Due to frction they may diffrent

Reaction is defined as the ratio of enthalpy drop across the rotor to the overall drop across the stage. For adiabatic flow one can use the Euler equation to relate reaction to a function of axial velocity, rotational speed and flow angles (inlet and exit). If the axial velocity is assumed constant the reaction can be defined as the difference in the tangents of exit angle and inlet angle. Hence for a zero reaction (impulse) turbine flow angle at the exit of the blade will be the same as that at the inlet. The velocity diagram will show clear symmetry in the relative frame. In this case the tangential load of the blade is created by impulsive force - leading to the specification of "impulse" stage.

I hope this is helpful.

I reaffirm what was said by Mr Stang. The drop in enthalpy in rotors and stators is that actually define the stage type and not (only) the form of speed triangles. Although they are not independent. You must see the complete panorama. I hold, as an example of this, a pair of blades, which although are of a high degree of impulse, appears to be of reaction to the untrained eye.

Thank you for your "reaffirmation" Mr. Rodriguez.  I would be curious to see the airfoils to which you refer.

Mr Stang. I intend to send a private message but your option is closed.

Those were from my time as an aircraft mechanic.

Yesterday I turned the box on the table but only found a second stage. I remembered that I lost the first, which I used as a keychain.

Anyway. Was the blades of an RR Spey (if I remember it correctly. Since I did not work on Speys.) Also I kept a bunch of Viper blades. From the "free-vortex design" era, that cause a similar effect and are very good to explain the fact that reaction degree varies with the radius.

The nose cutted blades of the old recuperative turbines have a similar effect. They are clearly of action type but the cut invites you to think they are of reaction type.

The interesting fact is that both, engineers and students, fail to determine whether they are action or impulse blades. The radial area gradient, the angle in each radius and the form of section contribute to blur the fact that reaction degree is a thermodynamic question and not a geometric one.

The origin of the problem are in books where you can find pictures that say "reaction blade (or stage) " and "impulse blade (or stage)" without clarify anything more.

I apologize for my English and I hope it has not hindered the understanding of the subject.

In the impulse turbine expansion of gas, vapor or liquid is in fixed nozzles and rotor blades only twist stream which moves inside the channel. The expansion of the fluid in the nozzles occurs as a result of decrease in enthalpy. For liquids directly corresponds to the pressure drop (constant density of the fluid). In accordance with the principle of conservation of energy, gas or steam (compressible flow) only enthalpy drop determines the amount of transferred energy. The ratio of static enthalpy drop in the rotor to the entire drop in the machine defines the reaction of the stage. So, a certain parameter is called "thermodynamic reactivity", see https://en.wikipedia.org/wiki/Degree_of_reaction. For the so-called "normal stage" it directly translates into the "kinematic reaction" of the stage and represented by the velocity triangles in the rotor. For the 50% reaction stage the velocity triangles are symmetrical, but in another case are "tilted" relatively to the circumferential velocity.

It is a common misunderstanding to relate the degree of reaction with the velocity triangle. A misunderstanding that dates back to the definition of "reaction".

One definition is. Variation of static enthalpy in a cascade over variation of enthalpy in the stage. But there is different similar criteria. Other definition is the ratio of variation of static enthalpy in a row times the sum of static (relative!) variation of enthalpy in the rows of the stage. I prefer this more rigorous and simple definition.

The change of relative enthalpy in a duct indicate you the degree of acceleration or deceleration of the flow regardless geometry has the conduit or machine if the fluid is compressible or not.

The geometry of speed triangles.. it depends of the del-Hs AND the geometry of the annulus AND the fluid bells (the revolution surface representing the flow passing a certain point in the machine). These discrepancies have been addressed in the concept of 'rotalpy'.

For example. A big radial expansion of the section between inlet and outlet of a pure (mean mass flow) axial turbine in otherwise ACTION turbine gibe you a typical REACTION triangle. And it is a TYPICAL aircraft engine.

And here another problem appears. The very definition of 'triangle'. The textbooks are wrong in that regard. They should call them 'planangles' or 'pure bi-dimensional AXIAL (or non-polar) flow triangles'.

En even more. In accelerating supersonic flows the exit of a tube is larger than the inlet. If it is a supersonic stage and you have not increased the radial section, even when there is a measurable expansion en EACH row, the resultant velocity triangle is characteristic of a typical action stage.

The importance of the degree of reaction is that a small or negative reaction involves a reduction of speed within a cascade and this causes losses, because of the thickening of the boundary layer and its possible detachment.

The only big question is . How much expansion'm getting in each row?