Numerical analysis of wind effects on aerodynamic characteristics of a ducted fan

Ducted fans have been extensively used in Unmanned Aerial Vehicles(UAVs)for a variety of missions because of high efficiency,high safety and low noise.Wind,as a kind of typical meteorological condition,brings significant aerodynamic interference to the ducted fan,which seriously threatens flight stability and safety.In this work,the numerical simulation with the Unsteady Reynolds Averaged Navier-Stokes(URANS)method and the sliding mesh technique is performed to evaluate the steady wind effect.The results show that the wind will lead to serious unsteady effects in the flow field,and the thrust fluctuates at the blade passing frequency of 200 Hz.As the wind speed increases,the rotor thrust increases,the duct thrust decreases,and the total thrust changes little.Flow instability may occur when the wind speed exceeds 8 m/s.As the angle of low-speed wind increases,the rotor thrust changes little,the duct thrust increases,and the total thrust increases.In addition,we figure out that cases with the same crosswind ratio are similar in results,and increasing the rotating speed or fan radius is beneficial to performance improvement in wind.The findings are essential to the ducted fan design and UAV flight control design for stable and safe operations in wind conditions.

Numerical investigation on unsteady characteristics of ducted fans in ground effect

Ducted fans are widely used in various applications of Unmanned Aerial Vehicles(UAVs)due to the high efficiency,low noise and high safety.The unsteady characteristics of ducted fans flying near the ground are significant,which may bring stability problems.In this paper,the sliding mesh technology is applied and the Unsteady Reynolds Averaged Navier-Stokes(URANS)method is adopted to evaluate the influence of ground on the aerodynamic performance of ducted fans.The time-averaged results show that the ground leads to the decrease of duct thrust,the increase of rotor thrust and the decrease of total thrust.The transient results show that there exist small-scale stall cells with circumferential movements in ground effect.The stall cells start to appear at the blade root when the height is 0.8 rotor radius distance,and arise at both the blade root and tip when the height drops to 0.2.It is found that the unsteady cells rotate between blade passages with an approximate relative speed of 30%-80%of the fan speed,and lead to thrust fluctuations up to 37%of the total thrust.The results are essential to the flight control design of the ducted fan flying vehicle,to ensure its stability in ground effect.

基于热管技术的动力电池热管理系统研究现状及展望

电池热管理是发展高性能动力电池系统的关键技术之一,也是工程热物理领域研究前沿和热点.本文介绍锂离子动力电池热特性,阐述热管理对动力电池的重要性.介绍动力电池热管理主要技术手段,重点介绍热管技术应用于电池热管理的研究现状,从电池运行工况对系统传热的影响研究、热管传热特性分析与设计、热管理系统散热结构设计与传热分析及采用热管的电池加热研究4个方面阐述当前基于热管技术的电池热管理研究现状.最后,总结当前研究存在的不足及需要突破的关键问题,以期促进先进动力电池热管理系统开发.

基于电池热管理系统的微通道热管阵列的传热性能

温度是影响动力电池性能的关键因素.高效热管理技术可有效控制动力电池温度和温差.本研究采用微通道热管阵列作为电池热管理系统的热传导元件,分析了其在高热功率密度下的传热性能,理论计算了其等效导热系数,优化分析了其槽道尺寸对流动传热的影响,对比了其与主流散热技术的性能差异.研究发现,热功率密度为0.3658 W cm^-2时,强制风冷散热条件下,采用微通道热管阵列技术可维持热源处表面温度45℃以下,温差1.3℃以下,低于无微通道热管阵列导热情况下的温升15℃,温差3.8℃.随着热功率密度增大至0.9176 W cm^-2,微通道热管阵列的等效导热系数增大为6027 W m^-1K^-1,其热源处表面最大瞬态温差约2.75℃.增大槽道尺寸参数可进一步改善微通道热管阵列的导热系数,改善其传热性能,但对液体回流驱动力有一定影响.该阵列具有较好的动态工况热稳定性和低温快速加热能力.与烧结热管组的温度性能相比,微通道热管阵列组最大温度可降低15.1℃,表面温差降低14℃,具有显著降温和均温优势,表明微通道热管阵列在动力电池热管理系统中具有广泛应用前景.

Thermal Performance of a Micro Heat Pipe Array for Battery Thermal Management Under Special Vehicle-Operating Conditions

The thermal management of battery systems is critical for maintaining the energy storage capacity,life span,and thermal safety of batteries used in electric vehicles,because the operating temperature is a key factor affecting battery performance.Excessive temperature rises and large temperature differences accelerate the degradation rate of such batteries.Currently,the increasing demand for fast charging and special on-vehicle scenarios has increased the heat dissipation requirements of battery thermal management systems.To address this demand,this work proposes a novel micro heat pipe array(MHPA)for thermal management under a broadened research scope,including high heat generation rates,large tilt angles,mild vibration,and distributed heat generation conditions.The experimental results indicate that the temperature difference is maintained 3.44°C at a large heat generation of 50 W for a limited range of tilt angles.Furthermore,a mild vehicle vibra-tion condition was found to improve temperature uniformity by 3.3°C at a heat generation of 10 W.However,the use of distributed heat sources results in a temperature variation of 3.88°C,suggesting that the heat generation distribution needs to be considered in thermal analyses.Understanding the effects of these special battery-operating conditions on the MHPA could significantly contribute to the enhancement of heat transfer capability and temperature uniformity improvement of battery thermal management systems based on heat pipe technologies.This would facilitate the realization of meeting the higher requirements of future battery systems.

A stepwise-responsive editor integrated with three copper ions for the treatment of oral squamous cell carcinoma

Cuprotosis,a new type of cell death,provides great opportunities for the treatment of oral squamous cell carcinoma,as nanocarriers of copper ions can induce cuprotosis and immunogenic death.Here,we studied an editor that enables production of a nanoparticle“storm”in oral squamous cell carcinoma,maximizing the toxic effect of these particles and reprogramming the tumor microenvironment;as a result,T cells and natural killer(NK)cells can infiltrate the tumor microenvironment to activate an antitumor immune response.On this basis,the editor can be combined with optical therapy to improve patient prognosis.In this study,the metal ratio was regulated in response to the nanocarrier of acid response type.Thus,in the presence of a specific copper ion content,the nanocarrier could change the permeability of the tumor cell membrane.Based on these results,the nanoparticles were cracked in an acidic environment and then released copper ions.Finally,the nanoparticles contributed to cuprotosis and immunogenic death.In addition,the editor could inhibit murine oral cancer 1(MOC1)tumors in C57BL/6 without toxicity.The rate of tumor growth inhibition was as high as approximately 80%.This strategy provides a new idea for immunotherapy.Moreover,it can improve the interaction between immunotherapy and the copper-induced death of oral squamous cell carcinoma.Above all,this study will provide a new opportunity for the effective treatment of oral squamous cell carcinoma.