scholarly journals Air drag coefficient of textile-covered elastic cylinders – preliminary aerodynamic studies

2021 ◽  
Vol 2 (2) ◽  
pp. 187-195
Author(s):  
Jana Siegmund ◽  
Ellen Wendt ◽  
Stefan Rothe ◽  
Yordan Kyosev ◽  
Veit Hildebrandt ◽  
...  
Keyword(s):  
Drag Coefficient ◽  
Aerodynamic Drag ◽  
Force Measurement ◽  
Reynolds Numbers ◽  
Measurement Technology ◽  
Soft Body ◽  
Air Drag ◽  
Gelatin Layer ◽  
Elastic Cylinders ◽  
The Given

This paper presents preliminary experimental results on the influence on the aerodynamic drag of a cylinder from the cylinder type (i.e., rigid or soft) and its textile surface. Both a rigid cylinder and a soft-body cylinder, with a gelatin layer, each with five different textile surfaces were measured in the wind tunnel using force measurement technology. The drag coefficient was determined for several Reynolds numbers. The study shows that the elasticity of a cylinder has a significant influence on the drag force and the airflow type. However, the influence of the soft-body cylinder depends on the respective fabric. With the given measurements, no exact statements can yet be made to quantify the influence. This influence must be studied independently and in conjunction with the textile surface in order to gain understanding of the overall system of airflow, textile and elastic body.

Drag coefficients of air rifle pellets with wide range of geometries

2021 ◽  
pp. 095440622199119
Author(s):  
Nicos Ladommatos
Keyword(s):  
Drag Coefficient ◽  
Aerodynamic Drag ◽  
Reynolds Numbers ◽  
Air Velocity ◽  
Drag Coefficients ◽  
Small Influence ◽  
Wide Range ◽  
Coefficient Increase ◽  
Air Rifle ◽  
Mach And Reynolds Numbers

Air rifle and air pistol target shooting are included in major intentional and national sports competitions and are also highly popular sport pastimes. Published scientific studies of pellet drag are very rare, in contrast to a large number of scientific studies published on aerodynamic drag of sports balls and other sports projectiles. Measurements are presented of the drag coefficients for 31 air rifle pellets of mainly 4.5 mm (0.177 in) calibre having a wide range of geometries. The drag coefficient measurements were made with a low-turbulence open wind tunnel at flow velocity of 200 m/s (Mach and Reynolds numbers 0.57 and 56,000 for 4.5 mm pellets). The detailed geometry of some pellets was altered systematically in order to improve understanding of how pellet geometry affects drag coefficient. The drag coefficient for the 31 pellets varied widely from 0.36 to 0.78, and it was influenced substantially by the curvature of the flow separating from the pellet head rim. Large curvatures delayed flow re-attachment onto the pellet tail, thereby lowering pellet base pressure and increasing the value of drag coefficient. Pellets with hemi-spherical or ogive-shaped noses generally had lower values of drag coefficient than pellets with other nose shapes. The presence of the pellet tail was beneficial by providing a surface onto which the flow detaching from the pellet rim could re-attach. However, for minimisation of drag coefficient, the pellet tail had to be of a certain optimum length which depended on the shape of the pellet nose. Small differences in pellet geometry had significant influence on the value of drag coefficient. Increase in air velocity from 120 to 200 m/s had small influence on the value of drag coefficient for three common sports pellets having flat, conical and dome-shaped noses.

Experimental investigations of flow over NACA airfoils 0021 and 4412 of wind turbine blades with and without Tubercles

2021 ◽  
pp. 0309524X2110071
Author(s):  
Usman Butt ◽  
Shafqat Hussain ◽  
Stephan Schacht ◽  
Uwe Ritschel
Keyword(s):  
Wind Tunnel ◽  
Drag Coefficient ◽  
Wind Turbine ◽  
Critical Region ◽  
Lift Coefficient ◽  
Turbine Blades ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Experimental Investigations ◽  
Wind Turbine Blades

Experimental investigations of wind turbine blades having NACA airfoils 0021 and 4412 with and without tubercles on the leading edge have been performed in a wind tunnel. It was found that the lift coefficient of the airfoil 0021 with tubercles was higher at Re = 1.2×105 and 1.69×105 in post critical region (at higher angle of attach) than airfoils without tubercles but this difference relatively diminished at higher Reynolds numbers and beyond indicating that there is no effect on the lift coefficients of airfoils with tubercles at higher Reynolds numbers whereas drag coefficient remains unchanged. It is noted that at Re = 1.69×105, the lift coefficient of airfoil without tubercles drops from 0.96 to 0.42 as the angle of attack increases from 15° to 20° which is about 56% and the corresponding values of lift coefficient for airfoil with tubercles are 0.86 and 0.7 at respective angles with18% drop.

scholarly journals The Profile Drag of Yawed Wings of Infinite Span

1951 ◽  
Vol 3 (3) ◽  
pp. 211-229 ◽  
Author(s):  
A.D. Young ◽  
T.B. Booth
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Drag Coefficient ◽  
Experimental Evidence ◽  
Flat Plate ◽  
Transition Point ◽  
Reynolds Numbers ◽  
External Pressure ◽  
Basic Assumptions ◽  
Angle Of Yaw

SummaryA method is developed for calculating the profile drag of a yawed wing of infinite span, based on the assumption that the form of the spanwise distribution of velocity in the boundary layer, whether laminar or turbulent, is insensitive to the chordwise pressure distribution. The form is assumed to be the same as that accepted for the boundary layer on an unyawed plate with zero external pressure gradient. Experimental evidence indicates that these assumptions are reasonable in this context. The method is applied to a flat plate and the N.A.C.A. 64-012 section at zero incidence for a range of Reynolds numbers between 106 and 108, angles of yaw up to 45°, and a range of transition point positions. It is shown that the drag coefficients of a flat plate varies with yaw as cos½ Λ (where Λ is the angle of yaw) if the boundary layer is completely laminar, and it varies as if the boundary layer is completely turbulent. The drag coefficient of the N.A.C.A. 64-012 section, however, varies closely as cos½ Λ for transition point positions between 0 and 0.5 c. Further calculations on wing sections of other shapes and thicknesses and more detailed experimental checks of the basic assumptions at higher Reynolds numbers are desirable.

Extra Drag Force on a Circular Cylinder Due to the Presence of Solid Particles in Subsonic Compressible Flow

1991 ◽  
Author(s):  
Stanley B. Mellsen
Keyword(s):  
Compressible Flow ◽  
Incompressible Flow ◽  
Aerodynamic Drag ◽  
Collection Efficiency ◽  
Reynolds Numbers ◽  
Solid Particles ◽  
Circular Cylinders ◽  
Critical Mach Number ◽  
Wide Range ◽  
Inertia Parameters

Abstract The effect of particles, such as dust in air on aerodynamic drag of circular cylinders was calculated for compressible flow at critical Mach number and for incompressible flow. The effect of compressibility was found negligible for particles larger than about 10 μm, for which the air can be considered a continuum. Drag coefficient and collection efficiency are provided for a wide range of inertia parameters and Reynolds numbers for both compressible and incompressible flow.

The aerodynamic resistance to a rotating sphere in the transition régime between free molecule and continuum creep flow

1964 ◽  
Vol 279 (1376) ◽  
pp. 39-49 ◽  
Keyword(s):  
Rarefied Gas ◽  
Aerodynamic Drag ◽  
Aerodynamic Resistance ◽  
Reynolds Numbers ◽  
Approximate Theory ◽  
Drag Torque ◽  
Free Molecule ◽  
Steel Sphere ◽  
Creep Flow ◽  
Wide Range

An experimental and theoretical study has been made of the aerodynamic drag torque on a sphere rotating in a rarefied gas. The drag torque on a magnetically suspended polished steel sphere rotating in air was measured over a wide range of Knudsen numbers from continuum to free molecule flow and for several different Mach numbers up to ca . 1. The drag under free molecule conditions was found to be consistent with the assumption of perfectly diffuse reflexion of molecules at the surface of the rotor. An approximate theory is derived which is analogous to Millikan’s solution to the problem of plane Couette flow and is valid for low Mach and Reynolds numbers. Theory and experiment are found to agree to within 10 % in the range investigated, for Reynolds numbers less than ca . 20.

scholarly journals Near-Wake Observations behind Azimuthally Perforated Disks With Varying Hole Layout and Porosity in Smooth Airstreams at High Reynolds Numbers

2018 ◽  
Vol 141 (5) ◽  
Author(s):  
Raf Theunissen ◽  
Robert Worboys
Keyword(s):  
Drag Coefficient ◽  
Experimental Studies ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Mean Flow ◽  
Flow Topology ◽  
Near Wake ◽  
Two Component ◽  
High Reynolds ◽  
Component Particle

Porous disks are commonly encountered in experimental studies dealing with flow through objects such as wind turbines, parachutes, and fluidic devices to regulate pressure and/or downstream turbulence. Perforations are typically staggered and only porosity is altered to attain the required disk drag coefficient, despite a documented influence of topology. Few works have reported, however, to which extent the spatial distribution of the circular perforations affect the mean flow pertaining freestanding disks, and for this reason, this work presents a first, more systematic study focused on the effect of azimuthally varying hole topology and porosity on disk drag and near-wake characteristics. An experimental study performed in airflows of negligible freestream turbulence at Reynolds numbers in the order of 105 is reported and related to the existing literature to ensure reliability. Complementary to drag measurements, near-wake surveys have been performed on a variety of perforation layouts using two-component laser Doppler velocimetry and two-component particle image velocimetry. It is shown that minor changes in perforations can cause drastic changes in near-wake flow topology and no perforation layout can be consistently associated with highest drag. Explicit empirical expressions for drag coefficient linked with the simplified topologies considered have been derived.

scholarly journals A Study of Drag Reduction on Cylinders with Different V-Groove Depths on the Surface

Water ◽  
2021 ◽  
Vol 14 (1) ◽  
pp. 36
Author(s):  
Jiyang Qi ◽  
Yue Qi ◽  
Qunyan Chen ◽  
Fei Yan
Keyword(s):  
Drag Reduction ◽  
Drag Coefficient ◽  
Vortex Structure ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Reynolds Numbers ◽  
Groove Surface ◽  
Smooth Cylinder ◽  
Groove Structure ◽  
Reduction Effect

In this study, the drag reduction effect is studied for a cylinder with different V-groove depths on its surface using a k-ω/SST (Shear Stress Transport) turbulence model of computational fluid dynamics (CFD), while a particle image velocimetry (PIV) system is employed to analyze the wake characteristics for a smooth cylinder and a cylinder with different V-groove depths on its surface at different Reynolds numbers. The study focuses on the characteristics of the different V-groove depths on lift coefficient, drag coefficient, the velocity distribution of flow field, pressure coefficient, vortex shedding, and vortex structure. In comparison with a smooth cylinder, the lift coefficient and drag coefficient can be reduced for a cylinder with different V-groove depths on its surface, and the maximum reduction rates of lift coefficient and drag coefficient are about 34.4% and 16%, respectively. Otherwise, the vortex structure presents a complete symmetry for the smooth cylinder, however, the symmetry of the vortex structure becomes insignificant for the V-shaped groove structure with different depths. This is also an important reason for the drag reduction effect of a cylinder with a V-groove surface.

Erfahrungen mit alternativen Kraftmessungen/Experiences with alternative force measurements - Comparing sensor-integrated toolholders to traditional piezo-based measurement technology

2020 ◽  
Vol 110 (01-02) ◽  
pp. 24-31
Author(s):  
Patrick Georgi ◽  
Ssrah Eschelbacher ◽  
Thomas Stehle ◽  
Hans-Christian Möhring
Keyword(s):  
Cutting Force ◽  
Force Measurement ◽  
Milling Process ◽  
The Other ◽  
Strain Gauges ◽  
Measurement Technology ◽  
Optimal Parameters ◽  
Force Measurements ◽  
Measuring Systems ◽  
The One

Die Prozessüberwachung spielt in der Zerspanung eine immer wichtiger werdende Rolle. So können zum Beispiel mittels Zerspankraftmessungen ökonomisch optimierte Parameter in Zerspanprozessen gefunden werden, die zu einer Verbesserung der Auslastung von Werkzeug und Maschine führen. Des Weiteren kann über die Zerspankraft auf den aktuellen Verschleißzustand der Werkzeuge im Prozess sowie auf die jeweils erreichbare Bearbeitungsgenauigkeit zurückgeschlossen werden. Für Zerspankraftmessungen gibt es eine Vielzahl an zur Verfügung stehenden Kraftmesssystemen; zum einen traditionelle Messtechnik auf Basis von Piezosensoren zur Kraftmessung und zum anderen Kraftmesstechnik auf der Basis von Dehnmessstreifen (DMS). Dieser Beitrag untersucht die Kraftaufnahme bei Fräs- und Bohrprozessen, bei denen beide Kraftmesssysteme simultan eingesetzt wurden.   Process monitoring plays an increasingly important role in machining. For example, through cutting force measurements, it is possible to find economically optimal parameters in the milling process, which lead to an improvement in the utilization of the tool and the machine. Furthermore, the cutting force can be used to deduce the state of wear of the tools in the process. There are varieties of available force measuring systems for this purpose; on the one hand, traditional measuring technology based on piezo sensors for force measurement and the other force measuring technology based on strain gauges (strain gauges). This article examines the force absorption in milling and drilling processes where both force-measuring systems were used simultaneously.

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