On the Penetrator Nose Drag Measurements

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.

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

2020 ◽  
Vol 34 (14n16) ◽  
pp. 2040087 ◽  
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.

scholarly journals A wind-tunnel case study: Increasing road cycling velocity by adopting an aerodynamically improved sprint position

2019 ◽  
pp. 175433711986696
Author(s):  
Timothy Crouch ◽  
Paolo Menaspà ◽  
Nathan Barry ◽  
Nicholas Brown ◽  
Mark C Thompson ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Drag Coefficient ◽  
Aerodynamic Drag ◽  
Time Trial ◽  
Force Measurements ◽  
Sampling Errors ◽  
Repeated Testing ◽  
Road Cycling ◽  
Wind Tunnel Study

The main aim of this study was to evaluate the potential to reduce the aerodynamic drag by studying road sprint cyclists’ positions. A male and a female professional road cyclist participated in this wind-tunnel study. Aerodynamic drag measurements are presented for a total of five out-of-seat sprinting positions for each of the athletes under representative competition conditions. The largest reduction in aerodynamic drag measured for each athlete relative to their standard sprinting positions varied between 17% and 27%. The majority of this reduction in aerodynamic drag could be accounted for by changes in the athlete’s projected frontal area. The largest variation in repeat drag coefficient area measurements of out-of-seat sprint positions was 5%, significantly higher than the typical <0.5% observed for repeated testing of time-trial cycling positions. The majority of variation in repeated drag coefficient area measurements was attributed to reproducibility of position and sampling errors associated with time-averaged force measurements of large fluctuating forces.

Videogrammetry of the Model’s Attitude in Wind Tunnel Testing

2012 ◽  
Vol 190-191 ◽  
pp. 1273-1277 ◽  
Author(s):  
Zheng Yu Zhang ◽  
Zhong Xiang Sun ◽  
Xu Hui Huang ◽  
Yan Sun
Keyword(s):  
Standard Deviation ◽  
Wind Tunnel ◽  
Drag Coefficient ◽  
Systematic Error ◽  
Measurement System ◽  
High Speed ◽  
Wind Tunnel Test ◽  
Wind Tunnel Testing ◽  
Supersonic Wind Tunnel ◽  
Tunnel Testing

The advanced precision of drag coefficient is 0.0001 for the high speed wind tunnel test of measuring forces, the model’s angle of attack precision is ≤0.01°following errors distribution. A videogrammetric method of model’s attitude is therefore proposed, its uncertainty is investigated, and a compensation method of its systematic error is also presented by this paper. The three engineering videogrammetric experiments of attack angle in 2 meter supersonic wind tunnel testing have demonstrated that measuring standard deviation of videogrammetric measurement system established by this paper is ≤0.0094°, in addition it neither destroys the model’s shape, nor changes the stiffness or strength, so it is useful and effective.

Experimental Model of the Aerodynamic Drag Coefficient in Alpine Skiing

2004 ◽  
Vol 20 (2) ◽  
pp. 167-176 ◽  
Author(s):  
Caroline Barelle ◽  
Anne Ruby ◽  
Michel Tavernier
Keyword(s):  
Wind Tunnel ◽  
Drag Coefficient ◽  
Experimental Model ◽  
Aerodynamic Drag ◽  
Aerodynamic Force ◽  
Alpine Skiing ◽  
Aerodynamic Properties ◽  
Speed Performance ◽  
Aerodynamic Drag Coefficient ◽  
The Impact

Aerodynamic properties are one of the factors that determine speed performance in Alpine skiing. Many studies have examined the consequences of this factor in downhill skiing, and the impact of postural modifications on speed is now well established. To date, only wind tunnel tests have enabled one to measure aerodynamic drag values (a major component of the aerodynamic force in Alpine skiing). Yet such tests are incompatible with the constraints of a regular and accurate follow-up of training programs. The present study proposes an experimental model that permits one to determine a skier's aerodynamic drag coefficient (SCx) based on posture. Experimental SCx measurements made in a wind tunnel are matched with the skier's postural parameters. The accuracy of the model was determined by comparing calculated drag values with measurements observed in a wind tunnel for different postures. For postures corresponding to an optimal aerodynamic penetration (speed position), the uncertainty was 13%. Although this model does not permit an accurate comparison between two skiers, it does satisfactorily account for variations observed in the aerodynamic drag of the same skier in different postures. During Alpine ski training sessions and races, this model may help coaches assess the gain or loss in time induced by modifications in aerodynamic drag corresponding to different postures. It may also be used in other sports to help determine whether the aerodynamic force has a significant impact on performance.

Gliding flight: drag and torque of a hawk and a falcon with straight and turned heads, and a lower value for the parasite drag coefficient

2000 ◽  
Vol 203 (24) ◽  
pp. 3733-3744 ◽  
Author(s):  
V.A. Tucker
Keyword(s):  
Wind Tunnel ◽  
Mathematical Models ◽  
Drag Coefficient ◽  
High Speed ◽  
Aerodynamic Drag ◽  
The Body ◽  
Head Turning ◽  
Drag Coefficients ◽  
Spiral Path ◽  
Gliding Flight

Raptors - falcons, hawks and eagles in this study - such as peregrine falcons (Falco peregrinus) that attack distant prey from high-speed dives face a paradox. Anatomical and behavioral measurements show that raptors of many species must turn their heads approximately 40 degrees to one side to see the prey straight ahead with maximum visual acuity, yet turning the head would presumably slow their diving speed by increasing aerodynamic drag. This paper investigates the aerodynamic drag part of this paradox by measuring the drag and torque on wingless model bodies of a peregrine falcon and a red-tailed hawk (Buteo jamaicensis) with straight and turned heads in a wind tunnel at a speed of 11.7 m s(−)(1). With a turned head, drag increased more than 50 %, and torque developed that tended to yaw the model towards the direction in which the head pointed. Mathematical models for the drag required to prevent yawing showed that the total drag could plausibly more than double with head-turning. Thus, the presumption about increased drag in the paradox is correct. The relationships between drag, head angle and torque developed here are prerequisites to the explanation of how a raptor could avoid the paradox by holding its head straight and flying along a spiral path that keeps its line of sight for maximum acuity pointed sideways at the prey. Although the spiral path to the prey is longer than the straight path, the raptor's higher speed can theoretically compensate for the difference in distances; and wild peregrines do indeed approach prey by flying along curved paths that resemble spirals. In addition to providing data that explain the paradox, this paper reports the lowest drag coefficients yet measured for raptor bodies (0.11 for the peregrine and 0.12 for the red-tailed hawk) when the body models with straight heads were set to pitch and yaw angles for minimum drag. These values are markedly lower than value of the parasite drag coefficient (C(D,par)) of 0.18 previously used for calculating the gliding performance of a peregrine. The accuracy with which drag coefficients measured on wingless bird bodies in a wind tunnel represent the C(D,par) of a living bird is unknown. Another method for determining C(D,par) selects values that improve the fit between speeds predicted by mathematical models and those observed in living birds. This method yields lower values for C(D,par) (0.05-0.07) than wind tunnel measurements, and the present study suggests a value of 0.1 for raptors as a compromise.

scholarly journals Experimental investigation of aerodynamic characteristics of bat carcasses after collision with a wind turbine

2020 ◽  
Vol 5 (2) ◽  
pp. 745-758 ◽  
Author(s):  
Shivendra Prakash ◽  
Corey D. Markfort
Keyword(s):  
Drag Coefficient ◽  
Wind Turbine ◽  
High Speed ◽  
Wind Farm ◽  
Aerodynamic Drag ◽  
Turbine Blades ◽  
Terminal Velocity ◽  
Maximum Distance ◽  
Series Data ◽  
Measured Velocity

Abstract. A large number of bat fatalities have been reported in wind energy facilities in different regions globally. Wind farm operators are required to monitor bat fatalities by conducting carcass surveys at wind farms. A previous study implemented the ballistics model to characterize the carcass fall zone distributions after a bat is struck by turbine blades. The ballistics model considers the aerodynamic drag force term, which is dependent upon the carcass drag coefficient. The bat carcass drag coefficient is highly uncertain; no measurement of it is available. This paper introduces a methodology for bat carcass drag coefficient estimation. Field investigation at Macksburg wind farm resulted in the discovery of three bat species: the hoary bat (Lasiurus cinereus), eastern red bat (Lasiurus borealis), and evening bat (Nycticeius humeralis). Carcass drop experiments were performed from a dropping platform at finite height, and carcass position time series data were recorded using a high-speed camera. Falling carcasses were subjected to aerodynamic drag and gravitational forces. Carcasses were observed to undergo rotation, often rotating around multiple axes simultaneously, as well as lateral translation. The complex fall dynamics, along with drop from a limited height, prohibit the carcasses from attaining terminal velocity. Under this limitation, the drag coefficient is estimated by fitting a ballistics model to the measured velocity. Multivariable optimization was performed to fit the ballistics model to the measured velocity resulting, in an optimized estimate of the drag coefficient. A sensitivity analysis demonstrated significant variation in the drag coefficient with a small change in initial position, highlighting the chaotic nature of carcass fall dynamics. Based on the limited sample, the bat carcass drag coefficient and terminal velocity were found to be between 0.70–1.23 and 6.63–17.57 m s−1, respectively. The maximum distance carcasses are predicted to fall after impact with a typical utility-scale onshore wind turbine was computed using a 2-D ballistics model. Based on the range of drag coefficients found in this study, hoary and evening bats are estimated to fall within the rotor plane up to a maximum distance of 92 and 62 m, respectively, from the wind turbine tower. The ballistics model of carcasses after being struck by wind turbine blades can be used to obtain fall distributions for bats, guide carcass survey efforts, and correct survey data for limited or unsearched areas.

A Wind-Tunnel Study of the Effect of Gap Flow and Gap Seals on the Aerodynamic Drag of Tractor-Trailer Trucks

1978 ◽  
Vol 100 (4) ◽  
pp. 434-438 ◽  
Author(s):  
F. T. Buckley ◽  
C. H. Marks
Keyword(s):  
Wind Tunnel ◽  
Drag Coefficient ◽  
Aerodynamic Drag ◽  
Motor Fuel ◽  
Center Line ◽  
Gap Flow ◽  
Yaw Angle ◽  
Wind Tunnel Study ◽  
Gap Width ◽  
Coefficient Reduction

The effect of gap width on the aerodynamic drag of a cab-over-engine tractor-trailer combination has been investigated for full-scale gap widths ranging from 0.61 m (24 in) to 1.83 m (72 in.) over a yaw angle range of 0 to 20 deg. The average drag on the vehicle was found to increase by 16 percent as the gap width increased from 0.61 m to 1.83 m. Drag reductions were found when a vertical seal was placed along the vehicle center line between the tractor and the trailer. Generally, the drag reduction increased as the percentage of gap width that was sealed increased, and as the yaw angle increased. The average drag coefficient reduction provided by a full gap seal increased from 0.02 to 0.05 as the gap width increased from 0.61 m to 1.4 m and then decreased slightly for gap widths up to 1.83 m. The effect of vehicle configuration on gap seal effectiveness was evaluated for a gap width of 1.3 m (51 in.) using models of six different tractors and two different trailers. The average drag coefficient reductions that were found ranged from 0.04 to 0.08 with 83 percent of the data being either 0.04 or 0.05. It is shown that the use of gap seals on the nearly half-million vehicles which comprise the nation’s long-haul trucking fleet can result in the conservation of about 1.4 × 109 liters (0.37 × 109 gal) of motor fuel each year.

scholarly journals Improvement of a sensitivity-adjustable three component force balance and its application to supersonic wind tunnel testing

2014 ◽  
Vol 9 (5) ◽  
pp. JFST0068-JFST0068
Author(s):  
Gouji YAMADA ◽  
Shingo IMAGAWA ◽  
Katuyuki INOUE ◽  
Hiromitsu KAWAZOE ◽  
Shigeru OBAYASHI
Keyword(s):  
Wind Tunnel ◽  
Force Balance ◽  
Wind Tunnel Testing ◽  
Supersonic Wind Tunnel ◽  
Component Force ◽  
Tunnel Testing

Effects of rear spoilers on ground vehicle aerodynamic drag

2014 ◽  
Vol 24 (3) ◽  
pp. 627-642 ◽  
Author(s):  
Halil Sadettin Hamut ◽  
Rami Salah El-Emam ◽  
Murat Aydin ◽  
Ibrahim Dincer
Keyword(s):  
Wind Tunnel ◽  
Drag Coefficient ◽  
Aerodynamic Drag ◽  
Lift Coefficient ◽  
Cfd Analysis ◽  
Content Type ◽  
Error Band ◽  
Race Car ◽  
Vehicle Aerodynamics ◽  
Rear Spoiler

Purpose – The purpose of this paper is to examine the aerodynamic effects of rear spoiler geometry on a sports car. Today, due to economical, safety and even environmental concerns, vehicle aerodynamics play a much more significant role in design considerations and rear spoilers play a major role in this area. Design/methodology/approach – A 2-D vehicle geometry of a race car is created and solved using the computational fluid dynamics (CFD) solver FLUENT version 6.3. The aerodynamic effects are analyzed under various vehicle speeds with and without a rear spoiler. The main results are compared to a wind tunnel experiment conducted with 1/18 replica of a Nascar. Findings – By the CFD analysis, the drag coefficient without the spoiler is calculated to be 0.31. When the spoiler is added to the geometry, the drag coefficient increases to 0.36. The computational results with the spoiler are compared with the experimental data, and a good agreement is obtained within a 5.8 percent error band. The uncertainty associated with the experimental results of the drag coefficient is calculated to be 6.1 percent for the wind tunnel testing. The sources of discrepancies between the experimental and numerical results are identified and potential improvements on the model and experiments are provided in the paper. Furthermore, in the CFD model, it is found that the addition of the spoiler caused a decrease in the lift coefficient from 0.26 to 0.05. Originality/value – This paper examines the effects of rear spoiler geometry on vehicle aerodynamic drag by comparing the CFD analysis with wind tunnel experimentation and conducting an uncertainty analysis to assess the reliability of the obtained results.

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