Prediction of Steady and Unsteady Loads and Hydrodynamic Forces on Counterrotating Propellers

Linearized unsteady-lifting-surface theory has been applied in the study of counterrotating propeller systems with equal or unequal number of blades operating in uniform or nonuniform inflow fields when both units are rotating with the same rpm. The mathematical model takes into account as realistically as possible the geometry of the propulsive device, the mutual interaction of both units and the three-dimensional spatially varying inflow field. The propeller blades lie on a helicoidal surface of varying pitch, have finite thickness and arbitrary planform, camber and sweep angle. The inflow field of the after propeller is modified by taking into account the effect of the race of the forward propeller, so that potential and viscous effects of the forward propeller are incorporated. These additional effects play an important role in determining the unsteady loading of the after propeller. This, together with some refinements introduced in the numerical procedure, has brought the theoretical results into better agreement with experiments. A computer program has been developed adaptable to a high-speed digital computer (CDC 6600-7600, Cyber 176) for counterrotating systems of equal and unequal number of blades, in uniform flow, for comparison with existing experiments.

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Application of an Implicit Relaxation Method Solving the Euler Equations for Time-Accurate Unsteady Problems

Journal of Fluids Engineering ◽

10.1115/1.2909436 ◽

1990 ◽

Vol 112 (4) ◽

pp. 510-520 ◽

Cited By ~ 14

Author(s):

A. Brenneis ◽

A. Eberle

Keyword(s):

Euler Equations ◽

Computing Time ◽

Three Dimensional ◽

Numerical Procedure ◽

Relaxation Method ◽

Coefficient Matrix ◽

Viscous Effects ◽

Left Hand ◽

Implicit Equations ◽

The Right

A numerical procedure is presented for computing time-accurate solutions of flows about two and three-dimensional configurations using the Euler equations in conservative form. A nonlinear Newton method is applied to solve the unfactored implicit equations. Relaxation is performed with a point Gauss-Seidel algorithm ensuring a high degree of vectorization by employing the so-called checkerboard scheme. The fundamental feature of the Euler solver is a characteristic variable splitting scheme (Godunov-type averaging procedure, linear locally one-dimensional Riemann solver) based on an eigenvalue analysis for the calculation of the fluxes. The true Jacobians of the fluxes on the right-hand side are used on the left-hand side of the first order in time-discretized Euler equations. A simple matrix conditioning needing only few operations is employed to evade singular behavior of the coefficient matrix. Numerical results are presented for transonic flows about harmonically pitching airfoils and wings. Comparisons with experiments show good agreement except in regions where viscous effects are evident.

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Ship Motion Computations Using a High Froude Number Time Domain Strip Theory

Journal of Ship Research ◽

10.5957/jsr.2006.50.1.15 ◽

2006 ◽

Vol 50 (01) ◽

pp. 15-30

Author(s):

D. S. Holloway ◽

M. R. Davis

Keyword(s):

Froude Number ◽

Time Domain ◽

High Speed ◽

Equations Of Motion ◽

Fluid Motion ◽

Three Dimensional ◽

Viscous Effects ◽

Strip Theory ◽

Large Amplitude Motions ◽

The Time Domain

High-speed strip theories are discussed, and a time domain formulation making use of a fixed reference frame for the two-dimensional fluid motion is described in detail. This, and classical (low-speed) strip theory, are compared with the experimental results of Wellicome et al. (1995) up to a Froude number of 0.8, as well as with our own test data for a semi-SWATH, demonstrating the marked improvement of the predictions of the former at high speeds, while the need to account for modest viscous effects at these speeds is also argued. A significant contribution to time domain computations is a method of stabilizing the integration of the ship's equations of motion, which are inherently unstable due to feedback from implicit added mass components of the hydrodynamic force. The time domain high-speed theory is recommended as a practical alternative to three-dimensional methods. It also facilitates the investigation of large-amplitude motions with stern or bow emergence and forms a simulation base for the investigation of ride control systems and local or global loads.

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Three-Dimensional Particle Tracking Velocimetry With Laser-Light Sheet Scannings

Journal of Fluids Engineering ◽

10.1115/1.2817385 ◽

1996 ◽

Vol 118 (2) ◽

pp. 352-357 ◽

Cited By ~ 9

Author(s):

Satoru Ushijima ◽

Nobukazu Tanaka

Keyword(s):

Particle Tracking ◽

High Speed ◽

Particle Tracking Velocimetry ◽

Laser Light ◽

Three Dimensional ◽

Numerical Procedure ◽

Light Sheet ◽

Optical Scanners ◽

Particle Images

This paper describes three-dimensional particle tracking velocimetry (3D PTV), which enables us to obtain remarkably larger number of velocity vectors than previous techniques. Instead of the usual stereoscopic image recordings, the present 3D PTV visualizes an entire three-dimensional flow with the scanning laser-light sheets generated from a pair of optical scanners and the images are taken by a high-speed video system synchronized with the scannings. The digital image analyses to derive velocity components are based on the numerical procedure (Ushijima and Tanaka, 1994), in which several improvements have been made on the extraction of particle images, the determination of their positions, the derivation of velocity components and others. The present 3D PTV was applied to the rotating fluids, accompanied by Ekman boundary layers, and their complicated secondary flow patterns, as well as the primary circulations, are quantitatively captured.

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Wake structure and kinematics in two insectivorous bats

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2015.0385 ◽

2016 ◽

Vol 371 (1704) ◽

pp. 20150385 ◽

Cited By ~ 17

Author(s):

Tatjana Y. Hubel ◽

Nickolay I. Hristov ◽

Sharon M. Swartz ◽

Kenneth S. Breuer

Keyword(s):

High Speed ◽

Lift Coefficient ◽

Three Dimensional ◽

Characteristic Root ◽

The Body ◽

Wing Loading ◽

Sweep Angle ◽

Tadarida Brasiliensis ◽

Wake Structure ◽

Weight Support

We compare kinematics and wake structure over a range of flight speeds (4.0–8.2 m s −1 ) for two bats that pursue insect prey aerially, Tadarida brasiliensis and Myotis velifer . Body mass and wingspan are similar in these species, but M. velifer has broader wings and lower wing loading. By using high-speed videography and particle image velocimetry of steady flight in a wind tunnel, we show that three-dimensional kinematics and wake structure are similar in the two species at the higher speeds studied, but differ at lower speeds. At lower speeds, the two species show significant differences in mean angle of attack, body–wingtip distance and sweep angle. The distinct body vortex seen at low speed in T. brasiliensis and other bats studied to date is considerably weaker or absent in M. velifer . We suggest that this could be influenced by morphology: (i) the narrower thorax in this species probably reduces the body-induced discontinuity in circulation between the two wings and (ii) the wing loading is lower, hence the lift coefficient required for weight support is lower. As a result, in M. velifer, there may be a decreased disruption in the lift generation between the body and the wing, and the strength of the characteristic root vortex is greatly diminished, both suggesting increased flight efficiency. This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’.

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Viscous Flows in Centrifugal Compressor Diffusers at Transonic Mach Numbers

Volume 1: Turbomachinery ◽

10.1115/92-gt-048 ◽

1992 ◽

Cited By ~ 1

Author(s):

I. Teipel ◽

A. Wiedermann ◽

W. Evers

Keyword(s):

Centrifugal Compressor ◽

Stokes Equations ◽

Three Dimensional ◽

Numerical Procedure ◽

Flow Fields ◽

Navier Stokes ◽

Viscous Effects ◽

Navier Stokes Equations ◽

Accelerate Convergence ◽

Mach Numbers

A numerical investigation of steady two- and three-dimensional flow fields in vaned diffusers of highly-loaded centrifugal compressors is described. The explicit MacCormack scheme was used to calculate inviscid and viscous effects because of the possibility of vectorization. Transonic Mach numbers are reached in the entrance of the diffuser and therefore time-dependent equations are solved. Two methods are employed to accelerate convergence of this explicit scheme. These techniques are (1) local time stepping and (2) applying a multigrid scheme. For the turbulent case an improved Baldwin-Lomax model given by Granville has been used. The numerical procedure has been used to compute two-dimensional transonic flow fields of a centrifugal compressor diffuser at different impeller speeds. It is shown that the predicted pressure field is in reasonable agreement with experimental data. Different approaches for the evaluation of global loss figures have been compared with each other. In addition, an evaluation of the complete three-dimensional Navier-Stokes equations is presented. The vanes in the diffuser are twisted such that the flow field contains a strong three-dimensional effect. Again a comparison with experiments is carried out and the agreement is fairly good.

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High-speed brightfield 3-D imaging and 3-D image analysis of thick and overlapped cell clusters in cytological preparations

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100168827 ◽

1994 ◽

Vol 52 ◽

pp. 218-219

Author(s):

Robert W. Mackin

Keyword(s):

Image Analysis ◽

High Speed ◽

Three Dimensional ◽

Image Data ◽

Ccd Camera ◽

Objective Lens ◽

Array Processor ◽

Vaginal Smears ◽

Low Contrast ◽

Computer Controlled

This paper presents two advances towards the automated three-dimensional (3-D) analysis of thick and heavily-overlapped regions in cytological preparations such as cervical/vaginal smears. First, a high speed 3-D brightfield microscope has been developed, allowing the acquisition of image data at speeds approaching 30 optical slices per second. Second, algorithms have been developed to detect and segment nuclei in spite of the extremely high image variability and low contrast typical of such regions. The analysis of such regions is inherently a 3-D problem that cannot be solved reliably with conventional 2-D imaging and image analysis methods.High-Speed 3-D imaging of the specimen is accomplished by moving the specimen axially relative to the objective lens of a standard microscope (Zeiss) at a speed of 30 steps per second, where the stepsize is adjustable from 0.2 - 5μm. The specimen is mounted on a computer-controlled, piezoelectric microstage (Burleigh PZS-100, 68/μm displacement). At each step, an optical slice is acquired using a CCD camera (SONY XC-11/71 IP, Dalsa CA-D1-0256, and CA-D2-0512 have been used) connected to a 4-node array processor system based on the Intel i860 chip.

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