Focused Practice

I. Answer the following questions:

1. What does output from the prototype pay special attention to?

2. Where are alternative HPUs described?

3. What does the prototype do once a selection of design options is made?

4. How many choices for actuation circuits does the program provide?

5. When does the prototype establish all ranking systems as guidelines for the user?

6. How can users address the design problem?

II. Analyse the grammar structures underlined in the above text.

III. Speak on: The ability to automatically size the circuits.

Unit 22 Grammar: Word-building. The Conjunctional and Prepositional Phrases Word List:

1. exhaust hood	выхлопной патрубок, вытяжной шкаф
2. transonic flow	поток, проходящий со скоростью звука
3. domain multi-domain	область; многоступенчатый
4. complexity	запутанность, сложность
5. diffuser	распылитель, рассеиватель
6. boundary conditions	граничные условия
7. three-dimensional	трехмерный
8. throughflow	прямой, сквозной поток
9. planes	решетки, подложки под граничным слоем
10. architecture	сеть, структура, строение
11. aerodynamics	аэродинамика
12. finite volume	ограниченный объём
13. mechanical stress	механическое напряжение

The Calculation of a Last Stage Low Pressure Steam Turbine and Exhaust Hood Flow

In large nuclear steam turbines, the last stage and exhaust hood are very important. Indeed, their high contribution to the total turbine output as well as the critical last stage operating conditions (transonic flow, wet steam, high mechanical stresses, ...) have led to a large number of various studies. Therefore, a greater attention is being devoted to the diffuser designed to recover kinetic energy and to increase last stage efficiency. Moreover, a reduction of diffuser length helps to reduce the shaft length which is always very interesting from the economic point of view.

Obviously, the calculation of a last stage low pressure steam turbine and exhaust hood flow is difficult due to the complexity of three dimensional flow in addition to the multi-domain. Indeed, it is quite impossible to determine appropriate boundary conditions for a local calculation without coupling techniques. A way to solve this problem is to perform a throughflow calculation of the whole cylinder. However, this method is not very useful for the complex low pressure last stage flow and quite impossible for the three-dimensional exhaust hood flow. Another way consists of simultaneously solving the aerodynamic flow problem in the stator, in the rotor and in the exhaust hood. Of course, this method seems very complex and expensive. However, in relation to the modern computers this method is nowadays realistic and very promising in relation to the new parallel architecture computers. The last stage flow is always unsteady because of the rotor. The principal assumption is that the flow is steady relative to each domain individually and that each domain can communicate via mixing planes These introduce circumferential averaging of the flow properties, but preserve quite general radial variations.