Influence of front airfoil leading-edge serrations on turbulence interaction noise characteristics of tandem airfoils at different angles of attack

In the present study a single expansion ramp nozzle (SERN) system is studied with nozzle pressure ratio (NPR) of 2.9. An interaction of subsonic ambient inflow with M∞ of 0.4 which is induced during take-off of a typical hypersonic vehicle with SERN is considered. Different ambient angles of attack of 0°, −5°, −10° and −15° have been studied. Results obtained by numerical computation are validated by available experimental data. A significant amount of separation is developed at the walls (on both ramp and flap) due to shock wave-boundary layer interaction (SWBLI). Due to the ambient inflow at different angles of attack the separation patterns changes from restricted shock separation (RSS) to free shock separation (FSS). This transition happens when angle of attack changes from 0° to −5° at ambient inflow Mach number of 0.4. Due to ambient stream interaction shock wave oscillates and wall pressure distribution on both ramp and flap changes with time for different ambient inflow conditions. This flow field instability is expressed by the distribution of root means square (RMS) value of pressure over ramp and flap. The main purpose of SERN is generation of thrust of hypersonic vehicles. So thrust and thrust vector angle are important parameters of SERN. Thrust and thrust vector angle of SERN is related to separation pattern. This study gives an insight to the flow structure in SERN when there is a strong ambient inflow and can be very beneficial to the design and performance analysis of SERN.In the present study a single expansion ramp nozzle (SERN) system is studied with nozzle pressure ratio (NPR) of 2.9. An interaction of subsonic ambient inflow with M∞ of 0.4 which is induced during take-off of a typical hypersonic vehicle with SERN is considered. Different ambient angles of attack of 0°, −5°, −10° and −15° have been studied. Results obtained by numerical computation are validated by available experimental data. A significant amount of separation is developed at the walls (on both ramp and flap) due to shock wave-boundary layer interaction (SWBLI). Due to the ambient inflow at different angles of attack the separation patterns changes from restricted shock separation (RSS) to free shock separation (FSS). This transition happens when angle of attack changes from 0° to −5° at ambient inflow Mach number of 0.4. Due to ambient stream interaction shock wave oscillates and wall pressure distribution on both ramp and flap changes with time for different ambient inflow conditions. This flow field...

本文根据以往翼身融合体飞机的一些设计经验，设计了一种翼身融合体飞机气动外形，并研究分析了翼身融合体飞机初始模型在不同风速和迎角的情况下的气动特性。利用CATIA生成翼身融合体飞机初始模型，由于考虑到该型飞机的具体尺寸、选用翼型以及制作重量，所以飞机的巡航速度设计为30 m/s，通过风洞实验和FLUENT计算流体力学软件计算得出初始翼身融合体飞机模型的速度云图和压力云图以及初始模型飞机周围流场分布情况，然后根据FLUENT计算流体力学软件得出的初始模型流场分布情况，确定4种在初始模型基础上经过改进的模型，分别为涡流器模型、翼梢小翼模型、鸭翼模型、平尾模型，研究经过改进的4个模型气动特性(包括升力系数，阻力系数，升阻比)随速度和迎角的影响的思路是：建立精确的改进涡流器模型、改进翼梢小翼模型、改进鸭翼模型、改进平尾模型，利用CFD计算流体力学软件计算在不同风速迎角分别从−4˚到14˚下飞机的气动特性，并分析在不同速度和迎角下的飞机的气动特性随迎角的变化规律，为今后翼身融合飞机的安全高效飞行提供理论依据。并对改进的4种模型在不同速度和迎角下的升阻比等气动特性与初始模型进行对比，再根据不同的改进模型在不同飞行状态下所具有的气动特性探讨其改进模型的用途及其发展价值。 This article based on the design experience of wing body fusion aircraft before designed a wing body fusion aircraft aerodynamic shape, and analyzed initial model of the wing fusion aircraft with different wind speed and angle of attack. In the process of research, CATIA was used to generate the initial model of wing body fusion aircraft. Taking into account the specific size of the aircraft, the choice of airfoil and for weight, the cruise speed of the aircraft is designed to be 30 m/s. Through the wind tunnel experiment and FLUENT computational fluid dynamics soft-ware calculations, we can get the initial model of wing fusion aircrafts speed cloud and pressure cloud and the distribution of the surrounding flow field. On the basis of FLUENT computational fluid dynamics software and the distribution of the surrounding flow field, four improved models based on the initial model were identified: Eddy swirl model, wingtip winglet model, canyon model, and flat tail model. This paper researched the aerodynamic performance of the four improved wing-body fusion aircraft models at different angles of attack and wind speed (including lift coefficient, drag coefficient, lift drag ratio). The idea of the impact is to establish an accurate improved swirl model, to improve the wing winglet model, to improve the duck wing model, to improve the flat tail model. The research has used CFD to calculate the aerody-namic characteristics of the airplane at different wind of angles at −4˚ to 14˚, and analyzed the aerodynamic characteristics of the aircraft at different speeds and angles of attack. It can pro-vide a theoretical basis for the safe and efficient flight of the aircraft. This research compared the aerodynamic characteristics of the improved four models with the initial model at different speeds and angles of attack. And then it used the aerodynamic characteristics of different im-proved models under different flight states to explore the use of the improved model and its development value.

The possibility of controlling the aerodynamic characteristics of wing airfoils in transonic regimes of flight using one-sided pulse-periodic energy supply has been studied. The flow structure near the symmetric airfoil at different angles of attack and its aerodynamic characteristics as functions of the value of energy in its nonsymmetric (about the airfoil) supply have been determined by numerical solution of two-dimensional nonstationary gasdynamic equations. A comparison of the obtained results and the data of calculation of flow past the airfoil at different angles of attack without energy supply has been made. It has been established that a prescribed lift can be obtained, using energy supply, with a much higher fineness ratio of the airfoil than that in the case of flow past it at an angle of attack.

The possibility of controlling the aerodynamic characteristics of airfoils in transonic flight regimes by means of one-sided pulsed-periodic energy supply is studied. Based on the numerical solution of two-dimensional unsteady gas-dynamic equations, the change in the flow structure in the vicinity of a symmetric airfoil at different angles of attack and the aerodynamic characteristics of the airfoil as functions of the amount of energy supplied asymmetrically (with respect to the airfoil) are determined. The results obtained are compared with the data calculated for the flow past the airfoil at different angles of attack without energy supply. It is found that a given lift force can be obtained with the use of energy supply at a much better lift-to-drag ratio of the airfoil, as compared to the case of the flow past the airfoil at an angle of attack. The moment characteristics of the airfoil are found.

Experiments are carried out to study flow and heat transfer characteristics over NACA0018 aerofoil when the body approaches the wall of a wind tunnel. Investigations have been done to study the effect of wall proximity due to flow separation around the body at Reynolds number 2.5 × 105, different height ratios and various angles of attack. The static pressure distribution has been measured on upper and lower surfaces of the aerofoil. The results have been presented in the form of pressure coefficient, drag coefficient for different height ratios. Pressure coefficient values are decreased and then increased on the lower surface of the aerofoil and decreased on the upper surface of the aerofoil at all angles of attack. The negative pressure coefficient and drag coefficient decreases as the body approaches the upper wall of wind tunnel. The maximum value of drag coefficient has been observed at an angle of attack 30° for the aerofoil at all height ratios. The Heat transfer experiments have been carried out under constant heat flux condition. Heat transfer coefficients are determined from the measured wall temperature and ambient temperature and presented in the form of Nusselt number. The variation of local as well as average Nusselt number has been shown with non dimensional distance for different angles of attack and for various height ratios. The local as well as average Nusselt number decreases as the height ratio decreases for all non-dimensional distance and angles of attack respectively. Maximum value of average Nusselt number has been observed at an angle of attack 40°.

Flow structures behind a vibrissa-shaped cylinder at different angles of attack: Complication on vortex-induced vibration

Nature-inspired flying robots are beneficial than other multi-rotor or fixed wing analogs, in many aspects. As wings play the key role on the hovering and maneuvering conditions of flying insects, structural functions and aerodynamic performances of the insect wings are needed to be analyzed for designing more effective wings for insect-sized flying robots. This study describes the method for experimental analysis of aerodynamic and vibration characteristics of dragonfly (Erythemis Simplicicollis) forewings and hindwings. Vibration testing of the dragonfly wings has been conducted to obtain natural frequencies and mode shapes of the wings. The wings have also been examined in a suction wind tunnel having pistol-grip sting balance to illustrate the vibration and aerodynamic characteristics. The structural aerodynamic response of the wing has been determined at different freestream velocities and at different angles of attack. From the experimental results, the deformation response and the coefficients of drag and lift of the insect wings have been obtained for different Reynolds numbers and angles of attack. The coefficient of lift of the wings increases with the Reynolds number and angle of attack. The coefficient of drag of the wings also increases with the Reynolds number and angle of attack.

A solar-powered unmanned aerial vehicle generally encounters the problems that it has low Reynolds effects and is highly susceptible to gust response. Therefore, the grid velocity method was used to analyze the gust response characteristics of the airfoil FX63-137 under low Reynolds number. First, the reliability of the numerical simulation method at low Reynolds number and grid velocity method were verified with experimental data. Second, the gust response characteristics of FX63-137 airfoil under different Reynolds numbers and different angles of attack were numerically simulated. The results show that the magnitude of incremental lift coefficient in gust response decreases because laminar separation bubbles are complete as the Reynolds number decreases at a small angle of attack. They also show that laminar separation bubbles have an unloaded effect on gust response. At a high angle of attack, as the airfoil enters into stalling stage, the incremental lift coefficient begins to decline before reaching maximum gust disturbance. Because of the stalling of the airfoil, when the gust disappears, the incremental lift coefficient has a negative value. What's more, although the effective angle of attack is equal, the flow structure of the airfoil is somewhat different in upstream and downstream moments. Compared with the downstream moment, the incremental lift coefficient at the upstream moment is generally larger, and the incremental lift coefficient curve of the airfoil forms a non-closed hysteresis loop.

It is well known that the flutter performance of a section is sensitive to the changing wind angles of attack. Exploring the thin plate’s flutter mechanism under different angles of attack is excellent, which helps understand inner flutter characteristics and ensures structural safety. This study investigated flutter derivatives of a thin plate with an aspect ratio of 40 under different wind angles of attack via the forced vibration technique. The otherness of aerodynamic damping and phase lag under different wind angles, which helps in understanding the flutter mechanism, are analyzed using the bimodal-coupled flutter method. It is shown that coupled vertical–torsional flutter dominated the flutter modality under 0° and 3° wind angles of attack. The critical flutter velocity dramatically decreased with increasing wind angles of attack which is attributed to the increasing negative aerodynamic damping induced by coupled self-excited forces and the decreasing positive aerodynamic damping induced by uncoupled self-excited forces. Moreover, the vertical motion lags behind the torsional motion under the 7° angle of attack, which was totally contrary to other angles of attack. Major works in this study reveal the aerodynamic mechanism of the weakened flutter performance of thin plates under large wind angles of attack and provide a reference for the flutter analysis of thin plates.

The performances of K-ω SST(Shear-Stress Transport) turbulence model and high order low dissipative Flux difference scheme of Roe are evaluated against experimental flow fields at different geometries and angle of attacks at supersonic mach no. The numerical predictions include lift, drag and pitching moment coefficients at different angle of attacks. Most significantly, this research provides a sensitivity study on the accuracy of the solutions with respect to the effects of free stream turbulence, grid resolution, grid spacing near the wall, initial conditions, numerical methods and free stream Mach number effects on compressible flows. Comparison of two geometries, cone cylinder and cone cylinder with fins is provided in order to study the effects on the aerodynamics characteristics by the addition of the lifting surfaces and the same is compared with the available experimental data. For the present study supersonic flow is simulated at Mach number 4 and the angle of attack is varied.

The beam trawl is one of the primary operational trawls for Antarctic krill, and its beam provides horizontal expansion support for the trawl net. The hydrodynamic performance of the beam significantly affects the vertical expansion and sinking performance of the trawl, as well as impacts the energy consumption of the fishing vessel. In this study, the beam of the Antarctic krill trawl used on the “Shen Lan” fishing vessel served as a prototype. Three types of beams, cylindrical, airfoil, and elliptical, were designed. The hydrodynamic performances of beams with different shapes at different angles of attack were studied using numerical simulation, and the accuracy of the numerical simulation was validated through the flume test. The results show that the cylindrical beam has a higher drag coefficient and a lower lift coefficient, compared to the airfoil beam and the elliptical beam. Under different angles of attack, the cylindrical beam’s drag coefficient is, on average, 49.54% higher than that of the airfoil beam and 59.74% higher than that of the elliptical beam. Its lift coefficient is 87.79% lower than that of the airfoil beam and 85.06% lower than that of the elliptical beam, respectively. At different angles of attack, the hydrodynamic coefficients of the airfoil beam and the elliptical beam are similar, and their trends, with respect to the angle of attack, are generally consistent. The drag coefficients increase with an increasing angle of attack, while the lift coefficients show a trend of initially increasing and then decreasing with an increasing angle of attack. The absolute values of the lift coefficients for the airfoil beam and the elliptical beam both reach their maximum values at an angle of attack of 45°, with values of 0.703 and 0.473, respectively. Compared to the cylindrical beam, the hydrodynamic performances of the airfoil beam and elliptical beam are superior.

In the current research, a numerical study of 53 airfoils inspired by the surface scales of the mako-shark skin based on NACA0009 airfoil has been performed. The airflow simulations were performed in different angles of attack from 4° to 11° and the validations are presented in two stages compared with two different studies. The diagrams of [Formula: see text] parameter, shear stress, pressure coefficient, and also the contours of velocity and streamlines are reported. The results of the lift, drag, and diagram of lift to drag ratios have been presented and analyzed for different geometries and angles of attack. The results show that by creating bumps’ pattern taken from the shark skin mounted over the suction side of the airfoils the ratio of lift to drag increases. For example up to 28% increment of average of Cl/Cd in the above mentioned range of angles of attack can be obtained utilizing just one bump with 0.7 mm thickness (0.7% of chord length) mounted at 23% of the chord on suction side.

Turbulent fluid flow and convective heat transfer over the wall mounted cube in different flow angle of attack have been studied numerically using Large Eddy Simulation. Cube faces and plate have a constant heat flux. Dynamic Smagorinsky (DS) subgrid scale model were used in this study. Angles were in the range 0???45 and Reynolds number based on the cube height and free stream velocity was 4200. The numerical simulation results were compared with the experimental data of Nakamura et al [6, 7]. Characteristics of fluid flow field and heat transfer compared for four angles of attack. Flow around the cube was classified to four regimes. Results was represented in the form of time averaged normalized streamwise velocity and Reynolds stress in different positions, temperature contours, local and average Nusselt number over the faces of cube. Local convective heat transfer on cube faces was affected by flow pattern around the cube. The local convective heat transfer from the faces of the cube and plate are directly related to the complex phenomena such as horse shoe vortex, arch vortexes in behind the cube, separation and reattachment. Results show that overall convective heat transfer of cube and mean drag coefficient have maximum and minimum value at ?=0 deg and ?=25 deg respectively.

Tube bundles can be used as a separation heat exchanger in the organic Rankine cycle power plants (ORC), while the hot gas passes over the outer surface, and the working substance ORC flows inside the tubes. A numerical study has been conducted to clarify heat transfer and hydrodynamics of a cross-flow heat exchanger with staggered drop-shaped tubes at different flow angles of attack in comparison with circular tubes of the same equivalent diameter. The study was performed for the Reynolds number Re= 1.8  103 ~ 9.4  103, the longitudinal and transverse spacing of the tubes in the bundle are the same and are equal to 37 mm. Four cases of the tube’s arrangement with different angles of attack were investigated: 0, 45, 135, and 180 angles. The article presents a literature review related to the subject of the study. A mathematical and numerical model has been developed to calculate the heat transfer coefficient of the studied staggered drop-shaped tubes bundle using the ANSYS package, taking into account the stress-strain state of the tubes. Correlations of the average Nusselt numbers and the friction coefficient for the considered bundles in terms of the Reynolds number and angle of attack were presented. The results reveal that the thermal–hydraulic performance of the drop-shaped tubes bundle with zero-angle of attack is about 1.6 ~ 1.7 times greater than the circular one.

Inflatable structures are characterized by being light and easy to manufacture and deploy. Hence, they find many applications in aerospace and aeronautical engineering. In this paper, an inflatable segment with a The National Advisory Committee for Aeronautics (NACA) 0021 airfoil cross-section is designed, fabricated, and tested. The geometrical accuracy of the manufactured inflatable segment is measured using laser scanning. Measurements show that the average normalized error of the chord length and thickness are 2.97% and 0.554%, respectively. The aerodynamic behavior of the inflatable segment is then tested in a wind tunnel at different wind speeds and angles of attack. Lift forces are measured using a six-component balance, while the drag forces are calculated from the wake measurements. The lift and drag coefficients of the inflatable section are compared to those of a standard NACA 0021 airfoil. Finally, flow visualization is examined at different angles of attack using two methods: smoke and tufts. Both methods show that flow separation starts at 15° and full stall occurs at 25°. Results indicate that inflatables can find more applications in the design and construction of aerodynamic structures, such as wings.