Outlet Of Chamber Research Articles

Investigation of Cavitation Phenomena in a “High-Power” Piezohydraulic Pump: A Computational Fluid Dynamics (CFD) Approach

Abstract Piezoelectric pumps, known as piezopumps, are highly versatile devices with applications in various fields due to their precise flow control, compact design, lack of magnetic interference, and low noise. These pumps are classified based on the number of pumping chambers, valve configuration, and driving power source mechanism. In fields requiring consistent flow rates and back pressures, particularly in fluid power applications, piezopumps employing a piezostack actuator as their power driving source are actively researched. This kind of piezopumps, also known as piezohydraulic pumps, operate using a piezostack actuator to drive a piston for fluid delivery, along with reed valves controlling fluid flow at the inlet and outlet of the pump chamber. The high operating frequency range of the piezostack actuator and reed valves, exceeding 1 kHz, allows piezohydraulic pumps to achieve significant flow rates despite the stack’s limited displacement. This enhances their performance without the need for increased size or power input. However, this also increases the risk of cavitation, which could lead to damage, reduced efficiency, and higher noise levels. Therefore, the purpose of this paper is to expand on previous research by using the CFD software Ansys Fluent to further investigate cavitation phenomena in a piezohydraulic pump developed at the University of Bath. In particular, the study focuses on simulating various oil flow scenarios through the pump with a fixed inlet pressure of 20 bar, while varying the opening of the inlet reed valve from the minimum (0.1 mm) to maximum (0.7 mm) value, as well as adjusting the pump chamber pressure.

Numerical study on flow and heat transfer of combustion chamber and turbine under thermal shock test

In order to more accurately analyze the influence of the interaction between the aero-engine combustion chamber and the turbine, this paper establishes a combustion chamber-turbine cross-component model based on a high-pressure first-stage guide vane thermal shock test device for numerical research. The SST k-ω turbulence model, non-premixed combustion model and P1 radiation model are selected, and the test conditions are used as boundary conditions to carry out fluid-solid coupling unsteady calculation in ANSYS FLUENT. The numerical results are in good agreement with the experimental results. The complex flow field information between the combustion chamber and the turbine is obtained by analyzing the numerical results. It is found that there is an interaction between the combustion chamber and the turbine. The results show that the hot spot at the outlet of the combustion chamber will cause a stronger thermal shock to the downstream of the high-pressure first-stage guide vane during the migration process. The influence of the high-pressure first-stage guide vane on its upstream can be traced back to the position 0.3 times the chord length from the outlet of the combustion chamber.

Optimization of atomization performance of external mixing air atomizing nozzle based on response surface agent model

Based on the finding that the atomization performance of the nozzle is affected by its structural parameters, a combination of finite element analysis and structural optimization calculations is used. Finite element analysis was performed through the VOF (Volume of Fluid) module of Fluent software to determine the structural parameters affecting the performance of the atomizing nozzle. The liquid cyclone tank inclination, the length of the flat section at the gas outlet, and the mixing chamber outlet diameter were used as optimization factors. The atomization cone angle and fuel atomization circumferential distribution uniformity index were used as the evaluation indexes of atomization performance. An orthogonal experimental design was carried out based on the above. Proxy model for atomization cone angle and fuel atomization circumferential distribution uniformity index based on response surface method. The optimal structure of the nozzle was obtained by optimization calculation of the agent model by genetic algorithm. The results show that the atomization performance is optimal when the inclination angle of the liquid rotating tank is 42.9, the length of the flat section at the gas outlet is 3.3, and the diameter of the mixing chamber outlet is 5.0. The atomization cone angle increased by 23.07 % compared with the original model, and the fuel atomization circumferential distribution uniformity index decreased by 45.06 %. A new solution for the design of externally mixed air atomizing nozzles is provided.

Study on Oxygen-Enriched Combustion Characteristics of Blast Furnace Gas Boiler

ABSTRACT To study the dynamic characteristics of OEC (oxygen-enriched combustion) in a BFG (blast furnace gas) boiler, the BFG boiler of an iron and steel enterprise is taken as the research object, and a thermal test bed for OEC of BFG is set up, and a thermodynamic simulation model of the BFG boiler is constructed based on the heat loss of chemical incomplete combustion obtained from thermal test, using MSP (Multi-Subject Simulation Platform). The effects of OC (oxygen concentration) and the position of oxygen entering the furnace chamber on the key parameters of the OEC process of the BFG boiler under different working conditions were analyzed. The results showed that the excess air coefficient of 1.2 and exhaust temperature of 120°C was kept constant during the thermal test. With a fuel volume of 2.4 Nm3/h, for example, after the OC was increased from 21% to 40%, the combustion flame temperature in the furnace was increased by about 34°C, the heat loss due to unburned gas was reduced by 0.21%, and the boiler efficiency was increased by 1.38%. In the dynamic model, at the instant when the OC is changed, the disturbance of the whole system is relatively large, and the FAT (furnace average temperature) outlet, the pressure of the steam ladle, and the MST (main steam temperature) will have a step change, and then gradually level off again. With the increase of OC, the combustion reaction is more and more intense, the steam side of the heat transfer process is strengthened, the boiler efficiency is improved, and the FAT chamber outlet, the steam ladle pressure and the MST after OEC in different ways of oxygen entry into the furnace chamber will be longer and longer to reach a stable value. The results of the study can provide a reference for the OEC operation of BFG boilers.

Film hole layout optimization for multi-row film cooling plate in continuous parameter space under non-uniform inlet temperature distribution

Film cooling is an advanced external cooling technology for protecting gas turbine blades from excessive temperatures. To counteract non-uniform heat loads caused by hot streak and swirl effects at the combustion chamber outlet, fine design of film hole positions is necessary. However, the complexity due to the numerous film holes and their positional parameters presents challenges in the independent optimization of film hole positions in a continuous parameter space. This study proposed an optimization method grounded in the divide and conquer approach to address optimization for film hole layout. The film hole layout was decomposed into multiple single rows and optimized systematically by iteratively refining the single-row film hole layout along the streamwise direction using the expectation maximization algorithm. Optimized layouts for five different inlet temperature distributions were obtained using the proposed method and adiabatic wall temperature distributions were compared and analyzed for optimized and staggered layouts. Additionally, the cooling performance of the optimized layout was evaluated against the staggered layout under conjugate heat transfer conditions and the robustness of the optimized layout under various blowing ratios and peak temperature positions was tested. The results demonstrated that the proposed method can optimize the positions of 52 film holes within 0.3h, and it was generalized to various inlet temperature distributions. By enhancing lateral interactions among downstream film jets, the lifting effect of kidney vortex in the optimized layout was weakened, bringing the film jets closer to the wall and significantly increasing coolant coverage during streamwise development. Comparative analysis reveals the superior cooling performance of the optimized layout at the blowing ratio of 1.0, evidenced by a 15.1% reduction in total input heat transfer rate and a 12.3% enhancement in overall cooling efficiency relative to the staggered layout. Under conditions with blowing ratios ranging from 0.5 to 1.5 and peak temperature position deviations, the average wall temperature of the optimized layout consistently remained lower than the staggered layout, indicating the robustness of the optimized layout to variations in blowing ratio and hot streak position.

CO formation characteristics in a centrally staged swirl combustor

Based on a validated numerical simulation methodology, this study focused on a centrally staged swirl combustor to investigate the combustion flow field inside the chamber under typical operating conditions. The CO formation characteristics of each region in the combustor were analyzed. In terms of elementary reactions, this study analyzed crucial reaction pathways contributing to CO formation in distinct regions utilizing the eddy dissipation concept model. Results reveal the occurrence of CO formation in the flame front and its rapid oxidation to form CO2 in the post-flame zone. CO2 partially dissociates into CO at high temperatures. Furthermore, air film quenching substantially impacts CO formation and emission, and air film greatly affects CO oxidation more than its formation. Local cooling and dilution effects from the air film contribute to the freezing of CO oxidation reactions. Therefore, a substantial quantity of CO remains unreacted, leading to increased CO emissions at the combustion chamber outlet.

Numerical simulation of VAM assisted combustion gas turbine

In order to save energy and protect environment, how to utilize ventilation air methane (VAM) is a subject that needed urgently to be studied. The methane concentration in VAM varies greatly, making it difficult for traditional burners to burn directly. Therefore, the feasibility of using VAM as a combustion gas for gas turbines is considered. When natural gas is used as the fuel for a micro gas turbine, the changes in air inlet parameters will directly affect its performance. This article uses experimental and numerical simulation methods to analyze the feasibility of using VAM as combustion air for micro gas turbines. The results show that factors such as intake pressure, temperature, and composition of gas turbines have an impact on combustion and pollutant emissions; the comparison between VAM and air as combustion gases shows that the rate of temperature increase in the combustion chamber increases, and the concentration of NO at the outlet of the combustion chamber increases by 0.97 % and the concentration of CO increases by 3.76 %. Based on the comprehensive analysis of gas turbine performance, it is concluded that the application of mine exhaust air to micro gas turbines has certain feasibility.

The effect of changing the combustion chamber head structure on turbine blades under thermal shock test

When the high-pressure turbine guide blade works in the aero-engine, it is in the complex gas-heat environment of the combustion chamber and the turbine. The temperature distribution and strength of the blade affect the reliability and life of the aero-engine. In order to more accurately analyze the complex flow field aero-thermal parameters between the aero-engine combustion chamber and the turbine, this paper considers the influence of the non-uniform aero-thermal parameters of the combustion chamber outlet on the turbine. Taking the first-stage guide vane of an aero-engine turbine as the research object, the high and low temperature cycle thermal shock test was carried out to obtain the crack location and strength of the turbine guide vane, which provided a certain reference for improving the design of the turbine guide vane. Through the test, it is found that after 750 thermal shock cycles, fatigue cracks appear in four concentrated areas of the blade, which are distributed in the leading edge and trailing edge of the blade respectively. This shows that the temperature at the leading edge and trailing edge of the blade is higher, the heat load is higher, and the risk of damage and ablation is also the highest. Based on the experiment, the cross-component model of the combustion chamber and the blade is established. On this basis, four kinds of swirler structures at the head of the combustion chamber are designed. ANSYS FLUENT software is used to study the unsteady parameters such as the surface temperature of the guide vane under the influence of strong swirling flow. The numerical results show that when the rotation direction of the cyclone is counterclockwise, the temperature of the guide vane wall is more uniform. Compared with the clockwise rotation of the cyclone, the temperature is reduced by about 5 %, and the installation angle of the 50° cyclone blade is better than the installation angle of the 45° blade.

Prediction of engine combustion chamber outlet temperature field based on deep Learning: Application in aero-engine life extension control

One of the current research hotspots is the prediction of combustion chamber flow field based on deep learning methods, but how to effectively utilize these prediction results is a key issue that needs to be addressed urgently. This paper further proposes a study on the predictive control method for engine life extension considering the dangerous point temperature of turbine guide vane based on the prediction of combustion chamber outlet temperature field. Firstly, a combustion chamber outlet temperature distribution prediction model is established through Computational Fluid Dynamics (CFD) numerical simulation and inception deconvolution network, and integrated into the variable cycle engine component level model to achieve real-time prediction of combustion chamber outlet temperature distribution. Furthermore, based on this, the dangerous point temperature of the high-pressure turbine (HT) guide vanes is introduced as a constraint into the prediction optimization, and a predictive control method for engine life extension considering the thermal mechanical fatigue life (TMFL) of the guide vanes is proposed. The simulation results show that compared to the traditional LEC control method, the temperature at the critical point of the blade is reduced by 12.28 K, and the TMFL of the blade is increased by 29.23 %. The research results of this article provide a good application example for predicting the temperature distribution at the outlet of the combustion chamber, expanding the application scenarios for predicting the flow field parameters inside the engine.

Effect of burner structural parameters on combustion characteristics and NOx emission of natural gas

The low-nitrogen combustion of natural gas has always been a crucial topic in environmental protection. Currently, small and medium-sized industries use straight-through pipelines as their burner nozzles. This design results in poor heat diffusion capacity after mixed combustion and a long time of temperature diffusion, leading to low combustion efficiency and high NOx emissions. To address this issue, a new type of natural gas low-nitrogen burner with a multi-port diffusion nozzle was developed. The burner’s structure was optimized through a combined approach of experiment and numerical simulation. The optimal structural parameters for the burner are a 40° swirl angle and 8 swirl blades, as indicated by the numerical simulation research results. The designed multi-port diffusion nozzle is matched with the appropriate swirl angle and number of blades to promote natural gas diffusion, forming an annular space region flames and a stable flame shape with a height of 0.64 m. After optimization, the average concentration of NOx at the outlet of the combustion chamber decreased from 61.5 ppm to 20.81 ppm. A natural gas low-nitrogen combustion experimental system was designed and constructed based on simulation results. The experimental results were analyzed in terms of flame structure characteristics, temperature distribution, and NOx emissions. The results indicate that the trend in temperature change is consistent with the simulation process. The NOx concentration at the outlet of the combustion chamber was measured by the flue gas analyzer to be 34.1 ppm, which was 5.3 ppm lower than the NOx concentration calculated by numerical simulation. The new burner exhibited better flame stability and a 12.6 % reduction in NOx emissions compared with a traditional straight-through pipeline burner of the same size. The designed natural gas low-nitrogen burner appears to be a suitable device for reducing NOx emissions in small and medium-sized industries.

Research on performance seeking control of turbofan engine in minimum hot spot temperature mode

Abstract The uneven temperature distribution at the combustion chamber outlet seriously affects the working life of the engine. In order to reduce the heat spot temperature at the combustion chamber outlet, a performance optimization control method of the engine minimum heat spot temperature pattern is proposed. Firstly, based on CFD method, the temperature distribution characteristics of combustion chamber outlet under different working conditions were obtained, and a component-level model of turbofan engine was established to characterize the heat spot temperature at combustion chamber outlet. Secondly, the high precision and high real-time engine on-board model is established by deep neural network. Compared with the component-level model, the average relative error of each performance parameter is less than 0.3 %, and the real-time performance is improved by 12 times. Finally, based on the feasible sequential quadratic programming algorithm, the performance optimization control of the minimum hot spot temperature model in the typical flight envelope is simulated and verified. The simulation results show that under the condition of ensuring the safe and stable operation of the engine and constant thrust, the heat spot temperature at the combustion chamber outlet decreases by 21 K maximum. Compared with the conventional minimum turbine front temperature optimization mode, the minimum heat spot temperature mode significantly reduces the heat spot temperature at the combustion chamber outlet.

Disturbed fluid flow reinforces endothelial tractions and intercellular stresses

Disturbed fluid flow is well understood to have significant ramifications on endothelial function, but the impact disturbed flow has on endothelial biomechanics is not well understood. In this study, we measured tractions, intercellular stresses, and cell velocity of endothelial cells exposed to disturbed flow using a custom-fabricated flow chamber. Our flow chamber exposed cells to disturbed fluid flow within the following spatial zones: zone 1 (inlet; length 0.676–2.027 cm): 0.0037 ± 0.0001 Pa; zone 2 (middle; length 2.027–3.716 cm): 0.0059 ± 0.0005 Pa; and zone 3 (outlet; length 3.716–5.405 cm): 0.0051 ± 0.0025 Pa. Tractions and intercellular stresses were observed to be highest in the middle of the chamber (zone 2) and lowest at the chamber outlet (zone 3), while cell velocity was highest near the chamber inlet (zone 1), and lowest near the middle of the chamber (zone 2). Our findings suggest endothelial biomechanical response to disturbed fluid flow to be dependent on not only shear stress magnitude, but the spatial shear stress gradient as well. We believe our results will be useful to a host of fields including endothelial cell biology, the cardiovascular field, and cellular biomechanics in general.

Gear-Shaped High-g Combustion Chamber for Micro Turbojet Engine Applications.

Enhancing combustion efficiency and optimizing the thrust-to-weight ratio are critical technical challenges encountered in the development, application, and growth of micro turbojet engines. The high-centrifugal (high-g) combustion chamber, as an innovative combustion chamber system, has the capability to replace the primary combustion chamber of the traditional turbojet engine, reducing the length of the combustion chamber while maintaining engine performance. Previous studies on the structure of the high-g combustor (HGC) have shown problems such as uneven temperature distribution of the turbojet rotor. To improve the feasibility of HGC integration into micro turbojet engines, this study conducts relevant experiments on a 120 N thrust engine. Subsequently, the results of these experiments were used to analyze the structural design of HGC through a simulation approach. Including six main configurations, the first four structural designs focused on establishing a suitable highly centrifugal environment to stabilize and improve the combustion performance, which was successfully achieved by designing the outer ring gear-shaped inlet with four different angles. Subsequent structural designs were based around improving the uniformity of the temperature distribution at the combustion chamber outlet. The final design of the HGC combustion efficiency is not much different from the original combustion chamber, and it can shorten the axial length of the combustion chamber by nearly 30%. The design of the air inlet holes and the baffle plate effectively improves the temperature uniformity at the outlet of the combustion chamber. Moreover, without changing the combustion chamber material, the corresponding engine weight can be reduced by about 10.7%, and the engine thrust-to-weight ratio can be improved by up to 12% with the same thrust, which provides design ideas for further lightweight applications.

The case study of the surface roughness influence at additively manufactured ejector and orifice plate and its impact on fluid flow

ABSTRACT Energy consumption and economic growth are strongly linked. In connection, great emphasis is nowadays placed on the accuracy and efficiency of machines and measuring equipment. This study compares the effect of surface roughness on airflow through a gas ejector and a centric orifice plate. Both devices are made from the same material but using two different methods of manufacturing, conventional and additive manufacturing. The study compares, experimentally and with numerical simulation, the subcritical ejector by adjusting the distance between the nozzle outlet and the mixing chamber outlet in the range of 16.9 mm, during the primary inlet pressure control from 10 to 50 kPa. The orifice is evaluated experimentally for different pressures from 0.6 to 7 bar(g). The study evaluates the level of substitutability of conventionally manufactured devices by those produced using the additive method. At design condition, the additively manufactured ejector exhibits a 12.97% lower ejection coefficient, i.e. lower effectivity. After control optimization, the decrease is reduced to 11.66%. For the additively manufactured orifice, the measured value of the pressure difference at nominal parameters deviated by 2.17%. In the case of the orifice, substitution is possible, assuming the calibration, but the orifice has a higher-pressure loss.

The individual tubular low-toxic combustion chamber

BACKGROUND: intensive works in improvement and development of microturbine power plants for energy and transport continues worldwide. These works are still relevant due to near-to-zero emissions of microturbines, as well as due to the fact that microturbines efficiency can be increased up to 50% and above, which opens the potential to compete with well-known power plants in the foreseeable future, including in terms of efficiency. Therefore, the work on the study of a low-toxic combustion chamber for a microturbine seems relevant as well. AIM: Сomputational and experimental study of an individual tubular low-toxic combustion chamber of a 50 kW microturbine with an increase in pressure at the inlet to the chamber. METHODS: The description of the experimental facility for combustion chamber testing and the results of its experimental study are given. A sufficient convergence of the experimentally obtained parameters of the combustion chamber with the parameters obtained from the simulation modeling of flow and combustion in the combustion chamber was obtained. RESULTS: In the course of the calculated and full-scale studies, hydraulic losses, nitrogen oxide emissions, and temperature unevenness at the outlet of the combustion chamber with increasing air pressure at its inlet were determined. CONCLUSIONS: The calculated study showed a significant effect of an increase in air pressure from 3 to 3.5 bar at the entrance to the combustion chamber on its main parameters. Thus, hydraulic losses have more than doubled and nitrogen oxide emissions have increased almost 1.3 times. The conducted experimental study of the combustion chamber generally confirmed the results of mathematical modeling and thereby tested the computational model used. Thus, the discrepancy in the experimentally and computationally obtained values of relative pressure losses in the combustion chamber does not exceed 15%, and in emissions of nitrogen oxides 7%.

Analysis of Tangential Leakage Flow Characteristics in a Variable Diameter Dual Circular Arc Vortex Compressor

(1) To address issues such as a low compression ratio and severe leakage in uniform wall thickness vortex compressors, this paper adopts a new scroll compressor model with a variable diameter double arc combined profile, which has a larger pressure ratio and smaller leakage than the scroll compressor with equal wall thickness that can bring new ideas and methods to the research in the field of scroll compressors. (2) This paper determines the theoretical equation of the variable diameter dual circular arc vortex profile and the combined profile, and infers mathematical models for the leakage line length, working chamber volume, and gas leakage per unit rotation angle of the vortex compressor, followed by simulation. (3) The results show that compared to the uniform wall thickness involute profile, the variable diameter dual circular arc combined profile model reduces the leakage line length by 25%, increases the average total pressure at the working chamber outlet by 2.38%, and decreases the leakage amount by 3.2%, consistent with theoretical analysis. (4) The tangential leakage caused by the radial gap in the variable diameter dual circular arc combined profile model has a significant impact on the uneven distribution of temperature and velocity fields in the working chamber of the vortex compressor, but a smaller impact on the pressure field.

Impact of steam flow into a combustion chamber of a contact gas-steam installation on its energy characteristics

Relevance. Reduction of natural gas consumption and emissions of harmful substances into the environment based on introduction of water vapor into a combustion chamber of a contact gas-steam installation. Aim. To carry out numerical studies on the influence of relative steam flow into the combustion chamber of the contact gas-steam installation on its energy characteristics. Objects. Contact gas-steam installations based on gas turbines with steam injection into the combustion chamber. Methods. Numerical methods based on material and energy balances of systems and elements of gas-steam installations. Results. Based on the calculation of the thermal circuit of the contact gas-steam installation, the authors have studied the influence of the relative steam flow into the combustion chamber on its energy characteristics. It was determined that the absolute electrical efficiency of the contact gas-steam installation increases linearly with growth of relative steam flow into the combustion chamber. The range of changes in the relative steam flow into the combustion chamber strongly depends on the temperature of the gases behind the combustion chamber and the compression ratio in the air compressor; the smaller these parameters are, the greater the range of changes. The maximum efficiency of 56% for all options is achieved at the maximum relative steam flow into the combustion chamber. It was established that the excess air coefficient, depending on the relative steam flow rate, decreases linearly, and the higher the temperature of the gases behind the combustion chamber and the compression ratio in the air compressor, the greater the rate of decline and the smaller the range of changes in the relative steam flow rate. It was revealed that the efficiency coefficient strongly depends on the relative steam flow into the combustion chamber, the temperature of the gases behind it and the degree of compression in the air compressor; with increasing these parameters, it increases linearly. It was determined that the temperature of the gases at the outlet of the gas turbine also strongly depends on the relative flow of steam into the combustion chamber, the temperature of the gases at its outlet and the compression ratio in the compressor. With an increase in the relative flow of steam into the combustion chamber, this temperature increases linearly from 600 to 700°C, while the higher the temperature of the gases at the outlet of the combustion chamber and the compression ratio in the compressor, the higher the temperature of the gases at the outlet of the gas turbine. The authors revealed the dependence of useful work on a gas turbine shaft on the relative steam flow into the combustion chamber. With an increase in the relative steam flow, the useful work on the gas turbine shaft increases along the branch of the parabola. The higher the temperature of the gases behind the combustion chamber and the compression ratio in the compressor, the steeper the branch of the parabola, but the smaller the range of changes in the relative steam flow. It was established that with an increase in the relative steam flow, the gas flow to the gas turbine decreases according to a hyperbola. Moreover, the lower the temperature of the gases behind the combustion chamber and the compression ratio in the compressor, the more the gas flow to the gas turbine drops.

Advancing the Engineering Approach to Improving the Quality Cracking Efficiency of Palm Nut Crackiing Machine

A Palm Nut cracking machine with an improved beater configuration was developed to effectively crack Palm Nuts of various species and sizes. This research aim at improving the quality of the Palm kernel recovered at relatively low cost during Palm kernel oil production. Durable materials were acquired locally to fabricate the machine for ease of usage and maintenance, also to make it affordable for small and large scale processors. Basic features of the machine are; hopper, electric motor (prime mower), cracking chamber, cracking beater and discharge outlet. The design of the cracking drum and beater configuration was based on the impact force required to crack the Palm Nut which is a function of Palm Nut shear strength. A 5 hp electric motor was selected based on the power required to effectively operate the machine. The machine was tested with “Tenera” varieties, three nut sizes (14.5, 22.15 and 29.43mm) and five speeds (970, 1200, 1450, 1750 and 2430rpm). Result shows that the change in machine speed significantly (P<0.05) affects all the machine performance irrespective of the Palm Nut size and variety, which agrees with the report of several other researchers. The obtained optimum machine performance values are 14,874 nuts/h, 89.5%, 98% for the machine capacity, quality performance efficiency and cracking efficiency for Tenera variety. The best crop and machine parameter for the optimum performance of the Palm Nutcracker are 29.43 mm and 970 rpm, nut size and machine speed. It was concluded that the overall performance of this developed Palm Nut cracking beater was effective because it fell within the range of 80 to 98% efficiency.

Numerical parametric study of a sweeping-vortex low-frequency fluidic oscillator

Fluidic oscillators are garnering increasing attention in various fields due to their self-induced oscillation characteristics. This study proposes a novel fluidic oscillator, the sweeping-vortex fluidic oscillator (SVFO), characterized by unique feedback properties. These properties exploit fluid feedback from the side opposite the attached wall and the spin delay of the captive vortex to yield low-frequency oscillating jets. The oscillation characteristics and the influence of main geometric parameters were investigated using computational fluid dynamics approach. Results show that the evolution of the flow field within the SVFO demonstrates an intricately dynamic interacting. The deflection switching of the main jet is primarily controlled by a pair of counter-rotating moving vortexes. Geometric parameters influence the stability of the dynamic evolution of both captive and moving vortexes, thereby altering the signal components of the output performance transmitted to the inlet. The overall width of the oscillator has a pronounced impact on the oscillation frequency, and with an increase in the overall width, a maximum frequency increase of 87 % can be observed. Furthermore, the height of the sweeping chamber and the diameter of the vortex chamber outlet have a noticeable effect on the pressure pulse amplitude. A pressure fluctuation coefficient greater than 1.1 was recorded. The results also suggest that the geometric parameters of the fluidic oscillator need to be designed within a reasonable range; otherwise, the jet oscillator will not function. A more refined optimization of geometric parameters could be obtained with the aim of achieving a stable main jet, feedback flow of appropriate intensity, and optimal attachment conditions. This work reveals the oscillation mechanism and the influence of geometric parameters on SVFOs, providing a theoretical basis for designing related oscillators.

A numerical modeling framework for predicting the effects of operational parameters on particle size distribution in the gas atomization process for Nickel-Silicon alloys

Gas atomization is utilized to produce good-quality metal powders. A numerical modeling framework is developed to simulate the gas atomization process. A two-phase VOF flow model in OpenFOAM is applied to track the primary breakup of the melt stream by a high-speed gas flow. The generation of primary melt droplets is extracted from the VOF field. A Lagrangian-Eulerian multiphase flow model in Ansys Fluent is adopted to track the secondary breakup of the primary melt droplets under the high-speed gas flow. The final particle size distribution is obtained by analyzing the particles sampled at the outlet of the atomization chamber. The process of gas atomization can be affected by many factors such as the atomization equipment, operating parameters, and material properties. Sensitivity analysis is conducted through modeling to investigate the effects of these factors on particle size distribution. The model predictions are validated by specially designed gas-atomization experiments.