Flow Angle Research Articles

Particle Image Velocimetry Measurements in a High-Speed Low-Reynolds Low-Pressure Turbine Cascade

Abstract Particle image velocimetry (PIV) measurements in the blade-to-blade (B2B) plane and cascade outlet plane (COP) of a high-speed low-pressure turbine (LPT) cascade were performed at engine-representative outlet Mach number (0.70–0.95), and Reynolds number (70–120 k) under steady flow conditions. The freestream turbulence characteristics were imposed by means of a passive turbulence grid. The PIV results on the B2B plane were compared against five-hole probe (5HP) and Reynolds-averaged Navier–Stokes (RANS) computations to assess the validity of measurement and simulation techniques in the engine-relevant LPT cascade flows. The PIV captured the wake depth and width measured by the 5HP whereas the RANS displayed an overprediction of the wake Mach number deficit. The 5HP was found to impose sinewave fluctuations of the measured flow angle downstream, around three times higher than PIV. Additionally, PIV estimated turbulence intensity (TI) in the cascade, showing TI decay along a streamline. At the highest Mach number, a peak TI occurred past a shock wave. Measurements of the outlet flow field highlighted a high TI in the secondary flow region whereas high degree of anisotropy (DA) was registered in the boundary of the secondary flow and freestream regions. The contribution of the streamwise fluctuation component was found to be less than the crosswise and radial components in the freestream region. Increasing the cascade outlet Mach number, the contribution of streamwise fluctuation to the DA was observed to decrease.

INFLUENCE OF DIFFERENT WIND ANGLES ON PEDESTRIAN WIND COMFORT IN 3D SPACE

Abstract. Wind can impact pedestrian comfort. This comfort can be observed by integrating a 3D city model into the study area. However, little research has been done on the influence of different wind angles on pedestrian wind comfort and rarely on implementing 3D city models in the wind environment. Therefore, this study aims to fill the gap in using 3D city models to examine the effect of wind flow angles on pedestrian wind comfort. The Computational Fluid Dynamics (CFD) wind simulation environment presented in this study was constructed through the applied steady Reynolds-Average Navier-Stokes (RANS) with K-epsilon (k-ε) turbulence model. It is integrated with the standalone building model with a roof overhang structure represented in LoD2.3 of the CityGML standard. Three wind angles have been introduced to allow for variation in the analysis of pedestrian wind comfort: 0°, 15°, and 30° wind angles. Through the observation of multiple locations, which are directed beneath the roof overhang structure, the highest wind velocity is recorded in 0° wind angles compared to 15° and 30° wind angles. Thus, from these recorded values, pedestrian wind comfort is based on the Beaufort wind scale (BWS). The computed average recorded values show that 3.24 m/s corresponds to a wind angle of 0°, 2.761 m/s for 15°, and 2.415 m/s for 30°, which shows that all these values fall in BWS Scale 2. Thus, these areas experience a light breeze. However, the lowest value from a 30-degree environment presents the most reposeful surrounding.

Aerodynamic Uncertainty Quantification of a Low-Pressure Turbine Cascade by an Adaptive Gaussian Process

Stochastic variations of the operation conditions and the resultant variations of the aerodynamic performance in Low-Pressure Turbine (LPT) can often be found. This paper studies the aerodynamic performance impact of the uncertain variations of flow parameters, including inlet total pressure, inlet flow angle, and turbulence intensity for an LPT cascade. Flow simulations by solving the Reynolds-averaged Navier–Stokes equations, the SST turbulence model, and γ−Re˜θt transition model equations are first carried out. Then, a Gaussian process (GP) based on an adaptive sampling technique is introduced. The accuracy of adaptive GP (ADGP) is proven to be high through a function experiment. Using ADGP, the uncertainty propagation models between the performance parameters, including total pressure-loss coefficient, outlet flow angle, Zweifel number, and the uncertain inlet flow parameters, are established. Finally, using the propagation models, uncertainty quantifications of the performance changes are conducted. The results demonstrate that the total pressure-loss coefficient and Zweifel number are sensitive to uncertainties, while the outlet flow angle is almost insensitive. Statistical analysis of the flow field by direct Monte Carlo simulation (MCS) shows that flow transition on the suction side and viscous shear stress are rather sensitive to uncertainties. Moreover, Sobol sensitivity analysis is carried out to specify the influence of each uncertainty on the performance changes in the turbine cascade.

The Application of a Laser-Printed Miniature Five-Hole Probe in the End-Wall Flow Measurement of a Multistage Axial Compressor

To make measurement of end-wall flow between blade rows in a compact multistage configuration possible, a miniature L-shaped five-hole probe was employed in this paper. This compact tip structure, realized by laser-printing instead of the conventional machining technique, reduces the blockage effect of this intrusive measurement on the flow and ensures high spatial resolution. The zonal method is introduced to extend the usable flow angle range up to 60 degrees. A local least-squares interpolation technique is utilized to acquire flow angle and static/total pressure. In order to improve accuracy for the points located at the sector boundary, the overlap region method is included in the interpolation. Additional test data indicate that the maximum error in flow angle is nearly within 1 degree, and the maximum errors of total pressure and static pressure are 0.56% and 1.9% respectively. The application in a low-speed multistage axial compressor indicates that the zonal method can decrease the number of points exceeding the measurable flow range and is of great significance for the end-wall flow measurement, especially for the near-stall condition. Compared with the traditional method, the proportion of available data for the near-stall state measurement was increased by 18% by using the zonal method.

Acoustically driven spin wave resonance in Ni/128° Y-cut LiNbO3 hybrid devices with the beam steering effect

We study the acoustically driven spin wave resonance (ADSWR) in a Ni film sputtered on a 128° Y-cut lithium niobate (LiNbO3) substrate under the condition that the beam steering effect exists due to the surface acoustic waves (SAWs) transmitted along several selected crystal orientations. SAW devices with that effect exhibit significantly different ADSWR spectra from devices without it. By using the magnetoelastic coupling theory and finite element simulation associated with SAW, we find that the beam steering effect of magnetoacoustic waves has an important influence on the acoustic attenuation. The relationship between its group velocity direction and the magnetization vector can be used to define the magnetoacoustic wave mode. The mode affects acoustic attenuation magnitude, which can break the fourfold symmetry. Increasing its power flow angle will significantly increase the maximum acoustic attenuation caused by magnon–phonon coupling.

Optical Flow-Based Stereo Visual Odometry With Dynamic Object Detection

Autonomous vehicles (AVs) play an important role in the next-generation intelligent transportation system (ITS), which requires AVs to have the ability of rapid decision-making and control. As a part of ITS, simultaneous localization and mapping (SLAM) technology is the basis for AVs to operate in a complex and unknown environment. In this article, a stereo vision odometry method in a dynamic environment is proposed, which can not only effectively overcome the influence of dynamic objects but also detect the position of dynamic objects. An optical flow filtering algorithm based on the quantitative histogram (QH) and the optical flow angle histogram (OFAH) of the feature points is proposed to obtain dynamic points. Furthermore, a multifeature fusion mechanism is used to perform binary segmentation and get the bounding box of dynamic object. Experiments show that the proposed method can improve the accuracy of pose estimation and detect moving objects in a dynamic environment.

Effect of Different Types of External Guide Vanes on the Performance of High-Pressure Centrifugal Compressor

In order to reduce exit swirl and obtain the desired Mach number, axial exit guide vanes (EGV) are often employed in a centrifugal compressor. NASA CC3 compressor, with wedge vane diffuser and without EGV, is considered as the base model for the analysis and validation. An axial flow domain with exit guide vane is added to this base model after the diffuser outlet to study the effect on the compressor performance. The performance of exit guide vane with different profiles: flat plate, symmetric wedge, circular arc, and airfoil vane profiles by maintaining the same chord, number of vanes, and flow angle of the vanes are studied. Numerical simulations are carried out with 60 number of exit guide vanes for all four types of vanes. Among several combinations, when the centrifugal compressor is equipped with 60 circular arc vanes as EGV, the efficiency and pressure recovery values at the design point have increased by 6.5% and 8.9%, respectively.

Prediction of the wall pressure spectrum over a curved structure excited by a non-homogeneous turbulent boundary layer in water

In the present study, we introduce a volume approach based on the Poisson equation solved using a Green's function and a semi-analytical turbulence model in space domain. This model can be built from either a Reynolds-Averaged Navier-Stokes (RANS) simulation or an estimation of the boundary layer parameters. Predictions for the power spectral density of the wall pressure fluctuations are compared against measured data obtained for various flow conditions inside a cavitation tunnel. Two geometries are considered. First, we use a NACA 0012 hydrofoil of constant chord length to validate predictions for different flow velocities and angles of attack. Then, we consider a NACA 0009 hydrofoil with a spanwise varying chord length to investigate the contribution of three-dimensional effects.

A non-parametric high-resolution prediction method for turbine blade profile loss based on deep learning

Obtaining the aerodynamic performance of the turbine blade by Computational Fluid Dynamics (CFD) methods is accurate. However, it consumes time and computational resources. This paper proposes an evaluation method based on Convolutional Neural Network (CNN) and Artificial Neural Network (ANN) to obtain the aerodynamic performance of the turbine blade accurately and quickly. Compared with the existing data-driven modeling methods, this method innovatively introduces the Residual Network (ResNet), employs a transfer learning strategy for network design, and realizes the automatic extraction of blade profile features and non-parametric input. In processing boundary conditions, the ANN is utilized to fuse the blade profile features with the boundary conditions to realize the mapping between blade profile and aerodynamic performance under different conditions. In addition, to minimize the prediction deviation caused by the severely uneven distribution of the data set, we combined ensemble learning with transfer learning and proposed a two-step prediction strategy. The numerical simulations results show that the ResNet-ANN model established in this paper has a prediction relative error of 5 % on turbine blade aerodynamic parameters under various working conditions. The error is reduced by more than 90 % under −40°-10° incidence angle of incoming flow compared with the empirical model.

Deep Learning Approach for Human Action Recognition Using a Time Saliency Map Based on Motion Features Considering Camera Movement and Shot in Video Image Sequences

In this article, a hierarchical method for action recognition based on temporal and spatial features is proposed. In current HAR methods, camera movement, sensor movement, sudden scene changes, and scene movement can increase motion feature errors and decrease accuracy. Another important aspect to take into account in a HAR method is the required computational cost. The proposed method provides a preprocessing step to address these challenges. As a preprocessing step, the method uses optical flow to detect camera movements and shots in input video image sequences. In the temporal processing block, the optical flow technique is combined with the absolute value of frame differences to obtain a time saliency map. The detection of shots, cancellation of camera movement, and the building of a time saliency map minimise movement detection errors. The time saliency map is then passed to the spatial processing block to segment the moving persons and/or objects in the scene. Because the search region for spatial processing is limited based on the temporal processing results, the computations in the spatial domain are drastically reduced. In the spatial processing block, the scene foreground is extracted in three steps: silhouette extraction, active contour segmentation, and colour segmentation. Key points are selected at the borders of the segmented foreground. The last used features are the intensity and angle of the optical flow of detected key points. Using key point features for action detection reduces the computational cost of the classification step and the required training time. Finally, the features are submitted to a Recurrent Neural Network (RNN) to recognise the involved action. The proposed method was tested using four well-known action datasets: KTH, Weizmann, HMDB51, and UCF101 datasets and its efficiency was evaluated. Since the proposed approach segments salient objects based on motion, edges, and colour features, it can be added as a preprocessing step to most current HAR systems to improve performance.

Influences of Yaw characteristics on the performance of an Archimedes screw hydrokinetic turbine

A system for in situ power generation that exploits deep-sea current energy has been developed to meet the electricity demands of deep-sea observational equipment. The Archimedes screw hydrokinetic turbine (ASHT) is notable for its self-starting capabilities and energy efficiency, making it well suited for deployment in the low-speed deep-sea environment. This study elucidates two distinctive hydrodynamic characteristics of ASHT and explicates the underlying operational principles for the first time. Specifically, the ASHT is capable of self-yawing without the need for auxiliary yawing mechanisms and, when fixed, can harness ocean currents from a wide array of directions. Based on these hydrodynamic characteristics, passive yaw and fixed installation methods are proposed. A rigorously validated numerical model, supported by water flume tests, is utilized to illuminate the real-time flow mechanisms and assess the effect of different geometric variables on the ASHT yawing performance. An in-house Simulink model evaluates the power supply capabilities of both installation options, revealing that fixed installations are preferable for locations with varied incoming flow angles, whereas passive yaw installations are more appropriate for sites with a restricted range of incoming flow angles.

Investigation on aeroelastic characteristics of mistuned low-speed axial compressor rotor: Numerical methodology and optimization

In this paper, the aerodynamic and aeroelastic characteristics of a low-speed axial compressor were explored by using a multidisciplinary optimization approach. The numerical methodology utilized the parametric benefits of the free-form deformation and Gaussian process-based Kriging in predicting and optimizing the aerodynamic performance (total pressure ratio and isentropic efficiency) and statistical results of forced response (mean μ and standard deviation σ of amplitude magnification) with frequency mistuning. Based on this point, an optimization framework was proposed, coupled with in-house codes for calculating the aerodynamic damping associated with flutter and vibration amplitude of the forced response. Since only the rotor blade was optimized, the exit flow angle at the rotor outlet combined with blade equivalent von Mises stress and aerodynamic damping were chosen as constraints. The results indicated that the total pressure ratio and isentropic efficiency experienced increases by 0.4% and 1.7%, respectively at the point near peak efficiency, while simultaneously achieving a statistical reduction in amplitude magnification. Specifically, aerodynamic analysis revealed that blade twist, backward sweep and forward lean can contribute to the improvement of aerodynamic performance. However, it should be noted that the forward lean of the blade tip led to an increase of equivalent von Mises stress on the blade pressure surface. From aeroelastic analysis, data mining results implied a negative correlation between blade twist and aerodynamic damping, indicating that, an increase in the blade twist angle led to a reduction in aerodynamic damping. These findings highlighted one of the significant conflicts between aerodynamic and aeroelastic performance. Additionally, a strong linear correlation was observed between the mean and standard deviation of forced response, which indicated that a larger blade amplitude magnification increased its sensitivity to frequency mistuning.

Experimental and numerical simulation studies of the flow characteristics and temperature field of Fe-based powders in extreme high-speed laser cladding

Extreme high-speed laser cladding technology (EHLA) is widely employed in critical parts manufacturing and repairing due to its high efficiency. The appearance and quality of the cladding layer are directly influenced by the powder flow characteristics and the interaction between powder trajectory and laser beam. In order to elaborate Fe-based powder flow characteristics of the EHLA process, this study established a powder flow model with a ring-shaped nozzle using a transient process bidirectional coupling. The accuracy of the powder flow model was verified using a high-speed camera. The results demonstrated that the error between the simulation results and the real-time images was within 10 %, confirming the validity of the powder flow model. The temperature profiles of laser-powder coupled model indicated that the optimal melting effect of Fe-based powder was achieved at a laser power of 1500 W. Moreover, the maximum elevation angle of the powder flow was mainly influenced by the carrier gas and protective gas flow rate. The experimental and simulation results showed that the optimal process was a protective gas flow rate of 40 L/min and a carrier gas flow rate of 7 L/min.

FORMULATION AND PHYSICAL EVALUATION OF EFFERVESCENT GRANULES OF MINT LEAF EXTRACT (Mentha x piperita L) AS STIMULANSIA

Indonesia is a country with a diverse biodiversity spread across various regions. Several types of plants in Indonesia can be utilised as herbal medicines. One such plant suitable for medicinal purposes is mint leaves (Mentha x piperita L.). The chemical content found in mint leaves includes essential oils that serve as stimulants. This research aims to determine whether mint leaf extract can be used to create an effervescent granule formulation. Effervescent granules are produced using the wet granulation method, incorporating the active ingredient of mint leaf extract with different concentrations: F0: without the addition of mint leaf extract; F1: mint leaf extract added with a concentration of 15%; and F2: mint leaf extract added with a concentration of 17%. The effervescent granule formula is then evaluated based on its physical characteristics. Phytochemical screening of mint leaves yielded positive results, indicating the presence of essential oils. All mint leaf extract formulations tested for physical evaluation met the specified criteria. Flow properties and angle of repose testing resulted in values between 2-3 seconds for flow properties and 35°-36° for the angle of repose. Compressibility testing produced results ranging from 5% to 15%, pH testing yielded results between 5 and 6, and dissolution time results ranged from 40 to 41 seconds. Keywords: Mint leaves, extraction, wet granulation, effervescent granules

Analysis of Group Pile Bearing Modes of Permeable Pile Dam with Different Incoming Flow Angles

Based on ABAQUS finite element analysis software, the group piles and single piles under different incoming flow angles are compared and calculated, the horizontal bearing characteristics of the group piles of permeable pile dam under different incoming flow angles are analyzed, the pile-soil force is solved, and the change rules of the load-displacement characteristics, the displacement distribution of the pile body, and the distribution of the pile body bending moment are analyzed in detail. The study shows that: for the group piles with flow angles of 0° and 45°, the stresses from the upstream piles to the downstream piles tend to increase along the flow direction, and a stress concentration occurs at the downstream pile; for the group piles with flow angles of 90°, the stresses gradually increase from the central pile to the piles on both sides, and the stress concentration area is distributed at the outermost pile. With the increase of the incoming flow angle, the horizontal bearing capacity of the whole group of piles shows an increasing trend, but due to the effect of the group piles, the bearing capacity of the unit piles is smaller than that of the single piles; The displacements of the group piles at different incoming flow angles were greater than those of the single piles, and the turning points were all at about 12 m below the mud surface; With the increase of incoming flow angle, the group pile starts to change from rigid deformation to flexible deformation, the maximum bending moment of the pile body decreases, and the maximum value of the bending moment of the pile body occurs at the burial depth of 5 m. The maximum value of the bending moment of the pile body decreases with the increase of incoming flow angle.

SIMULATION OF THE AUTOMATIC CONTROL SYSTEM OF A HORIZONTAL-AXIAL WIND POWER PLANT

We considered the results of modelling the operating modes of an electric power generation system of a horizontal-axial wind turbine. The system consist of an aerodynamic blades of a wind wheel connected by an elastic shaft to a generator through a multiplier. Engineering part of the automatic control system (ACS) is the mechanism of rotation of the blades relative to the angle of wind flow. A method for optimizing the main parameters: geometric, dynamic and ACS coefficients is proposed. The method allows a comprehensive assessment of the operation of wind turbines. The value of the average annual electricity generation was used as an optimization criterion. As a result, a deep optimization of the adjustment depth coefficient was carried out. Secondly, we investigated the system in dynamics. A stochastic wind model was used as a disturbing effect. We constructed the system by mathematic simulation methods. As a reference control algorithm, a direct linear dependence of the angular velocity of the turbine rotation on the wind speed with restrictions on the minimum and maximum values was used. Also we described the mathematical model of system and the initial results of the theoretical calculations of algorithms for controlling. The versatility of the calculation system makes it possible to use any aerodynamic profiles of the blades in its composition. The characteristics of aerodynamic moments for the calculation of force moments are obtained by converting Lilienthal curves as initial data for the considered aerodynamic profiles.

흡입구와 유동각의 변경에 따른 디젤발전기 인클로저의 최적화 연구

흡입구와 유동각의 변경에 따른 디젤발전기 인클로저의 최적화 연구

Numerical study of aeration flow angle on powder flow and thermal behaviors in fluidized bed particle solar receivers

The particle flow and thermal characteristics in fluidized bed particle solar receivers with different aeration flow angles were numerically investigated by employing the Eulerian-Eulerian two-fluid model. The filtered drag correlation was utilized to characterize the interaction between SiC particles of Geldart-A classification and gas. The model underwent validation using experimental data from the literature, confirming that the simulated solid holdup and local heat transfer rate agreed well with the experimental measurements. Simulation results show that the particle volume fraction was higher along the walls in the bottom section. In both +45° and + 60°, the particles returned to the aeration flow region. The aeration had a relatively small impact on the particle distribution at the center, whereas the other two regions (x / D = 0.5 and 0.95) exhibited a significant decrease in particle volume fraction at the height of aeration injection. For different aeration injection structures, the equilibrium temperature rise reached approximately 51% of the difference between the wall and inlet temperatures. The temperature rise of particles in FBPSR was attributed to the direct heat transfer from the heating wall to particles and he return of hot particles.

Curved-Line Path-Following Control of Fixed-Wing Unmanned Aerial Vehicles Using a Robust Disturbance-Estimator-Based Predictive Control Approach

In this research, the design of a robust curved-line path-following control system for fixed-wing unmanned aerial vehicles (FWUAVs) affected by uncertainties on the latitude plane is studied. This is undertaken to enhance closed-loop system robustness under unknown uncertainties and derive the control surface deflection angle directly used to control FWUAVs, which has rarely been studied in previous works. The system is formed through the mass center position control (MCPC) and yaw angle control (YAC) subsystems. In the MCPC, the desired yaw angle, which is treated as the reference signal for the YAC subsystem, is calculated analytically using path-following errors, current flow angles, and the yaw angle. In the YAC, a disturbance estimator is designed to estimate uncertainties such as nonlinearities, couplings, time variations, model parameter perturbations, and unmodeled dynamics. Predictive functional controllers are designed to target nominal systems in the absence of uncertainties, such that the estimations of the uncertainties can be incorporated through feedback for closed-loop system robustness enhancement. The simulation results show that higher path-following precision and stronger robustness for the FWUAVs based on the proposed approach can be achieved using only rough model parameters compared with the conventional nonlinear dynamic inversion, which requires detailed model information.

Robust Aerodynamic Parameter Estimation of Unmanned Aircraft Based on Two-step Identification

This paper presents the estimation of stability and control derivatives of an unmanned aircraft. The aerodynamics are described using regressors composed of velocity, angular rates, flow angles and control surface deflections. The flight data is generated from numerical simulation of postulated equations of motion describing the aerodynamics model. Least squares based on the equation error method is used to estimate the parameters representing the different force and moment aerodynamic coefficients. Statistical analysis is done on the estimates to determine the accuracy and adequacy of the estimates to describe the aerodynamic model. A dynamic simulation based on the identified aerodynamic model is used to improve the parameter estimates through regression of the errors between the flight data and the model response. The aircraft under consideration is a scaled Yak-54 fixed wing unmanned aerial vehicle.