Some initial results with an air bearing wind tunnel force balance

There is an obvious aerodynamic interference problem that occurs for a quad tilt rotor in near-ground hovering or in the conversion operating condition. This paper presents an aerodynamic interference test of the quad tilt rotor in a wind tunnel. A 1:35 scale model of the quad tilt rotor is used in this test. To substitute for the ground, a moveable platform is designed in a low-speed open-loop wind tunnel to simulate different flight altitudes of the quad tilt rotor in hovering or forward flight. A rod six-component force balance is used to measure the loads on the aircraft, and the flow field below the airframe is captured using particle image velocimetry. The experimental results show that the ground effect is significant when the hover height above the ground is less than the rotor diameter of the quad tilt rotor aircraft, and the maximum upload of the airframe is approximately 12% of the total vertical thrust with the appearance of obvious fountain flow. During the conversion operating condition, the upload of the airframe is reduced compared with that in the hovering state, which is affected by rotor wake and incoming flow. The aerodynamic interference test results of the quad tilt rotor aircraft have important reference value in power system selection, control system design, and carrying capacity improvement with the advantage of ground effect.

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A Wind Tunnel Study on the Shape, Oscillation, and Internal Circulation of Large Raindrops with Sizes between 2.5 and 7.5 mm

Journal of the Atmospheric Sciences ◽

10.1175/2008jas2777.1 ◽

2009 ◽

Vol 66 (3) ◽

pp. 755-765 ◽

Cited By ~ 45

Author(s):

Miklós Szakáll ◽

Karoline Diehl ◽

Subir K. Mitra ◽

Stephan Borrmann

Keyword(s):

Wind Tunnel ◽

Oscillation Frequency ◽

Force Balance ◽

Equivalent Diameter ◽

Drop Diameter ◽

Detailed Knowledge ◽

Shape Parameters ◽

Internal Circulation ◽

Frequency Method ◽

Axis Ratio

Abstract Precipitation prediction using weather radars requires detailed knowledge of the shape parameters of raindrops falling at their terminal velocities in air. Because the raindrops undergo oscillation, the most important shape parameters from the radar prediction point of view are the equilibrium drop shape, the time-averaged axis ratio, and the oscillation frequency. These parameters for individual water drops with equivalent diameter from 2.5 to 7.5 mm were investigated in a vertical wind tunnel using high-speed video imaging. A very good agreement was found between the measured and the theoretically determined raindrop shape calculated by a force balance model. A new method was developed to determine the equivalent drop diameter with the help of the oscillation frequency. The drop size determination by means of the frequency method was found to be three times more precise than by volumetric methods. The time-averaged axis ratio was found to be equal to the equilibrium axis ratio in the investigated raindrop size range. The analysis of the oscillation frequency of the raindrops revealed that the drops undergo multimode oscillations and are oscillating in a transverse mode in addition to an axisymmetric oblate–prolate mode. Experiments are included in which the internal circulation associated with drop oscillation was investigated and compared to theory.

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Wind-resistant structural optimization of supertall buildings based on high-frequency force balance wind tunnel experiment

Engineering Structures ◽

10.1016/j.engstruct.2021.113247 ◽

2021 ◽

Vol 248 ◽

pp. 113247

Author(s):

An Xu ◽

Haidong Lin ◽

Jiyang Fu ◽

Weixing Sun

Keyword(s):

Wind Tunnel ◽

Structural Optimization ◽

High Frequency ◽

Wind Tunnel Experiment ◽

Force Balance

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The influence of the flow separation bubble and transition location on the profile drag of three 4-digit NACA aerofoil profiles

Wind Engineering ◽

10.1177/0309524x211055055 ◽

2021 ◽

pp. 0309524X2110550

Author(s):

Moutaz Elgammi ◽

Tonio Sant ◽

Atiyah Abdulmajid Ateeah

Keyword(s):

Wind Tunnel ◽

Flow Separation ◽

Separation Bubble ◽

Reynolds Numbers ◽

Force Balance ◽

Navier Stokes ◽

Separation Mechanism ◽

Numerical Work ◽

Low Reynolds Numbers ◽

Low Reynolds

Modeling of the flow over aerofoil profiles at low Reynolds numbers is difficult due to the complex physics associated with the laminar flow separation mechanism. Two major problems arise in the estimation of profile drag: (1) the drag force at low Reynolds numbers is extremely small to be measured in a wind tunnel by force balance techniques, (2) the profile drag is usually calculated by pressure integration, hence the skin friction component of drag is excluded. In the present work, three different 4-digit NACA aerofoils are investigated. Measurements are conducted in an open-ended subsonic wind tunnel, while numerical work is performed by time Reynolds-averaged Navier Stokes (RANS) coupled with the laminar-kinetic-energy ( K-kl-w) turbulence model. The influence of the flow separation bubbles and transition locations on the profile drag is discussed and addressed. This paper gives important insights into importance of measurements at low Reynolds numbers for better aerodynamic loads predictions.

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Experimental study of wind load on tree using scaled fractal tree model

International Journal of Modern Physics B ◽

10.1142/s0217979220400871 ◽

2020 ◽

Vol 34 (14n16) ◽

pp. 2040087 ◽

Cited By ~ 1

Author(s):

Woei Leong Chan ◽

Yongdong Cui ◽

Siddharth Sunil Jadhav ◽

Boo Cheong Khoo ◽

Heow Pueh Lee ◽

...

Keyword(s):

Wind Tunnel ◽

Drag Coefficient ◽

Landscape Planning ◽

Reynolds Shear Stress ◽

Wind Load ◽

Force Balance ◽

Particle Image Velocimetry System ◽

Tree Model ◽

Daunting Task ◽

Species Specific

Green urbanism has stimulated more research on the aerodynamics of tree in recent years. The insight gained in studying wind load on trees would mitigate risk of tree falling and enable sustainable landscape planning. However, deciphering the effect of wind on trees is a daunting task because trees come in various species, shapes and sizes. In this study, we aim at conducting wind tunnel tests on various species of trees, including measuring the respective drag coefficient and turbulent flow field using a force balance and particle image velocimetry system. The wind tunnel experiment is conducted using scaled down fractal tree model at 10 and 15 m/s. The 3D-printed tree model is grown based on the data collected on the species-specific tree parameters, such as the height, trunk diameters, crown box dimensions, etc. In this paper, the wind tunnel result of Yellow Flame (Peltophorum pterocarpum) is presented. Results show that the drag coefficient for this inflexible tree model is not sensitive to wind speed. The Reynolds shear stress and turbulence kinetic energy are observed to be the largest at the top and bottom of the crown where the velocity gradients are the highest.

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Evaluation of Cryogenic Force Balance Calibration Methodologies Relative to Wind Tunnel Results

Journal of Aircraft ◽

10.2514/1.c035211 ◽

2019 ◽

Vol 56 (4) ◽

pp. 1398-1406

Author(s):

Devin E. Burns ◽

Kenneth G. Toro ◽

Peter A. Parker ◽

S. Melissa Rivers ◽

Harald Quix ◽

...

Keyword(s):

Wind Tunnel ◽

Force Balance ◽

Balance Calibration

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On the Penetrator Nose Drag Measurements

ASME 2010 Pressure Vessels and Piping Conference: Volume 4 ◽

10.1115/pvp2010-25074 ◽

2010 ◽

Author(s):

Joseph P. Holland ◽

Yesenia Tanner ◽

Phillip A. Schinetsky ◽

Semih Olcmen ◽

Stanley Jones

Keyword(s):

Wind Tunnel ◽

Power Series ◽

Viscous Fluid ◽

Drag Coefficient ◽

Aerodynamic Drag ◽

Terminal Velocity ◽

Force Balance ◽

Supersonic Wind Tunnel ◽

Buoyant Force ◽

Nose Shape

In the current study, a rigid body penetrator nose shape that is optimized for minimum penetration drag [1] has been tested to determine the aerodynamic drag of such a penetrator in comparison to three additional nose shapes. Other nose shapes tested were an ogive cylinder, a 3/4 power series nose, and a standard cone. Fineness ratio for the studied nose geometries was chosen as l/d = 1 to maximize variation of the aerodynamic drag forces acting on the nose shapes. This paper discusses the measurements carried out in the University of Alabama’s 6″ × 6″ supersonic wind tunnel, using a 4 component force balance system. In separate experiments, drop tests were made in a viscous fluid to determine the skin-friction effects on these nose shapes. Supersonic wind-tunnel experiments were performed on each of the nose shapes at nine different Mach numbers ranging from 2 to 3.65. Results show that the nose shape optimized for penetration has the lowest drag coefficient of all the shapes at each Mach number within an uncertainty of 5.75%. In the viscous flow drop-test experiments, each nose shape was dropped from rest through water and then separately through viscous fluid (Nu-Calgon vacuum pump oil) under freefall conditions. Each drop was recorded via videotape, and the video was then analyzed to find the terminal velocity of each individual nose shape. Using classical dynamics equations, the weight, buoyant force, and experimentally determined terminal velocity are used to determine the drag force applied to each nose cone shape. Results indicate that while the optimal shape has a lesser drag coefficient than tangent ogive and the cone, the 3/4 power series shape is observed to have the least drag coefficient. In addition to the experiments performed, results on further investigation of the optimal nose shape for penetration are presented. The nose shape has been split into a series of line segments, and a program written has been utilized to search through numerical space for the combination of line segment slopes that produces the nose geometry with the lowest nose shape factor. The results of the numerical analysis in this study point to a different nose shape than the “optimal nose” shape tested in the current study.

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