Various Angles Of Attack Research Articles

Numerical and analytical evaluation of airship configuration

Today, airships have many uses and have been considered because they combine the benefits of a ship and an aircraft and the low cost of energy consumption. In this research, with the help of numerical solutions and analytical solutions in Datcom, three common configurations of an airship at various angles of attack are investigated. The results of numerical and analytical solutions are compared. Flow condition was considered at an altitude of 4 km above the ground. The same results are not obtained in numerical and analytical solutions. Certainly, numerical results can be cited more than analytical solutions because Datcom software has computational errors and has been simplified. It has been developed for the analytical flow solution on the slender body. However, despite the existing error, this software can be used to extract computational processes and sensitization some parameters. The results show that the approach of the tail fins to the tip of the airship increases the lift-to-drag ratio, and with increasing the length-to-diameter ratio, the aerodynamic performance also improves. In all variants, converting the fins to a cross-type variant improves the vehicle's aerodynamic performance.

Numerical Studies on Fixed Wing Aircraft Aerodynamic Performance using Injection Suction Mechanism

In this current research work, a NACA 6321 flat bottom aerofoil has been altered to study its aerodynamic performance. A co-flow jet (CFJ) method was used with an injection slot located at 20% of chord length and the suction slot situated at 80% of chord length. Simulations have been carried out on the aerofoil models with various angles of attack (AOA) at a Mach number 0.05 to compute the variation in coefficient of lift (CL) and coefficient of drag (Cd) using a k-omega SST model. From the study, it was observed that CL and stalling AOA of an aircraft are increased by 27% and 33% respectively, with an introduction of the additional mass flow rate of 0.01 kg/sec in comparison with baseline aerofoil. It could be concluded that CFJ method enhanced the aerodynamic performance of fixed-wing aircraft due to boundary layer control over an aerofoil which reduces the overall aircraft weight and maintenance cost.

Three-dimensional computational analysis of flow over twisted hydrofoils

The hydrofoils are frequently employed in many different industrial applications, including submarines, rudders, ship motion controls, and marine propellers. The flow over hydrofoils has been the subject of various research in the past. The present study reports the effects of varying twist applied symmetrically along the span and the section thickness on the hydrodynamic performance parameters of non-cavitating three-dimensional hydrofoils for a relatively wide range of angles of attack. Twisted, half-twisted and untwisted hydrofoils with NACA0009 and NACA0015 sections are investigated numerically by incompressible non-cavitation model of Reynolds-Averaged Navier-Stokes (RANS) equations with the shear stress transport (SST) k-omega turbulence model. The impact of twisting, section thickness and freestream velocity are studied in terms of the distributions of lift, drag, and pressure coefficients for various angles of attacks −2°<AOA<8° following a series of successful validation processes. Twisted hydrofoils are evaluated for the implications of the altered incoming flow velocity on the hydrofoil performance. The Delft Twist-11 hydrofoil, which has been used as a benchmark geometry in the literature, are employed for validation investigations. The purpose of the study is to identify which of the hydrofoils under investigation (twisted, half-twisted, untwisted) has a higher lift force and efficiency, and whose application would be more suitable for a particular angle of attack. In particular, the twisted NACA0009 provides the highest lift and the highest efficiency in the range of −2°<AOA<2° compared to half-twisted and untwisted cases. From AOA = 2°–5°, half-twisted NACA0009 provides the maximum efficiency; at later angles, untwisted NACA0009 performs better. Additionally, the lift force is not much affected by the rise in Reynolds number of flows around twisted hydrofoils, while the drag coefficient significantly decreases.

A comparative study of learning techniques for the compressible aerodynamics over a transonic RAE2822 airfoil

In this study, the modeling of the compressible pressure field on the RAE 2822 airfoil using deep learning (DL) is investigated. The objective is to generate, at low cost, the complete Mach envelope from a given aerodynamic database. A dataset with more than 2.000 RANS simulations at various angles of attack and Mach numbers has been created, and validated, to train fast and accurate surrogate models model of the pressure field. The procedure is inspired by the well-known analytical Prandtl–Glauert transformation, which maps solutions from one Mach number to another, but however fails in the transonic regime because of the strong non-linearities due to shock waves. Thus, instead of a classical direct generation of the pressure fields, DL is used here to perform a geometric transformation from an incompressible pressure field towards a compressible solution. The key question addressed in this study is: how accurate and sample efficient are DL techniques compared with classical surrogate modeling tools? To answer this question, two types of DL are investigated (CNN and GCNN) and compared with Proper Orthogonal Decomposition (POD) coupled to a Gaussian Process Regression (GPR). These methods are trained on various input resolutions and database sizes. Results show that DL models are able to accurately predict the intensity and location of the shock over a wide range of angles of attack and Mach numbers up to the transonic regime. Predictions of the lift coefficient reveal a relative error lower than 2% with respect to the high-fidelity data. Because of their inherent nonlinear nature, CNN and GCNN provide more accurate results even for small training datasets, whereas POD encounters difficulties to reconstruct properly shock waves. Since CNN requires inputs and outputs in a pixel-like format, it suffers from interpolation errors that can only be mitigated with fine resolutions, making the training more difficult. By performing convolutions directly on unstructured data, GCNN eliminates this interpolation error and provides the best accuracy and sample efficiency. This study shows that advanced DL techniques, such as CNN and GCNN, are capable of predicting complex flows, and outperform classical tools on such tasks.

Research on the Effect of Lateral Jet on the Flow Field and Aerodynamic Characteristics of Projectile with Grid Fins

In this paper, an effectively structured grid generation scheme is adopted to generate high-quality body-fitted structured grids for jet and grid fins. Based on this, the effects of lateral jets on the flow field and the aerodynamic characteristics of the projectile with grid fins at various angles of attack are studied. The outcomes show that the influence of the jet on the aerodynamic characteristics of the projectile with grid fins is mainly composed of the interference of the jet itself and the interference of the jet developing downstream on grid fins. The variation in the angle of attack will change the bow shock height of the jet and the low-pressure interference region, which will interfere with the grid fins, thus affecting the overall aerodynamic characteristics of the projectile.

Theoretical and Computational Investigation on Swept Back Wing using CFD Method

The principles of flight deals with the motion of air and forces acting on an aircraft. The theoretical aspects of aircraft deals with four different forces. The main aim of the study was to analyse the Swept Back Wing for Supersonic and Hypersonic Mach Regimes at various angles of attack. The geometry and analysis were done using Ansys-Fluent. Calculations were done for constant air velocity altering only the angle of attack. The findings present up the contours of pressure and velocity along with evaluation of lift, drag and its coefficients

Aerodisk Effect on Hypersonic Boundary Layer Transition and Heat Transfer of HIFiRE-5 Vehicle

The substantial aerodynamic drag and severe aerothermal loads, which are closely related to boundary layer transition, challenge the design of hypersonic vehicles and could be relieved by active methods aimed at drag and heat flux reduction, such as aerodisk. However, the research of aerodisk effects on transitional flows is still not abundant. Based on the improved k-ω-γ transition model, this study investigates the influence of the aerodisk with various lengths on hypersonic boundary layer transition and surface heat flux distribution over HIFiRE-5 configuration under various angles of attack. Certain meaningful analysis and results are obtained: (i) The existence of aerodisk is found to directly trigger separation-induced transition, moving the transition onset near the centerline upstream and widening the transition region; (ii) The maximum wall heat flux could be effectively reduced by aerodisk up to 52.1% and the maximum surface pressure can even be reduced up to 80.4%. The transition shapes are identical, while the variety of growth rates of intermittency are non-monotonous with the increase in aerodisk length. The dilation of region with high heat flux boundary layer is regarded as an inevitable compromise to reducing maximum heat flux and maximum surface pressure. (iii) With the angle of attack rising, first, the transition is postponed and subsequently advanced on the windward surface, which is in contrast to the continuously extending transition region on the leeward surface. This numerical study aims to explore the effects of aerodisk on hypersonic boundary layer transition, enrich the study of hypersonic flow field characteristics and active thermal protection system considering realistic boundary layer transition, and provide references for the excogitation and utilization of hypersonic vehicle aerodisk.

Research on the hydrodynamic performance of double manta ray gliding in groups with variable attack angles

To investigate the effect of arrangement and attack angle on the hydrodynamic performance of double manta rays in group gliding, a manta ray model was first established based on the actual shape of manta rays, and then, numerical simulations were carried out with Fluent software to simulate the group gliding of double manta rays in three arrangements of tandem, parallel, and vertical with variable attack angle and variable spacing. Then, the average lift/drag of the group system and the lift/drag of each individual in the group were analyzed by combining with the flow field pressure cloud. From the drag performance, a systematic drag reduction was observed for the double manta rays in tandem and parallel group gliding; in vertical cluster gliding, with the change of attack angle, the individual in the group alternately gained drag reduction, but no systematic drag reduction was found. In terms of lift performance, the average system lift is basically the same as that received by the single body when gliding, regardless of the arrangement, and the difference in lift received by each individual in the group decreases with the increase in the arrangement spacing. This study provides useful results for the formation arrangement of group gliding with twin underwater vehicles.

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.

Simulation study of horizontal axis wind turbine using PVC pipe propeller with elbow tip

The potential of wind as an energy resource is still not widely used by the community through simple technology to produce electrical power. One simple technology is to use PVC pipe as the basic material for making wind turbine propellers. The purpose of this study was to determine the effect of variations in angle of attack and wind speed on the performance of a PVC pipe propeller wind turbine with an Elbow Tip. Material of blade propeller made by PVC pipe are slice half and twist from hub until tip with 90 degree of rotation. Dimension of width blade wider on the hub (3/4 of circular) and smaller on the tip (1/7 of circular). Face of blade on the hub side facing wind direction (axial) and face of blade on the tip side facing tangential direction or opposite with rotation. On the tip side installed the slice elbow with fit tip blade width. The propeller using PVC pipe with elbow tip is the important part of new design which has been test with CFD simulation and wind tunnel research with best result performance. This research uses CFD simulation and experimental methods with a comprehensive study of the aerodynamic behaviour characteristics in and around the turbine rotor. The results of the CFD simulation was found that the phenomenon positioning of momentum force were place on the outer radius due to addition elbow tip cause increasing the torque. By using elbow tip on blade propeller PVC Pipe Horizontal Axis Wind Turbine with 15° and 30° angle of attack could increasing torque about 200 % than without the elbow tip. Beside, using 45° angle of attack although additional with elbow tip could not increasing the torque when the wind speed on 7 m/s. The result of this research is important to know by public who interest build small grid wind turbine with low cost and easy manufacturing.

Artificial neural network-based one-equation model for simulation of laminar-turbulent transitional flow

A mapping function between the Reynolds-averaged Navier-Stokes mean flow variables and transition intermittency factor is constructed by fully connected artificial neural network (ANN), which replaces the governing equation of the intermittency factor in transition-predictive Spalart-Allmaras (SA)-γ model. By taking SA-γ model as the benchmark, the present ANN model is trained at two airfoils with various angles of attack, Mach numbers and Reynolds numbers, and tested with unseen airfoils in different flow states. The a posteriori tests 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 from the present two-way coupling ANN model almost coincide with those from the benchmark SA-γ model. Furthermore, the ANN model proves to exhibit a higher calculation efficiency and better convergence quality than traditional SA-γ model.

Evaluation of wind loads on high-rise buildings at various angles of attack by wall-modeled large-eddy simulation

This study is to validate the accuracy of large-eddy simulation (LES) of wind pressures and loads on high-rise buildings at various angles of attack based on approaching flow simulation framework with synthetized inflow turbulence. The wake flow field and pressure distribution on building surfaces are quite different at different angles of attack due to sensitivity of flow phenomena (separation, vortex, wake effects, etc.). To better capture such complex flow features around the building, local octree mesh refinement is proposed as an efficient meshing strategy to improve the simulation of wind loads statistics with acceptable additional computational cost. Its accuracy is demonstrated by comparing the simulation results from progressive levels of mesh refinement with experimental data. It is shown that octree mesh refinement can improve the prediction of skewness and kurtosis of wind pressures, which are important for the prediction of peak pressures. Moment-based Hermite model approach is introduced for better assessment of probability distribution of peak pressures from short duration of simulation samples.

Aeroelastic characterisation of a bio-inspired flapping membrane wing

Natural fliers like bats exploit the complex fluid–structure interaction between their flexible membrane wings and the air with great ease. Yet, replicating and scaling the balance between the structural and fluid-dynamical parameters of unsteady membrane wings for engineering applications remains challenging. In this study, we introduce a novel bio-inspired membrane wing design and systematically investigate the fluid–structure interactions of flapping membrane wings. The membrane wing can passively camber, and its leading and trailing edges rotate with respect to the stroke plane. We find optimal combinations of the membrane properties and flapping kinematics that out-perform their rigid counterparts both in terms of increased stroke-average lift and efficiency, but the improvements are not persistent over the entire input parameter space. The lift and efficiency optima occur at different angles of attack and effective membrane stiffnesses which we characterise with the aeroelastic number. At optimal aeroelastic numbers, the membrane has a moderate camber between 15% and 20% and its leading and trailing edges align favourably with the flow. Higher camber at lower aeroelastic numbers leads to reduced aerodynamic performance due to negative angles of attack at the leading edge and an over-rotation of the trailing edge. Most of the performance gain of the membrane wings with respect to rigid wings is achieved in the second half of the stroke when the wing is decelerating. The stroke-maximum camber is reached around mid-stroke but is sustained during most of the remainder of the stroke which leads to an increase in lift and a reduction in power. Our results show that combining the effect of variable stiffness and angle of attack variation can significantly enhance the aerodynamic performance of membrane wings and has the potential to improve the control capabilities of micro air vehicles.

Application of improved k-ω-γ model to deformed hypersonic Inflatable Aerodynamic Decelerator aeroshell

The scalloping surface of Hypersonic Inflatable Aerodynamic Decelerator (HIAD) promotes flow transition. Precise prediction of flow transition and surface aeroheating over the HIAD is imperative to the design of thermal protection system. In this paper, the improved k-ω-γ model considering the separation instability is first applied to the deformed HIAD aeroshell under various angles of attack to assess and verify its performance on such complex configuration, where multiple transition mechanisms coexist and interact. The results of the original k-ω-γ model are also provided for comparison and the prediction mechanisms of the improved model are further dissected. The results reveal that the flow separation and crossflow caused by the scalloping surface are highly sensitive to the angle of attack (α). With the α increasing, an opposite tendency between them can be found, that is, larger α causes stronger and earlier crossflow, but much later flow separation, which leads to the alternation of dominant instabilities for transition in turn. At the relatively high angle of attack, the crossflow becomes critical, at a small angle of attack, however, the separation instability is dominant. The first-mode disturbance can also accelerate the flow instability, while the influence of second-mode disturbance can be neglected due to relatively low post-shock Mach numbers. As a result, the original k-ω-γ model, not attempting to incorporate separated flow transition, predicts an opposite tendency to the experiments. While the transition onset, extent and shape simulated by the improved k-ω-γ model compare quite well with the experiments.

An experimental study on the effects of friction modifiers on wheel–rail dynamic interactions with various angles of attack

By modifying friction to the desired level, the application of friction modifiers (FMs) has been considered as a promising emerging tool in the railway engineering for increasing braking/traction force in poor adhesion conditions and mitigating wheel/rail interface deterioration, energy consumption, vibration and noise. Understanding the effectiveness of FMs in wheel–rail dynamic interactions is crucial to their proper applications in practice, which has, however, not been well explained. This study experimentally investigates the effects of two types of top-of-rail FM, i.e. FM-A and FM-B, and their application dosages on wheel–rail dynamic interactions with a range of angles of attack (AoAs) using an innovative well-controlled V-track test rig. The tested FMs have been used to provide intermediate friction for wear and noise reduction. The effectiveness of the FMs is assessed in terms of the wheel–rail adhesion characteristics and friction rolling induced axle box acceleration (ABA). This study provides the following new insights into the study of FM: the applications of the tested FMs can both reduce the wheel–rail adhesion level and change the negative friction characteristic to positive; stick–slip can be generated in the V-Track and eliminated by FM-A but intensified by FM-B, depending on the dosage of the FMs applied; the negative friction characteristic is not a must for stick–slip; the increase in ABA with AoA is insignificant until stick–slip occurs and the ABA can thus be influenced by the applications of FM.

Impact of local flexible membrane on power efficiency stability at wind turbine blade

The efficiency of wind turbines can negatively be affected by flow structures such as the formation of laminar separation bubble or abrupt stall. This can decrease the aerodynamic performance and cause flow-induced vibration and aerodynamic noises to occur. On behalf of hinder of these situations, recent advances have been investigated on a new turbine blade concept such as utilizing continuous morphing shape. In this paper, the effects of employing a local membrane material on the suction surface of a WASP airfoil at Re = 3.5 × 104, Re = 7 × 104, and various angles of attack were experimentally investigated. Experimental results revealed that employing a local flexible membrane over the suction surface positively affected the formation of the bubble by mitigating its size and height between α = 0° and α = 8°. Additionally, power spectrum densities belonging to the power efficiency graphs showed that utilizing local flexibility caused the effects of fluctuations owing to vortex-induced vibrations to reduce, resulting in existing less vibration over the WASP airfoil. These results suggested that employing local flexible structures over the surface of thinner and less camber airfoil ensured the external loads because of vortex-induced vibrations to drop rather than the increment of the aerodynamic performance of airfoil, especially at moderate angles of attack.

The numerical investigation of combustion performance of scramjet combustor with variation in angle of attack

The present article involves computational investigation of parallel fuel injection based scramjet combustor. The wedge shaped strut face is used as a fuel injector. Selected geometry is first validated and then further investigation is performed. Steady-state, two dimensional, scramjet combustor model has been chosen to complete the numerical convergence through ANSYS Fluent software. Grid independence analysis has also been performed. Reynolds Average Navier Stokes equation in addition with k-epsilon turbulence modelling have been utilised to reach the convergence at a lower computational cost. Finite rate eddy-dissipation based Species transport modelling is chosen to solve the chemical kinetics between hydrogen and air. The incoming boundary condition of free-stream air has been optimized to improved combustion efficiency. There are three selected model is utilised for comparison i.e. zero degree, positive five and negative five degree air angle of attack model. To change the angle of attack of the incoming air, a Modified isolator is added ahead of the combustor with constant length. It is observed that the behaviour of shock waves and flow properties are dependent on the angle of attack. Comparative observation has been analysed with monitoring the combustion efficiency graph. Maximum combustion efficiency reaches up to 93% in negative five degree air angle of attack model moreover, mixing is also improved by 4%. It can be summarized that the scramjet combustor performance is primarily highly influenced by the geometry configuration and the nature of flow of incoming air.

The behavior of unconstrained parachute fabric under aerodynamic loading

As parachute systems are required to make precise drops of increasingly heavy equipment, it is important that the simulation tools that are used to develop these systems have relevant data that they can use for validation. Before a detailed validation experiment can be run, it is necessary to understand how these fabrics behave over a wide range of conditions to determine the proper parameter space for the validation tests. In an effort to determine fabric behavior so that specific test points can be selected for validation, minimally constrained squares of F111 nylon fabric were tested in the United States Air Force Academy’s (USAFA’s) low speed wind tunnel and the Army Research Laboratory’s (ARL’s) Microsystem Aeromechanics Wind Tunnel. The tests at USAFA covered different angles of attack, freestream velocities, and amounts of excess length. Testing at ARL was conducted to obtain particle image velocimetry (PIV) measurements around the fabric while simultaneously tracking the motion of the fabric. The results of the experiments with varying excess length indicated that spanwise excess length had a more significant impact on the fabric mean shape and vibrations than excess length in the chordwise direction. Variations in angle of attack and freestream velocity indicated that the minimally constrained fabric experiences large amplitude vibrations at low angles of attack and vibrations beyond the trailing edge are insignificant at angles above 6°. Data from both the USAFA and ARL experiments indicated that this was true even when the leading edge shear layer was separated and undergoing unsteady oscillations. The PIV results from the ARL experiments indicated that at low angles of attack the fabric often experienced unsteady oscillations causing a leading edge region to flip into an up-or-down quasi-stable position. When this flipping occurred it induced vortex shedding which resulted in highly unsteady forces generated by the model. The lack of vibration of the fabric at angles of attack where the leading edge shear layer was undergoing unsteady separation indicates that the material properties of the F111 nylon make it less sensitive to small disturbances when under load. The presence of spanwise pre-strain eliminated large amplitude vibrations of the fabric at low angles of attack and the vortex formation was linked to leading edge oscillations, indicating that the leading edge state drives much of the fluid–structure interaction for minimally constrained fabric.

Numerical modeling of unsteady subsonic flow over the conical shape body

The article presents the results of a numerical study of the unsteady vortex motion of gas arising over the conical body with a segmental bottom surface for various angles of attack in a subsonic flow regime. The simulation is based on the viscous compressible gas model (Navier–Stokes model). For various attack angles, the patterns of vortex flow around the conical surface of the body, in the area of its conjugation with the segmental bottom surface and in the near wake are presented. Data on non-stationary behavior and the magnitude of pressure in the conjugation area are given. For numerical simulation the method of finite volumes is used. Taking into account phenomena of the flow separation, the computational grids used have condensation to the surface of the body. Numerical calculations were carried out on the basis of parallel algorithms of the method and were realized on multiprocessor computing complexes.

고도 변화에 따른 5공 프로브 보정오차의 특성에 관한 전산해석

In this study, calibration error characteristics of a five-hole probe according to altitude change were analyzed by computational analysis. Since the information on atmospheric and flight conditions is critical in the safe operation of an aircraft, accurate measurement through the air data system remains an important technological issue. To fully utilize the values from the five-hole multi-function probe, a calibration technique is needed to establish the relationship between the measured pressure value difference and the flow condition. Using a CFD code, computational calculations were performed at sea-level, 6km, and 12km altitude for various angles of attack and sideslip. The pressure coefficient was then calculated from the computed results, and a calibration method was applied. The results showed that the calibration error increases with increasing altitude, which is related directly to the change in the Reynolds number.