[u, v, w, y]

c = 1.0 - y
wrate = rxn_rate(c)
fsd = sqrt (sqr(ddx(c)) + sqr(ddy(c)) + sqr(ddz(c)))

sd = ((d2dx(c) + d2dy(c) + d2dz(c)) * $rod + wrate) / fsd

nx = - ddx(c) / fsd
ny = - ddy(c) / fsd
nz = - ddz(c) / fsd

vn = u * nx + v * ny + w * nz

absk = abs(ddx(nx) + ddy(ny) + ddz(nz))

fu = (vn + sd) * nx

t1 = sqr(fu')
t2 = sqr(absk')

avg { c, fsd }

avg fsd { t1, t2, fu, absk}