Question

When the nozzle angle is 30 degree, then the optimum blade speed ratio for a reaction turbine will be?

Answer 1

The nozzle outlet angle a, beside the velocity ratio

v and the degree of reaction p, belongs to the main

design parameters which together with cascade loss

coefficients determine the turbine stage

efficiency. The nozzle outlet angle a, affects the

stage flow kinetics, cascade losses, stage leaving loss

and even the leakage losses, though in an indirect way.

The relation between the stage efficiency and the

nozzle outlet angle is so complicated that the

analytical expression for the optimum value of the

angle a, cannot be obtained (Lewenberg, 1976).

Therefore the angle a, is very often determined by

means of numerical calculations during the optimization

of stage design parameters. The results of such

optimizations are usually presented as a function of

nondimensional factors (Belie and Binsley,1963;

Bojko,1980 and 1982; Lewenberg,1976; Duncombe,1964;

Shubienko-Shubin,1976), hut the authors use different

relations for the loss coefficients, different

simplifications and different nondimensional stage

parameters. Therefore it is very difficult to obtain

general relations for determining the value of angle a,

in a particular design task.

The values of angle a, applied earlier were greater,

but with the growth of initial steam pressure (the

decrease of volume steam flow) and with the coming into

use of better modern profiles, the lower values of

nozzle outlet angles became widely used, although the

results of some experimental investigations gave no

grounds for such an approach (Dejc and Troianowskij,

1973). The experimental results of the influence of the

nozzle outlet angle on the cascade losses

(Sobolev,1966; Dejc and Trojanovskij,1973) and on the

turbine stage efficiency (Pshenitchnyj,1964, 1966 and

1970) are very seldom presented in bibliography.

According to the bibliographical data it is possible to

determine the range of angles a, used in turbine stages

from about 12 0 to about 25-30° or more. Lower values

a,=8-10° are exceptionally used in steam turbines.

Usually the angle a, is determined by taking into

account similar turbines.

The data and opinions that the optimum angle a,

depends on such parameters as volume flow rate

Answer 2

Answer:

0.866

Explanation: