Nozzle Flow Research Articles

Laser-assisted magnetorheological polishing of SLM-fabricated 316L stainless steel surface

ABSTRACT A laser-assisted magnetorheological polishing device was used, which achieved flat polishing of SLM formed 316 L stainless steel by rotating the polishing head. Through orthogonal experiments, the effects of laser power, nozzle flow rate, polishing time, polishing gap, and spindle speed on polishing performance are comprehensively considered. The surface roughness of the samples before and after the experiment is measured, and signal-to-noise ratio analysis is utilized to determine the impact of independent variables on the polishing effect and to derive the optimal parameter combination. Experimental findings indicate that polishing time significantly influences surface roughness, followed by spindle speed, laser power, nozzle flow rate, and polishing gap; The optimal parameter combination is: polishing time of 40 min, spindle speed of 3600 rpm, laser power of 3 W, nozzle flow rate of 100 mL/min and polishing gap of 2 mm. Under this parameter combination, the sample exhibits the smoothest surface post-experiment.

Improve neural representations with general exponential activation function for high-speed flows

Characterizing flow fields with neural networks has witnessed a considerable surge in recent years. However, the efficacy of these techniques is typically constrained when applied to high-speed compressible flows, due to the susceptibility of nonphysical oscillations near shock waves. In this work, we focus on a crucial fundamental component of neural networks, the activation functions, to improve the physics-informed neural representations of high-speed compressible flows. We present a novel activation function, namely, the generalized exponential activation function, which has been specifically designed based on the intrinsic characteristics of high-speed compressible flows. Subsequently, the performance of the proposed method is subjected to a comprehensive analysis, encompassing training stability, initialization strategy, and the influence of ancillary components. Finally, a series of representative experiments were conducted to validate the efficacy of the proposed method, including the contact-discontinuity problem, the Sod shock-tube problem, and the converging–diverging nozzle flow problem.

Effect of shear-thinning rheology on the dynamics and pressure distribution of a single rigid ellipsoidal particle in viscous fluid flow

This paper evaluates the behavior of a single rigid ellipsoidal particle suspended in homogeneous viscous flow with a power-law generalized Newtonian fluid rheology using a custom-built finite element analysis (FEA) simulation. The combined effects of the shear-thinning fluid rheology, the particle aspect ratio, the initial particle orientation, and the shear-extensional rate factor in various homogeneous flow regimes on the particles dynamics and surface pressure evolution are investigated. The shear-thinning fluid behavior was found to modify the particle's trajectory and alter the particle's kinematic response. Moreover, the pressure distribution over the particle's surface is significantly reduced by the shear-thinning fluid rheology. The FEA model is validated by comparing results of the Newtonian case with results obtained from the well-known Jeffery's analytical model. Furthermore, Jeffery's model is extended to define the particle's trajectory in a special class of homogeneous Newtonian flows with combined extension and shear rate components typically found in axisymmetric nozzle flow contractions. The findings provide an improved understanding of key transport phenomenon related to physical processes involving fluid–structure interaction such as that which occurs within the flow field developed during material extrusion–deposition additive manufacturing of fiber-reinforced polymeric composites. These results provide insight into important microstructural formations within the print beads.

Temporal periodic solutions of non-isentropic compressible Euler equations with geometric effects

Abstract In this article, we investigate the general qusi-one-dimensional nozzle flows governed by non-isentropic compressible Euler system. First, the steady states of the subsonic and supersonic flows are analyzed. Then, the existence, stability, and uniqueness of the subsonic temporal periodic solutions around the steady states are proved by constructing a new iterative format technically. Besides, further regularity and stability of the obtained temporal periodic solutions are obtained, too. The main difficulty in the proof is coming from derivative loss, which is caused by the diagonalization. Observing that the entropy is conserved along the second characteristic curve, we overcome this difficulty by transforming the derivative of entropy with respect to x x into a derivative along the direction of first or third characteristic. The results demonstrate that dissipative boundary feedback control can stabilize the non-isentropic compressible Euler equations in qusi-one-dimensional nozzles.

Numerical Investigation of Unsteady Flow Characteristics of Planar Plug Nozzle in Over-Expanded Conditions

Abstract Plug nozzles are frequently regarded as a strong contender for futuristic single-stage-to-orbit space missions due to their inherent altitude-compensating properties. Optimizing the design of these nozzles to achieve peak performance during the initial ascent phase is of preeminent importance. The current research aims to deepen our comprehension of the unsteady behavior of plug nozzles during this ascent phase, commonly referred to as the overexpanded flow regime. It utilizes a full-spike plug nozzle and employs a finite volume-based solver within the OpenFOAM framework to investigate flow features across Nozzle Pressure Ratios (NPRs) ranging from 3 to 8. Additionally, the Ffowcs Williams Hawkings (FW-H) analogy is employed to assess the influence of acoustics in the nozzle's flow field at different NPRs.Spectral analysis and flow visualizations are employed to study the frequency content and the respective flow features of the system. It is observed that the flow exhibits separation beyond NPR 4 and is highly unsteady at NPR 6, which is inferred from the prominence of the recirculation bubble. However, beyond NPR 6, the flow tends to reattach the plug surface, dampening the disturbance.

Analysis of influencing factors and uncertainty assessment of high-pressure natural gas primary standard facility

The mass-time high-pressure natural gas flow standard device is the highest level natural gas flow measurement standard in China. It is mainly used to reproduce the mass flow of high-pressure natural gas and transfer the value. Due to its important position in the value traceability transmission systems, it is of great significance to improve its uncertainty. This article first introduces the working principle and component equipment of mass-time high-pressure natural gas flow standard device, and the influencing factors and control measures of the recurring mass flow uncertainty are given. Then the calculation model and uncertainty evaluation model of the mass flow rate of the standard device and the discharge coefficient of the critical flow nozzle are given. Finally, based on the calculation model, two critical flow nozzles are calibrated and tested, and their repeatability and stability indicators are discussed and analyzed. After analysis, it can be concluded that the measurement performance of the mass-time high-pressure natural gas flow standard device is stable, which can make the uncertainty of the reproduced mass flow rate less than 0.05 % (k = 2), and the uncertainty of the calibrated discharge coefficient of critical flow nozzle is less than 0.1 %(k = 2).

Charged atomization characteristics and influencing factors analysis of aviation kerosene/ethanol blended fuel

ABSTRACT In this study, an experimental apparatus for charged atomization was established to explore the charged atomization modes of blended aviation kerosene/ethanol fuels and the corresponding evolution of atomization modes for E0 (100% aviation kerosene), E10 (10% ethanol + 90% aviation kerosene), E30 (30% ethanol + 70% aviation kerosene), and E50 (50% ethanol + 50% aviation kerosene) blends with varying applied voltages. Furthermore, the influence of the ethanol blending ratio, electrode separation distance, fuel flow rate, nozzle diameter, and other influencing factors on the charged atomization characteristics was investigated. Experimental results within the 0 to 10 kV voltage range revealed that as the voltage increased, the E0 fuel transitioned from droplet formation to spindle shape without exhibiting atomization, while the E10, E30, and E50 fuels displayed a sequential progression of atomization modes including droplet, micro-droplet, pulsed-jet, cone-jet, deflected-jet, and multi-jet configurations. As the ethanol blending ratio increases, the critical voltage required for the transition to atomization mode decreases, while the atomization cone angle gradually increases. The average atomization cone angles are 38.98°, 49.97°, and 66.83° for E10, E30, and E50, respectively. When the nozzle diameter is reduced from 1.05 mm to 0.3 mm, the charged atomization cone angle does not change significantly. With increasing fuel flow, the critical voltage for the atomization mode transition increases progressively, and the charged atomization cone angle also increases. The average atomization cone angles are 65.80°, 88.45°, 93.04°, 103.63°, and 110.97°, respectively.

Analysis of non-equilibrium condensation characteristics of supercritical carbon dioxide during transcritical flow in the Laval nozzle

During near critical operation, the non-equilibrium phase transition risk of supercritical carbon dioxide compressors usually poses significant challenges to the stability of the whole system. Analyzing the condensation characteristics in the Laval nozzle is considered an effective and feasible method for understanding condensation behavoir of supercritical carbon dioxide in rotating machinery due to the similarity and measurability of flow. In this paper, the Euler-Euler Source numerical model coupled with high-accuracy carbon dioxide real gas property table is established for transonic compressible flow in the Laval nozzle. The non-equilibrium effects of expansion and condensation during transonic flow in the nozzle are discussed and the relationships between inlet parameters, droplet distribution and nucleation rates are also analyzed. The numerical result shows that the non-equilibrium characteristic during the expansion process causes the delay of condensation in the nozzle, resulting in an overestimation of the prediction of carbon dioxide condensation region based on the homogeneous equilibrium model. Shock wave of transonic flow further amplifies the deviation of results and leads to over 12 % overestimation of liquid mass fraction. Increasing the inlet pressure and decreasing the inlet temperature can cause the forward movement of the condensation onset and the reduce of the nucleation region. For supercritical carbon dioxide in the transonic flow, the value of critical pressure ratio can be taken as 0.54∼0.55. These results provide valuable suggestions in the analysis of non-equilibrium condensing flow and designing inlet conditions for experiments.

Modeling and analysis of fluid-solid coupling heat transfer and fluid flow in transonic nozzle

Solid rocket motors (SRMs) are the power units of modern aerospace transportation, and it is of great significance to predict their flow and heat transfer characteristics by numerical simulation. This numerical study is based on a self-developed code framework MHT (Multi-X Heat Transfer, where X represents the region, scale, physical field, and other aspects) and presents an effective method of analyzing fluid–solid coupling heat transfer problem in an axisymmetric supersonic nozzle. For the nozzle wall heat conduction and nozzle-in fluid flow there are two kinds of solution methods, the detached (solved separately in solid and fluid region and them coupling at the interface) and the whole field method (solve the conduction and convection simultaneously). The whole field method is more efficient but few scholars use it to solve the nozzle coupled problem. This paper introduces the numerical details of the whole field solution method, and provides a new idea for the coupling solution of the nozzle. In addition, a mixed grid system is proposed around the interface region of fluid and solid, in which the quadrilateral structured mesh is used at the fluid side, and the triangular unstructured mesh is used for the outer fluid region and the whole solid region to ensure the accuracy of the 1st-oder normal derivatives calculation. The self-developed code is validated by comparison with well-known commercial soft-ware. Transient results of temperature and velocity are presented for the instants of 1st 20 and 40 s of a practical nozzle.

Surface cleaning with atmospheric pressure plasma jet investigated by in-situ optical emission spectroscopy and laser-induced breakdown spectroscopy

Cleaning of surfaces with atmospheric pressure plasma jet (APPJ) is investigated by in-situ optical emission spectroscopy (OES) and laser-induced breakdown spectroscopy (LIBS). The APPJ device operates a spark discharge of kW power in Argon gas flow resulting in a powerful plasma jet expanding into air. For cleaning experiments samples are coated with lubricant layers of 1.1 to 7.1 µm thickness. Light collected at the sample surface during APPJ treatment is analyzed spectroscopically and used to monitor the cleaning process. LIBS chemical imaging delivers spatial cleaning profiles of plasma treated surfaces. From measured emission intensities of CN molecular band and Na atomic line the cleaning efficiencies for carbon and Na containing contaminants are determined. The power of APPJ plasma generator, distance between sample and jet nozzle, scan speed, and Argon gas flow are varied to optimize the surface treatment. Thermal and non-thermal processes contribute to cleaning. For the carbon containing contaminant thermal processes are dominating (∼90 %) while also non-thermal processes (∼30–45 %) are relevant for the Na containing component. A cleaned surface area per time from 0.3 to 10 cm2/s is investigated. Cleaning efficiency up to 95 % is obtained highlighting the potential of APPJ surface cleaning under ambient conditions.

Numerical Study of Facility Pressure Effects on Micronozzles for Space Propulsion

This study used a direct simulation Monte Carlo approach to investigate the effects of facility pressure on micronozzles for the propulsion systems of microspacecraft. The simulations quantitatively evaluated the effect of background pressure on the micronozzle performance in nozzle flows ranging up to a throat Reynolds number of 220. The results showed that the background pressure could reduce total thrust by more than 50% as the inverse of the nozzle pressure ratio increases from 0 to 5.0×10−3. The primary cause identified was the gas depletion created by the collision of the nozzle plume with the background gas, which creates a negative thrust on the wall surface surrounding the nozzle. The trend of the background-gas-pressure effect differed at each Reynolds number. The wall size also affected the thrust in finite background pressure. Furthermore, this study emphasized the critical role of test-facility conditions in accurately predicting the performance of micronozzles and provided the knowledge necessary to properly predict their performance during space operations.

Comparative Study on the Application Efficacy of Small Disturbance Equation versus One-Dimensional Euler Equation in Nozzle Flow Analysis

This paper presents a numerical simulation study of subsonic and supersonic nozzle flow regimes utilizing the Small Disturbance Equation (SDE), implemented through Python to analyze flow stability under various boundary conditions. The SDE, extensively applied in aerospace, meteorology, and fluid mechanics, offers a critical framework for examining aircraft stability and maneuverability, essential for ensuring flight safety. Additionally, its application extends to spacecraft stability and control in aerospace science. The findings from this study reveal that subsonic flows, characterized by their stability and smoothness, respond more predictably under varying boundary conditions compared to their supersonic counterparts. Conversely, supersonic flows demonstrate increased sensitivity to changes in boundary conditions, resulting in more complex flow patterns. This sensitivity underscores the need for precise control mechanisms in supersonic applications to maintain flow stability and ensure the safety and efficiency of aerospace operations. The simulations underscore the practical importance of the SDE in advancing the understanding of dynamic flow problems across different scientific and engineering disciplines.

Numerical Simulation of the Hysteresis Phenomenon and Asymmetrical Configuration of Turbulent Gas Flow in an Over-Expanded Nozzle Flows

The turbulent flow within Over-Expanded Nozzles is characterized by shock waves inducing unsteady separation of the boundary layer, which can exhibit both free and restricted detachment. This study investigates various physical phenomena encountered during the expansion regime, including supersonic jet formation, jet separation, adverse pressure gradients, shockwave interactions, turbulent boundary layers, compressible mixture layers, and large-scale turbulence. These complex phenomena significantly influence nozzle performance. Utilizing numerical simulations based on the resolution of Navier-Stokes equations via finite volume methods and employing the CFD-FASTRAN code, this research analyzes detachment characteristics, transition phenomena, and the predictive accuracy of different turbulence models. A test case from the ATAC project CNES-ONERA (Aerodynamics of Hoses and Back-bodies), is examined to elucidate the hysteresis phenomenon and asymmetrical configurations resulting from boundary layer detachment.

SU2-COOL: Open-source framework for non-ideal compressible fluid dynamics

We present a fully open-source framework for the numerical simulation of Non-Ideal Compressible Fluid Dynamics (NICFD). The open-source Computational Fluid Dynamics suite SU2 is coupled to the open-source thermophysical library CoolProp, which includes state-of-the-art thermodynamic models of numerous pure fluids and mixtures relevant to applications. Accurate thermodynamic models are needed due to non-ideal operating conditions in which the fluid thermodynamics cannot be described by the simple ideal-gas law (Pv=RT). The coupling interface implements new C++ classes, which allow the automatic exchange of information between SU2 and CoolProp, and it is made directly available as an additional module integrated into the open-source SU2 suite. To assess the performance of the NICFD simulation framework, we present three test cases: a nozzle flow exhibiting non-ideal thermodynamics effects, a nozzle flow with non-monotone Mach number variation, a representative non-ideal gasdynamics effect, and a non-classical rarefaction oblique shock over a wedge. Results are verified against available experiment data and solutions obtained with different implementations of non-ideal thermodynamics in SU2. Performance of the new framework is assessed on user-friendliness, scalability, solution accuracy, and computational efficiency.

An evaluation of the hybrid Fokker–Planck-DSMC approach for high-speed rarefied gas flows

The Direct Simulation Monte Carlo (DSMC) method has been widely used for simulations of rarefied gas flows. It has been proven that the numerical solution of the DSMC method converges to the Boltzmann equation, providing a solid physical foundation for high Knudsen numbers. However, many aerospace engineering problems include both low and high-density regions in a single domain, making the DSMC method computationally expensive. Over the past decade, the particle Fokker–Planck (FP) method has been studied as a means to reduce computational costs near the continuum regime. While enhancing efficiency, the FP method loses physical accuracy at high Knudsen numbers. Aiming for universal accuracy and efficiency across the whole range of Knudsen numbers, the hybrid FP-DSMC method has been studied. Nevertheless, consistent comparisons among the DSMC, FP, and hybrid FP-DSMC methods have received limited attention so far. This paper presents a consistent comparative study of the DSMC, FP, and hybrid FP-DSMC methods to assess the accuracy and efficiency of the hybrid FP-DSMC method. The hybrid FP-DSMC solver is developed based on the open-source SPARTA framework. The benchmark problems include supersonic flow in a planar nozzle, hypersonic flow around a cylinder, and hypersonic flow around a THAAD-like missile. The results demonstrate that the hybrid FP-DSMC method can be more efficient than the DSMC method while being more accurate than the FP method. The speed-up achieved by the FP-DSMC method ranged from 1.5 to 14 times compared to the converged DSMC simulation.

Experimental analysis of the R290 variable geometry ejector with a spindle

The aim of this work was to experimentally analyze the variable geometry gas ejector with a spindle designed for operation with the natural working fluid propane (R290). The performance of the ejector was evaluated based on the mass entrainment ratio and critical temperature, being the most crucial parameters for optimizing the cooling capacity in ejector refrigeration systems, as well as the ejector efficiency using common literature notation. Additionally, local pressure drop measurements allowed for the determination of pressure profiles inside for different spindle positions used for capacity regulation. The experimentally defined ejector efficiency curves demonstrated the ability to control the ejector capacity by means of the spindle, irrespective of the unfavorable operating conditions. By decreasing the effective throat area using spindle, the ejector mass entertainment ratio increased by 35%. Spindle movement allowed for the decrease of the motive nozzle flow rate by up to 65%, while still maintaining the suction of the secondary flow of the ejector. Moreover, the behavior of a slight increase in suction nozzle flow with a decrease in motive nozzle flow has been observed for the initial movement of the spindle followed by a huge drop for further reduction of the effective throat area, confirming the previous conclusions shown in the literature.

Shock waves characteristics and losses estimation of non-equilibrium condensation flow in nozzle and steam turbine cascade

The investigation of transonic non-equilibrium condensation is paramount due to its profound influence on the shock patterns and the distribution of losses. This study numerically investigates the shock wave morphology, evolution, and quantitative loss calculation under the influence of non-equilibrium condensation within the Moses-Stein nozzle and Dykas cascade. The results indicate that the vapor near the nozzle wall undergoes phase transition first and forms “X-shaped” condensation shock, which impervious to back pressure variations. Conversely, the “λ-shaped” aerodynamic shock moves towards the throat with increasing back pressure, triggering boundary layer separation. The entropy generation of “λ-shocks” accounts for over 98% and represents the primary source of shock losses. Strong pressure side shock induces shock wave-boundary layer interactions with the blade suction wall, resulting in reflected shocks. However, the latent heat released by non-equilibrium condensation mitigates this effect, increasing the total pressure loss coefficient by 0.188. The decrease in Mach number under high back pressure causes a notable increase in the trailing edge shock angle, with the wave foot shifting upstream. Notably, the proportion of shock losses attributed to the suction side of trailing edge exceeds 80%, significantly surpassing other regions, which progressively increases with rising back pressure. Therefore, it is crucial for cascade optimization. The findings can provide references for the optimization design of low-pressure steam turbine blade profiles. The results can serve as a guide for optimizing the blade profiles of low-pressure steam turbine.

Numerical Analysis of A Two-Phase Turbine: A Comparative Study Between Barotropic and Mixture Models

Abstract Two-phase turbines offer the potential to significantly enhance the performance of power generation and refrigeration systems. However, their development has been hindered by comparatively lower efficiencies resulting from additional loss mechanisms absent in single-phase turbines. To date, most multiphase CFD studies on turbomachinery have focused on condensation in the final stages of steam turbines, and on cavitation in hydraulic pumps and turbines. These applications, however, are not representative of the conditions in two-phase turbines, where a liquid-dominated mixture undergoes a large expansion ratio, leading to a significant increase in the gas phase volume fraction throughout the entire flow. This paper aims to identify a suitable modeling methodology for two-phase turbines. Our evaluation is centered around two models: the mixture model and the barotropic model. The validity and accuracy of these two modeling approaches is assessed using existing experimental data from a single-stage impulse turbine operating with several mixtures of water and nitrogen as working fluid. The results indicate that both the mixture and barotropic models are consistent and accurately predict the nozzle mass flow rate, yet, both models systematically overpredict the nozzle exit velocity and rotor torque. Adding correction terms for windage and unsteady pumping losses significantly improves the torque predictions, bringing them within the uncertainty range of the experimental data. In addition, refining the models to account for the effect of slip presents a promising avenue to enhance the prediction of nozzle exit velocity and overall performance of two-phase turbines.

Energy-economic-environmental analysis of bifacial photovoltaic thermal (BPVT) solar air collector with jet impingement

Jet impingement cooling enhances photovoltaic (PV) system efficiency by using high-speed fluid jets to reduce panel temperatures, improving performance and longevity. The effectiveness depends on factors like fluid flow rate, nozzle placement, and distance from the panel. While it boosts energy output, it may increase energy use for fluid circulation and add complexity to the system. This research explores a groundbreaking approach to enhancing the efficiency of bifacial photovoltaic thermal (BPVT) systems by integrating jet impingement technology. A novel design featuring a jet plate reflector is introduced, offering the dual benefit of cooling the PV panels while simultaneously reflecting light to optimize energy capture. The study comprehensively analyses the system’s performance, including energy output and a detailed techno-economic and environmental-economic evaluation. The modelling in this study was validated and reasonably consistent with experimental results. The system's output air temperature and thermal efficiency are 302.07–318.75 K and 33.83–62.28 %, respectively. The temperature and electrical efficiency range for PV systems are 304.39–339.54 K and 9.39–11.22 %. Reduced mass flow rate and increased solar irradiation are the most economically advantageous operating parameters for the proposed system, resulting in lower annual pumping costs and more significant annual energy gains for the system. CBR variations range from 0.1363 to 9.3445, with an average of 2. Additionally, by using BPVT with jet impingement to generate electricity rather than fossil fuels, it is possible to reduce annual carbon dioxide emissions by approximately 1.61 tons and save RM93.51 annually. In general, the proposed method should be used to minimize environmental pollution.

Inducing columnar-to-equiaxed transition by gradient impediment-flow optimization mechanism: The inheritance chain of solidification

Optimization of the metal solidification microstructure is a long-standing topic. It is the initial and critical guarantee of fabricating high performance metal materials, especially in the context of external field control, for example, for electromagnetic fields. However, tailoring the final solidification microstructure is extremely difficult because its mechanism is a long process inheritance chain which can be hardly observed by experiments. In this study, systematically simulations of the continuous casting using an electromagnetic swirling flow nozzle (EMSFN) was made to clarify this inheritance chain. It was newly found that a relatively uniform flow field inherited from a magnetic field generates a gradient impediment-flow optimization mechanism (GIFO), which is beneficial for both columnar-to-equiaxed transition (CET) and grain refinement. Specifically, 600 A increases the superheat dissipation, and the temperatures of the solidification front at 200 mm and 400 mm below the meniscus are increased by 15.47 K and 12.27 K, respectively, and the temperature gradient is decreased by 17.3 % and 22.8 %. The concentration gradient at the solidification front decreased by 89.9 %, 31.1 %, and 51.3 % at 200 mm, 400 mm, and 650 mm below the meniscus, respectively. Coupled changes in the temperature and concentration gradients impede dendritic growth and promote equiaxed grain nucleation. In addition, more equiaxed grain nuclei are transported to the forefront of the growing dendrite when the molten steel rotates and is transported from the inner to the outer regions. According to the simulation, the experimental validation proved that electromagnetic swirling flow nozzle was a convenient method for promoting this mechanism. It can optimize the solidification structure of Grade 70 carbon spring steel continuous casting billets with an increase of 21.26 % in the equiaxed grain ratio extremely low carbon segregation, and improved mechanical properties. This newly found mechanism can be considered as a generic theory for optimizing the solidification microstructure of alloys, which can guide the process design of various external field control technology.