Further improvements in aero-engine efficiencies require accurate prediction of flow physics and incurred loss. Currently, the computational requirements for capturing these are not known leading to inconsistent loss predictions even for scale-resolving simulations depending on the chosen convergence criteria. This work investigates two aspects of loss generation using high-fidelity simulation. In the first case study we look at the effect of resolution on capturing entropy generation rate by simulating a Taylor-Green vortex canonical flow. The second case study focuses on the effect of resolution on flow physics and loss generation and uses a compressor cascade subjected to freestream turbulence. The results show that both resolving local entropy generation rate and capturing the inception and growth of instabilities are critical to accuracy of loss prediction. In particular, the interaction of free-stream turbulence at the leading-edge and development of instabilities in the laminar region of the boundary layer are critical to capturing loss.

Further improvements in aero-engine efficiencies require accurate prediction of flow physics and incurred loss. Currently, the computational requirements for capturing these are not known leading to inconsistent loss predictions even for scale-resolving simulations depending on the chosen convergence criteria. This work investigates two aspects of loss generation using high-fidelity simulation. In the first case study we look at the effect of numerical resolution on capturing viscous dissipation by simulating a Taylor-Green vortex canonical flow. The second case study focuses on the effect of flow physics on loss generation and uses a transitional compressor cascade subjected to freestream turbulence.

In this paper we study the effect of rotor-stator axial gap on midspan compressor loss using high fidelity scale-resolving simulations. For this purpose we mimic the multi-stage environment using a new numerical method which recycles wake unsteadiness from a single blade passage back into the inlet of the computational domain. As a result a type of repeating-passage simulation is obtained such as observed by an embedded blade-row. We find that freestream turbulence levels rise significantly as the size of the rotor-stator axial gap is reduced. This is because of the effect of axial gap on turbulence production, which becomes amplified at smaller axial gaps and drives increases in dissipation and loss. This effect is found to raise loss by between 5.5 - 9.5% over the range of conditions tested here. This effect significantly outweighs the beneficial effects of wake recovery on loss.

Flows in modern compressors are highly complex. They are subject to adverse pressure gradients, high levels of unsteadiness and often operate at transonic conditions. Such conditions often render low order methods such as URANS unreliable. This is due to the inherently unsteady nature of shock-boundary layer interaction as well as the interaction between deterministic and stochastic unsteadiness. These issues are further exacerbated by the current design trends towards more compact machines with higher work coefficients. It is therefore desirable to study the flow within a transonic compressor stage using highly-fidelity scale resolving simulation. To enable fully wall resolved stage calculations at a realistic rotor Reynolds number of 1 × 106, a quasi three-dimensional translational setup was carefully generated to feature similar midspan blade loadings to the three-dimensional rotational set up of the Transonic Compressor Darmstadt. Two cases were considered, one with a laminar inflow to the rotor and one with inflow turbulence. It is found that the inflow turbulence suppresses the rotor suction side separation bubble with implications on the shock-boundary layer interaction, mainly in terms of an upstream moved shock location and changes to the shock oscillations, and the shock-related passage losses. The changes to the early development of the rotor suction side boundary layers also affects the boundary layer losses. The stator suction side boundary layer on the other hand appears insensitive to the introduction of inflow disturbances. However, a larger passage loss is found for the laminar inflow case in the stator. Additional URANS calculations of the same setup show overall good comparison with the high-fidelity results for most integral values, but lack in predictive accuracy for some details, such as shock boundary layer interaction as well as wake and passage losses.

In this paper we study the effect of rotor-stator axial gap on midspan compressor loss using high fidelity Large-Eddy Simulations. For this purpose we mimic the multi-stage environment using a new numerical method which recycles wake unsteadiness from a single blade passage back into the inlet of the computational domain. As a result a type of repeating-stage simulation is obtained such as observed by an embedded blade-row. We find that freestream turbulence levels rise significantly as the size of the rotor-stator axial gap is reduced. This is because of the effect of axial gap on turbulence production, which becomes amplified at smaller axial gaps and drives increases in dissipation and loss. This effect is found to raise loss by between 7–9.5% over the range of conditions tested here. This effect significantly outweighs the beneficial effects of wake recovery on loss.