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Constructing 2D Velocity Diagrams for Axial Flow Steam Turbines

Constructing 2D Velocity Diagrams for Axial Flow Steam Turbines

(OP)
Howdy,

I'm a new steam turbine engineer, working on my first project, but in a fairly new department such that I don't have anybody here with more experience in this particular area.

I've been reading as many textbooks, papers and other internet resources as I can find, and I can't find a definitive answer to this question. I need to construct (mid-span) 2D velocity diagrams for existing blades. My problem is that I can't seem to find information about which part of the geometry to use to build those diagrams (i.e. to measure the entry and exit angles). All the textbooks & other sources I've seen seem to show the various angles as floating in space mid-cascade, or pointing to the blade tips, without actually following the specific geometry of the blades.

So, my ultimate question is: should I be building these angles using the geometry from the suction side (convex), pressure side (concave), camber line, or mean-passage curve(i.e. a spline constructed using the center-points of circles tanget to both the suction and pressure sides of the passage)? I'm personally leaning towards the mean blade passage curve option, but I've seen figures that seem to variously indicate ALL of the above options are plausible.

To add some background detail, if it helps, I am attempting to perform a 2D flow analysis of a 5MW Single-Flow Axial, Impulse Steam Turbine. The ultimate purpose is to serve as an evaluation of a rebuild of the diaphragms for all stages. As such, it's basically a form of reverse engineering, since I'm attempting to evaluate the characteristics of already-built products.

The starting point of the analysis is 3D solid models reconstructed from heavily corroded source blades (such that the trailing edges of all original stator blades were completely destroyed by corrosion over the course of 20 years), based on best-fit curves.

My job, then, is to look at the re-built geometry, and determine the theoretical power generation capability. Neglecting losses for now, I'm beginning by trying to construct the velocity diagrams and use those to compute the diagram Power for each stage. This process is based on Eq 4.2 from Dixon "Fluid Mechanics and Thermodynamics of Turbomachinery", 4th Ed., which gives me the specific Work. See attachements for reference (there should be 3; let me know if they didn't all come through). From there, I get power from the equation of Power = mass flow * Specific Work (see http://www.engineeringtoolbox.com/pump-fan-power-d... for reference).

Once I have the diagram power computed for each stage, I plan to sum up the power contribution of each stage to give me the total power of the unit.

For reference, I already did a basic black-box turbine calculation (assuming adiabatic, incompressible flow of a non-ideal gas) to confirm that my provided steam entry and exit conditions do indeed provide the expected power output (which was a given, considering this plant has been operating for 20 years, but I figured it was a good starting point).

RE: Constructing 2D Velocity Diagrams for Axial Flow Steam Turbines

(OP)
dangit. failed again. Alright, I give up. I tried to upload a brand new, different but equivalent pic, and it gave me the same "Duplicate Header" error, so I'm gonna just stop trying for now.

Long story short, I'm trying to figure out how to measure the blade entry and exit angles, relative to the physical geometry of the blades at mean height.

RE: Constructing 2D Velocity Diagrams for Axial Flow Steam Turbines

(OP)
Partly to bump the thread, in case anybody might have some answers, and partly to add new info...

I looked at AxStream turbine analysis software, and it looks like that software uses the mean camber line to indicate the blade and stator angles. That being said, there are still many examples using the mean curve of the flow passage. So, this question is still unresolved for me.

Does anybody have any information at all on this subject?

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