Squirrel Cage Fan Research Articles

Interpretable reduced-order optimization research for improving indoor environmental quality in buildings based on dimensional analysis and surrogate-based optimization

Implementing large-scale optimization designs and identifying optimal design variables in fields such as architectural engineering is crucial for improving indoor environmental quality. However, the high-dimensional nonlinear characteristics complicate the understanding of the optimization process and increase the difficulty of finding optimal solutions. This study proposes an interpretable reduced-order optimization (ROO) method based on dimensional analysis, which integrates numerous variables into a single reduced-order coefficient through a power form. The goal is to develop a reduced-order and approximately one-dimensional nonlinear relationship during the optimization process and to reveal the mechanisms of single-objective and multi-objective optimization, thereby enhancing the interpretability of the optimization process. The reliability of the ROO is validated through single-objective optimization of building thermal bridges and multi-objective optimization of squirrel cage fans. The study shows that the power in the reduced-order coefficient can be used to determine the sensitivity and impact of design variables on optimization targets. The nonlinear relationship between the composite structural parameters of the building thermal bridge and the total heat flux can be reduced to an approximately one-dimensional linear relationship, significantly reducing the total heat flux of the thermal bridge by 10.3 %. The ROO accurately describes the aerodynamic performance of the fan and its high-dimensional nonlinear relationship with eight design variables, eliminating optimization conflicts among multiple operating conditions and significantly enhancing the aerodynamic performance. The ROO method proposed in this study offers a new approach to making the optimization process more interpretable, playing a crucial role in optimization design and revealing optimization mechanisms in engineering applications.

Analysis of internal flow characteristics of squirrel-cage fan with multi-directional air intake impeller

The separate flow in the inlet region of the squirrel-cage fan, caused by airflow steering, hinders the further improvement of internal flow state and aerodynamic performance. This study proposes a multi-directional air intake design of the impeller to solve this problem. Specifically, a new parameter known as D* is introduced in this study to represent the axial air intake parameter of the impeller. Subsequently, the key parameters of the multi-directional air intake impeller (D*, entrance blade angle, exit blade angle) are optimally designed using an orthogonal experimental and CFD numerical simulation. These results are further validated through experimentation, demonstrating that a well-designed multi-directional air intake impeller can increase the fan's air volume, total pressure, and total efficiency by 27.3%, 12.6%, and 5.2%, respectively. Furthermore, it has been observed that the inclusion of an axial air intake in the impeller diminishes the impact of the entrance blade angle on fan efficiency. When evaluating different-sized models, the influence of the axial dimensionless parameter D* on the fan total efficiency shows a consistent pattern, which is worth noting that the efficiency does not necessarily increase with increasing values of D*, but rather the fan efficiency peaks when D* is approximately 0.5. The analysis of the flow field and entropy generation inside the fan reveal that the design can weaken the separation vortex at the inlet and shift the position of vortex core towards the impeller's leading edge, so as to eclectically enhance the uniformity of the impeller inlet and outlet, ultimately optimizing the aerodynamic characteristics within the fan. This study presents a novel approach to controlling the inlet separation flow of a squirrel-cage fan and provides a reference to elucidate the mechanism of internal flow evolution with the multi-directional air intake impeller.

An Improved Passage-Flow Turning Model for Forward-Curved Blades of Squirrel-Cage Fan

Abstract An improved passage-flow turning model (IPTM) was developed in this study to design high-performance forward-curved blades for squirrel-cage fans. The flow separation in blade passages and the corresponding fan performance were compared between IPTM and traditional methods through computational fluid dynamics (CFD). The results show that correcting the blade inlet angle, based on the zero-incidence design, is crucial to prevent separation of the passage mainstream from the blade pressure surface. The blade shape with second-order smoothness also exhibits the thinnest separation and highest efficiency when other design parameters remain constant. Considering these findings, the blades designed by IPTM outperform traditional blades with the same inlet and outlet angles. The optimal values of the turning radius R¯T and the decelerating factor of the leading half blade ɛ were determined based on the CFD results. The designed blade achieves high pressure when these two parameters satisfy R¯T=−0.185ε+0.29175, while achieving high efficiency when they satisfy R¯T=−0.31ε+0.4425. To confirm the advantages of IPTM, an optimal IPTM-based blade was manufactured and measured. The results indicated that the maximum increase in fan pressure and efficiency reaches 10% and 6%, respectively.

Reduced-order model and attractor identification for large eddy simulation of squirrel cage fan

A large eddy simulation (LES) of a squirrel cage fan (SCF) provides a precise representation of turbulent flows with different degrees of complexity. This study comprehensively analyzes the coherent structures of turbulent flows in an SCF using an LES, proper orthogonal decomposition (POD), dynamic mode decomposition (DMD), and multi-resolution dynamic mode decomposition (mrDMD). An intelligent reduced-order model is established by integrating hierarchical deep learning and the sparse identification of nonlinear dynamics. The result shows that the evolution of the global DMD modes is attenuated due to the spatial distribution variations of localized high-frequency mrDMD modes, along with the fragmented and non-steady development of modal patterns. Unlike POD, DMD quantifies the quality of the impeller inlet environment and captures the antisymmetric low-dimensional flows associated with the shedding of rotating vortex structures. The interaction strength between stationary and dynamic rotating areas is accurately represented by attractors characterized by petal-like structures. The trajectory of the attractors faithfully maps the antisymmetric structural attributes, quasi-periodic behavior, and gradual attenuation characteristics exhibited by DMD modes. The number of petal-like systems and their temporal oscillations are in good agreement with the number of fan blades and their rotational cycles. This study provides new insight into fan engineering to advance flow control strategies and improve the understanding of the underlying flow mechanisms.

Optimization of a double-intake squirrel cage fan using OpenFoam and metamodels

In the present study, a powerful double-intake and rotor squirrel cage fan is designed and optimized by using a developed optimization process loop based only on open source libraries: Dakota, Salome and OpenFoam. Thirteen design parameters are selected for the trimming and in the impellers, blades and volute regions. The total efficiency and the force applied on the impeller are improved by maximizing and minimizing their values, respectively. A coupling was achieved between CFD, Latin Hypercube Sampling, Kriging metamodel and the Efficient Global Optimization to find the optimal design. Configuration 2 allows to improve the efficiency by 7.64% and to reduce the force by 33.36% compared to Configuration 1. The Kriging and the EGO models predict with accuracy the objective functions of the optimal design with a maximum error of 4.50%. Based on the optimal design of Configuration 2, a blade trimming was applied, which allows to improve the initial efficiency by 7.86%. The optimal prototype over all configurations was built and validated successfully against experimental data with a maximum error of 1.10%.

Flow Capacity Optimization of a Squirrel Cage Fan with a New Rounded Rectangle Volute under Size Limitation

Squirrel cage fans (SCFs) are widely used in a variety of household appliances. Due to the restriction on installation size, the design of high-efficiency SCFs with high flow capacities is an important topic. In this study, we proposed a novel rounded rectangle volute profile (RRVP) for the design of compact high-flow SCFs. At first, we used computational fluid dynamics (CFD) to simulate the aerodynamic performances of three SCFs having the same impeller but different volutes, which were the common logarithmic-spiral volute profile, the cutting volute profile, and the RRVP volute at the maximum flow rate working condition. The CFD simulations indicate that the fan with RRVP volute has the highest flow rate at the maximum flow rate working condition. Then, we proposed a parameterization method for the RRVP with 16 control variables. The multiobjective evolutionary algorithm based on decomposition (MOEA/D) and Kriging model was used to optimize the aerodynamic shape of the compact SCF with an RRVP volute. Twenty-three control variables were used in the multiobjective optimization process, including the optimization of the blade angles and the impeller position. Optimization results show that the maximum volumetric flow rate of the optimal SCF with an RRVP volute increases from 147.1 cubic feet per minute (CFM) to 191.1 CFM, and the fan efficiency also increases from 32.21% to 33.5%, compared with the original SCF with the common logarithmic-spiral volute. Two main factors were found to increase the flow capacity and efficiency of the optimal SCF under strict size constrains. First, the RRVP became smooth and large, which reduced the flow loss and increased the flow cross-section; second, the eccentrically mounted impeller of the optimal fan enlarged the flow section near the outlet of the volute.

Integrated aerodynamic optimization for stationary components of squirrel cage fan Considering impeller-Volute interaction

As the flow state in the volute plays an important role in the energy loss of the squirrel cage fan, the optimization design of the fan volute has drawn great attention. To further improve the overall performance of the fan, the aerodynamic match between the volute and the inlet nozzle as well as the local flow pattern within the fan components should be considered in the optimization. In the present work, a high-dimensional optimization method based on the genetic algorithm, support vector regression surrogate model, Latin hypercube sampling method and the mixed adaptive sampling algorithm is developed. Then, the integrated optimization for inlet nozzle and volute of the fan is carried out, in which both the aerodynamic performance and the impeller-volute interaction are considered. The optimization results show that the total efficiency of the fan increases by 2.24% and the static pressure recover coefficient increases by 2.18%. The reversed flow at the impeller outlet is restrained, and the flow uniformity at the impeller inlet is improved. This work is helpful for the design of squirrel cage fans with high aerodynamic performance.

Experimental Investigation on the Noise Characteristics of a Squirrel-Cage Fan with Different Blade Lengths

Squirrel-cage fans are widely applied in air conditioning systems, and their aerodynamic noise mainly related to blade length. The aerodynamic performance and noise spectrum of squirrel-cage fans are synchronously measured in an anechoic wind tunnel. The effect of blade lengths and different geometric configurations on the noise of a squirrel-cage fan is experimentally investigated. This paper focuses on the total sound pressure level and noise spectrum characteristics at different measurement points. Noise distributions of the outlet of the forward squirrel-cage fan exhibited axial-symmetry and large differences for those of vertical direction. In lower fan positions, the noise was greater than that of the top. In particular, it was found that blades were easy to generate higher noise when their length was reduced by 31.7%. The findings suggest that the broadband noise of the squirrel-cage fan should be fully considered for noise reduction. The purpose of this work is to provide a novelty reference for the low-cost modification method of cutting blades. The results show that fans with shorter blades have lower noise and kept an excellent performance. These finding have implications for fan manufacturers.

Large eddy simulation on the vortex evolution in a squirrel-cage fan based on a slice computational model

To investigate the hard-to-measure complex flow in a squirrel-cage fan, a slice model was established in the present study to perform a partial large eddy simulation calculations on an r-θ sectional flow field instead of the large-scale and time-consuming full three-dimensional flow calculations. The method used to build the slice model was first introduced, and then the model was verified by the results obtained by other models and flow measurements. It is shown that to calculated the correct flow field and detailed vortex evolution, the Courant number of the slice model should be below 1, and the model thickness should be at least 2.4% of the impeller outer diameter. Through this simplified model, vortex evolutions rarely observed in other studies were successfully captured, such as vortex shedding caused by leading-edge separation, periodic backflow in the blade cascade, and vortex cluster traveling across the impeller. The flow separations were also illustrated on the inner surface of the volute tongue, accompanied by tiny and high-frequency eddies. The evolution process and frequency characteristics of these flow patterns were analyzed in detail, providing references for the design and noise reduction of this type of fan.

Optimization of a Double-Intake Squirrel Cage Fan Using Openfoam and Metamodels

Optimization of a Double-Intake Squirrel Cage Fan Using Openfoam and Metamodels

Squirrel-Cage Fan System Optimization and Flow Field Prediction Using Parallel Filling Criterion and Surrogate Model

In this study, the blade shape of the squirrel-cage fan system inside the range hood was optimized using the surrogate model to improve the maximum volume flow rate. The influence of computational fluid dynamics (CFD) noise was concerned. The regression Kriging model (RKM) was used as a surrogate model to reflect the relationship between the design parameters of the blade and the volume flow rate. The parallel filling criterion after re-interpolation was used to improve the optimization efficiency further and ensure global optimization. Through experimental verification, we found that the relative error between the volume flow rate of the optimal sample of RKM and the experiment was only 0.4%. Compared with the prototype, the maximum volume flow rate of the optimal sample of RKM was increased by 2.9%, and the efficiency under the corresponding working conditions was increased by 2%. RKM was used to predict the velocity field of the volute and impeller exit section to explore the feasibility of the RKM in the flow field prediction. Research shows that the RKM cannot accurately predict the velocity of each grid on the cross-section. Still, it can accurately predict the changing trend of the velocity.

CFD modeling and optimization by metamodels of a squirrel cage fan using OpenFoam and Dakota: Ventilation applications

The constraints related to air quality are progressively increasing making the optimization of the air system crucial. Multiple fan configurations are currently used in vacuum systems, the most widely employed one being the squirrel cage fan (SCF), also known as forward-curved multi-blade centrifugal fan. Most of researches so far used commercial software to optimize the SCF focusing mostly on the impeller region. In the present work, a complete automatic optimization process loop is developed based only on open source libraries: Dakota to manage all the processes, Salome to generate the geometry and the mesh grid and OpenFoam for the numerical calculations. Up to seven design parameters are selected for the impeller, blades, and volute. The Latin Hypercube Sampling (LHS) method is preferred to determine the design points and then different metamodels are built. A 3D incompressible simpleFoam solver is coupled to the Multiple reference frame (MRF) approach to model the flow in the SCF. The total efficiency is improved by 8.46% by changing the hub shape and by adding further design parameters. A strong interaction is observed between the cut-off vortex and flow separation on the blade upper side. The optimal design is finally validated against the produced prototype, with an error of 3.4% on the pressure gradient at the design point.

Multi-objective optimization of squirrel cage fan for range hood based on Kriging model

In view of the multi-objective optimization design of the squirrel cage fan for the range hood, a blade parameterization method based on the quadratic non-uniform B-spline (NUBS) determined by four control points was proposed to control the outlet angle, chord length and maximum camber of the blade. Morris-Mitchell criteria were used to obtain the optimal Latin hypercube sample based on the evolutionary operation, and different subsets of sample numbers were created to study the influence of sample numbers on the multi-objective optimization results. The Kriging model, which can accurately reflect the response relationship between design variables and optimization objectives, was established. The second-generation Non-dominated Sorting Genetic algorithm (NSGA-II) was used to optimize the volume flow rate at the best efficiency point (BEP) and the maximum volume flow rate point (MVP). The results show that the design parameters corresponding to the optimization results under different sample numbers are not the same, and the fluctuation range of the optimal design parameters is related to the influence of the design parameters on the optimization objectives. Compared with the prototype, the optimized impeller increases the radial velocity of the impeller outlet, reduces the flow loss in the volute, and increases the diffusion capacity, which improves the volume flow rate, and efficiency of the range hood system under multiple working conditions.

Numerical and experimental investigations on non-axisymmetric D-type inlet nozzle for a squirrel-cage fan

ABSTRACT In this study, the unique reverse-flow around the inlet nozzle of a squirrel-cage fan was numerically studied by computational fluid dynamics (CFD), and a non-axisymmetric D-type inlet nozzle was proposed to inhibit it. It is shown that serious back flow develops at the volute tongue when the fan operates at a low flow coefficient that is lower than the best efficiency point. The airflow passing the blade passages in reverse further crosses the impeller, mixing the clearance leakage airflow, and finally blows into the intake chamber near the circumferential position of . By installing the inlet nozzle along this direction, D-type inlet nozzle schemes with different blockage extent were calculated by CFD. The scheme with a cut distance of 70% of its exit-section radius was chosen as the best design by comprehensively comparing the back flow ratio and fan performance of different working conditions. CFD results illustrated that reverse blowing at the fan entrance was significantly constrained by this D-type inlet nozzle, and the vortex in the inlet chamber correspondingly disappeared. Experimental data illustrated that the new nozzle increased the fan pressure rise under low-flow conditions by about 6% and barely reduced performance at other working points.

On the Aerodynamic and Acoustic Behavior of Double Outlet Squirrel Cage Fans

On the Aerodynamic and Acoustic Behavior of Double Outlet Squirrel Cage Fans

Blades optimal design of squirrel cage fan based on Hicks-Henne function

The traditional single-arc blade used in the squirrel cage fan is simple in structure and cannot meet relevant parameterized design requirements. In order to improve the aerodynamic performance of single-arc blades of squirrel cage fans an improved Hicks-Henne function was used in this study to parameterize the blade expression in a Q35 single-suction squirrel cage fan. The AE criterion was used to optimize the Latin hypercube design, a Co-Kriging agent model was established with High and low confidence samples, and the NSGA-II algorithm was combined with the flow rate and total pressure efficiency as a multi-objective optimization goal. A set of optimal blade parameters was selected under the premise that the flow meets the design requirements. The optimized fan's total pressure and total pressure efficiency were improved at each working point. At the design working point, the fan's total pressure increased by about 23Pa, the effective air volume increased by 1.18m³/min, and the total pressure efficiency improved by 3.31%.

Design for a Squirrel Cage Fan with Double Arc Blade

Design for a Squirrel Cage Fan with Double Arc Blade

Effects of the Guiding Tank on Flow Characteristics inside the Double-Suction Squirrel-Cage Fan for Range Hood

Effects of the Guiding Tank on Flow Characteristics inside the Double-Suction Squirrel-Cage Fan for Range Hood

Experimental and numerical investigations on effect of blade trimming on aerodynamic performance of squirrel cage fan

The impeller of squirrel cage fan exerts great effects on the internal flow fields and fan aerodynamic performance. On the premise of maintained impeller-volute tongue distance and production cost reduction, this paper proposes a blade trimming method focusing on axial modification of blade inlet in an attempt to improve the impeller flow condition and further the aerodynamic performance of squirrel cage fan, which is divided into blade full trimming and part trimming. Aerodynamic performance tests and numerical simulations are performed to explore the effect of blade trimming on the fan aerodynamic performance and the related flow mechanisms. The results show that the blade trimming with proper trimming parameter enables the fan to achieve higher fan aerodynamic performance in terms of total pressure efficiency and static pressure rise, between which full trimming is preferable to part trimming. With the optimum full trimming of blade, the axial distributions of mass flow at the impeller inlet and outlet become more uniform. The dimension of inactive zone near the front span is decreased. On the blade pressure surface, the forces are reduced with obvious improvement of gradients near the front span and back span. A better match between impeller and volute tongue is achieved as the decreases of reversed flow coefficients at the impeller inlet and outlet and recirculated flow coefficient in the volute.

Multi-objective optimization of dual-arc blades in a squirrel-cage fan using modified non-dominated sorting genetic algorithm

In this study, a dual-arc profile parameterized by four geometric variables was designed to replace the original single-arc profile of a squirrel-cage fan used in a range hood, in order to improve the efficiency of the entire machine and the fan pressure. A modified Non-dominated Sorting Genetic algorithm coupled with a three-dimensional Reynolds-averaged Navier–Stokes computation is applied to search the optimum blade shape. Moreover, a relatively coarse but proven reliable grid model is employed to accelerate the optimization process, and a dynamic crowding distance is applied to improve the broad diversity of the Pareto front. The optimization results show that the optimal dual-arc blades are formed by a leading arc with a relatively smaller curvature and a trailing arc with a larger curvature, and the shape of the leading arc dominates the aerodynamic performance of the dual-arc blade. The blade schemes at two end of the Pareto front have increased the fan pressure and efficiency at the optimization point by 5.3% and 1.5%, respectively, but also result in a decline in another performance indicator. The best compromised solution in the middle of the Pareto front has improved the pressure by 2.6% without reducing the efficiency in the numerical calculation. Compared with the single-arc blade with the same inlet and outlet angle, the dual-arc blade has a higher fan pressure, but at the same time, the efficiency is negatively affected. Finally, the new impeller with optimized dual-arc blades is manufactured and tested, and the experimental results show an increment exceeds 2% in pressure and an unexpected slightly improvement in fan efficiency.