Numerical Study on Flight Stability of Fin-Stabilized Shell of Small Length-Diameter Ratio and High Aspect Ratio

2013 ◽  
Vol 341-342 ◽  
pp. 540-545
Author(s):  
Fu Zhang ◽  
Da Yong Xie ◽  
Wen Jun Ruan ◽  
Hao Wang
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Numerical Study ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Static Stability ◽  
Diameter Ratio ◽  
Small Length ◽  
Flight Stability ◽  
Supersonic Viscous Flow

In order to obtain the flight stability of a flip-out tail fin shell of small length-diameter ratio and high aspect ratio, this paper calculates the supersonic viscous flow of the shell with the finite volume method, when the angle of attack exists. The six degree of freedom simulation is carried out with the previous results. The characteristics of the flow field around the shell ,static stability and dynamic stability are analyzed. The results show that lift coefficient can be described by linearity rule. Position of pressure center, which accounts for 10.3% of the total shell length, ranges from 0.3305 to 0.3945m. When initial disturbances are between 5and 9rad/s, maximum attack angle, which is apart from about 20m in the muzzle, is less than 5.5°. The amplitude of the angle of attack attenuates very fast and is close to 0° in 100m away.

scholarly journals Aerodynamic Analysis of Blended Wing Body - Unmanned Aerial Vehicle (BWB-UAV) Equipped with Horizontal Stabilizers

2019 ◽  
Vol 256 ◽  
pp. 02004
Author(s):  
Nornashiha Mohd Saad ◽  
Wirachman Wisnoe ◽  
Rizal Effendy Mohd Nasir ◽  
Zurriati Mohd Ali ◽  
Ehan Sabah Shukri Askari
Keyword(s):  
Unmanned Aerial Vehicle ◽  
Cfd Simulation ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Flight Test ◽  
Longitudinal Direction ◽  
Static Stability ◽  
Pitching Moment ◽  
Aerial Vehicle ◽  
Blended Wing Body

This paper presents an aerodynamic characteristic study in longitudinal direction of UiTM Blended Wing Body-Unmanned Aerial Vehicle Prototype (BWB-UAV Prototype) equipped with horizontal stabilizers. Flight tests have been conducted and as the result, BWB experienced overturning condition at certain angle of attack. Horizontal stabilizer was added at different location and size to overcome the issue during the flight test. Therefore, Computational Fluid Dynamics (CFD) analysis is performed at different configuration of horizontal stabilizer using Spalart - Allmaras as a turbulence model. CFD simulation of the aircraft is conducted at Mach number 0.06 or v = 20 m/s at various angle of attack, α. The data of lift coefficient (CL), drag coefficient (CD), and pitching moment coefficient (CM) is obtained from the simulations. The data is represented in curves against angle of attack to measure the performance of BWB prototype with horizontal stabilizer. From the simulation, configuration with far distance and large horizontal stabilizer gives steeper negative pitching moment slope indicating better static stability of the aircraft.

scholarly journals An Experimental Analysis on the Effects of Stagger on the Aerodynamic Forces of Tandem Wings

AVIA ◽  
2021 ◽  
Vol 2 (2) ◽  
Author(s):  
Y Parlindungan ◽  
S Tobing
Keyword(s):  
Experimental Analysis ◽  
Numerical Study ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Aerodynamic Performance ◽  
Open Loop ◽  
Aerodynamic Forces ◽  
Subsonic Wind Tunnel ◽  
Lift And Drag ◽  
Naca 0012

This study is inspired by the flapping motion of natural flyers: insects. Many insects have two pairs of wings referred as tandem wings. Literature review indicates that the effects of tandem wing are influenced by parameters such as stagger (the stream-wise distance between the aerodynamic center of the front and the rear airfoil), angle-of-attack and flow velocity. As a first stage, this study focuses on the effects of stagger (St) on the aerodynamic performance of tandem wings. A recent numerical study of stagger on tandem airfoils in turbulent flow (Re = 6000000) concluded that a larger stagger resulted in a decrease in lift force, and an increase in drag force. However, for laminar flow (Re = 2000), increasing the stagger was not found to be detrimental for aerodynamic performance. Another work also revealed that the maximum lift coefficient for a tandem configuration decreased with increasing stagger. The focus of this study is to perform an experimental analysis of tandem two-dimensional (2D) NACA 0012 airfoils. The two airfoils are set at the same angle-of-attack of 0° to 15° with 5° interval and three variations of stagger: 1c, 1.5c and 2c. The experiments are conducted using an open-loop-subsonic wind tunnel at a Reynolds number of 170000. The effects of St on the aerodynamic forces (lift and drag) are analyzed

Free Convective Flow in a Two Enclosure Arrangement With a High Aspect Ratio Side Enclosure Joined to a Large Square Enclosure

2000 ◽  
Author(s):  
Patrick H. Oosthuizen
Keyword(s):  
Nusselt Number ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Convective Flow ◽  
Numerical Study ◽  
Vertical Wall ◽  
Heated Wall ◽  
Free Convective Flow ◽  
Square Enclosure

Abstract A numerical study of free convective flow in a vertical joined two-enclosure arrangement has been undertaken. In this arrangement, a vertical heated wall kept at a uniform high temperature is contained in a high aspect ratio rectangular side enclosure. This enclosure is separated from a larger square enclosure by a vertical dividing wall which is impermeable but offers no resistance to heat transfer. The vertical wall of the main flow enclosure opposite to the dividing wall is maintained at a uniform lower temperature. All remaining walls in both enclosures are adiabatic. The situation considered is an approximate model of a window exposed to a hot outside environment and covered by a plane blind which in turn is exposed to cooled room. The flow has been assumed to be laminar and two-dimensional and results have been obtained for a Prandtl number of 0.7. The effects of Rayleigh number and the dimensionless width of the side enclosure on the Nusselt number have been investigated. The results show that there is a minimum in the Nusselt number variation with side enclosure width for a fixed Rayleigh number. The effect of Rayleigh number on the conditions under which this minimum occurs and on the value of the minimum Nusselt number has been investigated.

scholarly journals Power reduction and the radial limit of stall delay in revolving wings of different aspect ratio

2015 ◽  
Vol 12 (105) ◽  
pp. 20150051 ◽  
Author(s):  
Jan W. Kruyt ◽  
GertJan F. van Heijst ◽  
Douglas L. Altshuler ◽  
David Lentink
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Angle Of Attack ◽  
Radial Distance ◽  
Leading Edge ◽  
High Angle ◽  
High Angle Of Attack ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Low Aspect Ratio Wings

Airplanes and helicopters use high aspect ratio wings to reduce the power required to fly, but must operate at low angle of attack to prevent flow separation and stall. Animals capable of slow sustained flight, such as hummingbirds, have low aspect ratio wings and flap their wings at high angle of attack without stalling. Instead, they generate an attached vortex along the leading edge of the wing that elevates lift. Previous studies have demonstrated that this vortex and high lift can be reproduced by revolving the animal wing at the same angle of attack. How do flapping and revolving animal wings delay stall and reduce power? It has been hypothesized that stall delay derives from having a short radial distance between the shoulder joint and wing tip, measured in chord lengths. This non-dimensional measure of wing length represents the relative magnitude of inertial forces versus rotational accelerations operating in the boundary layer of revolving and flapping wings. Here we show for a suite of aspect ratios, which represent both animal and aircraft wings, that the attachment of the leading edge vortex on a revolving wing is determined by wing aspect ratio, defined with respect to the centre of revolution. At high angle of attack, the vortex remains attached when the local radius is shorter than four chord lengths and separates outboard on higher aspect ratio wings. This radial stall limit explains why revolving high aspect ratio wings (of helicopters) require less power compared with low aspect ratio wings (of hummingbirds) at low angle of attack and vice versa at high angle of attack.

Numerical Simulation of Thermal Performance of a High Aspect Ratio Thermal Energy Storage Device

2012 ◽  
Author(s):  
Jingde Zhao ◽  
Jorge L. Alvarado ◽  
Ehsan M. Languri ◽  
Chao Wang
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Energy Storage ◽  
Aspect Ratio ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
High Aspect Ratio ◽  
Numerical Study ◽  
Experimental Results ◽  
Heat Transfer Analysis

Heat transfer analysis of a high aspect ratio thermal energy storage (TES) device was carried out numerically. The three dimensional numerical study was performed to understand the heat transfer enhancement which results from internal natural convection in a high aspect ratio vertical unit. Octadecane was used as phase change material (PCM) inside TES system, which consisted of six corrugated panels filled with PCM. Each panel had a total of 6 tall cavities filled with PCM, which were exposed to external flow in a concentric TES system. Unlike traditional concentric-type TES devices where heat transfer by conduction is the dominant heat transport mechanism, the high aspect ratio TES configuration used in the study helped promote density-gradient based internal convection mechanism. The numerical model was solved based on the finite volume method, which captured the whole transient heat transfer process effectively. The time-dependent temperature profiles of the PCM inside a single TES panel are compared with the experimental results for two cases. Numerical and experimental results of the two cases showed a reasonable agreement. Furthermore, convection cells were formed and sustained when the PCM melted within the space between the solid core and the walls. The promising results of this numerical study illustrate the importance of internal natural convection on the speed of the PCM melting (charging) process.

scholarly journals Numerical and experimental investigation of the flow separation over NREL's S822 aerofoil and its control by suction and blowing

2021 ◽  
Vol 6 ◽  
pp. 5
Author(s):  
Nazar Aldabash‎‎ ◽  
Andrew Wandel‎ ◽  
Abdul Salam Darwish‎ ◽  
Jayantha Epaarachchi‎
Keyword(s):  
Experimental Investigation ◽  
Wind Turbine ◽  
Flow Separation ◽  
Numerical Study ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Volumetric Flow Rate ◽  
Aerodynamic Characteristics ◽  
Careful Selection ◽  
Suction And Blowing

In this study, a numerical and experimental investigation for the flow separation over 170 mm chord, the NREL S822 aerofoil low Reynolds number wind turbine blade aerofoil section has been investigated at 15.8 m/s wind speed using suction and blowing techniques for the locations between 0.15 and 0.41 of the chord to improve aerodynamic characteristics of a wind turbine rotor blade. In a numerical study, two-dimensional aerofoil (i.e. NREL S822), using Shear Stress Transport (SST (γ − Reθ)) turbulence model, is presented. Careful selection for the number of mesh was considered through an iterative process to achieve the optimum mesh number resulted in optimum values for the ratio of lift to drag coefficients (CL/CD). Values of the lift coefficient, drag coefficient, and separation location were investigated at an angle of attack 18°. Flow separation is monitored and predicted within the numerical results at the tested angles, which has been compared with the experimental results and should a fair agreement. The results revealed that the aerodynamic characteristics of NERL S822 aerofoil would be improved using the suction technique more than the suction and blowing techniques and there is a delay of flow separation with the increase of blowing or suction volumetric flow rate. Using these two techniques and careful selection of the mesh numbers with the right angle of attack can improve the aerofoil characteristics and therefore lead to improve the turbine performance characteristics.

Hydrodynamical Analysis on the Arrow

2014 ◽  
Vol 644-650 ◽  
pp. 527-530
Author(s):  
Ji He Zhou ◽  
Xiao An Long
Keyword(s):  
Lift Force ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Wind Tunnel Test ◽  
Static Stability ◽  
The State ◽  
Pitching Moment ◽  
Moment Coefficient ◽  
Attached Flow ◽  
Main Components

The water tunnel and wind tunnel test carried on the arrow aims to have a better understanding of the hydrodynamics performance of arrows and to improve the technical knowledge of the archery movement Through the experimental research, we can draw conclusions as follows: within the range of angle of attack ( -6°---6°), the arrow can keep the state of attached flow: The state of flow of the arrow with spiral plastic pinna is better than that of arrow with straight one; Within the experimental angle of attack, the lift coefficient Cy will become larger with the pitching moment coefficient Mz getting smaller with the increase of the angle of attack. The arrow has the vertical static stability; with or without arrow feather will have great impact on lift force Y and pitching moment coefficient Mz; the feather rolling will have some impact on lift coefficient Cy, The arrow feather is the main components to produce lift force Y and to give the arrow body relatively great static stability.

scholarly journals Longitudinal Aerodynamic and Stability Characteristics of High-Aspect-Ratio Unmanned Aerial Vehicles in Gust Response

2019 ◽  
Author(s):  
Junli Wang ◽  
Wensheng Zhang ◽  
Bolin Feng ◽  
Zhigui Ren ◽  
Qinghe Zhao
Keyword(s):  
Numerical Simulation ◽  
Aspect Ratio ◽  
Unmanned Aerial Vehicles ◽  
High Aspect Ratio ◽  
Stability Margin ◽  
Simulation Method ◽  
Static Stability ◽  
Aerial Vehicles ◽  
Numerical Simulation Method ◽  
Gust Response

The aim of this work is to propose an accurate and reliable numerical simulation method of gust response, so as to analyze longitudinal stability characteristics of high-aspect-ratio unmanned aerial vehicles (UAVs) under gust response. Based on the dual-time stepping method, the unsteady Navies-Stokes equation was solved. By introducing grid velocity to study the effects of gust, the numerical simulation of gust response was realized. Moreover, the numerical simulation method was verified to be accurate by using the theoretical value and reference value obtained in previous research. The calculation results of the high-aspect-ratio UAV under the 1-cos gust reveal that longitudinal aerodynamic forces of high-aspect-ratio UAVs changed. In the whole range of gust gradient length, the UAVs were always in the state of static stability. However, with the increase of gust velocity, static stability margin decreased. The numerical simulation method of gusts established in this study preferably overcomes the possible numerical oscillations and divergence problems caused by excessive gust velocity. The analysis on longitudinal static stability and stability margin of high-aspect-ratio UAVs under the effects of gusts can ensure flight quality and safety of UAVs under the effects of gusts.

Natural Convection in Vertical Annuli: A Numerical Study for Constant Heat Flux on the Inner Wall

1989 ◽  
Vol 111 (4) ◽  
pp. 909-915 ◽  
Author(s):  
J. A. Khan ◽  
R. Kumar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Natural Convection ◽  
Aspect Ratio ◽  
Numerical Study ◽  
Outer Cylinder ◽  
Diameter Ratio ◽  
Uniform Heat Flux ◽  
Inner Diameter ◽  
Vertical Annuli

A numerical investigation has been conducted to evaluate the effects of diameter ratio and aspect ratio in natural convection of gases within vertical annuli. The inner cylinder is maintained at uniform heat flux and the outer cylinder at constant temperature. The horizontal top and bottom walls are insulated. Detailed results of heat transfer rate, temperature, and velocity fields have been obtained for 1 ≤ κ ≤ 15, 1 ≤ A ≤ 10, and 100 < RaL* < 107. The inner wall temperature is a function of diameter ratio and aspect ratio. The heat transfer results have been compared with those for isothermal heating, and have been found to be higher. The inner diameter is seen to be the appropriate length scale for high Rayleigh number flows and/or high radius ratios, and the radius ratio effect on heat transfer is seen to be insignificant for radius ratios greater than 10. The heat transfer results based on the inner diameter are in very good agreement with published experimental results, although these experiments were conducted for very high aspect ratio. Heat transfer correlations are provided.

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