Influences of key parameters on flow features in the curved ducts with equal area

Abstract

Curved ducts are widely used in aircraft engines to improve some capability of aero-engines. Complex internal flow characteristics would be induced by the curvature in such components. In this study, the influence of parameters, including the arc angle α, the curvature radius R i, and the height H, on the local accelerating and transonic flow in the curved ducts with equal area were studied numerically and theoretically under different nozzle pressure ratios (NPRs). The range of the Re number based on the height of the duct and the velocity at the inlet was [Formula: see text] ∼ [Formula: see text]. The shear stress transport κ-ω turbulent model was proved by the test data to suitably simulate the flow field in curved ducts because it could accurately predict the flow separations under adverse pressure gradients. The uncertainty of the pressure scan value to obtain the test data was ±0.05%. Numerical results showed that the effect of α on the flow characteristics of the curved ducts is little. The maximum Ma number in the curved section reduces with the increase of R i, and that grows with the increase of H. The range of the maximum Ma number was 1.20∼1.80. The critical NPRs, which decided the special flow features, were found in the curved ducts. The critical NPR rises with the increase of R i; however, the effect of H on the critical NPR is irregular due to the flow separations located near the lower wall induced by the large adverse pressure gradient. The theoretical results based on the small perturbation theory of transonic flow in the polar coordinate system proved that the distribution of sonic line was just dependent on the inner diameter R1, the outer diameter R2, and the arc angle θmax of the curved section. The critical mass flow and the critical NPR2 are only related to R1 and R2.

Ideal and non-ideal planar compressible fluid flows in radial equilibrium

“…The flow curves downwards and possibly evolves towards a planar radial equilibrium condition. Sun & Ma (2022) considered a similar domain to study curved ducts for aero-engine applications. Different simulation approaches are considered here, depending on the subsonic or supersonic flow regime, as presented in the following subsections.…”

“…At the end of the curved portion of the duct, the increase in pressure along the internal wall results in the formation of a normal shock wave. The reader is referred to Sun & Ma (2022) for a detailed description of the shock formation mechanism. Due to the presence of a shock wave, the streamline curvature method, which relies on the isentropic hypothesis, is replaced by the finite-volume open-source software SU2 (Economon et al 2016).…”

“…At the outlet, a static pressure equal to half of the inlet total pressure value is set so that the flow transitions from subsonic to supersonic conditions. For further details on the problem set-up, the reader is referred to Sun & Ma (2022). The methodology and numerical tools employed in the present work are based on reference computational fluid dynamics (CFD) simulations of non-ideal flows performed by Gori et al (2020).…”

“…Several studies presented simulations and experimental observations of the flow evolution within curved and S-shaped ducts for ideal gases (see e.g. Vakili et al 1983;Harloff et al 1993;Crowe & Martin 2015;Sun & Ma 2022). In many applications, however, the thermodynamic operating conditions require accounting for complex thermodynamic models, and entail the possibility of observing thermodynamic and gasdynamic non-ideal effects.…”

“…1983; Harloff et al. 1993; Crowe & Martin 2015; Sun & Ma 2022). In many applications, however, the thermodynamic operating conditions require accounting for complex thermodynamic models, and entail the possibility of observing thermodynamic and gasdynamic non-ideal effects.…”