Flow Path Geometry Research Articles

Improving turbulent corrosion in Francis turbine from aspects of fluid mechanics

Turbulent corrosion within Francis turbines is a pressing concern in hydropower generation. This study investigates hydrodynamic factors contributing to this corrosion phenomenon and proposes strategies for mitigation, enhancing turbine performance and longevity. Employing Computational Fluid Dynamics (CFD) simulations, the study comprehensively analyzes the intricate water flow dynamics within the turbine, identifying areas susceptible to turbulence and guiding design adjustments. Turbulence reduction, achieved through optimizing blade and runner geometries, and the reduction of eddy currents through well-designed components, play pivotal roles in mitigating corrosion. Flow field analysis, turbulence reduction, and eddy current minimization emerge as central components in addressing turbulent corrosion. CFD simulations offer invaluable insights into flow dynamics, while optimized geometries reduce turbulence and associated corrosion risk. Acknowledging limitations, this research primarily addresses hydrodynamic aspects of turbulent corrosion, overlooking complex operational factors. Future research should encompass a holistic perspective by integrating additional variables for a more comprehensive understanding. In design and engineering, while optimizing blade profiles and flow path geometries is essential, exploring advanced materials, protective coatings, and innovative maintenance techniques is warranted. Interdisciplinary solutions should be sought to address multifaceted challenges presented by turbulent corrosion. Adopting a holistic approach and addressing these limitations promises to advance hydropower generation, ensuring safer and more efficient turbine operation.

Characterization of mass distribution in a biomimetic aerosol exposure system

Objective Lack of biomimicry in geometry and flow conditions of emissions systems for analytical testing and biological exposure has led to fundamental limitations, including a poor understanding of dose delivered to specific airway locations. This work characterizes mass distribution of a JUUL® brand e-cigarette in a Biomimetic Aerosol Exposure System (BAES). Materials and Methods A combination of mass balance, direct measurements, and inferences based on direct measurements were used to characterize regional and local dose as a function of system flow path configuration and emissions topography profile. Results Doses produced by the emissions topography profile with only puffing were significantly different from profiles with clean air inhalation following puffs. Mass characterization results support that dose can be manipulated using flow path geometry. Local and regional deposition was mapped throughout the system. Discussion and Conclusions We estimate the fraction of yield to the mouth deposited at several locations throughout the system for a variety of puffing and respiration topographies and show that emissions topography profile and system flow path geometry affect dose. This work provides proof-of-concept for assessing mass distribution as a function of aerosol generator (e-cigarette product), user airway geometry, and inhalation and puffing topography.

Optimal Design of Ejector Nozzle Profile with Internal and External Integrated Flow

Based on the orthogonal experimental method, a simulation case of the flow field of the ejector nozzle was designed to investigate the influence of the structural parameters of the ejector nozzle on the internal and external flow. This study explored the effects of throat area, outlet area, throat position, and ejector nozzle length on the ejector flow rate ratio, thrust coefficient, and net thrust coefficient. Subsequently, flow path geometry optimization was conducted to maximize the thrust coefficient or net thrust coefficient. The results revealed that the throat area ratio and the outlet area of the ejector nozzle are the primary factors affecting the aerodynamic performance. Compared to the baseline ejector nozzle model, the optimal model for thrust coefficient exhibited a 16.333% improvement, while the optimal model for net thrust coefficient demonstrated a significant enhancement of 46.674%.

Experimental and Numerical Analysis of Flow Force Acting on the Spool of Proportional Directional Valve

This paper deals with the experimental and numerical analysis of the flow force acting on the spool of a proportional directional valve. The flow force arises due to the fluid flow through the flow path of the proportional directional valve and significantly influences the dynamics of the valve spool. The valve under investigation is a three-position four-way proportional directional valve with zero spool lap and feedback from the spool position. The dependence of the valve spool flow force on the volumetric flow rate is measured as part of the experiment. The measurements are performed for different spool displacements. The measured data will be used to verify the numerical simulations. The proportional directional valve was modified so that a force sensor could be included on the spool axis to realize the experiment. Firstly, the flow force is measured as the fluid passes through the two flow paths of the valve (PB and AT). Subsequently, the experimental setup is modified to determine the flow force when the fluid passes through each flow path separately. The measurements are compared. Simulations of the flow through the proportional directional valve are performed using Ansys Fluent 2022 R2 software to determine the flow forces acting on the valve spool. Simulations are performed for the selected spool positions of the proportional directional valve. Finally, the results of the simulation and the experiment are compared. The contribution of this study is a CFD model of the flow paths of the proportional directional valve verified by experiment. The CFD model will allow the flow force analysis for different flow path geometries of the investigated valve. Experimental analysis of flow force is performed over the entire spool stroke at different volumetric flow rates. The flow forces are measured for each flow path separately and for both flow paths simultaneously.

Influence of the centrifugal pump impeller vanes parameters on its energy performance at operating with high-viscosity liquid

BACKGROUND: The currently existing methods for recalculating the operation of centrifugal pumps for viscous fluids cover a sufficiently small range of viscosities. In addition, the considered papers cover the recalculation only, not the search for the optimal geometry of the centrifugal pump for high-viscosity liquids. In this paper, computational fluid dynamics tools were used to test the ability of centrifugal impellers to pump liquids with a viscosity of up to 20,000 sSt, as well as to search for the optimal geometry of the flow path.
 AIM: Determination the dependence pattern of the geometric parameters, including vanes, of the optimal geometry of the centrifugal pump flow path at various values of flow rate and viscosity.
 METHODS: A numerical modeling method based on the solving of discrete analogs of the basic equations of hydrodynamics is used in this paper.
 RESULTS: It was proved that, with the considered viscosities, an impeller with a profiled vane, but with a smaller wrap angle and height, is capable of more efficient operation than a disk impeller. The dependences of the parameters of the optimal flow paths on the characteristics for which their optimization was carried out are given.
 CONCLUSION: Based on the study results, it can be stated that it is advisable to use centrifugal impellers in case of high viscosity of the liquid, taking into account the choice of non-classical values of the geometric parameters of the flow path, including the height and angle of its vanes.

Recharge dynamic and flow-path geometry controls of solute transport in karst aquifer

Solute transport is complex in karst aquifer due to its heterogeneous structure and polytropic hydrodynamic condition. Hydrological monitoring and artificial tracer test were conducted in two flow paths under different recharge conditions, and the Advection–Dispersion Equation and Dual Region Advection–Dispersion models were successfully calibrated to simulate the breakthrough curves. Intermittent concentrated recharge at sinkholes and quick hydrological response at spring outlet often occur after rainstorms. Single symmetrical shape and bimodal shape with long tail were characterized in the breakthrough curves. Stronger recharge hydrodynamic condition drives a larger transport velocity with higher solute transport efficiency. The tracer injection time during a concentrated recharge event is found to significantly affect the solute transport process. Constantly pushed by the follow-up recharge water, the piston transport process of solute in conduit enables higher recovery rate for the tracer injected at the initial recharge process. Solute transient storage in fissures occurs while tracer is injected at the peak flow. A negative correlation between dispersivity and flow velocity is found in karst conduits. The reduction in cross-section area of karst conduits causes high dispersivity and obvious tailing in breakthrough curves due to the blocking function of solute by the uneven bottom surface in karst conduits. The solute transport process is significantly controlled by the changes in hydrodynamic and flow cross-section due to concentrated recharge events, which deepen our understanding of solute transport in karst groundwater.

Shot-to-Shot Deviation of a Common Rail Injection System Operating with Cooking-Oil-Residue Biodiesel

<div>The shot-to-shot variations in common rail injection systems are primarily caused by pressure wave oscillations in the rail, pipes, and injector body. These oscillations are influenced by fuel physical properties, injector needle movement, and pressure and suction control valve activations. The pressure waves are generated by pump actuation and injector needle movement, and their frequency and amplitude are determined by fluid properties and flow path geometry. These variations can result in cycle-to-cycle engine fluctuations. In multi-injection and split-injection strategies, the pressure oscillation from the first shot can impact the hydraulic characteristics of subsequent shots, resulting in variations in injection rate and amount. This is particularly significant when using alternative fuels such as biodiesel, which aim to reduce emissions while maintaining fuel atomization quality. This study examines the shot-to-shot variations in a second-generation common rail system using cooking-oil-residue biodiesel. The results demonstrate that biodiesel properties impact pressure wave oscillation, shot-to-shot variation, and total injection rate. The study also finds that dwell time has a significant effect on the hydraulic characteristics of the second shot, with minimal influence up to a certain value. However, beyond a certain dwell time value (e.g., 0.8 ms in this study), the impact of dwell time on the pressure fluctuation generated by the second shot is limited. Conducting further research could help deepen our understanding of the influence of shot-to-shot deviations. This could involve exploring biodiesel spray characteristics using techniques such as shadowgraph imaging and studying the effect of these deviations on flame propagation and emission formation. Examining engine performance could also provide valuable insights into the effectiveness of the split-injection strategy and biodiesel blends. Additionally, characterizing biodiesel spray using the double-shot technique to examine spray penetration, cone angle, and/or spray impingement and combustion characteristics could be useful in linking it with the shot-to-shot variation investigated in this study. Such research can contribute to advancing the state-of-the-art knowledge on this topic.</div>

P77: Improvements in the cuff and graft interface of a rotary Total Artificial Heart

Purpose: To evaluate design improvements of the inlet cuff-port and outlet graft-port interface of a Total Artificial Heart (TAH) on pannus formation. The orifice size, interface, blood flow path geometry, blood flow velocity, materials, surface finish, and hematologic parameters (such as anti-coagulants and anti-platelets) all contribute to the hemocompatibility of the TAH inflow and outflow. The focus of this work is the blood flow path geometry and material change. Methods: The performance of progressive inflow and outflow design iterations of a rotary total artificial heart operated in continuous and pulsatile outflow were evaluated in Corrient calves for durations of 30-90 days. Design modifications included a smoother blood flow port transition, geometrical improvements to the diameter and tangent angle to the polyurethane connector/pump interface, and methods of securing the connection including a titanium ring on the cuff with biospan rings and PEEK zip ties on both the cuffs and grafts. The graft flow path includes a circumferential hump which allows the titanium outflow port to seat against this hump and eliminate a void which could be a source of thrombus or emboli. Additionally, the cuff and port materials were changed. Subjects were 6-12 month old calves with weights ranging from 82 kg to 108 kg, while conditions such as pump flow, pressures and anticoagulants were closely monitored. The TAH was run in pulsatile mode for the majority of the studies. At necropsy, photos of the cuff and graft interface to the pump were analyzed and any tissue samples were sent for histological evaluation. Results: A titanium ring on the cuff prevented the cuff from pulling away from the titanium port at the ostium and also prevented the cuff from being to be pulled too far onto the port during surgery. Pannus formation at the interface of the cuff and graft to the titanium ports was graded from Absent (0) to Extreme (5), (Extreme equals >75% area reduction). In earlier design iterations, pannus formation at the inflow cuff or outflow graft interface ranged from (2) mild to (5) extreme. After implementing the design improvements, pannus was (0) absent in all inflow cuff interfaces. One graft that was not fully installed on the port had moderate buildup and the remainder had (0) absent to (1) minor at the outflow graft interface despite minimal anticoagulation. Conclusion: Improvements to the inflow cuff/outflow graft-port interface significantly reduced pannus and thrombus formation in chronic animal implants treated with limited anticoagulation.

Combustion characteristics of a supersonic combustor model for a JAXA flight experiment

JAXA is conducting a flight-ground test comparison program to clarify the “facility effect” on hypersonic aerodynamics and combustion phenomena and to develop a CFD tool for predicting flight data from ground test data. The aim is a flight experiment to obtain data on aerodynamic heating and supersonic combustion under actual flight conditions and to validate the CFD tool using flight data and the corresponding ground test data. This study aimed at determining a flow-path geometry and a fuel injector configuration for a supersonic combustor suitable for clarifying the influence of the different test flow compositions between flight and ground test conditions on combustion. The candidate configurations proposed by the CFD study were evaluated by direct-connect combustion tests using ethylene fuel. The results showed that a combustor flow was symmetric when the fuel equivalence ratio was low and asymmetric when the equivalence ratio and the pressure in the combustor were high. Because an asymmetric flow is unsuitable for validating CFD based on steady RANS, the total equivalence ratio was limited to 0.44. The combustor model uses two-stage fuel injectors and cavity flame holders to combust ethylene fuel. The depth of the cavity flame holder had little influence on combustion. However, the number of injection holes for the injector located downstream of the cavity affected the combustor pressure. The combustor flow-path design was finalized based on the combustion test results. In addition, an ethylene fuel ignition method using pilot hydrogen injection, adopted for the flight experiment, was also demonstrated successfully.

Scramjet Engine Flowpath That Improves Specific Impulse Using JP-7 Fuel

A flowpath geometry was computed that improves the specific impulse of a dual-mode scramjet engine in a generic X-51 hypersonic vehicle. Six parameters were varied: inlet contraction ratio, the diameters and numbers of fuel injectors, divergence angle of the combustor wall, nozzle flap deflection angle, and flight Mach number. The maximum specific impulse was 2296 s in the ram mode and 832 s in the scram mode. A reduced-order model simulates the finite-rate chemistry of JP-7 fuel and the unstart limits. Results show that both combustion efficiency and drop to unacceptably low levels when the finite-rate chemical reaction rates are weakened by flame strain-out due to the large air velocities, or when the flame becomes longer than the combustor. Small occurs when the following are too small: the inlet contraction ratio, the inlet compression ratio, the number of fuel injectors, and the diameter of fuel injectors. When these parameters are too large, excessive heat release causes unstart. The operating range was identified between these limits. For JP-7 fuel, it was found that the inlet should raise the pressure to above 5 atm. Results are explained by the interactions between reactions, mixing, and flame strain-out.

Ensemble Learning Simulation Method for Hydraulic Characteristic Parameters of Emitters Driven by Limited Data

The emitter is one of the most critical components in drip irrigation. The flow path geometry parameters have a significant effect on the emitter’s hydraulic performance and have a direct impact on the emitter’s irrigation uniformity and lifetime. The hydraulic characteristics of the emitter are the key indicators of its performance. However, obtaining the hydraulic characteristics of the emitter is complex. Typically, only a small number of calibrations are performed for specific equipment models, making it difficult to obtain the parameter. Therefore, limited data corresponding to the morphological parameters and the flow rate were simulated using the FLUENT software, and the influence of the characteristics was analyzeanalyzed, based on which a flow rate prediction model was constructed using the ensemble learning (CatBoost) model. The extended data set was generated by stochastic simulation and parameter fitting. The flow index and flow coefficient prediction model were built and evaluated using the CatBoost model again with the augmented data set as a benchmark. The results show that the significant correlation between the geometric structure and the flow index and flow coefficient provides the basis for the correlation model. CatBoost can fit the complex nonlinear relationships between the parameters well, achieving excellent simulation accuracy for the flow rate (R2 = 0.9987), flow index (R2 = 0.9961), and flow coefficient (R2 = 0.9946), where the path width has the highest importance score in the model construction for the flow index (score = 55.97) and flow coefficient (score = 45.2). Furthermore, the CatBoost models used in this study achieved the best prediction results compared to seven typical models (XGBoost, Bagging, Random Forest, Tree, Adaboost, and KNN).

Non-equilibrium effect modeling and particle velocity estimation for particulate flow in porous media

The complex dynamics of fluid and particles flowing through pore space demands some relaxation time for particles to catch up with fluid velocity, which manifest themselves as non-equilibrium (NE) effects. Previous studies have shown that NE effects in particle transport can have significant consequences when relaxation time is comparable to the characteristic time associated with the fluid flow field. However, the existing models are lacking to account for this complicated relation between particles and fluid. In this paper, we adapt the general form of the harmonic oscillation equation to describe NE effects in the particulate flow system. The NE effect is evaluated by solving coupled mass balance equations with computational fluid dynamic (CFD) techniques using COMSOL Multiphysics®. A simplified straight-tube model, periodic converging–diverging tube model, and SEM image of a real pore network are applied in NE analyses. The results indicate that the time variation of the NE effect complies with the theory of stability. Two key parameters of the oscillator equation are amplitude (A) and damping ratio (ζ), where the former represents the magnitude of NE and the latter is an indication of flow path geometry. The velocity equations for particle transport in different flow path geometries are derived from the proposed NE equation, offering a quick estimation of particle velocity in the particulate flow. By conducting simulation on the SEM image of a real pore structure, the equivalent radii of the pores where particles move through were obtained. The outcome of this work can shed light on explaining the complex NE effects in porous media. The generalized equation to model NE can help temporarily decouple particle transport equations from fluid equations, facilitating much advanced particulate flow modeling problems in the large-scale problems.

A Stage Flow Parameter Analytical Model for Transonic Counter-Rotating Compressor and Its Application

This paper proposes a stage flow parameter analytical model for rapid evaluation of a counter-rotating compressor’s performance for design optimization and its application in the design of a transonic counter-rotating fan. In the first part, the velocity diagram method, considering the influence of flow-path geometry variation for enhancing the accuracy, is used to correlate the aerodynamic parameter between the inlet guide vane (IGV), the upstream rotor (R1), and the downstream CR rotor (R2). A profile loss correlation based on Lieblein’s diffusion factor and a shock loss model from a high-speed fan database are incorporated for predicting the rotor efficiency. In the second part, to verify its effectiveness, the analytical model is used for aiding in the aerodynamic design of a transonic CR fan for indicating the optimized combination of design parameters for good efficiency and a high pressure ratio. According to the analytical model and the simulation results, the final selected samples have higher efficiency, with a moderate pressure ratio (0.949/2.67, 0.890/2.99, and 0.841/2.99 for R = 0.1, 0.5, and 0.9, respectively). Finally, the aerodynamic characteristics of the designed transonic CR fan at a relative rotating speed of N = 1.05~0.8 are calculated by using the CFD software Numeca. Simulations indicate that the designed transonic CR fan has a pressure ratio of 2.76, with an efficiency of 0.8405 at the design point, and the efficiency is maintained above 0.821 with a stall margin of 13.3% for N=1.0. The maximum pressure ratio of this CR fan reaches 3.08 and 3.36 for N = 1.0 and 1.05, respectively. If used to provide thrust, calculations indicate that the thrust of this transonic CR fan is 71.8, 65.9, and 35.8 kN for N = 1.05, 1.0, and 0.8 at the near-choke point for the sea-level condition.

Efficiency of inertial particle separators

An Inertial Particle Separator (IPS) is a non-barrier system installed at the inlet of a gas turbine to mitigate effects of particulate ingestion on the engine. This study presents experimental data for a wide range of flow path designs and test dusts. The experiments were conducted in a bifurcating wind tunnel with a rectangular cross-section and aggressive flow turning, injecting particles with a range of sizes and shapes. A new flow path geometry exhibited higher particle separation efficiency for a variety of test dusts over a range of operating conditions, including off-design cases. The new flow path used a smaller scavenge channel than previous designs in order to reduce flow separation, though not so small as to stop large particles from entering. Data postprocessing highlights the importance of particle Stokes number, scavenge mass flow ratio, and scavenge flow expansion ratio as key parameters in IPS design. • Inertial particle separators (IPS) can prevent sand and dust from entering gas turbines. • A large number of IPS sand ingestion tests have been performed. • Certain geometric parameters of the IPS have a strong effect on sand separation efficiency. • Arizona road dust, AFRL-03, and C-spec test dusts have been used to evaluate IPS designs.

Vapor Overproduction Condition Monitoring in a Liquid–Vapor Ejector

We consider the influence of vapor content in the mixed flow leaving a liquid-vapor ejector on the energy efficiency of a vacuum unit. As shown by numerical studies of liquid-vapor ejectors, this issue is important as vapor overproduction, which accompanies the process of secondary flow ejection, directly impacts the efficiency of the working process of both the liquid-vapor ejector and the vacuum unit as a whole. The greater the degree of vapor overproduction, the greater the load on the vapor phase of the separator, which is part of the vacuum unit. In addition, the liquid phase must be returned to the cycle to ensure the constancy of the mass flow rate of the working fluid of the primary flow. Our numerical study results revealed the rational value of the degree of vapor overproduction at which the efficiency of the liquid–vapor ejector was maximized, and the amount of additional working fluid that needed to enter the cycle of the vacuum unit was minimal. Experimental condition monitoring studies on the liquid–vapor ejector were carried out on plane-parallel transparent models with different flow path geometries. Through experimental studies, we confirmed and adjusted the values of the achievable efficiency of the working process of a liquid–vapor ejector, depending on the degree of vapor overproduction. Using a comparative analysis of liquid–vapor ejectors with different flow path geometries, differences were revealed in their working processes, which consisted of the degree of completion of the mixing of the working media of primary and secondary flows. To determine the feasibility of using liquid–vapor ejectors with different flow path geometries, exergy analysis was performed, resulting in achievable efficiency indicators.

Optimization of Tunable Diode Laser Arrays for Inlet Mass Capture Measurement

Multibeam tunable diode laser absorption spectroscopy (TDLAS) sensors are used to measure mass flow in a complex, inhomogeneous flowfield with limited optical access. The cost and complexity of a TDLAS array increases with the number of beams, but adding beams does not necessarily improve accuracy. A technique to optimize the location and orientation of multiple laser beams for mass flow sensing in a 3D flow path geometry is developed and presented. We devised a statistical objective function that minimizes the uncertainty of estimates using a novel, linear formulation of absorption tomography with velocimetry (LATV). Beam arrangements that minimize the uncertainty of LATV reconstructions consequently maximize confidence in mass flow rate estimates; such arrangements are identified, subject to physical constraints on the pitch and catch optics. Our metric provides general guidance for the arrangement of a multibeam TDLAS mass flow sensor and does not require the use of tomographic reconstruction.

Demonstration of the model of physicochemical processes in heavy liquid metal cooled reactors in an example of the THEADES experiment simulation

Activities have been currently underway across the world to build heavy liquid metal-cooled reactors. Thus, for example, the ALFRED and BREST-OD-300 reactor designs use lead coolant, while the MYRRHA and CLEAR-I reactors use lead–bismuth coolant. The high corrosive and erosive activity of the coolant requires regulations oxygen concentration (1 ÷ 4E-6 wt.%) and flow velocity (0.5 ÷ 2.5 m/s). Due to the complex geometry of the reactor circulation circuit flow paths, numerical simulation methods are used extensively to justify scheduled modes of operation for liquid metal coolants. Correct justification of the complex oxygen transport processes in liquid metals requires the respective physicochemical computation model, which takes into account the main reactions of oxygen with the coolant and the structural materials.This paper presents a physicochemical model, which includes the following processes: erosion, growth, and dissolution of the two-layer oxide film, coagulation and dissolution of metal oxides in the circuit with subsequent deposition on filtering elements, and inflow from mass transfer apparatuses. StarCCM+, a commercial CFD code, was used as the tool in this study. The physicochemical model was implemented using models of passive impurities, which are used to simulate oxygen transport in the circulation circuit.Capabilities of the presented model were demonstrated based on the results of investigating thermohydraulic and physicochemical processes obtained at the THEADES experimental facility. The duration of the simulation was 1000 h.The distributions of impurity concentrations, increased erosive activity areas, as well as the total amount of oxides deposited on filter and the amount of oxygen entering the circuit have been obtained as a result of the calculations. The surface distribution of the oxide film thickness on the test facility surfaces contacting the coolant has also been calculated. These data can be extrapolated to reactor elements that operate under conditions that are similar to the considered experiment. For example, fuel assemblies.Simulation of thermocouples, as well as taking into account manufacturing technology made it possible to improve the accuracy of calculating the flow’s thermohydraulic characteristics as compared to earlier studies.

Analysis of temperature-deformation conditions for rolling aluminum alloy Al–Mg–Sc based on FEM modeling

The article discusses the features of Al–Mg–Sc aluminum alloy radial shear rolling (RSR). The RSR process was modeled by the finite element method in the QForm 3D program with the variable elongation ratio per pass and rolling speed. The results obtained were used as a basis for studying the temperature field of the rod in the deformation zone taking into account the cyclic nature of deformation and the configuration of flow paths. It was found that the temperature field in the deformation zone is determined by significant differences in the metal flow path geometry in surface layers and in the axial zone. When the elongation ratio is varied from 1.6 to 2.4, heating occurs inconsistently from the center to the surface. The highest temperature rise occurs for an area that is located ~0.3R from the surface. For the axial zone, temperature variation in the deformation zone occurs smoothly and with an insignificant temperature difference of 5–10 °C. Highest temperature fluctuations are observed on the rod surface, and this is explained by deformation heating and simultaneous contact with a cold roll during each deformation cycle. As the rolling speed decreases, a picture of the rod temperature field distribution in the deformation zone is observed with the temperature in central layers exceeding the surface temperature. Due to the long time of the rod contact with the roll, the surface temperature fluctuates up to 40–50 °C at each deformation cycle. As the rolling speed rises, the amplitude of temperature fluctuations on the surface decreases, and deformation heating increases. The data obtained on the relationship between control process parameters and rod temperature field variation can be useful in the design of rolling process modes.

Coupled thermo-hydro-mechanical modelling for geothermal doublet system with 3D fractal fracture

• 3D fractal fracture existed in a geothermal doublet system. • Coupled thermo-hydro-mechanical interaction for bedrock and fracture. • Normal and shear deformations of fracture based on thin elastic layer assumption. • Evaluation of thermal breakthrough due to preferential fracture flow. The existence of preferential flow paths, such as fractures and/or fault play an vital role on the thermal breakthrough of geothermal doublet system. The interaction between the preferential flow path and bedrock is often uneven and may have typical fractal characteristic. This study proposes a thermo-hydro-mechanical coupling model considering the deformation of fractal fractures. The fractal fracture is regarded as a thin elastic layer existed in the bedrock, whoes deformation depends to the bedrock and its own mechanical properties. Subsequently, the geothermal doublet system with a three-dimensional fractal fracture is modelled and the parameters affecting thermal breakthrough are investigated numerically. Research results indicate that the thin elastic layer assumption is remarkably robust for modelling fracture opening and closing under coupling conditions. Owing to complex fracture geometry, the fracture permeability evolution presents certain heterogeneity, which is related to fractal dimension, in-situ stress, and geothermal wells layout. The cool water in fracture with larger fractal dimension can interact with the bedrock more fully and further affect the thermal breakthrough. This further suggests that the site selection of geothermal wells should consider the specific geometry of preferential flow paths to avoid premature thermal breakthrough inducing low system efficiency.

Compressor Surge Frequencies Modeled by the Concept of Emptying and Filling Actions

Surge frequencies in compressors can vary much in dependence of many factors, such as compressor conditions, such as sizes, speeds, number of stages, and flowpath geometries, relative compressor locations, etc. The present investigation shows the basic behaviors of surge frequencies in multi-stage axial flow compressors, governed by a small number of essential parameters, which are obtained by physical insight to the phenomena and examinations in a trial-and-error manner on a n umber of numerical-experimental data. One of the essential parameters is a flowpath-average reduced resonance frequency, implying the number of excitations by the resonance frequency on the fluid particle in passing through the flowpath. Another one is also a reduced frequency formulated by modelling the emptying and filling actions in surge. A generalized basic framework of surge frequencies against resonance frequencies has been constructed by applying the numerical experimental data on a wide range of conditions of the compressors and the flowpaths in terms of both parameters. The framework thus prepared can be useful for practical purposes, such as for estimation of surge frequencies and surge degeneration (stall stagnation) boundaries, and also for understanding the effects of various related factors. It can provide a rule of thumb for estimation of surge frequency in the condition of sufficiently large values of the reduced resonance frequency parameter. It could serve also as a clue to further study on the details.