Fan Stage Research Articles

A rod-linear cascade model for emulating rotor-stator interaction noise in turbofans: A numerical study

This manuscript presents a rod-linear cascade model for emulating rotor-stator interaction noise. The model is intended as a test platform for studying noise mitigation techniques for a turbofan fan stage, while it also extends the classical rod-airfoil configuration by considering a row of blades based on realistic geometrical details. The rod-linear cascade model consists of a rod positioned upstream of a 7-blade linear cascade, such that the rod wake impinges onto the central blade. The rod is scaled to obtain a fundamental shedding frequency equal to the first blade passing frequency of the NASA-Glenn Source Diagnostics Test (SDT) fan stage at approach condition. The cascade blade profile is also based on the OGV of the SDT sampled at 90% of the radial span. Subsequently, numerical simulations are performed using lattice-Boltzmann Method on a computational setup comprised of a contraction and a test section enclosing the rod-linear cascade model. The integral length scales of the rod wake and the mean loading of the central blade have been found to be in good agreement with the trends observed in the SDT fan stage. The primary noise sources are localized at the central blade leading edge, although noise propagation to the far-field is influenced by additional diffraction by the other blades. Furthermore, the acoustic-blade row interaction causes intense pressure fluctuation within the inter-blade channels, including in those that are not directly affected by the rod wake.

Nonaxisymmetric Stator Design for Boundary Layer Ingesting Fans

In a boundary layer ingesting (BLI) fan system, the inlet flow field is highly nonuniform. In this environment, an axisymmetric stator design suffers from a nonuniform distribution of hub separations, increased wake thicknesses, and casing losses. These additional loss sources can be reduced using a nonaxisymmetric design that is tuned to the radial and circumferential flow variations at exit from the rotor. In this paper, a nonaxisymmetric design approach is described for the stator of a low-speed BLI fan. First, sectional design changes are applied at each radial and circumferential location. Next, this approach is combined with the application of nonaxisymmetric lean. The designs were tested computationally using full-annulus unsteady computational fluid dynamics (CFD) of the complete fan stage with a representative inlet distortion. The final design has also been manufactured and tested experimentally. The results show that a 2D sectional approach can be applied nonaxisymmetrically to reduce incidence and diffusion factor at each location. This leads to reduced loss, particularly at the casing and midspan, but it does not eliminate the hub separations that are present within highly distorted regions of the annulus. These are relieved by nonaxisymmetric lean where the pressure surface is inclined toward the hub. For the final design, the loss in the stator blades operating with BLI was measured to be 10% lower than that for the original stator design operating with undistorted inflow. Overall, the results demonstrate that the nonaxisymmetric design has the potential to eliminate any additional loss in a BLI fan stator caused by the nonuniform ingested flow field.

Reverse Thrust Aerodynamics of Variable Pitch Fans

Abstract Variable pitch fans are of interest for future low-pressure ratio fan systems since they provide improved operability relative to fixed pitch fans. If they can also be re-pitched such that they generate sufficient reverse thrust they could eliminate the engine drag and weight penalty associated with bypass duct thrust reversers. This paper sets out to understand the details of the 3D fan stage flow field in reverse thrust operation. This study uses the Advanced Ducted Propulsor variable pitch fan test case, which has a design fan pressure ratio of 1.29. Comparison with spanwise probe measurements show that the computational approach is valid for examining the variation of loss and work in the rotor in forward thrust. The method is then extended to a reverse thrust configuration using an extended domain and appropriate boundary conditions. Computations, run at two rotor stagger settings, show that the spanwise variation in relative flow angle onto the rotor aligns poorly to the rotor inlet metal angle. This leads to two dominant rotor loss sources: one at the tip associated with positive incidence and the second caused by negative incidence at lower span fractions. The second loss is reduced by opening the rotor stagger setting, and the first increases with rotor suction surface Mach number. The higher mass flow at more open rotor settings provide higher gross thrust, up to 49% of the forward take-off value, but is limited by the increased loss at high speed.

Tonal Noise Prediction of a Modern Turbofan Engine With Large Upstream and Downstream Distortion

Ultra-high bypass ratio (UHBR) engines are designed as compact as possible and are characterized by a short asymmetric air inlet and heterogeneous outlet guide vanes (OGVs). The flow close to the fan is therefore circumferentially nonuniform (or distorted) and the resulting noise might be impacted. This is studied here at take-off conditions by means of a simulation of the unsteady Reynolds-averaged Navier–Stokes (URANS) equations of a full-annulus fan stage. The model includes an asymmetric air inlet, a fan, heterogeneous OGVs, and homogeneous inlet guide vanes (IGVs). Direct acoustic predictions are given for both inlet and aft noises. A novel hydrodynamic/acoustic splitting method based on a modal decomposition is developed and is applied for the aft noise analysis. The noise mechanisms that are generally considered (i.e., interaction of fan-blade wakes with OGVs and fan self-noise) are shown to be impacted by the distortion. In addition, new sources caused by the interaction between the stationary distortion and the fan blades appear and contribute to the inlet noise.

Compressible Modal Instability Onset in an Aerodynamically Mistuned Transonic Fan

This paper describes observed modal oscillations arising from a feedback mechanism between an acoustic resonance in the exit flow channel and aerodynamic and aeroelastic disturbances in a transonic fan stage. During tests, the fan suffered from rotating stall and surge which were preceded by low frequency pressure fluctuations. Through a range of aerodynamic and aeromechanical instrumentations, it was possible to determine a clear chain of cause and effect, whereby geometrical asymmetries trigger local instabilities and modal oscillations through an interaction with the system acoustics. To the authors knowledge, this is the first time that modal oscillations occurring before stall are attributed to multiphysical interactions, showing that acoustic characteristics of the system can influence the aerodynamic as well as the aeromechanical stability of fans. This bears implications for the stability assessment of fans and compressors because first, the stability margin may be affected by standing waves generated in bypass ducts or combustion chambers, and second, geometrical variations of the rotor blades which are believed to be beneficial for aeromechanical stability may lead to complex coupling phenomena.

Turbomachinery Noise Predictions: Present and Future

In future Ultra-High By-Pass Ratio turboengines, the turbomachinery noise (fan and turbine stages mainly) is expected to increase significantly. A review of analytical models and numerical methods to yield both tonal and broadband contributions of such noise sources is presented. The former rely on hybrid methods coupling gust response over very thin flat plates of finite chord length, either isolated or in cascade, and acoustic analogies in free-field and in a duct. The latter yields tonal noise with unsteady Reynolds-Averaged Navier–Stokes (u-RANS) simulations, and broadband noise with Large Eddy Simulations (LES). The analytical models are shown to provide good and fast first sound estimates at pre-design stages, and to easily separate the different noise sources. The u-RANS simulations are now able to give accurate estimates of tonal noise of the most complex asymmetric, heterogeneous fan-Outlet Guiding Vane (OGV) configurations. Wall-modeled LES on rescaled stage configurations have now been achieved on all components: a low-pressure compressor stage, a transonic high-pressure turbine stage and a fan-OGV configuration with good overall sound power level predictions for the latter. In this case, hybrid Lattice–Boltzmann/very large-eddy simulations also appear to be an excellent alternative to yield both contributions accurately at once.

Acoustic Signal Separation and Noise Reduction of a Contra-Rotating Fan

How to reduce fan noise has always been a significant research topic in equipment ranging from small-scale devices, such as computer cooling fans and building ventilation fans, to large high bypass ratio turbo engines. In recent years, in order to produce higher pressure rise or larger flow rate with lower noise level in the fan stage, interest in the contra-rotating fan (CRF) configuration has been rekindled. The Vold-Kalman order tracking filter technique was employed to separate tonal and broadband noise components from CRF acoustic data to study the characteristics of the noise spectrum. Based on the spectrum peaks, noise reduction solution with casing treatment is proposed according to acoustic performance prediction by finite element simulation. In the simulation, the CRF is modelled at one end of a duct, which is surrounded by a semi-spherical space with perfect match layer to simulate the free field condition. The other end of the duct is modelled with non-reflecting boundary condition to simulate the anechoic termination. The simulated and experimental results show that casing treatment by micro-perforated panels can significantly reduce the CRF noise.

Impact of the turbulence modeling approach on the accuracy of the fan noise level prediction

The fan is the dominant source of noise for modern high bypass ratio aircraft engines. The article presents the results of investigating the influence of the approach to modeling the turbulence in modeling fan stage noise generation on the results of noise level prediction. Numerical investigation was performed for a model fan stage in test conditions in an anechoic chamber. Basic operating modes determining the acoustic performance of the fan were used. Calculation of far-field noise was performed using finite element modeling on the basis of the modal composition of generated noise. The influence of the turbulence model on the number and amplitude of acoustic modes excited in the flow on the fundamental frequency harmonics was analyzed. It is shown that modeling of the anisotropic flow turbulence in calculating non-stationary rotor-stator interaction makes it possible to obtain results close to the experimental ones.

Aeroacoustic study of a wavy stator leading edge in a realistic fan/OGV stage

The effect of sinusoidal serrations applied to the leading-edge of the vanes of a realistic fan stage is investigated using high-fidelity numerical simulations. The CFD solver PowerFLOW based on a hybrid lattice-Boltzmann/very-large-eddy-simulation model is used to compute the unsteady flow and radiated noise of the 22-in source diagnostic test fan rig of the NASA Glenn Research Center. A computational model validated for three different geometries of the outlet guide vanes with straight leading edge is used. A subset of validation results is reported to prove the capability of the solver to accurately predict the influence of the stator geometry on the far-field noise. Different sinusoidal leading edge serrations are investigated for a radial and a swept stator and the same rotor and operating conditions. The influence of the serrations on the acoustic far-field and noise power level is reported in relation to the statistical properties of the velocity fluctuations in the wake of the rotor. Some noise reductions are obtained when the undulation amplitude and wavelength are large enough compared to the integral scales of the impinging turbulence fluctuations.

LES-based simulation of the time-resolved flow for rotor-stator interactions in axial fan stages

PurposeThe purpose of this paper is the development of a CFD methodology based on LES computations to analyze the rotor–stator interaction in an axial fan stage.Design/methodology/approachA wall-modeled large eddy simulation (WMLES) has been performed for a spanwise 3D extrusion of the central section of the fan stage. Computations were performed for three different operating conditions, from nominal (Q_N) to off-design (85 per cent Q_N and 70 per cent Q_N) working points. Circumferential periodic conditions were introduced to reduce the extent of the computational domain. The post-processing procedure enabled the segregation of unsteady deterministic features and turbulent scales. The simulations were experimentally validated using wake profiles and turbulent scales obtained from hot-wire measurements.FindingsThe transport of rotor wakes and both wake–vane and wake–wake interactions in the stator flow field have been analyzed. The description of flow separation, particularly at off-design conditions, is fully benefited from the LES performance. Rotor wakes impinging on the stator vanes generate a coherent large-scale vortex shedding at reduced frequencies. Large pressure fluctuations in the stagnation region on the leading edge of the vanes have been found.Research limitations/implicationsLES simulations have shown to be appropriate for the assessment of the design of an axial fan, especially for specific operating conditions for which a URANS model presents a lower performance for turbulence description.Originality/valueThis paper describes the development of an LES-based simulation to understand the flow mechanisms related to the rotor–stator interaction in axial fan stages.

Aerodynamic Similarity Principles and Scaling Laws for Windmilling Fans

Windmilling requirements for aircraft engines often define propulsion and airframe design parameters. The present study is focused on two key quantities of interest during windmill operation: fan rotational speed and stage losses. A model for the rotor exit flow is developed that serves to bring out a similarity parameter for the fan rotational speed. Furthermore, the model shows that the spanwise flow profiles are independent of the throughflow, being determined solely by the configuration geometry. Interrogation of previous numerical simulations verifies the self-similar nature of the flow. The analysis also demonstrates that the vane inlet dynamic pressure is the appropriate scale for the stagnation pressure loss across the rotor and splitter. Examination of the simulation results for the stator reveals that the flow blockage resulting from the severely negative incidence that occurs at windmill remains constant across a wide range of mass flow rates. For a given throughflow rate, the velocity scale is then shown to be that associated with the unblocked vane exit area, leading naturally to the definition of a dynamic pressure scale for the stator stagnation pressure loss. The proposed scaling procedures for the component losses are applied to the flow configuration of Prasad and Lord (2010). Comparison of simulation results for the rotor-splitter and stator losses determined using these procedures indicates very good agreement. Analogous to the loss scaling, a procedure based on the fan speed similarity parameter is developed to determine the windmill rotational speed and is also found to be in good agreement with engine data. Thus, despite their simplicity, the methods developed here possess sufficient fidelity to be employed in design prediction models for aircraft propulsion systems.

Aerodynamic optimization design of aspirated highly loaded fan stage

In this paper, an aerodynamic design method for an aspirated compressor/fan is developed. In the S2 through-flow design, the loss feedback is used to solve the inapplicability of the conventional loss model. In S1 profile design, an optimization design method is constructed in which the profile and the suction flow parameters are simultaneously handled as design parameters to couple the optimization design. A 3D optimization method is used to modify the profiles at the hub and tip of the rotor blade and the sweep and lean of the stator blade. An aspirated highly loaded fan stage (load coefficient of 0.69) was designed using the design method. A flow field simulation shows that at the design point, with a modest suction flow (4.84% of the inlet mass flow), very high isentropic efficiency (0.9213) is achieved, and the total pressure ratio (3.445) achieves its design goal (3.40), but the mass flow rate of the designed fan stage is 6.2% lower than the design goal. From the comparisons between the 2D flow fields on the S1 stream surfaces and the 3D flow fields at the corresponding blade spans, it is concluded that the flow presents nearly a form of a 2D S1 stream surface at most of the spans, and the 2D design method which is based on the S1/S2 stream surface in this paper is effective. Moreover, the flow is analyzed around the rotor root of the aspirated rotor, revealing a weak flow capacity in that area. This result suggests that desirable flow might not be set up when the designed profile has a large camber at the rotor blade root because the total pressure ratio cannot be improved without compromising the static pressure ratio.

Investigation into the Development and Testing of a Simplex Capacitance Sensor for Rotor Tip Clearance Measurement in Turbo Machinery

The rotor tip clearance is a vital parameter to characterize turbomachinery performance. It is an essential measurement during engine development and testing. The efficiency of the major modules like fan, compressor and turbine depends on the optimum running clearances. The capacitive sensor is preferred for tip clearance measurements because of various inherent advantages. They are fabricated through complex processes for turbomachinery application and are expensive. These sensors are exposed to harsh engine environments and are likely to exhibit degraded performance. Insulation failure at sensing head, connector contamination and micro-cracks in the MI (Mineral Insulated) cable leads to noise in the signal output. Frequent mechanical failures are also seen due to work hardening of MI cables, lead connector detachments and failure of micro fins at interconnects. Fault fixing of these is tedious and very expensive. This paper presents the concerted effort in developing a simple capacitance sensor addressing potential sensor failure issues. The design features include simple construction, ease of sensor assembly, component realization and troubleshooting. The design also addresses all safety requirements. The sensor has a large sensing area (7.6 mm diameter) producing very stable, high-level signal. The developed sensor produces output that varies from 1 VP-P to 11 VP-P for blade-tip gaps between 3 mm to 0.4 mm respectively. Blade pass simulation studies across the sensor, display almost flat response at minimum clearance. This feature results in very minimal data acquisition errors. The sensor along with RC (Resistance-Capacitance) conditioning electronics was successfully used for clearance measurement on fan stage of gas turbine engine. Test results are in line with the predictions. Extensive tip clearance measurements on the engine validate the design. The current work provides an insight into the development of a simplex capacitance sensor for tip clearance measurement.

Numerical study of flows in axial compressors of aircraft gas-turbine engines

Design and adjustment of compressors at modern gas-turbine engines are based on the wide use of numerical analysis methods of a various level of complexity. Such approaches make it possible to analyze the alignment of joint operation of stages and to perform the required correction of geometrical parameters. The methods for calculating the 1D and 2D flow in compressors are distinguished by high flexibility, which allows the utilization of considerable experience in designing and experimental research. These methods are consequently in demand at all stages of the engine life cycle: when creating, adjusting, at operation.We present methods for the calculation of parameters and structure of current, as well as the summary characteristics of axial stages and multistage compressors. To solve a system of motion equations, we employed a matrix method, which makes it possible to apply small computation grids in a flow-through part of the compressor. The method is designed to numerically simulate the sub-, trans-, and supersonic flows in the flow-through part of axial compressor stages and multistage axial compressors at aircraft engines. The methods are implemented in the form of software complexes.The article reports certain results related to the verification of these complexes. We use data from experimental studies into various multi-stage compressors and high-head fan stages. We show a satisfactory agreement between calculated and experimental data over a wide range of modes of consumption and rotation frequency.The developed software package was used to improve the geometrical parameters for an axial multi-stage compressor, aimed at increasing the air flow rate through the compressor and enhancing the reserve of its gas-dynamic stability.Employing small computational grids made it possible to undertake a series of studies, previously available only for the calculation methods of spatial flow. We considered different variants for the execution of the bushing surface at a high-head fan stage. When analyzing the structure of flow in a stage, we show the change in the axial component of velocity in a blade-to-blade channel of the impeller along its axis.Development and application of the new methods of calculation will improve the quality of design of axial compressors and enhance competitiveness of the Ukrainian aircraft gas turbine engines.

The optimization and flow diagnoses for a transonic fan with stage flow condition

The redesign and optimization of a low-aspect ratio transonic fan is implemented in this study. An advanced 3D aerodynamic optimization design system is adopted, while flow diagnostic methods are employed to discuss the transonic flow in the blade passages. On the basis of maintaining high aerodynamic efficiency, the study seeks to improve the pressure ratio and through-flow capability of the redesigned fan stage. Furthermore, the dynamic principle for the redistribution of passage flow due to geometry change is revealed. In comparison with the prototype, the total pressure ratio of the redesigned fan is increased by 7.54% at the design point, while its mass flow rate and adiabatic efficiency are raised by 6.30% and 1.25%, respectively. Additionally, a wider high-efficiency operation range is also achieved by the optimization. Under stage flow condition, the control of shock wave at the rotor tip and the removal of low momentum fluid in the stator corner are the two keys in improving the aerodynamic performance of the redesigned fan. Moreover, tangential lean of the stator blade has also succeeded in delaying corner flow separations. Further research for these design techniques would give potential to expand the design system for transonic fan/compressor with low-aspect ratios.

Matching Performance Prediction Between Core Driven Fan Stage and High Pressure Compressor

Abstract Based on the aerodynamic matching configuration between a core driven fan stage (CDFS) and high pressure compressor (HPC), matching state point correlation equations have been established in this paper. The radial nonuniformity of the CDFS outlet flow and the aerodynamic loss caused by complex flow structure between these two components are taken full account in the equations, and a high-accuracy prediction program for matching performance has been developed. Based on the experimental performance data of two components, matching performance prediction at given bypass ratio is made and compared with experimental results. The results show that: 1) The outlet temperature of CDFS varies with its state points change, which makes the relative corrected rotation speed of HPC in matching environment change, and the characteristic line of HPC is not based on the same relative corrected rotation speed. 2) The difference exists between the matching performance prediction results and experimental results. One reason is that CDFS performance varies in the component environment and the matching environment due to the different back pressure regulation modes; another reason is that this prediction method doesn’t consider the effect of the CDFS’s outlet flow nonuniformity on the HPC’s performance, but the maximum relative deviation of the flow rate is only 0.74 %.

A discontinuity in the late Pleistocene alluvial deposits, Hwacheon‐ri, Gyeongju, Korea: Occurrences and paleoenvironmental implication

AbstractA sedimentary discontinuity is present in the late Pleistocene alluvial deposits exposed along the cliff in stream side, Gyeongju, Korea. Sedimentological study, Optically Stimulated Luminescence (OSL) age dating, and X‐ray diffraction (XRD), and X‐ray fluorescence spectrometer (XRF) analyses were conducted in order to interpret the origin of the discontinuity surface. Based on the sedimentological study, these deposits can be divided into three distinct stages, in ascending order: (Stage 1) development of a braided stream flowing from south to north and deposition by debris flows from the mountain aside the stream during and/or after deposition of the braided stream; (Stage 2) deposition by intermittent events during a state of stagnation after the abandonment or migration of the previously existed braided stream; and (Stage 3) deposition of gravels from debris flows from the mountain aside the stream. Hornfelsic gravels are common in Stage 1, whereas andesitic gravels are predominant in Stage 3, suggesting the provenance change from Stage 1 to Stage 3. The discontinuity surface is laterally extensive and marked by a distinct carbonaceous dark grey horizon between Stage 2 and Stage 3. It is characteristic that rootlets mineralized by vivianite are present, and iron‐oxide crusts are cutting across irregularly below the discontinuity surface. It is thus interpreted that the shift of depositional environment from an alluvial plain (Stage 2) (125 ka) to an alluvial fan (Stage 3) (94–55 ka) was an alluvial response to sea level change from the interglacial to the glacial. The development of iron‐oxide crusts and diagenetic vivianite in the discontinuity surface suggests humid condition persisted during the paleoclimatic shift from the last interglacial to the last glacial stages.

On the study of wavy leading-edge vanes to achieve low fan interaction noise

The application of wavy leading-edge vanes to reduce a single-stage axial fan noise is numerically studied. The aerodynamic and acoustic performance of the fan is numerically investigated using a hybrid unsteady Reynolds averaged Navier-Stokes (URANS)/acoustic analogy method (Goldstein equations). First, the hybrid URANS/Goldstein method is developed and successfully validated against experiment results. Next, numerical simulations are performed to investigate the noise reduction effects of the wavy leading-edge vanes. The aerodynamic and acoustic performance is assessed for a fan with vanes equipped with two different wavy leading-edge profiles and compared with the performance of conventional straight leading-edge vanes. Results indicate that a fan with wavy leading-edge vanes produces lower interaction noise than the baseline fan without a significant loss in aerodynamic performance. In fact, it is demonstrated that wavy leading-edge vanes have the potential to lead to both aerodynamic and acoustic improvements. The two different wavy leading-edge profiles are shown to successfully reduce the fan tone sound power level by 1.2 dB and 4.3 dB, respectively. Fan efficiency is also improved by about 1% with one of the tested wavy leading-edge profiles. Large eddy simulation (LES) is also performed for a simplified fan stage model to assess the effects of wavy leading-edge vanes on the broadband fan noise. Results indicate that the overall sound power level of a fan can be reduced by about 4 dB with the larger wavy leading-edge profile. Finally, the noise reduction mechanisms are investigated and analysed. It is found that the wavy leading-edge profiles can induce significant streamwise vorticity around the leading-edge protuberances and reduce pressure fluctuations (especially at locations of wavy leading-edge hills) and unsteady forces on the stator vanes. The underlying mechanism of the reduced pressure fluctuations is also discussed by examining the magnitude-squared coherence between the velocity and pressure fluctuations in the vicinity of the noise sources. Moreover, a reduction in the correlation level of the wall pressure fluctuations along the vane leading-edge is observed, as well as destructive phase interference along the vane leading-edge.

Impact of cyclostationarity on fan broadband noise prediction

One of the dominant noise sources of modern Ultra High Bypass Ratio (UHBR) engines is the interaction of the rotor wakes with the leading edges of the stator vanes in the fan stage. While the tonal components of this noise generation mechanism are fairly well understood by now, the broadband components are not. This calls to further the understanding of the broadband noise generation in the fan stage. This article introduces a new extension to the Random Particle Mesh (RPM) method, which accommodates in-depth studies of the impact of cyclostationary wake characteristics on the broadband noise in the fan stage. The RPM method is used to synthesize a turbulence field in the stator domain using a URANS simulation characterized by time-periodic turbulence and mean flow. The rotor-stator interaction noise is predicted by a two-dimensional CAA computation of the stator cascade. The impact of cyclostationarity is decomposed into various effects, which are separately investigated. This leads to the finding that the periodic turbulent kinetic energy (TKE) and periodic flow have only a negligible effect on the radiated sound power. The impact of the periodic integral length scale (TLS) is, however, substantial. The limits of a stationary representation of the TLS are demonstrated making this new extension to the RPM method indispensable when background and wake TKE are of comparable level. Good agreement of the predictions with measurements obtained from the 2015 AIAA Fan Broadband Noise Prediction Workshop are also shown.

Aerodynamic design schemes of the inlet guide vane in a core-driven fan stage

A core-driven fan stage operates in both single bypass and double bypass modes. There are large differences in aerodynamic parameters between the two modes. To accommodate the differences, the inlet guide vanes must turn in a very large angle, which may cause significant flow losses. To reduce the flow losses, this article investigates three design schemes in detail using the flow field simulation method. The three schemes investigated include the inlet guide vanes adjusting entirely (Scheme 1), the rear part of the inlet guide vanes adjusting (Scheme 2), and both the front and rear part of the inlet guide vanes adjusting (Scheme 3). Comparisons of the three design schemes suggest that the flow losses in Scheme 1 are higher than those in the other two schemes and that the flow losses in Scheme 3 are not evidently lower than those in Scheme 2. The key geometrical parameters of Schemes 1 and 2 are determined for low flow losses and are used to design the inlet guide vanes. The inlet guide vanes are applied to a core-driven fan stage, and the flow fields are simulated by a three-dimensional flow simulation method to confirm the designs.