National Advisory Committee For Aeronautics Research Articles

Numerical study on cavitation–vortex–noise correlation mechanism and dynamic mode decomposition of a hydrofoil

The large eddy simulation model coupled with the modified Schnerr–Sauer cavitation model has been used to numerically simulate the unsteady cavitation and noncavitation flow of the three-dimensional NACA66 (National Advisory Committee for Aeronautics) hydrofoil under different operating conditions. The results show that the magnitude of the cavitation number plays a decisive role in the hydrofoil cavitation quasiperiodic phenomenon. The cavitation number of 1.25 is used as a typical working condition for analysis. Using the Ffowcs Williams–Hawkings acoustic analogy approach accompanied by the vorticity transport equation splitting, the growth and shedding of cavitation also lead to the growth and shedding of the vortex structure. The cavitation–vortex interaction is mainly influenced by the vortex stretching term and vortex dilatation term and amplitude of them are larger than 500. The baroclinic torque term may be responsible for generating vorticity during the cloud cavitation collapse and has a lower amplitude about 200. The cavity volume acceleration is the main influencing factor of the low-frequency pressure fluctuation around the cavitating hydrofoil. Moreover, the NACA66 hydrofoil surface-pressure data are collected for dynamic mode decomposition to locate the hydrofoil surface noise sources. The alternate high and low amplitude regions in the mode results overlap highly with the cavitation transformation regions. The cavity transformation and pressure fluctuations are the main reason for the generation of periodic low-frequency noise source regions on the hydrofoil surface. Moreover, the corresponding frequencies of each order mode are linearly correlated with the cavitation shedding frequency of 5.70 Hz. Combined with the results of the multiple mode comparisons, it can be inferred that the hydrofoil suction surface under the cavitation effect will generate quasiperiodic waves starting from upstream and moving downstream.

On the transient cavitation characteristics of viscous fluids around a hydrofoil

Cavitation is a transient phase transition process between liquid and vapour, and it often occurs in machines using viscous fluids as working media owing to complex operating environments and the trend toward high temperature, high velocity, and high power density. To investigate the cavitation properties of viscous fluids, a visualization experimental system was proposed and developed in this study. In addition, a three-dimensional computational fluid dynamics (CFD) model considering cavitation was developed based on the finite volume method (FVM) to study the cavitation characteristics and unsteady cavitation behaviors of the cavitating flow in viscous oil around a NACA0012 (National Advisory Committee for Aeronautics) hydrofoil under various conditions. The results showed that cavitation started on the suction surface of the hydrofoil near the head, and the critical cavitation number and the critical velocity were 5.2 and 10 m/s at an operating pressure of zero. Smaller cavitation numbers and higher fluid velocity induced and intensified the cavitation. Additionally, the cavitation process of the viscous oil around the hydrofoil was highly unstable and periodic, and its development included birth, growth, separation, and disintegration, with an evolution frequency of 47 Hz. This study provides a theoretical basis, experimental means, and data support for cavitation of viscous fluids, especially oil. It has significant engineering applications for the development of fluid machinery.

Fast Prediction of Flow Field around Airfoils Based on Deep Convolutional Neural Network

We propose a steady-state aerodynamic data-driven method to predict the incompressible flow around airfoils of NACA (National Advisory Committee for Aeronautics) 0012-series. Using the Signed Distance Function (SDF) to parameterize the geometric and flow condition setups, the prediction core of the method is constructed essentially by a consecutive framework of a convolutional neural network (CNN) and a deconvolutional neural network (DCNN). Impact of training parameters on the behavior of the proposed CNN-DCNN model is studied, so that appropriate learning rate, mini-batch size, and random deactivation rate are specified. Tested by “unseen” airfoil geometries and far-field velocities, it is found that the prediction process is three orders of magnitudes faster than a corresponding Computational Fluid Dynamics (CFD) simulation, while relative errors are maintained lower than 1% on most of the sample points. The proposed model manages to capture the essential dynamics of the flow field, as its predictions correspond reasonably with the reconstructed field by proper orthogonal decomposition (POD). The performance and accuracy of the proposed model indicate that the deep learning-based approach has great potential as a robust predictive tool for aerodynamic design and optimization.

REKONSTRUKSI SUDU PRIMARY AIR FAN PLTU MENGGUNAKAN STANDAR NACA

This PA Fan is one of the vital components in the generating system that functions to drain air and carry fuel (coal) from the pulverizer to the boiler burner. The research has a focus on designing methods to reconstruct the blades in order to increase independence to maintain the reliability of turbo engine equipment. Damage to axial turbo engine equipment generally occurs as a defect in the blades. The method of self-constructing blades needs to be carried out to increase the speed of the repair process. The limitation in this study is that the blade airfoil profile is adjusted to the standards of the National Advisory Committee for Aeronautics (NACA). The benefit of the PA Fan blade reconstruction process is to find the technology of the PA Fan blade product and the basic concepts of the product design process as desired by the initial maker (design intent). The research methods used include: Measurement and geometric modeling of the PA Fan blade using the Mitutoyo Cyrsta-Apex S9106 Coordinate Measuring Machine which is connected to a non-contact laser scanner Mitutoyo Surface Measure 606 to obtain a collection of many coordinates of the measurement results (point clouds), then process point clouds processing to obtain a 3D model of the measurement results, after that identify the airfoil with the NACA standard, and the final stage is to process machine drawings of complete components with geometry specifications.

The effects of surface modification on aerodynamic characteristics of airfoil DU 06 W 200 at low Reynolds numbers,

In this paper the flow characteristics and velocity fields over the vertical axis wind turbines DU 06 W 200 airfoil developed by Delft University of Technology and some other innovative designs are examined by computational fluid dynamics (CFD) simulation and particle image velocimetry (PIV) measurements. In these case studies a modification of the plain airfoil upper and/or lower surfaces was applied with the assistance of different techniques. CFD was conducted using the turbulent model of RANS k- ω SST. The PIV experiments were performed using a wind tunnel test and smoke flow visualization. Different practical cases, namely riblet under surface, riblet above surface, cavity front, cavity back, double cavity, single riblet, and spoiler, were designed and examined. Moreover, two hybrid blade airfoils designed and inspired by combining the DU 06 W 200 and NACA 63215 developed by National Advisory Committee for Aeronautics (NACA) were also tested. The results show that the new design hybrid blade airfoil can significantly modify the flow pattern over the airfoil and improve aerodynamic performance. The new design hybrid blade airfoil could deliver improved efficiency for industrial applications, specifically for the design and development of vertical axis wind turbines.

A Lagrangian analysis of partial cavitation growth and cavitation control mechanism

Partial cavitation has a strong unsteadiness, which will cause serious damage to the hydraulic machinery. The spanwise obstacle is nearly the most efficient method for controlling unsteady cavitation. In this study, numerical simulations of partial cavitating flows around NACA (National Advisory Committee for Aeronautics) 66 hydrofoils in two dimensions (2D) were carried out both with and without obstruction. The obstruction is placed at 0.37c, and its height is 0.1c. Utilizing the finite-time Lyapunov exponent, the Lagrangian coherent structures (LCSs) were developed to investigate the dynamic characteristics of the unsteady flow. By showing the dynamic evolution of the Lagrangian behaviors, the time-dependent LCSs over the two different flows demonstrate the effectiveness of LCSs in explaining the evolution of the vortex during the partial cavitation process. With the use of LCSs, the vortex boundary and reentrant jet can be easily located, and the link between the vortexes can be readily seen. In the meantime, the vortex's origin and destination are shown by the stable and unstable manifolds, respectively. LCSs were then utilized to examine how the obstruction had an impact, and the following conclusions were reached. First, the obstruction can stop a portion of reentrant jets from passing through it. Second, the obstruction can curve the pathway of the reentrant jet, which has passed through it. Third, the obstruction prevents the cavity from flowing downstream. Finally, the obstruction continuously obliterates the expanding cavity across it. Simply said, the Lagrangian analysis based on LCSs provides a better understanding of the vortex dynamics than traditional visualization techniques, which is essential to understanding the great performance of the cavitation-induced unsteady flow.

Investigation on corner stall prediction and flow control by blended blade and end wall technology in a compressor cascade based on modified Spalart–Allmaras model

Corner stall has a significant impact on the performance of compressor cascades, but it is difficult to predict precisely using conventional Reynolds-averaged Navier–Stokes models. In view of this, first, the Spalart–Allmaras (SA) turbulence model modified with helicity is recalibrated to predict corner stall accurately. The internal reasons why the modified SA model does not overestimate the extent and intensity of corner stall as the original SA model is further explored through the analysis of turbulence transport nature. The investigation of corner stall control in a modified National Advisory Committee for Aeronautics 65 cascade by the blended blade and end wall (BBEW) technology is then carried out using the recalibrated MSA model. The numerical results indicate that the BBEW technology can eliminate the separation vortex on the end wall and change the flow field from corner stall to corner separation. The best BBEW scheme reduces the total pressure loss coefficient by 14.13%. The BBEW technology can most significantly enhance the aerodynamic performance of the compressor cascade when the maximum BBEW thickness is close to the trailing edge. When the maximum BBEW thickness is in the same position, the control effect rises first and subsequently falls as the maximum BBEW thickness grows. These research results serve as a guide for choosing turbulence models and designing the BBEW schemes.

Optimization design of the unsmooth bionic structure of a hydrofoil leading edge based on the Grey–Taguchi method

Hydrofoil sections are broadly used in the field of fluid machinery. The leading edge of a hydrofoil structure is closely related to drag and cavitation performance. In this study, we adopt the concept of a bionic design. The fin structure of a fish is simplified and applied to the traditional National Advisory Committee for Aeronautics 0015 hydrofoil. We adopt the Grey–Taguchi method to calculate the best layout. This helps obtain the best drag and cavitation performance. Large eddy simulations are used to verify the scheme. When the ratio of fin depth to length h/L is 0.3, the fin layout length Xn is 7 L, the inclination of fins θ is 7°, and the bionic hydrofoil exhibits the best hydrodynamic performance. Application of the best bionic hydrofoil to the fluid machinery (pump) demonstrates that the hydraulic performance of the pump has been considerably improved.

Two-equation turbulent viscosity model for simulation of transitional flows: An efficient artificial neural network strategy

Laminar-to-turbulent transition phenomena are ubiquitous in natural and industrial flows. As to the Reynolds-averaged Navier–Stokes (RANS) simulation method, the workhorse for accurate prediction of such flow regime boils down to the consideration of the transition effect in turbulence modeling. In this paper, an industrial–practical transition–turbulence model with excellent accuracy, robustness, and efficiency is established by the fully connected artificial neural network (ANN), which maps the relation between the RANS mean flow variables and an intermittency factor. A one-equation local correlation-based transition model coupled with Menter's shear stress transport (SST) model is taken as the benchmark. The present two-way coupling ANN model is trained with two National Advisory Committee for Aeronautics (NACA) airfoils, that is, NACA0012 and NACA2418, at various angles of attack and Mach numbers, while tested with the A-airfoil, NACA0015, and RAE 2822 supercritical airfoils in different flow states. The a posteriori test results manifest that the mean pressure coefficient, skin friction coefficient, size of laminar separation bubble, mean streamwise velocity, Reynolds shear stress, and lift/drag/moment coefficient predicted by the ANN model are all in good agreement with those given by the benchmark transition-based SST model. Furthermore, the ANN model exhibits higher calculation efficiency and convergence speed than the traditional transition-predictive SST model. The present work may pave a new way for machine learning methods to be used in integrated transition–turbulence modeling toward industrial applications.

Direct numerical simulation of transitional flow past an airfoil with partially covered wavy roughness elements

We perform direct numerical simulation of flow past the NACA (National Advisory Committee for Aeronautics) 0012 airfoil with partially covered wavy roughness elements near the leading edge. The Reynolds number Rec based on the freestream velocity (U0) and airfoil chord length (C), and the angle of attack (AoA) is fixed, i.e., Rec=5×104, AoA=10°. The leading edge roughness elements are characterized by streamwise sinusoidal-wave geometry that is uniform in the spanwise direction with fixed height, whereas varying wave numbers (k) from 0 to 12. Based on the validation of the smooth baseline case (k = 0), the roughness effects on the aerodynamic performance are evaluated in terms of the lift and drag coefficients. The drag coefficient decreases monotonically with k, while the variation of the lift coefficient with k is similar to the “drag crisis” phenomenon observed in cylinder flows. The sharp variations of lift and drag coefficients from k = 6 to 8 indicate that k = 8 is a critical case, beyond which massive separation occurs and almost covers the airfoil's suction side and dominates the airfoil aerodynamic performance. To further reveal the underlying mechanism, the flow structures, pressure, skin friction coefficients, shear layer transition onset, and boundary layer separation are quantified to investigate the roughness effects. The roughness elements strongly modify the separation behavior, whereas they have little effect on the transition onset. The unsteady interactions and convections of separation bubbles downward the trailing edge also change the wake evolution. Based on the scaling of the asymmetric wake profiles, we find that the wake defect is gently decreasing with k, but the increase in the wake width is much stronger. This scaling analysis gains a better insight into the roughness effects on the momentum deficit flow rate, which confirms the drag mechanism with different roughness wave numbers.

Multiscale modeling of different cavitating flow patterns around NACA66 hydrofoil

The multiscale effect of cavitation is a complicated multiphase phenomenon involving macroscale cavities and microscale bubbles. The cavitating flows at four different patterns around a (National Advisory Committee for Aeronautics) NACA66 hydrofoil are simulated based on the multiscale model under the Eulerian–Lagrangian framework. The volume-of-fluid method is used to capture the transportation of large-scale cavities in the Eulerian framework, while small-scale bubbles smaller than the threshold value of computational cells are solved using the Lagrangian method and the simplified Rayleigh–Plesset equation. The turbulent flow is solved using the large-eddy simulation approach, and the two-way coupling source for momentum is calculated by integrating interacting forces of discrete bubbles. This work proposes a multiscale model to better investigate the vapor structure with an extensive range of length scales, and analyzes the evolution mechanism of vapor morphology and scale in different cavitation patterns first. The simulation results are compared with the experimental observations to verify the accuracy of the numerical method. Meanwhile, the results illustrate that the turbulence has a significant influence on the bubble behavior. With a decrease in cavitation number, the number and size of discrete bubbles increase significantly, and the probability density function of discrete bubble diameter similarly conforms to Gamma distribution at all cavitation patterns. For inception cavitation, sheet cavitation, and supercavitation, the shape of large-scale cavity is relatively stable, and the standard deviation of the number and Sauter mean diameter of microscale bubbles are much smaller than cloud cavitating flow. In contrast, the large-scale cavity sheds periodically in the cloud cavitating flow leading to the periodical variation of the number and the Sauter mean diameter of microscale bubbles as well. Additionally, the discrete bubbles are mainly distributed in the region with strong turbulence intensity and high vorticity.

Vortex and cavity dynamics for the tip-leakage cavitation over a hydrofoil

Large eddy simulations were used to investigate unsteady tip-leakage cavitating flow over a National Advisory Committee for Aeronautics 0009 hydrofoil. The proper orthogonal decomposition (POD) was combined with fast Fourier transforms to help better understand the deformation dynamics of the vortex and cavity. The results show three typical vortices, i.e., the tip-leakage vortex (TLV), tip-separation vortex (TSV), and shedding–trailing vortex (STV) with their own helical core lines in the averaged cavitating flows. Upstream of x/C = 1.8, the mean TLV core carries the breathing mode waves through the vortex dilatation effect, while the TSV core generates the dilatation, shrinkage, and bending distortions near the cavity interface by vortex stretching and deflection effects. Further downstream, the TLV starts to intertwine with the TSV, and the STV gradually diffuses. The TLV wandering encourages large cavity deformations dominated by the breathing and bending modes. However, in the lower-order POD modes, the contribution of bending modes to the cavity fluctuation energy is greatly weakened due to the variation of the relative cavity radius, r*, which indicates that the breathing mode and the double helix mode play major roles in the cavity interfacial waves. The results also show that the cavity interfacial oscillations are highly correlated with the surrounding velocity fluctuations. Moreover, a modified theoretical dispersion equation can well reproduce the quantitative relation between the vibration frequencies and the axial wavenumbers of the TLV cavity, especially for the wave dynamics of the breathing modes and the double helix modes.

The fusion of flow field data with multiple fidelities

We propose a spatial-temporal multi-fidelity Gaussian process regression framework for the fusion of flow field data with various availabilities and fidelities but not sufficiently large to train neural networks commonly encountered in fluid mechanics studies. For example, fluid experiments lead to data with high fidelity but sparse in time and space, while most of the numerical data are generally regarded as less accurate but are spatially temporally continuous. The proposed framework aims at generating a new set of fused data by combining the merits of those in the spatial-temporal space. Numerical simulations [e.g., direct numerical simulation (DNS), large eddy simulation, Reynolds-averaged Navier–Stokes] of flow around a National Advisory Committee for Aeronautics 0012 airfoil are performed to collect the original raw data with various fidelities, and a fraction of the DNS result is used to mimic the high-fidelity but sparse experimental data. It is found that the accuracy of the fused data increases with the density of high-fidelity points until reaching a threshold, above which the fusion accuracy becomes insensitive. This limit can be overcome by introducing extra dimensions, such as the gradients of the low-fidelity data field. By examining the error fields, it is found that the high-fidelity points can tune low-fidelity fields but only within a limited local region. The accuracy can be firmly improved by introducing more high-fidelity points or higher levels of spatial gradients if the data set captures the temporal development.

Mechanisms of trace water vapor desublimation over airfoil in transonic cryogenic wind tunnels

Cryogenic wind tunnels can provide a larger operating Reynolds number compared to conventional ones. However, the internationally known “moisture contamination problem” resulting from the residual trace water vapor desublimation in the cryogenic wind tunnel may affect the accuracy of the aerodynamic data. Due to extreme difficulties in experiments, the detailed trace water desublimation characteristics remain unrevealed. An Euler–Euler two-phase flow model based on classical nucleation theory and a droplet growth model were established to predict the trace water vapor spontaneous desublimation in the nitrogen flow over airfoil in a transonic cryogenic wind tunnel. The proposed model was validated by experimental data obtained from the literature and showed good agreements. The verified model was applied to 0.152-m National Advisory Committee for Aeronautics 0012 airfoil in a Langley 0.3-m transonic cryogenic wind tunnel under a series of operating conditions. The simulated results reveal that the water vapor desublimation process in a transonic cryogenic wind tunnel can be divided into two patterns by a critical region. In pattern I, over the upper critical total temperature, the water vapor desublimates quickly during the rapid expansion of gas flow over the airfoil surface. In pattern II, below the lower critical total temperature, the water vapor is sufficiently supercooled and desublimates completely into small ice particles in the free-stream flow. For pattern I, the desublimation characteristics were analyzed in detail, and the influences of the desublimation process on the aerodynamic data were quantitatively evaluated, which can provide theoretical guidance for the practical operation of transonic cryogenic wind tunnels.

Numerical investigation on stall flutter of an airfoil with split drag rudder

This paper investigates the stall flutter characteristic of a National Advisory Committee for Aeronautics (NACA) 0012 airfoil with a split drag rudder (SDR). The effect of split angle and initial disturbance on stall flutter properties are studied by the computational fluid dynamics (CFD)/computational structure dynamics (CSD) coupling method. The inherent flow mechanism is illustrated with the vorticity and pressure distribution contours. The results show that stall flutter occurs when the pitch motion amplitude of the response exceeds the pitch instability branches of the energy maps. The increase in the split angle leads to an increase in the additional stiffness of the aerodynamic forces so that the amplitude of the pitching motion induced by the initial disturbance decreases and the bifurcation speed increases with the split angle. The trailing edge vortex and the standing vortex between the rudders form affected by the SDR, which reduces the nose-up moment of the airfoil at small angles of attack and increases the nose-down moment after stall occurs. It enables airfoil to obtain more energy from the flow field so that the LCO oscillation amplitude increases. Moreover, it is found that the SDR-induced trailing-edge vortices will excite a large-amplitude stall flutter of an airfoil with a zero initial angle of attack and disturbance.

Law of incipient separation for turbulent flows over airfoils as inferred by Reynolds-averaged Navier–Stokes

Lu, Aithal, and Ferrante [“Law of incipient separation over curved ramps as inferred by Reynolds-averaged Navier–Stokes,” AIAA J. 59, 196–214 (2021)] discovered a law that predicts the incipience of flow separation over curved ramps by knowing only a few geometrical parameters of the ramp and the Reynolds number of the flow. In that spirit, we have searched for a similar law for airfoils by performing simulations of incompressible turbulent flows over 32 NACA (National Advisory Committee for Aeronautics) airfoils using Reynolds-averaged Navier–Stokes (RANS) equations. First, we have carried out verification and validation of RANS against the experimental measurements by A. J. Wadcock (“Investigation of low-speed turbulent separated flow around airfoils,” NASA Contractor Report No. 177450, 1987), which show the accuracy of the RANS prediction at small angles of attack when flow separation begins to occur on the upper side of the airfoil. Then, we have investigated the effects of the angle of attack, airfoil thickness, and camber on the incipience of flow separation for the Reynolds number based on airfoil chord Rec∈[1.64×106,6×106]. From the analysis of the RANS results, we have determined a law for predicting the incipience of turbulent flow separation over airfoils that relies only on airfoil's newly defined characteristic slope, thickness, camber, and Rec.

High streamwise airfoil oscillations at constant low and high incidence angles

Ratios of streamwise airfoil oscillations to the freestream velocity above 30% have not been well investigated in the literature for a reduced frequency range relevant to unsteady applications. A known departure from the experimental correlation to analytical theory for lower magnitudes of this ratio, known as surge amplitude, motivates a parameter study for constant freestream, at constant low- and high-incidence angles, to understand the circulatory lift dependence on angle of attack, Reynolds number, surge amplitude, and reduced frequency in comparison with theory and higher-order computations. To better understand the increased deviation between theory and experiment with increasing velocity fluctuation, a detailed study of surge amplitude of 0.5 is investigated. The experiment for comparison was a free-surface water tunnel with a NACA (National Advisory Committee for Aeronautics) 0018 airfoil oscillated in the streamwise direction. Force measurements, normalized by instantaneous dynamic pressure, reveal that unsteady lift is dependent on Reynolds number and reduced frequency in both attached and fully separated conditions. In separated conditions, mean and fluctuating lift show a dependency on reduced frequency for larger velocity fluctuations than a relative surge amplitude of 10%. Two-dimensional computations were found to agree well with experimental data for Reynolds number 75 k, low incidence cases, and for high incidence with reduced frequencies less than 0.15, where a fully separated upper surface boundary layer condition occurred. Agreement between computations and experiments was not favorable for reduced frequencies above 0.15 for high incidence cases, where partial upper surface boundary layer reattachment is predicted.

Scale effect during the dynamic stall of dynamic airfoil

Studying the scale effect of dynamic airfoil is helpful for understanding the dynamic stall phenomenon and unsteady wall interference. In this paper, the scale effect of the dynamic stall characteristics of the dynamic National Advisory Committee for Aeronautics 0012 airfoil was studied using time-resolved pressure measurements for the first time, which is different from the Reynolds number effect as the experimental Reynolds number was not varied. The evolution of the pressure field and vortex development characteristics on different scaled models was investigated. Significant scale effects were observed on the dynamic airfoil during its dynamic stall. With the model scale increases from c = 500 to 900 mm, the shear layer vortex and the secondary separation were observed, indicating that vortices on the suction surface were enriched. Furthermore, the vortex-induced suction and its occurrence time were significantly affected. The vortex-induced suction varied from Cp ≈ −4.25 to −1.5. With the model scale increases from c = 500 to 900 mm, the vortex structure occurrence angle of attack was delayed by Δα ≈ 0.5°. Further analyses showed that the scale effects of the dynamic airfoil are attributed to the flow transition and unsteady wall interference interactions. Thus, two physical quantities, Sm and Sw, were innovatively defined to associate the vortex complexity, model scale, and wind tunnel wall pressure. This study helps deepen the understanding of the dynamic stall phenomenon and provides guidance for the unsteady wall interference correction.

Experimental investigation on the effect of fluid–structure interaction on unsteady cavitating flows around flexible and stiff hydrofoils

We experimentally investigated the effect of fluid–structure interaction on unsteady cavitating flows around flexible and stiff National Advisory Committee for Aeronautics 0015 hydrofoils in a low-pressure cavitation tunnel. We analyzed the cavitating dynamics by capturing the cavitation dynamics using two high-speed cameras at different cavitating regimes on the surface of the hydrofoils, made of polyvinyl chloride, brass, and aluminum. We then measured the associated structural deformations in specific cavitation regime such as cloud and partial cavitation dynamics, using a digital image correlation technique. The hydrofoil's angle of attack was set to 10°, and the flow's Reynolds number was adjusted to 0.6 × 106. Results showed that the cavity's shedding frequency on the flexible hydrofoil shifted faster to a higher frequency than on the stiff hydrofoils under similar cavitating conditions. The flexible hydrofoil underwent strong structural oscillations at the low cavitation number for the cloud cavitation regime. The associated amplitudes of the vibration were about 20 times higher than those of the hydrofoil made of brass. It was observed that the fluid–structure interaction can significantly affect the cavitation-induced vibration of the flexible hydrofoil.

AERODYNAMIC CHARACTERISTICS OF NACA 0012 AIRFOIL BY CFD ANALYSIS


 
 
 The wind turbine's aerodynamic efficiency is heavily influenced by the aerodynamic airfoil blades. It's critical to choose the right aerofoil section for the blade. The angle of attack and its impact on lift and drag forces, such as high lift and low drag or vice versa, are key elements that determine the wind turbine system's efficiency. Using this as inspiration, the NACA 0012 airfoil profile is used to investigate the influence of angle of attack on the aerodynamic performance of wind turbine blades. The airfoil geometry is produced using computational fluid dynamics, according to the National Advisory Committee for Aeronautics (NACA) guidelines. The aerodynamic findings are evaluated in terms of static pressure and velocity distributions, as well as different angles of attack, in this study. The angle of attack increases as the lift/drag ratio decreases, according to the CFD study. Other elements, such as blade backflow turbulence and blade forces, should be addressed when evaluating the aerodynamic performance of NACA aerofoils.