Hi I'm simulating a flapping airfoil(Naca0015) by AnsysFluent
How can I simulate a flapping motion which the phase difference between pitching and heaving is not zero? I used this UDF for flapping motion while phase difference equals to zero:
#include "udf.h" DEFINE_CG_MOTION(plunge,dt,vel,omega,time,dtime) { Thread *t; face_t f; real w,a, pi; pi = 3.14159265; a = (pi*15)/180; /*pitch amplitude*/ w = 1.168; /*angular velocity*/
/*defining the flapping motion*/ vel[1] = 0.5*w*cos(w*time); /*Heaving motion*/ omega[2]=a*w*cos(w*time); /*pitching motion*/ } It's OK!
I tried the followed UDF for the case which phase difference is 90 :
#include "udf.h" DEFINE_CG_MOTION(plunge,dt,vel,omega,time,dtime) { Thread *t; face_t f; real w,a, pi,fi; pi = 3.14159265; a = (pi*15)/180; /*pitch amplitude*/ w = 1.168; /*angular velocity*/ fi = 90*pi/180; /*phase difference*/ /*defining the flapping motion*/ vel[1] = 0.5*w*cos(w*time+Fi); /*Heaving motion*/ omega[2]=a*w*cos(w*time+Fi); /*pitching motion*/ } By using the second UDF the airfoil pitches in the range of -30 to 0 and heaves in the range of -1 to 0.
if I change the UDF in this way: vel[1] = 0.5*w*cos(w*time+Fi); /*Heaving motion*/ omega[2]=a*w*cos(w*time); /*pitching motion*/ Just the heaving amplitude would be wrong,in the range of -1 to 0
It's expected to pitches in the rage of -15 to 15 and heaves in the range of -0.5 to 0.5
How could I fit this problem and define the phase difference for the fluent without getting false results? Again, simulating a flapping motion which phase difference is zero has been simulated well! Thanks in advance
https://www.sciencedirect.com/search?qs=simulate%20a%20flapping%20motion&show=25&sortBy=relevance
Hanye Azimi
You may please try
vel[1] = 0.5*w*cos(w*time); /*Heaving motion*/
omega[2]=a*w*sin(w*time); /*pitching motion*/ since, sin(th+90)=cos (th)
Also, please plot your motion profile using excel or Matlab to better understand the motion profiles to sort out the issue of wrong range -1.0 to 0 as it depends on the starting position and which trigonometric function you are using.
Hope this answer helps.
Please don't hesitate to ask if you need any further clarification.
@ M. A. Ashraf
Thanks for replying my question. I tried what you said.
vel[1] = 0.5*w*cos(w*time); /*Heaving motion*/
omega[2]=a*w*sin(w*time); /*pitching motion*/
The animation is attached.Still, the amplitudes are wrong. You're right. The initial position of L.E is at (x=0,y=0.03). It's supposed to be at (0,0).
The position of the L.E at the beginning of the unsteady solving is shown in the attached image.
I'm doing sth wrong. Help me to find it.
Thanks again
Hanye Azimi,
Apologies for late response.
You may please try following:
vel[1] = 0.5*w*cos(w*time); /*Heaving motion*/
omega[2]= -a*w*cos(w*time+Fi); /*pitching motion*/ /* -ve since Fluent uses ccw +ve */
The animation is attached.Still, the amplitudes are wrong. You're right. The initial position of L.E is at (x=0,y=0.03). It's supposed to be at (0,0).
You may adjust the position of the mesh as before running the simulation using mesh translate or rotate (see if your starting angle is not right) options. I think it should start LE pointing upwards at maximum theta at the mid stroke position.
Hope this helps.
@ M. A. Ashraf
I'm really appreciative of your help and your time. I'll take your word and try it.
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