Unsteady flow fields in a multistage axial flow compressor

An attempt was made to resolve experimentally, the unsteady flow fields downstream of the second stator of a three stage axial flow compressor representative of the aft stages of a high pressure core compressor which will provide information on rotor-stator interaction effects and the nature of the unsteadiness in an embedded stator of a three stage axial flow compressor. Detailed area traverse measurements using pneumatic five hole probe, thermocouple probe, semi-conductor total pressure probe (Kulite) and an aspirating probe downstream of the second stator were conducted at the peak efficiency operating condition. The unsteady data was then reduced through an ensemble averaging technique which splits the signal into deterministic and unresolved components. Various analysis techniques were used to quantify the flow field.;Based on these measurements, it was observed that the stator wakes, hub leakage flow region, casing endwall suction surface corner region, and the casing endwall region away from the blade surfaces were the regions of highest losses in total pressure, lowest efficiency and highest levels of unresolved unsteadiness. The deterministic unsteadiness was found to be high in the hub and casing endwall regions as well as on the pressure side of the stator wake.;Significant changes occur to the stator exit flow features with passage of the rotor upstream of the stator. As the rotor passes across the stator leading edge, the wakes start increasing in size and the corner region starts reducing in size. The hub leakage flow region starts contracting in the circumferential direction and starts moving radially. Some of the stator hub wall flow is then transported across the stator passage and deposited on the pressure surface of the stator. It was found that the deterministic unsteadiness contributes significantly to the mixing of the flow along with the mean flow motion in the midpitch region near the hub. It was also found that the dominant advection is due to the circumferential velocity compared with the radial velocity for all three momentum and the energy equations of the average passage equation system.