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-   -   why pressure increases a lot at wall corner? (http://www.cfd-online.com/Forums/openfoam-solving/112799-why-pressure-increases-lot-wall-corner.html)

immortality February 5, 2013 14:38

why pressure increases a lot at wall corner?
 
1 Attachment(s)
I use this condition for p at outlet:
Code:

p0_2/pow(part1,3.5)
when :
Code:

"part1=1+(gamma-1)/2*sqr(internalField(U.x))/(gamma*R*internalField(T));"
these all make the well-known isentropic relation.
but at the corner where there is a wall a cell makes troubles for all the solution.why this behaves so at corner of outlet?
my whole BC for p is like below that I extrude above relations from that:
Code:

right
    {
        type groovyBC;

        variables (

                  "r=0.02325;"
                  "rpm=25899.28055;"
                  "omega=rpm*pi/30;"
                  "v_r=r*omega;"
                  "w_cell=.004;"
                  "n=1;"
                 
                  "w_w0=n*w_cell;"
                  "w_w3=(21.6-0)*r*pi/180;"
                  "w_w4=(83-61.6)*r*pi/180;"
                  "w_w5=(180-128)*r*pi/180;"
                  "w_p2=(71.1-21.6)*r*pi/180;"
                  "w_p4=(129-84)*r*pi/180;"
               
                  "c1=w_p2/v_r;"
                  "c2=(w_p2+w_w4)/v_r;"
                  "c3=(w_p2+w_w4+w_p4)/v_r;"
                  "c4=(w_p2+w_w4+w_p4+w_w5+w_w3)/v_r;"
                  "t1=(w_w0+w_w3-pos().y)/v_r;"
                  "t2=t1+c4;"
                  "t3=t1+2*c4;"
                  "t4=t1+3*c4;"
                  "t5=t1+4*c4;"
                  "t6=t1+5*c4;"
                  "t7=t1+6*c4;"
                  "t8=t1+7*c4;"
                  "t9=t1+8*c4;"
                  "t10=t1+9*c4;"
                  "t11=t1+10*c4;"
                 
                  "p0_2=1023382.5;"
                  "T0_2=907;"
                  "p0_4=374902.5;"
                  "T0_4=973;"
                  "gamma=1.4;"
                  "R=287.14;"
                  "part1=1+(gamma-1)/2*sqr(internalField(U.x))/(gamma*R*internalField(T));"
                  "part2_inflow=1-(gamma-1)*magSqr(internalField(U))/(2*gamma*R*T0_2);"
                  "part4_inflow=1-(gamma-1)*magSqr(internalField(U))/(2*gamma*R*T0_4);"
 

);

        fractionExpression "(t1<time()&&time()<t1+c1)||(t2<time()&&time()<t2+c1)||(t3<time()&&time()<t3+c1)||(t4<time()&&time()<t4+c1)||(t5<time()&&time()<t5+c1)||(t6<time()&&time()<t6+c1)||(t7<time()&&time()<t7+c1)||(t8<time()&&time()<t8+c1)||(t9<time()&&time()<t9+c1)||(t10<time()&&time()<t10+c1)||(t11<time()&&time()<t11+c1)||((t1+c2<time()&&time()<t1+c3)||(t2+c2<time()&&time()<t2+c3)||(t3+c2<time()&&time()<t3+c3)||(t4+c2<time()&&time()<t4+c3)||(t5+c2<time()&&time()<t5+c3)||(t6+c2<time()&&time()<t6+c3)||(t7+c2<time()&&time()<t7+c3)||(t8+c2<time()&&time()<t8+c3)||(t9+c2<time()&&time()<t9+c3)||(t10+c2<time()&&time()<t10+c3)||(t11+c2<time()&&time()<t11+c3))&&(mag(internalField(U))/sqrt(gamma*R*internalField(T))<1)?1:0";
        valueExpression "(t1<time()&&time()<t1+c1)||(t2<time()&&time()<t2+c1)||(t3<time()&&time()<t3+c1)||(t4<time()&&time()<t4+c1)||(t5<time()&&time()<t5+c1)||(t6<time()&&time()<t6+c1)||(t7<time()&&time()<t7+c1)||(t8<time()&&time()<t8+c1)||(t9<time()&&time()<t9+c1)||(t10<time()&&time()<t10+c1)||(t11<time()&&time()<t11+c1)?((phi>=0)?p0_2/pow(part1,3.5):p0_2*pow(part2_inflow,3.5)):((phi>0)?p0_4/pow(part1,3.5):p0_4*pow(part4_inflow,3.5))";
        gradientExpression "0";
        value uniform 1023382.5;
    }


immortality February 5, 2013 14:43

1 Attachment(s)
also U becomes very much around the outlet corner.


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