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Old   September 22, 2000, 23:54
Default steam turbine design
  #1
sameer mohrir
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Hello everybody

Can anyone please answer my question While designing a steam turbine what are the major factor to be taken into consideration (i.e thermodynamic, mechanical design and rotordynamic), whether inlet nozzle design also plays a critical role in designing a steam turbine.

thanking you

sameer mohrir
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Old   September 23, 2000, 11:40
Default Re: steam turbine design
  #2
John C. Chien
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(1). The basic problem in turbine design is that the 1-D method commonly used (which can be found in the text book)has missing information, which must be obtained from the real world 3-D flow field. Yet the real world 3-D flow field is unknown at the time of design.(even after it is designed, in most cases it is still unknown) You really have to take this very seriously to understand it. (2). So, as the real world 3-D flow field (which is unknown to most of us today, with or without cfd or testing) is folded into 1-D model design procedure, we are dealing with something fictitious. (3). If you still don't quite get it, you should look into the 3-D inviscid Euler code, which has been widely used in the industries in the last several decades. Even at the 3-D inviscid level, you know that the real world 3-D flow field is completely different from the solution of the 3-D inviscid equation. (yet even today, it is used on the routine basis) (4). What I am trying to say is that, the 1-D design procedure, the 2-D axisymmetric procedure, 3-D inviscid code solution, and even the 3-D Navier-Stokes solutions recently become available, do not in any way represent the real world 3-D flow field at all. (5). The consequence of this is that you always have some problems with the final machine, either the mechanical or the thermodynamic efficiency. (6). And in many cases, in order to save cost, most of these designs were not tested first. You simply do not have the large enough facility to do so, or time and money to spend. So, I would say that, the turbomachinery design is largely based on the wrong design procedures, that is based on non-realistic simplified equations.(if you ask three companies to design the turbine, you will get three different designs, each will claim that they are the best. ) (7). My answer to your question is: most designer in turbomachinery industries do not have any slightest idea of the real 3-D flow field, yet they are running some 1-D code to design the machine. And even after the machine is designed, they still don't know what is going on in the machine, and they don't do the flow field survey at all (too difficult and expensive to do). As a result, there are always problems when the machine is installed at the customer's site. I would say that the turbomachinery design is still very primitive. (and most turbomachinery companies do not have cfd department at all, not to mention the testing facilities.) There is a long way to go in the turbomachinery design. The most serious issue is the 3-D aerodynamic flow field. Once you have accurate knowledge of that, the mechanical part can be handled properly. (in gas turbine, you will have added complexity of heat transfer design problem) So, the main problem is 3-D aerodynamics in the turbomachinery!!!
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Old   September 24, 2000, 02:34
Default Re: steam turbine design
  #3
sameer mohrir
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Hello John,

Thanks for your clarifications . But i would like to know whether 3-D inviscid Euler code which had developed by some world reknown university (like turbomachinery department of cambridge department, UK) are useful . And also can Rotordynamic design plays major role in designing a steam turbine

regards

sameer mohrir
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Old   September 24, 2000, 10:37
Default Re: steam turbine design
  #4
John C. Chien
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(1). How can you design things with inviscid codes, while the goal is to predict loss and efficiency? (Wait until the winter, when you have to pay the heating bill. ) (2). Rotordynamic is important, but it is not the focal point. (The failure comes from the aerodynamic design, because of lack of knowledge about the detailed flow field.) (3). In the past, turbomachinery design depends mainly on testing. (4). A new blade design without testing (costs time and money, and difficult to obtain detail flow field) and the detailed cfd flow field analysis (3-D simulation is still far from ideal, at most, is still in the research stage. Would you trust the flow field and loss prediction from your 3-D cfd code, today?) (5). Without the understanding of the 3-D flow fields, the design is just theory, even with some test data included. (recently, someone used a commercial cfd code to study a new blade design and openly claimed that the efficiency was greatly improved. When I used the same code to study the similar configurations with great care and attention to the mesh, the results show no improvement at all. This is from one of the world leading company. ) (6). If you use the current state of the art commercial cfd codes to do the design, you have to be very careful about the results. By the way, even if a tire company knows nothing about one of their tire performance, they can still sell the same tire by millions. It is a joke to know that a company can claim that they know how to design high efficiency turbine, without knowing the detailed aerodynamics flow field. (if they tell you they have been using inviscid 3-D Euler code, then how did they come up with the loss and efficiency? based on the rule of thumb, or based on the flat plate chart? )
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Old   September 24, 2000, 23:29
Default Re: steam turbine design
  #5
sameer mohrir
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Hello John

Thanks for giving clear picture regarding design of steam turbine.

Regards

Sameer mohrir
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