Aerodynamic Characteristics of Uneven Inlet Flow in a Transonic Axial Compressor Operations

Multi-stage axial compressors are essential component of aerospace propulsion system because the structure of the exit flow field of an axial compressor directly influences the performance and stability of an aerospace engine. In this research paper, the numerical simulations of the first 3 stages of a transonic multi-stage axial compressor were carried out to study the characteristics of the exit flow field of the compressor under four operating conditions. The main focus of the research was airflow deflection angle, patterns of radial velocity distribution, and its changes. Also, the influence of the angle of inlets air direction and pressure on the outlet flow system on the unsteady conditions of inlet airflow were considered. The findings show that when rotational speed reaches a level of 68 %, exit flow field of the axial compressor degrades significantly. The operating conditions, the velocity and airflow angle is positively correlated with the rotational speed as the rotational speed decreases. In comparison to the design condition, the peak velocity reduces by 2%, 3.7% and 7%, whereas airflow deflection angle deviations are less than 3°. Under non-uniform inlet conditions, as the airflow angle at inlet reduced by 90° to 70°, the differences in peak and mean exit velocity do not exceed 2 % and the differences in peak and mean airflow deflection angle do not exceed 1 %. A relatively small effect of alteration in a local pressure field on the inlet pressure in a non-uniform environment produces a very significant impact on the local distributions. When inlet pressure is changed between 1 atm and 1.05 atm, the value of the peak velocity changes by 0.98 percent and that of the average velocity by 3 percent. Maximum difference in velocities is 6 %, and average airflow deflection angle has a difference of 0.7 %, but its maximum deviation valued 1.9°. In general, the characteristics of the flow field on the exit of the compressor demonstrate considerable changes under various operating conditions. The flow in the compressors with low rotational velocities will be more unstable, which causes the flow separation and accumulation of fluid with low energy and non-uniform pressure distribution. On the contrary, variable inlet conditions can have a relatively small impact on the whole flow field, with significant local alterations, which can be used in the theoretical basis to optimized design and performance assessment of compressors.