FredGarvin said:
Degree of reaction is the ratio of static enthalpy drop across the turbine nozzle to the drop across the turbine. That being said, a hydraulic turbine is a reaction turbine with no nozzle drop so its degree of reaction would be 0. A gas turbine engine will vary depending on the drops. A degree of reaction of 50% means there is an equal drop across the nozzle as the turbine. Usually losses increase greatly after a R=1, so in that aspect a R<1 is more optimal. However, that is simply looking at the R value and no other design criteria.
Either I am completely wrong or I am completely confused.
All gas turbines have enthalpy drop in the nozzle(that means energy is been converted to kinetic energy). Right??
An Impulse turbine(eg. Curtis turbine & Rateau turbine ) has all its enthalpy drop in the nozzle(stator) and no drop in moving blades(theoretically), so degree of reaction is 1 for an impulse turbine??
A reaction turbine has enthalpy drop in both stator and rotor blades(both act as nozzle), so degree of reaction is less than 1(DoR = ΔHs/(ΔHs + ΔHr)). How can DoR be greater than 1?
I take DoR as "the ratio of enthalpy drop in rotor blades to the enthalpy drop in one stage(rotor + stator)". I studied Power plant Technology, M. M. El-Wakil, Tata McGraw Hill.
My original question was actually more inclined towards the hydraulic turbines. Head replaces the enthalpy. As previous, I took, DoR as "the ratio of head drop in rotor, to the head drop in the turbine".
In pelton(& turgo turbine) wheel, all head is converted to KE upto turbine inlet, so the DoR is 0.
In Francis and Kaplan turbine, some head converts in the rotor itself, so degree of reaction is between 0 & 1.
Total head drop, He = [(V1^2 - V2^2) + (u1^2 -u2^2) + (Vr2^2 -Vr1^2)]/(2*g)
head drop in rotor,Hr = [(u1^2 -u2^2) + (Vr2^2 -Vr1^2)]/(2*g)
therefore, DoR = Hr/He
V = absolute velocity
u = peripheral velocity of blade
Vr = relative velocity(to blade)
1&2 = Inlet & outlet of turbine
The reason I wanted to confirm the above said definition of DoR for a hydraulic turbines is that I am getting negative values of DoR for a Francis turbine, below a particular rpm and values greater than 1 above a particular rpm. So I suppose this definition is wrong, and I am probably confused alot.
