Analysis of the Losses in an Axial Fan With Small Blade Aspect Ratios Using CFD-Technique and Laser Doppler Anemometry

2020 ◽  
Author(s):  
Anika Theis ◽  
Thomas Reviol ◽  
Martin Böhle
Keyword(s):  
Aspect Ratio ◽  
Laser Doppler Anemometry ◽  
Axial Flow ◽  
Axial Fan ◽  
Laser Technique ◽  
Ratio Distribution ◽  
Aspect Ratios ◽  
Blade Thickness ◽  
Spacing Ratio ◽  
3D Simulation Model

Abstract In this contribution an axial flow fan is designed with four different blade aspect ratios. These four blade aspect ratios are obtained by using four different numbers of blades. The blade aspect ratios are varied between 0.2 and 0.6. For this investigation the thickness ratio distribution and the spacing ratio are kept constant in the design process for all four blade aspect ratios. This means, the blade thickness, the spacing and the blade chord are adjusted for every blade aspect ratio. Analysing low aspect ratios is challenging. Previous literature treating compressors suggests that at low aspect ratio the secondary losses and the freestream losses combine, making it difficult to separate the profile loss from the secondary flow losses. An approach to quantifying profile losses at the midspan of the blades for blade aspect ratios lower than 0.5, 2D simulations at the midspan are carried out for supplementary examination. The Reynolds number of all investigations is related to the chord length of each blade. It is varied from 2.38 × 105 to 7.13 × 105. During the survey, the same stator with a constant blade aspect ratio as well as a constant spacing ratio is used. In this contribution, LDA is applied as experimental method. Transient numerical simulations are performed for a full 3D simulation model to obtain a detailed view into the machine. Because of the low Reynolds numbers, the k-ω-SST transition model with the intermittency function is applied. With both methods, the flow is investigated on different planes inside the fan. The velocity distribution on the planes is analysed and compared to the transient simulation results. In the boundary layer, the velocity is resolved as well using the laser technique.

Topology of vortex breakdown in closed polygonal containers

2017 ◽  
Vol 820 ◽  
pp. 263-283 ◽  
Author(s):  
Igor V. Naumov ◽  
Irina Yu. Podolskaya
Keyword(s):  
Aspect Ratio ◽  
Cross Section ◽  
Vortex Breakdown ◽  
Laser Doppler Anemometry ◽  
Reynolds Numbers ◽  
Cylindrical Container ◽  
Stagnation Points ◽  
Aspect Ratios ◽  
Particle Visualization ◽  
Cross Section Geometry

The topology of vortex breakdown in the confined flow generated by a rotating lid in a closed container with a polygonal cross-section geometry has been analysed experimentally and numerically for different height/radius aspect ratios $h$ from 0.5 to 3.0. The locations of stagnation points of the breakdown bubble emergence and corresponding Reynolds numbers were determined experimentally and numerically by STAR-CCM+ computational fluid dynamics software for square, pentagonal, hexagonal and octagonal cross-section configurations. The flow pattern and velocity were observed and measured by combining seeding particle visualization and laser Doppler anemometry. The vortex breakdown size and position on the container axis were identified for Reynolds numbers ranging from 500 to 2800 in steady flow conditions. The obtained results were compared with the flow structure in the closed cylindrical container. The results allowed revealing regularities of formation of the vortex breakdown bubble depending on $Re$ and $h$ and the cross-section geometry of the confined container. It was found in a diagram of $Re$ versus $h$ that reducing the number of cross-section angles from eight to four shifts the breakdown bubble location to higher Reynolds numbers and a smaller aspect ratio. The vortex breakdown bubble area for octagonal cross-section was detected to correspond to the one for the cylindrical container but these areas for square and cylindrical containers do not overlap in the entire range of aspect ratio.

Aspect Ratio Analysis Using Image Processing for Rice Grain Quality

2010 ◽  
Vol 6 (5) ◽  
Author(s):  
Amit K Aggarwal ◽  
Ratan Mohan
Keyword(s):  
Image Processing ◽  
Aspect Ratio ◽  
Local Market ◽  
Rice Grain ◽  
Ratio Analysis ◽  
Ratio Distribution ◽  
Aspect Ratios ◽  
Percent Accuracy ◽  
Aspect Ratio Distribution

Determination of aspect ratio distribution is important for elongated, needle-shaped particles whose utility and/or value may depend on this feature. In this work rice grain is taken as an example of such a particle and its aspect ratio distribution in various samples is found using image processing. The samples examined were from three different grades (commonly termed as full, half and broken) sold in local market and priced according to their size. From the analysis, reference aspect ratios were assigned to classify the grains and hence determine the extent of off-size in each market grade. Further, the effectiveness of the technique to quantify mixed or adulterated grades was studied. It was found that it is possible to know the undesired content within 10 percent accuracy.

scholarly journals A General Method for Estimating Bulk 2D Projections of Ice Particle Shape: Theory and Applications

2019 ◽  
Vol 76 (1) ◽  
pp. 305-332 ◽  
Author(s):  
Edwin L. Dunnavan ◽  
Zhiyuan Jiang
Keyword(s):  
Aspect Ratio ◽  
Particle Shape ◽  
Ratio Distribution ◽  
Aspect Ratios ◽  
Shape Uncertainty ◽  
Aspect Ratio Distribution ◽  
Spheroidal Geometry ◽  
Orientation Parameters ◽  
General Method

Abstract The orientation of falling ice particles directly influences estimates of microphysical and radiative bulk quantities as well as in situ retrievals of size, shape, and mass. However, retrieval efforts and bulk calculations often incorporate very basic orientations or ignore these effects altogether. To address this deficiency, this study develops a general method for projecting bulk distributions of particle shape for arbitrary orientations. The Amoroso distribution provides the most general bulk aspect ratio distribution for gamma-distributed particle axis lengths. The parameters that govern the behavior of this aspect ratio distribution depend on the assumed relationship between mass, maximum dimension, and aspect ratio. Individual spheroidal geometry allows for eccentricity quantities to linearly map onto ellipse analogs, whereas aspect ratio quantities map nonlinearly. For particles viewed from their side, this analytic distinction leads to substantially larger errors in projected aspect ratio than for projected eccentricity. Distribution transformations using these mapping equations and numerical integration of projection kernels show that both truncation of size distributions and changes in Gaussian dispersion can alter the modality and shape of projection distributions. As a result, the projection process can more than triple the relative entropy between the spheroidal and projection distributions for commonly assumed model and orientation parameters. This shape uncertainty is maximized for distributions of highly eccentric particles and for particles like aggregates that are thought to fall with large canting-angle deviations. As a result, the methods used to report projected aspect ratios and the corresponding values should be questioned.

scholarly journals Proxy development: a new facet of morphological diversity in the marine diatom <i>Eucampia antarctica</i> (Castracane) Mangin

2014 ◽  
Vol 33 (2) ◽  
pp. 131-142 ◽  
Author(s):  
Claire S. Allen
Keyword(s):  
Aspect Ratio ◽  
Austral Summer ◽  
Morphological Diversity ◽  
Polar Front ◽  
Marine Diatom ◽  
Morphological Data ◽  
Ratio Distribution ◽  
Amundsen Sea ◽  
Aspect Ratios ◽  
Sw Atlantic

Abstract. The varied aspect ratios observed in the Antarctic marine diatom Eucampia antarctica are described and quantified. Data are compiled from detailed measurements of the gross morphology of winter stage specimens found in samples of modern marine sediments. Surface sediment samples come from a range of oceanographic settings spanning almost 20° of latitude from north of the Polar Front in the SW Atlantic to close to continental Antarctica in the southern Amundsen Sea. Results are compared with previously recorded morphological data ascribed to the polar and sub-polar varieties of E. antarctica (E. antarctica var recta and E. antarctica var antarctica) and reveal that the aspect ratio of both varieties responds independently of symmetry and colony structure. The discussion considers the likely basis of the observed aspect ratio distribution and whether the morphological diversity offers any potential for use as proxy evidence in Antarctic palaeoceanographic reconstructions. Although it requires further study, valve symmetry offers promising potential as a quantitative proxy for austral summer sea surface temperatures.

Low Aspect Ratio Axial Flow Compressors: Why and What It Means

1989 ◽  
Vol 111 (4) ◽  
pp. 357-365 ◽  
Author(s):  
A. J. Wennerstrom
Keyword(s):  
Aspect Ratio ◽  
Mechanical Design ◽  
Axial Flow ◽  
Early Years ◽  
Turbine Engine ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Design Systems ◽  
The 1960S ◽  
Axial Flow Compressors

One of the more visible changes that has occurred in fans and compressors for aircraft turbine engines that have entered development since about 1970 has been a significant reduction in the aspect ratio of the blading. This has brought with it a greatly reduced engine parts count and improved ruggedness and aeroelastic stability. This paper traces the evolution of thinking concerning appropriate aspect ratios for axial flow compressors since the early years of the aircraft turbine engine. In the 1950’s, moderate aspect ratios were favored for reasons of mechanical design. As mechanical design capability became more sophisticated, several attempts were made, primarily in the 1960s, to employ very high aspect ratios to reduce engine size and weight. Four of these programs are described that were largely unsuccessful for both mechanical and aerodynamic reasons. After 1970, the pendulum swung strongly in the other direction and designs of very low aspect ratio began to emerge. This has had a significant impact on compressor design systems, and a number of the ways in which design systems have been affected are discussed. Some concluding remarks are made concerning the author’s opinion of trends in the near future in aerodynamic design technology.

scholarly journals Numerical Computations for Flow Patterns and Force Statistics of Three Rectangular Cylinders

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Hamid Rahman ◽  
Shams-ul-Islam ◽  
Waqas Sarwar Abbasi ◽  
Raheela Manzoor ◽  
Fazle Amin ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Vortex Shedding ◽  
Lift Coefficient ◽  
Flow Characteristics ◽  
Drag And Lift Coefficients ◽  
Aspect Ratios ◽  
Spacing Ratio ◽  
Drag And Lift ◽  
Rectangular Cylinders

In this work, numerical simulations are performed in order to study the effects of aspect ratio (AR) and Reynolds number (Re) on flow characteristics of three side-by-side rectangular cylinders for fixed spacing ratio ( g ), using the lattice Boltzmann method (LBM). The Reynolds number varies within the range 60 ≤ Re ≤ 180, aspect ratio is between 0.25 and 4, and spacing ratio is fixed at g  = 1.5. The flow structure mechanism behind the cylinders is analyzed in terms of vorticity contour visualization, time-trace analysis of drag and lift coefficients, power spectrum analysis of lift coefficient and variations of mean drag coefficient, and Strouhal number. For different combinations of AR and Re, the flow is characterized into regular, irregular, and symmetric vortex shedding. In regular and symmetric vortex shedding the drag and lift coefficients vary smoothly while reverse trend occurs in irregular vortex shedding. At small AR, each cylinder experiences higher magnitude drag force as compared to intermediate and large aspect ratios. The vortex shedding frequency was found to be smaller at smaller AR and increased with increment in AR.

scholarly journals The Effect of Aspect Ratio on Compressor Performance

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Ho-On To ◽  
Robert J. Miller
Keyword(s):  
Aspect Ratio ◽  
Flow Field ◽  
Pressure Rise ◽  
Rate Of Change ◽  
Maximum Efficiency ◽  
Order Model ◽  
Aspect Ratios ◽  
Blade Thickness ◽  
Compressor Performance ◽  
Low Order

Abstract The optimum aspect ratio at which maximum efficiency occurs is relatively low, typically between 1 and 1.5. At these aspect ratios, inaccuracies inherently exist in the decomposition of the flow field into freestream and endwall components due to the absence of a discernible freestream. In this paper, a unique approach is taken: a “linear repeating stage” concept is used in conjunction with a novel way of defining the freestream flow. Through this approach, physically accurate decomposition of the flow field for aspect ratios as low as ∼0.5 can be achieved. This ability to accurately decompose the flow leads to several key findings. First, the endwall flow is found to be dependent on static pressure rise coefficient and endwall geometry, but independent of the aspect ratio. Second, the commonly accepted relationship that endwall loss coefficient varies inversely with the aspect ratio is shown to be physically inaccurate. Instead, a new term, which the authors refer to as the “effective aspect ratio,” should replace the term “aspect ratio.” Moreover, not doing so can result in efficiency errors of ∼0.6% at low aspect ratios. Finally, there exists a low aspect ratio limit below which the two endwall flows interact causing a large separation to occur along the span. From these findings, a low-order model is developed to model the effect of varying aspect ratio on compressor performance. The last section of the paper uses this low-order model and a simple analytical model to show that to a first order, the optimum aspect ratio is just a function of the loss generated by the endwalls at zero clearance and the rate of change in profile loss due to blade thickness. This means that once the endwall configuration has been selected, i.e., cantilever or shroud, the blade thickness sets the optimum aspect ratio.

Experiments on Vortex Shedding From Reconfigured Flexible Filaments Vibrating in Flow

2019 ◽  
Author(s):  
Jorge Silva-Leon ◽  
Andrea Cioncolini
Keyword(s):  
Aspect Ratio ◽  
Vortex Shedding ◽  
Flow Direction ◽  
Axial Flow ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Aspect Ratios ◽  
Inclination Angles ◽  
Spanwise Vortex ◽  
Vortex Shedding Frequency

Abstract This paper describes an experimental study of the spanwise vortex shedding frequencies from cantilever flexible filaments which are bent (reconfigured) when exposed to air crossflow. At a reduced velocity of approximately U* = 1500 (based on filament diameter) the filaments started to vibrate in the inline direction. Hot-wire anemometry was thus employed to investigate the wake flow of filaments of three aspect ratios (L/D = 38, 80, and 113) at Reynolds numbers Re &lt; 300. Despite the large relative inclination angles between the filament and the flow direction, the vortex shedding frequency measured along the span of the filaments remained close to those of a cylinder in pure crossflow. Moreover, it was found that as the aspect ratio (axial length) of the filaments was increased, vortex shedding lost coherence towards the free end of the filaments, whereas this was not the case for the shortest aspect ratio filament currently tested. This is thought to be due to the interaction between the crossflow vortex shedding and the axial flow component developing along the wake of the inclined filaments. Through comparisons with stiff inclined wires it was confirmed that the spanwise vortex shedding behaviors observed (frequency and coherence) were not modulated by the motions of the filaments.

scholarly journals The Effect of Aspect Ratio on Compressor Performance

2015 ◽  
Author(s):  
Ho-On To ◽  
Robert J. Miller
Keyword(s):  
Aspect Ratio ◽  
Flow Field ◽  
Order Model ◽  
Aspect Ratios ◽  
Blade Thickness ◽  
Rate Of Increase ◽  
Unique Approach ◽  
Compressor Performance ◽  
Relationship Of ◽  
Low Order

This paper considers the effect of aspect ratio on compressor performance. It is shown that the aspect ratio at which max efficiency occurs is relatively low, typically between 1 and 1.5. At these aspect ratios, decomposition of the flow field into freestream and endwall flows becomes difficult. In this paper, a unique approach is taken; McKenzie’s ‘linear repeating stage’ concept is used and a novel way of defining freestream flow is proposed. Through these simplifications and methods, physically accurate decomposition of the flow field for aspect ratios as low as ∼0.7 can be achieved. This ability to accurately decompose the flow field leads to two key findings. Firstly, the commonly accepted relationship of endwall loss coefficient varying inversely with aspect ratio is inaccurate. Instead, a new term, which the authors refer to as ‘effective aspect ratio’, should replace aspect ratio. It is shown that not doing so can result in efficiency errors of ∼0.6% at low aspect ratios. Secondly, there exists a low aspect ratio limit below which the two endwall flows interact causing a large separation to occur along the span. From these findings, a low order model is developed to model the effect of varying aspect ratio on performance. The last section of this paper uses this low order model as well as a simple analytical model to show that to a first order, the optimum aspect ratio is just a function of the loss generated by the endwalls at zero clearance and the rate of increase in profile loss due to blade thickness. This means that once the endwall configuration has been selected i.e. cantilever or shroud, the blade thickness sets the optimum aspect ratio.

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