Learning Forum

[atulsbhat]

PROBLEM EXPLANATION : A NATURAL CONVECTION PROBLEM

Geometry : 2D Rectangular Flat Plate

Link for all My Files

https://drive.google.com/drive/folders/1v-cl_aCg5rN6EjibgOcT8vE0ybGxsE-D?usp=sharing

SOLVER: PRESSURE BASED,STEADY STATE , LAMINAR, SINGLE PHASE AND WITH ENERGY MODEL

GRAVITY: Y= -9.81

MATERIAL PROPERTIES: UDF (CELL BASED)

BOUNDARY CONDITIONS:

ISO (WALL) = 649.16 K (Near Critical Region TEMP) {Non LINEAR}

VELOCITY INLET= 0.0001 m/sec and 643.16 K

PRESSURE OUTLET: 22500000 (No Back Flow)

Method :COUPLED AND ALL RELAXATION FACTORS UNDER 0.8

UDF IS ATTACHED in the link above(NAMED PRO)

ERRORS WHICH I GOT; INVALID CP (I SET TEMP BOUNDS RIGHT)

Regards ATUL S

[DrAmine]

As ANSYS employee I do ignore attachments and links to Deive ObeDrive etc...

Paste your UDF here. Just for superficial verification as we do not debug UDFs

[atulsbhat]

#include "udf.h"

DEFINE_PROPERTY(cell_density, c, t) 

{ 

double T2 = C_T(c, t); 

double rho;

if (635.00< T2 <=647.65)

{

rho = (-1.80375321498E-008*pow(T2,3)+4.37725881273E-003*pow(T2,2)-5.72870568035E+000*T2+1.87919262419E+003)/(5.73224251694E-009*pow(T2,3)-5.29420035132E-006*pow(T2,2)-5.19145559843E-004*T2+1);

}

else if (647.65< T2 <=648.70)

{

rho = (3.17383063793E-005*pow(T2,3)-4.67841673791E-002*pow(T2,2)+2.04434456269E+001*T2-2.23825052795E+003)/(6.58499450671E-009*pow(T2,3)-6.85372588417E-006*pow(T2,2)+1.33555488262E-004*T2+1);

}

else if (648.70< T2 <=649.00)

{

rho -4.34313022431E-005*pow(T2,3)+3.32633967077E-002*pow(T2,2)+1.16448492280E+001*T2-9.69578668950E+003)/(-8.21772033015E-009*pow(T2,3)+1.25803346920E-005*pow(T2,2)-6.24451347023E-003*T2+1);

}

else if (649.00< T2 <=660.00)

{

rho = (-9.94061577245E-007*pow(T2,3)+2.29499012449E-003*pow(T2,2)-1.71573797723E+000*T2+4.18604178695E+002)/(1.54441783415E-009*pow(T2,3)+4.23867511741E-007*pow(T2,2)-2.46639558372E-003*T2+1);

}

else

{

rho = 145;

}

return rho; 

}

DEFINE_SPECIFIC_HEAT(cell_SpecificHeat, T, Tref, h, yi)

{  

double cp;

if (635.00< T <=648.00)

{

cp=(-1.22158459347E-003*pow(T,3)+2.17569323612E+000*pow(T,2)-1.29281382835E+003*T+2.56632684171E+005)/(-1.54130619189E-003*T+1);

}

else if (648.00< T <=648.73)

{

cp=(3.55323794766E-004*pow(T,3)-4.48432744279E-001*pow(T,2)+ 1.33037573218E+002*T+5.40783052792E+003)/(4.28000889300E-012*pow(T,4)+2.41784831000E-010*pow(T,3)-3.34155028245E-006*pow(T,2)-6.43985888337E-004*T+1);

}

else if (648.73< T <=649.50)

{

cp=(-5.18823303098E-008*pow(T,4)+8.61428212182E-004*pow(T,3)-1.43401674862E+000*pow(T,2)+8.29938510799E+002*T-1.60895776843E+005)/(4.17611916514E-009*pow(T,3)-3.04175710540E-006*pow(T,2)-1.32571651328E-003*T+1);

}

else if (649.50< T <=660.00)

{

cp=(3.63087828676E-007*pow(T,4)-5.05376552107E-004*pow(T,3)+7.74302775445E-002*pow(T,2)+1.42466716874E+002*T-5.13360638841E+004)/(6.70506677622E-009*pow(T,3)-6.23021496014E-006*pow(T,2)-3.21570998725E-004*T+1);

}

else

{

cp = 10000;

}

*h = cp*(T-Tref);

return cp; 

}

 

[atulsbhat]

Continuation.....

DEFINE_PROPERTY(cell_ktc, c, t) 

{ 

double T3 = C_T(c, t); 

double ktc;

if (635.00< T3 <=647.95)

{

ktc = (9.67327651787E-010*pow(T3,3)+ 1.07198980062E-006*pow(T3,2)-2.65628458181E-003*T3+1.00798585123E+000)/(5.00871983799E-009*pow(T3,3)-4.30553217646E-006*pow(T3,2)-8.56213098793E-004*T3+1);

}

else if (647.95< T3 <=648.73)

{

ktc = (-3.15665107745E-011*pow(T3,4)+5.74316328609E-008*pow(T3,3)-8.00570356905E-005*pow(T3,2)+6.58380991564E-002*T3-1.91080817698E+001)/(-1.88933190656E-007*pow(T3,3)+2.47518298176E-004*pow(T3,2)-8.26013714844E-002*T3+1);

}

else if (648.73< T3 <=649.10)

{

ktc = (9.21882104159E-010*pow(T3,3)+9.66700804229E-007*pow(T3,2)-2.41830902924E-003*T3+9.10302469777E-001)/(6.85095548536E-009*pow(T3,3)-6.51237771764E-006*pow(T3,2)-1.99926781030E-004*T3+1);

}

else if (649.10< T3 <=649.90)

{

ktc = (1.55340145958E-009*pow(T3,3)-2.08750317819E-006*pow(T3,2)+7.41797773475E-004*T3-2.68104657893E-002)/(3.01622383420E-011*pow(T3,3)+2.30136429280E-006*pow(T3,2)-3.04713864718E-003*T3+1);

}

else if (649.90< T3 <=660.00)

{

ktc = (1.57649522842E-010*pow(T3,3)+2.60321568704E-007*pow(T3,2)-5.21436191042E-004*T3+1.85693253101E-001)/(6.17253403657E-009*pow(T3,3)-5.52538004836E-006*pow(T3,2)-5.54654898842E-004*T3+1);

}

else

{

ktc = 0.15000;

}

return ktc; 

}

DEFINE_PROPERTY(cell_viscosity, c, t) 

{ 

double T4 = C_T(c, t); 

double mu_lam;

if (635.00< T4 <=647.20)

{

mu_lam = (9.89197719095E-015*pow(T4,4)-1.71009457131E-011*pow(T4,3)+9.33538304205E-009*pow(T4,2)-1.41644707543E-006*T4-9.28741686026E-005)/(-1.53533206630E-003*T4+1);

}

else if (647.20< T4 <=648.60)

{

mu_lam = (3.99280946668E-013*pow(T4,3)-1.98818294190E-010*pow(T4,2)-3.35610542542E-007*T4+1.92473554834E-004)/(-1.53822789587E-003*T4+1);

}

else if (648.60< T4 <=648.80)

{

mu_lam = (4.49491045673E-011*pow(T4,2)-5.82458544750E-008*T4+1.88689994165E-005)/(2.09494866252E-009*pow(T4,3)-3.38328960437E-007*pow(T4,2)-2.20364870424E-003*T4+1);

}

else if (648.80< T4 <=649.10)

{

mu_lam = (-3.70888390134E-016*pow(T4,4)-2.66822899344E-013*pow(T4,3)+2.04526782970E-010*pow(T4,2)+4.75118757913E-007*T4-2.55763296559E-004)/(2.20110380648E-009*pow(T4,3)-6.08541480188E-007*pow(T4,2)-2.07309915781E-003*T4+1);

}

else if (649.10< T4 <=660.00)

{

mu_lam = (-1.05232848074E-014*pow(T4,4)+1.59353912056E-011*pow(T4,3)-4.11811500648E-009*pow(T4,2)-3.32793940923E-006*T4+1.40518231742E-003)/(-1.54325740965E-003*T4+1);

}

else

{

mu_lam = 0.000027000;

}

return mu_lam; 

}

 

[DrAmine]

Can you then start debugging a bit by setting some properties constant and focusing on the one causing the issue?

[ani4377]

Dear Atul, 

Did you find the reason for error?.

Regards 

Anirudh

[ani4377]

Can you then start debugging a bit by setting some properties constant and focusing on the one causing the issue?

Sir I am facing the same kind of error.

Can you please take a look at my post.

Thank you.

Anirudh

[atulsbhat]

Hello

I did not find any error but the property plot at end of my results, Showed me different set of properties, Well I cross checked all polynomials again , The polynomials seemed correct but properties fed into fluent didnt match with the Polynomial properties.. 

Regards

[Rob]

If you're using polynomials with that many significant figures it's very likely that single/double precision and rounding error will generate significant errors.  Post an image of what the curve should look like. 

[atulsbhat]

Nature of Graphs Sir

Regards

 

[Rob]

And if you overlay polynomial on top?