{"id":368817,"date":"2024-05-28T04:38:45","date_gmt":"2024-05-28T04:38:45","guid":{"rendered":"\/forum\/?post_type=topic&p=368817"},"modified":"2024-05-28T04:38:45","modified_gmt":"2024-05-28T04:38:45","slug":"heat-flux-estimation-for-a-lox-lch4-rocket-engine-using-udf","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/heat-flux-estimation-for-a-lox-lch4-rocket-engine-using-udf\/","title":{"rendered":"Heat flux estimation for a LOX LCH4 rocket engine using UDF"},"content":{"rendered":"

I’m working on the design of a pressure-fed LO2 and LNG rocket engine. I’ve been using Fluent to estimate the heat flux for an ablative-cooled engine. I was able to solve all the compilation errors for my UDF.<\/p>\n

I’m attaching my boundary conditions and mesh. My model is axisymmetric and I have a fluid-solid domain in my problem, so all my methods are second order. But I keep getting this error whenever I run my calculations.<\/p>\n

“Divergence detected in AMG solver. temporarily reducing Courant number to 0.5 and trying again…”<\/p>\n

Is there a problem with my mesh? I’ve used a multi-zone and face mesh with 15 inflation layers.
I’ve tried all the methods I know to simplify the problem, my mesh quality is fairly good. I still keep getting the same error<\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

(The actual mesh is much more refined, the picture quality is quite poor)<\/p>\n

\"\"<\/p>\n

I’m attaching my UDF below:<\/p>\n

#include “udf.h”<\/span><\/div>\n
#define pi 3.14159<\/span><\/div>\n
 <\/div>\n
DEFINE_PROFILE(Boun_cond,t,i)<\/span><\/div>\n
 <\/div>\n
{<\/span><\/div>\n
 <\/div>\n
real x[ND_ND];<\/span><\/div>\n
 <\/div>\n
real rt, dt, At, vis, Cp, Pr, Pc, Tc, gamma, Cstar,Cstareff, g, r, A, M, Mnew, N1, N2, N3, Taw, Thotgas,T,hgas,func, ffunc, fCO2, fH2O, Le, qrad, qCO2, qH2O, P, mdot,kt;<\/span><\/div>\n
 <\/div>\n
face_t f;<\/span><\/div>\n
 <\/div>\n
int k,NI;<\/span><\/div>\n
 <\/div>\n
rt=0.015085; \/* m        *\/<\/span><\/div>\n
vis=0.000075018; \/*Kg\/m-s    *\/<\/span><\/div>\n
Cp=2328.6; \/*J\/Kg-K    *\/<\/span><\/div>\n
Pr=0.6552;<\/span><\/div>\n
Pc=2500000; \/*Pa *\/<\/span><\/div>\n
Tc=3235; \/*K *\/<\/span><\/div>\n
gamma=1.20;<\/span><\/div>\n
Cstar=1855.4; \/*m\/s *\/<\/span><\/div>\n
Cstareff = 0.92;<\/span><\/div>\n
kt = 0.2662; \/*W\/mK *\/<\/span><\/div>\n
 <\/div>\n
NI=1000;<\/span><\/div>\n
 <\/div>\n
dt=rt*2;<\/span><\/div>\n
At=pi*pow(rt,2);<\/span><\/div>\n
 <\/div>\n
fCO2=0.10511; \/*Mole fraction of CO2 *\/<\/span><\/div>\n
fH2O=0.46300; \/*Mole fraction of H2O *\/<\/span><\/div>\n
mdot = 0.987; \/*Mass flow rate of exhaust *\/<\/span><\/div>\n
 <\/div>\n
begin_f_loop(f,t)<\/span><\/div>\n
 <\/div>\n
{<\/span><\/div>\n
 <\/div>\n
F_CENTROID(x,f,t);<\/span><\/div>\n
r=sqrt(pow(x[0],2)+pow(x[1],2));<\/span><\/div>\n
A=pi*pow(r,2);<\/span><\/div>\n
Le=0.6*2*r;<\/span><\/div>\n
 <\/div>\n
\/*For combustion chamber *\/<\/span><\/div>\n
 <\/div>\n
if (x[0]<0.06604)<\/span><\/div>\n
 <\/div>\n
{<\/span><\/div>\n
 <\/div>\n
M=0;<\/span><\/div>\n
P=Pc\/pow((1+(gamma-1)*pow(M,2)\/2),(gamma\/(gamma-1)));<\/span><\/div>\n
T=Tc\/(1+(gamma-1)\/2*pow(M,2));<\/span><\/div>\n
Taw=Tc*((1+pow(Pr,0.33)*((gamma-1)\/2)*pow(M,2))\/(1+((gamma-1)\/2)*pow(M,2)));<\/span><\/div>\n
Thotgas=T+0.9*(Tc*pow(Cstareff,2)-T);<\/span><\/div>\n
hgas=0.01975*pow(k,0.18)*pow((mdot*Cp),0.82)\/pow((2*r),1.82)*pow((Thotgas\/(F_T(f,t))),0.35);<\/span><\/div>\n
 <\/div>\n
\/*Radiation heat transfer              *\/<\/span><\/div>\n
 <\/div>\n
qCO2 = 5.74*pow((P*fCO2*r\/(pow(10,5))),0.3)*pow((F_T(f,t)\/100),3.5);<\/span><\/div>\n
qH2O = 4*pow((P*fH2O*r\/(pow(10,5))),0.3)*pow((F_T(f,t)\/100),3.5);<\/span><\/div>\n
 <\/div>\n
qrad=qCO2+qH2O;<\/span><\/div>\n
 <\/div>\n
}<\/span><\/div>\n
 <\/div>\n
 <\/div>\n
\/*For subsonic region                   *\/<\/span><\/div>\n
 <\/div>\n
if (x[0]<0 && x[0]>=0.06604)<\/span><\/div>\n
 <\/div>\n
{<\/span><\/div>\n
 <\/div>\n
for (k=1;k<=NI;k++)<\/span><\/div>\n
{<\/span><\/div>\n
if (k==1)<\/span><\/div>\n
M=0.05;<\/span><\/div>\n
else<\/span><\/div>\n
M=Mnew;<\/span><\/div>\n
 <\/div>\n
N1=2\/(gamma+1);<\/span><\/div>\n
N2=(gamma+1)\/(2*(gamma-1));<\/span><\/div>\n
N3=1+(gamma-1)*pow(M,2)\/2;<\/span><\/div>\n
 <\/div>\n
func = pow(N1, N2) * pow(N3, N2) \/ M – A \/ At;<\/span><\/div>\n
ffunc=-pow(N1,N2)*pow(N3,N2)*pow(M,-2)+pow(N1,N2)*N2*pow(N3,N2-1)*(gamma-1);<\/span><\/div>\n
 <\/div>\n
Mnew=M-func\/ffunc;<\/span><\/div>\n
if(fabs(Mnew-M)<0.01)<\/span><\/div>\n
break;<\/span><\/div>\n
}<\/span><\/div>\n
 <\/div>\n
P=Pc\/pow((1+(gamma-1)*pow(M,2)\/2),(gamma\/(gamma-1)));<\/span><\/div>\n
T=Tc\/(1+(gamma-1)\/2*pow(M,2));<\/span><\/div>\n
Taw=Tc*((1+pow(Pr,0.33)*((gamma-1)\/2)*pow(M,2))\/(1+((gamma-1)\/2)*pow(M,2)));<\/span><\/div>\n
Thotgas=T+0.9*(Tc*pow(Cstareff,2)-T);<\/span><\/div>\n
hgas=0.01975*pow(k,0.18)*pow((mdot*Cp),0.82)\/pow((2*r),1.82)*pow((Thotgas\/(F_T(f,t))),0.35);<\/span><\/div>\n
 <\/div>\n
\/*Radiation heat transfer              *\/<\/span><\/div>\n
 <\/div>\n
qCO2 = 5.74*pow((P*fCO2*r\/(pow(10,5))),0.3)*pow((F_T(f,t)\/100),3.5);<\/span><\/div>\n
qH2O = 4*pow((P*fH2O*r\/(pow(10,5))),0.3)*pow((F_T(f,t)\/100),3.5);<\/span><\/div>\n
 <\/div>\n
qrad=qCO2+qH2O;<\/span><\/div>\n
 <\/div>\n
}<\/span><\/div>\n
 <\/div>\n
 <\/div>\n
\/*For Supersonic region*\/<\/span><\/div>\n
 <\/div>\n
if (x[0]>=0)<\/span><\/div>\n
 <\/div>\n
{<\/span><\/div>\n
 <\/div>\n
for (k=1;k<=NI;k++)<\/span><\/div>\n
{<\/span><\/div>\n
if (k==1)<\/span><\/div>\n
M=5;<\/span><\/div>\n
else<\/span><\/div>\n
M=Mnew;<\/span><\/div>\n
 <\/div>\n
N1=2\/(gamma+1);<\/span><\/div>\n
N2=(gamma+1)\/(2*(gamma-1));<\/span><\/div>\n
N3=1+(gamma-1)*pow(M,2)\/2;<\/span><\/div>\n
 <\/div>\n
func = pow(N1, N2) * pow(N3, N2) \/ M – A \/ At;<\/span><\/div>\n
ffunc=-pow(N1,N2)*pow(N3,N2)*pow(M,-2)+pow(N1,N2)*N2*pow(N3,N2-1)*(gamma-1);<\/span><\/div>\n
 <\/div>\n
Mnew=M-func\/ffunc;<\/span><\/div>\n
if(fabs(Mnew-M)<0.01)<\/span><\/div>\n
break;<\/span><\/div>\n
}<\/span><\/div>\n
 <\/div>\n
P=Pc\/pow((1+(gamma-1)*pow(M,2)\/2),(gamma\/(gamma-1)));<\/span><\/div>\n
T=Tc\/(1+(gamma-1)\/2*pow(M,2));<\/span><\/div>\n
Taw=Tc*((1+pow(Pr,0.33)*((gamma-1)\/2)*pow(M,2))\/(1+((gamma-1)\/2)*pow(M,2)));<\/span><\/div>\n
Thotgas=T+0.9*(Tc*pow(Cstareff,2)-T);<\/span><\/div>\n
hgas=0.01975*pow(k,0.18)*pow((mdot*Cp),0.82)\/pow((2*r),1.82)*pow((Thotgas\/(F_T(f,t))),0.35);<\/span><\/div>\n
 <\/div>\n
\/*Radiation heat transfer              *\/<\/span><\/div>\n
 <\/div>\n
qCO2 = 5.74*pow((P*fCO2*r\/(pow(10,5))),0.3)*pow((F_T(f,t)\/100),3.5);<\/span><\/div>\n
qH2O = 4*pow((P*fH2O*r\/(pow(10,5))),0.3)*pow((F_T(f,t)\/100),3.5);<\/span><\/div>\n
 <\/div>\n
qrad=qCO2+qH2O;<\/span><\/div>\n
 <\/div>\n
}<\/span><\/div>\n
 <\/div>\n
F_PROFILE(f,t,i)=(hgas*(Taw-F_T(f,t))+qrad);<\/span><\/div>\n
}<\/span><\/div>\n
 <\/div>\n
end_f_loop(f,t)<\/span><\/div>\n
 <\/div>\n
}<\/span><\/div>\n
 <\/div>\n
 <\/div>\n
 <\/div>\n
 <\/div>\n
 <\/div>\n","protected":false},"template":"","class_list":["post-368817","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_author_ip":["23.216.133.155"],"_bbp_subscription":["349801"],"_btv_view_count":["343"],"_bbp_topic_status":["unanswered"],"_bbp_topic_id":["368817"],"_bbp_forum_id":["27792"],"_bbp_engagement":["199","349801"],"_bbp_voice_count":["2"],"_bbp_reply_count":["1"],"_bbp_last_reply_id":["370147"],"_bbp_last_active_id":["370147"],"_bbp_last_active_time":["2024-07-02 14:30:22"]},"test":"vijay-adhi2021vitstudent-ac-in"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/368817","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics"}],"about":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/types\/topic"}],"version-history":[{"count":1,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/368817\/revisions"}],"predecessor-version":[{"id":368818,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/368817\/revisions\/368818"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=368817"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}