Aerodynamic Field Research Articles

Shock wave prediction in transonic flow fields using domain-informed probabilistic deep learning

Transonic flow fields are marked by shock waves of varying strength and location and are crucial for the aerodynamic design and optimization of high-speed transport aircraft. While deep learning methods offer the potential for predicting these fields, their deterministic outputs often lack predictive uncertainty. Moreover, their accuracy, especially near critical shock regions, needs better quantification. In this paper, we introduce a domain-informed probabilistic (DIP) deep learning framework tailored for predicting transonic flow fields with shock waves called DIP-ShockNet. This methodology utilizes Monte Carlo dropout to estimate predictive uncertainty and enhances flow-field predictions near the wall region by employing the inverse wall distance function-based input representation of the aerodynamic flow field. The obtained results are benchmarked against the signed distance function and the geometric mask input representations. The proposed framework further improves prediction accuracy in shock wave areas using a domain-informed loss function. To quantify the accuracy of our shock wave predictions, we developed metrics to assess errors in shock wave strength and location, achieving errors of 6.4% and 1%, respectively. Assessing the generalizability of our method, we tested it on different training sample sizes and compared it against the proper orthogonal decomposition (POD)-based reduced-order model (ROM). Our results indicate that DIP-ShockNet outperforms POD-ROM by 60% in predicting the complete transonic flow field.

A novel pneumatic dry high-intensity magnetic separator for the beneficiation of fine-grained hematite

This study focuses on the development of a novel pneumatic dry high-intensity magnetic separator (PDHIMS) (maximum magnetic induction of 2 T) to enhance the efficiency of separating hematite ore fines. Force analysis of the novel separator demonstrated that it can potentially reduce the lower size limit of hematite dry beneficiation from 58 μm to 10 μm. A series of experiments of mixed samples, such as hematite–quartz/feldspar/chlorite/augite indicated that PDHIMS is successful in achieving highly selective separation of hematite particles fine to 13 μm, overcoming the slime coating of −13 μm quartz particles on the surface of −150 + 38 μm hematite particles, and improving the separation efficiency between hematite and poorly intergrown particles (or magnetic gangues). Energy dispersive spectrometer (EDS) and microscopic imaging of the concentrate confirmed that −13 μm particles form stable aggregates and cannot be disrupted by the employed aerodynamic field in PDHIMS, resulting in a notable entrapment of quartz particles within the concentrate. Lastly, the induced roll magnetic separators (IRMS) with gravity feed and airflow feed were selected as the objects compared with the PDHIMS. The comparison revealed that PGHIMS exhibits a marked superiority in eliminating slime coatings from coarser magnetic products.

Experimental and Numerical Investigation of the Control of the Flow Structure on Surface Modified Airfoils

In this study, experimental and numerical flow analysis was performed on three different blade profiles with a chord length of 165 mm using passive flow control method. The first of the airfoil is the standard NACA 0018 profile. The second airfoil type has a NACA 0018 profile with a gap in the suction surface. The last airfoil is the NACA 0018 profile which is 66% of the trailing edge cut from the chord length. All airfoil profiles were analyzed at the Reynolds number, Re=2x104, and angles of attack α=0o, 5o, 10o, 12o and 14o in both experiment and numerical studies. The experiments were carried out using the Particle Image Velocimetry (PIV) method in a closed-loop open water channel, and the time-averaged velocity vectors, streamlines, and vorticity contours of the flow field were obtained. Subsequently, numerical analyses were performed using the ANSYS Fluent package program, one of the Computational Fluid Dynamics (CFD) programs used frequently in the literature. The streamlines and pressure contours of the airfoil profiles have been compared visually at the same Re and different angles of attack. In addition, according to the angle of attack of the airfoil profiles, lift coefficient CL, drag coefficient CD, and the ratio of lift coefficient to drag coefficient CL/CD graphs were presented. It has been shown that the gap on the airfoil at high attack angles caused changes in lift (up to 0.7) and drag (up to 0.15). These features can allow these models to be used for different purposes in the aerodynamics field.

Experimental design for a novel co-flow jet airfoil

The Co-flow Jet (CFJ) technology holds significant promise for enhancing aerodynamic efficiency and furthering decarbonization in the evolving landscape of air transportation. The aim of this study is to empirically validate an optimized CFJ airfoil through low-speed wind tunnel experiments. The CFJ airfoil is structured in a tri-sectional design, consisting of one experimental segment and two stationary segments. A support rod penetrates the airfoil, fulfilling dual roles: it not only maintains the structural integrity of the overall model but also enables the direct measurement of aerodynamic forces on the test section of the CFJ airfoil within a two-dimensional wind tunnel. In parallel, the stationary segments are designed to effectively minimize the interference from the lateral tunnel walls. The experimental results are compared with numerical simulations, specifically focusing on aerodynamic parameters and flow field distribution. The findings reveal that the experimental framework employed is highly effective in characterizing the aerodynamic behavior of the CFJ airfoil, showing strong agreement with the simulation data.

Characteristics of aerodynamic interference and flow phenomenology around inclined square prisms

This study conducts large eddy simulations (LES) to investigate the aerodynamic interference effects and flow field characteristics of the flow around square cylinders, taking into account the inclination of the disturbed structure. The configurations of the structures involve tandem and side-by-side arrangements with the inclination angles of the disturbed structure including +15°, 0°, and −15°. The identification of flow field characteristics involves the examination of multiple components, particularly time-averaged velocity streamlines, axial flow patterns, instantaneous spanwise vortices, and time-averaged wake vortex structures. The results indicate that the vortex structure features of the flow field are significantly influenced by the arrangement type and the inclination angle of the disturbed structure. In contrast to the tandem arrangement, structures arranged in the side-by-side arrangement undergo a considerably reduced intensity of influence from aerodynamic interference effects. The blocking effect of the tandem arrangement and the channel effect of the side-by-side arrangement are undermined when the inclination angle is positive (α > 0). This study enhances the comprehension of aerodynamic interference in inclined prisms and simultaneously establishes a theoretical foundation for the wind resistance design of building structures.

CNN-based flow field prediction for bus aerodynamics analysis

The aim of this article is to evaluate the ability of a convolutional neural network (CNN) to predict velocity and pressure aerodynamic fields in heavy vehicles. For training and testing the developed CNN, various CFD simulations of three different vehicle geometries have been conducted, considering the RANS-based k-ω SST turbulent model. Two geometries correspond to the SC7 and SC5 coach models of the bus manufacturer SUNSUNDEGUI and the third one corresponds to Ahmed body. By generating different variants of these three geometries, a large number of representations of the velocity and pressure fields are obtained that will be used to train, verify, and evaluate the convolutional neural network. To improve the accuracy of the CNN, the field representations obtained are discretized as a function of the expected velocity gradient, so that in the areas where there is a greater variation in velocity, the corresponding neuron is smaller. The results show good agreement between numerical results and CNN predictions, being the CNN able to accurately represent the velocity and pressure fields with very low errors. Additionally, a substantial improvement in the computational time needed for each simulation is appreciated, reducing it by four orders of magnitude.

Experimental Study on Gas-Solid Two-Phase Flow Characteristics of a Vertical Cyclone Combustor System.

According to the design and operational parameters of the cyclone liquid slag-discharging boiler, an experimental platform for the cyclone burner was designed and constructed in a cold state based on the principle of similarity. The experimental study investigated the effects of parameters, such as swirl-vane angles, coal concentration, operating parameters, and particle size, on the flow distribution and vertical riser resistance characteristics of the vertical cyclone burner. The results showed that there were differences in flow distribution among the cyclone burners, and the most uniform flow distribution was achieved when the swirl-vane angle of the primary air was 30°. The concentration of pulverized coal significantly influenced the pressure drop in the vertical ascending section, which increased with higher concentrations of pulverized coal. When the concentration of pulverized coal remains constant, the pipeline pressure drop is minimized at a primary air velocity of 7.5 m/s. As the secondary wind speed increased, the pressure drop consistently rose; when the secondary wind speed is 22 m/s, the pressure drop of the pipeline is the maximum; however, excessively high secondary wind speeds were found to be detrimental to the formation of an optimal aerodynamic field in the burner. Furthermore, when the pulverized coal concentration was held constant, materials with larger particle sizes exhibited the highest pressure drop. When the particle size increases from 50 to 150 μm, the pressure drop of the vertical riser segment also increases. Finally, based on the Barth additional pressure drop theory, the pressure drop formula of the vertical riser is fitted by a dimensional analysis method, and the correlation formula of the pressure drop test of gas-solid two-phase flow in the vertical riser is obtained.

Aerodynamic and Thermal Field Development of Cooled Transonic HP NGV

Abstract In this study we present detailed aerodynamic and thermal field measurements downstream of an annular cascade of fully-cooled nozzle guide vanes (NGVs). The experiments were conducted in the Engine Component Aerothermal (ECAT) facility at the University of Oxford, at engine-matched conditions of Reynolds number and Mach number, and high turbulence intensity. The experimental data are unusually high-fidelity and allow for detailed comparison with modern computational fluids dynamics (CFD) methods. We compare the experimental data to simulations of fully-featured geometry (resolved internal geometry and film cooling holes). We analyze distributions of whirl angle, kinetic energy loss, and non-dimensional temperature at three axial planes downstream of the NGVs. The aerodynamic and thermal wakes are also characterized in terms of their spreading and decay rates. The analysis is deepened with detailed comparison to a previous data-set for a different design of heavily-cooled NGV. The analysis is a useful reference point for assessing the accuracy of the current state-of-the-art numerical methods used in the engine design process.

Convolutional-neural-network-based DES-level aerodynamic flow field generation from URANS data

The present paper culminates several investigations into the use of convolutional neural networks (CNNs) as a post-processing step to improve the accuracy of unsteady Reynolds-averaged Navier–Stokes (URANS) simulations for subsonic flows over airfoils at low angles of attack. Time-averaged detached eddy simulation (DES)-generated flow fields serve as the target data for creating and training CNN models. CNN post-processing generates flow-field data comparable to DES resolution, but after using only URANS-level resources and properly training CNN models. This document outlines the underlying theory and progress toward the goal of improving URANS simulations by looking at flow predictions for a class of simple, two-dimensional, streamlined profiles (i.e., an NACA0006 airfoil simulated at Mach 0.3 over an angle-of-attack range of −8° to 8°). After several design iterations, two trained CNN models predict the pressure and density fields immediately surrounding the airfoils, and those results compare well to DES ground truth data. Generally, the trained models match the DES resolution for the model training data. However, to accurately predict the flow conditions outside of the training set, other approaches are necessary. For this portion of the research, all computational fluid dynamic calculations use NASA’s fully-unstructured-Navier–Stokes-3D solver. The rest of the software comes from Python libraries within the public domain to encourage follow-on research. These libraries include TensorFlow for machine learning models and the sequential model-based optimization to generate the algorithm configuration for hyperparameter optimization.

Dynamic numerical simulation method and flow characteristic analysis on the mode transition in variable cycle compression system

Studying the dynamic aerodynamic characteristics and flow field characteristics for the dynamic mode transition in the variable cycle compression system (VCCS) can guarantee that the variable cycle engine (VCE) achieves high performance and stable mode transition. The common quasi-steady state analysis method cannot reflect the transient performance of the dynamic mode transition. Moreover, the dynamic simulation based on the dynamic grid technology will encounter the problem of negative volume grids because the adjustment range of variable components for VCCS is usually very large. To solve the problem, a dynamic simulation method based on real-time variation for geometry and aerodynamic boundaries of the dynamic mode transition in VCCS is first established in this paper. Using this method, the dynamic simulation was completed for the couple adjustment process of the outer bypass valve and variable stators of the dynamic mode transition in VCCS. The results of the dynamic simulation are compared with the quasi-steady state results. The results show that the rotor work ability and stator separation degree are affected by the stator variable angle degree and the mass flow rate (MFR) during the dynamic opening process of the outer bypass valve. For the MFR variation of 14.8%, when the stator variable angle is small (less than 3.3° in this study example), the flow separation on the variable stator blade pressure surface is increased during the dynamic opening process of the outer bypass valve. And the work ability of the downstream rotor is weakened. Therefore, in order to reduce the flow separation of stator blades with a small variable angle during the dynamic opening process of the outer bypass valve, a larger positive incidence angle can be adopted for stators at a small bypass ratio. For the whole dynamic process, the variation trend of the rotor work ability and stator separation state is opposite in the opening and closing process of the outer bypass valve. However, there is a dynamic effect of the flow field variation lagging behind the geometry variation in the opening and closing process. Therefore, the transient flow field in the opening and closing process is different from the quasi-steady state results, and the difference is more significant in the case of a small valve opening. Under a small valve opening, the work ability of the stage before the outer bypass entrance in the open process is significantly smaller than that in the closing process. And the difference in the flow field is mainly that the stator separation state of the stage before the outer bypass entrance in the open process is significantly weaker than that in the closing process. Therefore, the dynamic effect of the opening and closing process is more significant under a small valve opening, and the flow stability problem is more likely to occur during the dynamic mode transition in VCCS.

Toward formulating coalescence filtration: Characterizing wetting saturation via centrifugal force

Coalescence filtration is the removal of dispersed droplets from a gas or from an immiscible liquid using a fibrous filter. Coalescing filters operate under a partially-saturated condition where some of the filter pores are filled with accumulated droplets. To date, there exists no theory that can predict the filtration efficiency of a coalescing filter and this is due to the complicated coupling between the aerodynamic field inside the filter and the capillarity of the fibers. This paper presents a new approach to study coalescence filtration by replacing the aerodynamic field inside the filter with a centrifugal force field and to thereby decouple the role of fiber properties from that of the airflow in fluid accumulation in a filter. This paper is only the first step towards developing the above mathematical theory for coalescence filtration. In the current study, we use numerical simulation and experiment to compare desaturation of a liquid-saturated fibrous media via centrifugal force (new) and via compressed air (traditional). For the simulations, we used the volume-of-fluid (VOF) method implemented in ANSYS software, and for the experiments, we used a Porometer for the pressure-driven desaturation, and a custom-made setup inside a swing-bucket centrifuge for the centrifugal desaturation. The experiments were conducted using a nonwoven fabric infused with mineral oil. Pressure-driven and centrifugal desaturation processes were compared with one another, and the advantages of the latter were discussed in detail.

Effect mechanism of cooling delta aerodynamic field equalizing on the cooling characteristics of dry cooling tower

As the key heat transfer components for large-scale natural draft dry cooling tower (NDDCT), the cooling deltas perform poorly when subjected to ambient crosswinds, thus leading to the cooling performance degradation of NDDCT. To enhance the cooling delta's heat transfer capabilities, the effect mechanisms of aerodynamic field equalizing, i.e. air equalizing, on the deltas were studied by the validated three-dimensional (3D) numerical model. For the deltas arranged around NDDCT, the aerodynamic fields, the air flow rates, and the water temperature were all analyzed for cooling columns composing deltas. By comparing the two situations with air equalizing or without in the midst of cooling delta, it could find that the air equalizing diminished the air flow rate differences between the two columns in one delta, which improved the cooling characteristics of the poorer-performing columns mostly at the delta's leeward but deteriorated those of the better-performing columns mostly at the delta's windward. With the air equalizing, the cooling characteristics of the two columns in one delta were balanced. And then the cooling characteristics of most deltas and the whole NDDCT were improved to some extent at varying crosswind speeds, which was significant for the design optimization of conventional delta-type radiators.

Coupling of OpenFOAM with a Lagrangian vortex particle method for external aerodynamic simulations

In the field of computational aerodynamics, it is vital to develop tools that can accurately, but also efficiently, simulate the flow around bluff objects and calculate the aerodynamic forces acting on them. When strong body–vortex interactions take place, the simulations become more demanding, since complex phenomena appear. To address this issue, hybrid Eulerian–Lagrangian solvers have been developed and are increasingly used in the field. In this paper, a Vortex Particle Method (VPM) is coupled with the OpenFOAM software. The Eulerian solver (OpenFOAM) resolves the regions close to the solid boundaries, while the vortex particles evolve the wake downstream, significantly reducing artificial diffusion. The coupling strategy and the validation results of a hybrid code based on the domain decomposition technique are presented. This work is the first to couple OpenFOAM with a Lagrangian solver in the framework of a hybrid solver. Our objective is twofold: to verify the capability of OpenFOAM to run with a VPM and to validate the hybrid solver using benchmark cases. We demonstrate the validation of the solver on the Lamb–Oseen vortex case, the dipole case in the unbounded domain, and the flow around a cylinder at Re = 550. Our results show that coupling OpenFOAM with a VPM can be achieved without complications and efficiently reproduces the results of pure Eulerian simulations.

Effects of taper ratio on the aerodynamic forces and flow field of two tandem square cylinders

To explore the influence of taper ratio on aerodynamic characteristics of tandem square cylinders, three-dimensional (3D) large eddy simulations of flow around two tandem square cylinders at the Reynolds number (Re) = 2 × 103 are carried out with a spacing ratio G/D = 4, where G is the cylinder center-to-center distance and D is the cylinder width. Different taper ratios of ξ = 0%, 5%, 10%, and 15% are considered. The influence of taper ratio on aerodynamic coefficient, wind pressure coefficient, mean, and instantaneous flow fields are comprehensively studied. The mechanism of variation in flow fields is revealed, and the mathematical relationship between the taper ratio and aerodynamic characteristics is established, which can provide theoretical reference for design and construction of tandem structures. The results indicate that the taper ratio has significant influence on the mean force coefficient, fluctuating force coefficient, surface mean and fluctuating pressure coefficients, and vortex shedding frequency (fvs). As increase in the taper ratio, the mean force in the along-wind direction, fluctuating force in the across-wind direction, and surface pressure of the two cylinders will be decreased, but the vortex shedding frequency will be increased. The taper ratio has negligible influence on the flow separation location of the upstream cylinder. However, reattachment location of the shear layer moves backward along the leeward surface of the downstream cylinder, and width of the shear layer gradually becomes narrower and closer to surface of the two cylinders. The vortex shedding strength and vortex energy distribution of the two cylinders will be reduced as a result of the narrower shear layer. Meanwhile, coherence and periodicity of the vortex shedding will also be weakened, which results in reduction in the aerodynamic forces and increase in the vortex shedding frequency.

Numerical simulation of flow-induced noise generation and propagation of a floating offshore wind turbine with prescribed pitch motion

It is important to evaluate flow-induced noise emitted due to operations of floating offshore wind turbines since noise pollution can damage the environments of seabirds and aquatic species. This paper studies the aerodynamic and aeroacoustic performance of a laboratory three-blade wind turbine model with an airfoil profile of NREL S826. The wind turbine blade rotation motion is coupled with the prescribed pitch motion of the floating offshore wind power platform. The influence of prescribed pitch motions on the noise generated by wind turbine blades and noise propagation was discussed. Adopting the computational fluid dynamics (CFD) method, the aerodynamic noise field on a blade is simulated by the improved delayed detached eddy simulation (IDDES) model and Ffowcs Williams–Hawkings (FW-H) acoustic analogy. The overset grid technique is adopted to simulate the six degrees of freedom (DoFs) motions of the floating offshore wind turbine model. The sound source distributions on blades for noise generation are obtained, and the flow-induced noise propagation characteristics are analyzed. It is found that the influence of the pitch amplitude and frequency on the flow-induced noise field as well as the wake vortex characteristics should not be neglected.

On the Definition of Exergy in the Field of Aerodynamics

The exergy concept originates from the field of static thermodynamics and expresses the maximum theoretically recoverable mechanical work from a system while it evolves toward its dead thermodynamic state. It accounts for both mechanical and thermal mechanisms, and it allows to separate reversible and irreversible losses in the system’s transformations. The physical insight provided by this concept motivated the development of an exergy-based performance evaluation method in the field of aerodynamics. The resulting formulation has the advantage of being independent of the feasibility of a drag/thrust breakdown (ambiguous for highly integrated engine concepts) and includes thermal effects in the performance metrics. It, however, relies on an adapted definition of exergy, in particular involving a dead state in motion. This adapted definition is not trivial and raises theoretical concerns due to fundamental thermodynamic properties of exergy not being always satisfied. This paper aims at proposing a corrected version of this definition that ensures that the fundamental properties of exergy are respected. First, the exergy concept is presented alongside the concerns raised by its original adaptation, which, to the best of the authors’ knowledge, has been used in all exergy-based flowfield analyses in the field of applied aerodynamics. Then, an unsteady exergy balance is derived in the geocentric reference frame (in which there are no ambiguities in the definition of exergy) and then transformed to a reference frame in translation. The corrected adaptation of the exergy definition for aerodynamics applications is extracted from this transformation and the impact on the exergy balance is analyzed.

Numerical Simulation and Computational Fluid Dynamics Analysis of Two-Dimensional Lid-Driven Cavity Flow Within the Weapon Bay of an Autonomous Fighter Drone

The efficient deployment of weapons in military operations is critical for mission success, and the flow of air within the weapon bay of an autonomous fighter drone plays a vital role in achieving this objective. In this paper, we present a comprehensive numerical simulation and computational fluid dynamics (CFD) analysis of the three-dimensional lid-driven cavity flow within the weapon bay of an autonomous fighter drone. To address this challenging problem, we employ CFD analysis and a multigrid approach to solve the Navier-Stokes equations for the aerodynamic problem. Our simulations include high Reynolds numbers of up to 10,000, which demonstrates the potential of CFD analysis in optimizing the design of autonomous fighter drones for military operations. We evaluate the effectiveness of the linked strongly implicit multigrid technique in estimating high-Re fine-mesh flow solutions using the vorticity-stream function formulation of the two-dimensional incompressible Navier-Stokes equations. The model issue is the driven flow in a square cavity, and we consider meshes up to 1024 x 1024 points and combinations with Reynolds numbers as high as 1000. To further improve the accuracy of our simulations, we employ one-dimensional grid clustering coordinate transformations instead of uniform mesh refinement, as the flow field exhibits one or more secondary vortices. Our findings demonstrate that CFD analysis can provide valuable insights into the complex flow dynamics within the weapon bay of autonomous fighter drones, which can lead to the optimization of their design for enhanced mission capabilities. Overall, our study highlights the significance of numerical simulations and CFD analysis in the design and optimization of autonomous fighter drones for military applications. Our results can serve as a basis for future research in the field of UAV aerodynamics and contribute to the development of more efficient and effective military operations.

Fast Multipole Boundary Element Method for Aerodynamic Sound Field Analysis Based on Lighthill’s Equation

The primary disadvantage of the aerodynamic sound field analysis based on the Lighthill’s equation using the boundary element method (BEM) is the computational time; this is mainly because contributions from numerous aerodynamic sound sources are computed at all boundary element nodes and sound-receiving points. This study proposes a fast method for computing source contributions based on the fast multipole method (FMM). Along with the fast multipole BEM, which is already in practical use as a fast BEM, the analysis is substantially accelerated. The use of a common hierarchical cell structure for grouping boundary element nodes, sound-receiving points and aerodynamic sound sources, enables coefficients of the FMM to be reused, thereby further accelerating the analysis. To deal with the increasing hierarchical level, a wideband FMM is applied. In the sound radiation analysis of a quadrupole source located in a free field, the accuracy is validated. Sound radiation from a cylinder located in a flow is analyzed as a practical problem; the accuracy and numerical settings are discussed. Finally, the proposed method is applied to a problem with more than 0.4 million degrees-of-freedom and more than 3 million aerodynamic sound sources to demonstrate its applicability to large-scale problems.

Active flutter suppression on a flexible wing via leading-edge blowing and circulation control

Flutter is a classical aeroelastic phenomenon that seriously affects the performance of flexible wings. This study investigates flutter suppression through flow control for a flexible wing. Aerodynamic force, flow field, and dynamic aeroelastic response measurements are conducted to analyze the mechanism of flutter suppression through flow control on a flexible wing modified to include leading-edge blowing (LEB) and circulation control (CC) actuators around the wing tip. Furthermore, the flutter control effects of two control strategies, i.e., steady state control and proportion–integral–differential (PID) control, are compared. The results show that steady LEB and steady CC can effectively reduce the flutter amplitude and increase the critical flutter velocity. When the mass flow coefficient CQ≥1.46×10−3, the Coanda jet has better flutter suppression effect than the leading-edge jet. Moreover, a closed-loop CC control based on the PID algorithm demonstrates that PID control can effectively improve the flutter control efficiency. Compared to steady flow control, PID control increases the critical velocity by more than 52.60% and reduces the air consumption by 90.44%.

Aerodynamic characteristics simulation of helicopter rotor in hover using HeliX software

In order to predict hover performance of a new helicopter rotor, the aerodynamic performance and flow field of the rotor in hover is calculated by using HeliX software. The comparison between numerical results and wind tunnel test data of S-76 rotor as a validation case of CFD method demonstrate that HeliX software has the capability to consistently and reliably predict performance parameters for a helicopter rotor. The numerical results of the new rotor in hover suggest that the maximum hover efficiency of the new rotor is about 73% with collective pitch angle of 9.2°, while the shock induced separation and the reattachment phenomenon begin to appear on the upper surface near the blade tip. As the increase of collective pitch angle from 9.2° to 11.2°, hover efficiency decreases significantly due to the serious flow separation near the blade tip. The research in this paper can provide reference and guidance for aerodynamic optimization design of helicopter rotor.