Aerodynamic Behavior Research Articles

Novel Induction Blade Design for Horizontal Axis Wind Turbines to Improve Starting Phase: CFD and Testing Analysis

This article introduces a novel Induction Blade (IB) prototype modeled by Blade Element Momentum (BEM) theory, which develops higher torque during the starting phase for Horizontal Axis Wind Turbines (HAWT), especially for micro-turbines. The IB is composed of two parallel blades joined at their tips and roots, forming a distinctive hole in the space between the blades that generates a Venturi effect as air passes through. This phenomenon in the IB hole together with the extra lift generated by the area of the second blade produce extra valuable torque during the starting phase. We used Computational Fluid Dynamics (CFD) analysis to evaluate the aerodynamic properties of this design compared with a traditional blade design of the same radius. The IB and traditional prototypes were built (50W, diameter 0.62m, λ=9 and at speed rated 8m/s) by additive manufacturing in a 3D printer and their aerodynamic behaviors tested in a small wind tunnel (square section 0.7m x 0.7m). Our results using CFD analysis show that this novel IB produces up to 65% extra torque without losing output power for low wind velocity (5-8 m/s). IMPI (Mexican Institute of Industrial Protection) protects this prototype shape.

Wind tunnel tests of a hexadecagonal cylinder with imperfections and ancillaries: aerodynamic characterization and technical discussion

This paper evaluates and discusses the aerodynamic properties of a 16-sided polygonal cylinder with imperfections and ancillaries investigated by wind tunnel tests. Two sectional models with different size have been realized, reproducing the peculiarities of real structures, such as the rounded corners, local protuberance due to weld bead, cables, ducts and the external ladder. The models have been subjected to static tests to measure the mean force coefficients and the Strouhal number varying angle of attack, flow velocity, turbulence intensity focusing on the effects of the imperfections and ancillaries on the aerodynamic loads with consideration of Reynolds number effects. The results provide an estimate of the aerodynamic coefficients for this type of elements, quantify the influence of geometrical and flow properties on the aerodynamic behaviour and point out the sensitivity of such polygonal cross-section to galloping instability.

Nonlinear, Rate-Dependent Evaluation of Flight Damping Derivatives of the Orion Crew Module

In the continued development of the Orion crew module, NASA is challenged with characterizing and predicting static and dynamic stability during the atmospheric reentry of the capsule. A thorough understanding of the aerodynamic behavior of the crew module in the subsonic regime is essential for safe return, as this flight regime presents the largest dynamic instability recently demonstrated by the Ascent Abort-2 (AA2) flight test. Forced oscillation wind-tunnel tests were conducted with varying frequency, amplitude, and offset angles to determine the rate-dependent static and dynamic derivatives. A novel data reduction technique was employed to obtain a nonlinear representation of the damping derivatives of the capsule as a function of both its angular position and rate from the aerodynamic force/moment measurements. Finally, a nonlinear, second-order model, two-degree-of-freedom ordinary differential equation was formulated to predict the response of the crew module based on initial angular positions, and , and angular rates, and . The accuracy of the model was assessed through direct comparisons with the NASA Ascent Abort-2 flight test. Through benchmark comparisons against the AA2 flight-test data and rate-invariant models, the utility of the second-order model was proven, establishing a low-cost, computationally efficient manner of predicting crew module motion and stability that could be leveraged in flight to improve guidance and navigation control algorithms.

Effects of tail shapes/lengths of Hyperloop pod on aerodynamic characteristics and wave phenomenon

This study provides a view of the primary aerodynamic design of Hyperloop pod considering the influence of tail shape and length on aerodynamic forces (drag and lift) and flow behaviors (pressure, Mach number, and temperature). Numerical simulations are performed considering two tail shapes (i.e., upward and downward tails) and five lengths of the downward tail (i.e., 1.725, 3.45, 6.9, 13.35, and 13.8 m). The dynamic overset mesh method utilizing polyhedral meshes is applied to simulate the movement of the pod. A simplified three-dimensional model is simulated using the unsteady Reynolds-averaged Navier–Stokes shear stress transport k–ω turbulence model, compressible ideal gas, and a pod speed of 300 m/s. The results indicate that the two tail shapes only have a minor effect on aerodynamic drag (i.e., the difference between the upward and downward tails is only 0.75%), generating two tendencies of aerodynamic lift (i.e., the upward tail provides negative lift, and the downward tail yields positive lift). When tail length of the pod increases, it effectively reduces the aerodynamic drag (approximately 7%) and pressure on the pod surface. Meanwhile, the variation of lift observes an intriguing tendency (which the lift is maximum at 6.9 m – tail length). When the tail length is increased over 6.9 m, the lift starts to reduce; however, the lift is increased when the tail is shorter than 6.9 m. The flow fields around and behind the pod tail are significantly affected by the change in tail length, particularly when considering the intensity and generation of the first OS. The highest intensity of the first OS is attained when the tail length is 6.9 m. The increase in tail length considerably reduces the pressure on the pod but slightly affects the pod temperature (exhibiting a maximum difference of 0.4% among the five cases).

Steady-State Aerodynamic Modeling Architecture Overview

An aerodynamic model is a mathematical representation of the behavior of a vehicle in free flight, and the architecture defines the set of variables and equations used to construct the aerodynamic forces and moments. Aeromodels are widely used to represent aerodynamic performance during the design, development, and validation of air vehicles. Architecture selection drives source data requirements and therefore has ramifications for simulation accuracy, program cost, and schedule. This paper describes four approaches appropriate for simple cruciform airframes and provides selection rationale for each. These architectures employ table lookups and the principle of superposition to combine basic stability and control effectiveness components. Body axis mixed architecture provides an efficient method for modeling winged vehicles with limited maneuver requirements. Maneuver mixed-panel architecture enables efficient data collection for a wide range of airframe configurations, providing high accuracy around trim points. Single-panel architecture allows a large domain of flight conditions to be modeled with first-order accuracy using a relatively small data set. Lastly, polar architecture is ideal to reduce the number of independent variable dimensions for spinning projectiles. The architectures described are for the core of the aerodynamic model: steady-state aerodynamic behavior without detailed drag buildup, uncertainty, stability derivatives, transient effects, or application-specific elements.

Performance Investigation of Airfoils for Axial Flow Fans in Low Solidity Cascades Operating at High Inlet Flow Angles

Abstract Axial flow fans are usually characterized by blade sections with low solidity and high inlet flow angles. Two main approaches are followed in the preliminary design phase, to take into account blade interaction effects: the use of available airfoil cascades data (or related correlations) and that of isolated airfoil data together with interference coefficients. The working conditions of low solidity airfoil cascades with highly tangential inflow are not widely studied in the literature, leaving the designer the possibility to rely on limited cascade data or often on the use of isolated airfoil data, with the assumption of negligible interference effects. A systematic investigation of the above working conditions for airfoil cascades is performed with Reynolds-averaged Navier–Stokes simulations. Three different airfoils are used to evaluate the influence of the design lift coefficient and maximum blade thickness. The results provide a better insight into the aerodynamic behavior of airfoil sections in such operating conditions, showing that interactions cannot be neglected. The use of metamodeling coupled with computational fluid dynamics (CFD) simulations is presented as a suitable tool for treating interference effects within the fan design process. The main findings of the present work can be used as a support for design choices as well as for developing design strategies both for the fan blades and for the airfoil sections.

The transitional states of a floating wind turbine during high levels of surge

With the deployment of floating offshore wind turbines, the effect of their wind- and wave-induced platform motion on the turbine’s performance and life is of concern and requires low-order models to develop appropriate control strategies. This work focusses on platform surge as one of the main additional degrees of freedom. The aerodynamic behaviour during the rotor’s transition into propeller state is explored by assessing the spanwise and rotor-integrated aerodynamic forces on the rotor of the NREL 5 MW turbine through a 3D URANS CFD simulation. The CFD findings are compared with a modified actuator disk (AD) theory and 2D Blade-Element Momentum (BEM) approach. In addition to propeller state, where both rotor torque and thrust are negative, two other states were observed with opposite signs of torque and thrust: a braking state, with negative torque but positive thrust, and the second a quasi-windmill state with thrust negative yet torque positive. The results demonstrate that BEM coupled with AD can reliably predict the transitions to these states during such high levels of platform surge and give hints to how the underpinning force balances are affected by temporal perturbations.

Wind Resistance Mechanism of an Anole Lizard-Inspired Climbing Robot.

The stable operation of climbing robots exposed to high winds is of great significance for the health-monitoring of structures. This study proposes an anole lizard-like climbing robot inspired by its superior wind resistance. First, the stability mechanism of the anole lizard body in adhesion and desorption is investigated by developing adhesion and desorption models, respectively. Then, the hypothesis that the anole lizard improves its adhesion and stability performance through abdominal adjustment and trunk swing is tested by developing a simplified body model and kinematic model. After that, the structures of the toe, limb, and multi-stage flexible torso of the anole lizard-like climbing robot are designed. Subsequently, the aerodynamic behavior of the proposed robot under high-speed airflow are investigated using finite element analysis. The results show that when there is no obstacle, the climbing robot generates the normal force to enhance toepad friction and adhesion by tuning the abdomen’s shape to create an air pressure difference between the back and abdomen. When there is an obstacle, a component force is obtained through periodic oscillation of the spine and tail to resist the frontal winds resulting from the vortex paths generated by the airflow behind the obstacle. These results confirm that the proposed hypothesis is correct. Finally, the adhesion and wind resistance performance of the anole lizard-like climbing robot is tested through the developed experimental platform. It is found that the adhesion force is equal to 50 N when the pre-pressure is 20 N. Further, it is shown that the normal pressure of the proposed robot can reach 76.6% of its weight in a high wind of 14 m/s.

Efficacy of an elasto-flexible morphing wing at high lift using fluid-structure-interaction simulations

The wide field of applications is the driving force behind the scientific interest in unmanned and micro air vehicles. For these aircraft, morphing wing technologies offer the possibility to adapt the aerodynamics to different flight stages. A morphing wing configuration with two elasto-flexible membrane wings is investigated numerically at a low Reynolds number of Re = 264000. The concept enables wing folding over a wide range and it allows the wing to adapt to changing aerodynamic loads. The focus is set on the benefits of the membrane in the high lift regime. Therefore, fluid-structure-interaction simulations are performed for the model equipped with a flexible and with a rigid wing. The comparison of the numerical results to data from previous experimental measurements show a good agreement. Compared with the rigid wing, the elasto-flexible membrane increases the gradient in the linear region and the maximum lift coefficient. In addition, the maximum lift coefficient is shifted to higher angles of attack. For selected wing positions and angles of attack, the aerodynamic behavior of the flexible and the rigid wing are investigated by means of the lift coefficient, the deformation of the membrane, the wall shear stresses and the wing surface pressure distribution. The deformation of the wing surface directly influences the area of flow separation at the extended wing and the separating leading-edge vortex at the folded wing. Both effects increase the generated lift of the wing with a flexible membrane.

Shaping Effects on Long Span Bridge Deck Aerodynamics

An aerodynamic circumstance of wind pressure surrounding the long-span bridge allocates many theoretical and experimental research to this topic. Determination of the materials and optimal cross-sectional shape of bridge decks that affected a dynamic behavior of long span bridge deck is still included in current research issues and works to be continued in this path. These include the Lack of sufficient awareness of wind forces, stemming from complex nature, and the unpredictability of the wind nature. In this study, in addition to recognizing the aerodynamic behavior of the flutter, the acting pressure forces on the bridge deck are investigated. The geometrical shape of decks, wind velocity, and flutter conditions are adopted as design variables that affected the dynamic forces exerted on bridge decks. A common type of geometric sections of the long-span bridge deck and effective aerodynamic phenomena are examined. The hollow box steel suspended deck and double cells box girder linked via upper flanges and cells linked via the top and bottom flanges are adopted for Computational Fluid Dynamic (CFD) approach. Thus, aerodynamic instability and turbulent torsional flutter flows, as well as a trail of shedding vortices around the bridge decks, are investigated. By changing some geometrical parameters of commonly used bridge sections, the optimal cross-section in terms of turbulence created above and below the deck section is examined and an optimal cross-sectional shape variable is proposed. The shape variable and section dimensions adopted for CFD-Simulations are similar to the dimensions and materials used in previous laboratory specimens of wind tunnels to be able to interpret the results and possibly verify them with the result of the current study.

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.

Experimental investigation of aerodynamics behavior of a new generic of unmanned air vehicle (heliplane)

The aeronautics studies and particularly the development of drones represent an important field, in which there is a very large number of research and studies.This article aims to present an experimental aerodynamic study of an autonomous surveillance unmanned aerial vehicle (UAV) that is capable of combining the advantages of both categories, namely the fixed-wing drones and the rotary-wing drones. To achieve this objective, a wind tunnel was used to study the flow around this drone in order to better understand the aerodynamic phenomena and to obtain some initial estimates of the lift, drag and moment coefficients, at three different Reynolds numbers of 4.02×104, 6.03×104 and 8.04×104, and for different angles of attack, from [−45°, +45°] with step of 1°.The experimental results obtained in this work show an casi-symetrical variation bertwen the negatif and positif incidence angles of the lift coeffecient, wiche indicate that the heliplane can fly in an inverted position, whatever the angle of incidence. Moreover, the minimum mean value of drag coeffecient according 1° incidence angle is 0.0478 then the drag due to geometry and pitching moment can never be canceled.

Aeroelastic Experimental Investigation of Hyperbolic Paraboloid Membrane Structures in Normal and Typhoon Winds

The lightweight and flexible membrane structure of roofs are susceptible to wind loads with the risk of damage and failure. Compared with uniform and low-level turbulence flow cases (i.e., normal winds) that have been well investigated, the wind-induced vibration problem of membrane structures in high-level turbulence flows such as typhoons has been paid little attention. To address the gap, this paper aimed at investigating the aerodynamic behavior of hyperbolic paraboloid membrane structures in normal and typhoon winds by a series of wind tunnel tests. Some distinct wind characteristics of upcoming normal and typhoon flows in terms of vertical profiles of wind velocity, turbulence intensity, and power spectrum density of fluctuating winds were well simulated in an automatically controlled wind tunnel. The aeroelastic behavior of a scaled model was analyzed and discussed in terms of displacement time-history responses, probability distribution characteristics, and dynamic characteristics including the natural frequency, mode shape, and damping ratio. Results show that the increasing suction in a typhoon leads to significant growth in maximum deformations and more risks to suffer from aeroelastic instability. Non-Gaussian characteristics appear more remarkable with skewness and kurtosis increasing almost two-fold in typhoons. Structural modal parameters are influenced by both turbulence intensity and wind velocity. This study provides basic insights into the deficiency of dynamic response of membrane structures in typhoons, and promotes the applications of membrane structures in green buildings.

Comparative analysis of the aerodynamic behavior on Ahmed body mounted with different wheel configurations

Wheel configuration is the great significance for vehicle aerodynamics, and understanding the influences of wheel configuration on the aerodynamic behaviors of vehicle is a good choice to effectively decrease aerodynamic drag and optimize aerodynamic efficiency. In this study, the aerodynamic characteristics of Ahmed body mounted with different wheels configurations were evaluated by Computational Fluid Dynamics (CFD) using the lattice Boltzmann method. The simulation results were compared with published research data to study resolutions independence and verify the accuracy of the numerical method. The four opening areas of the rim were used to form different wheel configurations. The result showed that the drag of the front and rear wheels increases linearly with the increase of the rim opening area, while the drag of the bodywork decreases linearly. Downstream the body region, the structures of vortex shedding and surface pressure presented differences for each wheel configuration, which further resulted in different fluctuation intensities in wake vortices. The order of the width of the wake vortices in wheel region was as follows: W4 > W3 > W2 > W1. The front wheel had a mainly affect on the time-averaged slipstream peak around the outside of vehicle body.

Ice accretion, shedding, and melting on cable-stayed bridges: A laboratory performance assessment

Ice accretion on cable-stayed bridge surfaces increases loading, affects the structures' aerodynamic behavior, and heightens the risk of ice pieces detaching and falling onto bridge traffic. Here we propose a comprehensive laboratory-based procedure for evaluating materials to reduce ice accretion and prevent ice shedding on cable-stayed bridge. We then assess our laboratory-based procedure by testing four high-density polyethylene sheath configurations for cable-stayed bridges. These sheaths differ in their surface finishes, chemistry, and surface roughness. We present a three-step controlled-environment procedure involving (i) the physical characterization of the surface; (ii) an evaluation of surface behavior under laboratory icing tests; and (iii) an assessment of ice accretion at −10 °C under freezing rain conditions, followed by shedding and melting phases. This testing procedure provides a simple means of evaluating geometric changes and surface modifications, including icephobicity, under repeatable and comparable conditions. Our approach could serve in the design and optimization of materials prior to their deployment under actual operational conditions.

Fluid-solid coupled simulation on thermal management of hydrodynamic gas foil bearing with an axial cooling throughflow

The axial throughflow cooling is a realistic solution for the purpose of thermal management in the hydrodynamic gas foil bearings operating at ultra-high rotational speed and mini bearing clearance. In order to illustrate the effects of axial throughflow cooling within the fluid-solid coupled heat transfer mode on the aerodynamic and thermal behaviors of hydrodynamic gas foil journal bearing, a steady three-dimensional fluid-solid coupled numerical simulation is performed in the present study by assuming that the journal-bearing works in a steady-state condition with a fixed eccentricity ratio of 0.9. The results show that the shearing-induced circumferential flow is significantly dominant in the hydrodynamic air film layer. At both edges of the foil bearing section, local suction flow into the bearing clearance and local leakage flow out the bearing clearance happen simultaneously at different circumferential positions. The increase of axial throughflow mass flowrate plays an effective role on improving the cooling capacity. However, it should be noteworthy that the bleeding air pressure is prompted in a nearly quadratic relationship along with the increase of axial throughflow mass flowrate. Due to the non-uniformity nature of viscous-shearing heat generation inside the hydrodynamic gas foil bearing with a big eccentricity, the temperature on the shaft and top foil surfaces takes on a non-uniform distribution. The peak temperature generally has a 20 K–30 K difference with respect to the mean temperature.

Use of aerodynamically favorable tapered form in contemporary supertall buildings

Today, supertall buildings can be constructed in unusual forms as a pragmatic reflection of advances in construction techniques and engineering technologies, together with advanced computational design tools for architectural design. As with many other buildings, architectural and practical principles play a crucial role in the form of a supertall building, where aerodynamic behavior shaped by wind-induced excitations also becomes a critical design input. Various methods are used to meet the functional needs of these towers and reduce excitations, including aerodynamic modification methods directly related to the building form. Tapered forms are one of the most frequently used and most effective methods in today's skyscrapers, which significantly affect architectural design. To date, no study has been conducted in the literature that provides an understanding of the interrelationships between tapered building forms and main planning criteria, considering the aerodynamic design concerns of the tapering effect in supertall buildings (≥300 m). This important issue is explored in this article with data gathered from 41 supertall case studies, considering location, function, structural system, and structural material as well as the aerodynamic taper effect. The main findings of the study highlighted the following: (1) Asia was where tapered towers were most favored, with a wider margin in all regions; (2) mixed-use was the most preferred function in selected supertall buildings with tapered form; (3) outriggered frame systems were mainly used; (4) tapered supertall cases were mostly built in composite; (5) the sample group included 17 cases that used the tapering effect with aerodynamic design concerns, some of which were accompanied by corner modifications. It is believed that this study will be a basic guide for design and construction professionals including architectural and structural designers, and contractors.

Aerodynamic Behavior of a Biomimetic Wing in Soaring Flight – A Numerical Study

Multi-element wing tips based on bird wings appear attractive in soaring flight, where a minimal sink velocity is the design goal. The present study aims to reproduce the soaring flight observed from white storks (ciconia ciconia) in a biomimetic computational model in order to visualize and investigate the flow around and through the wing tip cascade. RANS and hybrid RANS–LES computations have been performed allowing access to all features of the flow field. The resulting properties in soaring flight have been compared to measured data of free flying birds from the literature to qualify the results of the re-engineered wing. Further, the flow field has been analyzed in detail to understand the underlying flow physics and to point out relevant phenomena such as a system of vortices associated with the wing and tip design which contributes to the observed aerodynamic properties.

Elucidation of lactose fine size and drug shape on rheological properties and aerodynamic behavior of dry powders for inhalation

Pulmonary drug delivery has gained great attention in local or systemic diseases therapy, however it is still difficult to scale-up DPI production due to the complexity of interactions taking place in DPI systems and limited understanding between flowability and inter-particle interactions in DPI formulations. Therefore, finding some quantitative parameters related to DPI delivery performance for predicting the in vitro drug deposition behavior is essential. Therefore, this study introduces a potential model for predicting aerodynamic performance of carrier-based DPIs, as well to find more relevant fine powder size and optimal shape to improve aerodynamic performance. Using salbutamol sulfate as a model drug, Lactohale®206 as coarse carrier, Lactohale®300, Lactohale®230, and Lactohale®210 as third fine components individually, the mixtures were prepared at 1% (w/w) drug content accompanied with carriers and the third component (ranging from 3% to 7%), influence of lactose fines size on DPI formulation’s rheological and aerodynamic properties was investigated. The optimum drug particle shape was also confirmed by computer fluid dynamics model. This study proved that pulmonary deposition efficiency could be improved by decreasing lactose fines size. Only fines in the size range of 0–11 μm have a good linear relationship with FPF, attributed to the fluidization energy enhancement and aggregates mechanism. Once exceeding 11 μm, fine lactose would act as a second carrier, with increased drug adhesion. Computational fluid dynamics (CFD) models indicated fibrous drug particles were beneficial to transfer to the deep lung. Furthermore, good correlations between rheological parameters and FPF of ternary mixtures with different lactose fines were established, and it was disclosed that the FPF was more dependent on interaction parameters than that of flowability.

A computational analysis of the aerodynamic and aeromechanical behavior of a thermo-well for steam temperature measurement in a steam turbine

ABSTRACT The goal of the paper is twofold: firstly, it presents computational fluid dynamics analysis for finding maximum unsteady flow forces (and their frequencies) acting on a thermo-well for measuring steam temperature in a steam turbine control stage and secondly, it presents computational solid dynamics analysis of possibility of entry into resonance of the thermo-well structure. There have been analyzed two cases of flow with changing temperature, pressure, and mass flow rate in the control stage chamber of a turbine high-pressure cylinder. The problem is also described in the ASME standard PTC19.3 TW-2010 providing detailed guidelines for thermo-well calculations. The problem under consideration is only a part of whole technical analysis and obeys a primary hypothesis that a reason of the thermo-well damage was a resonance phenomenon.