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首页> 外文期刊>International Journal of Heat and Mass Transfer >Direct numerical simulation of the compression stroke under engine-relevant conditions: Evolution of the velocity and thermal boundary layers
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Direct numerical simulation of the compression stroke under engine-relevant conditions: Evolution of the velocity and thermal boundary layers

机译：发动机相关条件下压缩冲程的直接数值模拟：速度和热边界层的演变

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摘要

The unsteady velocity and thermal boundary layers during the compression stroke under engine-relevant conditions are investigated using direct numerical simulation (DNS). The initial conditions are derived by a precursor DNS of the intake stroke, avoiding the use of any artificial initial and boundary conditions. The results show decreasing velocity and thermal boundary-layer thicknesses towards Top Dead Center (TDC) as a result of the decreasing kinematic viscosity. Compared to the fluctuating flow field, the azimuthally-averaged velocities are found to have a minor effect on the boundary-layer profiles, and as a result the boundary-layer structures at all engine walls during compression are similar. The averaged velocity and thermal boundary-layer profiles deviate strongly from the law of the wall, which is the basis for many wall heat transfer models in internal combustion engines. In density wall-normal units, the averaged as well as the rms boundary-layer profiles for velocity and temperature show a collapse onto a single curve during the whole compression stroke. This finding can serve as base for the development of novel wall heat transfer models. Finally, the DNS data showed that between 60% and 80% of the total wall heat losses during the compression stroke are attributed to convective transport due to wall-normal velocity fluctuations.
机译：使用直接数值模拟（DNS）研究了在发动机相关条件下压缩冲程期间的非定常速度和热边界层。初始条件是通过进气冲程的前体DNS得出的，从而避免了使用任何人为的初始条件和边界条件。结果表明，由于运动粘度的降低，速度和热边界层厚度朝着上止点（TDC）的方向减小。与波动流场相比，发现方位角平均速度对边界层轮廓的影响较小，因此压缩期间所有发动机壁的边界层结构都相似。平均速度和热边界层轮廓与壁的定律有很大的偏离，这是内燃机中许多壁传热模型的基础。在密度壁法线单位中，速度和温度的平均值以及均方根边界层轮廓在整个压缩冲程中均显示为一条曲线。这一发现可以作为开发新型壁传热模型的基础。最后，DNS数据显示，在压缩冲程期间，壁总热量损失的60％至80％是由于壁法向速度波动引起的对流传输。

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