Various Angles Of Attack Research Articles

Numerical study on aerodynamics of small scale horizontal axis wind turbine with Weibull analysis.

This paper presents a computational fluid dynamics (CFD) analysis and blade element momentum (BEM) analysis of horizontal small-scale wind turbines under various parameters. Random airfoils such as the NACA 0012, NACA 0018, NACA 4412, S1016, S1210, S1223, and SC20402 are chosen, and the glide ratio is analysed. A Reynolds number of 100,000 is considered because of the small wind turbine design. The foil with the highest glide ratio is selected. Various notations are used to represent the chord and the twist angle of the blade, and the blade with the best chord and twist angle is chosen. The lift, drag, and power coefficients and power curves are analysed via the BEM. The power curves are evaluated for different air densities, and a higher value of power is obtained. Finally, via CFD, the SST model for turbulence is analysed for various angles of attack via Ansys Fluent for different air densities. The results are satisfactory compared with those of the CFD and BEM analyses. The Weibull distribution is analysed to understand the required frequencies for various wind speeds so that the installation of wind turbines can be made convenient in preferred areas with suitable wind properties.

CFD Investigation of Dual Synthetic Jets on an Optimized Aerofoil's Trailing Edge

In fluid dynamics, a flow control device is used to control, manage, or modify the behavior of a fluid flow. Jet actuators work by releasing high-velocity jets of fluid, usually air or gas, into the surrounding environment to control or manipulate the flow of fluids. In this study, the flow control device, which was a dual synthetic jet actuator (DSJA), acted as a lift enhancement device over an optimized NACA 0012 aerofoil with a rounded trailing edge (TE) (Coanda surface approximately 9% of the trailing edge was modified) to enhance the lift at various angles of attack (AOAs). Fluctuating pressure inlets were introduced in two slots. When the dual synthetic jets were in control, the out-of-phase jets from the upper and lower trailing edge jets helped to boost the lift coefficient. The suction stroke from the lower half of the jet made the Coanda effect stronger in the upper half. The upper trailing edge jet deflected downwards merged with the lower one and helped to deflect the flow field closer to the bottom half. An unsteady CFD analysis was performed on optimized airfoils with and without a DSJ, with a driving frequency of 40.6 and a reduced frequency of 0.025 at a Reynolds number of 25000. The results obtained at different angles indicated that the L/D ratio was improved by 13.5% at higher angles of attack in the presence of the DSJA.

The impact of finite span and wing-tip vortices on a turbulent NACA0012 wing

High-fidelity simulations are conducted to investigate the turbulent boundary layers around a finite-span NACA0012 wing with a rounded wing-tip geometry at a chord-based Reynolds number of $Re_c=200\,000$ and at various angles of attack up to $10^\circ$ . The study aims to discern the differences between the boundary layers on the finite-span wing and those on infinite-span wings at equivalent angles of attack. The finite-span boundary layers exhibit: (i) an altered streamwise and a non-zero spanwise pressure gradient as a result of the variable downwash induced by the wing-tip vortices (an inviscid effect typical of finite-span wings); (ii) differences in the flow history at different wall-normal distances, caused by the variable flow angle in the wall-normal direction (due to constant pressure gradients and variable momentum normal to the wall); (iii) laminar flow entrainment into the turbulent boundary layers near the wing tip (due to a laminar–turbulent interface); and (iv) variations in boundary layer thickness across the span, attributed to the variable wall-normal velocity in that direction (a primarily inviscid effect). These physical effects are then used to explain the differences in the Reynolds stress profiles and other boundary layer quantities, including the reduced near-wall peak of the streamwise Reynolds stress and the elevated Reynolds stress levels near the boundary layer edge, both observed in the finite-span wings. Other aspects of the flow, such as the downstream development of wing-tip vortices and their interactions with the surrounding flow, are reserved for future investigations.

Behaviour of Whitcomb Integral Supercritical airfoil at various angles of attack in sonic condition using CFD

Understanding the aerodynamic behaviour of an airfoil is crucial for evaluating its performance in generating lift and drag. In this study, the aerodynamic performance of the Whitcomb Integral Supercritical Airfoil is analysed across a range of angles of attack—specifically, 2°, 4°, 6°, 8°, and 10°—under sonic conditions. The primary objective is to investigate and characterize the lift and drag properties exhibited by the airfoil at these various angles of attack. This analysis will provide insights into how the airfoil performs in terms of efficiency and stability at sonic speeds.

Benchmark experimental study on cavitating flow around Clark-Y 11.7 % hydrofoil at various angles of attack under controlled levels of dissolved air

The present research aims to study cavitating flow around a CLARK-Y 11.7 % hydrofoil with variable angles of attack (α) while maintaining controlled levels of dissolved air in the operating fluid, which is water. A series of experiments were conducted using a water tunnel facility, where the cavitation characteristics were measured and observed using sensors and high-speed imaging techniques. The variables studied in the present work are cavitation number (1 ≤ σ ≤ 2.2) and angle of attack (α = 4°, 6°, 8°, 10°, and 12°), with dissolved air levels (DAL) in the range of 9.3 ppm to 13.1 ppm. The dimensionless cavity length decreases significantly with increasing values of σ/α, indicating an inverse relationship where higher cavitation numbers or lower angles of attack result in shorter cavities. The cavity length follows a power-law scaling relationship, with the empirical equation Lmax/C=4.78×σ/α−0.76.Increasing the angle of attack transitions the cavitation nature from stable (Mode I) to dynamic (Mode II) and highly oscillating (Mode III). Larger cavities result in lower Strouhal numbers, which indicates reduced vortex shedding activity. The relationship between the Strouhal number and the normalized cavitation number σ/α is characterized by the power-law equation St=0.041×σ/α0.3. The pressure coefficient at the leading-edge increases with the angle of attack at low cavitation numbers, while higher cavitation numbers lead to greater pressure coefficient differences between the leading and trailing edges.The present study offers an extensive dataset and empirical correlations that may serve as a benchmark framework, which facilitates the validation of computational and experimental models of cavitating flow under similar conditions.

Effects of wind barriers on the aerodynamic forces and driving safety of vehicles on a wide bridge girder at various angles of attack

This paper presents the effects of angles of attack (AOA) on the windproof effect of wind barriers and the driving safety of highway vehicles on a wide bridge girder. The aerodynamic force coefficients of the vehicles were obtained using the force measurement technique. Computational fluid dynamics simulations were employed to investigate the mean wind velocity field on the upper surface of the girder. A comparison was made between the aerodynamic forces on a vehicle at various AOA on a bridge deck with guardrails and a deck with wind barriers. The windproof effect of wind barriers at various AOA was accessed by the safety factor of a vehicle. The results showed that the maximum of the aerodynamic forces of vehicles was not typically observed at a 0° AOA. The windproof effect of wind barriers became more pronounced as the magnitude of the AOA increased. As AOA increases, the height of the low wind velocity zone above the deck shows an upward trend. Compared to the deck with the guardrails, the height of the low wind velocity zone was much higher in the presence of wind barriers. The increase in the height of the low wind velocity zone will result in a decrease in the aerodynamic side force and an increase in the rolling moment acting on vehicles. It is also noteworthy that the installation of wind barriers can cause a reduction of overturning and side-slip safety factors of vehicles at specific AOA. This suggests that the wind barrier may potentially compromise driving safety at specific AOA.

Proper orthogonal decomposition analysis for two-dimensional wake transition behind a NACA 0012 airfoil in a soap film

Abstract An experimental study has been conducted to analyze the flow characteristics around a NACA 0012 airfoil in a horizontal soap film tunnel. The investigation involves both the qualitative observations and the quantitative measurements at various angles of attack (0° to 20°) for Reynolds numbers ∼ 3000 and 5000. Flow visualizations were carried out using the interference technique, while particle image velocimetry (PIV) was used for velocity field measurements. The study examines the two-dimensional wake transition of the NACA 0012 airfoil under different Reynolds numbers and angles of attack in a soap film tunnel. Results indicate that changes in the trailing flow within the soap film are primarily influenced by the Reynolds number and angle of attack. The visualization of the flow exposes different states of wakes and their corresponding flow structures. At lower angles of attack α ≤ 6°, vortex shedding occurs in an alternating mode, while at intermediate angles (8° to 16°), the wake widens. The vortices exhibit more chaotic and turbulent behavior at higher angles of attack, i.e., α ≥ 16°. Furthermore, the study indicates that the same wake transition takes place at lower angles of attack as Reynolds numbers rise.

The broad study of blade cascade under controlled torsional flutter: Dynamics of the flow and stability analysis

The experimental and numerical investigation of the flow instabilities acting on rigid blades and vice versa was conducted for both compressor and turbine configuration. The blade cascade consisted of five rectangular NACA 0010 blades, with three middle blades capable of performing harmonic motion with one degree of freedom (pitching) using force excitation. The base case (all blades fixed) and excited regime were examined. The influence of various angles of attack, harmonic frequency values, amplitude values, inter-blade phase angles and Reynolds numbers (Re) were tested. The mean flow properties as well as the fluid - structure interaction (FSI) were studied using Particle Image Velocimetry (PIV), Reynolds-averaged Navier-Stokes (RANS) CFD methods and using force measurement. Additionally, two different approaches, namely traveling wave mode (TWM) and aerodynamic influence coefficient (AIC), were adopted to estimate the aeroelastic stability of the blade cascade, and the results were compared. The results show significant aeroelastic coupling between the blades in both compressor and turbine configuration. However, the aerodynamic coupling effect for torsional flutter is more prominent in turbine configuration.

Single degree of freedom vortex induced vibration of undulatory seal whiskers at low Reynolds number and various angles of attack: A computational fluid dynamics study

The cross-flow vortex-induced vibration (VIV) response of an elastically mounted idealized undulatory seal whisker (USW) shape is investigated in a wide range of reduced velocity at angles of attack (AOAs) from 0° to 90° and a low Reynolds number of 300. The mass ratio is set to 1.0 to represent the real seal whisker. Dynamic mode decomposition is used to investigate the vortex shedding mode in various cases. In agreement with past studies, the VIV response of the USW is highly AOA-dependent because of the change in the underlying vortex dynamics. At zero AOA, the undulatory shape leads to a hairpin vortex mode that results in extremely low lift force oscillation with a lowered frequency. The frequency remains unaffected by VIV throughout the tested range of reduced velocity. As the AOA deviates from zero, alternating shedding of spanwise vortices becomes dominant. A mixed vortex shedding mode is observed at AOA = 15° in the transition. As the AOA deviated from zero, the VIV amplitude increases rapidly by two orders, reaching the maximum of about 3 times diameter at 90°. An infinite lock-in branch is present for AOA from 60° to 90°, where the VIV amplitude remains high regardless of the increase in reduced velocity.

تعزيز الخصائص الديناميكية الهوائية عن طريق تعديالت سطح الجنيح

The enhancement of the aerodynamic characteristics of the NACA0012 airfoil is studied numerically. ANSYS Fluent is used to simulate the airfoil's performance by applying certain surface modifications in the form of dimples and protrusions. Different shapes were used, namely, semicircular, v-shaped and square. Analysis has been done on an airfoil of 1m chord length with these modifications, which were implemented on the upper surface of a twodimensional airfoil model and placed at 75% of chord length. A comparative study of surfacemodified airfoil models was done to investigate lift and drag for a constant at Re = 3.0E6 at various angles of attack and compare them with smooth airfoils. The results reveal that the aerodynamic characteristics were improved by applying surface modifications, and the flow separation on the airfoil can be delayed by using dimples and protrusions on the upper surface. It was found that the semicircular dimples and v-shaped bumps have the best aerodynamic enhancement, where the lift coefficient was improved by 11% and 9% compared to smooth airfoils, respectively, while the drag coefficients were reduced by 3% for both shapes. Also, based on these surface-modified airfoil analyses, the stall angle was increased by two degrees. In comparison, the semicircular dimples are more suitable for enhancing the performance characteristics of airfoils.

A quick 3D BEM iterative algorithm for partially cavitating flows over cylindrical bodies at angles of attack

An iterative three dimensional Boundary Element Method (BEM) is formulated to investigate partial cavitating flows around cylindrical bodies at various angles of attack and validation is pursued through comparison with other numerical models. Also, in this article the effect of angle of attack on two types of head (conical and blunt-head) is investigated. The results show that the effect of angle of attack on variation of cavity shape at blunt-head cylinder is more considerable. The need for a very short time (less than 10 min) to reach the desirable convergence and also proper accuracy in calculating the properties of cavitating flows are considerable advantages of this method. Also, in this research, the effect of the length of a cylindrical body on the cavity length has been investigated. The results confirm that if the length of the body is greater than 1.7 times the cavity length, the effects of the negative pressure behind the cylindrical body on the cavity length can be neglected.

An XAI Framework for Predicting Wind Turbine Power under Rainy Conditions Developed Using CFD Simulations

Renewable energy sources are essential to address climate change, fossil fuel depletion, and stringent environmental regulations in the subsequent decades. Horizontal-axis wind turbines (HAWTs) are particularly suited to meet this demand. However, their efficiency is affected by environmental factors because they operate in open areas. Adverse weather conditions like rain reduce their aerodynamic performance. This study investigates wind turbine power prediction under rainy conditions by integrating Blade Element Momentum (BEM) theory with explainable artificial intelligence (XAI). The S809 airfoil’s aerodynamic characteristics, used in NREL wind turbines, were analyzed using ANSYS FLUENT and symbolic regression under varying rain intensities. Simulations at a Reynolds number (Re) of 1 × 106 were performed using the Discrete Phase Model (DPM) and k–ω SST turbulence model, with liquid water content (LWC) values of 0 (dry), 10, 25, and 39 g/m3. The lift and drag coefficients were calculated at various angles of attack for all the conditions. The results indicated that rain led to reduced lift and increased drag. The innovative aspect of this research is the development of machine learning models predicting changes in the airfoil coefficients under rain with an R2 value of 0.97. The proposed XAI framework models rain effects at a lower computational time, enabling efficient wind farm performance assessment in rainy conditions compared to conventional CFD simulations. It was found that a heavy rain LWC of 39 g/m3 could reduce power output by 5.7% to 7%. These findings highlight the impact of rain on aerodynamic performance and the importance of advanced predictive models for optimizing renewable energy generation.

Upgrade in the elastic surface algorithm for airfoil inverse design with variable attack angle via controlled leading-edge movement

Upgrade in the elastic surface algorithm for airfoil inverse design with variable attack angle via controlled leading-edge movement

Complex flow dynamics for a static triple-box girder under various angles of attack

Complex flow dynamics for a static triple-box girder under various angles of attack

Aerodynamic Analysis of Fixed-Wing Unmanned Aerial Vehicles Moving in Swarm

This paper presents a close-formation flight of two unmanned aerial vehicles (UAVs) and the aim of the study is to improve the understanding of the vortex effects between fixed-wing UAVs in a swarm using computational fluid dynamics (CFD) tools. To validate the numerical method, results of a variable-density wind tunnel test from the literature were used. This numerical CFD analysis was used to determine the lift coefficient (CL) and the drag coefficient (CD) values for a single UAV at various angles of attack. When examining the aerodynamic impact areas behind the UAV, the longitudinal distance between the two UAVs is not particularly effective for close flight. Therefore, CFD analyses were carried out on the two UAVs for both vertical and lateral distances. The optimum position for close-formation flight was identified using CL/CD ratios. The results of the analysis indicate that the most effective flights, across all lateral positions, occur when the two UAVs are vertically at the same height. In terms of aerodynamic efficiency, the most effective points for close-formation flight for wingspan b are at lateral distances of 0.875 b and 1 b. At these positions, flight efficiency can be increased by approximately 11.5%.

Role of Partial Flexibility on Flow Evolution and Aerodynamic Power Efficiency over a Turbine Blade Airfoil

In this study, the aerodynamic performance of a cambered wind turbine airfoil with a partially flexible membrane material on its suction surface was examined experimentally across various angles of attack and Reynolds numbers. It encompassed physical explanation at the pre/post-stall regions. The results of particle image velocimetry revealed that the laminar separation bubble was diminished or even suppressed when a local flexible membrane material was employed on the suction surface of the wind turbine blade close to the leading edge. The results of the deformation measurement indicated that the membrane had a range of flow modes. This showed that the distribution of aerodynamic fluctuations due to the presence of LSB-induced vortices was reduced. This also led to a narrower wake region occurring. Aerodynamic performance improved and aerodynamic vibration significantly lowered, particularly at the post-stall zone, according to the results of the aerodynamic force measurement. In addition to the lift force, the drag force was enormously reduced, corroborating and matching well with the results of PIV and deformation measurements. Consequently, significant benefits for a turbine blade were notably observed, including aerodynamic performance enhancement, increased aerodynamic power efficiency, and reduced aerodynamic vibration.

КОМПЬЮТЕРНОЕ МОДЕЛИРОВАНИЕ УСЛОВИЙ РАБОТЫ ДИСКОВ БОРОН

The working parts of tillage machines, including harrow discs, wear out and fail during tillage. Basically, they are hardened at the manufacturing stage to increase wear resistance. Conducting tests to verify their operability in order to select the most effective hardening technologies requires a lot of time and material costs. A modern alternative to these tests is the use of computer simulation at the initial stage of the selection and development of hardening technologies. (Research purpose) The research purpose is investigating and evaluating the influence of technological factors on the wear resistance of the working parts of tillage machines, in particular harrow discs, using computer modeling tools. (Materials and methods) Carried out computer simulation of their working conditions using the computational fluid dynamics method by using the SOLIDWORKS Flow Simulation program to evaluate the effectiveness and selection of various hardening technologies. We created solid-state disk models that were used to simulate the operating conditions of harrow disks with various parameters. (Results and discussion) As a result of modeling, pressure distribution patterns were obtained, which are a color gradient on the selected surface of the model, showing the values of soil pressure on the disk. The pressure distribution on the disc of the disc harrow in the factory version and with reinforcing rollers at various angles of attack of 10, 15 and 20 degrees and speeds of 6, 12 and 24 kilometers per hour was shown. The patterns of pressure distribution on the disk with various geometric parameters of the applied reinforcing rollers were revealed. (Conclusions) With all the various technological factors presented, the harrow discs with reinforcing rollers showed a decrease in soil pressure on their surface. It was found that the pressure of the soil on the disk is most strongly reduced when applying rollers with a width of 6 and a height of no more than 2 millimeters.

Splitter-plate proximity-induced transitions in flow-induced vibration of a triangular prism

The effect of a splitter-plate downstream of an elastically mounted equilateral triangular prism on flow-induced vibration is numerically investigated at Reynolds number Re = 100, mass ratio m* = 10, damping ratio ζ = 0.005, cylinder-plate gap G* = 0.3, and various angle of attacks α = 0°–60°. The α = 0° and 60° correspond to vertex and edge of the cylinder facing the free stream. Under the effect of the splitter plate, a single transition from vortex-induced vibration (VIV) to proximity-induced galloping (PIG) in the vibrational response for an axisymmetric circular cylinder is reported, whereas, for the present non-axisymmetric triangular prisms, the varying α exhibits four proximity-induced transitions: VIV to modified VIV at smaller α = 0° and 25°, VIV to PIG at α = 35°, distinct VIV-galloping to combined PIG-galloping at α = 40°, and asymmetric to symmetric-galloping at larger α = 60°. The plate results in more symmetric vibration for high α ≥ 35°, while a reduction is observed for α ≤ 25°. The gap-flow leads to onset (α = 35°) and enhancement (α = 40°) of afterbody re-attachment on the prism, which significantly enhances the galloping instability and vibrational amplitude. A reduction in galloping instability leading to a slight reduction in amplitude is found for α = 60° prism. The study shows that the presence of the splitter-plate downstream influences near-wake structure and far-wake vortex shedding modes, which lead to stabilizing and destabilizing near-wake flow and distinct vibrational characteristics—depending on the angle of attack (α).

Experimental investigation of the occurrence of transonic flow effects on the FFA-W3-211 airfoil

For the largest wind turbines currently designed, when operating at rated power and at high wind speeds, the tip airfoils can experience large negative angles of attack. For these conditions and in combination with turbulence, the airfoils are at risk of reaching locally supersonic flow, even at low free-stream Mach numbers. The possibility of shock wave formation and its consequences endangers the lifetime of these largest rotating machines ever built. So far only numerical analyses of this challenge have been attempted with significant modelling uncertainty. Here, for the first time, a wind turbine airfoil (the FFA-W3-211, used at the blade tip of the IEA 15MW reference wind turbine) is studied under transonic conditions using experimental techniques. Schlieren visualization and Particle Image Velocimetry were employed for free-stream Mach numbers of 0.5 and 0.6 and various angles of attack. It was shown that calculations based on isentropic flow theory and compressibility corrections were able to predict the situations where supersonic flow occurred. However, they could not predict the frequency of occurrence and whether shock waves were formed. In conclusion, an unsteady characterization of such airfoil behavior in transonic flow seems to be warranted.

Study of implicit CFD modeling of riblets on wind turbine airfoil in transitional flow

The study introduces a novel hybrid boundary condition, derived from existing literature, crafted for predicting the impact of riblets on airfoils in transitional flow. In contrast to models tailored for fully turbulent flow, the hybrid approach successfully captures the operational dynamics of riblets, as demonstrated through meticulous testing. The boundary condition integrates slip length and a modified specific dissipation rate (ω) boundary to encompass the entire riblet regime. Adjusting the model to match measured drag behavior enables predictions of riblet effects at higher Reynolds numbers pertinent to wind turbine blades. Validation reveals the model’s proficiency in capturing the order of magnitude in drag reduction and aligns the change in drag in the correct direction for diverse riblet heights, yet highlights discrepancies in replicating absolute drag reduction values, particularly at smaller angles of attack. This underscores the imperative for further refinement and tuning, necessitating additional experimental data at higher Reynolds numbers and across various angles of attack to ensure the model’s robust applicability across a broader spectrum of conditions.