Aerodynamic Study Research Articles

An Improved Unsteady CFD Analysis of Plunging Airfoils by using OpenFoam

Unsteady Aerodynamics study of Plunging Airfoils at various frequencies and amplitude at low Reynolds Numbers of the order of Insect/Birds flight is of importance to the design and flying of Micro Aerial Vehicle to meet the requirement of Para-military forces, Border Security forces and other homeland service forces. A new methodology has been developed for the analysis of plunging airfoil based on CFD tool 'OpenFoam'. Since the experimental data available for NACA 0012 Airfoil is in plunging motion, conditions relevant to the experiment are chosen for the analysis. As plunging velocity increases there is an increase in thrust coefficient. Similar trends are observed from experiment and commercial CFD code, Fluent. However, OpenFoam agreement with experiment is better and comparable with commercial CFD code. Also, from the analysis of NACA 4412 airfoil, it has been found that Cl, Cd behavior is unimodal at low frequency and multimodal at high frequency plunging motions.

Aerodynamics and Conceptual Design Studies on an Unmanned Combat Aerial Vehicle Configuration

The ability to accurately predict both static and dynamic stability characteristics of air vehicles using computational fluid dynamics methods could revolutionize the air vehicle design process, especially for military air vehicles. A validated computational fluid dynamics capability would significantly reduce the number of ground tests required to verify vehicle concepts and, in general, could eliminate costly vehicle “repair” campaigns required to fix performance anomalies that are not adequately predicted before full-scale vehicle development. This paper outlines the extended integrated experimental and numerical approach to assess the stability and control prediction method capabilities, as well as the design and estimation of the control device effectiveness, for highly swept low observable unmanned combat aerial vehicle configurations. The aim of the AVT-201 Task Group is to provide an assessment of the computational fluid dynamics capabilities using model-scale experiments and transfer this knowledge to real-scale applications.

Rotor‐tower interactions of DTU 10MW reference wind turbine with a non‐linear harmonic method

AbstractIn this paper, a computational study of the DTU 10MW reference wind turbine unsteady aerodynamics is presented. The whole wind turbine assembly was considered, including the complete rotor and the tower. The FINE/Turbo flow solver developed by NUMECA International was employed for the simulations. In particular, the Non‐Linear Harmonic (NLH) method was applied in order to accurately model flow unsteadiness at reduced computational cost. Important vortex shedding structures were identified at low blade span range and all along the tower height. A strong interaction between rotor and tower flows was also observed. Lastly, the performance of the NLH approach was compared against a standard Unsteady Reynolds‐Averaged Navier Stokes simulation. The same complex unsteady flow phenomena were captured by both technologies. Nevertheless, the NLH approach was found to be 10 times faster than the Unsteady Reynolds‐Averaged Navier Stokes method for this particular application. Copyright © 2016 John Wiley & Sons, Ltd.

Aerodynamic Study of Advanced Airship Shapes

AbstractThe present paper reports a numerical study of the aerodynamic properties for a novel disc-shaped airship. Different configurations are considered, some of which present a circular opening connecting the bottom and top surface of the airship. The aim of the study is to understand the flow dynamics, in order to define the aerodynamic efficiency and the stability properties of the flying vehicle. Such information is crucial for the design of the propulsion system and of the mission profile of these innovative airships. Results show that, in general, disc-shaped airships are characterized by large values of drag and small levels of lift. Interestingly, it appears that lift keeps increasing up to very high angles of attack. This feature is found to be related with strong tip effects, which induce a significant flow of air from the high-pressure region at the bottom surface to the low-pressure region at the top surface. This air flow energizes the upper boundary layer, thus contrasting the flow separat...

Identification of Unsteady Aerodynamic Forces from Forced Motion Wind Tunnel Experiments

The Active Aeroelastic Test Bench is used for the study of low subsonic unsteady aerodynamics through forced motion experiments of rigid wings in pitch and plunge. The use of highly dynamic electric linear actuators allows for arbitrary motion in both the pitch and plunge degrees of freedom. In this paper, we discuss the forces measured on a constant section NACA 0018 wing subjected to isolated single and multisine motion in pitch or plunge. A data-driven approach is used, in which the importance of filtering and averaging of the noisy wind tunnel data is discussed. It is concluded from the forced motion experiments that a good agreement between the single and multisine experiments exists. However, only the pitch experiments agree with predictions from Theodorsen’s unsteady aerodynamics theory. The plunge experiments show the presence of major nonlinear contributions in the measured force response. Because of friction in the linear bearings of the setup, it cannot be excluded that these are generated by the plunging mechanism or the setup itself. Additionally, it is illustrated how the use of multisine signals for the identification of unsteady aerodynamic transfer function models allows for a reduction of wind tunnel test time by a factor of 10.

Voice Therapy Effect on Mutational Falsetto Patients: A Vocal Aerodynamic Study

The study aims to evaluate the effectiveness of voice therapy (VT) and analyze the vocal aerodynamic characteristics in mutational falsetto (MF) patients. From October 2010 through May 2014, 26 patients with MF at Sun Yat-sen Memorial Hospital were studied retrospectively. Vocal assessment, including the 10-item Voice Handicap Index (VHI-10), fundamental frequency (F0), and vocal aerodynamic parameters (subglottic pressure [SGP]), aerodynamic power [AP], mean expiratory airflow, and maximum phonation time [MPT]), was proceeded before and after VT. Before VT, the mean F0, AP, and SGP of MF patients were significantly higher than Control Group, whereas mean MPT was significantly shorter. After a 4-week VT, the mean F0, AP, and SGP were decreased, and the mean MPT was significantly increased compared with the measurements obtained before VT. After the 4-week VT, the VHI-10 scores in 21 patients reverted to normal Control Group's level (Effective Subgroup), whereas the VHI-10 scores in the other 5 patients remained higher than the normal Control Group (Ineffective Subgroup). Subgroup analysis showed the mean AP and SGP of the Ineffective Subgroup were similar to the Control Group, whereas the Effective Subgroup showed higher AP and SGP. After the 4-week VT, MPT in both the Effective Subgroup and Ineffective Subgroup increased significantly, but AP and SGP in the Ineffective Subgroup did not change significantly. VT is an effective treatment for MF patients with laryngeal hyperfunction. Most MF patients can return to normal voice in 4 weeks. Vocal aerodynamic examination can help in predicting the VT effect and deciding the treatment plan. MF patients without laryngeal hyperfunction may need longer VT period or other adjuvant treatment.

“Aerodynamics Study of Co2 Car Design”

“Aerodynamics Study of Co2 Car Design”

Automotive shape optimization using the radial basis function model based on a parametric surface grid

By optimizing the aerodynamic shape parameters, the aerodynamic performance of the vehicle becomes better as the aerodynamic drag decreases. The driving stability also becomes better as the aerodynamic lift decreases. This research presents aerodynamic shape optimization which employs the multi-variable parametric model and the iterative optimal approach to reduce the aerodynamic drag and the aerodynamic lift. For aerodynamic studies with computational fluid dynamics simulations, a parametric surface grid model was used to morph and enhance the mesh quality by linear deformation of the exterior surfaces. This method employed the radial basis function model, and integrated optimization with multi-software provides excellent morphing ability and reasonable optimal designs. In this paper, the process of aerodynamic optimization for a vehicle body is divided into two phases. The first phase is two-dimensional body optimization aimed at a global search, and the second phase aims at a local approximation by running three-dimensional body optimization. The iterative optimal approach can optimize efficiently the aerodynamic characteristics with a reduction in the aerodynamic drag of 13.23% and a marked improvement in the aerodynamic lift. Sensitivity analysis of the design parameters demonstrated that the hood angle is the major factor in the aerodynamic drag coefficient CD. For the aerodynamic lift coefficient CL, the trunk lid angle is the major factor. In addition, the angle of the windshield and the angle of the side window have small influences on CL. The results obtained are accurate reference values for application in automotive engineering.

Analysis of Kinematics of Flapping Wing UAV Using OptiTrack Systems

An analysis of the kinematics of a flapping membrane wing using experimental kinematic data is presented. This motion capture technique tracks the positon of the retroreflective marker(s) placed on the left wing of a 1.3-m-wingspan ornithopter. The time-varying three-dimensional data of the wing kinematics were recorded for a single frequency. The wing shape data was then plotted on a two-dimensional plane to understand the wing dynamic behaviour of an ornithopter. Specifically, the wing tip path, leading edge bending, wing membrane shape, local twist, stroke angle and wing velocity were analyzed. As the three characteristic angles can be expressed in the Fourier series as a function of time, the kinematics of the wing can be computationally generated for the aerodynamic study of flapping flight through the Fourier coefficients presented. Analysis of the ornithopter wing showed how the ornithopter closely mimics the flight motions of birds despite several physical limitations.

Wind tunnel tests of two free-standing lighting protection masts in different arrangements with surroundings roof objects and roof conditions

The paper presents results of wind tunnel experiments of wind action on two free-standing lighting-protection masts with additional supporting ballast placed on building roofs. Aerodynamic laboratory studies were accomplished in a boundary layer wind tunnel. The main objective of the research was to determine extremal values of aerodynamic coefficients. A cantilevered mast and a tripod mast were tested in different roof conditions and different arrangements with surroundings roof objects. A big influence of aerodynamical interference phenomena between masts and adjacent objects was revealed. Moreover, detailed analysis of the experimental results as well as practical approach to design of such kind of structures with respect to wind action was made.

Aerodynamic shape study of supersonic surface to surface missiles with continuous flexible nose

The aerodynamic characteristics of nine configurations of supersonic continuous deflectable nose guided missiles have been investigated. The optimized geometry was achieved based on the accuracy of confliction with constant target in ground to ground mission. The studied configurations consist of a spherical nose tip, a tangent ogive, one set of stabilizing tail fines and a cylindrical body whose midsection is flexible to form an arc of a circle. So the cylindrical body consists of a fixed part in the vicinity of the nose, middle flexible part and main body with stabilizers. The effects of fixed length (Fix = 0, 1.5, 3Cal) and flexible length (Flex = 1, 2.5, 5Cal) parameters on the aerodynamics and flight dynamics of guided missile have been studied. A code has been developed to solve full Navier-Stokes equations using finite volume and Runge-Kutta time stepping techniques and modified Baldwin-Lomax turbulence model. Multi-block technique was also used to solve the main body and fin parts flow fields. Further, a 3 degree of freedom code along with a pure pursuit guidance subroutine was developed to compare planar flight dynamics of missiles. It was found that although the missiles with bigger lengths for fixed and flex parts show more maneuverability, but this is not favorable for all missile missions as sometimes it decreases the confliction accuracy. Flight dynamic analysis shows that a change in initial launch angle may shift the favorite configuration. This means only the aerodynamic defined aim functions cannot completely supersede flight dynamic analysis in geometric optimization. Further, the thrust vector moment is an important portion of total control moment as it enhances the hitting accuracy and also decreases the importance of geometry.

Aerodynamic and Structural Studies of a Flapping Wing in Forward Flight

Flapping flight is commonly seen in nature at low Reynolds numbers. This work investigates the physical aspects of forward flight for flapping unmanned aerial systems. The kinematics discussed in this paper is based on an anticlockwise figure-8-shaped flapping cycle. The evolution of the complex, unsteady vortical flow system that develops during the flapping motion is presented. Mechanisms for generating the lift and thrust are discussed, with emphasis on the unsteadiness of the flow features during both the downstroke and upstroke phases. A one-way fluid–structure interaction has been investigated, and the relative importance of aerodynamic forces is compared with respect to the inertial forces. The inhomogeneity of the wing in terms of mass distribution is studied, and it is shown that a higher density at the wing root is beneficial in respect to the mechanical power required to achieve the forward flight. Limited benefit is observed when higher material density at the leading edge is adopted.

Transition study of 3D aerodynamic configures using improved transport equations modeling

As boundary layer transition plays an important role in aerodynamic drag prediction, the proposal and study of transition prediction methods simulating the complex flow phenomena are prerequisite for aerodynamic design. In this paper, with the application of the linear stability theory based on amplification factor transport transition equations on the two-equation shear stress transport (SST) eddy-viscosity model, a new method, the SST-NTS-NCF model, is yielded. The new amplification factor transport equation for the crossflow instability induced transition is proposed to add to the NTS equation proposed by Coder, which simulates Tollmien–Schlichting wave transition. The turbulent kinetic energy equation is modified by introducing a new source term that simulates the transition process without the intermittency factor equation. Finally, coupled with these two amplification factor transport equations and SST turbulence model, a four-equation transition turbulence model is built. Comparisons between predictions using the new model and wind-tunnel experiments of NACA64(2)A015, NLF(2)-0415 and ONERA-D infinite swept wing and ONERA-M6 swept wing validate the predictive quality of the new SST-NTS-NCF model.

Using adjoint-based optimization to study kinematics and deformation of flapping wings

The study of flapping-wing aerodynamics faces a large control space with different wing kinematics and deformation. The adjoint-based approach, by solving an inverse problem to obtain simultaneously the sensitivity with respect to all control parameters, has a computational cost independent of the number of control parameters and becomes an efficient tool for the study of problems with a large control space. However, the adjoint equation is typically formulated in a fixed fluid domain. In a continuous formulation, a moving boundary or morphing domain results in inconsistency in the definition of an arbitrary perturbation at the boundary, which leads to ambiguousness and difficulty in the adjoint formulation if control parameters are related to boundary changes (e.g. the control of wing kinematics and dynamic deformation). The unsteady mapping function, as a traditional way to deal with moving boundaries, can in principle be a remedy for this situation. However, the derivation is often too complex to be feasible, even for simple problems. Part of the complexity comes from the unnecessary mapping of the interior mesh, while only mapping of the boundary is needed here. Non-cylindrical calculus, on the other hand, provides a boundary mapping and considers the rest of domain as an arbitrary extension from the boundary. Using non-cylindrical calculus to handle moving boundaries makes the derivation of the adjoint formulation much easier and also provides a simpler final formulation. The new adjoint-based optimization approach is validated for accuracy and efficiency by a well-defined case where a rigid plate plunges normally to an incoming flow. Then, the approach is applied for the optimization of drag reduction and propulsive efficiency of first a rigid plate and then a flexible plate which both flap with plunging and pitching motions against an incoming flow. For the rigid plate, the phase delay between pitching and plunging is the control and considered as both a constant (i.e. a single parameter) and a time-varying function (i.e. multiple parameters). The comparison between its arbitrary initial status and the two optimal solutions (with a single parameter or multiple parameters) reveals the mechanism and control strategy to reach the maximum thrust performance or propulsive efficiency. Essentially, the control is trying to benefit from both lift-induced thrust and viscous drag (by reducing it), and the viscous drag plays a dominant role in the optimization of efficiency. For the flexible plate, the control includes the amplitude and phase delay of the pitching motion and the leading eigenmodes to characterize the deformation. It is clear that flexibility brings about substantial improvement in both thrust performance and propulsive efficiency. Finally, the adjoint-based approach is extended to a three-dimensional study of a rectangular plate in hovering motion for lift performance. Both rigid and flexible cases are considered. The adjoint-based algorithm finds an optimal hovering motion with advanced rotation which has a large leading-edge vortex and strong downwash for lift benefit, and the introduction of flexibility enhances the wake capturing mechanism and generates a stronger downwash to push the lift coefficient higher.

Three-dimensional simulation for fast forward flight of a calliope hummingbird

We present a computational study of flapping-wing aerodynamics of a calliope hummingbird (Selasphorus calliope) during fast forward flight. Three-dimensional wing kinematics were incorporated into the model by extracting time-dependent wing position from high-speed videos of the bird flying in a wind tunnel at 8.3 m s−1. The advance ratio, i.e. the ratio between flight speed and average wingtip speed, is around one. An immersed-boundary method was used to simulate flow around the wings and bird body. The result shows that both downstroke and upstroke in a wingbeat cycle produce significant thrust for the bird to overcome drag on the body, and such thrust production comes at price of negative lift induced during upstroke. This feature might be shared with bats, while being distinct from insects and other birds, including closely related swifts.

Obstructive Sleep Apnea Following Pharyngeal Flap Surgery for Velopharyngeal Insufficiency: A Prospective Polysomnographic and Aerodynamic Study in Middle-Aged Adults.

To compare the frequency and severity of obstructive sleep apnea (OSA) in middle-aged adults who underwent pharyngeal flap surgery for velopharyngeal insufficiency (VPI) with matched subjects who did not undergo pharyngeal flap surgery and to verify the relationship between OSA severity and internal pharyngeal dimensions. National referral care center for cleft lip and palate. Prospective study on 42 nonsyndromic subjects with repaired cleft palate with flap (F group, n = 22) and without flap (NF group, n = 20), aged 40 to 58 years. The main outcome measure was the apnea-hypopnea index (AHI), measured by in-lab nocturnal polysomnography (PSG). The OSA-related symptoms were investigated by Pittsburgh, Epworth, and Berlin questionnaires. The nasopharyngeal or velopharyngeal (NP/VP) cross-sectional area was measured by modified anterior rhinomanometry in subgroups of the F (n = 14) and NF (n = 10) groups at rest and during speech. Differences were considered significant at P < .05. Questionnaire scores and frequency of self-reported symptoms of snoring, nasal obstruction, and breathing interruptions during sleep did not differ between groups. OSA was diagnosed by PSG in 60% and 77% of the NF and F subjects, respectively. The difference was not significant. No cases of severe OSA were observed. There was no correlation between AHI and NP/VP area. A significant number of middle-aged adults with repaired cleft palate had OSA and related symptoms, regardless of the presence of a pharyngeal flap. Results suggest that VPI treatment with a flap may not cause sleep-disordered breathing in the cleft population. Besides advancing age, congenital upper airway abnormalities may be involved.

On the presence of voiceless nasalization in apparently effaced Somali Chizigula prenasalized stops

Somali Chizigula (G311; xma; also Mushungulu) is an endangered language spoken in Somalia and by Somali-Bantu refugees abroad. We report on an acoustic and aerodynamic study of N + stop sequences in Somali Chizigula. Our findings illustrate that while the only acoustic cue for the nasal in voiceless prenasalized stops is aspiration of the oral stop, appearing to have undergone total effacement, aerodynamic data show robust nasal airflow prior to the oral stop. Although nasal devoicing is not rare in Bantu languages (e.g., Bura and Bondei; Maddieson and Ladefoged 1993), the lack of acoustic cues during the nasal is. The current state of the devoiced nasal in Somali Chizigula could lead to a reanalysis of effacement as [nt → ntʰ → (n ̥tʰ)→ tʰ]. In addition to providing acoustic and aerodynamic data, we propose an articulatory phonology (Browman and Goldstein 1993) account for the voiceless prenasalized stop as it compares to other nasal + stop sequences in the language.

Conceptual design of a hybrid solar MALE UAV

This study presents the conceptual design of a hybrid solar Medium-Altitude-Long-Endurance Unmanned-Aerial-Vehicle (MALE UAV) designed to perform surveillance-related missions, such as border patrolling, wildfires monitoring, atmospheric data recording, search and rescue missions and telecommunications. For this purpose, a conceptual design methodology was also developed, focusing on the energy management of the aerial platform. Specifically, the presizing calculations are presented, including the methods for estimating weight, aerodynamic and performance parameters. In order to perform a complete aerodynamic study and accurately estimate the aerodynamic coefficients, theoretical analytical methods were employed, along with Computational Fluid Dynamics (CFD) analysis. A refined weight sizing methodology is presented in detail, including a solar power estimation technique, which allows for a balanced selection between fuel amount, panel area and battery size. The conceptualization of the power system, the selection of appropriate solar panels and the sizing of the batteries are also discussed. Finally, the results of the conceptual design procedure are presented and appropriate conclusions are drawn.

Numerical investigations of Fenestron™ noise characteristics using a hybrid method

The present article gives an overview of numerical investigations performed during a research project aimed at in-depth understanding of noise generation mechanisms of a shrouded helicopter tail rotor such as Airbus Helicopters Fenestron $$^\mathrm{TM}$$ . Both aerodynamic and aeroacoustic studies are performed based on a full-scale lightweight transport helicopter configuration with detailed geometry of the Fenestron $$^\mathrm{TM}$$ and by neglecting of the main rotor downwash effect. Analysis is carried out by using a hybrid method, combining Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulation with Ffowcs Williams and Hawkings (FW-H) acoustic analogy. Two representative helicopter flight conditions, namely fast forward flight and hovering, are considered. Thereby, it is intended to assess the influence of cross flow in forward flight condition on the Fenestron $$^\mathrm{TM}$$ acoustic property. Effect of turbulence model on the accuracy of noise prediction is also investigated by comparing the Shear Stress Transport (SST) turbulence model with the Scale Adaptive Simulation (SAS). The capability of the applied hybrid methodology is estimated by means of flight test measurements. A good agreement is found between the predicted and measured sound spectra in terms of blade passing frequency (BPF) and its corresponding sidebands for both flight conditions investigated.

Implementation of an aerodynamic lens for TRIGA-SPEC

We report on the optimization of the gas-jet system employed to couple the TRIGA-SPEC experiment to the research reactor TRIGA Mainz. CdI2 aerosol particles suspended in N2 as carrier gas are used for an effective transport of fission products from neutron induced 235U fission from the target chamber to a surface ion source. Operating conditions of the gas-jet were modified to enable the implementation of an aerodynamic lens, fitting into the limited space available in front of the ion source. The lens boosts the gas-jet efficiency by a factor of 4–10. The characterization of the gas-jet system as well as the design of the aerodynamic lens and efficiency studies are presented and discussed.