The effects of synthetic jet control on unsteady dynamic stall over rotor airfoil are investigated numerically. A moving-embedded grid method and an Unsteady Reynolds Averaged Navier-Stokes（URANS） solver coupled wit...The effects of synthetic jet control on unsteady dynamic stall over rotor airfoil are investigated numerically. A moving-embedded grid method and an Unsteady Reynolds Averaged Navier-Stokes（URANS） solver coupled with k-x Shear Stress Transport（SST） turbulence model are established for predicting the complex flowfields of oscillatory airfoil under jet control. Additionally, a velocity boundary condition modeled by sinusoidal function has been developed to fulfill the perturbation effect of periodic jet. The validity of present CFD method is evaluated by comparisons of the calculated results of baseline dynamic stall case for rotor airfoil and jet control case for VR-7 B airfoil with experimental data. Then, parametric analyses are conducted emphatically for an OA212 rotor airfoil to investigate the effects of jet control parameters（jet location, dimensionless frequency, momentum coefficient, jet angle, jet type and dual-jet） on dynamic stall characteristics of rotor airfoil. It is demonstrated by the calculated results that efficiency of jet control could be improved with specific momentum coefficient and jet angle when the jet is located near separation point of rotor airfoil. Furthermore, the dual-jet could improve control efficiency more obviously on dynamic stall of rotor airfoil with respect to the unique jet, and the influence laws of dual-jet＇s angles and momentum coefficients on control effects are similar to those of the unique jet. Finally,unsteady aerodynamic characteristics of rotor via synthetic jet which is located on the upper surface of rotor blade in forward flight are calculated, and as a result, the aerodynamic characteristics of rotor are improved compared with the baseline. The results indicate that synthetic jet has the capability in improving aerodynamic characteristics of rotor.展开更多
Natural soils are more durable than almost all man-made materials. Evapotranspiration （ET） covers use vegetated soil layers to store water until it is either evaporated from the soil surface or transpired through ve...Natural soils are more durable than almost all man-made materials. Evapotranspiration （ET） covers use vegetated soil layers to store water until it is either evaporated from the soil surface or transpired through vegetation. ETcovers rely on the water storage capacity of soil layer, rather than low permeability materials, to minimize percolation. While the use of ET covers in landfills increased over the last decade, they were mainly used in arid or semi-arid regions. At present, the use of ET covers has not been thoroughly investigated in humid areas. The purpose of this paper is to investigate the use of ETcovers in humid areas where there is an annual precipitation of more than 800 mm. Numerical analyses were carried out to investigate the influences of cover thickness, soil type, vegetation level and distribution of precipitation on performance of ET covers. Performance and applicability of capillary barriers and a new-type cover were analyzed. The results show that percolation decreases with an increasing cover thickness and an increasing vegetation level, but the increasing trend becomes unclear when certain thickness or LAI （leaf area index） is reached. Cover soil with a large capability of water storage is recommended to minimize percolation. ET covers are significantly influenced by distribution of precipitation and are more effective in areas where rainy season coincides with hot season. Capillary barriers are more efficient than monolithic covers. The new cover is better than the monolithic cover in performance and the final percolation is only 0.5% of the annual precipitation.展开更多
In this study,a system that recovered waste heat from data center’s centralized water-cooling system to preheat centralized heating systems was proposed,and the optimal design parameters were investigated,resolving t...In this study,a system that recovered waste heat from data center’s centralized water-cooling system to preheat centralized heating systems was proposed,and the optimal design parameters were investigated,resolving the mismatch between waste heat and building demand.Firstly,parametric analyses were conducted under the design condition of centralized heating.Effects of mass flow rate and temperature after heat recovery of the data center’s chilled water on performances of the system were investigated.The results showed that,there existed an optimal temperature after heat recovery minimizing primary energy consumption of the system for each mass flow rate,and the values of optimal temperature after heat recovery for different mass flow rate were quite different.Then,the optimal mass flow rate and temperature after heat recovery were determined for different heat capacity ratio between heat supply from data center and heat demand of the centralized heating system.With the data center’s heat density being 500,800,and 1100 W/m2,and the ratio varying from 0.25 to 2,the optimal parameters were summarized.Based on the optimized values,a random forest-based parameter estimation model for machine learning tool was yielded to determine the optimal parameters.Percentage errors of the model were within±15%.With the system being designed following the optimization values,primary energy saving ratio was from 58.7%to 78.2%compared with the traditional ones.This work provides a replicable tool a to assist optimal design and equipment selection of the heat recovery system.展开更多
基金co-supported by the National Natural Science Foundation of China (Nos. 11272150 and 11572156)
文摘The effects of synthetic jet control on unsteady dynamic stall over rotor airfoil are investigated numerically. A moving-embedded grid method and an Unsteady Reynolds Averaged Navier-Stokes（URANS） solver coupled with k-x Shear Stress Transport（SST） turbulence model are established for predicting the complex flowfields of oscillatory airfoil under jet control. Additionally, a velocity boundary condition modeled by sinusoidal function has been developed to fulfill the perturbation effect of periodic jet. The validity of present CFD method is evaluated by comparisons of the calculated results of baseline dynamic stall case for rotor airfoil and jet control case for VR-7 B airfoil with experimental data. Then, parametric analyses are conducted emphatically for an OA212 rotor airfoil to investigate the effects of jet control parameters（jet location, dimensionless frequency, momentum coefficient, jet angle, jet type and dual-jet） on dynamic stall characteristics of rotor airfoil. It is demonstrated by the calculated results that efficiency of jet control could be improved with specific momentum coefficient and jet angle when the jet is located near separation point of rotor airfoil. Furthermore, the dual-jet could improve control efficiency more obviously on dynamic stall of rotor airfoil with respect to the unique jet, and the influence laws of dual-jet＇s angles and momentum coefficients on control effects are similar to those of the unique jet. Finally,unsteady aerodynamic characteristics of rotor via synthetic jet which is located on the upper surface of rotor blade in forward flight are calculated, and as a result, the aerodynamic characteristics of rotor are improved compared with the baseline. The results indicate that synthetic jet has the capability in improving aerodynamic characteristics of rotor.
基金funded by the National Natural Science Foundation of China (51178260)Open Project of MOE Key Laboratory of Soft Soil and Geoenvironmental Engineering, Zhejiang University (2011P02)
文摘Natural soils are more durable than almost all man-made materials. Evapotranspiration （ET） covers use vegetated soil layers to store water until it is either evaporated from the soil surface or transpired through vegetation. ETcovers rely on the water storage capacity of soil layer, rather than low permeability materials, to minimize percolation. While the use of ET covers in landfills increased over the last decade, they were mainly used in arid or semi-arid regions. At present, the use of ET covers has not been thoroughly investigated in humid areas. The purpose of this paper is to investigate the use of ETcovers in humid areas where there is an annual precipitation of more than 800 mm. Numerical analyses were carried out to investigate the influences of cover thickness, soil type, vegetation level and distribution of precipitation on performance of ET covers. Performance and applicability of capillary barriers and a new-type cover were analyzed. The results show that percolation decreases with an increasing cover thickness and an increasing vegetation level, but the increasing trend becomes unclear when certain thickness or LAI （leaf area index） is reached. Cover soil with a large capability of water storage is recommended to minimize percolation. ET covers are significantly influenced by distribution of precipitation and are more effective in areas where rainy season coincides with hot season. Capillary barriers are more efficient than monolithic covers. The new cover is better than the monolithic cover in performance and the final percolation is only 0.5% of the annual precipitation.
基金The authors appreciate the support of the project from Outstanding Youth Team of USTB(Fundamental Research Funds for the Central Universities)under grant FRFEYIT-23-06.
文摘In this study,a system that recovered waste heat from data center’s centralized water-cooling system to preheat centralized heating systems was proposed,and the optimal design parameters were investigated,resolving the mismatch between waste heat and building demand.Firstly,parametric analyses were conducted under the design condition of centralized heating.Effects of mass flow rate and temperature after heat recovery of the data center’s chilled water on performances of the system were investigated.The results showed that,there existed an optimal temperature after heat recovery minimizing primary energy consumption of the system for each mass flow rate,and the values of optimal temperature after heat recovery for different mass flow rate were quite different.Then,the optimal mass flow rate and temperature after heat recovery were determined for different heat capacity ratio between heat supply from data center and heat demand of the centralized heating system.With the data center’s heat density being 500,800,and 1100 W/m2,and the ratio varying from 0.25 to 2,the optimal parameters were summarized.Based on the optimized values,a random forest-based parameter estimation model for machine learning tool was yielded to determine the optimal parameters.Percentage errors of the model were within±15%.With the system being designed following the optimization values,primary energy saving ratio was from 58.7%to 78.2%compared with the traditional ones.This work provides a replicable tool a to assist optimal design and equipment selection of the heat recovery system.
