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about nodimensition of two ideal enstropic eqation

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Old   August 30, 2007, 11:49
Default about nodimensition of two ideal enstropic eqation
Stu. NO0523
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Hi, I am using CFD method to calculate a nozzel internal performance,there are two equations: ideal mass-flow rate (1) W_i=sqrt(gamma/R)*(2/(gamma+1))**((gamma+1)/2/(gamma-1))*At*P_tj/sqrt(T_tj) ideal enstropic thrust(2) F_i=sqrt(2*gamma*R/(gamma-1))*W_p*sqrt(T_tj)*sqrt(1-(1/NPR)**((gamma-1)/gamma)) (John R. Carlson A Nozzel Internal Performance Prediction method, NASA TP3221,1992) after nodimension,reading: W_i=gamma*(2./(gamma+1))**((gamma+1)/(gamma-1)/2.)*at*p_tj/ sqrt(t_tj)/mach_inf (3) F_i=2*w_i/mach_inf*sqrt(2.*T_tj/(gamma-1))*sqrt((1.-(1./p_tj)**((gamma-1)/gamma))) (4)


I use eq.(3),(4) to get discharge coefficent C_d = W_p/W_i and thrust ratio coefficent C_f=F_r/Fi. for a nozzel the calculating C_d=74%,C_f=45%,all much smaller than the experiment, are eq.(3)&(4) wrong?but I have checked them again and again, I can't find problem, would anyone like to give me some advice?
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