> dimensions at the entry to the working wheel are determined in the gas-dynamic calculation of the designed engine. At first area at the exit from the nozzle diaphragm is calculated
,
and are stagnated temperature and full pressure of the flow at the exit from the nozzle diaphragm;;; mg - constant magnitude, which can be computed by the formula
В
kg = 1,33 and Rg = 288 J/(kg Г— K) we will have mg = 0,0396 (kg Г— K)/J.density can be determined from tables of gas-dynamic functions using value of the reduced velocity or by the formula
.
he given working wheel middle diameter other geometrical dimensions are computed by the following formulas:
;;.
At he given relative sleeve diameter geometrical dimensions in the considered section are computed by the formulas:
В В
sleeve diameter for first stages is within the limits of, and for last stages. first turbine stages the nozzle diaphragm is profiled to provide turbine blending with combustion chamber. In this case meridional profile of the nozzle diaphragm can be of arbitrary shape with the obligatory observance of sections areas.calculate section area at the exit from the stage (behind working wheel) it is necessary to compute gas parameters and behind calculated stage.gas temperature is determined from the energy equation:
В
gas pressure behind stage is calculated by the formula
В
- stage efficiency.component of the jet velocity at the exit from the working wheel is assumed on 20-80 m/s more then gas velocity at the entry to the working wheel, ie
; m/s,.
area at the exit from the working wheel is determined from following expression:
,
is computed by the value of
.
for chosen profiling law determine main dimensions at the exit from turbine stage in a similar manner as have been done turbine stage entrance.the base of computed diameters values ​​draw turbine stage scheme.
Turbine stage calculation on the middle radius
At given circumferential velocity value on the middle radius of the inlet edge calculate circumferential velocity behind working wheel from the relation
В
Performing approximate calculations it is possible to suppose.loading coefficient on the middle radius is determined by the formula
В
the first turbine stage. jet velocity at the exit from the nozzle diaphragm is determined from the equation
В
reduced velocity - by the formula
В
of must not exceed 1,25. If it is possible to decrease it by increasing the circumferential velocity, decreasing of the angle of the stream output from nozzle diaphragm, increasing of the stage work, applying of airtwist at the exit from the working wheel in the opposite direction of rotation. If first three methods can not be used, can be obtained from the Eulers equation, have assigned:
,
where.
of must not exceed, otherwise it is necessary to decrease to meet this requirement.long as all of calculations are carried out for middle radius in what follows we will withdraw subscript md. Following formulas flow parameters calculation are legible for every blade section.components of the jet velocity at the entry to the working wheel and behind turbine stage, and parameters, and are calculated by the formulas:
;;;
.
component of the jet velocity and parameter at the entry to the working wheel are calculated by the formulas:
;.
component of the relative velocity and the relative velocity at the entry to the working wheel are calculated by the formulas:
;.
of the stream inlet into the working wheel in the relative direction is computed by formula
.
component of the relative velocity behind turbine stage is determined on the base of the following expression
В
axial turbine stage
Axial component of the jet velocity at the exit from the working wheel is assigned such that is on (20-80) m/s more then.velocity and reduced velocity at the exit from the working wheel are calculated by the formulas:
;.
output angle at the exit from the working wheel is calculated by the formula
.
must be close to 90 В°, but for first stages it can be n the range of (75-85) В°. output angle at the exit from the working wheel in the relative direction can be found by the formula
. velocity at the exit from the working wheel and its circumferential component are determined by the formulas:
;.
temperature and critical gas velocity in the relative direction are computed from the equations:
В В
velocities at the entry to the working wheel and behind turbine stage are calculated by the formulas:
