来流方向对百叶窗翅片‒后扩型涡产生器热工水力性能的影响

Influence of Inflow Direction on Thermal-Hydraulic Performance of Louvered Fin-Common Flow Down Vortex Generator

为改善百叶窗翅片-扁管式热交换器(LFHE)的热工水力性能,将后扩型涡产生器(CFDVG)布置于LFHE冷却管表面,得到百叶窗翅片-后扩型涡产生器(LF-CFDVG)。考虑到主动进气格栅(AGS)的使用将引起热交换器芯部空气来流方向的改变,进一步研究了空气速度为3 m/s时来流方向对LF-CFDVG热工水力性能的影响。结果表明:受CFDVG出现后最小自由流面积减小、空气流速增大而导致的摩擦阻力增加以及CFDVG引起的压差阻力增大的影响,LF-CFDVG的压降Δp总是大于未布置CFDVG的LFHE(Baseline)。在来流方向角γ由0°增加到30°的过程中,受空气流速减小的影响,Baseline和LF-CFDVG中的压降Δp均减小,因此增加γ可降低空气流动阻力。与此同时,在CFDVG诱导形成的纵向涡输送的高速、低温主流对CFDVG间冷却管壁的冲击下,相较于Baseline,LF-CFDVG的对流换热能力显著增强。在γ由0°增加到30°的过程中,受空气流速及纵向涡强度、尺度减小的影响,Baseline和LF-CFDVG中的对流换热系数均减小,因此增加γ有损于换热能力。另外,在γ由0°增加到30°的过程中,LF-CFDVG的综合性能不断降低,因此增加γ不利于综合性能的改善。

In order to improve the thermal-hydraulic performance of louvered fin and flat tube heat exchangers(LFHE),by arranging common flow down vortex generator(CFDVG)on LFHE’s flat tubes,this paper proposes louvered fin-common flow down vortex generator(LF-CFDVG).Then,considering the use of active grille air shutter(AGS)may change the inflow direction of air at the core of LFHE,the influence of inflow direction on the thermalhydraulic performance of LF-CFDVG is further studied at the air velocity of 3 m/s.The results show that the pressure dropΔp of LF-CFDVG is always greater than that of Baseline(namely the LFHE without CFDVG)due to the impact of minimum free flow area reduction after the appearance of CFDVG,the increase in frictional resistance caused by the air velocity increment and the differential pressure resistance caused by CFDVG.In the process ofγ(inflow direction angle)increasing from 0°to 30°,under the influence of air velocity reduction,Δp of both Baseline and LF-CFDVG decreases,so that increasingγhelps to reduce the resistance to air flow.At the same time,under the impact of highspeed and low-temperature main stream transported by the longitudinal vortices on the tube wall between CFDVGs,the convective heat transfer ability of LF-CFDVG is significantly enhanced,as compared with the Baseline.Moreover,in the process ofγincreasing from 0°to 30°,the convective heat transfer coefficients of Baseline and LF-CFDVG both reduce due to the decrease of longitudinal vortex strength and scale,so that increasingγimpairs heat exchange ability.It is also found that the comprehensive performance of LF-CFDVG continuously decreases in the process ofγincreasing from 0°to 30°.Thus,increasingγis not conducive to the improvement of comprehensive performance.