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gsphelp  Compressor

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compressor

 

The compressor component represents various types of compressors used in the main gas path except for the Fan. Usually the compressor is driven by a turbine and consequently shares a shaft number with it. Design point input includes rotor speed, pressure ratio and efficiency. Design inlet mass flow is obtained from the exit mass flow of the preceding component (such as an Inlet, Fan or other Compressor). 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.

 

Three simulation options for the compressor exist:

Free state rotor speed

The standard option, where the compressor rotor speed is a "free state variable" in the model dependent on the system performance. steady state rotor speed then is an equilibrium value where the compressor has just sufficient power to maintain rotor speed. During transient the compressor will accelerate or decelerate depending on the available shaft power.

User specified rotor speed

 In this case the rotor is fixed to a  user specified value. With this option power required is calculated for the specified speed. All other components (e.g. turbines) must have this option set also. GSP simulation output usually reports a power surplus or deficit for the shaft. This option is necessary to perform steady state simulation of single shaft turboprop or turboshaft engines which usually have a system where the shaft load is varied to maintain rotor speed. The operating line uses the same map format as the normal component maps, the only differences are that a surge line will not be required and that there is only a single value for Beta (by definition 1).

Externally controlled rotor speed

This option allows other components (custom components) to set rotor speed explicitly. The compressor and fan components and descendant component model classes need the 'Externally controlled' option set when the shaft speed is not a free state and determined by another component such as a turbine with the 'Power balance at rotor speed' option set.

 

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

Map

The standard option uses a compressor map of type component map. The map file consists of tables with corrected mass flow, efficiency and pressure ratio as a function of corrected normalised 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.

Operating Line

 This advanced option allows the engine modeller to use the compressor operating line. In case the maps of the compressors cannot be obtained from the manufacturer, the operating line of an existing engine can inserted (or a predicted operating line for a new engine). When using this option note that the mass flow error equation for the turbine needs to be deactivated to obtain a solvable equation system. In case the operating line is the actual running line of the engine, the error will remain very small (can be visualised through the option Werror on the turbine output tab sheet). Using a predicted operating line, the error increases the further the operating point is located from the real operating point.

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. Off-design calculation will not be possible.

 

The map file consists of tables with corrected mass flow, efficiency and pressure ratio as a function of corrected normalised 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 Graph button in 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.

 

An unlimited number of compressor bleed flows can be specified in the Bleeds tab sheet. Compressor bleed flows are secondary air flows extracted from the compressor air flow for various purposes: bleed flows can be used to model customer bleeds or turbine cooling bleeds used in the turbine component or air flows entering bypass ducts in the duct component. The bleed flow numbers used must be unique for the model.

 

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

 

When using a map, the surge margin (parameter name SM) is calculated during iteration (and not only at final output as an additional output value) to enable direct control of SM using limiters and schedulers.

 

Bleed control and enabling/disabling cells in (compressor) bleeds table depending on case or config. Bleeds can only be defined in configs, in cases, only bleed values and bleed control nrs. can be changed.

 

Changes in geometry caused by inlet guide vanes or variable stator vanes can be modeled using tab sheet Variable Geometry. Two options are available to model variable geometry, using a schedule on the tab sheet, or using an external geometry controller. For both options the Effects per degree vane- or blade angle group box needs to be populated with reference values for the modifiers for the map, where dAngle is deviation in degrees of reference vane/blade position. There are modifiers for mass flow, pressure ratio and efficiency. Note that when using the schedule the values are ascending.

 

Modelers can model deterioration using the map modifying parameters on the Deterioration tab sheet. There are modifiers for mass flow, pressure ratio and efficiency. Note that to enable deterioration effects in your model, the Apply deterioration effects option must be active, which can only be used in off-design analysis.

 

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

 

 

 


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