Purpose

This study aims to get a better understanding of the impact of streamlined high-speed trains (HSTs) with geometric uncertainty on aerodynamic performance, as well as the identification of the key parameters responsible for this impact. To reveal the critical parameters, this study creates a methodology for evaluating the uncertainty and sensitivity of drag coefficient induced by design parameters of HST streamlined shapes.

Design/methodology/approach

Bézier curves are used to parameterize the streamlined shape of HSTs, and there are eight design parameters required to fit the streamlined shape, followed by a series of steady Reynolds-averaged Navier–Stokes simulations. Combining the preparation work with the nonintrusive polynomial chaos method results in a workflow for uncertainty quantification and global sensitivity analysis. Based on this framework, this study quantifies the uncertainty of drag, pressure, surface friction coefficient and wake flow characteristics within the defined ranges of streamline shape parameters, as well as the contribution of each design parameter.

Findings

The results show that the change in drag reaches a maximum deviation of 15.37% from the baseline, and the impact on the tail car is more significant, with a deviation of up to 23.98%. The streamlined shape of the upper surface and the length of the pilot (The device is mounted on the front of a train’s locomotive and primarily serves to remove obstacles from the tracks, thereby preventing potential derailment.) are responsible for the dominant factors of the uncertainty in the drag for HSTs. Linear regression results show a significant quadratic polynomial relationship between the length of the pilot and the drag coefficient. The drag declines as the length of the pilot enlarges. By analyzing the case with the lowest drag, the positive pressure area in the front of pilot is greatly reduced, while the nose tip pressure of the tail is enhanced by altering the vortices in the wake. The counter-rotating vortex pair is significantly attenuated. Accordingly, exerts the impacts caused by geometric uncertainty can be found on the wake flow region, with pressure differences of up to 900 Pa. The parameters associated with the shape of the upper surface contribute significantly to the uncertainty in the core of the wake separation region.

Originality/value

The findings contribute to a better understanding of the impact of streamlined HSTs with geometric uncertainty on aerodynamic performance, as well as the identification of the key parameters responsible for this impact. Based on this study, future research could delve into the detailed design of critical areas in the streamlined shape of HSTs, as well as the direction of shape optimization to more precisely and efficiently reduce train aerodynamic drag under typical conditions.

中文翻译：

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流线型几何不确定性的高速列车空气动力学量化分析

 目的

本研究旨在更好地了解具有几何不确定性的流线型高速列车 （HST） 对空气动力学性能的影响，并确定导致这种影响的关键参数。为了揭示关键参数，本研究创建了一种方法来评估由 HST 流线型形状的设计参数引起的阻力系数的不确定性和敏感性。

设计/方法/方法

贝塞尔曲线用于参数化 HST 的流线型形状，需要八个设计参数来拟合流线型形状，然后是一系列稳态雷诺平均纳维-斯托克斯仿真。将准备工作与非侵入性多项式混沌方法相结合，可以得到一个用于不确定性量化和全局敏感性分析的工作流程。基于这个框架，本研究量化了流线形状参数定义范围内的阻力、压力、表面摩擦系数和尾流特性的不确定性，以及每个设计参数的贡献。

 发现

结果表明：阻力变化与基线的最大偏差达到 15.37%，对尾车的影响更为显著，偏差高达 23.98%。上表面的流线型形状和飞行员的长度（该装置安装在火车机车的前部，主要用于清除轨道上的障碍物，从而防止潜在的脱轨）是 HST 阻力不确定性的主要因素。线性回归结果显示飞行员的长度和阻力系数之间存在显着的二次多项式关系。阻力随着飞行员长度的增加而下降。通过分析阻力最小的情况，飞行员前部的正压面积大大减少，而尾部的鼻尖压力则通过改变尾流中的涡流而增强。反向旋转的涡旋对明显衰减。因此，几何不确定性对尾流区域的影响可以发现，压力差高达 900 Pa。与上表面形状相关的参数对尾流分离区核心的不确定性有很大影响。

 原创性/价值

这些发现有助于更好地了解具有几何不确定性的流线型 HST 对空气动力学性能的影响，以及确定导致这种影响的关键参数。基于这项研究，未来的研究可以深入研究 HST 流线型形状中关键区域的详细设计，以及形状优化的方向，以更精确、更有效地减少典型条件下的列车气动阻力。