The aerodynamic resistance to a sphere rotating at high speed

1963 ◽  
Vol 271 (1345) ◽  
pp. 143-153 ◽  
Keyword(s):  
Boundary Layer ◽  
High Speed ◽  
Aerodynamic Resistance ◽  
Point Of View ◽  
Magnetic Suspension ◽  
Gas Flows ◽  
Drag Torque ◽  
Rotating Sphere ◽  
Theoretical Predictions

An attempt has been made to adapt the technique of magnetic suspension of steel rotors to the study of high-speed aerodynamic problems. Surface speeds up to ca. 800 m/s are possible. The advantages and shortcomings of the technique from the aerodynamic point of view are discussed together with the different regimes of flow at present attainable with the apparatus. The particular case of a rotating sphere in the boundary-layer regime is considered and some results obtained with this technique are presented. Observations with smoke and with schlieren photographs show that the gas flows from the poles to the equator where it is thrown off as a narrow plane radial jet. These results are in accord with Howarth’s theoretical predictions. The measured drag torque on the sphere is however somewhat higher than the predicted value and possible reasons for this are considered. The work is now being extended to other regimes of flow.

The aerodynamic resistance to a sphere rotating at high Mach numbers in the rarefied transition régime

1966 ◽  
Vol 293 (1433) ◽  
pp. 156-168 ◽  
Keyword(s):  
Experimental Study ◽  
Aerodynamic Resistance ◽  
Pressure Gauge ◽  
Transition Regime ◽  
Drag Torque ◽  
Free Molecule ◽  
Rotating Sphere ◽  
Mach Numbers ◽  
High Mach ◽  
Molecule Flow

An experimental study has been made of the gaseous drag torque on an isolated sphere rotating at high Mach numbers. The sphere was suspended electromagnetically and spun by induction. The drag torque has been measured through the transition régime from continuum to free molecule flow at Mach numbers (based on equatorial speed) of up to about five. These high Mach numbers were achieved in heavy vapours (diiodomethane, germanium tetrabromide and stannic bromide) with sonic speed as little as a quarter of that in air. To measure the pressure in the vapour a second (smaller) rotating sphere was used as a pressure gauge. The results agree well with those previously obtained and show an unexpected Mach number dependence in the transition régime.

scholarly journals Receptivity of a high-speed boundary layer to temperature spottiness

2013 ◽  
Vol 722 ◽  
pp. 533-553 ◽  
Author(s):  
A. V. Fedorov ◽  
A. A. Ryzhov ◽  
V. G. Soudakov ◽  
S. V. Utyuzhnikov
Keyword(s):  
Boundary Layer ◽  
Acoustic Waves ◽  
High Speed ◽  
Free Stream ◽  
Plate Boundary ◽  
Second Mode ◽  
Theoretical Predictions ◽  
Order Of Magnitude ◽  
Pass Through ◽  
Upper Boundary

AbstractTwo-dimensional direct numerical simulation (DNS) of the receptivity of a flat-plate boundary layer to temperature spottiness in the Mach 6 free stream is carried out. The influence of spottiness parameters on the receptivity process is studied. It is shown that the temperature spots propagating near the upper boundary-layer edge generate mode F inside the boundary layer. Further downstream mode F is synchronized with unstable mode S (Mack second mode) and excites the latter via the inter-modal exchange mechanism. Theoretical assessments of the mode F amplitude are made using the biorthogonal eigenfunction decomposition method. The DNS results agree with the theoretical predictions. If the temperature spots are initiated in the free stream and pass through the bow shock, the dominant receptivity mechanism is different. The spot–shock interaction leads to excitation of acoustic waves, which penetrate into the boundary layer and excite mode S. Numerical simulations show that this mechanism provides the instability amplitudes an order of magnitude higher than in the case of receptivity to the temperature spots themselves.

Modification of the Classical Theory of the Virtual Mass of an Accelerating Spherical Particle

2006 ◽  
Author(s):  
Abdullah Abbas Kendoush
Keyword(s):  
Boundary Layer ◽  
Spherical Particle ◽  
High Speed ◽  
Boundary Layer Separation ◽  
Solid Sphere ◽  
Virtual Mass ◽  
Original Solution ◽  
Rotating Sphere ◽  
A Value ◽  
Mass Coefficient

A semi-analytical solution to the virtual mass of a spherical particle accelerating at high speed is obtained. Boundary layer separation coupled with potential flow was assumed around the solid sphere. The new solution of the virtual mass coefficient CV converges to the original solution of 0.5 upon removing the separation. The author showed earlier (Kendoush, J. Appl. Mech. 72(801)2005) that the virtual mass coefficient could reach a value of five for a rotating sphere in fluids.

A Statistical Study of Process Variables to Optimize a High Speed Curtain Coater: Part I

TAPPI Journal ◽  
2009 ◽  
Vol 8 (1) ◽  
pp. 20-26 ◽  
Author(s):  
PEEYUSH TRIPATHI ◽  
MARGARET JOYCE ◽  
PAUL D. FLEMING ◽  
MASAHIRO SUGIHARA
Keyword(s):  
Boundary Layer ◽  
Experimental Design ◽  
High Speed ◽  
Statistical Study ◽  
Process Variables ◽  
High Speeds ◽  
The Stability ◽  
Air Removal ◽  
Removal System

Using an experimental design approach, researchers altered process parameters and material prop-erties to stabilize the curtain of a pilot curtain coater at high speeds. Part I of this paper identifies the four significant variables that influence curtain stability. The boundary layer air removal system was critical to the stability of the curtain and base sheet roughness was found to be very important. A shear thinning coating rheology and higher curtain heights improved the curtain stability at high speeds. The sizing of the base sheet affected coverage and cur-tain stability because of its effect on base sheet wettability. The role of surfactant was inconclusive. Part II of this paper will report on further optimization of curtain stability with these four variables using a D-optimal partial-facto-rial design.

scholarly journals Modeling and theoretical description of magnetic hybrid materials—bridging from meso- to macro-scales

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Andreas M. Menzel ◽  
Hartmut Löwen
Keyword(s):  
Colloidal Particles ◽  
Colloidal Particle ◽  
Theoretical Description ◽  
Point Of View ◽  
Material Behavior ◽  
Theoretical Point ◽  
Mechanical Stiffness ◽  
Theoretical Approaches ◽  
Theoretical Predictions ◽  
Particle Level

Abstract Magnetic gels and elastomers consist of magnetic or magnetizable colloidal particles embedded in an elastic polymeric matrix. Outstanding properties of these materials comprise reversible changes in their mechanical stiffness or magnetostrictive distortions under the influence of external magnetic fields. To understand such types of overall material behavior from a theoretical point of view, it is essential to characterize the substances starting from the discrete colloidal particle level. It turns out that the macroscopic material response depends sensitively on the mesoscopic particle arrangement. We have utilized and developed several theoretical approaches to this end, allowing us both to reproduce experimental observations and to make theoretical predictions. Our hope is that both these paths help to further stimulate the interest in these fascinating materials.

Stationary cross-flow breakdown in a high-speed swept-wing boundary layer

2021 ◽  
Vol 33 (2) ◽  
pp. 024108
Author(s):  
Jianqiang Chen ◽  
Siwei Dong ◽  
Xi Chen ◽  
Xianxu Yuan ◽  
Guoliang Xu
Keyword(s):  
Boundary Layer ◽  
High Speed ◽  
Cross Flow ◽  
Swept Wing

Comparison of the reluctance laminated and solid rotor synchronous machine operating at high temperatures

2019 ◽  
Vol 38 (4) ◽  
pp. 1111-1119 ◽  
Author(s):  
Marcin Lefik ◽  
Krzysztof Komeza ◽  
Ewa Napieralska-Juszczak ◽  
Daniel Roger ◽  
Piotr Andrzej Napieralski
Keyword(s):  
High Speed ◽  
Design Methodology ◽  
Three Dimensional ◽  
Synchronous Machine ◽  
Point Of View ◽  
Heat Sources ◽  
Model Calculations ◽  
Content Type ◽  
Thermal Phenomenon ◽  
Practical Implications

Purpose The purpose of this paper is to present a comparison between reluctance synchronous machine-enabling work at high internal temperature (HT° machine) with laminated and solid rotor. Design/methodology/approach To obtain heat sources for the thermal model, calculations of the electromagnetic field were made using the Opera 3D program including effect of rotation and the resulting eddy current losses. To analyse the thermal phenomenon, the 3D coupled thermal-fluid (CFD) model is used. Findings The presented results show clearly that laminated construction is much better from a point of view of efficiency and temperature. However, solid construction can be interesting for high speed machines due to their mechanical robustness. Research limitations/implications The main problem, despite the use of parallel calculations, is the long calculation time. Practical implications The obtained simulation and experimental results show the possibility of building a machine operating at a much higher ambient temperature than it was previously produced for example in the vicinity of the aircraft turbines. Originality/value The paper presents the application of fully three-dimensional coupled electromagnetic and thermal analysis of new machine constructions designed for elevated temperature.

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