我们来讨论下涵道风扇系统的气动特性,涵道风扇是将风扇置于环形涵道内所构成的推力或升力装置.其结构紧凑,气动噪声低,使用安全性好,且在同样功耗下较之相同直径的孤立风扇会产生更大的拉力,因此涵道风扇是一种高效、安全和安静推进装置,但涵道风扇的气动特性比较复杂,这主要来自涵道和风扇的相互影响:由于风扇的吸流作用,在涵道的唇口处产生绕流,使涵道产生拉力,并且由于唇口的作用,风扇桨叶处的气流速度会发生变化,进而改变了风扇的拉力;由于涵道壁的阻碍,风扇桨尖处绕流减轻,从而降低了风扇的桨尖损失.
在讨论之前,我们先了解下涵道风扇系统的推力有哪几部分组成:
T涵道风扇系统拉力=Tr (涵道中风扇的拉力)+Td (涵道的拉力)
Tr 涵道风扇拉力指涵道风扇高速旋转将气流高速喷出获得的拉力
Td 涵道拉力指气流高速流过涵道唇口后产生一个低压区,由此涵道获得的拉力。(如果这点想不明白,你可以吧唇口想成机翼,唇口产生的涵道拉力与机翼产生的省力其空气动力学是一样的)
Td涵道拉力很少有人去关注,这就是我一直对魔友说必须要安装唇口的原因。
现今的涵道气动模型主要由滑流理论,叶素理论和涡流模型三个方面总结涵道风扇的分析计算模型,直到现在,涵道风扇还缺乏一个统一、准确、全面的计算模型.现有的分析模型还不能完整、准确的概括涵道风扇所表现出来的特殊气动特性.只有较好的处理了涵道和风扇的相互作用,模型才能变的完整而精确.用OAV 的方法在初步设计时能够给出符合要求的计算结果,对初步设计起着指导性的作用.
以上分析可以参考如下文档:
参考文献
[1]徐国华,王适存, “涵道螺桨的滑流理论” 第十界全国直升机年会论文 1994
[2]葛劳渥(英), “螺旋桨理论” 1949 (出版社不详)
[3]Robin B. Gray, Terry Wright, “Determination of the Design Parameters for Optimum Heavily Loaded
Ducted Fans” AIAA 69-222
[4]Terry Wright, “Evaluation of the Design Parameters for Optimum Heavily Loaded Fans”, J.Aircraft,
Nov-Dec,1970
[5]Barnes W. McCormick, JR. “Aerodynamics of V/STOL Flight”, ACADEMIC PRESS, New York 1967
[6]柴达科夫(俄),“涵道风扇” 莫斯科航空学院教科书 1997
[7]Ignacio Guerrero, Kelly Londenberg, Paul Gelhausen, Arvid Myklebust, “A Powered Lift Aerodynamic
Analysis for the Design of Ducted Fan UAVS” AIAA 2003-6567
[8]Rafi Yoeli, “Ducted Fan Utility Vehicles and Other Flying Cars” AIAA 2002-5995
[9]D.Kuchemnan and J.Weber, “Aerodynamics of Propulsion”, McGraw-Hill Book Company, New York,
1953
[10]屠秋野和唐狄毅“涵道螺旋桨桨叶环量强度分布计算” 航空动力学报 2004 年 2 月
[10]Fletcher, Herman S., “Experimental Investigation of Lift, Drag, and Pitching Moment of Five Annular
Airfoils” NACA TN 4117, 1957
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转帖自 Rc Group 作者:Jacques 英国
原帖地址:http://www.rcgroups.com/forums/showthread.php?t=1852061&page=1
我想选购买一个120-127mm的高可靠性电动涵道并且正在查看可用的选项。我找到很多测试数据,这些数据来源于厂商网站以及网友提供,我把这些数据用图表的方式进行简单的对
比。
几点提示说明:
1.测试台的数据并不意味最终的涵道装机效率。装机(静态)和动态飞行中的数据相比较可能反差很大。引起(以上反差)不同结果的因素包括很多变量(包括测试台、电流表等
等),据我所知,这些测试都是装了某种进气唇口且没有排气道。
2.依照公布的电流(而不是功率)数据,我假设单片电池负载电压为3.7V计算出功率。依我看来,所有的测试都该引用功率(至少要提到负载电压)因为一些人有可能会公布他们
在电压从峰值下降前得到的推力和安培值。在这种情况下我将低估功率(使用3.7v/片X电流)避免夸大效率。
3. 解释下数据表中的g/W(2/3),就是一瓦的功率可以推动多少克,用以衡量效率。这是个非常有使用价值的参数,他可以提供对比不同功率级的效率,g/w这个值本身可能会误
导别人,因为它会随着功率增加而下降(大部分的增量转化为输出)
4.缺少尾喷空气流速不见得是个问题,动量原理告诉我们在差不多大小的风扇、排气导管、尾喷口情况下推力和尾喷空气流速成正比,这个情况因电机大小的原因也许会受些影响
,但这些细微的影响可以忽略掉。还有,注意到一些风扇测试时实际上都是120mm而非127mm,这对仅针对推力的对比很不利。
I’m in the market for a 120-127mm EDF and looking at the options available. I have seen lots of test data out there, both on vendor websites and posted by
users here on RCG. I thought it would be useful to pull some of this together to enable easy comparison on a chart.
A Few Points to Note:
1. Bench tests are by no means the final say in EDF efficiency. Comparison of installed-in-airframe and dynamic scenarios may look very different. There are
many variables that could lead to skewed results, including test rigs, Amp/Watt meters, etc. To my knowledge, most of these tests have been done with an
inlet lip of some sort and no thrust tube.
2. Where Amps (rather than Watts) have been posted, then I have assumed 3.7 loaded voltage to derive Watts. In my opinion all tests should really quote watts
(or at least mention loaded voltage) as some people may be posting their thrust and Amp values before voltage falls off from peak. In such cases, I will be
understating Watts (as I am using 3.7V per cell x Amps) and therefore overstating efficiency.
3. I have also shown g/W^(2/3) in the data table, as this is a very useful value and allows comparison of efficiency across different power levels. g/W as a
value on its own can be misleading, as it drops off as power increases (much of the incremental energy converts to efflux).
4. The absence of efflux is not really an issue, as momentum theory tells that thrust and efflux are proportional for similar sized fan/duct/outlet. There
may well be differences due to motor can/hub size, but these are probably negligible. However, note that some fans tested are actually 120mm rather than
127mm and these will obviously be at a disadvantage in these thrust-only comparisons. (, 下载次数: 58)