Experimental studies of a model pump-turbine S-curve characteristics and its improvement by misaligned guide vanes （MGV） were extended to prototype pump turbine through 3-D transient flow simulations. The unsteady R...Experimental studies of a model pump-turbine S-curve characteristics and its improvement by misaligned guide vanes （MGV） were extended to prototype pump turbine through 3-D transient flow simulations. The unsteady Reynolds-averaged Navier-Stokes equations with the SST turbulence model were used to model the transient flow within the entire flow passage of a reversible pump-turbine with and without misaligned guide vanes during turbine model start-up. The unstable S-curve and its improvement by using misaligned guide vane were verified by model test and simulation. The transient flow calculations were used to clarify the variations of pressure pulse and internal flow behavior in the entire flow passage. The use of misaligned guide vanes can eliminate the S-curve characteristics of a pump-turbine, and can significantly increase the pressure pulse amplitude in the entire flow passage and the runner radial forces during start-up. The MGV only decreased the pulse amplitude on the guide vane suction side when the rotating speed was less than 50% rated speed. The hydraulic reason is that the MGV dramatically changed the flow patterns inside the entire flow passage, and destroyed the symmetry of the flow distribution inside the guide vane and runner.展开更多
对于大厚度焊接试件的超声衍射时差法检测(time of flight diffraction,TOFD),常规超声激励难以同时满足信噪比、检测距离以及检测分辨率的要求.文中将线性调频脉冲压缩技术应用在超声TOFD检测中,线性调频(linear frequency modulated,L...对于大厚度焊接试件的超声衍射时差法检测(time of flight diffraction,TOFD),常规超声激励难以同时满足信噪比、检测距离以及检测分辨率的要求.文中将线性调频脉冲压缩技术应用在超声TOFD检测中,线性调频(linear frequency modulated,LFM)激励可综合改善检测信噪比(signal to noise ratio,SNR)与分辨率.首先对试验用10 MHz超声换能器进行了LFM信号参数测试,选择了合适的时宽和带宽.对埋藏3 mm高的横槽缺陷的钢板分别进行了超声LFM激励的TOFD检测及常规超声TOFD检测,对比发现超声LFM激励的TOFD检测精度高达0.01μs,可准确区分缺陷上下端衍射波.在较低的激励电压和系统增益下,实现了较高的检测信噪比及分辨率.展开更多
基金supported by the National Natural Science Foundation of China(51009077)State Key Laboratory of Hydroscience and Engineering(2014-KY-05)
文摘Experimental studies of a model pump-turbine S-curve characteristics and its improvement by misaligned guide vanes （MGV） were extended to prototype pump turbine through 3-D transient flow simulations. The unsteady Reynolds-averaged Navier-Stokes equations with the SST turbulence model were used to model the transient flow within the entire flow passage of a reversible pump-turbine with and without misaligned guide vanes during turbine model start-up. The unstable S-curve and its improvement by using misaligned guide vane were verified by model test and simulation. The transient flow calculations were used to clarify the variations of pressure pulse and internal flow behavior in the entire flow passage. The use of misaligned guide vanes can eliminate the S-curve characteristics of a pump-turbine, and can significantly increase the pressure pulse amplitude in the entire flow passage and the runner radial forces during start-up. The MGV only decreased the pulse amplitude on the guide vane suction side when the rotating speed was less than 50% rated speed. The hydraulic reason is that the MGV dramatically changed the flow patterns inside the entire flow passage, and destroyed the symmetry of the flow distribution inside the guide vane and runner.
文摘目的比较支气管哮喘患儿在肺通气和脉冲振荡两种方法学检测的支气管舒张试验(bronchodilation test,BDT)中各参数敏感性与相关性。方法根据纳入及排除标准,选取157例哮喘患儿完成肺通气功能、脉冲振荡检查及舒张试验。按肺通气功能检查舒张试验中第1秒用力肺活量(forced expiratory volume in one second,FEV 1)改善率数值,将所有患儿分为四组,研究此两种方法学舒张试验前、后各气道参数的敏感性与各气道参数改善率之间的相关性。结果两种肺功能检查方法的舒张试验主要参数结果:四组FEV 1改善率分别为(2.94±1.54)%、(8.59±1.52)%、(15.25±2.06)%、(31.01±11.86)%,对应的呼吸总阻抗(respiratory impedance,Zrs)改善率分别为(10.83±6.71)%、(20.11±9.01)%、(27.06±10.67)%、(30.52±13.93)%,气道总阻力(respiratory resistance at 5 Hz,R5)改善率分别为(10.37±6.91)%、(18.25±7.60)%、(26.14±10.56)%、(29.05±13.56)%,外周弹性阻力(respiratory reactance at 5 Hz,X5)改善率分别为(17.36±26.60)%、(28.12±19.67)%、(36.19±17.36)%、(41.19±19.58)%;舒张试验后FEV 1与Zrs、R5、X5的相关性r值分别为0.499、0.478、0.386,存在不同程度的正相关性。结论舒张试验中,哮喘患儿的小气道参数与X5敏感性较高;脉冲振荡Zrs、R5、X5与肺通气FEV 1的改善率数值呈正相关性,脉冲振荡舒张试验中Zrs、R5、X5改善率作为衡量与推断结果的参数特异性更高,而在小气道方面,脉冲振荡R5更倾向反映总体情况。
文摘对于大厚度焊接试件的超声衍射时差法检测(time of flight diffraction,TOFD),常规超声激励难以同时满足信噪比、检测距离以及检测分辨率的要求.文中将线性调频脉冲压缩技术应用在超声TOFD检测中,线性调频(linear frequency modulated,LFM)激励可综合改善检测信噪比(signal to noise ratio,SNR)与分辨率.首先对试验用10 MHz超声换能器进行了LFM信号参数测试,选择了合适的时宽和带宽.对埋藏3 mm高的横槽缺陷的钢板分别进行了超声LFM激励的TOFD检测及常规超声TOFD检测,对比发现超声LFM激励的TOFD检测精度高达0.01μs,可准确区分缺陷上下端衍射波.在较低的激励电压和系统增益下,实现了较高的检测信噪比及分辨率.
