| A power generation cabin,which uses a diesel engine as the prime mover to drive a generator to generate electricity,is a van diesel genset that can be applied to the field of defense.The infrared and noise signatures of the power generation cabin are of great concern.Weak-infrared signature is requisite for achieving infrared stealth of the power generation cabin,and low-noise signature can provide personnel with a comfortable acoustic environment.To suppress the infrared and noise signatures,the following works have been conducted starting from the generation mechanism and inducement relationship of both infrared radiation and sound wave.The power generation cabin is mainly composed of a diesel genset enclosed by a cabin wall.The genset is mainly composed of an engine body,an intake manifold,an exhaust manifold,an exhaust pipe,a reactive muffler,a radiator module and a generator.Along the airflow direction,the cabin is divided into an air-inlet cabin and an air-outlet cabin by a partition,and the cabin wall is composed of the inlet,lateral and outlet sides.To obtain the infrared and noise signatures,the thermocouples and infrared imager were used to collect the heat sources’ temperatures and the infrared images of the outer wall of the power generation cabin,and the heat sources’ characteristics and the infrared signatures’ distribution of the outer wall were analyzed.Also,a noise spectrum analyzer was used to collect the noise spectrums of the noise sources,the near-field noise levels,the noise spectrums and levels at a 1 m distance from the cabin,and the results were analyzed.It is found through experimental investigation on infrared signature that,the main heat sources are the exhaust system,the engine body and the radiator module.The maximal infrared temperature of the inlet side is only 39℃,showing a weak infrared signature,while the the maximal infrared temperature of the lateral and outlet sides are 65℃ and 73℃ respectively,showing a prominent infrared signature.It is found through experimental investigation on noise signature that,there are mainly the surface vibration noise sources and the aerodynamic ones,all of which show a high noise levels with a wide frequency band.The former includes engine and generator,which noises mainly cover the mid and high frequency range(500～4k Hz),with the noise levels of 97.6～100.0 dB(A).The latter includes intake,exhaust and cooling fan,which noises cover the low,mid and high frequency range(63～4k Hz),with the noise levels of 95.0～99.6 dB(A).Because of the effects of the two types of noise sources,the near-field noise levels on the inlet,lateral,and outlet sides are 82.0～94.1 dB(A),81.2～87.8 dB(A)and 80.2～91.3 dB(A)respectively,among which the high near-field noise levels locate at the inlet and outlet.Additionally,the cabin wall has a more significant suppression effect on the high-frequency noise,which can reduce the average noise level from 92.2 dB(A)to 81.0 dB(A)at a 1 m distance,higher than the noise limit of 75.0 dB(A)specified by ISO8528-10.To suppress the infrared signature,we proposed and conceived a cold plate system to shield the thermal characteristics of the genset.The heat load of the cold plate is dissipated to the ambient air through a radiator,enabling the outer wall temperature to approach the ambient temperature.In this system,a flat cold plate integrated by the cold plate modules were adopted as the lateral sides,while a louvered cold plate integrated by the cold plate modules was designed as the outlet side of the power generation cabin.Based on the above conception,the power generation cabin with the cold plate system was constructed,and its feasibility to suppress infrared signature was experimentally demonstrated.To optimize and evaluate the infrared suppression effect,the simulation models of the power-generation cabin and that with the cold plate system were established by a finite element software I-DEAS to optimize the module structure and layout of the flat cold plate and the louvered cold plate.Finally,the infrared suppression effect of the optimized cold plate system was experimentally validated and evaluated by simulation.It is experimentally confirmed that the cold plate system can effectively suppress the infrared signature of the power generation cabin.When adopting the cold plate system,the maximal temperature difference of the measuring points on the lateral and outlet sides with the ambient air is only 3.9℃ and 8.4℃,respectively.It is found through simulation that only the lateral sides for the air outlet cabin need the flat cold plates with a 1-row tube to suppress the infrared signatures,and the optimized louvered cold plate is composed of 5 blades with a 240 mm width,a 48° inclination angle and a 30 mm tube spacing.Compared with the original power generation cabin,the optimized cold plate system can reduce the maximal temperature difference of the lateral and outlet sides with the ambient air from 28.6℃ to 1.0℃ and from 34.8℃ to 5.2℃,significantly suppressing the infrared signature of the power generation cabin.To consider the noise and infrared suppression,the causes of both signatures are analyzed based on the experimental results.The inducements of the noise and infrared signatures of the power generation cabin are diverse and closely interrelated.The main noise sources,such as the engine generating mechanical noise,the exhaust system and radiator module generating aerodynamic noise,are also the main heat sources that lead the infrared signature of power generation cabin to be significant.To achieve low-noise and weak-infrared signatures simultaneously,starting from the key source items,we propose a conception of decoupling the radiator module from the power generation cabin.To this end,the built-in radiator was modified as an external one and a low-noise cooling fan with an electronic control unit was configured for the radiator,and an independent airduct with a wind screen was designed for the radiator module,shielding the infrared signature by the airduct wall with a buoyancy-driven air curtain.To suppress the wideband aerodynamic noises of the exhaust,an impedance composite muffler was adopted.To shield the noise and infrared signatures of the genset,a multi-layer structure with "steel sheet+damping blanket+insulation cotton" from outside to inside was designed as the cabin wall,and the dimensions and position of the inlet and outlet were improved.Then,the simulation models of the designed power generation cabin and the radiator airduct were construced by I-DEAS to demonstrate the feasibility of the weak-infrared signature design.Finally,the experimental system was built based on the above design,and the noise and infrared suppression effects of the new design were experimentally evaluated.It is found through experimental investigation with the new design that,the high near-field noise levels of the radiator airduct only locate at its inlet and outlet of airduct,with levels of 74.1 dB(A)and 77.3 dB(A),respectively,making an insignificant contribution to the noise of power generation cabin.Also,the maximal temperature difference of the radiator.airduct wall with the ambient air is as low as 10℃,effectively lowering the infrared signature.Adopting the impedance muffler can eliminate the wideband exhaust noise level by 13.9 dB(A),significantly reducing its contribution to the noise of power generation cabin.After the design,the near-field noise levels of the power generation cabin gradually increase from top side to bottom one,and the average near-field noise levels of the inlet,lateral and outlet sides decrease from 87.5 dB(A)to 77.5 dB(A),from 84.1 dB(A)to 76.0 dB(A)and from 84.8 dB(A)to 79.5 dB(A),respectively.The average noise level dropped from 81.0 dB(A)to 72.5 dB(A)at a 1 m distance,reaching the noise limit of 75.0 dB(A)specified by ISO8528-10.Also,the maximal temperature differences of the lateral and outlet sides with the ambient air drop from 29℃ to 12℃ and from 37℃ to 8℃,respectively,significantly suppressing the infrared signature.This design provides an effective solution to simultaneously achieve a low-noise and weak-infrared power generation cabin.Based on the investigations on the themal characteristics of the heat sources,heat transfer characteristics,the frequency spectrums of the noise sources as well as noise propagation characteristics,targeted solutions to the infrared and noise suppression are proposed from the aspects of the heat,sound sources and the cabin wall,realizing a weak-infrared and low-noise power generation cabin.This work has an important reference value for the application of mobile equipment in the field of defense. |
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