An unsteady analysis of the MIT counterrotating aspirated compressor (CRAC) has been conducted using the Numeca FINE/Turbo 3D viscous turbulent flow solver with the Nonlinear Harmonic (NLH) method. All three blade rows plus the aspiration slot and plenum were included in the computational domain. Both adiabatic and isothermal solid wall boundary conditions were applied and simulations with and without aspiration were completed. The aspirated isothermal boundary condition solutions provide the most accurate representation of the trends produced by the experiment, particularly at the endwalls. These simulations provide significant insight into the flow physics of the aspiration flow path. Time histories and spanwise distributions of flow properties in the aspiration slot and plenum present a flow field with significant temporal and spatial variations. In addition, the results provide an understanding of the aspiration flow path choking mechanism that was previously not well understood and is consistent with experimental results. The slot and plenum had been designed to aspirate 1% of the flow path mass flow, whereas the experiment and simulations show that it chokes at about 0.5% mass flow.

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An unsteady analysis of the MIT counter-rotating aspirated compressor (CRAC) has been conducted using the Numeca FINE™/Turbo 3D viscous turbulent solver with the Non-Linear Harmonic (NLH) method. All three blade rows plus the aspiration slot and plenum were included in the computational domain. Both adiabatic and isothermal solid wall boundary conditions were applied and simulations with and without aspiration were completed. Comparison of the aspirated case with data is good. When compared to the adiabatic boundary condition, the isothermal boundary condition solutions showed improvements in predicting stage performance, most notably at the endwalls. The aspiration has a significant impact on the flow field and provides a 4.2% increase in efficiency over the non-aspirated case. Although the slot and plenum had been designed to aspirate 1% of the inlet mass flow, the experiment and simulations show that it chokes at about 0.5%. Details of the aspiration flow path choking mechanism, which was previously not well understood, are presented.

The 3D time accurate simulation of the MIT counter-rotating aspirated compressor is presented. The unsteady solver, TURBO, has been used with a phase-lag boundary condition to solve for the two counter-rotating rotors. An inlet boundary condition has been imposed to simulate the swirl and loss of the IGV. Cases with and without aspiration have been simulated. Comparison with data of the aspirated solution is good, especially near the tip picking up detailed features of the measured profile. On a 1D basis, the experimental efficiency is 87.9%, and the aspirated simulation is 89.4%. A comparison between the aspirated and non-aspirated simulations show the aspirated simulation is 2.2% higher in efficiency than the non-aspirated case. Flow details of the time-averaged solution in the second rotor show dramatic radial migration of high entropy fluid from the tip that gets ingested into the suction slot. This and other flow details shed light on the details of the counter-rotating aspirated design.

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