Study on the influence of geometric dimensions on the profile design of flexible nozzle in wind tunnel

几何尺寸对风洞柔壁喷管型面设计的影响研究

Facility Design and Instrumentation Institute, China Aerodynamics Research and Development Center, Mianyang 621000, China

Received: 20 November 2024

Abstract

With the numerical simulation method, the nozzle design results on a basic model and a scaled model are studied through analyzing symmetric plane Mach number distribution, density gradient distribution and central axis Mach number distribution curve in the wind tunnel test section. The main purposes of the study are: to compare the flow field uniformity of the two models, including the root mean square deviation of Mach number in the first diamond region, axial Mach number gradient and average Mach number, to obtain the preliminary influence of geometric dimensions on nozzle design results and to provide guidance for nozzle design in wind tunnels of different scales. The results show that: with the increase of the geometric dimensions of the wind tunnel, the Reynolds number of the flow field increases, the wall viscosity weakens, the boundary layer is thinner and the flow is easier. Under the same flow condition, the thickness of the boundary layer of the scaled model accounts for about 8% of the cross-section dimension, while that of the basic model accounts for only about 5%. Smaller boundary layer thickness has less influence on laminar flow profile. The adverse effect caused by boundary layer correction is weakened, thus improving the quality of the flow field. Compared with the scaled model, the average Mach number in the first diamond region of the basic model increases by 2-3 times, the root mean square deviation of Mach number basically improves by more than 30%, and the axial Mach number gradient increases by at least one order of magnitude. The average Mach number of the basic model is closer to the design value; the root mean square deviation of Mach number and the axial Mach number gradient are smaller than those of the scaled model; the flow field improves comprehensively.

摘要

采用数值模拟方法, 通过分析风洞试验段对称面马赫数分布云图、密度梯度分布云图和中心轴线马赫数分布曲线, 研究了基础模型和缩比模型的喷管设计结果。通过对比2种模型的流场均匀性如第一菱形区马赫数均方根偏差、轴向马赫数梯度和平均马赫数等流场均匀性指标, 获取几何尺寸对喷管设计结果的初步影响, 为不同规模风洞的喷管设计提供指导。结果表明, 风洞几何寸增大引起流场雷诺数增大, 壁面黏性减弱, 边界层更薄, 流动越容易, 相同来流工况下, 缩比模型边界层厚度约占截面尺寸的8%, 而基础模型只占约5%。较小的边界层厚度对层流型线的影响更小, 由边界层修正带来的不利影响减弱, 流场品质更佳。基础模型相比缩比模型, 第一菱形区平均马赫数指标提升2~3倍, 马赫数均方根偏差基本改善30%以上, 轴向马赫数梯度则至少提升一个量级, 即基础模型相比缩比模型平均马赫数更接近设计值、马赫数均方根偏差和轴线马赫数梯度更小, 流场指标全面提升。