Bleed flow invisible objects represent secondary air or gas flows among the components such as:

•compressor bleed used as customer bleed

•compressor bleed for turbine cooling

•compressor handling bleed (variable bleed)

•small leakage bleed flows flowing into the duct

•small leakage bleed flows flowing from the fan core

•duct bleed for customer bleed or cooling

In the Bleeds tab sheet in the compressor, duct or fan data window an unlimited number of bleed flows can be specified. The bleed flow numbers used must be unique for the model. Reusing numbers will raise a warning on simulation and stop calculation. The type of bleed flow can be selected from a drop-down list box activated when clicking in the grid cell on the arrow on the right. The following types are available:

•None

The row in the table represents no bleed

•Flow W constant

A constant flow rate in [kg/s] must be specified

•Fraction constant

A constant fraction (in the 0-1 range) of the compressor inlet flow must be specified

•Externally controlled

The bleed flow rate is controlled by an external component; e.g. a bleed control component

•Determined by map (not in standard compressor, only available in derived compressor classes)

A bleed flow determined by the compressor operating point data in the map. The third map output table represents compressor inlet corrected bleed flow values. In effect, the bleed flow can be set depending on corrected compressor speed and beta value. It is a means to include variable handling bleed without using control system components. Handling bleed is usually controlled as a function of corrected compressor rotor speed only.

Note that the Bleed Nr and Type columns are only accessible in Configurations since they are considered configuration properties. The other columns can be adapted both in configurations and cased, both DP and OD.

For separate control of DP and OD bleed flows, use the Externally controlled type in conjunction with a bleed control component which allows separate DP and OD input.

The bleed flow is specified as a massflow W bleed or a fraction Bleed fraction of the compressor flow (or no flow rate data for the last two options), depending on the bleed type. The dH fraction parameter indicates how much of the total compressor air enthalpy rise is applied to the bleed air. In other words, dH fraction indicates at about where between the high pressure exit (dH fraction=1) and lower pressure entry (dH fraction=0) the air is extracted. The higher dH fraction, the more power is taken from the compressor in terms of pressurized bleed air. Both Bleed fraction and dH fraction range between 0 and 1.

Note that depending in the Type selected, the W bleed or Bleed fraction columns can or cannot be edited. With the Externally controlled option, only dH fraction can be set.

Use the Externally controlled option in connection with a bleed control component if you want manual off-design control over the bleed flow rate.

Note that with bleed flow output data such as bleed mass flow rate, the parameter identifier is followed by the bleed nr. (e.g. Wbld2_3 means bleed flow nr. 2 of component nr.3).