Hi, I am analyzing results of my turbine simulation. I have created one line from hub to tip at downstream of the turbine rotor(not downstream of flow) ...please see attachment. I want to investigate along this line how the axial velocity changes. In one of my results, my new blade(VT in last Figure or blue line in last figure) has the lower axial velocity than to base blade at hub and tip. (Please see attachment.) What does this mean? I think that this is due to low separation in downstream of flow of new blade(VT). Am I right?
Dear Ali,
First, i guess from the foil shape that this line is not in the downstream, It is supposed to be upstream of the blade. Therefore, you have to check your setup and the turbine rotational direction. The attached image may be helpful.
Secondary, if my hypothesis is correct and the line is upstream, your line may be in the region affect be the blade leading edge and the flow is escaping from the blade nose. I guess that the reason could be that the to blades have a different thickness or different blockage.
My advice is to plot three velocity contours or vectors at three planes (at mid span, near the hub, and near the tip)
Kind regards,
Mohamed
Thanks.
Yes, you are right. My means is downstream of the turbine rotor not downstream of the flow.
turbine rotational direction and axial flow are in attachment.
Flow is bi directional in this turbine. the turbine is named Wells turbine.
Yes , this is because of different thickness along of blade height but this decreasing axial velocity at hub and tip is good or not? I am grateful that guide me more about this case.
https://en.wikipedia.org/wiki/Wells_turbine
I have another question:
I have created one line from hub to tip at upstream of the turbine rotor ..please see attachment. I ploted the axial velocity distribution on the line according to attachment. I think that the axial velocity distribution has not changed in these two blade because of unchanging flow blockage. Am i right?
About the first question, if decreasing the axial velocity at hub and tip is good or not, My suggestion is to calculate the turbine torque to see which blade is better, However, you could notice that by decrease of velocity near the hub and the tip is associated with an increase in the axial velocity on the mid span on the figures in your first post, so it is difficult to predict the turbine performance based on these axial velocity profiles.
For the second question, i agree with you that the similar velocity profile is associated to the similar blockage.
For you third question, it is v component but you have to read about the difference between (Velocity V) and (Velocity in Stn frame V) because i am not sure which of them is needed in your analysis.
Best wishes,
Mohamed
If the characteristics of this turbine is an essential part of your current work, you may try to draw the pressure coefficient around different blades at mid-span, 20% of span (bear the hub) and 80% span (near the shroud). This will give you a detailed data for your discussion.
Thanks Mohamed Elsakka,
I have already plotted this your suggestion. And pressure coefficient plot(area) is bigger in new blade approximately. Please see attachments. Is pressure coefficient plot OK in your opinion? But however, i want to analyze axial velocity distribution plot. and i can't understand this plot well. I am grateful that help me.
Dear Ali,
The pressure distribution looks good and may be used to discuss the enhancement of efficiency and torque.
Regarding to the axial velocity distribution, i think that the flow structure is complicated around your blade. In addition, the 3 dimensionallity of the flow have a great effect (like the vortices in the attached image). However, an expert with axial gas turbine could provide more guidance.
My suggestion is to release streamlines from your line and two neighboring lines like that in the second attached image. (don't forget to increase the default samples option from 10 to 100 when you create the lines)
I hope you the best of luck
Thanks...I did your suggestion. For VT blade, there are smaller and lower vortices at tip. but How does this relate to axial velocity distribution?
I have one question about CFX:
In the following picture, X axis is according to z distance not radial distance. How can i solve this problem? I want that X axis be non dimensional radial form..For example r/r tip.
In your results, you could see the relation between the vorteces, pressure distribution, and velocity profile. However, due to periodicity, i see that your blades is laid into the wake of the previous one (you could see this clearly if you apply transformation with two copies and see the interaction between the stream lines over the two blades). I suggest you may to make a new question, with the streamline, pressure distribution, and velocity profile to consult an expert in turbo-machinery.
For you question about the radial position, i usually make something like a new expression with a name r and equal to sqrt(x^2 +z^2). Then, you could define a new variable based on the expression. Therefore, you will find a new variable in the variable list return the radial coordinates.
Best wishes,
It is also due to the influence of the boundary layer at the hub and shroud of the axial turbine
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