[dmaz]

Hello,
I'm trying to simulate a centripetal gas turbine with CFX-Pre. I haven't found any tutorial so I had to try to set the simulation by myself.
I'm analyzing onle the rotor blade, the simulation works but I'm not sure about the results and the setting.
At the Inlet, how have I to set the flow direction? I tried with the cylindrical components. I entered the values of the vector: axial component=0, radial component=0.2233 theta component=0.9748. However the resulting triangle of velocities after the simulation is not the set(in the picture). I'm not able to have a relative velocity entirely radial at the inlet. The rotational velocity is 4666 rad/s.
Where I'm wrong?
Another question, in a rotating domain, is the Velocity Stn the absolute velocity of the flow (c)? And the Velocity is the relative velocity (w)?
Thanks in advance,
Dmaz

[ghorrocks]

If you want to see your initial or boundary conditions then run a simulation where you save a results file at time=0 or iteration=0.

[dmaz]

Thanks for answering me! But I'm not able to solve the proble, I did many attempt...
The complete data of my problem are:
Ptot,inlet=3.02bar
Ttot,inlet=467.6K
Pstat,outlet=1.8bar
Rotation velocity= -4666.67rad/s
The frame type is stationary and the inlet is at a radius coordinate of 0.084m. I don’t succeed in imposing the correct flow direction at the inlet.
The values I’m trying to impose (triangle of velocity A) are:
Absolute velocity c=396m/s
Tangential velocity u=388m/s
Relative velocity w=80m/s
So I set the cylindrical coordinates of the flow direction at inlet as:
r=-0.2019 (w/c)
a=0 no axial direction
t=-0.9795 (u/c)
Is it right? Are they referred to the absolute velocity c right?
However, after the simulation, the triangle of velocities at the inlet is not correct (evaluated as an average of the values at inlet, span 0.5). The calculated values are:
c= 276m/s (wrong)
w=138m/s (wrong)
u=388m=s (right)
And the triangle of velocities is different (triangle of velocity B).
Where I’m wrong? Am I missing something?

I attached also the plot of the vectors of the relative velocity w (Velocity) and the absolute velocity c (Velocity Stn).

[dmaz]

Anyone can help me?

[ghorrocks]

Can you post your CEL? And an image of the entire flow domain?

[dmaz]

Thanks for answer me!
I post the image of the entire flow domain in the blade to blade (Theta-M') view.
I did my simulation using blade gen-turbogrid-ansysCFX in the Workbench enviroment.
I have exported the CCL file from the cfx-pre, is that the file you mean?
How can I attach it to the message? The forum doesn't accept the file..

[mjgraf]

set expert parameter

backup file at start = t

Controls whether a backup file is written at the start of every run (that is,
showing the initial values field for the run).

[givermzp]

Originally Posted by dmaz

Thanks for answer me!
I post the image of the entire flow domain in the blade to blade (Theta-M') view.
I did my simulation using blade gen-turbogrid-ansysCFX in the Workbench enviroment.
I have exported the CCL file from the cfx-pre, is that the file you mean?
How can I attach it to the message? The forum doesn't accept the file..

Hello Dmaz, I got the same problem with you... May I ask how you solved the problem finally?

[svaezi]

hi everybody
I have some problem in simulation radial turbine' impeller. when i want to get results from cfd-post the impeller act like a compressor for example the absolute mach number increase from inlet to outlet.what do i have to for this problem????
i set this boundary condition:
PO=1.55 bar
To=1239
Ps=.982
rpm=80000

[Opaque]

Have you plot the Rotational Velocity vectors ? is the impeller rotating in the correct direction ?

Bizarre..

[Rad_Turb]

I am simulating a radial inflow turbine. The velocity triangle at the rotor inlet is known in u,v,w velocity components, however I am clearly making a mistake when converting to cylindrical components.

u = 540.127 m/s
v = 457.7828 m/s
w = 226.5001 m/s

This suggests a relative flow angle of about 33 deg.

a = 0 = no axial direction
r = (w/v) = - 0.494776
t = (u/v) = -1.17987

When reviewing the results only the u velocity component is correct, and the flow angle is much smaller than 33 deg.

If possible could you give some pointers on the situation.

Thanks in advance.

[ghorrocks]

Are you looking at the right velocity? velocity or velocity in stationary frame?

[Rad_Turb]

Looking at the correct velocity, do you mean with regards to the results?

So as a start, do you agree with the method used to convert u,v,w velocity components into cylindrical?

[ghorrocks]

No. Have a look at https://en.wikipedia.org/wiki/Cylind...rdinate_system

[turbo]

Originally Posted by dmaz

Hello,
I'm trying to simulate a centripetal gas turbine with CFX-Pre. I haven't found any tutorial so I had to try to set the simulation by myself.
I'm analyzing onle the rotor blade, the simulation works but I'm not sure about the results and the setting.
At the Inlet, how have I to set the flow direction? I tried with the cylindrical components. I entered the values of the vector: axial component=0, radial component=0.2233 theta component=0.9748. However the resulting triangle of velocities after the simulation is not the set(in the picture). I'm not able to have a relative velocity entirely radial at the inlet. The rotational velocity is 4666 rad/s.
Where I'm wrong?
Another question, in a rotating domain, is the Velocity Stn the absolute velocity of the flow (c)? And the Velocity is the relative velocity (w)?
Thanks in advance,
Dmaz

Your velocity triangle at radial-inflow turbine rotor is right. The velocity component BCs are calculated from your nozzle exit flow angle you want.

[turbo]

Originally Posted by dmaz

Thanks for answering me! But I'm not able to solve the proble, I did many attempt...
The complete data of my problem are:
Ptot,inlet=3.02bar
Ttot,inlet=467.6K
Pstat,outlet=1.8bar
Rotation velocity= -4666.67rad/s
The frame type is stationary and the inlet is at a radius coordinate of 0.084m. I don’t succeed in imposing the correct flow direction at the inlet.
The values I’m trying to impose (triangle of velocity A) are:
Absolute velocity c=396m/s
Tangential velocity u=388m/s
Relative velocity w=80m/s
So I set the cylindrical coordinates of the flow direction at inlet as:
r=-0.2019 (w/c)
a=0 no axial direction
t=-0.9795 (u/c)
Is it right? Are they referred to the absolute velocity c right?
However, after the simulation, the triangle of velocities at the inlet is not correct (evaluated as an average of the values at inlet, span 0.5). The calculated values are:
c= 276m/s (wrong)
w=138m/s (wrong)
u=388m=s (right)
And the triangle of velocities is different (triangle of velocity B).
Where I’m wrong? Am I missing something?

I attached also the plot of the vectors of the relative velocity w (Velocity) and the absolute velocity c (Velocity Stn).

Your results look OK, but your thought that W should be aligned with rotor inlet blade angle, which means zero incidence, is wrong. Generally W should be aligned like what you have to give better efficiency. Study turbomachinery books.

[dinesh1700]

i just started doing simulation of radial gas turbine in ansys cfx, but i am stuck at the inlet velocity condition, as i don't know how to calculate the axial, circumferential and radial velocity.


Initially i did the simulation of both nozzle and turbine and gave the inlet velocity condition based on nozzle angle.
but now i am doing the simulation of only turbine.

[hectorwerke]

Originally Posted by dmaz

Anyone can help me?

İ ve same problem with u. But i think when we make a simulation with a volute i hope olur problem May be solved. Because when we add the volute condituons to the whole calculations, rotor inlet flow direction May be calculated auromatically according to volute shape and flow condituons on volute? Thats my opinion