Pressure Thrust Research Articles

Effect of surface square textures on the physical field of static and dynamic pressure thrust bearings and multi-objective optimization

Purpose The lubrication performance of static and dynamic pressure thrust bearings is improved by introducing texture on the sealing edge. Design/methodology/approach Through model building, meshing and boundary condition setting, the influence of square texture on oil film lubrication performance was simulated and analyzed, and an improved algorithm was applied to perform optimization of lubrication performance. Findings The findings of this study reveal that the optimum lubrication performance is attained when adjusting the parameters of the square texture to 0.12 mm, 0.1 mm, 1 mm and 34 mm. In such circumstances, the thrust bearing with square textures demonstrates an increase in loading capacity of around 19% and a temperature reduction of about 2ºC compared to a smooth thrust bearing. Originality/value The original Reynolds equation is revised, and the influence of square texture on the physical field of oil film is analyzed, considering the turbulence state and cavitation phenomenon. The multi-objective function under square texture parameters was established using BP neural network, and the improved multi-objective salp swarm algorithm was used to optimize the process parameters.

Flow-field analysis and performance assessment of rotating detonation engines under different number of discrete inlet nozzles

This study explores in depth rotating detonation engines (RDEs) fueled by premixed stoichiometric hydrogen/air mixtures through two-dimensional numerical simulations including a detailed chemical kinetic mechanism. To model the spatial reactant non-uniformities observed in practical RDE combustors, the referred simulations incorporate different numbers of discrete inlet nozzles. The primary focus here is to analyze the influence of reactant non-uniformities on detonation combustion dynamics in RDEs. By systematically varying the number of reactant injection nozzles (from 15 to 240), while maintaining a constant total injection area, the study delves into how this variation influences the behavior of rotating detonation waves (RDWs) and the associated overall flow field structure. The numerical results obtained here reveal significant effects of the number of inlets employed on both RDE stability (self-sustaining detonation wave) and performance. RDE configurations with a lower number of inlets exhibit a detonation front with chaotic behavior (pressure oscillations) due to an increased amount of unburned gas ahead of the detonation wave. This chaotic behavior can lead to the flame extinguishing or decreasing in intensity, ultimately diminishing the engine's overall performance. Conversely, RDE configurations with a higher number of inlets feature smoother detonation propagations without chaotic transients, leading to more stable and reliable performance metrics. This study uses high-fidelity numerical techniques such as adaptive mesh refinement (AMR) and the PeleC compressible reacting flow solver. This comprehensive approach enables a thorough evaluation of critical RDE characteristics including detonation velocity, fuel mass flow rate, impulse, thrust, and reverse pressure waves under varying reactant injection conditions. The insights derived from the numerical simulations carried out here enhance the understanding of the fundamental processes governing the performance of RDE concepts.

Effects of differently shaped textures on the tribological properties of static and dynamic pressure thrust bearings and multiobjective optimization

PurposeThe purpose of this study is to evaluate three types of textures designed to enhance the tribological performance of static and dynamic pressure thrust bearings.Design/methodology/approachTo explore the effects of different types of textures on tribological performance, the Reynolds equation is modified using lubrication theory and computational fluid dynamics methods while considering the influence of cavitation and turbulence on the physical field. In addition, the tribological performance is optimized through an improved selection algorithm based on Pareto envelope (PESA).FindingsThe results indicate that textured thrust bearings exhibit superior tribological performance compared to untextured ones. The circular texture outperforms other textures in terms of load-bearing and friction performance, with improvements of approximately 28.8% and 18.9%, respectively. In addition, the triangular texture exhibits the most significant temperature improvement, with a reduction of approximately 1.93%.Originality/valueThe study proposes three types of textures and evaluates the friction performance of thrust bearings by modifying the Reynolds equation. In addition, the optimal texture design is determined using an improved selection algorithm based on PESA.

A novel coupled algorithm for Studying the performance characteristics of water ramjet in the flight of supercavitating vehicle

When a supercavitating vehicle performs a flight, the water ramjet of the vehicle exploits the water in the surrounding environment as an oxidiser and is inevitably affected by the vehicle motions. In this study, the characteristics of the performance change in a water ramjet were investigated when a supercavitating vehicle performs a flight to gain more insights into the design of underwater power systems. Given the principle of independent cross-section expansion of cavities, a longitudinal ventilated supercavity model was built to predict the development of a ventilated cavity and its interaction with the body. A thermal calculation model was developed based on the minimum free energy method to calculate the performance parameters of water ramjets. A novel coupling algorithm was proposed based on the aforementioned model to integrate the motion of a supercavitating vehicle with the operation of a water ramjet. The integration described above was achieved by linking the water intake and body motion and calculating the performance change characteristics of the water ramjet during the flight of the supercavitating vehicle. The operating characteristics of the water ramjet with changes in the designed water-fuel ratios were investigated to provide a basis for exploring the unperturbed flight of the vehicle, depth regulation, and underwater environmental changes. The thrust of the water ramjet is less affected by external factors, and its performance feedback tends to exacerbate external disturbances at a designed water-fuel ratio lower than the optimal water-fuel ratio. A water ramjet with a designed water-fuel ratio higher than the optimal water-fuel ratio has a rapid response time, adaptive thrust, and stable combustion chamber pressure. External disturbances slightly affected the thrust and combustion chamber pressure of the water ramjet when the designed water-fuel ratio was equal to the optimal water-fuel ratio. The results of this study provide technical support for optimising the design of water ramjet.

Optimization of Process Parameters for Flow Nozzle with Different Geometry using Computational Fluid Dynamics Method

A nozzle is a tubular structure designed to facilitate the flow of hot gases. Rocket nozzle designs typically consist of a stationary convergent section and a stationary divergent section. The term "CD" is an abbreviation for "convergent-divergent" and is used to refer to this specific nozzle type. Upgrades are being made to nozzles and other engine components in order to enhance performance and optimise thrust delivery. Application-specific improvements will be made to rocket nozzles and other current combustion expansion systems. An instance of such progress is the implementation of the bell and twin bell nozzle. This study conducted a comparative analysis of two kinds of nozzles, namely bell and conical, at different Mach speeds to ascertain which one yields the most optimal flow. Subsequently, the flow parameters were modelled with computational fluid dynamics (CFD). Ensuring optimal pressure thrust integral throughout the supersonic zone of the nozzle surface while taking the base pressure into account was the aim of the problem formulation. The research focused on irrotational flow, taking into consideration the impacts of boundary layers.

The influence of background co-flow on the propulsive characteristics of starting jets

The influence of uniform background co-flow on the propulsive characteristics of starting jets with stroke ratios (length to diameter ratio, L/D) from 1 to 5 and velocity ratios (ratio of co-flow velocity to maximum jet velocity, Rv) from 0 to 0.6 has been investigated numerically. The total impulse generated increases with increasing Rv for L/D<1.5, but increases initially and then decreases for 1.5≤L/D≤3.5. Furthermore, it decreases with increasing Rv for L/D>3.5. The co-flow affects the generation of total impulse mainly by modifying the development of pressure thrust FP(t). The influence on FP(t) can be divided into three stages. During the initial and final stages, FP(t) decreases with increasing Rv, and increases during the middle stage. These three stages are explained by the influence of co-flow on wake vortex ring, leading vortex ring and stopping vortex ring, respectively. Transition between stages can also be related to the instantaneous velocity ratio Rv(t), which is the ratio of co-flow velocity to instantaneous jet velocity. The negative influence of co-flow on the generation of impulse can be mitigated by the velocity program with faster acceleration and shorter deceleration duration, which is equivalent to reducing the average value of Rv(t).

Experimental and numerical comparison of aerodynamics for a wind turbine rotor model under turbulent inflow conditions

Computational prediction of aerodynamics for a two-bladed wind turbine rotor model at the profile, blade, and rotor scale are compared to wind tunnel experimental data. Wind tunnel tests are carried out in the large subsonic wind tunnel at the University of Orleans with an instrumented rotor model to obtain power and thrust coefficients, bending moments and pressure chordwise distributions. A passive uniform turbulence grid is used to obtain a turbulence intensity of 3.8% at the front of the rotor. A k − ω SST unsteady Reynolds-averaged Navier-Stockes (URANS) simulation with the ISIS-CFD flow solver is conducted with a fully resolved rotor, with and without automatic grid refinement. The focus of this study is to examine the prediction capabilities of the simulation for various physical variables. The simulation demonstrates a relatively good prediction of power and thrust coefficients compared with experimental data with a maximum scatter of 8.5%. The prediction of the pressure coefficient distribution at three different radial positions is satisfactory, but shows discrepancies when it comes to accurately predicting flow separation and Reynolds effects.

Numerical simulations of bio-inspired approaches to enhance underwater swimming efficiency

The present study discusses the numerical simulation results of swimming similar to manta rays. The complex three-dimensional kinematics of manta rays were implemented to unravel the intricacies of its propulsion mechanisms by using the discrete vortex method (DVM). The DVM replaces the requirement for a structured grid across the computational domain with a collection of vortex elements. This method simplifies grid generation, especially for intricate geometries, resulting in time and effort savings in meshing complex shapes. By modeling the pectoral fins with discrete panels and utilizing vortex rings to represent circulation and wake, the study accurately computes the pressure distribution, circulation distribution, lift coefficient, and thrust coefficient of the manta ray. This study focuses on the modulation of aerodynamic performance by altering the span length and the length change ratio during the downstroke and upstroke motion (SV). The manta ray's three-dimensional vortex configurations comprise a combination of vortex rings, vortex contrails, and horseshoe vortices. Analysis of the three-dimensional vortex structure indicates the presence of multiple vortex rings and horseshoe vortex rings at higher SV values, while adequate formation of horseshoe vortices is not observed at lower SV values. In terms of propulsive performance, both lift and thrust increase with SV, while the propulsive efficiency demonstrates its peak at SV = 1.75. The analysis reveals that at higher SV values, the net thrust generated primarily originates from the tip of the fins. Moreover, the study illustrates a significant enhancement in propulsive efficiency, particularly in association with optimal Strouhal numbers ranging between 0.3 and 0.4. The key findings of this study may be used in efficient design of agile autonomous underwater vehicles for marine exploration and surveillance applications.

The propulsion performance of the semi-active tandem flapping foils for wave gliders: A study on vortex interactions and hydrodynamic performance

An investigation is conducted on the propulsion performance of semi-active flapping foils in tandem configuration of the wave glider, considering different vortex effects and tandem distances. The Finite Volume Method is utilized with commercial CFD software Fluent to solve the URANS equations around the flapping foil. A mesh comprising a 2D NACA0012 foil with Reynolds number Re = 42,000 is used in all simulations. The study investigates the propulsion performance of tandem flapping foil systems, focusing on the differing impacts of wave interaction on the front and rear foils. It explores how varying tandem distances and reduced frequencies influence thrust enhancement and degradation. The research reveals that while the front foil consistently benefits from thrust enhancement, the rear foil's performance is more complex, being subject to thrust enhancement or reduction due to wake vortex interactions. Detailed analyses of instantaneous thrust coefficients, pitching trajectories, and pressure contours provide insights into the hydrodynamic performance of these systems. The findings emphasize the importance of synchronization in motion between the foils for optimal propulsion and highlight the rear foil's susceptibility to changes in the wake flow, affecting its thrust generation capability. Thus, the optimal tandem distance can fully capitalize on the thrust enhancement effect of the wake interaction to improve the performance of the tandem flapping foil propulsion system.

Data-driven intelligent prediction of TBM surrounding rock and personalized evaluation of disaster-inducing factors

With the widespread application of tunnel boring machines (TBM) in underground tunnel construction, the accurate and real-time identification of geological indicators has become a key factor for ensuring construction safety. In this study, we introduced the nomogram method into the field of civil engineering for the first time to predict surrounding rock grades. Against the backdrop of a major water conservancy project in China, an in-depth analysis of construction data from the ascending phase was conducted to establish the relationship between surrounding rock grade predictions and key construction parameters. Compared with traditional models, the nomogram method has shown advantages in terms of prediction accuracy. Furthermore, by providing a personalized scoring mechanism for specific construction data, the nomogram method not only achieves the real-time prediction of rock grades but also clearly reveals the dynamic relationships between input parameters and rock grades, clarifying the entire prediction process. We identified the main factors related to rock grade prediction among TBM construction parameters, including the slurry conveyor belt speed, jacking pressure, cutterhead torque, cutterhead thrust, thrust pressure, and actual rotation speed. The training process revealed that the nomogram prediction model achieved optimal performance with seven input parameters, balancing accuracy and training time. According to the prediction results, the nomogram model’s area under the curve index is 0.92, providing greater accuracy than the traditional random forest model (0.89). Therefore, this study enhances the transparency and interpretability of model predictions by providing personalized assessments of construction parameters for predicting surrounding rock grades, overcoming the black-box issue of existing prediction methods and offering a novel and effective tool for rock grade prediction.

Effect of texture parameters on the lubrication performance of static and dynamic pressure thrust bearings and multi-objective optimization

PurposeThis paper aims to study the influence of cylindrical texture parameters on the lubrication performance of static and dynamic pressure thrust bearings (hereinafter referred to as thrust bearings) and to optimize their lubrication performance using multiobjective optimization.Design/methodology/approachThe influence of texture parameters on the lubrication performance of thrust bearings was studied based on the modified Reynolds equation. The objective functions are predicted through the BP neural network, and the texture parameters were optimized using the improved multiobjective ant lion algorithm (MOALA).FindingsCompared with smooth surface, the introduction of texture can improve the lubrication properties. Under the optimization of the improved algorithm, when the texture diameter, depth, spacing and number are approximately 0.2 mm, 0.5 mm, 5 mm and 34, respectively, the loading capacity is increased by around 27.7% and the temperature is reduced by around 1.55°C.Originality/valueThis paper studies the effect of texture parameters on the lubrication properties of thrust bearings based on the modified Reynolds equation and performs multiobjective optimization through an improved MOALA.

Air-breathing rotating detonation engine supplied with liquid kerosene: propulsive performance and combustion stability

Experimental results are presented for a rotating detonation engine supplied with liquid kerosene and preheated air without liquid or gaseous additions to the propellant mixture. Various combustion modes for the generic combustor geometry design were observed—from deflagration, through pulsed combustion and high-frequency instabilities, to stable detonation propagation. Attention was paid to detonation stability (if present), its characteristics, and the propulsive performance of the combustor with a focus on specific thrust and pressure gain through thrust and outlet total pressure measurement. These parameters measured for the observed modes were compared. The stability of the detonation combustion proved not to be critical to achieve high performance of the combustion chamber. For example, high performance was achieved for combustion modes with high-frequency instabilities.

Transient Characteristics of Fluidic Pintle Nozzle in a Solid Rocket Motor

The fluidic pintle nozzle, a new method to control the thrust of a solid rocket motor, has been proposed in recent years by combining the pintle with the aerodynamic throat (fluidic throat). The study of static characteristics has proved that it has a remarkable effect on thrust control. To study the transient characteristics of the fluidic pintle nozzle, 2D transient simulations of a fluidic pintle nozzle propulsion system were conducted, employing dynamic meshing techniques. The Reynolds-averaged Navier–Stokes equations were meticulously solved, implementing a k–ω SST turbulence model. The thrust control principle of the fluid pintle nozzle was studied, and the wave structure was summarized. The transient characteristics of the secondary flow opening, secondary flow closing, pintle moving forward (pressure rise), and pintle moving backward (pressure drop) were obtained, and the effects of the injection angle and injection port position were studied. The response process after injection can be roughly divided into three stages: pressure propagation, pressure oscillation, and equilibrium stability, with time distributions of 0.4%, 5.39%, and 94.21%, respectively. In the process of the pintle moving forward, the rate of combustion chamber pressure increases and thrust decreases gradually because of the arc wall of the nozzle throat upstream, and the process of throats moving backward is just the opposite. Compared with the condition with a maximum throat opening and no secondary flow, the thrust of the condition with a minimum throat opening and a 0.3-flow-ratio secondary flow is increased by 80.95%. Under conditions of constrained flow ratio, the injection angle of the secondary flow ostensibly exerts negligible influence on the dynamic modulation of thrust. Nevertheless, it remains evident that a reduction in throat opening accentuates the impact of reverse injection. Furthermore, the proximity of the injection port to the head of the pintle is directly proportional to the efficacy of thrust control.

Numerical research on the resonance frequency characteristics of the Sparkjet actuator using modal analysis

In this study, the resonance frequency characteristics of the SparkJet actuator are examined through numerical investigation using modal analysis. First, an eigenvalue problem is established to compute the resonance frequencies of the SparkJet actuator, considering its configuration, boundary conditions and internal physical phenomena. To validate the eigenvalue problem, computational fluid dynamics (CFD) simulation is conducted utilizing unsteady three-dimensional Navier-Stokes equations with plasma energy source term, assuming local thermal equilibrium (LTE). Subsequently, the resonance frequencies are obtained by performing fast Fourier transform (FFT) on the thrust and average pressure data obtained from the CFD. In our investigation of the resonance frequency characteristics, eigenmode decomposition on the pressure contour obtained from the CFD is conducted utilizing the eigenfunctions obtained from the eigenvalue problem and their orthogonality. The eigenmode decomposition enables us to quantitatively evaluate the contribution of each eigenfunction to the thrust. Comparisons between the frequencies corresponding to the eigenfunctions significantly influencing on the thrust and the resonance frequencies obtained by FFT reveal a maximum error of 5.29 % and an average error of 2.35 % Moreover, when the taper angle is relatively large (approximately 45∘ or more), eigenfunctions significantly influencing on the thrust can be categorized into two distinct geometric patterns. These physically represent the waves that propagate and reflect in the streamwise or radial direction within the SparkJet actuator. This observation implies that the complex interactions of shock waves within the SparkJet actuator can be reduced to a few waves with simple physical interpretations. This may potentially aid in analyzing the physical phenomena within the SparkJet actuator.

The experiment of rotating detonating engine using an asymmetric vortex shape on an annulus chamber

Rotating detonating engine is new propulsion technology with promising advantages. Higher thermal efficiency and simple design with higher thrust attracted intention worldwide to make it realistic. The normal design uses a circular shape of an annulus chamber. The circular shape of the annulus chamber was well-known and tested with various conditions. The new interest area of changing a circular shape into an asymmetric shape is still unknown. Exploring the new shape of the annulus chamber was done by applying the new shape of the annulus chamber on RDE. The experiment was successfully done using methane at different conditions. Three modes can be observed from pressure product and thrust result: a mode of detonation, unstable detonation, and failure on transition. The highest thrust happens at an equivalence ratio of 1.2 with 18N. The new shape of the annulus offers the versatility of RDE.

Continuous Injector Geometry Variation to Augment Rotating Detonation Combustor Operation and Performance

Sensitivity of rotating detonation combustor operation and performance to oxidizer injector pressure drop was characterized using continuous variation of the injector area during combustor operation. As the oxidizer injector area was both increased and decreased, the sensitivity of the combustion process to varying injector pressure drop was characterized using high-frequency measurements of pressure and chemiluminescence intensity. Detonation wave strength and coherence were characterized using peak-to-peak intensity and power fraction calculated from point-chemiluminescence measurements. Propulsive performance of the combustor was evaluated using thrust and equivalent available pressure, relating them back to reactant supply pressures for assessment of combustor pressure gain. Pressure gain increased during a test as the oxidizer injector area was increased and the corresponding manifold pressure was decreased. At larger injector areas, pressure gain decreased as the operating mode of the combustor transitioned from detonation to deflagration, concomitant with a reduction of gross thrust. Modeling of injector recovery time revealed that the injector operated in both choked and unchoked regimes, which was used to explain detonation wave number transitions in the experiment. A broadened range of detonative operability enabled by active variation of combustor geometry resulted in higher performance with a lower injector pressure drop.

Propulsive characteristics of single-pulsed jets with tube and orifice openings

The effects of the nozzle exit geometry on the unsteady propulsive characteristics of single-pulsed jets are studied numerically. For both tube and orifice nozzles, the jet exit configuration is parameterized by the diameter ratio RD, which is defined as the ratio of the nozzle entrance D0 to the jet exit diameters D. It is found that the diameter ratio has significant influence on the propulsive characteristics of the single-pulsed jet during its entire ejection phase. The total impulse production is augmented considerably as the diameter ratio increases until a critical value of RD_cir≈2.0 is approached. The larger impulse production by the orifice nozzles over the tube nozzle stems from the persistent over-pressure contribution at the jet exit due largely to the fact that the flow contraction near the jet exit of the orifice nozzle results in the intensification of the radial velocity gradients and higher local pressure. By using the existing prediction of the contraction coefficient Cc to account for the flow contraction, a theoretical model has been developed with the quasi-one-dimensional flow approximation to predict the pressure thrust at the jet exit during the steady discharging stage, showing good agreement with the present numerical results. Moreover, the pressure force acting on the vertical wall of the orifice nozzle, which is proportional to the wall area, is found to be primarily responsible for the larger transient variations in the jet impulse during the onset and end of the jet ejection phase as the diameter ratio increases.

Characterizing and predicting bluff-body solid fuel ramjet performances via shape design and multi-objective optimization model

In this work, we propose a rapid optimization approach to examine its application potential for the design and performance prediction and optimization of a solid fuel ramjet (SFRJ) with a bluff body. For this, the shape of the bluff body is parameterized first using the non-uniform rational B-spline method. We then develop a model for predicting SFRJ performances by incorporating both levy motion-gradient descent and support vector regression methods. It is found that a faster prediction is achievable, while the average error is maintained to be less than 5%. We then develop a multi-objective optimization model by considering the full thrust and minimum total pressure loss (TPL). The optimization model is examined using the non-dominated sorting genetic algorithm. A cost parameter is also created to facilitate the tradeoffs between the thrust and TPL in the Pareto front, when different bluff-body design configurations are considered. The present results reveal that an increase in the cost parameter will elevate the turbulence intensity within the SFRJs while drawing the incoming air closer to the fuel surface, resulting in an increase in thrust and regression rate, but the TPL will also increase. When prioritizing the TPL reduction in the design stage, the optimized solution reduces TPL by 50%. Meanwhile, the net thrust is shown to be decreased by less than 3.5%. Furthermore, flow-field investigation reveals that the improved performance of the optimized SFRJ is due to more uniform flow velocity gradients around the bluff body and a reduced rear vortex, resulting in reduced momentum loss. Our proposed optimization approach's robustness has been further confirmed with consistent performances, as the ramjet inlet speed varies over a broad range. It shows that our approach has great potential to be applied for the SFRJ performance prediction and optimization, being operated under various conditions.

Measurement and enhancing prediction of EPBM torque using actual Machine data

The cutterhead torque of an Earth Pressure Balance Machine (EPBM) plays a critical role in determining the performance of mechanized tunneling in urban areas. However, as this parameter is not directly set by the operator but is a function of geological conditions, thrust force, screw conveyor revolution speed, and soil conditions, it is closely linked to geotechnical parameters and machine settings. Despite previous attempts to predict EPBM torque using Shi's physical model, accuracy has been lacking. This study aims to improve the accuracy of this prediction by utilizing actual data from an EPBM used in a metro line tunneling project to identify the primary factors influencing torque and to modify related equations accordingly. To evaluate the performance of existing models and the predictions made by the presented method, various metrics are utilized, including the correlation between all torque values, the relationship between torque and thrust values, and the connection between thrust pressure and penetration. The results indicate that in addition to geotechnical parameters, machine settings such as thrust force, cutterhead revolution speed, arching pressure, soil conditions, and chamber pressure significantly impact the torque value. The study found that the thrust force exerted by the EPBM is a key factor influencing torque.

Numerical Simulation of Underwater Supersonic Jet of Vehicle with Shell-Shaped Flow Control Structure

When the underwater vehicle engine operates under the condition of over-expansion, the violent pulsation of the flow field pressure at the rear of the nozzle can cause violent fluctuations in engine thrust, leading to engine instability. In order to improve the engine's stability, this study drew inspiration from the wave attenuation characteristics of the shell-shaped surface texture structure and added a multi-layer shell-shaped texture structure to the rear wall to reduce pressure fluctuations in the flow field at the rear of the nozzle . Based on the numerical simulation method, the effects of different bionic shell-shaped structures on jet morphology, wall pressure and engine thrust were compared and analyzed. The results show that the multi-layer bionic shell-shaped texture structure can effectively inhibit the occurrence of periodic phenomena such as bulge, necking, and return stroke in the rear flow field, so as to effectively reduce the pressure fluctuation in the rear flow field of the nozzle. In addition, when the momentum thrust is almost unchanged, it is found through calculations that during the initial stage of the jet, the suppression of thrust is not significant. After 0.005 seconds, the oscillation amplitude of the combined force of pressure difference thrust and back pressure thrust decreased by 22%, and the oscillation amplitude of the total thrust decreased by 20%.