光学球罩气动热及其响应分析 | |
Alternative Title | Analysis of the aerodynamic heating and it’s effects on spherical optical dome |
张代军1,2 | |
Department | 光电信息技术研究室 |
Thesis Advisor | 罗海波 |
Classification | TP391.41 |
Keyword | 气动热 球形整流罩 气动光学效应 热障效应 热冲击 |
Call Number | TP391.41/Z31/2017 |
Pages | 121页 |
Degree Discipline | 模式识别与智能系统 |
Degree Name | 博士 |
2017-05-25 | |
Degree Grantor | 中国科学院沈阳自动化研究所 |
Place of Conferral | 沈阳 |
Abstract | 随着高速末制导以及炮弹、火箭弹、空空导弹等高速武器成像制导化的发展，光学制导系统急需适应越来越高的飞行速度，但高速飞行也给光学制导系统带来了多重不利影响，包括激波层光学传输效应、高温气体辐射、整流罩的热冲击应力以及热障效应等，这些也是制约光学制导系统高速化发展的难点问题。针对应用最为广泛的前置球形整流罩，本文对上述问题进行了分析和研究，主要研究内容和结论如下： 1. 前置光学球罩激波层的光学传输效应分析。为提高光学制导系统成像质量，从激波层时不变流场、湍流边界层和激波层与整流罩的高温热辐射三个方面得出激波层的气动光学效应结论。通过调制传递函数和点扩散函数分析，激波层时不变密度场的光学传输效应为轻微模糊；从流动稳定性、边界层厚度和折射率脉动三方面对湍流边界层光学传输效应进行了分析，结果表明该光学传输效应主要为图像强度衰减及轻微模糊，火箭撬试验验证了上述分析结论，其红外图像中未见扭曲摆动或明显的模糊退化现象，而激波层与整流罩的高温热辐射对红外成像的影响较大，为了提高对目标的捕获、跟踪及打击能力，需先进行热、流、固、光、电多物理场耦合分析得到焦平面热辐射噪声分布，并对该噪声进行整体滤除，再对解耦出的目标与背景信息进行图像增强，以提高目标与背景间对比度；高温平板玻璃热辐射试验表明高温热辐射对可见光系统影响较小，对于可见光系统的光学传输效应，可直接利用图像增强的方法来予以校正。 2. 基于驻点热流的等效热导率修正方法。通过对湍流模型能量方程的合理简化，分析得出驻点热流计算偏高的主要原因是湍流模型受整流罩前激波层涡量影响而使流场的涡粘系数计算偏高；针对该问题，提出了等效热导率修正方法，通过流场的热传导降低来提高湍流模型在驻点处的热流的计算精度。该方法可作为对湍流模型的丰富和补充，使湍流模型可更灵活地根据自身参数调整来提高对其它流场参数的计算精度；对相同马赫数条件下不同飞行高度的整流罩进行数值实验，结果表明，等效热导率修正值与飞行高度几乎无关，即受来流密度和温度的影响很小，从而验证了本文关于驻点热流计算偏高的原因分析；该方法同样适用于其他计算模型，且简单高效，具有一定的工程意义。 3. SST模型湍流换热的Bradshaw数修正方法。首先通过壁面第一层网格高度敏感度分析来细化网格以降低网格对数值计算结果的影响；通过数值实验分析了SST模型主要参数对整流罩壁面热流计算结果的影响，其中Bradshaw数仅对峰值热流影响较大，并以Eckert参考温度法为基础，对Bradshaw数进行修正，使SST模型对球形整流罩湍流换热计算达到工程精度。经等效热导率和Bradshaw数修正的SST模型，可作为热、流、固、光、电多物理场耦合分析的流场及对流换热的计算环节，用于光学传输效应和热辐射噪声等气动光学效应的分析与校正，有利于提高气动光学效应校正的精度，为光学制导系统的末制导弹道设计或任务飞行轨迹规划提供基础。 4. 整流罩抗热冲击能力分析。长波红外因积分时间短，能降低整流罩的热障效应影响，CVD ZnS兼具中波和长波红外的透射能力，是目前唯一工程可用的抗热冲击长波红外整流罩材料，本文针对CVD ZnS整流罩，较系统地对其抗热冲击能力进行了分析和测试；利用三点弯曲法测得ZnS晶体材料的高温弯曲强度；对于给定飞行条件，将基于Eckert参考温度法的湍流换热系数作为边界条件，利用有限元法求解固体瞬态传热微分方程，得到整流罩在对换热过程中的瞬时温度及热应力分布，通过与高温弯曲强度比对，得到整流罩在该飞行条件下的安全系数，并据此安全系数对飞行条件进行调整；同样利用有限元法分析了整流罩厚度对抗热冲击能力的影响，结果表明较薄整流罩因温升快而具有更高的抗热冲击能力，但较薄整流罩也因其温升较快，而更易产生热障效应问题，因此，需根据实际情况综合考虑整流罩厚度、半径以及末制导飞行参数的选择；最后，通过热风洞试验考核了对于给定飞行条件下的整流罩抗热冲击能力。相关试验数据能为后续整流罩以及末制导弹道设计提供参考，但由于ZnS的强度随制备及热处理工艺有一定的散布，应根据实际应用情况来选择和管控相关工艺，必要时可设计专门实验对材料进行筛选，以保证其抗热冲击能力。 5. 基于来流雷诺数的球形整流罩换热状态工程判别。从熵层涡干扰势的角度并结合Stetson的转捩实验，分析了基于整流罩直径的来流雷诺数对整流罩表面边界层流动稳定性的影响机理，根据Stine等的风洞试验及作者单位的火箭撬试验结果，给出的判断整流罩表面流动状态的临界来流雷诺数为2.7×106，可用于2~3马赫飞行条件下、整流罩直径约为80~170mm的制导系统的初步设计阶段，该值具有一定的鲁棒性和工程精度；根据Van Driest球面层流公式和正激波后等熵关系推导出当地换热参数仅是来流马赫数和物面倾角的函数，从而可证当来流马赫数固定不变时，Stine关于当地换热参数在球面层流换热条件下独立于来流雷诺数的结论；进一步推导出当地换热参数的马赫数无关属性，这与Stine的预测相一致，并在Crawford及Beckwith的实验中得到体现；通过与Stine的风洞试验结果比对验证了Van Driest球面层流公式对较大张角球面处的适用性，而非仅对驻点附近区域。根据当地换热参数在给定马赫数下的来流雷诺数无关属性以及马赫数无关属性，可通过风洞或飞行试验来细致研究球面转捩问题，也可为气动热数值计算程序的开发和校核提供理论判据。 6. 长航时复合整流罩的设计。针对高速长航时整流罩的热障效应问题，以Van Driest球面层流换热系数为边界条件，采用有限元法计算了球形整流罩层流换热条件下的瞬时温升，结果表明，整流罩的温升较快，对于红外制导系统，需要结合任务轨迹规划来规避热障效应问题；针对高速长航时的应用需求，提出了一种分段小球头钝锥型复合整流罩结构设计，其前部采用多孔功能陶瓷材料，以其低热导率所产生的高温度梯度来阻滞小钝头处强烈对流换热的向后传导，截锥型ZnS整流罩布置在小球头后的层流区，采用同样的间接流固耦合方法对新型复合整流罩的瞬时温升进行了计算，结果表明，该复合整流罩能够有效延长飞行时间，且相对于侧窗系统，该复合整流罩的气动光学效应小，比较适用于长波红外制导系统的应用；在复合整流罩的基础上，提出了设计一种适于长航时应用的复合制导系统方案。 |
Other Abstract | Optical guidance systems need to adapt to increasingly high speed because of the development of high speed terminal guidance as well as the improvements of optical guidance of the conventional high-speed weapons such as shells, rockets and air-to-air missiles. However, high-speed flight also has multiple effects on the guidance system, including optical transmission effects of shock layer, heat radiation of high temperature air in shock layer, thermal shock stress and thermal barrier effect of the dome. Meanwhile, these restrict the development of optical guidance systems. In this paper, based on the most widely used front spherical fairing, we investigate the problems mentioned above. The main contents and conclusions are listed as following: 1. To analyze optical transmission effects of shock layer in front of spherical dome. In order to improve the image quality of optical guidance system, aero-optical effects of shock layer were summarized as the optical transmission effects of time invariant flow field and turbulent boundary layer as well as heat radiation of shock layer and optical dome. By analysis of modulation transfer function and point spread function, the optical transmission effects of time invariant flow field reflects as slight image blur. By analysis based on flow stability, boundary layer thickness and pulsation of refractive index, the optical transmission effects of turbulent boundary layer reflects as intensity attenuation and slight blur. The experiment of high-speed rocket sled verifies the above analysis. The phenomenon of twisting oscillation and blur degradation were not found in the infrared images gained from the experiment, but the infrared imaging detection was deeply influenced by the heat radiation of shock layer and dome. In order to improve the ability of capturing, tracking and attacking target, the noise distribution of heat radiation should be gained first by couple field analysis, and then the aero-optical effects of infrared system could be corrected using image enhancement after the noise of heat radiation was removed. The experiment of heat radiation showed that visible light system is slightly influenced by heat radiation, so that the aero-optical effects of visible light system can be corrected using image enhancement directly. 2. The correction method of equivalent thermal conductivity based on heat flux at stagnation point. Based on the simplified energy equation of turbulence model, the cause of higher results of heat flux at stagnation point calculated by turbulence models was that the calculation result of eddy viscosity was higher because of the influence of the vorticity in shock layer. Aimed on this problem, we propose a correction method of equivalent thermal conductivity to deal with the problem of higher calculation results. This method can be used as an enrichment and supplement to the turbulence model, so that the turbulence model can more flexibly adjust its own parameters to improve the calculation accuracy of other parameters in flow field. The equivalent thermal conductivity method is used to test the guidance system with the same flying Mach number and different flight height. Experimental results show that the correction value of equivalent thermal conductivity has little to do with flight height. This furtherly illustrates that the vorticity in the shock layer has effect on the computational accuracy for the turbulence model. This method also can be used to other computational models and has certain engineering significance. 3. The correction method of the Bradshaw number based on SST model for the calculation of turbulent heat transfer. Firstly, the wall grid sensitivity is analyzed to reduce the influence of grid on numerical results. According to numerical experiments, we analyze the influence of the main parameters in the SST model on the calculation of heat flux over spherical dome. The Bradshaw number only affects the peak heat flux. Based on the reference temperature method of Eckert, the Bradshaw number is corrected to improve the computational accuracy of turbulent heat transfer. The SST model after the corrections of equivalent thermal conductivity and Bradshaw number could be used as the calculation process of flow field and heat transfer for the couple field analysis of heat, flow, solid, light and electricity, so that the calculation of heat radiation of shock layer and dome should be in the engineering accuracy. This could provide the basis for the terminal guidance trajectory design and the planning of flight path. 4. Analysis of thermal shock resistance of spherical dome. The long-wave infrared system could reduce thermal barrier effect of dome at the period of high speed terminal guidance because of the shorter integration time. CVD ZnS has the ability both in the long-wave infrared transmission and medium-wave infrared transmission, and its application will be more and more widely. In this paper, the thermal shock resistance of CVD ZnS dome was analyzed. The high temperature flexure strength of ZnS crystal was measured by three point bending method. For the given flight conditions, the turbulent heat transfer coefficient based on reference temperature method of Eckert was taken as the boundary condition, and the finite element method is used to solve the differential equations of solid transient heat transfer. The instantaneous temperature and thermal stress distributions of dome during the heat transfer process were obtained. By comparing with the high temperature flexure strength, the safety factor of dome under the flight condition was obtained, and the flight condition was adjusted according to the safety factor. The influence of the fairing thickness on the thermal shock resistance was also analyzed by using the finite element method. The results showed that the thinner fairing has lower thermal shock stress due to the rapid temperature rise at inner surface, and could resist the thermal shock. Finally, the thermal shock resistance of dome under given flight condition was assessed by the arc tunnel test. The results of test of flexure strength at high temperature and thermal shock resistance could prove a reference for the designs of dome and flight parameters of high speed terminal guidance. 5. To identify the state of heat transfer over spherical dome with the Reynolds number based on dome diameter and free stream conditions. Based on the vortex potential in entropy layer and the Stetson transition experiments, the influence mechanism of the Reynolds number based on dome diameter and free stream conditions on the flow stability of the boundary layer over dome was analyzed. According to the results of wind tunnel experiments of Stine et al. and the rocket sled experiment, the critical Reynolds number for judging the state of heat transfer over dome was given as 2.7×106. This value has a certain degree of robustness, and it can be more easily applied to the initial design stage of the guidance system with the dome diameter in the range of 80~170mm and at the flight condition of 2~3Ma. The expression of the local heat transfer parameter of Stine was derived by using the Van Driest spherical laminar heat transfer formula and the isentropic relation after the shock wave. The express also showed that the local heat transfer parameter is the function of inflow Mach number and surface inclination angel, so that the conclusion of Stine that the local heat transfer parameter was independent of the Reynolds number at given Mach number was derived out. And then conclusion that the local heat transfer parameter has the trend of being independent of inflow Mach number was also derived out, which is consistent with the prediction of Stine and can be found in the experiments of Crawford and Beckwith. By comparing with Stine's wind tunnel experiment results, the local heat transfer parameter obtained in the larger spherical angle position are also consistent with the Stine measurement results. This shows that the Van Driest laminar heat transfer formula is equally valid for the heat transfer at the larger central angle of dome, rather than on the area near the stagnation point. Based on the properties of independent of Reynolds number and Mach number at laminar heat transfer condition, the local heat transfer parameter could be used to research the transition process through wind or flight experiments, and could also be used to provide the theoretical criterion for the development and verification of calculation programs of aerodynamic heating. 6. To design composite dome under high speed and long endurance. Aiming at the thermal barrier effect of dome, the Van Direst spherical laminar heat transfer coefficient was taken as the boundary condition, and the finite element method was used to calculate the instantaneous temperature rise of the dome under laminar heat transfer. The results showed that the temperature rise of the dome was faster. For infrared guidance systems, the task trajectory planning needs to be combined to avoid the thermal barrier effect. For the application requirement of high speed and long-endurance flight, a new composite dome is designed by using the structure of segmental sphere cone with small sphere nose. The sphere nose was designed by using porous ceramic material that could block the backwards conduction of temperature in the form of high gradient of temperature. The rear part is the truncated ZnS infrared dome. The instantaneous temperature rise of the new composite dome was calculated by the same indirect fluid-solid coupling method. The results showed that the composite fairing can effectively extend the flight time. The aero-optical effect of the new composite dome is smaller than the side window system and the composite dome is especially suit for the applications in long-wave infrared guidance systems. Based on the composite fairing, we designed the composite guidance system which is suit for the application of long endurance. |
Language | 中文 |
Contribution Rank | 1 |
Document Type | 学位论文 |
Identifier | http://ir.sia.cn/handle/173321/20538 |
Collection | 光电信息技术研究室 |
Affiliation | 1.中国科学院沈阳自动化研究所 2.中国科学院大学 |
Recommended Citation GB/T 7714 | 张代军. 光学球罩气动热及其响应分析[D]. 沈阳. 中国科学院沈阳自动化研究所,2017. |
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