Optimal Angle Of Attack Research Articles

The unsteady hydrodynamic response of lightly loaded tidal turbines

An investigation on the unsteady hydrodynamic behaviour of a new scale model tidal turbine at the University of Auckland has been conducted, using FAST software from National Renewable Energy Laboratory. The turbine blades are designed to achieve the optimal angle of attack based on maximizing lift-to-drag ratio, and then the distribution of chord lengths and pitch angles is determined. In this way, a highly efficient but a lightly loaded tidal turbine model design utilizing the S814 profile, is achieved. Oscillatory motions of flows with single frequency over a range of current numbers and reduced frequencies have been considered. The investigation shows that the unsteadiness of the hydrodynamics on the blades is governed by the dynamic inflow phenomenon. The mean angle of attack along the blade is maintained at or very near the initial optimal value. The effects of the oscillatory frequency and velocity amplitude on the unsteady hydrodynamic loading are explored. A quasi-steady analysis is used to clarify the hydrodynamic response of the model as a lightly loaded rotor. A mathematical model is added to the investigation to analyse the role of the forcing components relative to oscillatory velocity and acceleration on the phase of the unsteady loading.

A Case Study on Three-Dimensional Single-Beacon Localization for Autonomous Underwater Vehicles

Circular trajectory is most frequently used when an autonomous underwater vehicle calibrates positions of underwater acoustic beacons or corrects its own navigation errors using beacons. However, the space-time effect on control and navigation data processing and the impact of the angle of attack on three-dimensional localization performance of AUVs have rarely been mentioned in previous studies. To improve the three dimensional localization performance of AUVs with a single-beacon aiding, methods for space-time trade-offs from a control perspective and determination of the optimal angle of attack are investigated in this study. Through theoretical deduction aided with numerical simulation, concerned quantitative values with their corresponding preconditions are given, and some general conclusions which can greatly improve the navigation capability of AUVs have been made.

Thermo-hydraulic performance optimization of wavy fin heat exchanger by combining delta winglet vortex generators

Wavy fins and vortex generators are effective methods for enhancing heat transfer of heat exchangers. In general, wavy fins and vortex generators are studied separately in the literature. A novel combination of a wavy fin and vortex generators is proposed in the present study. The effects of different corrugation angles of the wavy fin and different attack angles of the vortex generators are numerically studied to optimize the thermo-hydraulic performance of the novel combination. The Nusselt number, friction factor, and thermal performance factor are compared between different corrugation angles and attack angles and between wavy fins with and without vortex generators. The heat transfer performance is improved considerably by the novel combination. The maximum thermal performance factor increases by 26.4% owing to the combination of the vortex generator and wavy fin. The optimum attack angle of the vortex generator, which yields the highest heat transfer performance of the wavy fin plate heat exchanger, is reported as 45°.

Effect of flexibility on unsteady aerodynamics forces of a purely plunging airfoil

Introducing flexibility into the design of a vertically flapping wing is an effective way to enhance its aerodynamic performance. As less previous studies on the aerodynamics of vertically flapping flexible wings focused on the lift generated in a wide range of angle of attack·a 2D numerical simulation of a purely plunging flexible airfoil is employed using a loose fluid–structure interaction method. The aerodynamics of a fully flexible airfoil are firstly studied with the flexibility and angle of attack. To verify whether an airfoil could get aerodynamic benefit from the change in structure, partially flexible airfoil with rigid leading edge and flexible trailing edge were further considered. Results show that flexibility could always reduce airfoil drag while lift and lift efficiency both peak at moderate flexibility. When freestream velocity is constant, lift is maximized at a high angle of attack about 40° while this optimal angle of attack reduces to 15° in drag-balanced status. The airfoil drag reduction, lift augmentation as well as efficiency enhancement mainly attribute to the passive pitching other than the camber deformation. Partially deformed airfoil with the longest length of moderate flexible trailing edge can achieve the highest lift. This study may provide some guidance in the wing design of Micro Air Vehicle (MAV).

사다리꼴 와류발생기의 경사각과 충돌각이 열전달 성능에 미치는 영향에 대한 수치해석

The effect of inclination angle and attack angle on heat transfer enhancement of trapezoidal vortex generator was numerically investigated. The commercial package STAR-CCM+ was utilized to analyze the heat transfer and flow characteristics with various inclination and attack angle of vortex generator. The result shows that the optimum inclination angles are α =30°~40° in terms of the heat transfer and pressure drop. At more than 40° of inclination angle, the transverse vortex is dominant, so that the pressure drop is severe and the heat transfer is reduced. As the attack angle is increased, the transverse vortex is reduced, so that the pressure drop is improved. The optimum attack angle is β =30° because the heat transfer performance is maintained. However, more than 30° of attack angle, the heat transfer is decreasing.

Enhancement of thermal and hydraulic performance of compact finned-tube heat exchanger using vortex generators (VGs): A parametric study

In this study, a numerical analysis is conducted to investigate the influence of interrupted surfaces on compact heat exchangers (CHXs). The performance of CHXs in terms of heat transfer enhancement and pressure drop can be augmented by incorporating innovative passive techniques. In relation to that the influence of delta winglet vortex generators (DWVGs) on thermal-hydraulic features of heat exchanger is elucidated. The effect of vortex generators (VGs) with different number of rows (N), attack angles (θ) and configuration on heat transfer performance (j) and pressure drop (f) are demonstrated. Moreover, the influence of tube arrangements such as inline and staggered placement of tubes and different tube shape (circular, oval and rectangular) are also deduced. The optimum attack angle (θop) of VGs is concluded i.e. 1650, which provides higher transfer performance at moderate pressured drop (ΔP). Array of winglet rows gives comparatively higher heat transfer rate than one row of winglets and also common flow down (CFD) configuration of winglets are preferable over common flow up (CFU) configuration of winglets. Moreover, staggered tubes arrangement tends to provide relatively better thermodynamic features as compared to inline arrangement of tubes. Finally, it is concluded that oval and circular tubes deliver quite comparative act in terms of thermal and hydraulic performance as compared to rectangular tubes.

Thermal-hydraulic performance and optimization of attack angle of delta winglets in plain and wavy finned-tube heat exchangers

This work is related to numerical investigation and optimization of the attack angle of delta winglet type vortex generators in plain and wavy finned-tube heat exchangers. For this purpose, three-dimensional numerical simulation data and a multi-objective genetic algorithm with Artificial neural network are employed. The heat exchanger models considered in this study are three rows of tubes in staggered arrangement. The angle of attack (α) of delta winglets and Reynolds number varies from 15° to 75° and 500 to 1300, respectively. Results are illustrated by investigating the flow structures and local heat transfer coefficient. Results show that compared to plain fins, wavy fins enhance the heat transfer performance of the heat exchanger due to constant disruption of thermal boundary. Applying delta winglets on the plain and wavy fins further increased the heat transfer by energizing flow in the wake of tubes while friction factor is also increased. To achieve a maximum heat transfer enhancement and a minimum pressure drop, the optimal angle of attack for varying Reynolds numbers are calculated using the Pareto optimal strategy. For this purpose, CFD data, artificial neural network and a multi-objective genetic algorithm are combined. Results show that compared to the corresponding smooth fins, heat transfer per unit volume (Qv) and pumping power per unit volume (Pv) performances of delta winglets in wavy finned-tube heat exchanger has increased up to 12.5% and 7.41%, respectively. Similarly, for plain finned-tube heat exchangers, the maximum increase in Qv is 14.7% while Pv is increased by 6.93%.

COMPUTATIONAL STUDY OF FLOW CHARACTERISTICS OVER HIGH LIFT AIRFOIL AT VARIOUS ANGLES OF ATTACK

A numerical simulation aiming to study and investigate flow behavior over a high lift low speed airfoil type AG-16 at various angles of attack ranging from 0 degree to 15 degree and constant Reynolds number “39,709” was performed. Computational fluid dynamic CFD technique was applied to study the flow characteristics around the complicated shape airfoil; for better calculation results and smoother meshing generation process unstructured mesh with tetrahedron grid element was used. SOLIDWORKS program was used for modeling requirements; the modeling process includes designing three-dimensional wing with airfoil cross section AG-16 to take into account the influence of third dimension on the flow variables. The magnitude of adverse pressure gradient and flow separation point was investigated, the critical/stall angle of attack of this type airfoil was specified and the aerodynamic efficiency was studied and analyzed with respect to various angles of attack. The numerical results illustrate that the lift coefficient rise rapidly with decreasing angle of attack. The critical angle of attack that gives the maximum lift was recorded at 14 degree on the other hand the drag increased rapidly at high angles of attack due to flow separation, the optimum angle of attack that provide the maximum aerodynamic ratio was 4 degree.

Assessment of the selected parameters of aerodynamics for Airbus A380 aircraft on the basis of CFD tests

Abstract This article presents a several-step method for estimating selected aerodynamic parameters and characteristics of an aircraft. The proposed method is based on the analysis of the CFD simulation results of the aircraft model on the example of the Airbus A380. The first stage of the research concerns the determination of aerodynamic force component values: lift force and drag under specific flight conditions, and determination of lift force coefficient and drag coefficient values. As part of the work, the comparison of the lift force coefficient values and drag coefficient depending on the angle of attack in order to determine its optimal value was made. The second stage of research concerns the estimation of the operational ceiling and the maximum ceiling of the Airbus A380 aircraft based on the standard atmosphere parameters and model simulation results for the optimal angle of attack. The proposed test method allows determining the height characteristics of aerodynamic force components depending on the speed of the aircraft flight, and can be used as a method of supporting the design stage of aircraft constructions.

Parametric modeling and aerodynamic optimization of EXPERT configuration at hypersonic speeds

With the rapid development of aviation and space industry, hypersonic vehicles with high lift-to-drag ratio have attracted an increasing attention. The aerodynamic performance of the aircraft plays a dominant role in the conceptual design of flight vehicles. Based on the sketch of the European EXPERT re-entry vehicle, this investigation provides readers with detailed instructions for the Free Form Deformation (FFD) parametric modeling and aerodynamic optimization of the design of hypersonic vehicles. The aerodynamic characteristics of the vehicle are numerically investigated by the panel method. The Multi-Island Genetic Algorithm (MIGA) is utilized to optimize the aerodynamic shape. The obtained results show that the value of the objective function (L/D)max increases from 0.7141 to 1.4133, and the optimum angle of attack decreases from 21° to 12°. The further analysis digs out the potential effects of the upper and lower surfaces to the vehicle. The impact of the upper surface is greatly diminished. The influence of the body flap, as well as the other objective functions, would be taken into consideration in the oncoming work.

How to utilize the kinetic energy of pulsed detonation products?

The possibility of utilizing the kinetic energy of detonation products by a pulse turbine of the simplest water-wheel-like design during the implementation of the Zel'dovich thermodynamic cycle with pulse detonation combustion of fuel is investigated computationally and experimentally. The coefficients of utilization of the momentum and kinetic energy of detonation products in the pulse turbine with unoptimized mass and dimensions are found to be as low as 8%–16%. To improve the efficiency of the pulse turbine, it is necessary to take measures for eliminating unnecessary reflections of shock waves, to select the optimal mass and dimensions of the turbine rotor and the number of blades, to profile the blades and to select the optimal angle of attack, to optimize the size of the lateral gap between the rotor and the housing, and to select the optimum location of the exhaust duct. It is expected that the efficiency of a combined cycle including the optimized pulse turbine and conventional gas and/or steam turbines attached to the exhaust duct could be higher than the efficiency of a conventional hybrid cycle by at most 9%.

Investigating the interaction of two oscillating foils in tandem arrangement, using 3D unsteady boundary element method

Interaction of an oscillating foil in uniform flow would produce a forwarding thrust. The efficiency of this phenomenon is very dependent on the heave and pitch frequencies, and especially different phase angles. It is also well known that in the case of two foils in tandem arrangement, the frequency of heave and pitch motion of forward foil affects the lift/drag force of aft ward foil and thus the shape of emanating vortex sheet. In this paper, the thrust coefficient and efficiency of two oscillating foils in tandem arrangement are investigated. The interference of airfoils frequencies is investigated. A three-dimensional unsteady code is developed, based on boundary element method, and applied to simulate all the targeted cases. The trailing edge vortex sheet is also modeled using vortex filament and time stepping method. This approach is adopted due to its powerful ability for estimating the hydrodynamic forces on the lifting bodies. In order to model the heave/pitch motion, it is imperative to solve the 2-DOF equations for each foil in conjunction with BEM solver. For validation purpose, the developed program is applied to a single stationary and flapping foil and the thrust coefficient is compared against existing experimental data. Subsequently, the developed code is used to analyze tandem flapping foils. The induced wake shape behind foils is compared with the single flapping foil. Based on the obtained results, the effects of forward flapping foil are clearly observed on the aft ward foil wake shape. It is also demonstrated that for better efficiency, the optimum angle of attack for the aft ward foil is zero.

THEORETICAL AND EXPERIMENTAL INVESTIGATIONS TO DEFINE OPTIMAL PARAMETERS OF THE STRAIGHT-FLOW TURBINE FOR NON-DAM HYDRO POWER STATION

In the article, there are theoretical and experimental investigations presented with regards to determination of optimal parameters of the straight-flow turbine for non-dam hydro power stations. The goal for conducting theoretical and experimental investigations is to increase electric power of the hydro turbine. The most optimal angle of attack of the flow direction at the inlet has been calculated. Accordingly, the results of velocity, pressure, lift and drag forces as well as lift and drag coefficients along the blade have been received. Also, hydro turbine’s work with non-rotating and rotating shaft modes have been taken into account. The achieved results executed in 2D and 3D simulation software modes allowed visualization of the hydro turbine performance through depicting arrows, streamlines, contours, surfaces and line graphs. The calculations with regards to incompressible liquids were measured with the help of COMSOL Multiphysics and ANSYS Fluent software packages through application of Direct Numerical Simulation (DNS) and K-epsilon methods on the base of Navier-Stokes equations. Changing water discharge through a ball valve, the amount of the rotation of the hydraulic turbine rotor was determined using a tachometer. The produced electric power due to the rotation of the hydraulic turbine rotor in minutes is calculated according to Ohm's law.

Ship pitch-roll stabilization by active fins using a controller based on onboard hydrodynamic prediction

The reduction of roll and pitch motions is important to improve the safety and operability of a ship. A pitch-roll stabilization (PRS) control approach for a ship with two pairs of active fins is proposed. In this approach, the key part is the onboard forecasting of the ship's hydrodynamic forces. According to the proposed approach, a PRS controller was developed by integrating a short-term predictor, a force estimator and a fin angle allocator. The PRS controller outputs the optimal attack angles for the active fins by inputting the collected ship's motion time series. First, the short-term predictor serves to predict the future motions of the ship. Second, the predicted ship motions are used in the force estimator to estimate the external hydrodynamic forces. Finally, the predicted hydrodynamic forces, regarded as the expected stabilizing forces, are further employed to evaluate the optimal effective attack angles for the fins' actuator. The active fins are actuated based on the specified optimal effective attack angles. To evaluate the performance of the proposed PRS control approach, numerical simulations and experimental tests under various sea states were investigated. Both the numerical and experimental results suggest that the proposed control approach provided a satisfactory reduction of the pitch and roll motions simultaneously.

Take-off characteristics for NACA 4612 aerofoil in a twin-wing configuration with optimum angles of attack

Unmanned Aerial Vehicles are used generally at low levels and speeds. The research reported in this article investigates the possible use of twin-wing designs for higher altitudes with a focus on the possible lift capable for either short runways or high payloads. The wing aerofoil and unique Angles of Attack, AoA, are set 5o on the upper wing and 10o on the lower. There is a positive upper wing stagger of 50% of the chord length at height separation of 1 chord. These parameters have been established from previous research and this research investigates how they generate lift at take-off and what lift and drag properties exist. It also determines if these parameters are in-line with those for high altitude flight.

Ducted Wind Turbine Optimization

This study presents a numerical optimization of a ducted wind turbine (DWT) to maximize power output. The cross section of the duct was an Eppler 423 airfoil, which is a cambered airfoil with a high lift coefficient (CL). The rotor was modeled as an actuator disk, and the Reynolds-averaged Navier–Stokes (RANS) k–ε model was used to simulate the flow. The optimization determined the optimal placement and angle for the duct relative to the rotor disk, as well as the optimal coefficient of thrust for the rotor. It was determined that the optimal coefficient of thrust is similar to an open rotor in spite of the fact that the local flow velocity is modified by the duct. The optimal angle of attack of the duct was much larger than the separation angle of attack of the airfoil in a freestream. Large angles of attack did not induce separation on the duct because the expansion caused by the rotor disk helped keep the flow attached. For the same rotor area, the power output of the largest DWT was 66% greater than an open rotor. For the same total cross-sectional area of the entire device, the DWT also outperformed an open rotor, exceeding Betz's limit by a small margin.

Can This Dinosaur Glide? by NOVA

NOVA. ‘Can This Dinosaur Glide?’ PBS.org, http://www.pbs.org/wgbh/nova/nature/can-dinosaur-glide.html. Accessed 15 February 2017. In 2008 NOVA, the long-running science series produced by PBS, created an interactive wind tunnel test to explore the glide capabilities of the Microraptor, a small feathered dinosaur discovered in China in 2000. The premise for the test is certainly intriguing for both children and adults: site visitors are invited to take the dinosaur for ‘a spin in this virtual wind tunnel’ (NOVA, ‘Can This Dinosaur Glide?’). However, the actual interactivity is less exciting than suggested. Instead of trying to keep a Microraptor aloft in a wind tunnel, the visitor is directed to position the legs and angles of attack to try to optimise Microraptor’s glide path, and subsequently provided with feedback regarding each position’s effectiveness. While some users still may find this interesting and educational, NOVA spoils the discovery aspect of the activity by stating the optimum angle of attack before you even begin.The organisation of the activity is straightforward. There are only a few areas to explore so there is no confusion when navigating, and information appears in textboxes after selecting the appropriate command. Furthermore, the graphics are generally effective, and the colour scheme allows the site to be readable - a benefit, considering the amount of text. The Wind Tunnel Test has enough user engagement to qualify as interactive but it is very limited and rather uninspiring. Where it fails the most, however, is in the lack of enhancements. There is no video or audio, or even advanced graphics, to engage the user on multiple levels. NOVA has included a transcript from the original scientific tests on which this activity is based, but I feel it would not be very absorbing for children to read. The premise of the activity is intriguing, and some older children might be interested enough in dinosaurs and physics to see past the basicness of the activity to the fascinating scientific discoveries it represents. I feel that younger children, however, will be bored and lose interest by its reliance on text, rather than action.Recommended with reservations: 2 out of 4 starsReviewer: Elizabeth Linville Elizabeth is a graduate student in the School of Library and Information Studies at the University of Alberta. When she was a child, she thought dinosaurs were terrifying until it was discovered they had feathers.

Design and Pitch Angle Optimisation of Horizontal Axis Hydrokinetic Turbine with Constant Tip Speed Ratio

Booming population and associated energy demands, looming threat of exhaustion of conventional sources of energy and the severe environmental repercussions of the same call for alternate sources of clean energy. Hydrokinetic turbine is one such developing technology which harnesses zero-head free flow of water and affects hydrological ecology minimally. This paper discusses the optimisation of Horizontal Axis Hydrokinetic Turbine (HAHkT) blade chord length and twist angle using blade element momentum (BEM) theory to achieve a constant optimal angle of attack (AoA), thus maximising the power output. To achieve this while maintaining robustness at the hub end and eliminate cavitation, two different hydrofoils (S832 and E817) are selected. S832 is simulated using ANSYS 14.0 at low (0 0 ) and high (15 0 ) angles of attack and compared against more widely used NACA 4412 to study flow separation characteristics. This is followed by calculating angles of relative flow, ratios of chord length and subsequently twist angles for each blade element using MATLAB simulations. A blade model is thus developed for visualisation using computer aided designing after obtaining optimal chord lengths and pitch angles.

An aerodynamic performance analysis of a perforated wind turbine blade

Wind power is one of the important renewable energy sources. Currently, many researches are focusing on improving the aerodynamic performance of wind turbine blades through simulations and wind tunnel testing. In the present study, the aerodynamic performance of the perforated Eqwin blade (shell type blade) is investigated by using numerical simulation. Three types of slots namely circular, horizontal rectangular and vertical rectangular were evaluated. It was found that the optimum angle of attack for a perforated shell type blade was 12° with maximum Cl/Cd value of 6.420. In general, for all the perforated blade cases, Cl/Cd tended to decrease as the slot size increased except for the circular slot with 5 mm diameter. This was due to the disturbance of the airflow in lower side region which passed through the bigger slot size. Among the modified slots; the circular slot with diameter of 5 mm would be the best slot configuration that can be considered for blade fabrication. The Cl/Cd obtained was 6.46 which is about 5% more than the value of the reference blade. Moreover, the introduced slot would also reduce the overall weight of the blade by 1.3%.

Aerodynamic performances of cruise missile flying above local terrain

Cruise missile can be classified as a smart bomb and also Unmanned Aerial Vehicle (UAV) due to its ability to move and manoeuvre by itself without a pilot. Cruise missile flies in constant velocity in cruising stage. Malaysia is one of the consumers of cruise missiles that are imported from other nations, which can have distinct geographic factors including their local terrains compared to Malaysia. Some of the aerodynamic performances of missile such as drag and lift coefficients can be affected by the local geographic conditions in Malaysia, which is different from the origin nation. Therefore, a detailed study must be done to get aerodynamic performance of cruise missiles that operate in Malaysia. The effect of aerodynamic angles such as angle of attack and side slip can be used to investigate the aerodynamic performances of cruise missile. Hence, subsonic wind tunnel testings were conducted to obtain the aerodynamic performances of the missile at various angle of attack and sideslip angles. Smoke visualization was also performed to visualize the behaviour of flow separation. The optimum angle of attack found was at α=21° and side slip, β=10° for optimum pitching and yawing motion of cruise missile.