船用大功率柴油机瞬态工况油气响应及燃烧特性研究

针对船用大功率柴油机瞬态性能提升的需求，开展了增压中冷船用大功率柴油机瞬态工况动态响应及燃烧特性实验研究。研究表明，涡轮增压器惯性导致的进气滞后是柴油机瞬态工况下性能恶化的主要原因；突加载工况下，进气量响应滞后供油量响应4~5个工作循环，且进气量响应速度随初始负荷增加而增加，指示平均有效压力（Indicated Mean Effective Pressure，IMEP）等燃烧特征参数加载过程中响应速度较快，波动较小；缸内燃烧过程恶化，燃烧重心和燃烧终点较同负荷下稳态工况值均推迟。     

An intelligent approach for flight risk prediction under icing conditions

Flight risk prediction is significant in improving the flight crew’s situational awareness because it allows them to adopt appropriate operation strategies to prevent risk expansion caused by abnormal conditions, especially aircraft icing conditions. The flight risk space representing the nonlinear mapping relations between risk degree and the three-dimensional commanded vector(commanded airspeed, commanded bank angle, and commanded vertical velocity) is developed to provide the crew with practi...     

Compressor geometric uncertainty quantification under conditions from near choke to near stall

Geometric and working condition uncertainties are inevitable in a compressor, deviating the compressor performance from the design value. It’s necessary to explore the influence of geometric uncertainty on performance deviation under different working conditions. In this paper, the geometric uncertainty influences at near stall, peak efficiency, and near choke conditions under design speed and low speed are investigated. Firstly, manufacturing geometric uncertainties are analyzed. Next, correlation models between geometry and performance under different working conditions are constructed based on a neural network. Then the Shapley additive explanations (SHAP) method is introduced to explain the output of the neural network. Results show that under real manufacturing uncertainty, the efficiency deviation range is small under the near stall and peak efficiency conditions. However, under the near choke conditions, efficiency is highly sensitive to flow capacity changes caused by geometric uncertainty, leading to a significant increase in the efficiency deviation amplitude, up to a magnitude of ?3.6%. Moreover, the tip leading-edge radius and tip thickness are two main factors affecting efficiency deviation. Therefore, to reduce efficiency uncertainty, a compressor should be avoided working near the choke condition, and the tolerances of the tip leading-edge radius and tip thickness should be strictly controlled.     

圆弧型指尖密封迟滞特性的数学计算方法

为了预测指尖密封迟滞特性，提出了用能够直观反映指尖密封迟滞特性的最小迟滞量来表征指尖密封的迟滞，建立了指尖密封最小迟滞量计算的数学模型，确定了模型中的修正系数，并进行了试验验证，采用修正后的计算模型研究并获得了结构和工况参数对指尖密封迟滞的影响规律。研究结果表明:采用修正后的模型进行考虑迟滞效应的泄漏特性数值计算与试验结果误差最大为7.64%，最小迟滞量的计算模型合理可靠；指尖密封结构参数对其最小迟滞量影响程度从小到大依次为:指梁型线圆、指梁间隙、指梁根圆、指梁顶圆、指梁基圆、周向角、指尖片厚度。研究结果为进一步开展迟滞对指尖密封泄漏特性影响和指尖密封结构优化设计的研究提供了依据和理论基础。