# Definition of strain rate magnitude for axisymmetric case in FLUENT

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The strain rate magnitude(STRAIN_RATE-MAG(c,t)) is defined in header files as:

sqrt(ND_SUM(ND_DOT(C_DUDX(c,t), C_DUDY(c,t), C_DUDZ(c,t),(C_DUDX(c,t) + C_DUDX(c,t)),(C_DUDY(c,t) + C_DVDX(c,t)),(C_DUDZ(c,t) + C_DWDX(c,t))),ND_DOT(C_DVDX(c,t), C_DVDY(c,t), C_DVDZ(c,t),(C_DVDX(c,t) + C_DUDY(c,t)),(C_DVDY(c,t) + C_DVDY(c,t)),(C_DVDZ(c,t) + C_DWDY(c,t))),ND_DOT(C_DWDX(c,t), C_DWDY(c,t), C_DWDZ(c,t), (C_DWDX(c,t) + C_DUDZ(c,t)),(C_DWDY(c,t) + C_DVDZ(c,t)),(C_DWDZ(c,t) + C_DWDZ(c,t))))

+ (rp_axi ? (2.*SQR(C_V(c,t)/C_AVE_Y(c,t)) + (sg_swirl ? (SQR(C_AVE_Y(c,t))*NV_MAG2( C_STORAGE_R_NV(c,t,SV_OMEGA_G))): 0.)): 0.))

I understand the first part of the definition which is basically the second invariant of the strain rate tensor. But for axisymmetric case part(rp_axi part) I don't get how those terms appear. Can anyone explain/refer to any theory resource to learn how those terms appear for axisymmetric case? Also, I can't find definition of the terms too in the manual.

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