Study On Some Thermophysical Problems In Infrared Stealth And Decoy

With the development of the infrared(IR) detecting technology,various infrared detecting and remote sensing equipments of high accuracy and resolution are developed in the world,the safety of weaponry is seriously threatened,IR camouflage capacity of the weaponry should be enhanced urgently.There are two categories of IR camouflage technology according to the purpose, one is IR stealth and the other is IR decoy.IR stealth is to reduce the thermal infrared signal of the target by the method of material selecting and structure designing, making the thermal signal of target similar to the background,and reducing the probability of the target being identified from the background.IR decoy is to make a false target whose configuration and dimensions are same as real target and of similar infrared characteristic to real target.The false target is used in battlefield to protect the real target by puzzling enemy's precision-guided weapon.Surface emissivity and surface temperature are two key parameters that influence the infrared radiant intensity of the target.The essential of IR camouflage is to limit the infrared radiation of the target in a certain range by controlling surface emissivity and temperature of the target.Surface emissivity is determined by surface material and structure,while the surface material and structure are definite,surface temperature is the only influence factor.In order to achieve a satisfying camouflage effect,the key point is the surface temperature control by choosing an appropriate thermophysical method.This paper studies the application of some thermal control technologies in infrared camouflage and decoy.In the study of IR decoy technology,the method of active heating is commonly adopted in the standard false target,which is appropriate for simulating the infrared characteristic of real target at night,but the simulation is not satisfying during the daytime as lack of cooling ability.In this work,two methods are presented to solve that problem.The first method is the application of phase change material(PCM). PCM is used to store the heat of false target in the form of latent heat during the daytime,to avoid fast temperature increasing,while at night,the heat stored in PCM during the daytime is released by phase changing to slow down the surface temperature decreasing.The other method is storing and releasing heat of false target in the form of sensible heat by convection heat transfer to achieve the purpose of surface temperature control.In the study of the application of PCM in IR false target,through numerical simulation,the feasibility of the use of PCM is analyzed and the range of PCM parameters that suit for IR false target is determined.Based on the results,paraffin is selected as the candidate material.A theoretical model is built to investigate the simulation of the infrared characteristic of the metal structure with the PCM false target.Structure parameters of the PCM false target that suit for the simulation are investigated numerically.According to the results,further request on the improvement of the thermal conductivity of PCM is presented.An experimental platform is built and the numerical model is validated experimentally.Three key thermal characteristic components of the false tank(barbette,wheel and front armor plate) are manufactured and tested,and good results are obtained.A method for the thermal conductivity enhancing of PCM by using aluminum fins is studied,the influence of the structure parameters of PCM plates to the simulation effects are investigated numerically,and the reasonable configuration parameters of the PCM plates used to simulate the steel plates of different thickness are obtained.In the study of the application of heat convection method in IR false target,a passive infrared simulation system is designed to simulate the infrared characteristic of metal constructions.The system is made up of pipe-plate,pump,receiver,and working fluid.The working fluid circulates in the system,to control the pipe-plate surface temperature for simulating the infrared characteristic of metal constructions. By numerical simulation,the influences of the pipe distribution density,working fluid mass flow rate and the total mass of working fluid to the simulation effects are discussed.Results show that such a system can show a good performance in simulating the surface thermal characteristic of armor plates of four typical thicknesses of 2,5,10 and 20cm,the evenness degree of the surface temperature of pipe-plate is within 0.6℃,and the maximum surface temperature difference between pipe-plate and armor plate is within 4℃in a whole day.In the study of the IR stealth technology,the final goal of IR stealth is to make the infrared radiation of target same as the background.The infrared characteristic of plant leaf is greatly influenced by transpiration.Take advantage of the seepage flow and surface evaporation of the liquid in porous material,the IR stealth equipment made from porous material of suitable porosity and material can be used to simulate the IR characteristic of plant leaf.A thermophysical model of plant leaf considering transpiration is built and the surface temperature variation of the plant leaf is investigated theoretically.A kind of porous artificial leaf is proposed,the influences of the porosity,thickness and particle diameter of the artificial leaf to its surface temperature are discussed.According to the simulation results,it is found that the artificial leaf of the thickness of 0.5cm,porosity of 0.05 and particle diameter of 2.5mm is suit for simulating the infrared characteristic of realistic leaf,the surface temperature difference is within 3℃in a typical diurnal periodicity.