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Characteristics of Helicity Variation during a Low Vortex Event Caused by Easterly Wave
一次东风波及其诱生低涡的螺旋度特征分析

ZHENG Feng,XU Hai-Ming,DING Yi-Hui,
郑峰
,徐海明,丁一汇

大气科学 , 2008,
Abstract: 利用美国国家环境预报中心NCEP 1°×1°再分析资料,详细阐述了2001年8月3~4日浙南闽北的东风波暴雨过程的螺旋度的计算方法,并根据螺旋度(Helicity)和Q矢量(Q vector divergence)分析了过程中的暴雨演变以及雁荡山脉诱生中尺度低涡发生发展的原因。同时,利用中尺度有限区域模式MM5V2对该东风波诱生中尺度低涡进行模拟。结果表明:螺旋度大值中心强度和位置的演变较好地反映了暴雨落区和中尺度低涡的诱生、移动,螺旋度的时空演变对暴雨发生有一定的预示意义,螺旋度计算较中尺度模式诱生低涡的初生位置、路径预报准确率高,两者集成可以提高诱生低涡的预报准确率。同时,螺旋度梯度大值区和Q矢量散度梯度大值区叠加区的时空演变对暴雨发生、 诱生低涡的初生位置预示准确,说明该叠加区对降水和系统的诊断能力强,具有很好的指示意义。
高原涡诱生西南涡特大暴雨成因的个例研究  [PDF]
赵玉春,王叶红
高原气象 , 2010,
Abstract: 利用多途径探测与再分析资料,通过诊断分析、数值模拟和敏感性试验,对2008年7月20~21日一次高原涡东移诱生西南涡并引发川中特大暴雨的天气过程进行了初步分析,探讨了西南涡特大暴雨发生的中尺度环境场特征,特殊地形和非绝热物理过程在高原涡东移诱生西南涡特大暴雨中的作用。结果表明,高原涡形成后沿高原东北侧下滑,在四川盆地诱生出西南涡,川中特大暴雨在西南涡形成过程中由强中尺度对流系统(MCSs)的活动造成。高原涡东移诱生的低层偏东气流在川西高原东侧地形的动力强迫抬升作用下,释放对流有效位能激发出MCSs产生强降水,降水凝结潜热加热反馈驱动西南涡快速发展。地形的动力作用仅能形成浅薄的西南涡,降水凝结潜热的加入才能使西南涡充分发展。高原涡的发展主要受地面热通量影响,它的发展与否在很大程度上决定西南涡能否形成。盆地周边高大山脉对西南涡的位置分别有不同程度的影响,而盆地周边高大山脉上叠加的中小尺度地形对西南涡和暴雨带的整体位置影响不大,在一定程度上影响暴雨的落区。
一次东风波及其诱生低涡的螺旋度特征分析  [PDF]
郑峰 ZHENG Feng,徐海明 XU Hai-Ming,丁一汇 DING Yi-Hui
大气科学 , 2008, DOI: 10.3878/j.issn.1006-9895.2008.01.16
Abstract: 利用美国国家环境预报中心NCEP1°×1°再分析资料,详细阐述了2001年8月3~4日浙南闽北的东风波暴雨过程的螺旋度的计算方法,并根据螺旋度(Helicity)和Q矢量(Qvectordivergence)分析了过程中的暴雨演变以及雁荡山脉诱生中尺度低涡发生发展的原因。同时,利用中尺度有限区域模式MM5V2对该东风波诱生中尺度低涡进行模拟。结果表明:螺旋度大值中心强度和位置的演变较好地反映了暴雨落区和中尺度低涡的诱生、移动,螺旋度的时空演变对暴雨发生有一定的预示意义,螺旋度计算较中尺度模式诱生低涡的初生位置、路径预报准确率高,两者集成可以提高诱生低涡的预报准确率。同时,螺旋度梯度大值区和Q矢量散度梯度大值区叠加区的时空演变对暴雨发生、诱生低涡的初生位置预示准确,说明该叠加区对降水和系统的诊断能力强,具有很好的指示意义。
基于嵌套粒子群算法的多涡环微下击暴流模型参数选择方法  [PDF]
吴扬,姜守达
电子学报 , 2012, DOI: 10.3969/j.issn.0372-2112.2012.01.034
Abstract: 提出一种使用嵌套粒子群算法,根据微下击暴流水平垂直风速最大峰值比选择多涡环微下击暴流模型参数的方法.设计了包括目标群和中间群的嵌套式粒子群结构,使用中间群寻找水平垂直最大风速,并使用目标群最终选择模型参数.用该方法计算了水平垂直风速峰值比在0.3~0.7之间的多组多涡环微下击暴流模型参数,最终生成的微下击暴流场的水平垂直风速峰值比与预设值误差的数量级在10-4以内.
一次东风波及其诱生低涡发生发展的诊断和数值试验  [PDF]
郑峰?
气象科学 , 2006,
Abstract: 利用ncep1x1再分析资料诊断2001年8月3~4日发生在浙南闽北的东风波及其诱生中尺度低涡的暴雨过程。根据螺旋度(helicity)分析了过程中的暴雨演变以及雁荡山脉[1]诱生中尺度低涡发生发展的原因。同时,利用中尺度有限区域模式mm5v2对该东风波诱生中尺度低涡进行模拟。结果表明:螺旋度大值中心和锋区的强度和位置的演变较好反映了暴雨落区和中尺度低涡的诱生、移动。螺旋度的时空演变对暴雨发生有很好的预示意义,高、低层螺旋度的低层正值辐合与高层负值辐散的配置是引起降水的重要机制;螺旋度计算较中尺度模式诱生低涡的初生位置、路径预报准确率高,两者集成可以提高诱生低涡的预报准确率。
水槽涡的变化规律数值模拟 Numerical simulation of vortex evolution in a tank
Numerical simulation of vortex evolution in a tank
 [PDF]

罗志强,黄玉萍
- , 2017, DOI: 10.7511/jslx201706017
Abstract: 建立了不可压缩Navier-Stokes方程的Crank-Nicolson有限差分方法,数值模拟水槽晃动中流场及其涡流的数值变化规律。将数值解与解析解和前人的数值解进行比较,数值验证了不可压缩Naver-Stokes方程有限差分方法的有效性。通过数值模拟得到水槽在不同程度的倾斜激励晃动下流场及涡流的数值变换规律,当倾斜激励晃动的频率接近或远离共振频率时,水槽涡场的变化逐步由双涡变成单涡,再到不规则的涡场。当倾斜激励晃动的频率靠近共振频率ωp=0.95ω1附近时,水槽流场上部形成一个小涡,然后小涡扩大成整个水槽中的大涡,大涡下沉分裂成两个单涡,最后在底部消失;当倾斜激励晃动的频率在ωp=0.75ω1附近时,水槽底部形成一个小涡,然后扩大成大的单涡,最后在自由面消失;当倾斜激励晃动的频率在ωp=0.55ω1附近时,水槽底部出现小涡,然后扩大成大的单涡,大涡在自由面消失,继而出现不规则的大涡和不规则的小涡。
The Crank-Nicolson finite difference method for incompressible Navier-Stokes equations is developed in this paper,and the evolution regular of the vortexes and flow field are simulated under forced pitching oscillation.The numerical results are compared with the linearized analytical solution and the previous reported numerical calculation to validate the effectiveness of the present numerical method.From the numerical results,we find the evolution process of the flow field and the vortex under different degrees of pitching excitation in a tank.When the excited frequency approaches to or goes far away the oscillation frequency,the vortex field appears double vortexes,then the double vortexes convert into a single vortex and the single vortex vanishes finally in complex flow fields.When the excited frequency is ωp=0.95ω1,the profile of vortex near the free surface appears a small vortex and the vortex becomes a large vortex along the tank and splits into two vortexes,finally the vortexes disappear near the base wall.When the excited frequency is ωp=0.75ω1,the profile of vortex near the base wall appear a small vortex,then become a large vortex,then the vortex diminishes near the free surface.When the excited frequency is ωp=0.55ω1,the profile of little vortex appear on the base wall,then becomes a large vortexes,finally the large vortex diminishes near the free surface,the flow field exists big irregular vortexes and small vortexes.
基于壁面射流的下击暴流非稳态风场大涡模拟
Large Eddy Simulation of Unsteady Downburst Outflow Based on Wall Jet Model
 [PDF]

钟永力, 晏致涛, 王灵芝, 游溢
ZHONG Yongli
, YAN Zhitao, WANG Lingzhi, YOU Yi

- , 2018, DOI: 10.3969/j.issn.0258-2724.2018.06.013
Abstract: 为研究边界层风洞中下击暴流大缩尺比试验的可行性,基于冲击射流和壁面射流模型,采用大涡模拟方法,分析了静止和移动下击暴流的风场特性;通过与Wood模型、Oseguera模型、Victory模型以及经典壁面射流实验对比,验证了采用冲击射流和壁面射流模型在模拟稳态下击暴流出流段的一致性和有效性;在壁面射流模型入口处引入3种速度函数,模拟了下击暴流非稳态风速时程.研究结果表明:与冲击射流一样,无协同流壁面射流能够有效地模拟静止下击暴流的稳态出流段;当冲击射流平移速度为出流速度的15%时,其最大水平风速较静止冲击射流增大了15.8%;协同流速度为射流速度的19.2%时,其最大风速较无协同流壁面射流增大了16.9%,带协同流壁面射流能够有效地模拟移动下击暴流;提出的速度入口函数模型作为壁面射流入流条件,能够较为真实地模拟出Andrews AFB下击暴流非稳态风场.
:The feasibility of a large-scale experiment for downburst in a boundary layer wind tunnel was investigated. Large eddy simulation (LES) was employed to investigate the characteristics of stationary and travelling downburst using the impinging jet and wall jet methods,respectively. The velocity profiles from LES were compared with those obtained from the Wood model,the Oseguera model,the Victory model,and the classical wall jet experiment to verify the reasonableness of the two methods. Then,three time functions of the inlet velocity were used to obtain similar time series of the full-scale data. The results show that the fully-developed velocity profiles of the wall jet cohere with those of the three theoretical models and the classical wall jet experiment. When the translational velocity is 15% of the impinging jet velocity,the maximum horizontal wind speed increased by 15.8% compared to that of the stationary impinging jet,while when the velocity of co-flow is 19.2% of the wall jet velocity,the maximum horizontal wind speed increased by 16.9% compared to that of the wall jet without co-flow. The stationary downburst can be appropriately simulated using the wall jet model without co-flow,while the travelling downburst can be effectively simulated using the wall jet model with co flow. The results from large eddy simulation (LES) and data obtained from Andrews AFB downburst are in good agreement. The unsteady characteristics of downburst outflow can be perfectly reproduced by the time functions of the velocity inlet
中层涡旋诱生南海热带低压形成的位涡反演分析  [PDF]
袁金南,谷德军,廖菲
高原气象 , 2015, DOI: 10.7522/j.issn.1000-0534.2013.00145
Abstract: 利用NCEP1°×1°最终分析资料FNL和位涡反演方法,对2006年8月下旬一次中层涡旋诱发南海热带低压的形成过程进行了分析.结果表明,在中层涡旋诱发南海热带低压形成时高层暖心结构经历了由上向下逐渐发展的过程,而中层气旋性环流经历了由上向下快速发展的过程.高层暖心结构的向下发展主要与中低层凝结潜热加热作用和干空气从高层侵入有关,而高层波动的影响不明显,暖心发展到达近海面需要有底层热力异常和中低层凝结潜热加热作用的共同配合.中层气旋性环流的向下发展主要与中低层凝结潜热加热作用有关,高层波动对中低层涡度的影响不明显,而底层热力异常主要在900hPa以下产生负涡度.综合分析表明,中低层凝结潜热加热对南海热带低压的生成和发展起关键作用.
槽道内涡波流场展向涡的分布特征
Distribution characteristics of spanwise vortex of vortex wave field in channel flow
 [PDF]

陈彬,刘阁,金兴,邓阳琴
- , 2017, DOI: 10.13700/j.bh.1001-5965.2016.0934
Abstract: 摘要 通过2DPIV测量了槽道内涡波流场的瞬态速度矢量场,利用雷诺分解和旋转强度的λci准则进行了展向涡的识别;并从识别的逆时针和顺时针展向涡的尺度属性、力学属性和运动属性方面分析了展向涡的分布特征。结果表明,流场中的顺时针展向涡的数量大于逆时针展向涡的数量;在法向位置0.05~0.45范围内,逆时针展向涡的旋转强度呈抛物线形状变化,顺时针展向涡整体呈下降趋势;逆时针展向涡的平均直径和椭圆平均长轴长度随着法向位置的增加而缓慢增加,而顺时针展向涡趋于下降;逆时针展向涡的椭圆长轴倾角最大值为67.28°,顺时针展向涡的等效椭圆的离心率呈下降趋势,似圆性较好;逆时针展向涡对全局平均的〈vωz〉分量在法向位置0.15处出现最大值61%;展向涡对流场雷诺应力的影响较小;逆时针展向涡的数量密度在0~0.08法向位置范围内呈急剧上升趋势,并达到最大值0.36,顺时针展向涡数量密度整体呈倒U形分布;不同旋向的展向涡占总展向涡数量密度的比值都大于0.3;展向涡的流向对流速度整体上小于流场的平均速度,且在槽道中心区域差值较大;展向涡的法向对流速度随着法向距离增加,从负值上升到正值,在中心主流两侧分别发生喷射和扫掠2种现象。
Abstract:The instantaneous velocity vector fields of the vortex wave field in the channel flow were measured by 2DPIV. The identification of the spanwise vortices is carried out by using the criteria of Reynolds decomposition and swirling strength λci criteria. The distribution characteristics of spanwise vortices are analyzed from scale properties, mechanical properties and motion properties of the counter-clockwise and clockwise vortices identified by swirling strength λci criteria. The results show that the number of clockwise vortices is larger than that of the counter-clockwise vortices in the flow field. The swirling strength of the counter-clockwise vortices is in the form of parabolic shape in the range of normal direction 0.05-0.45, while the clockwise vortices show the overall downward trend. And the average diameter and the long axis of the ellipse of the counter-clockwise vortices increase slowly with the increase of the normal position, while the clockwise vortex tends to decrease. The largest value of the inclination angle of the long axis of the ellipse of the counter-clockwise spanwise vortices is 67.28°. The eccentricity of the equivalent ellipse of the clockwise vortices shows a decreasing trend, and the circularity is better. The contribution of the counter-clockwise spanwise vortices to the total mean 〈vωz〉 has a maximum value of 61% at normal direction 0.15, and the contribution of the spanwise vortices to the total Reynolds stress is smaller; the population densities of counter-clockwise spanwise vortices in the 0-0.08 normal displacement range have a sharp upward trend, and achieve the maximum 0.36; The distribution of the clockwise spanwise vortices shows the inverted "U"-shape; The population density ratio of spanwise vortices with different directions of swirling to total spanwise vortices is greater than 0.3; the streamwise convective velocity of the spanwise vortices is less than that of the mean velocity of flow field in general, and the difference between them is larger in the central region of the channel. The
基于涡方法生成大涡模拟进口条件的数值计算
Generation of unsteady inflow conditions for compressible LES with a modified vortex method
 [PDF]

谢宝林,邵亮
- , 2015, DOI: 10.13700/j.bh.1001-5965.2014.0281
Abstract: 摘要 探索改进涡方法来生成大涡模拟的非定常进口条件.改进方法中,为了避免局部漩涡数量过多或者过少,采用密度分布方式放置漩涡场.并用Langevin方程控制漩涡运动,模拟实验方法中的蜂窝器,使改进后的涡方法生成的脉动速度场更加符合湍流的特征.在已知雷诺平均的流场结果下,利用涡方法产生漩涡场,进而生成能满足大涡模拟所需要的非定常进口流场.为了检验改进后的涡方法在生成脉动速度过程中的效果,在槽道中进行了对比数值试验,并借助于直接数值模拟数据做对比,对比分析槽道进出口的平均速度、涡量以及雷诺应力统计,证明改进后的涡方法在生成大涡模拟进口条件下是非常有效的.
Abstract: This article is to explore and modify vortex method to generate large eddy simulation (LES) inlet condition. In the modification, a density distribution of vortex which can avoid unreasonable vortex quantity in local place was used. The movement of vortex was controlled by Langevin equation, which mimics the active grid turbulence so as to generate an unsteady flow field which is more like the real turbulence. Knowing the results of Reynolds-averaged Navier-Stokes equations (RANS) and reconstructing the turbulence by vortex method (VM), the method was tested in the experimental channel. The statistical results of both inlet and outlet of the channel were given, which include the mean velocity, the vorticity and the Reynolds stress. By analyzing the generated field with the reference of direct numerical simulation (DNS) results and comparing with the results of original method, during the development of turbulence in the channel, it shows that the modified vortex method is viable and cost-effective for generating unsteady inflow condition for LES.
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