Axial Flow Compressor

The task of the compressor is to increase the pressure of air required by the engine. The axial flow compressor is considered here i.e. one in which the flow enters in an axial direction parallel to the axis of rotation. The overall performance maps are used to represent the steady performance of the compressor which is good enough for real-time simulation. The typical performance maps and the governing equations are similar for the fan, low-pressure compressor, and high-pressure compressor. The map values of airflow and efficiency are computed from functions of pressure ratio and corrected speed using 2-D lookup tables were through interpolation the mass flow and efficiency are determined [10]. The following equations are used to calculate

In this model the turbine is assumed to be an axial flow turbine and both low and high-pressure turbines are modelled with same equations [11]. But while modelling the engine in Simulink, the turbine is modeled as a single block by stacking the stages of the turbine into a single block. Dynamic behavior of all the individual stages is also stacked into a single block with only the inlet and final exit conditions of the turbine. From the values of the corrected mass flow rate and the turbine efficiency, the actual mass flow rate and the temperature can be calculated from the expressions,

Actual mass flow rate, ………..……………………………………………………..……….....(11)

Temperature, ………………………………………………………..….(12)

Work of the turbine, ……………………………………………………..………(13)

2.4 Nozzles A convergent nozzle is considered in modeling the engine. The partially expanded gas coming from the turbine is accelerated to a high velocity in the nozzle and expand to the ambient pressure.

The nozzle is to be checked first to define whether it is choked or not. Thus the critical pressure is calculated from the relationship: ………………………………………………………………………………….………..(14)

Thrust can be calculated from the following equation ……………………………………………………………………......(15)