Aerodynamic Property Research Articles

Evaluation and Modeling of the Aerodynamic Characteristics of Watermelon Seed of Different Varieties

In this study, the aerodynamic properties of three varieties of watermelon seeds as a function of moisture content were evaluated and modeled. The watermelon seed varieties used were Charleston grey, Kaolack, and Sugar baby, and their moisture content ranged from 8.61 to 24.26, 10.30 to 26.11, and 7.78 to 23.23% wet basis (wb), respectively. The results showed that the terminal velocity of the Charleston grey, Kaolack, and Sugar baby varieties increased from 5.27 to 6.67, 4.40 to 6.23, and 4.00 to 6.60 ms–1, respectively, as the moisture content increased. The Reynolds number of the three watermelon seed varieties increased with the increasing seed moisture content, while the drag coefficient generally decreased as the seed moisture content increased. Analysis of variance showed that the moisture content of the three watermelon seed varieties had significant effects on all the aerodynamics properties (p < 0.05). Mathematical models were developed to relate the moisture content of watermelon seeds with the values of the aerodynamic properties investigated.

A new approach for optimization of Vertical Axis Wind Turbines

A new approach has been developed for the optimization of Vertical Axis Wind Turbines (VAWTs). The approach is derived from double multiple streamtube theory (DMST) and adopts the concept of “Representative streamtube” wherein the entire aerodynamic property of the VAWT is assumed to be represented by a single streamtube occupying a specific azimuthal location. Five input parameters namely; power, wind velocity, aspect ratio, air viscosity and air density and six output parameters that are minimally required for the construction of a straight bladed, constant pitch VAWT are considered in the study. The discrete data of lift and drag coefficients pertaining to specific values of Reynolds number and angle of attack are arranged in the order of decreasing lift to drag ratio and starting with the first set of coefficients, a check is made if it is eligible to become Representative streamtube for the particular problem. The check is done through a tri-directional “Demand Factor” test that seeks the compatibility of Reynolds number and angle of attack values of the aerofoil data under consideration. The first set which gains the eligibility to become “Representative streamtube” marks the solution for the particular problem.

ディンプルパターンの異なるゴルフボール周りの流れの違い

For more than 100 years, manufactures have studied on dimple configurations including dimple arrangement, depth, size, shape, surface occupancy ratio and so forth, but in addition to these traditional approaches, a new scientific approach is expected to improve aerodynamic property further. Nike has been exploring micro roughness concept for several years to improve aerodynamic property. Nike has applied a new dimple technology called “Flightsuit” for their new 2016 golf ball, Nike RZN Tour. The “Flightsuit” consists of 13,558 micro dimples on 344 traditional dimple surface. The difference of flow patterns was investigated by PIV in order to confirm the effectiveness of micro dimples. The results showed the lift inclination pattern in the ball of “Flightsuit.”

Research on motion of wind-driven rain and rain load acting on transmission tower

This study derives the formula of rain load based on the motion state of droplets and the law of conservation of momentum to study the rain load acting on a transmission tower. By simulating the motion of a single raindrop, the phenomenon of that the horizontal velocity of raindrop is larger than the corresponding wind speed is certified and explained, and the fitting formula of the velocity ratio is obtained from simulation results. The specific catch ratio under uniform flow is derived and then extended to the atmospheric boundary layer wind field. The vertical raindrop spectrum is calculated with the specific catch ratios obtained from two different concepts. The formula for calculating rain load is derived based on the law of conservation of momentum, and a methodology for simulating a transmission tower’s response induced by wind and rain loads is presented. When the basic wind speed is 40m/s, the maximum displacement percentages induced by rain loads relative to wind loads can only reach 1.78%. The results indicate that the influence of raindrop impinging force on a tower’s response during extreme weather conditions is not very significant and that more attention should be paid to the influence of rainfall on the aerodynamic property due to the existence of water film on the surface of tower and line.

Evaluation and modeling of aerodynamic properties of mung bean seeds

Abstract Aerodynamic properties of solid materials have long been used to convey and separate seeds and grains during post harvest operations. The objective of this study was the evaluation of the aerodynamic properties of mung bean seeds as a function of moisture content and two grades referred to above and below a cut point of 4.8 mm in length. The results showed that as the moisture content increased from 7.8 to 25% (w.b.), the terminal velocity of seeds increased following a polynomial relationship, from 7.28 to 8.79 and 6.02 to 7.12 m s-1, for grades A and B, respectively. Seeds at grade A had terminal velocities with a mean value of 8.05 m s-1, while at grade B had a mean value of 6.46 m s-1. The Reynolds number of both grades increased linearly with the increase of seeds moisture content, while the drag coefficient decreased with the increase of moisture content. Mathematical relationships were developed to relate the change in seeds moisture content with the obtained values of aerodynamic properties. The analysis of variance showed that moisture content had a significant effect, at 1% probability level, on all the aerodynamics properties of mung beans.

Autopilot Design Method for the Blended Missile Based on Model Predictive Control

This paper develops a novel autopilot design method for blended missiles with aerodynamic control surfaces and lateral jets. Firstly, the nonlinear model of blended missiles is reduced into a piecewise affine (PWA) model according to the aerodynamics properties. Secondly, based on the equivalence between the PWA model and mixed logical dynamical (MLD) model, the MLD model of blended missiles is proposed taking into account the on-off constraints of lateral pulse jets. Thirdly, a hybrid model predictive control (MPC) method is employed to design autopilot. Finally, simulation results under different conditions are presented to show the effectiveness of the proposed method, which demonstrate that control allocation between aerodynamic control surfaces and lateral jets is realized by adjusting the weighting matrix in an index function.

J2340104 スポーツウェア用布地の流体力学特性

J2340104 スポーツウェア用布地の流体力学特性

102 弾性を有する翼の飛行中の空力特性(GS-5 翼・飛翔体周り流れ)

102 弾性を有する翼の飛行中の空力特性(GS-5 翼・飛翔体周り流れ)

The Design of New Mechanism of Birdlike MAV

MAV- Micro Air Vehicle which acts like bird has attracted many studies because of outstanding aerodynamic property. Former studies on birdlike MAV with flapping wing had just focused on the flapping motion, but passed over the change of flapping angular velocity and deformation of wing, therefore lost the good aerodynamic capacity. One new mechanism of the birdlike MAV is designed and studied. The mechanism can bring out 3 motions at one time, including flapping, spanning and twisting, so has movement as bird. The kinematic performance including the flapping angle, flapping angular velocity, and the folding angle etc., has been studied and compared with other relative works. The design can help the birdlike aircraft into reality.

Computer Simulation of the Filling Process of Air Intake Hood Based on ProCAST

The intake hood is the part which riveted in the external skin of the aircraft. During the flight of the aircraft, the engine casing is cooled down by the high-speed airflow which flows through the air intake duct. As the components suffer the impact of the high-speed airflow, the appearance of the intake hood must meet the requirements of the aerodynamic property. At the same time, its manufacturing quality has a certain impact on the aerodynamic performance of the aircraft, so its synthetic mechanical property is required high. The traditional air intake hoods are block-combination welded by the aluminum alloy sheet. Its complicated working procedure, long production cycle, high costs and the difficult weld methods make it difficult to guarantee the welding quality. In order to improve the useful life of the air intake hood, to lower the production difficulty and to solve the quality risks in the production due to the method of weld, in this article, the high-strength aluminum alloy ZL101A and plaster mould investment casting were used to mold the intake hood based on the three-dimensional geometric modeling of the air intake hood by software Pro/E, and then, the filling and solidification process of the air intake hood was simulated by the casting simulation software ProCAST to predict the defects such as misrun, cold shut, wrapped in air, the thermal centre and the residual stress and deformation which were displayed in the filling and the solidification processes of the metal. Then, the casting process of the air intake hood can be optimized to achieve a decrease or avoid casting defects in the actual production.

1016 弾性を有する羽ばたき翼の空力特性に関する研究(GS-5 生物流体)

1016 弾性を有する羽ばたき翼の空力特性に関する研究(GS-5 生物流体)

A Method of Dual Number for the Aerodynamic Property Analysis of Gas-Lubricated Mechanism：Self-Pressurizing Thrust Bearings and Non-Contacting Face Seals

By using dual number, the dynamic property of gas-lubricated thrust bearings or non-contacting face seals is analyzed in the small perturbation approximation, then an essential conclude, that the perturbation dynamic Reynolds’ equations independently of its whirl frequency, is advanced. According to this, the calculation of the stiffness and damping coefficients independently of system motion equations of bearings and seals is expedited.

Bluntness impact on performance of waverider

Waverider serves as a good candidate for hypersonic vehicles, especially for high lift-to-drag ratio aircraft. Restricted by aerodynamic heat and manufacture techniques, the sharp leading edge of waverider needs to be blunted. In order to study the blunt leading edge’s influences on the waverider, computational fluid dynamics tools are used to study the aerodynamic and aero-thermodynamic property of waverider with different blunt radii. The numerical methods are validated by test case and empirical formula. Numerical simulations show that blunting the leading edge could reduce the maximum heat flux effectively, but it also degrades the aerodynamic performances. When the blunt radius increases, the aerodynamic performance degrades significantly, while the heat flux wears off. With a fixed blunt radius, the aerodynamic performance mainly depends on the angle of attack; while the heat flux is less affected by the angle of attack. When designing waverider, the influence of bluntness on aerodynamic force and heat flux should be considered synthetically and the optimal balance point needs to be determined.

Aerodynamic damping properties of two transmission towers estimated by combining several identification methods

Based on full-scale measurement data, we report on several aerodynamic damping properties of two transmission towers under conditions of strong winds. In estimating the damping ratio from data that contain many components of close frequencies of tower and conductor vibrations, we cannot estimate the damping ratio of each component if we use an estimation method available for only a single-degree-of-freedom system. Therefore, we combined several identification methods and are introducing a new method of estimating damping properties. This method is applicable to the response record of a multi-degree-of-freedom system such as the coupled structure of a transmission tower-and-conductors. Using the new estimation procedure, we were able to extract the component of every vibration mode of the towers from a measured time history and estimate the accurate damping ratios individually; and, our results revealed that the wind speed dependency of the aerodynamic damping property of the coupled tower-and-conductors system had wide differing characteristics depending on the vibration mode. Moreover, using a three-dimensional nonlinear analysis, we discuss, in detail, the effects of the progressive deformation of a transmission–conductor–plane due to an increase in wind speed on the development of the aerodynamic damping of the coupled tower-and-conductors system.

Coaxial Rotor Helicopter in Hover Based on Unstructured Dynamic Overset Grids

C OAXIAL rotor configuration is one of the technological solutions for increasing helicopter forward speed, maneuverability, and load-carrying ability. Since two rotors produce the net thrust instead of a single rotor in the conventional design, the diameter of the rotors can be reduced to carry the same amount of weight. Themost attractive feature of a coaxial design is the resulting compactness and safety of the vehicle. Second, the antitorsional moment generated by the two rotors would be canceled due to the opposite rotational directions, and the tail rotor and tail boom can be eliminated, resulting in a smaller and lighter vehicle. Compared to the individual-rotor helicopter, the aerodynamics and flow physics of coaxial rotor helicopter are relatively less studied and understood. The method of slipstream theory was first used to study the coaxial rotor, and then the predicted wake vortex model [1,2], free wake vortex model [3], and vorticity transport model [4,5] were applied to the coaxial rotor analysis. All the methods above carry out some approximations to the rotor, and the detailed flow feature near the blades and blade vortex in the wake cannot be simulated. Recently, the unsteady Navier–Stokes equations were used to simulate the coaxial rotor flows [6–8] to provide a detailed understanding of the flow physics of coaxial rotor. In the present Note, the three-dimensional unsteady Euler equations were solved to simulate the unsteady flows around coaxial rotor helicopter and individual-rotor helicopter in hover based on the unstructured dynamic overset grids. The aerodynamic interaction property of the coaxial rotor helicopter in hover and the effect of fuselage on the unsteady performance were studied.

풍력터빈 토크제어의 특성 고찰

The aerodynamic torque and power caused by the interaction between the wind and blade of wind turbine are highly nonlinear. For this reason, the overall dynamic behaviors of wind turbine have nonlinear characteristics. The aerodynamic nonlinearity also affects properties of torque control for wind turbine. In this paper, the nonlinear aerodynamic property according to the wind speed below rated power and its effects on the torque control system are investigated. Nonlinear parameter representing change of aerodynamic torque with respect to rotor speed is obtained by linearization technique. Effects of this aerodynamic nonlinear parameter on the closed-loop torque system with PI controller for an 1.5 MW wind turbine are presented.

One-Dimensional Multiple-Temperature Gas-Kinetic Bhatnagar-Gross-Krook Scheme for Shock Wave Computation

Accurately computing the inner structure of normal shock waves or oblique shock waves is crucial for many hypersonic applications. As such, it will improve the prediction accuracy of aerodynamics properties and aerothermal effects on hypersonic vehicles and spacecraft during atmospheric entries. Because a shock wave usually has a thickness of a few mean free paths, it is very difficult to accurately compute the detailed nonequilibrium inner structure across a shock wave with a continuum method. This paper reports a gas-kinetic Bhatnagar-Gross-Krook scheme for computations of one-dimensional vibrationally nonequilibrium nitrogen flows through a planar shock wave. The present gas-kinetic Bhatnagar-Gross-Krook scheme solves for the shock structure with multiple temperatures, including two translational temperatures, one rotational temperature, and one vibrational temperature. The salient features of the present gas-kinetic Bhatnagar-Gross-Krook method are multifold. Its applicability covers a wide simulation regime, extending that of continuum flows to the transition flows; it is more computationally efficient in time than the traditional direct simulation Monte Carlo method for shock wave simulation. To provide proper downstream subsonic boundary conditions for very strong shock waves, it is required to determine a proper postshock equilibrium state in which all temperatures have accomplished relaxation processes to a common equilibrium temperature. Analytical expressions of a complete set of generalized Rankine-Hugoniot relations across a planar shock wave are obtained to account for the variant specific heat ratio due to inner energy excitations. Numerical simulation results by the present gas-kinetic Bhatnagar-Gross-Krook scheme and the direct simulation Monte Carlo method are found to be in good agreement.

Single Port 하이브리드 로켓의 고체연료 물질전달수(B Number)를 고려한 연소특성 연구

하이브리드 로켓 고체 연료의 연소율(Burning Rate)을 묘사하는 후퇴율은 연료 유속, 산화제 유속과 더불어 연료길이의 함수로 나타내어지나 일반적으로 가장 영향이 큰 산화제 유속만의 함수로 모델링된다. 그러나 이는 연료가 갖고 있는 고유의 열화학적 특성에 대한 영향이 내포되어 있지 않아 다양한 연료에 대한 공통된 관계를 나타내기 어렵다. 본 연구에서는 고체연료의 열화학적 특성과 연소에 따른 공기역학적 특성이 고려된 물질전달수(B Number)를 도입하여 다양한 연료에 공통으로 사용될 수 있는 연소율 관계식을 제시하고, 물질전달수 내의 공기역학적 특성의 영향을 분석하였다. 물질전달수와 산화제 유속의 함수로 표현된 연소율 식은 고정된 실험 지수항과 상수항으로 PMMA, PP 및 PE의 연소율을 모두 묘사할 수 있었고, 연소율 관계식에서 B Number에 내포된 공기역학적 효과는 미미하였다. Most of burning rate models used in hybrid combustion depend solely on oxidizer flux. But this empirical relation can not represent well the important effect of the thermo-chemical properties of solid fuel and thereby requires different value of empirical exponent and constant for each fuel considered. In this study, a new burning rate correlation was proposed using the mass transfer number(B number) which encompasses the thermochemistry effect of solid fuel and the aerodynamic effect caused by the combustion on the solid fuel surface where the effect of aerodynamic property in the mass transfer number was studied. The PMMA, PP, and PE were chosen as fuel, and gas oxygen as oxidizer. The new empirical burning rate expression depending on both the oxidizer flux and the mass transfer number was able to predict the burning rate of each fuel with just a single exponent value and constant, and it was found that the aerodynamic effect on the blowing effect did show a minor effect on the burning rate correlation.

Investigation of Surface Roughness on Aerodynamics Properties

This paper describes the effects of surface finish models on aerodynamic coefficients for constructed wind-tunnel testing models. Three models were evaluated. These models were fabricated from aluminum 2024-T4 by computer numerical control (CNC) machining. The roughness of surfaces for each model was 6.3, 60, and 150 μm, which was determined by PERTHOMETER2. A wing-body-tail configuration was chosen for the actual study. Testing covered the Mach range of Mach 0.3 to 1.2 at an angle-of-attack range of +6 to +26 deg at zero sideslip and an angle-of-sideslip range of -8 to +8 deg at a 16-deg angle of attack; the coefficients of normal force, axial force, pitching moment, and lift over drag are shown at each of these Mach numbers. Results from this study show that surface finish does have an effect on the aerodynamic characteristics in general; the data differ between the three models by less than 5%. The surface finish does have more effect on the aerodynamic characteristics when the Mach number is decreased and has the most effect on the aerodynamic characteristics of axial force and its derivative coefficients.

スパイク付き飛しょう体の空力特性制御に関する実験研究

Experimental studies on telescopic aerospikes for aerodynamic control are reported in this paper. Parametric study on the aerodynamic characteristics of the aerospike has performed including the effect of spike length L, base diameter of tip cone D, spike translating speed and direction. The Axial force coefficient Ca of the aerospike suddenly increases at L/D=3.0 due to flow mode transition from the separation to the reattachment. Reattachment/separation flow mode transition phenomenon can be applicable to a newly invented aerodynamic control device, which is called air-breathing aerospike. In this paper, verification test results of this air-breathing aerospike are also reported. A small solenoid valve in the body cylinder successfully controls reattachment/separation flow mode transition at the angle of attacks from 0 to 12 degree. The spiked bodies’ Ca varies according to the mode transition. As a result, we can control the aerodynamic property of the spiked body by opening/closing the valves periodically.