This paper applies the method of numerical simulation and field detection, and studied energy-saving insulation characteristics on the external wails of high-rise buildings in cold area, analyze and recommend the best...This paper applies the method of numerical simulation and field detection, and studied energy-saving insulation characteristics on the external wails of high-rise buildings in cold area, analyze and recommend the best arrangement of building and the most generous exterior wall insulation system suitable for cold area, and the degree of insulation materials were studied. The results show that： the mode preferred cold area is exterior insulation, insulation material made of extruded polystyrene board, frame structure filling wall preferred ceramsite hollow block.展开更多
Invasive plants usually experience population differentiation as they expand from their initial invasive range to the edge.Moreover,invasive plants usually encounter competitors which shared different co-evolutionary ...Invasive plants usually experience population differentiation as they expand from their initial invasive range to the edge.Moreover,invasive plants usually encounter competitors which shared different co-evolutionary histories with them.These factors may lead to varying responses of invasive plant populations to elevated nitrogen deposition during expansion.However,this issue has received limited attention in prior research.To address these challenges,we conducted a greenhouse experiment to investigate how population differentiation of Galinsoga quadriradiata interacts with the presence of various competitors in response to increased nitrogen deposition.Competitor types(new or old that shared short or long co-evolutionary history with the invader,respectively)were set to compete with the invasive central and edge populations under different nitrogen addition treatments.Individuals from the central population of G.quadriradiata,originating from the initial invasion range,showed greater total mass,reproduction and interspecific competitiveness compared with the edge population.Nitrogen addition improved growth and reproductive performance in both populations,and the central population had a stronger response compared with the edge population.The performance of G.quadriradiata was inhibited more effectively by old competitors than new competitors.Our results indicate that population differentiation occurs in terms of growth and competitiveness during the range expansion of G.quadriradiata,with the central population exhibiting superior performance.Co-evolutionary history with competitors is considered unfavorable for invasive plants in this study.Our results highlight the combined effects of population differentiation in invasive species and their co-evolution history with competitors in the context of global change factors.展开更多
This paper deals with the effect of the blade tip-groove of the low solidity cascade diffuser (LSD) on the blowercharacteristic and the noise generated by the LSD. The small grooves were set up at the root and/or tip ...This paper deals with the effect of the blade tip-groove of the low solidity cascade diffuser (LSD) on the blowercharacteristic and the noise generated by the LSD. The small grooves were set up at the root and/or tip near theleading edge of the LSD blade. In order to clarify the mechanism of noise increase due to LSD and also to reducethe noise, the relationships between the noise increase based on the LSD, the LSD performance and the secondaryflow formed additionally by the tip-groove were investigated experimentally as well as numerically, especiallyanalyzing flow behaviors in the LSD in view points of flow separation on the suction surface of the LSD bladeand the secondary flow on the side walls. By reducing the stagnation region smaller near the root and/or tip of theLSD blade leading edge, the secondary flow behavior changes remarkably around the LSD blade, as a result, thenoise level and the blower characteristics vary. It can be concluded that, by means of a small tip-groove locatedonly at the shroud side near the LSD blade leading edge, the noise generated by the LSD can be reduced withoutdeteriorations of the LSD performance and the blower characteristics as well.展开更多
The characteristics of a rotating stall of an impeller and diffuser and the evolution of a vortex generated at the diffuser leading-edge(i.e., the leading-edge vortex(LEV)) in a centrifugal compressor were investigate...The characteristics of a rotating stall of an impeller and diffuser and the evolution of a vortex generated at the diffuser leading-edge(i.e., the leading-edge vortex(LEV)) in a centrifugal compressor were investigated by experiments and numerical analysis. The results of the experiments revealed that both the impeller and diffuser rotating stalls occurred at 55 and 25 Hz during off-design flow operation. For both, stall cells existed only on the shroud side of the flow passages, which is very close to the source location of the LEV. According to the CFD results, the LEV is made up of multiple vortices. The LEV is a combination of a separated vortex near the leading-edge and a longitudinal vortex generated by the extended tip-leakage flow from the impeller. Therefore, the LEV is generated by the accumulation of vorticity caused by the velocity gradient of the impeller discharge flow. In partial-flow operation, the spanwise extent and the position of the LEV origin are temporarily transmuted. The LEV develops with a drop in the velocity in the diffuser passage and forms a significant blockage within the diffuser passage. Therefore, the LEV may be regarded as being one of the causes of a diffuser stall in a centrifugal compressor.展开更多
文摘This paper applies the method of numerical simulation and field detection, and studied energy-saving insulation characteristics on the external wails of high-rise buildings in cold area, analyze and recommend the best arrangement of building and the most generous exterior wall insulation system suitable for cold area, and the degree of insulation materials were studied. The results show that： the mode preferred cold area is exterior insulation, insulation material made of extruded polystyrene board, frame structure filling wall preferred ceramsite hollow block.
基金supported by the National Natural Science Foundation of China(32271584,31600445 and 32071520)the Natural Science Basic Research Plan in Shaanxi Province of China(2020JM-286)+1 种基金the Fundamental Research Funds for the Central Universities(GK202103072,GK202103073 and 2020CSLY014)the Research Funds of Shaanxi Association for Science and Technology and the Research Funds of Xi’an Association for Science and Technology(202113).
文摘Invasive plants usually experience population differentiation as they expand from their initial invasive range to the edge.Moreover,invasive plants usually encounter competitors which shared different co-evolutionary histories with them.These factors may lead to varying responses of invasive plant populations to elevated nitrogen deposition during expansion.However,this issue has received limited attention in prior research.To address these challenges,we conducted a greenhouse experiment to investigate how population differentiation of Galinsoga quadriradiata interacts with the presence of various competitors in response to increased nitrogen deposition.Competitor types(new or old that shared short or long co-evolutionary history with the invader,respectively)were set to compete with the invasive central and edge populations under different nitrogen addition treatments.Individuals from the central population of G.quadriradiata,originating from the initial invasion range,showed greater total mass,reproduction and interspecific competitiveness compared with the edge population.Nitrogen addition improved growth and reproductive performance in both populations,and the central population had a stronger response compared with the edge population.The performance of G.quadriradiata was inhibited more effectively by old competitors than new competitors.Our results indicate that population differentiation occurs in terms of growth and competitiveness during the range expansion of G.quadriradiata,with the central population exhibiting superior performance.Co-evolutionary history with competitors is considered unfavorable for invasive plants in this study.Our results highlight the combined effects of population differentiation in invasive species and their co-evolution history with competitors in the context of global change factors.
文摘This paper deals with the effect of the blade tip-groove of the low solidity cascade diffuser (LSD) on the blowercharacteristic and the noise generated by the LSD. The small grooves were set up at the root and/or tip near theleading edge of the LSD blade. In order to clarify the mechanism of noise increase due to LSD and also to reducethe noise, the relationships between the noise increase based on the LSD, the LSD performance and the secondaryflow formed additionally by the tip-groove were investigated experimentally as well as numerically, especiallyanalyzing flow behaviors in the LSD in view points of flow separation on the suction surface of the LSD bladeand the secondary flow on the side walls. By reducing the stagnation region smaller near the root and/or tip of theLSD blade leading edge, the secondary flow behavior changes remarkably around the LSD blade, as a result, thenoise level and the blower characteristics vary. It can be concluded that, by means of a small tip-groove locatedonly at the shroud side near the LSD blade leading edge, the noise generated by the LSD can be reduced withoutdeteriorations of the LSD performance and the blower characteristics as well.
文摘The characteristics of a rotating stall of an impeller and diffuser and the evolution of a vortex generated at the diffuser leading-edge(i.e., the leading-edge vortex(LEV)) in a centrifugal compressor were investigated by experiments and numerical analysis. The results of the experiments revealed that both the impeller and diffuser rotating stalls occurred at 55 and 25 Hz during off-design flow operation. For both, stall cells existed only on the shroud side of the flow passages, which is very close to the source location of the LEV. According to the CFD results, the LEV is made up of multiple vortices. The LEV is a combination of a separated vortex near the leading-edge and a longitudinal vortex generated by the extended tip-leakage flow from the impeller. Therefore, the LEV is generated by the accumulation of vorticity caused by the velocity gradient of the impeller discharge flow. In partial-flow operation, the spanwise extent and the position of the LEV origin are temporarily transmuted. The LEV develops with a drop in the velocity in the diffuser passage and forms a significant blockage within the diffuser passage. Therefore, the LEV may be regarded as being one of the causes of a diffuser stall in a centrifugal compressor.
