Preliminary Experimental Investigation of Small Scale Propellers at High Incidence Angle

2018 ◽  
Author(s):  
Murat Bronz ◽  
Sertac Karaman
Keyword(s):  
Experimental Investigation ◽  
Incidence Angle ◽  
Small Scale ◽  
High Incidence

UNDERWATER ACOUSTIC SENSING OF SEA SURFACE WAVES

2008 ◽  
Vol 16 (01) ◽  
pp. 55-70 ◽  
Author(s):  
SUZANNE T. MCDANIEL
Keyword(s):  
Fourth Order ◽  
Cross Sections ◽  
Incidence Angle ◽  
Sea Surface ◽  
Surface Scattering ◽  
Acoustic Frequency ◽  
Acoustic Data ◽  
High Incidence ◽  
Sea Surface Waves ◽  
Scattering Cross Sections

Rough surface scattering theory is applied to the problem of estimating gravity-capillary wavenumber spectra from measurements of sea surface backscatter at high acoustic frequencies. Ensemble averaged scattering cross sections predicted by small-slope expansions are evaluated to examine the inversion of acoustic data assuming Bragg scatter. The ratio of the full fourth-order small-slope and Bragg predictions is found to exhibit a minimum value of ~ 2dB at moderate angles of incidence. At such angles, the corrections to perturbation theory depend weakly on acoustic frequency and environmental conditions. This latter finding indicates that only a modest effort is required to monitor sea surface conditions to estimate the correction. Corrections to Bragg predictions increase rapidly with increasing incidence angle and at high angles, the fourth-order contributions of the small-slope and extended small-slope expansions differ. This finding casts some doubt on the applicability of small-slope approximations to predict scattering at high-incidence angles.

scholarly journals Experimental Investigation of Tandem Blade Cascades With Double-Circular ARC Profiles

1985 ◽  
Author(s):  
Wu Guochuan ◽  
Zhuang Biaonan ◽  
Guo Bingheng
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Mach Number ◽  
Total Pressure ◽  
Incidence Angle ◽  
Axial Direction ◽  
Geometrical Parameters ◽  
Optimal Conditions ◽  
Turning Angle ◽  
Circular Arc

24 double circular are tandem blade cascades of three different chord-ratios were investigated under different displacements in peripheral and axial direction. The inlet Mach number was 0.3. The Reynolds number based on blade chord was 2.7×105. The characteristics of the tandem blade cascades, such as the dependence of turning angle and coefficient of total pressure loss on incidence angle were obtained. The ranges of main geometrical parameters under optimal conditions were recommended.

scholarly journals Unsteady Pressure Measurements on a Biconvex Airfoil in a Transonic Oscillating Cascade

1986 ◽  
Vol 108 (1) ◽  
pp. 53-59 ◽  
Author(s):  
L. M. Shaw ◽  
D. R. Boldman ◽  
A. E. Buggele ◽  
D. H. Buffum
Keyword(s):  
Mach Number ◽  
Incidence Angle ◽  
Dynamic Pressure ◽  
Leading Edge ◽  
Pressure Transducers ◽  
High Incidence ◽  
Shock Motion ◽  
Plate Analysis ◽  
Phase Angles ◽  
Unsteady Pressure Measurements

Flush-mounted dynamic pressure transducers were installed on the center airfoil of a transonic oscillating cascade to measure the unsteady aerodynamic response as nine airfoils were simultaneously driven to provide 1.2 deg of pitching motion about the midchord. Initial tests were performed at an incidence angle of 0.0 deg and a Mach number of 0.65 in order to obtain results in a shock-free compressible flow field. Subsequent tests were performed at an angle of attack of 7.0 deg and a Mach number of 0.80 in order to observe the surface pressure response with an oscillating shock near the leading edge of the airfoil. Results are presented for interblade phase angles of 90 and −90 deg and at blade oscillatory frequencies of 200 and 500 Hz (semichord reduced frequencies up to about 0.5 at a Mach number of 0.80). Results from the zero-incidence cascade are compared with a classical unsteady flat-plate analysis. Flow visualization results depicting the shock motion on the airfoils in the high-incidence cascade are discussed. The airfoil pressure data are tabulated.

Experimental Investigation on Laser Pretreatment of Optical Films

2011 ◽  
Vol 189-193 ◽  
pp. 3713-3716
Author(s):  
Zhi Lin Xia
Keyword(s):  
Experimental Investigation ◽  
Energy Density ◽  
Pulse Width ◽  
Incidence Angle ◽  
Damage Threshold ◽  
Negative Influence ◽  
Damage Probability ◽  
Optical Films ◽  
Laser Induced Damage ◽  
K9 Glass

Optical films have been prepared on K9 glass by electronic beam evaporation. Parameters of S-polarized Nd: YAG laser used for pretreatment and damage tests are: wavelength is 355nm, pulse width is 8ns, and incidence angle is 33.75 degree. The results reflect that: the influence of laser pretreatment on laser induced damage threshold of films is uncertain. Laser pretreatment not always improve the laser induced damage threshold of films, and sometimes it will cause negative influence. As for damage probability, for a certain testing energy density, there is an energy density scope, pretreatment pulse with energy density in which can reduce the laser induced damage probability of films. The energy density of laser pretreatment pulse should be selected according to the serving conditions of films.

Stone for My House

2020 ◽  
pp. 98-116
Author(s):  
William Ringle ◽  
Tomás Gallareta Negrón ◽  
George Bey
Keyword(s):  
Building Materials ◽  
Small Scale ◽  
Masonry Structures ◽  
Economic Implications ◽  
Considerable Evidence ◽  
Royal Patronage ◽  
Terminal Classic ◽  
High Incidence

Survey in the Puuc region, Yucatán, has revealed considerable evidence for small-scale quarrying and lime burning for construction purposes, as well as a high incidence of masonry architecture. In this chapter we discuss what must have been a substantial component of the Puuc Terminal Classic economy, especially if the construction of palaces and civic-ceremonial structures is included. This chapter addresses the stages involved in the procurement of building materials for housing and subsequent construction processes, especially of masonry structures. We then assess how construction may have been managed and its economic implications, suggesting that elite houses may have been tokens within a royal patronage network in which the size and elaboration of dwellings were subject to sumptuary considerations.

A Critical Analysis on Low-Order Simulation Models for Darrieus VAWTs: How Much Do They Pertain to the Real Flow?

2018 ◽  
Author(s):  
Alessandro Bianchini ◽  
Francesco Balduzzi ◽  
Giovanni Ferrara ◽  
Giacomo Persico ◽  
Vincenzo Dossena ◽  
...  
Keyword(s):  
Flow Field ◽  
Incidence Angle ◽  
Computational Cost ◽  
Simulation Models ◽  
Small Scale ◽  
Critical Issues ◽  
Overall Performance ◽  
Lift And Drag ◽  
Real Flow ◽  
Low Order

To improve the efficiency of Darrieus wind turbines, which still lacks from that of horizontal-axis rotors, Computational Fluid Dynamics (CFD) techniques are now extensively applied, since they only provide a detailed and comprehensive flow representation. Their computational cost makes them, however, still prohibitive for routine application in the industrial context, which still makes large use of low-order simulation models like the Blade Element Momentum (BEM) theory. These models have been shown to provide relatively accurate estimations of the overall turbine performance; conversely, the description of the flow field suffers from the strong approximations introduced in the modelling of the flow physics. In the present study, the effectiveness of the simplified BEM approach was critically benchmarked against a comprehensive description of the flow field past the rotating blades coming from the combination of a two-dimensional unsteady CFD model and experimental wind tunnel tests; for both data sets, the overall performance and the wake characteristics on the mid plane of a small-scale H-shaped Darrieus turbine were available. Upon examination of the flow field, the validity of the ubiquitous use of induction factors is discussed, together with the resulting velocity profiles upstream and downstream the rotor. Particular attention is paid on the actual flow conditions (i.e. incidence angle and relative speed) experienced by the airfoils in motion at different azimuthal angles, for which a new procedure for the post-processing of CFD data is here proposed. Based on this model, the actual lift and drag coefficients produced by the airfoils in motion are analyzed and discussed, with particular focus on dynamic stall. The analysis highlights the main critical issues and flaws of the low-order BEM approach, but also sheds new light on the physical reasons why the overall performance prediction of these models is often acceptable for a first-design analysis.

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