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I studied about the effect of turbine blade thickness on flow separation in following. The blade section is Naca 00 XX in this turbine.

The paper states that if blade thickness increases, separation on the blade delays. Why does this happen?

The paper also states that if the blade thickness increases, there is higher pressure on the suction surface and hence this gives a delayed separation. Why does this happen? Why is there high pressure on the suction surface?

The paper also states: Blade (A) has lower torque than blade (E). Why?

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    $\begingroup$ It'd be really helpful if you could include a link to the paper. $\endgroup$ – Dan May 20 '16 at 10:56
  • $\begingroup$ Please add a link to the paper $\endgroup$ – 706Astor Jan 27 '18 at 16:11
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In a isolated blade, the flow separates in the upper side due to adverse pressure gradient.

But in the case of turbines, It is well guided flow between the blades. So the effect of adjacent blades come into picture. for the same mass flow rate but different passagae dimensions, it alters the pressure on the blades such that the flow don't seperate. but there are cases in which flow seperates for the same solidity (no of blades or thickness of blades) with less mass flow rate.

We can also refer the below plots (from my own potential flow code.)

enter image description here

the above is coefficient of pressure plot for isolated airfoil. When we put the same aerofoil as a cascade of aerofoils(NACA 0012), We can see how the pressure distribution changes for different solidity. the outer most curve is for very less no of blades (~isolated) and the inner most profile is for high solidity. So we can't think it as a isolated blade anymore. we have to consider effect of other blades too.

enter image description here

Hence we can't say there is a suction pressure on the upper side of cascade airfoil as compared to isolated. Hope this helps for your first two quastions.

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