Numerical simulation method of surge experiments on gas turbine engines

In order to obtain the surge margin of an aero-engine during its operation,an engine surge experiment is required.A multi-dimensional simulation method for an aero-engine is established in this paper.The simulation of a surge experiment using high-pressure air-injection is then carried out on a turbo-shaft engine to obtain the surge boundary using this method.More specifically,firstly,a body-force model is employed to calculate the compressor performance owing to its capability of capturing the main three-dimensional features of compressor surge and avoiding excessive simulation time required by the traditional fully-three-dimensional Reynolds Averaged Navier-Stokes(RANS)method.Then,a one-dimensional model combining a lumped-parameter plenum model is used for the combustor to account for the propagation of pressure waves and the heat-release process,and a zero-dimensional throttle model is used to mimic the choking effect at the turbine nozzle.Finally,the air-injection system is modeled by imposing an injection boundary condition,which can be used conveniently in changing injection parameters.Based on the established method,the influences of different test parameters,such as the air-injection location,the pressure,the orifice size,the number of injection orifices,and the injection time duration on the surge characteristics and boundary are further studied,which offer effective guidance to optimize an actual experimental design.

Influence of Fe-rich phases and precipitates on the mechanical behaviour of Al-Cu-Mn-Fe-Sc-Zr alloys studied by synchrotron X-ray and neutron

A multiscale methodology using scanning and transmission electron microscope,synchrotron X-ray nano-tomography and micro-tomography,small angle neutron scattering,and in situ synchrotron X-ray diffrac-tion has been used,to reveal the effect of Fe-rich phases and precipitates on the mechanical behaviour of an Al-Cu-Mn-Fe-Sc-Zr alloy.Theα-Al grains size is reduced from 185.1μm(0 MPa)and 114.3μm(75 MPa)by applied pressure.Moreover,it has been demonstrated that suitable heat treatments modify the 3D morphology of Fe-rich phases from interconnected to a disaggregated structure that improves the mechanical properties of the alloy.The size and morphology evolution of fine precipitates under differ-ent ageing temperature and time are revealed.At ageing temperature of 160℃,the precipitates change from GP zones toθ’(around 75 nm in length)with ageing time increasing from 1 h to 24 h;the Vick-ers hardness increases from 72.0 HV to 110.7HV.The high ductility of the Sc,Zr modified Al-Cu alloy is related to the complex shape and the loss of interconnectivity of the Fe-rich particles due to the heat treatment.The evolution of the crystal lattice strains inα-Al,andβ-Fe calculated during tensile test us-ing in-situ synchrotron X-ray diffraction corroborates the influence of the microstructure in the ductility of the modified alloy.

Compressor geometric uncertainty quantification under conditions from near choke to near stall

Geometric and working condition uncertainties are inevitable in a compressor,deviating the compressor performance from the design value.It’s necessary to explore the influence of geometric uncertainty on performance deviation under different working conditions.In this paper,the geometric uncertainty influences at near stall,peak efficiency,and near choke conditions under design speed and low speed are investigated.Firstly,manufacturing geometric uncertainties are analyzed.Next,correlation models between geometry and performance under different working conditions are constructed based on a neural network.Then the Shapley additive explanations(SHAP)method is introduced to explain the output of the neural network.Results show that under real manufacturing uncertainty,the efficiency deviation range is small under the near stall and peak efficiency conditions.However,under the near choke conditions,efficiency is highly sensitive to flow capacity changes caused by geometric uncertainty,leading to a significant increase in the efficiency deviation amplitude,up to a magnitude of-3.6%.Moreover,the tip leading-edge radius and tip thickness are two main factors affecting efficiency deviation.Therefore,to reduce efficiency uncertainty,a compressor should be avoided working near the choke condition,and the tolerances of the tip leading-edge radius and tip thickness should be strictly controlled.

骨搬运治疗胫骨骨缺损中滑移段外固定取出后发生回缩现象的相关因素分析

目的探讨骨搬运治疗胫骨骨缺损过程中在对合端愈合前滑移段外固定去除后发生回缩现象的相关因素。方法回顾性研究。纳入2009年1月—2019年12月无锡市人民医院和无锡市骨科医院胫骨骨缺损应用骨搬运治疗,在对合端愈合前滑移段外固定去除或失效发生不同程度回缩的41例患者,男25例、女16例,年龄18~71(40±15)岁。用Pearson相关分析滑移段回缩距离与患者年龄、性别、受伤至手术时间、骨缺损长度、手术次数、滑移段长度、骨搬运长度、滑移段固定时间和外固定去除或松动失效前、后两次影像学检查的间隔时间等9个因素的相关性,筛选出有统计学意义的影响因素再行多元线性回归分析。结果41例患者中,受伤至骨搬运时间7~95(40.54±25.65)d,骨缺损长度5.0~11.0(6.90±1.20)cm,手术次数1~5(1.64±0.82)次,滑移段长度4.8~12.0(9.68±2.24)cm,骨搬运长度4.5~11.0(6.76±1.64)cm,滑移段固定时间3.5~11.5(7.47±1.94)个月,间隔时间5~21(10.16±4.07)d,滑移段回缩距离1.5~30.0(8.73±7.99)mm。Pearson相关分析显示,滑移段回缩距离与滑移段固定时间呈负相关,与骨搬运长度和滑移段长度呈正相关,差异均有统计学意义(r=-0.897、0.501、0.419,P值均<0.05);滑移段回缩距离与年龄、性别、受伤至手术时间、骨缺损长度、手术次数和间隔时间均无相关性,差异均无统计学意义(P值均>0.05)。多元线性回归分析显示,骨搬运长度和滑移段固定时间与滑移段发生回缩存在线性关系(t=-10.385、3.027,P值均<0.05)。回归方程:Y_(回缩距离(mm))=27.081-2.805X_(滑移段固定时间(月))+0.447X_(骨搬运长度(cm))(R^(2)=0.805,F=13.256,P<0.01)。结论骨搬运过程回缩程度与滑移段长度、骨搬运长度、固定时间相关,其中骨搬运长度和固定时间与滑移段回缩程度存在线性关系。

The effects of simulated nitrogen deposition on extracellular enzyme activities of litter and soil among different-aged stands of larch

Aims Nitrogen(N)addition could affect the rate of forest litter and soil organic matter decomposition by regulating extracellular enzyme activity(EEa).The impact of N addition on EEa may differ across different age stands with different organic matter quality.We were interested in whether the impact of N addition on EEa in litter and mineral soil during the growing season was dependent on stand age of a larch plantation in North China.Methods We added three levels of N(0,20 and 50 kg N ha^(−1) year^(−1))in three age stands(11,20 and 45 years old)of Larix principis-rupprech-tii plantation in North China.We measured potential activities of β-1,4-glucosidase(b),cellobiohydrolase(Cb),β-1,4-N-acetyl-glucosaminidase(Nag)and phenol oxidase(Po)in litter(organic horizon)and mineral soil(0-10 cm)during the second growing sea-son after N amendment.We also measured C and N concentrations,microbial biomass C and N,and KCl-extractable ammonium and nitrate in both litter and mineral soil.Important Findings We observed unimodal patterns of EEa during the growing season in all three stands,consistent with the seasonal variations of soil temperature.stand age had a strong effect on EEa in both litter and mineral soil,and this effect differed between litter and mineral soil as well as between different enzymes.N addition did not significantly affect the activities of b or Cb but significantly suppressed the activity of Nag in litter.We also found stand age-specific responses of Po activity to N addition in both litter and mineral soil.N addition suppressed Po activity of the high C:N ratio litters in 20-and 45-year-old stands but had no significant effect on Po activity of the low C:N ratio litter in 11-year-old stand.moreover,N addition inhibited Po activity of the high C:N ratio soil in 20-year-old stand but had no significant impact on Po activity of the low C:N ratio soils in 11-and 45-year-old stands.overall,stand age had a greater effect on EEa in litter and mineral soil compared to 2 years of N addition.moreover,the effect of N addition on Po activity is stand age dependent,which may affect the long-term soil carbon storage in this forest.

Effect of bent inlet pipe on the flow instability behavior of centrifugal compressors

Bent inlet pipes are often used in centrifugal compressors due to limited installation space,and an understanding of the effect on compressor stability is essential for safety and durability.This paper firstly investigates flow instability behaviors in two compressors,one with a straight inlet pipe and the other with an S-shaped bent pipe.In detail,it analyzes the resulting flow fields,instability evolution paths and surge boundaries.The results show that the S-shaped pipe obviously affects the flow field at high mass flow rates,while reverse flow mainly influences the flow field at low mass flow rates.Reverse flow first occurs at certain flow passages with a high pressure difference that is predominantly decided by the volute rather than the S-shaped bent pipe.In addition,centrifugal compressors can tolerate reverse flow to some extent so that surge would not occur immediately if reverse flow occurs unless the reverse flow region extends circumferentially and radially to a sufficiently large size.Since the S-shaped pipe is not dominant in the creation and extension of reverse flow,it does not exacerbate the stability of the central compressor to a great extent.Last but not least,the S-shaped pipe is noted to delay the occurrence of surge at 90%rotating speed,which suggests the possibility of improving compressor stability with bent inlet pipes.This result differs from the conventional understanding that inlet distortion usually deteriorates compressor stability and emphasizes the particularity of centrifugal compressors.

Contrasting effects of N addition on the N and P status of understory vegetation in plantations of sapling and mature Larix principis-rupprechtii

Aims The productivity of forest plantations in temperate areas is often lim-ited by nitrogen(N),but may shift towards phosphorus(P)limitation with increasing atmospheric N deposition.Nutrient resorption is a nutrient conservation strategy in plants.Although data on nutrient resorption are available for overstory trees,there are few data for understory vegetation.Methods We examined leaf N and P concentrations and N and P resorption efficiencies(NRE and PRE,respectively)in eight understory species in 11-and 45-year-old Larix principis-rupprechtii stands subjected to N supplementation over a 3-year period.Important findings Leaf N concentrations and N:P ratios increased and P concentrations decreased,with N input in species within the 45-year-old stand,but not in the 11-year-old stand.NRE and PRE were not altered by N input in any of the species in either stand,but N resorption pro-ficiency decreased and P resorption proficiency increased,in the species in the 45-year-old stand.Thus,the growth of understory species may be more P-limited in the 45-versus 11-year-old stand,and nutrient resorption proficiency was more sensitive to N add-ition than nutrient resorption efficiency.These results will improve the understanding of nutrient use strategies and their responses to N addition in understory vegetation.The contrasting effects of N addition on nutrient status between stand ages cannot be ignored when modeling ecosystem nutrient cycling under global N depos-ition conditions.

Nucleation and growth of Fe-rich phases in Al-5Ti-1B modified Al-Fe alloys investigated using synchrotron X-ray imaging and electron microscopy

Plate-like Fe-rich intermetallic phases directly influence the mechanical properties of recycled Al alloys;thus, many attempts have been made to modify the morphology of these phases. Through synchrotron X-ray imaging and electron microscopy, the underlying nucleation and growth mechanisms of Fe-rich phases during the solidification of Al-5 Ti-1 B-modified Al-2 Fe alloys were revealed in this study. The results showed that the Al-5 Ti-1 B grain refiner as well as the applied pressure both resulted in reduction of the size and number of primary Al_(3)Fe phases and promoted the formation of eutectic Al_(6)Fe phases.The tomography results demonstrated that Al-5 Ti-1 B changed the three-dimensional(3 D) morphology of primary Fe-rich phases from rod-like to branched plate-like, while a reduction in their thickness and size was also observed. This was attributed to the fact that Ti-containing solutes in the melts inhibit the diffusion of Fe atoms and the Al_(3)Fe twins produce re-entrant corner on the twin boundaries along the growth direction. Moreover, the TiB_(2) provides possible nucleation sites for Al_6Fe phases. The nucleation mechanism of Fe-rich phases is discussed in terms of experimental observations and crystallography calculations. The decrease in the lattice mismatch between TiB_(2) and Al_(6)Fe phases was suggested, which promoted the transformation of Al_(3)Fe to Al_(6)Fe phases.

Fertilization regulates the response of wheat yield to interannual temperature variation in North China

Aims understanding the effect of long-term fertilization on the sensitivity of grain yield to temperature changes is critical for accurately assess-ing the impact of global warming on crop production.In this study,we aim to assess the impacts of temperature changes on grain yields of winter wheat(Triticum aestivum l.)under different fertilization treatments in a long-term manipulative experiment in North China.Methods We measured grain yields of winter wheat under four fertilization treatments at the Yucheng Comprehensive Experimental station each year from 1993 to 2012.We also measured air temperature at 0200,0800,1400 and 2000 h each day since 1 January 1980.We then used the first-difference method and simple linear regres-sion models to examine the relationship of crop yield changes to mean air temperature,mean daytime and nighttime air temperature in crop growing seasons.Important Findings We found that increases in mean daily temperature,mean day-time temperature and mean nighttime temperature each had a positive impact on the grain yield of winter wheat.grain yield increased by 16.7-85.6%for winter wheat in response to a 1°C increase in growing season mean daily temperature.Winter wheat yield was more sensitive to variations of nighttime temperature than to that of daytime temperature.The observed temperature impacts also varied across different fertilization treatments.balanced fertilization significantly enhanced grain yields for winter wheat under a warming climate.Wheat plots treated with nitrogen and phosphorous balanced fertilization(NPK-and NP-treated plots)were more responsive to temperature changes than those without.This report provides direct evidence of how temperature change impacts grain yields under different fertiliza-tion treatments,which is useful for crop management in a chang-ing global climate.