Fast Algorithm for Prediction of Airfoil Anti-icing Heat Load

Many flight and icing conditions should be considered in order to design an efficient ice protection system to prevent ice accretion on the aircraft surface. The anti-icing heat load is the basic knowledge for the design of a thermal anti-icing system. In order to help the design of the thermal anti-icing system and save the design time, a fast and efficiency method for prediction the anti-icing heat load is investigated. The computation fluid dynamics (CFD) solver and the Messinger model are applied to obtain the snapshots. Examples for the calculation of the anti-icing heat load using the proper orthogonal decomposition (POD) method are presented and compared with the CFD simulation results. It is shown that the heat loads predicted by POD method are in agreement with the CFD computation results. Moreover, it is obviously to see that the POD method is time-saving and can meet the requirement of real-time prediction.

多步法冰晶积冰数值模拟

近年来,冰晶结冰问题逐渐成为飞机/发动机防除冰领域研究的热点。为了实现对冰晶积冰过程的准确预测,建立了冰晶结冰计算模型,包括考虑了不规则形状的冰晶运动轨迹模型、冰晶结冰质量动量守恒模型、黏附模型、侵蚀模型。采用时间多步法模拟积冰过程,在每个时间步长内更新空气流场、冰晶粒子运动轨迹、结冰热力学计算结果,并利用动网格技术更新冰形的几何边界。研究结果表明,利用时间多步法进行计算,能够实现稳定冰形的模拟。稳定冰形形成的原因在于:一方面,积冰减少了表面冰晶的黏附量;另一方面,积冰增大了对已形成积冰的侵蚀量,最终使黏附积冰过程与侵蚀过程达到动态平衡。本文模型和计算方法适用于低融化率情况,能够对三维结构冰晶结冰数值模拟提供指导,但对于高融化率情况还需要进一步考虑积冰向下游流走的情况。

Sensitivity analysis of flowfield modeling parameters upon the flow structure and aerodynamics of an opposing jet over a hypersonic blunt body

Implementation of an opposing jet in design of a hypersonic blunt body significantly modifies the external flowfield and yields a considerable reduction in the aerodynamic drag.This study aims to investigate the effects of flowfield modeling parameters of injection and freestream on the flow structure and aerodynamics of a blunt body with an opposing jet in hypersonic flow.Reynolds-Averaged Navier-Stokes(RANS)equations with a Shear Stress Transport(SST)turbulence model are employed to simulate the intricate jet flow interaction.Through utilizing a Non-Intrusive Polynomial Chaos(NIPC)method to construct surrogates,a functional relation is established between input modeling parameters and output flowfield and aerodynamic quantities in concern.Sobol indices in sensitivity analysis are introduced to represent the relative contribution of each parameter.It is found that variations in modeling parameters produce large variations in the flow structure and aerodynamics.The jet-to-freestream total-pressure ratio,jet Mach number,and freestream Mach number are the major contributors to variation in surface pressure,demonstrating an evident location-dependent behavior.The penetration length of injection,reattachment angle of the shear layer,and aerodynamic drag are also most sensitive to the three crucial parameters above.In comparison,the contributions of freestream temperature,freestream density,and jet total temperature are nearly negligible.

Review of nanofluids for heat transfer applications

Research on nanofluids has progressed rapidly since its enhanced thermal conductivity was first reported about a decade ago, though much controversy and inconsistency have been reported, and insufficient understanding of the formulation and mechanism of nanofluids further limits their applications. This work presents a critical review of research on heat transfer applications of nanofluids with the aim of identifying the limiting factors so as to push forward their further development.

Experimental investigation and correlation development of jet impingement heat transfer with two rows of aligned jet holes on an internal surface of a wing leading edge

Extensive experimental studies on the heat transfer characteristics of two rows of aligned jet holes impinging on a concave surface in a wing leading edge were conducted, where50000 Rej 90000, 1.74 H/d 27.5, 66° a 90°, and 13.2 r/d 42.03. The finding was that the heat transfer performance at the jet-impingement stagnation point with two rows of aligned jet holes was the same as that with a single row of jet holes or the middle row of three-row configurations when the circumferential angle of the two jet holes was larger than 30°. The attenuation coefficient distribution of the jet impingement heat transfer in the chordwise direction was so complicated that two zones were divided for a better analysis. It indicated that： the attenuation coefficient curve in the jet impingement zone exhibited an approximate upside-down bell shape with double peaks and a single valley; the attenuation coefficient curve in the non-jet impingement zone was like a half-bell shape, which was similar to that with three rows of aligned jet holes; the factors,including Rej, H/d and r/d, affected the attenuation coefficient value at the valley significantly.When r/d was increased from 30.75 to 42.03, the attenuation rates of attenuation coefficient increased only by 1.8%. Consequently, experimental data-based correlation equations of the Nusselt number for the heat transfer at the jet-impingement stagnation point and the distributionof the attenuation coefficient in the chordwise direction were acquired, which play an important role in designing the wing leading edge anti-icing system with two rows of aligned jet holes.

Thermal performance of a 3D printed lattice-structure heat sink packaging phase change material

Thermal storage technology is becoming more and more significant with the increase of high-power equipment in space applications.In this paper,3 D printing technology and Phase Change Material(PCM)were combined into a Thermal Energy Storage(TES)system,which could fulfill the requirements of light weight and high thermal conductivity.A 3 D-printed lattice-structure TES plate with N-tetradecane as the PCM and aluminum alloy as the thermal conductivity enhancer was manufactured,and experimentally tested in a thermal vacuum chamber.In addition,a simplified simulation model of the lattice cell was established to clearly analyze the heat transfer process of the TES plate.The effects of initial temperature distribution and heat load gradient on the thermal storage performances were investigated experimentally and theoretically.The equivalent thermal conductivity of the 3 D-printed lattice-structure TES plate turns out to be 13 times of the pure PCM thanks to the aluminum skeleton.The heat transfer enhancement appears at the end of the phase change stage due to the sudden mixture of the PCM with different temperature.The simulation results agree well with the experimental data.The equivalent thermal conductivity obtained by the phase change simulations are a little higher than those of the experiments,which is mainly caused by the initial uneven temperature distribution in the tests.Additionally,the effects of non-uniform heat load and the presence of the PCM in the TES plate are studied.This work successfully validates the feasibility and effectiveness of 3 D printing technology and TES technology for the temperature control in space applications.

Analysis and control optimization of positive pressure fluctuation in electromechanical oxygen regulator

The Electromechanical Oxygen Regulator(EMOR)is a new type of aviator oxygen equipment.Positive pressure refers to the pressure difference between the breath pressure and the ambient pressure during pressurized oxygen supply.The phenomenon of positive pressure fluctuation was believed to reduce the system performance.The current open-loop control method cannot solve this problem.In this paper,the mathematical model was established and main factors were analyzed.By combining experimental research and simulation calculation,it was determined that pressure fluctuation was caused by inlet pressure and diaphragm deformation together.With the increase of pulmonary ventilation volume,the influence of inlet pressure on fluctuation decreases gradually,while the proportion of diaphragm deformation increases rapidly.A closed-loop control strategy of Proportional Resonant with Feedforward Compensation(PRFC)was proposed to solve the problem and control parameters were obtained through co-simulation.The effectiveness of the control strategy was verified by experiments.The results show that the control strategy can enhance the anti-disturbance ability of the system and significantly reduce the pressure fluctuation range,which is beneficial to improving the overall system performance.