Fast and accurate monitoring or prediction of wind turbine wakes is essential for real-time optimization of wind farm power generation. However, conventional approaches face significant challenges: direct field measurements using instruments like LiDAR are often economically infeasible due to high costs, high-fidelity numerical simulations are computationally prohibitive and slow for real-time applications, and purely data-driven machine learning methods typically suffer from poor physical interpretability and uncontrolled errors in full-field predictions. To address these limitations, we propose wakeEvoNet, a novel hybrid physics-data driven framework for real-time wind turbine wake monitoring/prediction. This approach strategically deploys sparse but high-fidelity measurement points in the near-wake region (within 3 rotor diameters downstream) to capture flow velocity profiles, which are then used as input for convolutional neural network (CNN) based encoder-decoder models to infer the downstream wake field (from 4D to 14D downstream). By feeding real-time monitored data at each time step, the model prevents temporal error accumulation common in sequential predictions. This hybrid methodology-combining direct measurements in the near-wake with neural network-based evolution for the farwake-significantly reduces the number of required instruments while maintaining high accuracy across the entire wake field. In this study, we demonstrate the framework using the NREL 5 MW reference turbine under neutral atmospheric boundary layer conditions. High-fidelity computational fluid dynamics simulations employing large eddy simulation and the actuator line method are leveraged to generate the training datasets, and three convolutional neural network-based encoder-decoder architectures are developed: a benchmark U-Net (wakeEvoNet-1), a CBAM-enhanced U-Net (wakeEvoNet-2), and a novel CA-TA-UNet (wakeEvoNet-3) incorporating a physics-guided lightweight spatial attention mechanism tailored for wind turbine wake flows. The models utilize three consecutive upstream cross-sections to predict subsequent downstream fields, with results showing high accuracy (R2 scores consistently above 0.80) and robust temporal performance on test data, offering an efficient alternative to traditional methods for real-time wind turbine wake monitoring/prediction.

Centrifugal pumps serve as key equipment in water conveyance systems. Different tee inlet structures distort the internal inflow field, induce extra hydraulic losses and reduce system energy efficiency, since pump power consumption and operational stability are highly sensitive to tee pipeline layouts. Pressure pulsation directly reflects internal flow disorder and reveals the root causes of hydraulic performance attenuation, so it is adopted as the core analytical tool in this work. Using the Shear Stress Transport (SST) k-ω turbulence model, numerical simulations are carried out on an 80 mm centrifugal pump with four inlet structures: straight pipe (SP), reducing tee (RT), reducing wye (RW), and asymmetric reducing wye (ARW). Combined with pressure pulsation signals, this study reveals the propagation rules of flow disturbances induced by tee inlet structures and their inherent energy loss mechanisms. The results show that tee inlet structures barely affect overall pump performance, except RT, which reduces the hydraulic head by 0.44 m and efficiency by 1.47%, accompanied by higher power consumption. Impeller pulsation intensity increases from the leading edge to the trailing edge, with the mid-passage leading edge being the most sensitive region. Impeller spectra are dominated by low-order shaft frequency harmonics, while volute signals are dominated by blade frequency (BF) harmonics. Different tee inlet structures have little impact on circumferential volute pulsation but significantly alter flow characteristics at the volute tongue and outlet diffuser, where 2BF becomes the primary dominant frequency. Disturbance propagation laws differ greatly between the impeller and downstream volute. Centered on low-energy pump system design, this study provides theoretical support for inlet pipeline optimization and energy-saving operation of municipal, industrial, marine and water conservancy pumping facilities.

Wall-resolved large-eddy simulation (WRLES) and wall-modeled large-eddy simulation (WMLES) of turbulent channel flow at Reτ ≈ 1000 are performed to explore their capabilities in predicting the space-time correlations of near-wall velocity and pressure fluctuations. Our findings indicate that both WRLES and WMLES can effectively capture the essential features in the wavenumber-frequency spectra. Doppler shifts due to the convection velocity and Doppler broadening caused by the random sweeping effects of large-scale eddies are observed in the wavenumber-frequency spectra. Both methods predict the near-wall velocity fluctuations with reasonable accuracy, but predicting wall pressure fluctuations seems to be more challenging for the current wall modeling approach. Without resolving the viscous sublayer, WMLES slightly overestimates the spectral levels of wall pressure fluctuations in low-wavenumber (or frequency) region. In addition, the two-dimensional spatial spectra indicate that isotropic subgrid-scale models may struggle to accurately capture the anisotropy of small-scale eddies near the wall.

During the hydraulic performance experiment, significant vibration and noise were observed in the mixed-flow pump operating in the hump region. Cavitation occurrence in the impeller flow channels was confirmed through the transparent chamber. To analyze cavitation flow structure evolution in the mixed-flow pump, this paper integrates numerical and experimental approaches, capturing cavitation flow structures under the valley condition through high-speed photography technology. During the various stages of cavitation development, the cavitation forms are mostly vortex cavitation, cloud cavitation, and perpendicular vortex cavitation. Impeller rotation induces downstream transport of shedding cloud cavitation shedding structures. Flow blockage occurs when cavitation vortexes obstruct specific passages, accelerating cavitation growth that culminates in head reduction through energy dissipation mechanisms. Vortex evolution analysis revealed enhanced density of small-scale vortex structures with stronger localized core intensity in the impeller and diffuser. Despite larger individual vortex scales, reduced core intensity persists throughout the full flow domain. Concurrently, velocity profile characteristics across flow rates and blade sections (spanwise from tip to root) indicate heightened predisposition to flow separation, recirculation zones, and low-velocity regions during off-design operation. This study provides scientific guidance for enhancing anti-cavitation performance in the hump region.

ObjectivesThis study proposes a vortex-generator array (VGA) design to effectively suppress the enhancement of circumferential non-uniformity and flow unsteadiness in the propeller wake fields, which are caused by the downstream evolution of horseshoe vortices generated at the tail fins of underwater vehicles. The proposed configuration aims to achieve hydrodynamic noise suppression and improve the stealth capability of the vehicle through precise flow control. MethodsFirst, the present work is performed on the SUBOFF standard submarine configuration and a pump-jet propeller. A high-fidelity flow field simulation was conducted using the finite volume method (FVM) and an improved delayed detached-eddy simulation (IDDES) turbulence model, establishing a high-precision numerical model for low-frequency excitation forces generated by underwater vehicle thrusters. The model was validated against published experimental data, showing an error within 4%. Second, the vibration reduction and acoustic suppression effects were evaluated by comparing the vortex-generator-equipped configuration with the basic configuration through excitation force and noise analyses, with the underlying mechanism explained in terms of flow field evolution. Subsequently, several VGA configurations with different numbers of vortex generators were simulated to optimize their quantity. Finally, high-speed simulations were performed to investigate the speed dependency of the VGA's vibration and noise reduction performance. ResultsThe results show that the vortex-generators significantly reduced vibration and noise. The optimal configuration achieved a 68.56% reduction in the rotor excitation force peak at the first blade-passing frequency (BPF), while the far-field radiated noise decreased by 1.81 dB in the transverse plane and 2.84 dB in the horizontal plane at an equivalent sound pressure level measured 1 m away.ConclusionsThe vortex-generator array effectively improves the wake field by segmenting large-scale vortex structures, thereby mitigating thruster-induced vibration and noise. The number of vortex generators should be optimized, not simply maximized, and the performance remains stable at high speeds. This study provides a novel approach for reducing noise in underwater vehicle thrusters.

This study investigated the impact of different load distribution ratios between two rotors on the unsteady performance of dual-stage pump-jet propulsors using Computational Fluid Dynamics (CFDs) and experimental methods. The Shear Stress Transport (SST) k-ω model was employed to solve turbulence problems, and the numerical simulation method used was validated. The following conclusions were drawn: Different load distribution ratios of the dual-stage rotors have no significant impact on the overall propulsion performance of the propulsor. As the load distribution ratio is aft-shifted, the axial unsteady force of the entire propulsor continuously decreases, with a reduction of up to 53.6%. This is due to the gradual reduction in the energy of the first-stage rotor, leading to a more uniform Blade-Passing Frequency Velocity Harmonic Coefficient (BPFVHC) in front of the second-stage rotor, thereby gradually reducing the unsteady force of the second-stage rotor. The experimental results also indicate that the aft-shifted load model can reduce the sound pressure level of the propulsor. Compared to the prototype propulsor, the sound pressure level at the Blade-Passing Frequency decreases by 6.67 dB, or about 78.5%, in sound energy. This study has important implications for the low-excitation design of dual-stage pump-jet propulsors.

The vibration and noise level significantly influence passenger ship comfort, and the marine elevator device is an important vibroacoustic excitation source in passenger ships. The dynamic model for marine elevators in passenger ships is built, in which the ship motion factors are considered. According to numerical analysis, the influences of ship motion are discussed. Finally, to validate the feasibility and effectiveness of the proposed methods, the experiment test is conducted. The results provide a better understanding of passenger ships' vibration and noise reduction design.

Modal decomposition is a data-driven method widely used in fluid mechanics to extract energy and dynamically significant features of fluid flow. However, traditional modal decomposition methods have failed to capture physically interpretable multi-time-scale flow characteristics for complex flow phenomena, such as cavitation with multiple states. To address this issue, this paper combines the Proper Orthogonal Decomposition (POD) and Hidden Markov Models (HMM) methods, proposing a new approach termed state-based POD, applied to three-dimensional cavitating flow. This method comprises three steps: utilizing POD to extract cavitating flow features and visualizing them as spatiotemporal trajectories, employing HMM to probabilistically model these trajectories, obtaining flow field states, and probability models representing multi-time-scale flow information, and applying POD to perform modal decomposition on the multi-time-scale flow field information. This method provides a more detailed characterization of physical phenomena and offers a novel approach to analyzing cavitating flow.

When we tested the water jet propulsion pump, we found that there were significant vibrations in the pump, especially at small flow points that deviated from the design conditions. The water jet propulsion pump is a mixed-flow pump with guide vane, which is commonly employed for water jet propulsion. However, the guide vane mixed-flow pump is susceptible to a phenomenon known as “hump”, which can cause flow disturbances, increased vibration, and noise when the pump operates within the hump region. According to the vibration phenomenon found in our experiment, the mechanism of vibration needs to be revealed. This study focuses on vorticity and turbulence distributions of a mixed flow water jet propulsion pump under the valley and peak operating conditions of the hump region. The research is conducted using experimental and numerical simulation methods. The SST k-ω turbulence model is employed for turbulence calculations. The experiments are conducted on a closed test rig for axial (mixed) flow pumps. A comparison of experimental and numerical simulation results of hydraulic performance curves are conducted to validate the accuracy of the numerical simulation. Cavitation flow structures of the critical cavitation stage under valley conditions and under peak conditions are compared. A comparative analysis is conducted to examine the differences in internal vortex core distribution and turbulence kinetic energy distribution between the valley and peak operating conditions when working within the hump region. The pressure and velocity vectors of the pump impeller blades and the velocity streamline distribution between the impeller and the guide vane blades are compared. To further analyze the flow state in different flow channels under valley and peak conditions, the streamline distribution at Span = 0.5 in the impeller and diffuser basin is extracted. This study provides theoretical foundations and technical support for the design of high-performance, low-vibration water jet propulsion pumps.

In order to improve the efficiency of water-jet pump and reduce or eliminate the hump phenomenon, it is necessary to optimize the impeller design. In this paper, the optimization of water-jet propulsion pump is studied by combining numerical simulation and experiment. The orthogonal optimization design scheme is established. Based on the numerical simulation method, the hydraulic performance indexes such as energy coefficient, torque coefficient and efficiency of the design points of different design schemes are obtained. The final optimization design is completed by further optimizing the profile and spatial position of the optimal efficiency factor level combination A2B1C1D1 at different spanwise heights. The efficiency of the optimized model pump is 81.1%, which is 3.7% higher than the original model. The efficiency of the optimized impeller is 94.7%, which is 1.9% higher than the original model. The internal pressure distribution and streamline distribution of the optimized impeller are more uniform, and the difference between different flow channels is smaller. Then, based on the results of numerical simulation by CFX, using Python and LabVIEW programming software, a pump flow head curve fitting and hump judgment program is developed, which can realize the function of curve fitting of flow head, giving the position of trough and peak, and calculating the value of hump climbing coefficient Chump. The influence of different blade structure parameters on the hydraulic performance and energy characteristic curve hump of the water-jet pump is analyzed, and the optimization design of the high-performance water-jet pump considering the hump index is completed.In summary, this method is not only applicable to the hydraulic optimization of the water-jet propulsion pump, but also the research results can provide theoretical basis and technical support for the high-performance and low-vibration design of the water-jet propulsion pump.

For safety of the ship manoeuvring and propulsor operating, crashback condition is of great concern because of the complicated nonlinear flow resulted from rotating the propellers in reverse while the vehicle is moving forward. The hydrodynamic performance of the integrated propulsor under crashback condition is drawing much attention for its wide application on underwater vehicles. In this paper, the feasibility of a Reynolds-Averaged Navier-Stokes equations (RANS) method for study of flow characteristics around the propulsors and underwater vehicles is firstly verified by its predicted results in good agreements with experimental values. Then, comparative analysis of open-water performance and flow field details is conducted between three configurations (single propeller, propeller with pre-stator, propeller with pre-stator and duct, respectively) to distinguish their effects on flow field characteristics around the propulsor under forward and crashback conditions. Finally, the dynamic numerical simulation for the axial motion of the underwater vehicle is performed using overset grid technique to predict the hydrodynamic load and the complicated flow field around its integrated propulsor during the process when the propulsor rotation transfers from positive to negative speed. The formation and development of the vertex ring are observed and analyzed.

该文利用DDES模型和Zwart-Gerber-Belamri空化模型开展了空化对螺旋桨性能及流动结构的影响研究.首先,采用三套系统加密的全结构化网格预测了螺旋桨非定常空化演变过程,并从敞水性能、空化形态和DDES V&V三个角度说明了模拟结果精度较高.随后,该文分析了非定常空化对螺旋桨水动力性能和流动结构的影响.结果表明,片空化发展前期,空化区域内存在导边分离流动、回射流及梢涡等主要流动结构,而片空化发展后期,导边分离流动减弱,梢涡流动明显增强.结合涡量输运方程的结果表明,非定常空化促进了桨叶附近涡量的产生和演变,而涡量的变化又使不同状态的流动结构相互作用加强,最终造成螺旋桨空化流动的不稳定性增强.

This paper introduces a local piston theory with viscous correction for the prediction of hypersonic unsteady aerodynamic loads at high attitudes and large Mach numbers. A semi-empirical relation accounting for the viscous interaction effects to determine the effective shape is proposed. The method is validated by applying to thin airfoils at various Mach numbers, angles of attack, and operating altitudes. Sample two-and three-dimensional aerodynamic forces calculations are conducted demonstrating this method. Furthermore, flutter boundary predictions for a two-dimensional airfoil and pitching-in-damping derivative evaluations for a three-dimensional waverider configuration are performed with this unsteady aerodynamic model. Compared with the Euler-based local piston theory, this model performs much better at high altitudes for a wide range of Mach numbers, angles of attack, and shapes. Results suggest the feasibility of using the effective shape of hypersonic vehicles to efficiently and accurately obtain the unsteady aerodynamic characteristics in hypersonic flow environment.

高超声速滑翔飞行器在高空、高马赫数飞行时所面临的多物理效应对其气动性能会产生较大的影响.本文利用锥导乘波体进行工程化设计,生成了一种高超声速远程滑翔乘波飞行器,采用计算流体动力学(CFD)方法数值模拟了该飞行器在高空、高马赫数飞行状态下的流动,分析了高空多物理效应(主要关注粘性干扰效应和真实气体效应)对飞行器气动性能的影响,并通过比较分析得到了不同气动力系数对不同物理效应的敏感程度,可以为高超声速滑翔飞行器的设计及气动性能评估提供参考.

A numerical study is presented on three- dimensional power-law shaped leading edge for waveriders in hypersonic flow. This work is motivated by interest in researching the flow field properties of power-law shaped leading edge as a possible candidate for blunting leading edges of waveriders. Both aerodynamic and aerothermal characteristics are calculated for a waverider forebody in hypersonic flow. Comparisons are made between power-law shaped leading edges and round leading edge. For the flow conditions considered, the power-law leading edges of waveriders can provide small drag, and at the same time it can bring enough bluntness for the necessity of thermal protection.

针对高空高马赫数飞行环境和强黏性干扰的物理特性,在当地流活塞理论的基础上引入有效外形修正,发展了黏性修正当地流活塞理论,结合定常N--S方程解给出了高空高马赫数下针对该方法的有效外形的判据,并通过数值算例对该判据进行了验证.通过对典型尖头薄翼和典型钝头翼的一系列二维非定常算例,将该方法与一阶活塞理论、基于欧拉（Euler）方程的当地流活塞理论和非定常N--S方程数值解进行了对比.结果显示在高度为40~70 km、马赫数为10~20范围内,通过该方法计算得到的非定常气动力与非定常N--S方程数值解吻合较好,明显优于活塞理论和基于Euler方程的当地流活塞理论.该方法克服了传统的活塞理论和当地流活塞理论不能用于高空高马赫数这类强黏性效应情况的弊端,在较宽的马赫数、攻角、飞行高度范围内都有良好的适用性,同时其计算效率远高于非定常N--S方程.

The aerodynamic characteristics of waverider under equilibrium gas condition have been studied by computational fluid dynamics（CFD） method,and the results have been compared with that under perfect gas condition.The analysis reveals equilibrium gas effects on aerodynamics of waverider are due to the decrease of induced pressure of boundary layer,which is caused by the chemical reaction in the boundary layer.In comparison with the angle of attack,equilibrium gas affects little on lift to drag ratio and pitching moment coefficients of waverider,but it has some effects on the pressure center,and the effects are different from that on the reentry vehicle.The results are valuable for the design of gliders based on waverider.

Aerodynamic performance of hypersonic waveriders aircraft basing on cone-derived waveriders with the consideration of volumetric efficient and thermal protection is being studied by computational fluid dynamic (CFD) and wind tunnel experiment (WTE). Both the results from CFD and WTE proved that, waveriders with design condition Mach number 6 and attack angle 4°, at off-design conditions that Mach number vary within 5～7, attack angle vary within 4°～6°, it can maintain excellent aerodynamic performance. The lift-to-drag ratio is only a little below 4. At the same time, a simple viscous drag analysis method basing on reference temperature method is being given to cooperate using the results of CFD and WTE. It can be used to give viscous drag that can not be got from WTE directly, and it can be used to validate viscous drag of CFD, which is hard to be calculated accuracy too. Though it is very coarse, it is very useful for engineer application.