Boundary-layer ingested engines have the potential to offer significantly reduced fuel burn, but the fan stage must be designed to run efficiently with a distorted inflow. It must also be able to withstand unsteady aerodynamic loads resulting from a complex nonuniform flowfield. This paper applies different numerical methods for an improved understanding of the aerodynamic interaction between a transonic fan and inlet distortion. A single-stage transonic tail cone thruster fan was designed using both in-house and commercial tools operating in an inlet distortion flowfield. This paper demonstrates that the relevant metrics required to compute the aerodynamic performance of a fan stage in distorted conditions can be reasonably modeled with a few harmonics using the nonlinear harmonic method in a fraction of time in comparison to a full annulus time marching solution. The nonlinear harmonic method also reduces the computational domain, and hence reduces the solution runtime by an order of magnitude. However, it fails to accurately resolve the wake and potential field transfer across the blade rows due to a limited number of harmonics being applied. A detailed aerodynamic description of the unsteady inflow distortion, the interacting blade-row mechanisms, the flow redistribution upstream of the rotor, the distortion transfer across the different blade rows, and the corresponding aerodynamic losses can be analyzed accurately using only a full annulus time-marching method.
Boundary Layer Ingestion (BLI) engines have the potential to offer significantly reduced fuel burn, but the fan stage must be designed to run efficiently with a distorted inflow. It must also be able to withstand unsteady aerodynamic loads resulting from a non-uniform flowfield. In a multidisciplinary turbomachinery design cycle involving such a complicated flowfield, high fidelity numerical solutions are required. Two high fidelity unsteady Reynolds Averaged Navier-Stokes (URANS) methods for accurate analysis of a Tail Cone Thruster (TCT) transonic fan stage subjected to inlet distortion have been implemented. They are frequency domain based non-linear harmonic (NLH) and full-annulus complete time domain based time marching methods. This paper demonstrates that the relevant parameters required to accurately compute aerodynamic performance of a fan stage in distorted conditions can be accurately modelled with a few harmonics using the NLH method in a fraction of time compared to the full annulus time marching method. However, the complete aerodynamics of distortion transfer across different blade rows of a fan stage can only be analyzed using the time marching solution. Several physical mechanisms which govern the fan response to an inlet distortion and how different distortion profiles impact the aerodynamic performance of this fan stage are also explained.
The effects of boundary layer ingested inlet distortion on the unsteady flowfield between an inlet guide vane (IGV) and rotor of a single stage transonic fan are important, as they result in significant changes in the massflow rate, stagnation pressure rise and stage efficiency. The three dimensional time accurate commercial URANS code EURANUS (Cadence Inc.) was used to generate and analyze periodic quarter annulus simulations of the IGV-Rotor fan stage. A comparison of mixing plane and time averaged solutions showed the unsteadiness of the blade row interactions especially along the interface between the IGV and the rotor. The mixing plane solution predicted a decrease in efficiency of 1.11 % in the fan stage compared to that of a rotor, while a time averaged solution predicted a 1.36 % efficiency decrease in the fan stage compared to that of the rotor. At design speed, significant non-linear interaction was observed with very high levels of unsteady loading occurring at the vane trailing edge region because of it’s interaction with the rotor generated oblique shock waves. These shock waves move upstream and get reflected through the vane passages creating additional fan stage loss. It can also be observed that the strong vortices of the inlet guide vane wake break up the detached rotor bow shock. These shed vortices are chopped by the rotor leading edge and ingested by the rotor. Both the time averaged and the time accurate results show that the wake vortices strongly interact with the rotor blade boundary layer. These cause a decrease in the rotor efficiency and stagnation pressure rise, while the high frequencies of the inlet guide vane wakes can be a potential cause of rotor high cycle fatigue (HCF). Additionally, small flow separations due to shock boundary layer interactions can be observed at the IGV suction surface near the tip and contribute to the IGV flow losses.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.