for explosions with the reaction front represented as a discontinuity with a velocity equal to the maximum expected based on the turbulence level in a conservative sense.
Regarding computing as a straightforward routine, some
theoreticians still tend to underestimate its intellectual value and challenge , while practitioners often ignore its
accuracy and overrate its validityC.K.Chu , 1978