There is a consensus in the aerospace field that the development of reusable liquid rockets can effectively reduce the launch expense.The pursuit of a long service life and reutilization highly depends on the bearing ...There is a consensus in the aerospace field that the development of reusable liquid rockets can effectively reduce the launch expense.The pursuit of a long service life and reutilization highly depends on the bearing components.However,the rolling element bearings(REBs)used in the existing rocket turbopumps present obvious and increasing limitations due to their mechanical contacting mode.For REBs,high rotational speed and long service life are two performance indexes that mutually restrict each other.To go beyond the DN value(the product of the bearing bore and rotational speed)limit of REBs,the major space powers have conducted substantial explorations on the use of new types of bearings to replace the REB.This review discusses,first,the crucial role of bearings in rocket turbopumps and the related structural improvements of REBs.Then,with the prospect of application to the next generation of reusable liquid rocket turbopumps,the bearing candidates investigated by major space powers are summarized comprehensively.These promising alternatives to REBs include fluid-film,foil,and magnetic bearings,together with the novel superconducting compound bearings recently proposed by our team.Our more than ten years of relevant research on fluid-film and magnetic bearings are also introduced.This review is meaningful for the development of long-life and highly reliable bearings to be used in future reusable rocket turbopumps.展开更多
Turbopump condition monitoring is a significant approach to ensure the safety of liquid rocket engine （LRE）.Because of lack of fault samples,a monitoring system cannot be trained on all possible condition patterns.T...Turbopump condition monitoring is a significant approach to ensure the safety of liquid rocket engine （LRE）.Because of lack of fault samples,a monitoring system cannot be trained on all possible condition patterns.Thus it is important to differentiate abnormal or unknown patterns from normal pattern with novelty detection methods.One-class support vector machine （OCSVM） that has been commonly used for novelty detection cannot deal well with large scale samples.In order to model the normal pattern of the turbopump with OCSVM and so as to monitor the condition of the turbopump,a monitoring method that integrates OCSVM with incremental clustering is presented.In this method,the incremental clustering is used for sample reduction by extracting representative vectors from a large training set.The representative vectors are supposed to distribute uniformly in the object region and fulfill the region.And training OCSVM on these representative vectors yields a novelty detector.By applying this method to the analysis of the turbopump＇s historical test data,it shows that the incremental clustering algorithm can extract 91 representative points from more than 36 000 training vectors,and the OCSVM detector trained on these 91 representative points can recognize spikes in vibration signals caused by different abnormal events such as vane shedding,rub-impact and sensor faults.This monitoring method does not need fault samples during training as classical recognition methods.The method resolves the learning problem of large samples and is an alternative method for condition monitoring of the LRE turbopump.展开更多
The relationship between entropy production and vortex evolution affects the efficiency and stability of rotating machinery.This study investigated the energy characteristics of a rocket turbopump and revealed the cor...The relationship between entropy production and vortex evolution affects the efficiency and stability of rotating machinery.This study investigated the energy characteristics of a rocket turbopump and revealed the correlated mechanisms of the entropy production rate using the dissipation effects and characteristic vortex evolution.For the first time,direct and turbulent dissipation and rigid and shear vorticity decomposition methods were utilized to analyze the correlation between flow loss and characteristic vorticities in rotating machinery.With an increase in the flow rate,the hydraulic losses of the dissipation effects and wall decreased by 60%and 38.3%,respectively,and the proportions of the input energy decreased(from 13%to 8%)and remained stable(8%),respectively.The local direct dissipative entropy production(DDEP)in the inducer-impeller is strongly related to shear entropy,and the correlated effect of total enstrophy on DDEP is weaker than that of shear vorticity,indicating that rigid enstrophy suppresses direct dissipation.The correlation between turbulent dissipation and rigid enstrophy was significantly weaker in the static flow passage of the turbopump owing to the weak rigid rotational effect.The correlation between the rigid entropy and local turbulent dissipative entropy production(TDEP)gradually increased with increasing flow rate,reaching a medium correlation(the maximal correlated degree in the turbopump)and exhibiting rigid rotation effects on the hydraulic loss.Moreover,the flow rate significantly affected the correlation(except for the diffuser),and the two characteristic vorticities reached a maximum at the designed flow rate owing to optimal efficiency and minimum hydraulic loss.展开更多
作为重要的动力学参数,刚度辨识及预测对于涡轮泵动力特性具有关键意义,为此提出一种融合注意力机制和双向长短期记忆(Bi⁃directional long short⁃term memory,BiLSTM)网络的预测模型。将动力学响应融合输入,使用LSTM神经网络有效挖掘...作为重要的动力学参数,刚度辨识及预测对于涡轮泵动力特性具有关键意义,为此提出一种融合注意力机制和双向长短期记忆(Bi⁃directional long short⁃term memory,BiLSTM)网络的预测模型。将动力学响应融合输入,使用LSTM神经网络有效挖掘时序相关的历史特征。再将两层LSTM网络反向叠加组成BiLSTM模型,适应动力学信息复杂、序列冗长特点,深入挖掘参数间的非线性特征。随后引入Attention层,利用注意力机制获取特征分配权重,增强关键信息。最后通过某型涡轮泵的动力学数据训练辨识模型。结果表明,对于涡轮泵刚度特性,Attention⁃BiLSTM模型在序列数据处理方面具有显著优势,预测平均绝对百分比误差(Mean absolute percentage error,MAPE)可达2.1945%。而单一结构的RNN、LSTM和BiLSTM模型的预测MAPE分别为10.4977%、5.4973%和2.7986%。可见该方法有效避免了复杂的动力学反问题求解,实现了非线性参数的动态识别。展开更多
基金Supported by National Natural Science Foundation of China(Grant No.51805131)Postdoctoral Research Foundation of China(Grant No.2018M640580)Fundamental Research Funds for the Central Universities(CN)Fundamental Research Funds for the Central Universities of China(Grant No.JZ2018HGBZ0155).
文摘There is a consensus in the aerospace field that the development of reusable liquid rockets can effectively reduce the launch expense.The pursuit of a long service life and reutilization highly depends on the bearing components.However,the rolling element bearings(REBs)used in the existing rocket turbopumps present obvious and increasing limitations due to their mechanical contacting mode.For REBs,high rotational speed and long service life are two performance indexes that mutually restrict each other.To go beyond the DN value(the product of the bearing bore and rotational speed)limit of REBs,the major space powers have conducted substantial explorations on the use of new types of bearings to replace the REB.This review discusses,first,the crucial role of bearings in rocket turbopumps and the related structural improvements of REBs.Then,with the prospect of application to the next generation of reusable liquid rocket turbopumps,the bearing candidates investigated by major space powers are summarized comprehensively.These promising alternatives to REBs include fluid-film,foil,and magnetic bearings,together with the novel superconducting compound bearings recently proposed by our team.Our more than ten years of relevant research on fluid-film and magnetic bearings are also introduced.This review is meaningful for the development of long-life and highly reliable bearings to be used in future reusable rocket turbopumps.
基金supported by National Natural Science Foundation of China (Grant No. 50675219)Hu’nan Provincial Science Committee Excellent Youth Foundation of China (Grant No. 08JJ1008)
文摘Turbopump condition monitoring is a significant approach to ensure the safety of liquid rocket engine （LRE）.Because of lack of fault samples,a monitoring system cannot be trained on all possible condition patterns.Thus it is important to differentiate abnormal or unknown patterns from normal pattern with novelty detection methods.One-class support vector machine （OCSVM） that has been commonly used for novelty detection cannot deal well with large scale samples.In order to model the normal pattern of the turbopump with OCSVM and so as to monitor the condition of the turbopump,a monitoring method that integrates OCSVM with incremental clustering is presented.In this method,the incremental clustering is used for sample reduction by extracting representative vectors from a large training set.The representative vectors are supposed to distribute uniformly in the object region and fulfill the region.And training OCSVM on these representative vectors yields a novelty detector.By applying this method to the analysis of the turbopump＇s historical test data,it shows that the incremental clustering algorithm can extract 91 representative points from more than 36 000 training vectors,and the OCSVM detector trained on these 91 representative points can recognize spikes in vibration signals caused by different abnormal events such as vane shedding,rub-impact and sensor faults.This monitoring method does not need fault samples during training as classical recognition methods.The method resolves the learning problem of large samples and is an alternative method for condition monitoring of the LRE turbopump.
基金supported by the Heilongjiang Postdoctoral Fund(Grant Nos.LBH-Z18071,LBH-TZ2015)the Fundamental Research Funds for the Central Universities(Grant No.HIT.NSRIF.2019063).
文摘The relationship between entropy production and vortex evolution affects the efficiency and stability of rotating machinery.This study investigated the energy characteristics of a rocket turbopump and revealed the correlated mechanisms of the entropy production rate using the dissipation effects and characteristic vortex evolution.For the first time,direct and turbulent dissipation and rigid and shear vorticity decomposition methods were utilized to analyze the correlation between flow loss and characteristic vorticities in rotating machinery.With an increase in the flow rate,the hydraulic losses of the dissipation effects and wall decreased by 60%and 38.3%,respectively,and the proportions of the input energy decreased(from 13%to 8%)and remained stable(8%),respectively.The local direct dissipative entropy production(DDEP)in the inducer-impeller is strongly related to shear entropy,and the correlated effect of total enstrophy on DDEP is weaker than that of shear vorticity,indicating that rigid enstrophy suppresses direct dissipation.The correlation between turbulent dissipation and rigid enstrophy was significantly weaker in the static flow passage of the turbopump owing to the weak rigid rotational effect.The correlation between the rigid entropy and local turbulent dissipative entropy production(TDEP)gradually increased with increasing flow rate,reaching a medium correlation(the maximal correlated degree in the turbopump)and exhibiting rigid rotation effects on the hydraulic loss.Moreover,the flow rate significantly affected the correlation(except for the diffuser),and the two characteristic vorticities reached a maximum at the designed flow rate owing to optimal efficiency and minimum hydraulic loss.
