The mixer component is used to simulate the mixing of two gas flows to a single flow, such as the mixing of the bypass and core flows in a mixing turbofan engine. The mixing of the two flows to a uniform gas condition (i.e. temperature, composition) is assumed to completely occur in an infinitely short distance without losses. To incorporate pressure losses, use a preceding or downstream duct component. Mixer exit flow conditions are determined using the equation for conservation of momentum with the assumption that the ratio of entry flow static pressures remains constant. For applying this equation, entry and exit flow static conditions and velocities need to be calculated and therefore the flow cross-areas need to be specified. 5 options for specification are available:

•Specify both entry cross section areas for duct and core.

In this case the static pressure ratio is determined in the design point calculation and maintained for off-design calculations.

•Specify total cross section area and static pressure ratio.

In this case the duct and core cross section areas are determined from the static pressure ratio during the design point calculation.

•Specify core mixing plane entry parameter (depending on parameter selection) and static pressure ratio.

In this case the duct and core cross section areas are determined from the static pressure ratio during the design point calculation.

•Specify duct mixing plane entry parameter (depending on parameter selection) and static pressure ratio.

In this case the duct and core cross section areas are determined from the static pressure ratio during the design point calculation.

•Join 2 flows: no conservation of momentum is maintained, only conservation of energy joining the flows into one.

Important note:

At design point calculation the inflow areas are either specified or calculated from the gas inflow V or Mach. The duct inflow and core inflow areas or static conditions are determined by the mixer input options, and therefore do NOT correspond anymore to upstream connected components exit conditions! Mixing plane entries are to be considered connected to upstream via perfect duct with varying area (if upstream areas are specified).

The specification of this data often requires some trial-and-error cycles, especially if the area data is not known. In that case, use the second option for example and set static pressure ratio to 1. Repeat design point calculations until mixer entry Mach numbers are in a reasonable range (around 0.5). Illegal mixer parameter values include Mach numbers exceeding 1 and static entry pressures exceeding the total pressure of the other entry (this would cause reverse flow) and are reported as errors (see 4.7). The exit flow cross-area is assumed equal to the sum of the entry cross-areas.

Static mixing plane conditions

The mixer calculates separate mixing plane static conditions, required to calculate the equations relating the two mixing flows (usually using conservation of momentum and assuming a user specified relation between the two entry flow static conditions).

Note that the mixing plane entry is assumed to be between component inlet and exit stations. These are NOT the mixer inlet station static conditions corresponding to the upstream component Exit static conditions that are calculated if non-zero upstream component exit area, mach or velocity values are specified. Since the mixing plane entry is not coinciding with an engine station, mixing plane entry mach, area and velocity output parameter ID's are Mach_mduct, Mach_mcore, A_mduct, A_mcore, V_mduct, V_mcore followed by component ID string.

The mixing plane exit is corresponding to the component exit conditions and therefore the exit station number, so mixing plane exit conditions are simply represented exit station conditions.