Along with the diversification and sophisticated development of detection methods in modern warfare, helicopters are increasingly subject to unilateral or simultaneous threats from radar and infrared ...detectors. In order to improve the survivability and operational effectiveness of the helicopter, a comprehensive stealth approach based on Pareto solution is presented. Considering the geometric constraints and aerodynamic characteristics of the engine intake and exhaust system, the model of the system is established by the full factorial design, the internal, central and external flow fields are constructed, then the high-precision computational fluid dynamics method is used to simulate the total flow field under the rotor downwash airflow in hovering state. The radar cross section of the system is evaluated by the physical optics and physical theory of diffraction. Based on the Monte Carlo and ray tracking method, the infrared signature of the system is calculated and analyzed in detail. Under the comprehensive evaluation and selection of comprehensive stealth approach, the optimization model of the system is continuously established and updated. The ultimate design has achieved good results in both radar cross section reduction and infrared radiation suppression and the proposed method is effective and efficient for radar/infrared integrated stealth of helicopter engine intake and exhaust systems.
•Developed mathematical model for kitchen exhaust system.•Model accuracy improved for different opening rates.•Thermal pressure affects kitchen exhaust in high-rise buildings during winter.
In ...high-rise buildings with large indoor and outdoor temperature difference, neglecting the effect of stack effect in smoke exhaust shafts may cause calculation error of the fluid network model. In this paper, the mathematical model of kitchen smoke exhaust system considering the influence of stack effect was put forward and it can be inserted different range hood sub-models. Compared with the results of six working conditions of the model without considering the stack effect, the error of the proposed model were reduced by 7.6%, 4.3%, 4.1%, 2.8%, 2.4%, and 2.1%. While the indoor and outdoor temperature difference varies from −5 °C to 49 °C, the effect of stack effect on the pressure in the flue and the flow rate for each user was studied for six operating rates s. The results show that under the combined effect of stack effect and flue resistance, the static pressure of the kitchen smoke exhaust system showed a low-high-low distribution, and the maximum static pressure in the flue moved toward the bottom with the increase of temperature difference. User flow rates exhibit a low-high-low-high distribution, with an increased flow rate in the bottom users and the largest flow rate in the top users.
Display omitted
Bypass dual throat nozzle (BDTN) is a new kind of fluidic thrust vectoring nozzle. A nozzle based on BDTN is designed, numerically simulated, and experimented to achieve short/vertical ...takeoff/landing (SVTOL). This novel nozzle, named BDTN-SVTOL, can realize the mode transition by rotating a specially-designed crescent-shaped component. The prominent advantage is that the aircraft can overcome the limitation of the runway length using bypass dual throat nozzle with a slightly different downwall. The main results show that the novel nozzle can obtain the ability of short/vertical takeoff/landing and supermaneuverability assisted by the fluidic thrust vectoring in only one set of nozzle. Therefore, the crescent-shaped component is the most important component of the novel nozzle. If the outer surface of the crescent-shaped component has no separation, the thrust direction changes by more than 80°. Results indicate that the separation occurs when the nozzle pressure ratio (NPR) is more than 1.5, leading to the decrease of the thrust vectoring angle (δ) and the lift efficiency (Cfy). Finally, the novel nozzle is not sensitive to size and Reynolds numbers of the inlet.
Proper design of exhaust systems in marine high-power turbocharged diesel engines can contribute to improve the low-speed performance of these engines and make the working conditions of the cylinders ...more uniform. Here a high-power marine 16-cylinder V-type turbocharged diesel engine is simulated using the GT-Power software. The results reveal the differences induced by different exhaust system structures, such as an 8-cylinder-in-pipe exhaust system with single/double superchargers and a 4-cylinder-in-pipe exhaust system with a single supercharger. After a comparative analysis, the 8-cylinder type with double superchargers is determined to be the optimal solution, and the structure of the exhaust system is further optimized. The simulations show that the optimized maximum exhaust temperature difference among cylinders is reduced by 66%. Finally, the simulation results and the optimized performance of the designed exhaust system are verified through experiments.
Modern diesel engines are struggling to enhance the power density. This is usually realized by being equipped with a turbocharger, which demands higher performances on exhaust flow and exhaust waste ...energy recovery (WER). In the present study, we investigated the variations of exhaust flow and exhaust energy recovery performance with different geometrical parameters of exhaust system and proposed an evaluation and optimal design method of the exhaust system for a turbocharging diesel engine with a module pulse converter (MPC) system. The macro engine performances and the micro flow fields in exhaust system are obtained from the one/three dimensional (1D-3D) coupling simulation, and the energy of exhaust gas is quantified and analyzed with a concept of air power. It can be concluded that with a view to the exhaust performance and exhaust energy utilization, the diameter of the exhaust pipe should be set equal to the outlet diameter of the manifold and there is an optimized value of the contraction rate of the exhaust manifold. Besides, a parameter of the exhaust system called power potential coefficient is proposed to qualitatively evaluate the exhaust performance and exhaust energy.
In this paper, the mode transition process of an over-under exhaust system for a turbine based combined cycle (TBCC) is investigated experimentally. The method of characteristics (MOC) and truncation ...method are employed to design the single expansion ramp nozzle (SERN) at the cruise condition, and the final configuration of the exhaust system is determined by resolving the turbine nozzle performance. The crank-link mechanisms are applied to convert the rotation modes of the splitter and cowl to the linear motion modes in the experimental model. The flowfield structure and pressure distribution along the symmetric plane are measured in the experiment. Furthermore, the computational fluid dynamics (CFD) approach is also adopted to simulate the flowfield of the exhaust system for comparison. The results denote that although the flowfield is greatly complicated as the interaction of the exhaust system plume with the external freestream, the internal flowfield of the exhaust system is independent of the external flow. The flowfield of the entire exhaust system is occupied by the turbine nozzle flow at the initial condition, while it is dominated by the ramjet nozzle flow at the end of the mode transition. At the afterburner and throttle stages of the turbine, the shear layer deflects toward the turbine nozzle flowfield, and the influence of the ramjet nozzle jet on the turbine nozzle flowfield is increased. The internal flow of the turbine nozzle is not influenced by the ramjet nozzle plume at the afterburner stage, while it is greatly affected by the ramjet nozzle plume at the throttle stage. Instead, the shear layer deflects toward the ramjet nozzle flowfield at the transitional stage, and the effect of the turbine nozzle flow on the ramjet nozzle flowfield is increased. Furthermore, the calculated flowfield structure and pressure distributions agree well with the experimental results, and the numerical method can be capable of capturing the flowfield feature of the exhaust system.
Thermo-electric generators (TEGs) have been identified as promising solid-state devices to recover exhaust waste in internal combustion engines (ICEs). As the TEGs are able to convert heat directly ...into electricity, they can be used to down size the alternator of the ICEs. However, the addition of new devices to the engine exhaust system leads to increase the back pressure of the engine and reduces the overall efficiency of the engine. Therefore, this study is conducted to understand the possibility of integrating the TEG to the muffler of the engine, without interrupting the functionality of the muffler to recover the waste heat of the engine exhaust system. Findings of the study shows that the thermo-electric modules (TEMs) can be easily integrated to the muffler and electricity can be conveniently generated using the exhaust energy available in the hot exhaust gas.
In order to improve the backward-facing radar stealth capability of the engine exhaust system, five coating schemes for afterburner, which is radar wave strong scattering source, are formulated. The ...influence of afterburner coating absorbing materials on the horizontal polarization and vertical polarization RCS distribution pattern of the exhaust system in the range of -30°~+30° azimuth of the typical frequency point in the S-band and X-band is analyzed by using the shooting and bouncing rays, also SAR imaging of typical frequency points in the X-band at an azimuth angle of 0° is simulated.The results show that the distribution of strong scattering sources in S-band and X-band is basically the same, and the influence of different coating schemes of absorbing materials on the RCS reduction effect of two bands is similar. The flame stabilizer is the strongest scattering source of radar characteristic signal, and coating it with radar absorbing materials has the greatest benefit on reducing the radar characteris
In this study, the similarity criteria for thermal radiation characteristics of the target, such as gas flow, heat transfer, mass transfer and thermal radiation coupling effect, were considered. Only ...in the case where the criteria are based on the similarity of geometry, gas flow, heat transfer and component transportation, can the similarity of thermal radiation be possible. Similarity criteria of different physical mechanisms were obtained by adopting a dimensionless analysis of their governing equations. Every similarity criterion features the impact of each physical mechanism on thermal radiation of target. Thermal radiation similarity theory was applied to a single duct exhaust system and after theoretical analysis, the dominant similarity criteria were selected, while the others were neglected. It was pronounced that there are only three dominant similarity criteria for single duct exhaust system: a) the nozzle pressure ratio, b) the total temperature of the inlet and c) the optical depth. Three cases were simulated numerically using k-ε turbulent viscosity model and backward Monte-Carlo method for the verification of the above conclusion. The boundary conditions and characteristic lengths of the three cases were different but the dominant similarity criteria were respectively the same. Therefore, the results coincided adequately with each other, conclusion that corresponds to the predictions of the theory.
PDF
