## 1 Introduction  
A centrifugal impeller's entrance region typically experiences substantial turbulence, significant spiral flow losses, and flow stalling at the shroud as a result of abrupt changes in the flow direction. These flow losses tend to disturb the flow pattern at the inlet region, thereby causing both energy loss and a substantial reduction in the performance parameters of the devices. CFD is capable of analyzing the inlet flow domain, and whole field-flow analysis can capture the flow-loss phenomena effectively. A CFD study of relevant geometric interventions in the centrifugal fan's inlet flow route demonstrates the potential for improved fan performance. Various methods for increasing the energy efficiency of the fan system result in the achievement of the aim set by the UN's Sustainable Development Goals (SDG) for 2030. Significant contributions are made by various researchers to augment the performance of the fan by streamlining the flow characteristics of the device, particularly in the vicinity of the inlet region. [PERSON] et al. [1] studied the effects of the axial flow fan's entry hub length and corner shape on efficiency. The losses as well as the efficiency were evaluated by performance parameters, such as total pressure loss. SC/Tetra v12, a commercial and popular CFD solver, was used for analyzing the fluid flow. The results revealed that for a certain entry hub length, efficiency improves, and the authors stated that this gain is due to the interaction between the hub vortex and the blade. Using CFD calculations, [PERSON] et al. [2] deliberated the start of stall events in a radial compressor of the transonic type. In the presence of inlet flow disturbances, the bent pipe provided at the impeller's inlet eye region was evaluated. The authors revealed that the inlet flow losses are minimized in the presence of inlet guide vanes and these vanes essentially suppress the inlet flow disturbances. [PERSON] et al. [3] analyzed a 90-degree curved pipe numerically for the performance assessment of two different types of inlet ducts: a normal straight duct and a radially bent duct. Their studies concluded that the inlet flow distortions are significantly suppressed in the case of a straight duct due to flow acceleration. Numerical research of centrifugal fans with diffuser and nozzle types of inlet arrangements was conducted by [PERSON] et al. [4]. The results of the investigation showed that the flow geometry of the impeller inlet has a significant impact on the inlet flow losses. The authors concluded that nozzles with smaller diameters enable the fan to recover static pressure more effectively. To find out the impact of bell mouth forms on blower output, [PERSON] et al. [5] carried out a CFD analysis on a centrifugal blower. Twelve numerical models were created parametrically, each with a distinct bell mouth radius and gap between the upper fan casing and the mouth of the bell. To examine the blower's transient characteristics, the frozen rotor approach was selected. The well-known realizable k-\(\epsilon\) turbulence model successfully captures the turbulence behavior. Results showed that the flow coefficient is greatly improved by the bell mouth geometry. [PERSON] et al. [6] performed numerical studies on a radial compressor with an intake bleed flow and discovered that the relative Mach number significantly decreases toward the blade tip's leading edge. The authors found that the recirculation avoids the separation of flow on the suction side of the impeller blade. In a multi-stage compressor, [PERSON] [7] conducted a comparison between stator and cantilever hub topologies and found that the cantilever hub arrangement somewhat improves performance. He reasoned that the improvement was possible because the revolving hub offsets the gradients of static pressure along the route, thereby reducing the secondary flow.