Influence of Domain Definition and Interface Placement on the CFD Performance Prediction of Centrifugal Fans
- This study investigates the influence of domain definition and interface placement on the steady-state CFD prediction of performance curves of centrifugal fans. The focus is on the separation between rotating and stationary flow domains as well as on the effects of the selected interface treatment (Frozen Rotor vs. Mixing Plane). The results show that a physically consistent definition of the rotating domain—comprising the impeller and the surrounding vaneless space while the inlet nozzle and casing remain stationary — is essential for obtaining realistic total pressure predictions. Extending the rotating region into geometrically stationary components such as the inlet nozzle or volute casing introduces artificial shear work and erroneous inertial effects, resulting in increased losses and an underestimation of the pressure rise. A realistic rotor–outlet interface that spans the full axial height of the impeller exit yields markedly better efficiency predictions than an idealised, radially truncated interface that numerically acts asThis study investigates the influence of domain definition and interface placement on the steady-state CFD prediction of performance curves of centrifugal fans. The focus is on the separation between rotating and stationary flow domains as well as on the effects of the selected interface treatment (Frozen Rotor vs. Mixing Plane). The results show that a physically consistent definition of the rotating domain—comprising the impeller and the surrounding vaneless space while the inlet nozzle and casing remain stationary — is essential for obtaining realistic total pressure predictions. Extending the rotating region into geometrically stationary components such as the inlet nozzle or volute casing introduces artificial shear work and erroneous inertial effects, resulting in increased losses and an underestimation of the pressure rise. A realistic rotor–outlet interface that spans the full axial height of the impeller exit yields markedly better efficiency predictions than an idealised, radially truncated interface that numerically acts as an extension of the impeller end-walls. For the present low-specific-speed fan, a moderate transition region within the vaneless space, corresponding to approximately 3–16 % above the impeller exit radius R₂, allows sufficient flow relaxation and leads to stable and physically consistent results. For steady-state simulations, Frozen Rotor solutions benefit from an interface distance of about 13 % above R₂, whereas Mixing Plane models provide the most robust and accurate performance predictions for interface positions around 6–7 % above R₂ in combination with a realistic interface geometry. Correct specification of wall motion, use of the SST k–ω turbulence model and appropriate near-wall resolution (y⁺ ≈ 1–3) are additional key factors for numerical consistency. Overall, the study demonstrates that careful domain definition, suitable interface placement, and a consistent numerical setup are essential prerequisites for physical fidelity and comparability of CFD-based performance curve simulations of centrifugal fans.…
