临近空间螺旋桨叶素非定常等离子体增效实验研究

基于等离子体诱导射流雷诺相似原则和螺旋桨叶素理论,开展了螺旋桨叶素地面风洞实验,比较了定常与非定常两种激励模式对螺旋桨拉力的影响,以及非定常模式下占空比、频率的影响。结果表明：相同电压幅值下,定常模式对螺旋桨拉力增效为9.8%,非定常模式对螺旋桨增效大于定常模式,非定常模式下最大增效 20.4%。螺旋桨桨叶相对半径在0.4 与0.85 之间时,非定常等离子体流动控制对螺旋桨叶素拉力增效较好,将等离子体激励器布置在桨叶相对半径0.4 与0.85 之间可提高能量利用率。相同重复频率下,螺旋桨增效随着占空比的减小而增大,占空比为10%时,增效最大。相同占空比下,重复频率存在一个最优值,频率为30Hz 时,等离子体对螺旋桨的增效最大。     

船舶无空泡螺旋桨非定常推力脉动及其诱导线谱噪声分析

对船舶无空泡螺旋桨非定常推力脉动及其诱导的线谱噪声进行了研究,主要目的在于螺旋桨非定常推力脉动理论预报方法的验证。基于速度势面元法计算得到非均匀流场中无空泡螺旋桨的推力脉动,在大型循环水槽中利用非定常动力仪测试得到全附体船后螺旋桨的脉动推力,以脉动推力作为声源项预报得远场线谱噪声。一阶叶频非定常推力系数理论计算值与试验值最大相差29.3%,由此引起的线谱噪声差别为3.0 dB。上述结果表明,面元法预报船后螺旋桨非定常推力脉动已达到较高精度,为船舶螺旋桨低频线谱噪声的预报提供了物理基础和重要参数。      

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基于介质阻挡放电等离子体的体积力气动激励机理,仿真研究了等离子体增升减阻技术对沿螺旋桨桨径方向均匀分布的10个叶素气动特性的改善效果.采用叶素理论,对比分析了等离子体对螺旋桨整体气动性能的提高效果.主要结论有:桨尖和桨叶根部的叶素容易发生气动分离现象,其中根部叶素处于负攻角的工况中;采用介质阻挡放电等离子体流动控制技术可以完全抑制流动分离不太严重的桨叶中部区域的叶素气动分离,对桨尖处翼型的严重气动分离不能完全抑制但也有改善作用,但对处于负攻角工况的叶素作用不大;等离子体增升减阻技术确实可以提高螺旋桨的气动性能,对本文所研究的情况,螺旋桨的拉力和效率分别提高了28.27％和 12.3％.     

Prediction and validation of tonal noise from underwater propellers

Prediction and validation of low-frequency line spectrum noise from ship propeller under non-cavitating condition is presented.The flow field is analyzed with potential-based panel method,which requires the hydrodynamic forces to be integrated over the actual blade surface,rather than over the mean-chord surface.Then the pressure data is used as the input for Ffowcs Williams-Hawkings formulation to predict the far field acoustics.At the same time,propeller unsteady force is measured in hull-behind condition in China Large Cavitation Channel(CLCC).Line spectrum noise of the 1st blade passage frequency(BPF) of a five-bladed propeller operating in a non-uniform flow field is got according to the calculated and measured unsteady forces,in which good agreement is obtained,and the 1st BPF noise difference is within 3.0 dB.The investigation reveals that prediction precision of the propeller's 1st BPF unsteady force with panel method have reached engineering practical degree,providing significant parameters for prediction of propeller line spectrum noise.     

Instantaneous orifice discharge coefficient of a physical, driven model of the human larynx

The quasisteady approximation is often made in the study of phonatory aerodynamics to facilitate the modeling of time-varying air flows through the self-oscillating vocal folds. The unsteady, pulsating flow is approximated by a sequence of steady flows through representative configurations of the vocal folds at rest. Previous studies have discussed the accuracy of this approximation for a range of orifice geometries, and flow conditions. The purpose of the present study was to further evaluate the quasisteady approximation experimentally using an improved procedure, from a direct comparison between the discharge coefficients of steady jets through fixed orifices and unsteady jets through modulated orifices of identical shape, area, and transglottal pressures at a given time. Life-scale convergent and divergent glottis-shaped rubber orifices were used in a rigid-walled tube and a low Mach number flow representative of human phonation. It was found that the quasisteady approximation is valid during 70% of the duty cycle, when the Reynolds number was above 3000, for a frequency of oscillations of 100 Hz. The steady form of Bernoulli's equation along a streamline, and Bernoulli's flow obstruction theory were found to be reasonably accurate for the unsteady flows. These models break down at low Reynolds numbers, near the beginning and the end of the duty cycle, due to viscous effects and to the influence of flow displaced by the motion of the walls.     

不均匀伴流场中螺旋桨空化的黏性流数值模拟和低频噪声预报

阐述了采用空化黏流CFD瞬态模拟和脉冲球形气泡辐射噪声理论相结合的思路在螺旋桨空化低频噪声谱预报上的应用方法。预报了全附体SUBOFF潜艇标称伴流条件下的NSRDC4383五叶大侧斜桨和某七叶大侧斜桨的片空化低频噪声谱,分析了桨叶负载和空化程度对线谱成分及其谱源级的影响。空化模拟时采用作者提出的且可信性经过验证的改进Sauer空化模型和修正SST湍流模型。噪声谱预报时空化体积由空化特征长度求取,较空泡表面球形等价假设更加合理。计算表明,七叶桨较五叶桨的确具有负载小、空化初生延迟、空化低频线谱噪声低的特征。在相同的基于航速的空化数下,非均匀进流与桨叶相互作用会明显增加线谱成分及其谱源级。在伴流、空化数和转速一定时,随着负载减小,推力、力矩和桨叶空化面积均会减小,但空化体积加速度幅度却变大,离散线谱噪声级增加且由奇次谐频为主转变为以偶次谐频为主;当仅减小空化程度时,谐频线谱成分明显被抑制,且1 kHz频率处谱源级减小2.54 dB。较完整地构建了螺旋桨空化水动力和噪声性能评估的数值平台,可用于指导艇尾低噪声桨的数值设计。      

多级轴流压气机间隙流动数值模拟

本文对某亚音轴流压气机的中间三排叶片进行定常与非定常数值模拟,分析在不同的动叶叶顶间隙和静叶气封间隙组合下压气机的流动特性。计算结果表明:定常计算条件下,叶顶间隙由0．5％叶高增大到2％叶高时,压气机的效率下降1．028％-1．034％,相同的气封间隙变化使效率下降0．108％-0．114％;非定常计算条件下,效率比定常计算高出 1％左右,并且叶顶间隙与气封间隙同时增大1％叶高时,效率下降约1％,与定常计算的规律相同。     

叶型优化在非定常流动条件下效果的数值分析

本文对叶型优化在非定常流动条件下的效果进行数值研究。叶型优化基于比较成熟的在定常流动条件下的反问题解法，非定常流动则考虑到动静叶栅之间的相互作用，非定常流动的求解在Ｎ－Ｓ方程的基础上采用分区计算的方法来完成。数值计算的结果表明，定常流动条件下优化得到的叶型在非定常流动条件下同样具有较好的气动性能。     

On vortex–airfoil interaction noise including span-end effects,with application to open-rotor aeroacoustics

A linear analytical model is developed for the chopping of a cylindrical vortex by a flat-plate airfoil, with or without a span-end effect. The major interest is the contribution of the tip–vortex produced by an upstream rotating blade in the rotor–rotor interaction noise mechanism of counter-rotating open rotors. Therefore the interaction is primarily addressed in an annular strip of limited spanwise extent bounding the impinged blade segment, and the unwrapped strip is described in Cartesian coordinates. The study also addresses the interaction of a propeller wake with a downstream wing or empennage. Cylindrical vortices are considered, for which the velocity field is expanded in two-dimensional gusts in the reference frame of the airfoil. For each gust the response of the airfoil is derived, first ignoring the effect of the span end, assimilating the airfoil to a rigid flat plate, with or without sweep. The corresponding unsteady lift acts as a distribution of acoustic dipoles, and the radiated sound is obtained from a radiation integral over the actual extent of the airfoil. In the case of tip–vortex interaction noise in CRORs the acoustic signature is determined for vortex trajectories passing beyond, exactly at and below the tip radius of the impinged blade segment, in a reference frame attached to the segment. In a second step the same problem is readdressed accounting for the effect of span end on the aerodynamic response of a blade tip. This is achieved through a composite two-directional Schwarzschild's technique. The modifications of the distributed unsteady lift and of the radiated sound are discussed. The chained source and radiation models provide physical insight into the mechanism of vortex chopping by a blade tip in free field. They allow assessing the acoustic benefit of clipping the rear rotor in a counter-rotating open-rotor architecture.     

Unsteady loading on an airfoil of arbitrary thickness

The unsteady loading on an airfoil of arbitrary thickness is evaluated by using the generalized form of Blasius theorem and a conformal mapping that maps the airfoil surface onto a circle. For a blade vortex interaction the results show that the time history of the unsteady loading is determined by the passage of the vortex relative to the leading edge singularity in the circle plane. The singularity lies inside the circle and moves to a smaller radius as the thickness is increased, causing the unsteady loading pulse to be smoothed. The effect of angle of attack is to move the stagnation point relative to the leading edge singularity and this significantly increases the unsteady lift if the vortex passes on the suction side of the airfoil. These characteristics are different for a step upwash gust, which is considered as a simplified model of a large scale turbulent gust. It is shown that the time history of the magnitude of the unsteady loading is almost completely unaltered by angle of attack for the step gust, but it's direction of action rotates forward by an angle equal to the angle of attack, extending an earlier result by Howe for a flat plate in a turbulent flow to airfoils of arbitrary thickness. However spectral analysis of the gust shows that the high frequency blade response is reduced as the thickness of the airfoil is increased.