# sliding grids

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 July 1, 2003, 04:25 sliding grids #1 Giuseppe Guest   Posts: n/a Hi, I have a problem when I try to use sliding grids; by the way, the simulation of the centrifugal pump produce high residual mass. this cause the end of the simulation. have you an idea ? Thank you very much! Giuseppe

 July 2, 2003, 10:28 Re: sliding grids #2 Nyatoto Guest   Posts: n/a It is difficult to understand your problem at this stage. Would you be more generous with your information. When does this occur, immediately or...? What are your: -speed -mesh -time step -underelaxation factors -descritization schemes (spatio-, temporal-) etc..?? regards Nyatoto

 July 3, 2003, 03:57 Re: sliding grids #3 Giuseppe Guest   Posts: n/a Hi, Nyatoto The simulation diverge immedyately, after 7-8 iterations. I have 1400 rpm , my model of rotor has structured mesh with 4 elemet for each arc with an angle of ten degrees. the fluid was water I used : >>FIXED TIME STEPPING TIME STEPS #NSTEP * #DT with #CALC PI=3.1415926; DEG=PI/180.0; #ENDCALC /* ... ASTEP IS GRID MOVEMENT ANGLE PER TIME STEP ... */ #CALC NSTEP = 144; MAXIT = 50; CRIT = 1000; ASTEP = 2.5*DEG; #ENDCALC /* ... WORKING VALUES ... */ #CALC RPM = 100; OMEGA = RPM*2.0*PI/60.0; REVOLT = 2.0*PI/OMEGA; DT = REVOLT*ASTEP/(360.0*DEG); #ENDCALC i used default under relaxation factors and the options: THREE DIMENSIONS BODY FITTED GRID UNMATCHED GRIDS CARTESIAN COORDINATES TURBULENT FLOW ISOTHERMAL FLOW INCOMPRESSIBLE FLOW TRANSIENT FLOW TRANSIENT GRID furthermore i have: >>FALSE TIMESTEPS U VELOCITY 0.8 V VELOCITY 0.8 W VELOCITY 0.8 :>REDUCTION FACTORS K 0.55 EPSILON 0.55 :>DEFERRED CORRECTION K START 0 K END #MAXIT EPSILON START 0 EPSILON END #MAXIT I ran two simulations with the following boudaries conditions: 1) inlet + outlet with inlet velocity of 3,5 m/s 2) simulation all circuit No inlet No outlet I hope for some help Thanks in advance! Giuseppe