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gsphelp  Turbine

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turbine

 

The turbine component is used to obtain mechanical power from hot gas in order to drive a rotating shaft and represents various types of turbines used in the main gas path. When the turbine drives a compressor it must share a shaft number with it. For a power turbine any shaft number can be used. If transient simulations are to be performed the rotor moment of inertia must be specified. The turbine moment of inertia applies to the entire spool (including any compressors, gearboxes and load components (e.g. generators, propellers etc.) rotating with it). Mechanical efficiency also applies to the entire spool and determines how much power is lost before it is extracted by a compressor or load outside the gas turbine.

Turbine design point input includes rotor speed and efficiency. Design inlet mass flow is obtained from the exit mass flow of the preceding component (such as a combustor or other turbine). Specify a shaft number or suffix corresponding to the engine specification, such as 2 for a typical gas generator compressor resulting in N2 for the rotor speed parameter name. Design pressure ratio is not specified but calculated from the power required by compressors, fans and external turbine design loads in the design point calculation.

 

A series of turbine cooling flows can be defined to accurately model the thermodynamic effects of turbine cooling, including separate nozzle guide vane cooling (note that you can change the station number of the nozzle guide vane outlet on the Output tab sheet).

 

For the determination of the rotor speed three options are available (also see compressor and turbo shaft models), user-linked to the options of the fan and compressor:

Free state rotor speed

The rotor speed is determined with use of the other components in the iteration process of the model. If the free power turbine checkbox is checked, no compressor is driven and the speed is determined by torque surplus and spool moment of inertia (causing acceleration or deceleration). Note that free power turbine speed only changes during transient simulation!

User specified rotor speed

The rotor speed is user specified and fixed. This option can be used for both Gas Generator (GG) and Free Power Turbine (PT) turbines. In case of a free PT, the free power turbine checkbox must be checked, see also free power turbines. Note that enforcing the rotational spool speed of the GG turbine (the model option of the compressor of the GG must also have the User specified rotor speed model option selected) may result in a power surplus or deficit for the shaft.

Speed determined by shaft (external control)

The rotor speed is user specified and the user can add an error variable (check box Add Power Balance equation, see also turbo shaft models) for the turbine power balance to calculate other components' (free state) parameters such as fuel flow or a control system variable (e.g. trimming signal) with the specified rotor speed as input. Any compressors or fans attached to this turbine must then have the Externally controlled option set.

 

GSP is able to calculate through a series of turbines (or stages; provided that stage maps can be obtained from the turbine manufacturer) to drive a single shaft. However, the user should provide the model the division of the overall power over the series of turbines (or stages) at design time. To accomplish this the user can choose from 6 options in the Power delivered to shaft in design point group box to divide the power per turbine:

All required

Used for the last turbine or a single turbine on one shaft; all power to shaft,

Part of req. pwr.

Specify the fraction of the total (all turbines) power to be given to the shaft for this turbine,

Power

Specify the amount of power from this turbine to be given to the shaft,

Torque

Specify the torque from this turbine to be given to the shaft,

PR

Specify the pressure ratio of this turbine determining the power to be given to the shaft,

TR

Specify the temperature ratio of this turbine determining the power to be given to the shaft.

 

Note that the in case there are multiple turbines placed on the same shaft the mass moment of inertia is taken from the last turbine on the shaft (with the highest component ID). Also note that the turbine moment of inertia applies to the entire spool including any compressors, gearboxes and load components (e.g. generators, propellers etc.) rotating with it (see above).

 

For both the compressor drive and free power drive option, (extra) power may be absorbed from the shaft using the PTO power and Torque specification fields. In this case it is also possible to use the Load Control component. Note that PTO power and Torque can be specified, which are summed.

 

The checkbox Calculate max. Design load of the Design External load / PTO box is very useful when modeling industrial gasturbines. When checked, the maximum amount of power that can be generated by the turbine will be calculated. The relative losses in the exhaust system can be given in the field ass. exit to ambient rel. press.loss to directly account for the exhaust pressure losses during design calculation.

 

For off-design performance several options are available. Using the option group box one of the following options can be chosen:

Map

The standard option uses a  turbine map of type component map. The map file consists of tables with corrected mass flow, efficiency and pressure ratio as a function of corrected normalized rotational speed and beta. The map operating point corresponding to the design operating point is specified using the map design rotational speed and beta values. Click the Show Graph button on the Map tab sheet to view the map graphically and note the yellow rectangle which can be used to move the map design point. In the map graph also the beta-lines can be show after activating the appropriate item in the Options menu.

No map (DP only)

This advanced option allows the engine modeller to calculate design point performance without having to specify an off-design component map.

 

The option Reset map scale factors sets the map scaling factors to 1 during off-design calculations. This enables the engine modeler to match existing turbo components using their actual/original maps.

 

Variable Geometry and Deterioration are similar to the functionality described in the Compressor section.

 

Heat sink and heat soakage heat fluxes affect turbine work significantly. See Heat transfer on how this effect is modeled.

 

 


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