Jet Exhaust Research Articles

Aerodynamics and Power Balance of a Distributed Aft-Fuselage Boundary Layer Ingesting Aircraft

This paper presents a first investigation into the aerodynamics and performance breakdown of a distributed aft-fuselage boundary layer ingesting (BLI) tube-and-wing aircraft using fully coupled Unsteady Reynolds-Averaged Navier-Stokes (URANS) calculations that resolve the complete fan and installation geometries. Through the URANS simulations, the interaction between the turbulence from the fuselage boundary layer (BL) and the BLI propulsor is identified as an area that warrants further research. Using the URANS approach, the ingested turbulence leads to a 4.5% reduction in the propulsor stage total–total isentropic efficiency. A mechanical power balance has been drawn up to compare the power sources and sinks throughout the installation and propulsor for two test cases with different thicknesses of ingested BL. The test case with a thinner BL was found to generate significantly more dissipation in the BL development upstream of the propulsor, the flow separation over the outer cowl, and the interaction between the reversed flow over the cowl and the propulsor exhaust jet. Due to this increase in dissipation, the case with thinner ingested BL consumes 7% more power relative to a baseline case with thicker BL, representative of the upstream fuselage at cruise. This demonstrates the importance of matching the installation with the incoming fuselage BL.

Modeling Exhaust-Generated Aerodynamic Pressure Loads on Airfield Matting Repair Systems

Airfield matting systems are commonly used for rapid repair of damaged runways to facilitate continuity of critical operations. Under normal service conditions, matting repair systems are subject not only to wheel loads exerted by airfield traffic but also to aerodynamic pressure loads resulting from high-speed, turbulent exhaust plumes produced by jets during taxi and take-off. Matting systems employed by the U.S. Air Force have been tested with respect to wheel loads, but probabilities of failure because of pressure loads produced by jet exhaust have not yet been established. This study presents a numerical approach for preliminary estimation of worst-case matting anchor forces resulting from exhaust-generated pressure loads. Using a two-dimensional computational fluid dynamics model, system behavior is evaluated by means of a parametric study of six system variables, of which the most significant are: (1) distance between engine and matting, (2) depth of cavity openings at matting edges, and (3) engine exhaust velocity. The results demonstrate that matting systems are likely to experience net uplift in typical service scenarios, driven by the combined effects of flow separation and cavity pressurization. Worst-case anchor pull-out forces, computed according to a tributary-area approach, are estimated to fall in the range of 130 lb (581 N) to 979 lb (4,350 N), depending on assumed load-sharing behavior among anchors and the size of the repair site. Field testing of instrumented matting systems during jet taxi and take-off sequences is recommended as the best next step toward understanding system behavior.

Numerical Simulations on the Performance of Two-Dimensional Serpentine Nozzle: Effect of Cone Mixer Angle and Aft-Deck

The current study addresses the effect of different designs of the exhaust mixer and aft-deck on the performance of a two-dimensional convergent nozzle represented by the internal and external flows and heat transfer process. The effect of different exhaust mixer cone angles of 10°, 15°, and 20°, and different aft-deck lengths of 140 mm, 280 mm, and 420 mm on the nozzle performance was investigated. To address the effect of an aft-deck, the flow behavior of a nozzle with an aft-deck was compared to that of a nozzle without an aft-deck. Then, the effect of different aft-deck lengths and different aft-decks with rectangular and trapezoid shapes was investigated. The results demonstrated that increasing the mixer cone angle resulted in decreasing the high-temperature core flow and increasing the low-temperature bypass flow. Increasing the mixer cone angle resulted in reducing the velocity inside the nozzle and at the exhausted jet, which can reduce the noise generated by the engine. Furthermore, increasing the mixer cone angle decreased the internal temperature of the nozzle and, along with the exhausted jet, decreased the infrared radiation. The results also illustrated that the presence of the aft-deck resulted in decreasing the pressure, temperature, and velocity inside the nozzle. The aft-deck also decreased the length and size of the potential core. The aft-deck length had no clear effect on the internal flow. However, increasing the aft-deck length resulted in a decrease in the exhaust gas temperature, which can decrease the infrared radiation. On another hand, using trapezoid and triangle aft-deck can enhance the performance of the nozzle by decreasing the velocity and temperature inside the nozzle and at the exhausted jet.

EXPERIMENTAL STUDY OF THE ACOUSTIC INTERACTION OF A SUBSCALE ROCKET NOZZLE EXHAUST JET AND DIFFERENT GUIDE TUBES

The noise emission of rocket engine test facilities and their impact on the environment comes more and more into focus. The key drivers are the engine exhaust jet itself, and its interaction or even coupling with a subsequent guide tube. To increase understanding of the interaction, and in preparation of future test facility design, a cold gas subscale test campaign was conducted with a reference guide tube. It was found that the main influencing parameter is the distance between the nozzle exit and guide tube inlet. This article is published with the permission of the authors granted to 3AF - Association Aéronautique et Astronautique de France (www.3AF.fr) organizer of the Space Propulsion International Conference.

Re-entry high speed commercial air vehicles: Improving the environmental eligibility at take-off and approach accounting the flight safety restrictions

In addition to the flight safety of re-entry high speed commercial air vehicles their environmental eligibility come into particular important issue due to environmental requirements for commercial subsonic aviation are becoming more stringent. During the re-entry take-off and approach cycles the vehicles are a subject to almost the same type of environmental requirements as the commercial subsonic aviation. The requirements are primarily concern the limitations of community noise and engine exhaust emissions levels, as well as the sonic boom level (for commercial supersonic aviation). Meeting the requirements may significantly complicate the development, certification and further operation of the vehicles. The paper discusses one of the potential ways of increasing the acoustic eligibility of the vehicles during take-off and approach cycles at using the some number of turbofan engines as part of the propulsion system. The way is based on the creation of a special control of turbofan engines thrust/power (so called low noise thrust management) accounting the provision of flight safety restrictions. The assessment of the acoustic impact (community noise) of the vehicle is carried out taking into account the contribution of major noise sources of turbofan engines, i.e. the fan and exhaust jet. The impact of two parameters of turbofan engines such as the bypass ratio and the number of turbofan engines was evaluated. The variation of these parameters was performed under the condition meeting the specified mission requirements in term of the required field (runway) length and the approach speed. The estimations shown that using the created low noise turbofan engine thrust management at the take-off and approach may significantly increase the acoustic eligibility of the vehicles using turbofan engines.

Aero-thermal investigation of thermal interactions between turboprop engine exhaust and selected parts of the airplane skin for tractor configured aircraft

PurposeDevelopment or upgradation of airplanes requires many different analyses, e.g. thermal, aerodynamic, structural and safety. Similar studies were performed during configuration change design of commuter category aircraft equipped with pusher turboprop engines. In this paper, thermo-fluid analyses of interactions of the new propulsion system in tractor configuration with selected elements of airplane skin are carried out. This study aims to check the airplane skin material, and its geometry, including the Plexiglas passenger window material degradation, due to hot exhaust gas plume impingement. The impact of change in exhaust stub angle and asymmetric inboard-outboard stubs on the jet thrust at various flight operating conditions like minimum off-route altitude and cruise performance is assessed.Design/methodology/approachCommercial software-based numerical models were developed. In the first stage, heat and fluid flow analysis was performed over a twin-engine airplane’s nacelle, wing and center fuselage with its powerplant mounted in the high wing configuration. Subsequently, numerical simulations of thermal interactions between the hot exhaust gases, which leave the exhaust system close to the nacelle, flaps and the center fuselage, were estimated for various combinations of exhaust stub angles with asymmetry between inboard-outboard stubs at different airplane configurations and operating conditions.FindingsThe results of the simulations are used to recommend modifications to the design of the considered airplane in terms of material selection and/or special coatings. The importance and impact of exhaust jet thrust on the overall aircraft performance are investigated.Originality/valueThe advanced numerical model for the exhaust jet-airplane skin thermal interaction was developed to estimate the temperature effects on the propeller blades and aircraft fuselage surfaces during different flight operating conditions with multiple combinations of stub orientations.

Helicon Injected Inertial Plasma Electrostatic Rocket

The Helicon Injected Inertial Plasma Electrostatic Rocket (HIIPER) is a space propulsion system developed at the University of Illinois Urbana-Champaign. The HIIPER couples a helicon tube with an inertial electrostatic confinement (IEC) fusion system. Its operating principle involves a helicon ionization stage followed by an electrostatic grid (IEC cathode grid) extraction stage. The helicon setup used in the HIIPER is modified to include a helicon bias grid at the upstream end of the tube. This grid is applied with a positive direct-current voltage to increase the plasma potential and the most probable ion energy of the plasma injected into the IEC fusion chamber. The IEC cathode grid in the HIIPER uses an innovative asymmetric design, graphically depicted through a computational model, that ejects a stream of electrons that accelerate the exhaust ions and simultaneously neutralize the exhaust jet. The model is also used to plot ion trajectories inside the HIIPER to identify any wall collision losses. A separate numerical study was undertaken to show augmentation of plasma kinetic energy on adding a magnetic nozzle as the final propulsion stage of the HIIPER. Experimental results were used to establish a relation between the input parameters and the ion density of the resulting plasma. Langmuir probe measurements were performed at two locations to validate corresponding computational results, indicating ion losses due to ion-wall collisions inside the helicon-IEC coupling. The results in this study add to the proof of concept of the HIIPER and allow for designing an upgrade of the propulsion system. Increasing thrust while maintaining plasma densities between 1017 and 1018 throughout the system is the current aim of HIIPER research. This study summarizes the various performance parameters of the propulsion system, along with a discussion of ongoing research and future scope.

Розрахунково-методичне забезпечення для проведення комплексних розрахунків надзвукового обтікання летальних апаратів з прямоточними повітряно-реактивними двигунами

This paper discusses the use of the authors’ fast methods and programs for the calculation of 3D supersonic flow about a flying vehicle and thermogas dynamic processes in the components of an airframe-integrated ramjet. To conduct fast comprehensive calculations, use is made of marching methods, which are two to three orders of magnitude faster than pseudoviscosity methods. 3D supersonic flows about the airframe, in the inlet section of the air intake, and in the exhaust jet are calculated using a “viscous layer” model or Godunov’s scheme for the inviscid approximation. Subsonic flows in the outlet section of the air intake and in the combustion chamber are calculated using a “narrow channel” or a quasi-one-dimensional model. The elements of the presented methods and programs that complement a previously proposed fast comprehensive model are described in more detail. A method for assigning the spatial shape of the flying vehicle surface and the ramjet duct walls is described. A simplified approach to determining the critical area of the exit nozzle in the one-dimensional approximation is proposed. The paper substantiates the advantages of marching methods over pseudoviscosity ones in the predesigning of ramjets with direct account for flow choking, which may occur in the combustion chamber or the exit nozzle. The calculated 3D flows in the individual components and the full assembly of a stylized-shape flying vehicle are presented. The main advantages of the proposed methods and programs are their comprehensiveness and fast computation speed. Their use in the calculation of 3D supersonic flow about a ramjet flying vehicle shortens the ramjet component predesigning time.

Experimental and numerical investigation on the effect of turboprop engine exhaust gas impingement on pusher aircraft

Abstract Turboprop engines require an exhaust nozzle or stub to duct the engine exhaust flue gas outboard of the aircraft. The design of these exhaust stubs are dictated primarily by the aircraft’s configuration. In pusher aircraft, the exhaust stubs are designed to minimize the exposure of the flue gases from the engine exhaust on the propeller blades and fuselage. A fluid-thermal-structure coupling analysis is performed to understand the thermal effects of the engine exhaust jet flow on the thermo-mechanical behavior of pusher configured light transport aircraft propeller and structure. The steady thermal flow field of the aircraft with forward and reverse thrust, in which propeller blade angle variations were analyzed for different aircraft speed. The present work investigates a three-dimensional analysis of flow around the nacelle-airframe and the effect of exhaust flue gas impingement on the propeller blade surface. Based on the insights from the numerical results, the designed exhaust duct was integrated on the aircraft and carried out ground static and flight testing for various flight operating conditions in which propeller blade and fuselage surface temperature were measured. Numerical and experimental results are compared and validated for certain flight conditions and found satisfactory.

Box model trajectory studies of contrail formation using a particle-based cloud microphysics scheme

Abstract. We investigate the microphysics of contrail formation behind commercial aircraft by means of the particle-based LCM (Lagrangian Cloud Module) box model. We extend the original LCM to cover the basic pathway of contrail formation on soot particles being activated into liquid droplets that soon after freeze into ice crystals. In our particle-based microphysical approach, simulation particles are used to represent different particle types (soot, droplets, ice crystals) and properties (mass/radius, number). The box model is applied in two frameworks. In the classical framework, we prescribe the dilution along one average trajectory in a single box model run. In the second framework, we perform a large ensemble of box model runs using 25 000 different trajectories inside an expanding exhaust jet as simulated by the LES (large-eddy simulation) model FLUDILES. In the ensemble runs, we see a strong radial dependence of the temperature and relative humidity evolution. Droplet formation on soot particles happens first near the plume edge and a few tenths of a second later in the plume centre. Averaging over the ensemble runs, the number of formed droplets and ice crystals increases more smoothly over time than for the single box model run with the average dilution. Consistent with previous studies, contrail ice crystal number varies strongly with atmospheric parameters like temperature and relative humidity near the contrail formation threshold. Close to this threshold, the apparent ice number emission index (product of freezing fraction and soot number emission index) strongly depends on the geometric-mean dry core radius and the hygroscopicity parameter of soot particles. The freezing fraction of soot particles slightly decreases with increasing soot particle number, particularly for higher soot number emissions. This weakens the increase of the apparent ice number emission index with rising soot number emission index. Comparison with box model results of a recent contrail formation study by Lewellen (2020) (using similar microphysics) shows a later onset of our contrail formation due to a weaker prescribed plume dilution. If we use the same dilution data, our evolution and Lewellen's evolution in contrail ice nucleation show an excellent agreement cross-verifying both microphysics implementations. This means that differences in contrail properties mainly result from different representations of the plume mixing and not from the microphysical modelling. Using an ensemble mean framework instead of a single trajectory does not necessarily lead to an improved scientific outcome. Contrail ice crystal numbers tend to be overestimated since the interaction between the different trajectories is not considered. The presented aerosol and microphysics scheme describing contrail formation is of intermediate complexity and thus suited to be incorporated in an LES model for 3D contrail formation studies explicitly simulating the jet expansion. Our box model results will help interpret the upcoming, more complex 3D results.

Cooling of rocket plume using aqueous jets during launching

With an increase in rocket motor thrust, the thermal loads on the launch platform by the impingement exhaust jet are significantly increased, this poses serious safety risks to rocket launch. Therefore, a water cooling system should be designed to improve the thermal environment. In this study, the cooling effects of a water spray system with different injection velocities were analyzed through numerical simulation of high precision, and the afterburning effect of the exhaust gas was also considered to improve the calculation accuracy. The results showed that afterburning primarily occurred in the mixing layer, leading to a larger high-temperature region in the impingement plate. The water cooling system realized thermal protection for the launch platform, which was achieved by decreasing the temperature and velocity of impingement jet. With an increase in the aqueous jet velocity, a more significant cooling effect of the water spray system was obtained. However, the guiding performance of the deflector was decreased owing to the large amount of water vapor formed in the channel. It is suggested that the water spray system design should adopt an aqueous jet velocity of 20 m/s as a parameter after considering the cooling effect and guiding performance of the deflector.

Are anemometers at airports affected by taxiing aircraft?

This study provides evidence to discount any need to correct wind speeds measured at airports for jet exhaust from aircraft taxiing past the anemometer. The figure shows the manufacturer's data for an Airbus 320 engine at ‘ground idle’ extrapolated into the far field as a Gaussian wall jet model, showing that the jet exhaust is expected to pass underneath anemometers at 10m above ground. This is confirmed by matching 503 large-jet departures from runway 1L at Tampa International, FL, to the 1min interval gust speed and direction data recorded by the anemometer.

Characterization of tornado like flows for improving vortex ventilation performance

The innovative local ventilation systems using vortex flows resembling a tornado have been proposed to improve ventilation performance. The effect of two primary operating conditions, the side jet velocity and exhaust flow rate which are essential for the formation of vortex structures and significantly affect the resulting vortex characteristics, on the vortex characteristics are investigated by employing a particle image velocimetry (PIV) technique. The vortex core is widened and the vortex strength increased when the side jet velocity is increased. When the induced swirling force is sufficient, a higher exhaust flow rate can form a stronger and more stable vortex. Vortex characteristics revealed that the optimal side jet velocity is 1.73 m/s corresponding Res of 2332.4 with a normalized exhaust flow rate of 0.155. In order to quantify the effectiveness of the vortex ventilation system, the concentration of ultra-fine particulate matters was monitored. The ventilation performance has a similar trend with vortex size, circulation and swirl ratio over core region. We herein propose a new-type ventilation system and a useful analysis method based on PIV to characterize tornado-like flows in vortex ventilation systems. In addition, these flow and ventilation results can be used as basic data in the design and operation of vortex ventilation systems.

A method to minimize the intake of exhaust air in a climate control system in livestock premises

This paper presents a method of aerodynamic separation of supply-exhaust airflows in a supply and exhaust climate control unit for livestock facilities in order to minimize back suction. The air removed from livestock buildings contains a large amount of moisture, carbon dioxide, ammonia, hydrogen sulfide and other harmful gases and in mine units, the outlet and inlet openings are located close enough, which is why exhaust air can be sucked together with the supply air. The paper presents a set of measures to minimize back suction. In particular, the distance between the supply and exhaust openings is substantiated. Moreover, it was proposed to give an additional velocity to the exhaust air due to the energy of natural traction. In order to solve this problem, a nozzle with a convergence angle of 45 ° was installed at the outlet of the unit. The effectiveness of the proposed solution was tested experimentally and it was found that when the inlet and outlet openings were located at a distance of more than 0.5 m, as well as when the exhaust jet was given a velocity of 3 m / s, the amount of back suction did not exceed 5%.

Numerical Investigation of a Rectangular Jet Exhausting over a Flat Plate with Periodic Surface Deformations at the Trailing Edge

Multiple competing factors are forcing aircraft designers to reconsider the underwing engine pod configuration typically seen on most modern commercial aircraft. One notable concern is increasing environmental regulations on noise emitted by aircraft. In an attempt to satisfy these constraints while maintaining or improving vehicle performance, engineers have been experimenting with some innovative aircraft designs which place the engines above the wings or embedded in the fuselage. In one configuration, a blended wing concept vehicle utilizes rectangular jet exhaust ports exiting from above the wing ahead of the trailing edge. While intuitively one would think that this design would reduce the noise levels transmitted to the ground due to the shielding provided by the wing, experimental studies have shown that this design can actually increase noise levels due to interactions of the jet exhaust with the aft wing surface and flat trailing edge. In this work, we take another look at this rectangular exhaust port configuration with some notional modifications to the geometry of the trailing edge to determine if the emitted noise levels due to jet interactions can be reduced with respect to a baseline configuration. We consider various horizontal and vertical offsets of the jet exit with respect to a flat plate standing in for the aft wing surface. We then introduce a series of sinusoidal deformations to the trailing edge of the plate of varying amplitude and wave number. Our results show that the emitted sound levels due to the jet–surface interactions can be significantly altered by the proposed geometry modifications. While sound levels remained fairly consistent over many configurations, there were some that showed both increased and decreased sound levels in specific directions. We present results here for the simulated configurations which showed the greatest decrease in overall sound levels with respect to the baseline. These results provide strong indications that such geometry modifications can potentially be tailored to optimize for further reductions in sound levels.

Analysis for design optimization of high thrust liquid engine hot test facility

A high thrust liquid oxygen-kerosene fuelled engine is being developed for future launch vehicle applications. Comprehensive hot testing of engine at sea level conditions is required for qualification and acceptance of flight engine and launch vehicle stage. The engine and stage will be tested in a specialized rocket engine and stage hot test facility which deflects the flame safely to avoid any hazard to engine and adjoining mechanical structures. The facility is equipped with water jets to sufficiently cool the rocket plume before impinging on deflector pit walls. The high temperature and high-pressure rocket exhaust jet is cooled with sufficient quantity of water to maintain the impingement wall temperature within safe working limits.In this study, a multi-phase computational fluid dynamics (CFD) methodology is developed for design of water-cooling jet configuration of deflector facility. Multi-phase model validation study using full phase treatment and droplet assumption for water injection is performed prior to water jet optimization analysis of high thrust LOX-kerosene test facility. Validation studies based on simulation and analysis of existing test stand is developed. A discrete particle (DPM) based two phase methodology is chosen to model water injection in RANS framework. The optimum cooling configuration is determined iteratively through numerous multi-phase simulations. The multi-phase analysis showed ineffectiveness of initial water injection scheme which results in facility wall temperature above safe limit. A multi-plane water injection scheme is devised there on with provision of water injection at two axial locations from the nozzle exit. A detailed parametric multi-phase analysis is carried out for design optimization of multi-plane water injection scheme and to determine thermal condition of the test facility. Analysis showed effective rocket plume cooling and lower facility wall temperature with two plane water injection schemes in comparison to initial single plane design configuration. The study highlights the role of CFD based methodology to formulate an engineering solution for design optimization of LOX-kerosene engine hot test facility.

A computational study of two-dimensional serpentine nozzle performance with different annular mixer configurations

Serpentine nozzles are widely utilized in many types of military aircraft to maximize survivability due to their ability to suppress infrared radiation emitted from the engine exhaust system. An annular mixer is used in a serpentine nozzle to improve the performance of the nozzle by intensifying the mixing between the ambient air and exhausted gases. Therefore, this study aims to numerically investigate the performance of a two-dimensional single serpentine nozzle with different annular mixer configurations. The performance of the nozzle based on the internal flow behavior and the external jet of different models of an annular mixer is investigated. Herein, different models of annular mixers with different annular diameters of 320 and 340 mm, different annular lengths of 140 and 280 mm, and different mixer shapes are investigated. The simulations are conducted with a 3-dimensional model using commercial STAR CMM+ software. The results demonstrate that a smaller mixer diameter, indicating a higher bypass ratio nozzle, has a lower temperature inside the nozzle and at the external jet compared to a larger mixer diameter, indicating that a lower bypass ratio nozzle can improve the nozzle performance by reducing the infrared radiation. The smaller mixer length can decrease the temperature inside and outside the nozzle but increase the velocity outside the nozzle. Finally, the conical shape of the mixer can reduce the temperature inside the nozzle due to the reduction of the core flow rate but increases the temperature of the exhausted jet due to the lower expansion of flow inside the nozzle compared to the nozzle with a cylindrical shape. This study demonstrates that a mixer with a smaller diameter and shorter length with a cylindrical shape can provide better performance for a nozzle.

Automated detection of hot-gas path defects by Support Vector Machine based analysis of exhaust density fields

Defects in the hot-gas path of aero engines have been shown to leave typical signatures in the density distribution of the exhaust jet. These signatures are superposed when several defects are present. For improved maintenance and monitoring applications, it is important to not only detect that there are defects present but to also identify the individual classes of defects. This diagnostic approach benefits both, the analysis of prototype or acceptance test and the preparation of Maintenance, Repair, and Overhaul. Recent advances in the analysis of tomographic Background-Oriented Schlieren (BOS) data have enabled the technique to be automated such that typical defects in the hot-gas path of gas turbines can be detected and distinguished automatically. This automation is achieved by using Support Vector Machine (SVM) algorithms. Choosing suitable identification parameters is critical and can enable SVM algorithms to distinguish between different defect types. The results show that the SVM can be trained such that almost no defects are missed and that false attributions of defect classes can be minimized.

Sound propagation through elevated, heated jets in cooler cross-flow: An experimental study.

Sound propagation through hot exhaust plumes with cooler cross-winds is present in many real world systems. One particular example is the sound propagation from exhaust stacks attached to open cycle gas turbine power stations. The research presented in this paper investigates the sound propagation from a reduced-scale exhaust stack, with a cross-flow from experiments conducted in a wind tunnel. Experimental measurements of the flow and temperature fields provide insight into the complex sound radiation characteristics. Results from the acoustic measurements show the change in the sound directivity arising from the inclusion of the hot exhaust plume, leading to non-axisymmetric sound directivity and a concentration of sound downwind of the exhaust stack outlet. In certain cross-flow conditions, the hot exhaust plume can increase the sound observed downwind by up to 11 dB when compared to the scenario of sound propagation from an exhaust stack in the absence of a heated jet or cross-flow. This paper describes the acoustic directivity at various radial distances from the exhaust stack, acoustic frequencies, jet temperatures, and cross-flow free-stream velocity. The results from this paper emphasise the importance of taking into consideration the hot exhaust plume with cooler cross-flow when estimating sound levels downwind of the stack.

REDUCTION OF EXTERNAL NOISE VEHICLE of SPAI “BOHDANA” ON THE BASIS OF THE KrAZ-63221 IMPROVED TWO-CHAMBER REACTIVE NOISE SILENCER

High-quality military equipment is a vital necessity for the independent state of Ukraine, especially in the conditions of aggravation of the situation at the front. One of the parameters that determines the quality of military vehicles is the level of external noise. The external noise of this type of car, in addition to the negative impact on human health (including the crew), is also an unmasking factor. In order to reduce the level of external noise of SPAI “Bogdan” on the basis of the chassis KrAZ-63221, the use of an advanced two-chamber jet muffler of the exhaust gases of the internal combustion engine is proposed. The known two-chamber jet muffler of exhaust gases has a fixed internal partition. Its acoustic efficiency is described by a known formula. It is proposed to make the inner partition of the muffler movable. This need arises from the fact of constant changes in the speed of the engine crankshaft during the movement of the car. The change in the position of the inner partition is consistent with the change in the speed of the crankshaft, because these two processes are synchronized. The mathematical package IDL was used to analyze the known formula for the efficiency of a two-chamber jet exhaust muffler of an engine with a movable inner partition. Given the need to show the dependence of the efficiency of the muffler simultaneously on two parameters – the speed of the crankshaft and the position of the movable inner partition of the muffler – the method of color coding was chosen. The design of a two-chamber jet noise muffler developed for ACS “Bogdan” is given. As a result of introduction of the developed muffler noise reduction of level of external noise of the SPAI “Bogdan” on the basis of the chassis KrAZ-63221 car on 2–3,5 dBA in the range of speeds of movement of 45–85 km/h is forecasted.