Backpressure Levels Research Articles

Experimental and numerical investigation of the effects of porous bleed systems on a model scramjet inlet under high backpressure conditions

In this study, we conducted experimental and numerical investigations to assess the effects of backpressure and configurations of porous bleeds on a scramjet inlet's performance at Mach 5. Experiments in a high-enthalpy wind tunnel, using a backpressure controller and a porous bleed with 1 mm holes and 10 mm lateral spacing, were paired with Reynolds-averaged Navier-Stokes simulations to explore the mitigation of flow separation and the prevention of inlet unstart under various backpressure conditions. The simulations provided insights into how backpressure levels and porous bleed geometries impact internal flow structures, as well as the critical backpressure ratio at which inlet unstart occurs. Additional simulations varied the bleed system's hole diameter and spacing, identifying configurations that optimize aerodynamic performance by enhancing total pressure recovery and Mach number at the isolator exit, while reducing bleed mass flow rates. The study also quantified the impact of these configurations on engine thrust, determining that certain bleed system designs significantly improve thrust by efficiently suppressing the interaction between the core flow and corner recirculation zones. This study examined the internal three-dimensional flow structure characteristics under high back pressure and provided insights into porous bleed configuration capable of efficiently suppressing inlet unstart.

Análise numérica de barreiras físicas para mitigar os efeitos da explosão de tanques de gás usando fluidodinâmica computacional

Abstract In many urban buildings, there is the presence of gas central storage, which contain pressurized tanks. One of the main risks in these places is an explosion, which may or may not is followed by fire. In general, the shock wave formed by this phenomenon is disastrous and can cause material damage and even fatalities. Recent research has contributed to understanding protective systems against this phenomenon; however, it is necessary to advance in developing protection devices for gas central storage. From this perspective, the implementation plan of these devices in order to mitigate the harmful effects of explosions are essential to raise the safety level in construction. Physical protection barriers are appropriate solutions for the protection of buildings, especially in places where it is impossible to bury gas reservoirs. In addition to the potential to reduce back pressure levels, protective walls, when properly designed, can also prevent the spread of debris from the explosion. Another kind of barrier that influences the propagation of the shock wave close to the ground is the ditches, whose function is related to the absorption and redirection of wave energy. Understanding the positioning, geometry, and overpressure attenuation potential of physical barriers are essential in developing safer and more reliable projects. This article aims to study protective barriers in buildings with pressurized gas tanks. The study was developed numerically using the Autodyn software. This program is a tool based on computational fluid dynamics (CFD). The protective capacity of the proposed types of protection regarding the mitigation of incident overpressures was evaluated qualitatively and quantitatively.

Study of Backpressure on the Composition and Characteristics of the AA5083 Alloy During ECAPed

Equal Channel Angular Processing Process at room temperature along varying backpressure level and numbers of passes produced hefty billets of 25 mm×25 mm×100 mm industrial alloy AA5083 with an ultrafinegrained microstructure. Supersaturated solid iron in an aluminium matrix was treated in brittle cast AA5083 during Equal Channel Angular Processing with Sixteen passes and a 285 MPa backpressure. The Equal Channel Angular Processing alloy’s strength, ductility, and microhardness were all greatly improved. Increased backpressure improves ductility of Equal Channel Angular Processing alloys, the workability and delays the craking of intermetallic particles. Alloys treated by Equal Channel Angular Processing have improved workability due to backpressure. The AA5083 alloy’s strength and microhardness were greatly improved. When an initially coarse-grained alloy undergoes 3 passes of Equal Channel Angular Processing with a 220 MPa backpressure, its microhardness and room strength (185 HV, UTS = 327 MPa) are significantly higher than their typical values following conventional processing with cold rolling or hot pressing. In Equal Channel Angular Processing, a super saturated solution was generated with a peak soluble of 0.6 wt.% of iron allow the ageing of the usually non-hardenable metal. The cast alloy treated using the Multi-pass approach has positively impacted toughness, elasticity, and microhardness.

Effect of static pore water pressure on shear behavior of saturated kaolin clay

To study the mechanical properties of sedimentary marine clays in deep seabed, static pore water pressure (SPWP) is often prescribed in triaxial shear tests by applying different back pressure levels (B.P.) corresponding to in-situ position of the water table. In this paper, several undrained and drained triaxial tests have been conducted to study the effect of SPWP on the mechanical behaviors of kaolin clay, which is often used to create artificial marine clay or as a subgrade material in the centrifuge tests of offshore geotechnical engineering. The magnitude of SPWP is found to impact undrained shear strength, initial growth rate of excess pore pressure, friction angle, while has little effect on initial undrained shear stiffness and ultimate excess pore pressure. A new unique line can be determined which is parallel to total stress path by fitting all the critical failure points during undrained shearing. The influence mechanism is considered to be related to a nonuniform distribution of SPWP in different kinds of pores, which makes the clay microstructure changeable under different SPWP. There may exist a "pseudo-suction" when certain SPWP is applied, resulting in a higher friction angle of kaolin clay.

Research of forming and sintering processes of copper powder blanks for equal channel angular pressing

Copper-based powder materials have found their application in many industries. These include classical powder metallurgy, automotive and aviation industries, microelectronics, instrument engineering, and nanotechnology. In this paper, the processes of forming and sintering copper powders obtained by various methods are considered. The main part of the research was carried out on powders of the PMS-1 brand obtained by electrolysis. Four batches of samples (18 pieces each) were pressed at different pressures. Based on the results of the research, a molding mode was proposed, which should ensure the density of blanks not less than 70 % of the density of compact material. To find the simplest and most rational modes of sintering blanks, the process was carried out in air and in dissociated ammonia. The parameters of the samples were calculated after each technological operation, and the volume shrinkage of the samples was calculated depending on the initial density. Draft tests were carried out. Sediment tests were performed up to a maximum pressure of 400 MPa. Despite the fact that the degree of high-altitude deformation was 37–40 %, none of the samples collapsed during the tests, and no visible cracks were observed. Based on preliminary experiments, the masses and forming modes of rectangular blanks that were used for equal channel angular pressing were calculated. Equal channel angular pressing was performed for two samples parties obtained using different sintering modes. When pressing the first samples party, the lack of the required level of back pressure led to either a complete or significant violation of the material integrity. Before pressing the samples of the second party, a copper sample was previously placed into the channel to create a natural backpressure. It was also possible in principle to carry out the process of equal channel angular pressing of porous sintered workpieces without violating the integrity of the material.

Analysis on influence factors of back pressure in an asymmetrical algebraic scroll compressor

The back-pressure mechanism plays an important role in the performance and efficiency of the scroll compressor. In this work, the level of back pressure of an asymmetrical algebraic scroll compressor is experimentally measured and it is shown that the back pressure decreases with the increase of compressor frequency under all tested operating conditions. The mathematical model of the scroll compressor is also developed in order to further investigate other influence factors of back pressure. The predicted back pressure is compared with experiment result, showing a similar trend to them. The pressures in each working chamber and back-pressure chamber are studied to identify the effect of leakage through flank and radial leakage gaps. The influences of compressor frequency, leakage gap size, back-pressure volume on back pressure are discussed in detail based on developed model. The axial forces and stability of the orbiting scroll are also evaluated under these operating conditions by using interpolation method to calculate the pressure distribution on tips.

Hydraulic Interactions between Injection Events Using Multiple Injection Strategies and a Solenoid Diesel Injector

An experimental study was performed to explore the influence of dwell time on the hydraulic interactions between injection events using pilot injection strategy, split injection strategy, post injection strategy and a solenoid diesel injector. To do so, a sweep of dwell time from 0.55 up to 2 ms using all multiple injection strategies and levels of rail pressure, of 80, 100 and 120 MPa, and single level of back pressure, of 5 MPa, was performed. The hydraulic interactions between injection events were characterized through the second injection hydraulic delay and second injection mass in an injection discharge curve indicator equipped with all the components required for its operation and control. In order to define the operating conditions of the multiple injection strategies, to ensure the same injected fuel mass in all cases, the characteristic curves of injection rate for the solenoid diesel injector studied were obtained. The second injection hydraulic delay increases with dwell time values in the range of 0.55–0.9 ms for all multiple injection strategies and levels of rail pressure tested. Conversely, the second injection hydraulic delay decreases with dwell time values higher than 0.9 ms. Moreover, the second hydraulic delay depends mainly on the dwell time and not on the injected fuel mass during the first injection event. The second injection mass increases with dwell values less than 0.6 ms. By contrast, the second injection mass is not significantly affected by that of the first injection at a dwell time higher than 0.6 ms.

EFFECTS OF BOUNDARY CONDITIONS ON A BOSCH-TYPE INJECTION RATE METER

Spread and evolution of Common Rail (CR) injection systems enable to influence injection events more efficiently than ever, while injection mass flow rate during an injection event crucially affects the combustion process. A measurement device based on the work of Bosch was set up, and measurements were made with different boundary conditions to explore the capabilities of the measurement system and to validate a detailed model of a CR injector. The main finding of this research work is, that orifice size had no noticeable effect on the measured injection rate traces, while it was stated in the original work that a small orifice is needed to terminate the measuring tube to maintain stable measurement conditions. Moreover, the backpressure level in the measuring system has a significant effect on the measured injection traces. If pressure in the measuring tube is low, gradient at the injection rate rise is lower, while if the pressure is comparable with that of a combustion chamber maximal compression pressure, measurement of higher doses is unaccomplishable due to the long pressure decrease time in the measuring tube after the end of the injection. Based on the results of the investigation, it can be stated that the Bosch-type injection rate measurement method does not give back the exact injection rate shape, a supplementing method would be necessary to calculate real nozzle flow rate.

Forced oscillation phenomenon of normal/oblique shock trains in a rectangular duct at Mach 2 and 3

The forced shock train oscillation is a common phenomenon in a practical working scramjet isolator. To evaluate the similarities and differences between the forced normal shock train oscillation and the forced oblique shock train oscillation, experiments were conducted in a rectangular duct at Mach 2 and 3. The normal/oblique shock trains were forced to oscillate for different back-pressure levels by changing the mechanical throttling ratio. High-frequency pressure measurements were mainly utilized for data acquisition and analysis. The frequency contents, the intermittency characteristics and the perturbation propagation of forced shock train oscillations were investigated in this work. Experimental results illustrate that the forced oscillation at Mach 3 is a composite pattern, which is dominated by the excited frequency and coupled with the inherent unsteadiness. This phenomenon is not obvious for the forced oscillation at Mach 2. For the forced oscillations at Mach 2 and 3, the maximum zero-crossing frequency is close to the downstream excitation frequency, and the whole intermittent region almost holds this value, which is very different from the self-excited oscillation pattern. By using the cross-spectral analysis, the frequency-dependent correlation was evaluated. It shows that the excitations and its harmonic contents can propagate upstream to affect the intermittent region and its downstream. Besides the excitation frequency and its harmonic contents, low-frequency contents (tens to more than a hundred Hz) can propagate nearby the separation region, and the propagation to downstream the separation bubble is very weak. Considering the time-lag between different transducers, the propagation speed of perturbations can be obtained. It implies that the propagation speed is independent of the magnitude of the back-pressure, but affected by the velocity of the incoming flow. Specifically, the higher the freestream Mach number is, the greater the propagation speed will be.

Design of organic Rankine cycle power systems for maritime applications accounting for engine backpressure effects

The installation of an organic Rankine cycle unit on the exhaust line of a marine engine imposes an increase in the backpressure on the engine, resulting in a decrease of the engine performance and a variation of the available waste heat. In this paper, a method is presented for the optimal design of organic Rankine cycle power systems for waste heat recovery in marine applications. The method is based on the use of performance maps for the engine and numerical models for the organic Rankine cycle unit and the waste heat recovery boiler, thereby enabling consideration of the effect of the increased backpressure on the performance of both the main engine and the organic Rankine cycle unit. The method is evaluated on a hypothetical containership fuelled by liquefied natural gas. The results of the study indicate that the overall system fuel consumption can be reduced by 0.52 g/kWh to 1.45 g/kWh by allowing higher backpressure levels on the engine. In addition, the results of the study indicate that for a fixed power output of the organic Rankine cycle unit, a reduction of the space requirement for the waste heat recovery boiler by up to 35% can be attained when increasing the maximum allowed engine backpressure from 3 kPa to 6 kPa.

Numerical analysis of a small ducted wind turbine for performance improvement

ABSTRACTIn this study, Computational Fluid Dynamics simulations are carried out to assess the effect of duct geometry on power output and flow characteristics for a custom-designed wind turbine. The results show that the elevation of power output for a wind turbine is strongly reliant upon the shape of the duct. While before reaching a certain tip speed ratio, ducting would actually decrease the power output level. It is also argued that the velocity recovery index can also be considered dependent upon to the duct geometry. While the record power coefficient for the bare turbine is calculated to be 0.46, a power coefficient of 0.78 is shown to be reachable by adding a duct, which indicates an increase of approximately 70%. The near wake flow was analysed and a relation between the back-pressure level and the calculated power output was verified. The study also presents a framework for sizing the optimum duct.

EFFICIENCY EVALUATION OF IMPLEMENTATION OF OPTIMIZATION METHODS OF OPERATION MODES OF THE "PLAST - GAS PIPELINE" SYSTEM BY THE METHODS OF MATHEMATICAL MODELING

To date, Ukraine's mature gas fields, which are being developed in the gas regime, are at the final stage of development, which is characterized by a significant depletion of reservoir energy. The final stage of development requires solving complex problems related to watering wells, destruction of the reservoir, removal of formation water and mechanical impurities, increasing back pressure in the system, as well as the moral and physical wear and tear of industrial equipment. In the conditions of falling gas production, a significant part of the operating well stock is unstable, in the mode of unauthorized stops due to the accumulation of liquid at the bottom and insufficient gas velocities for removal to the surface, and also the accumulation of the liquid phase in the lowered places of the gas gathering system. Within the framework of the conducted studies, the gas dynamic models of the operation of the gas collection system of 3 oil/gas-condensate fields (OGCF) are created. A single model of the gas production system "reservoir - well - gas gathering system - inter-field gas pipeline - main facilities" is built. The current efficiency of the gas production, collection and transportation system is assessed. On the basis of model calculations, the current production capabilities of the wells are defined, as well as the "narrow" places of the system. It is established that the introduction of modern technologies for the operation of watered wells without optimizing the operation of the entire gas production system is irrational, since the liquid that is carried out from the wellbore will accumulate in the plumes and increase the back pressure level in the ground part. In conditions of increasing gas sampling, liquid flowlines can be taken out of the loops and deactivated the separation equipment. The feasibility of introducing methods for optimizing the operation modes of the gas production - gathering and transportation system is estimated, which allows choosing the optimal method for increasing the efficiency and reliability of its operation. For the first time in the Ukrainian gas industry, an integrated model of the field is created as a single chain of extraction, collection, preparation and transportation of natural gas, which can be adapted for the development and arrangement of both new and mature deposits. The main advantage of the application for the hydrocarbon production sector is the simulation of the processes, which makes it possible to evaluate the operating mode of the well in the safe zone while reducing the working pressure and introducing various intensification methods, and also to estimate the increase in hydrocarbon production. For the equipment of the ground infrastructure – "midstream" – the main advantage is a reduction in the time required to perform design calculations for gas pipelines, trains and pipelines for transporting multiphase media using public models. The creation and use of integrated models of gas fields gives an understanding of the integral picture of available resources and ensures an increase in the efficiency of field development management. The results of the calculation are clearly correlated with the actual data, which makes it possible to use the models constructed to obtain numerical results.

Gas-Dynamic Designing of the Exhaust System for the Air Brake

Each gas turbine engine is tested some times during the life-cycle. The test equipment includes the air brake that utilizes the power produced by the gas turbine engine. In actual conditions, the outlet pressure of the air brake does not change and is equal to atmospheric pressure. For this reason, for the air brake work it is necessary to design the special exhaust system. Mission of the exhaust system is to provide the required level of backpressure at the outlet of the air brake. The backpressure is required for the required power utilization by the air brake (the air brake operation in the required points on the performance curves). The paper is described the development of the gas dynamic canal, designing outlet guide vane and the creation of a unified exhaust system for the air brake. Using a unified exhaust system involves moving the operating point to the performance curve further away from the calculated point. However, the applying of one exhaust system instead of two will significantly reduce the cash and time costs.

Back-pressure effects on unsteadiness of separation shock in a rectangular duct at Mach 3

To evaluate back-pressure effects on unsteadiness of separation shock in a rectangular duct, some test cases were designed and conducted in a supersonic air-breathing wind tunnel. High-speed Schlieren technique and high-frequency pressure measurements were utilized for data acquisition. Different back-pressure levels were applied by changing downstream throttling ratio. Some parameters for estimating canonical separation flows, such as zero-crossing frequency and intermittency, have been introduced to analyze the duct separation flow. The experimental results show that the separation shock oscillation frequencies increase and the intermittent region lengths decrease with the increasing back-pressure level. A comparison between the unsteadiness of shock/boundary layer interactions for the canonical flow and the duct internal flow were made. It is found that the normalized Strouhal number for the duct internal separation flow ranges from 0.01 to 0.03, which share the similar range with canonical separation flows. That is to say, the physics of separation shock unsteadiness is similar over a wide range of interaction flows, which may share the inherent flow mechanism.

Numerical analysis of back pressure equal channel angular pressing of an Al-Mg alloy

Ultrafine grain size provides enhanced mechanical and/or physical properties such as strength and high ductility, superplasticity at relatively low temperatures and high strain rate and better corrosion resistance. Well-known as one of the most promising and effective structure refining method among other severe plastic deformation (SPD) techniques, equal channel angular pressing (ECAP) has been intensively investigated due to spectacular improvements in structure and therefore properties of bulk ultrafine grained/nanostructured materials. A successful ECAP requires surpassing two obstacles: the necessary load level which directly affects tools and a favourable stress distribution so the material withstanding the accumulated strain of repeated deformation. Materials could withstand more passes if a back pressure (BP) is applied. In traditional ECAP, tensile stress along the contact surface between the work piece and the upper wall of the outlet channel leads to crack initiation, while in the presence of BP, a negative (compressive) stress appears during the process balancing the tensile stress. In this study a comparative tridimensional finite element analysis (FEA) is performed to evaluate the flow of an Al-Mg alloy depending on different BP levels and process parameters. The results in terms of load level and strain distribution show the influence of BP on the material behaviour, opening opportunities for industrial applications.

Geneza i klasyfikacja antropogenicznych zagłębień bezodpływowych w Górach Świętokrzyskich

<p>W pracy przedstawiono problem zagłębień pozbawionych odpływu powierzchniowego, powstałych w wyniku ingerencji człowieka w rzeźbę terenu w Górach Świętokrzyskich. Na podstawie materiałów kartograficznych i kartowania terenowego przeprowadzono identyfikację powyższych form terenu. W granicach mezoregionu stwierdzono występowanie 1276 antropogenicznych zagłębień bezodpływowych, które obejmują powierzchnię 13,37 km<sup>2</sup>, stanowiącą 0,7% powierzchni całego mezoregionu. W pracy dokonano również próby klasyfikacji zidentyfikowanych zagłębień. Ze względu na genezę zagłębienia podzielono na cztery główne typy: poeksploatacyjne, spowodowane podpiętrzeniami terenu, pracami ziemnymi oraz melioracją lub regulacją cieków. W dalszej części wydzielono również podtypy genetyczne tychże zagłębień. W Górach Świętokrzyskich najliczniej reprezentowane są zagłębienia związane z podpiętrzeniami terenu spowodowanymi przez nasypy drogowe i stanowią one ok. 51% wszystkich zagłębień. Jednakże pod względem zajmowanej powierzchni dominują zagłębienia poeksploatacyjne wyrobiskowe, obejmując 77% powierzchni wszystkich antropogenicznych zagłębień bezodpływowych w Górach Świętokrzyskich. Przedstawiona klasyfikacja obejmuje wyłącznie typy zagłębień, których występowanie stwierdzono na analizowanym obszarze i nie ma charakteru uniwersalnego. </p>

Droplet Mobility Manipulation on Porous Media Using Backpressure

Wetting phenomena on hydrophobic surfaces are strongly related to the volume and pressure of gas pockets residing at the solid-liquid interface. In this study, we explore the underlying mechanisms of droplet actuation and mobility manipulation when backpressure is applied through a porous medium under a sessile pinned droplet. Reversible transitions between the initially sticky state and the slippery states are thus incited by modulating the backpressure. The sliding angles of deionized (DI) water and ethanol in DI water droplets of various volumes are presented to quantify the effect of the backpressure on the droplet mobility. For a 50 μL water droplet, the sliding angle decreases from 45 to 0° when the backpressure increases to ca. 0.60 bar. Significantly smaller backpressure levels are required for lower surface energy liquids. We shed light on the droplet actuation and movement mechanisms by means of simulations encompassing the momentum conservation and the continuity equations along with the Cahn-Hilliard phase-field equations in a 2D computational domain. The droplet actuation mechanism entails depinning of the receding contact line and movement by means of forward wave propagation reaching the front of the droplet. Eventually, the droplet skips forward. The contact line depinning is also corroborated by analytical calculations based on the governing vertical force balance, properly modified to incorporate the effect of the backpressure.

Numerical and experimental analysis of low-pressure steam turbine blades coupled with lacing wire

Many industrial steam turbine applications require the capability for variable speed operation in combination with high mass flow rates and high back pressure levels. Especially the low-pressure blading has to be designed carefully with respect to the mechanical integrity. An effective way to reduce blade vibration is the introduction of a simple lacing wire to couple the moving blades. In this paper, the structural behavior of blades coupled by a wire is verified by means of linear and nonlinear finite element method. Different modeling techniques for the coupling effects are presented and discussed. Special focus is put on the nonlinear effects of the contact between blade and wire to investigate the frictional damping performance of the system. The obtained numerical results are validated by strain gauge measurements on a full-scale test turbine under real steam conditions in an industrial steam turbine test rig. The experimental data show low blade vibration amplitudes in the whole operational range indicating a high damping performance of the investigated wire design. The calculation results from the forced response analysis including the frictional effects are in good agreement with the experimental data.

Investigation into the effect of backpressure on the mechanical behavior of methane-hydrate-bearing sediments via DEM analyses

Backpressure has been extensively applied in experimental tests to improve the water saturation of samples, and its effect on the strength of saturated soils has been traditionally regarded as trivial in Soil Mechanics. However, a non-negligible influence of backpressure on the macro mechanical properties of methane-hydrate-bearing-sediments (MHBS) has been surprisingly observed in several recent experiments reported in the literature. This paper aims to shed light on this phenomenon. A theoretical analysis on the microscopic interaction between soil grains and inter-particle methane hydrate (MH) was carried out to highlight how backpressure affects the mechanical properties of the inter-particle MH which in turn affect the macroscopic mechanical behavior of MHBS. The influence of backpressure is accounted for in a new bond contact model implemented into the Distinct Element Method (DEM). Then, a series of DEM biaxial compression tests were run to investigate the link between mechanical properties of MHBS and backpressure. The DEM numerical results show that shear strength, small strain stiffness and shear dilation of MHBS increase with the level of backpressure. As the critical state is approached, the influence of backpressure ceases. Moreover, the elastic modulus and cohesion of MHBS increase linearly while the internal friction angle decreases at a decreasing rate as the backpressure increases. Simple analytical relationships were achieved so that the effect of backpressure on the mechanical properties of MHBS can be accounted in the design of laboratory tests to characterize the mechanical behavior of MHBS.

Using Advanced Diagnostics in Differential Pressure Measurements

This paper discusses a diagnostic method of monitoring the integrity of dip-pipe legs applied in back-pressure level and density measurement. Applications are often vulnerable to two common faults in instrument pipework: leaks and blockages. Both are surprisingly difficult to diagnose on plant, so a new diagnostic technique has been jointly developed for use at Sellafield site.