CFD Modeling Of Flow Research Articles

Collaborative modelling of gas-solid reacting flow in a fuel reactor equipped with process controllers in chemical looping combustion/conversion

Chemical reactors usually feature complex internal reacting flows, and they are usually equipped with process controllers to stabilise their operations, especially for highly dynamic reactors including chemical looping combustion/conversion (CLC). However, their dynamic internal states are not well understood due to the lack of reliable research tools. In this work, for the first time, an innovative numerical collaborative model is developed to describe the reacting flow details and simulate the response to a process controller. The collaborative model is applied to a fuel reactor (FR) in a CLC to demonstrate its effectiveness. The detailed internal flow patterns in the FR are obtained and described by the three-phase reacting flow CFD model, and the circulating rate of oxygen carrier (OC) is controlled and optimised by the fuzzy logic controller (FLC). The controller is designed to operate at varying control time intervals, 1 s, 2 s, and 5 s, to study the optimal frequency for data sampling and feedback. The efficiency of the controller to the FR is tested in terms of OC circulation, gas components and the general performance of the reactor. The results show that the stability of OC circulating rate and performance are effectively improved by the process controller; among the three control intervals, the 2 s interval shows the highest feasibility and capability of maintaining stable OC circulation and CO2 yield in the FR. Quantitatively, compared to the base case without a controller, the range of OC circulating rates has been narrowed from [0.014, 0.534] to [0.018, 0.385] in control case A, [0.075, 0.342] in control case B, and [0.004, 0.530] in control case C. Meanwhile, the CO2 yield increased from 86.93 % in the base case to 87.98 % in control case A, 88.16 % in control case B, but decreased to 85.4 % in control case C due to poor controlling performance. The combustion efficiency increased from 84.20 % in the base case to 84.87 % in control case A, 86.22 % in control case B, and 85.88 % in control case C. Among all control cases, control case B presents the narrowest data range and highest efficiency, indicating optimal control performance in improving OC circulation stability. The deviation of OC circulating rate values decreases from 0.123 to 0.058, and the CO2 yield increases from 86.93 % to 88.16 % in control case B with a 2 s interval. This work provides a new cost-effective tool for real-time simulating and controlling the reacting flow system including CLC for clean combustion and solid wastes conversion.

Design and modeling of a co-flow reactor for turquoise hydrogen production

This work focuses on the design of a reactor for producing clean hydrogen from methane pyrolysis in the form of the so-called “turquoise hydrogen”. In addition to its simple geometry, the fundamental concept and the main novelty of the proposed method rely on using part of the methane to produce the required heat needed for the thermal decomposition of methane (TDM). The reactor configuration for hydrogen production is shown to produce significant advantages in terms of greenhouse gas (GHG) emissions. A reactive flow CFD model incorporating also soot formation mechanism has been first developed and validated with experimental results available in the literature and then used to design and characterize the performances of proposed reactor configuration. 3D CFD simulations have been carried out to predict the behavior of the reactor configuration; a sensitivity analysis is used for clearing the aspect related to key environmental parameters, e.g., the global warming impact (GWI). The real potential of the proposed design resides in the low emissions and high efficiency with which hydrogen is produced at the various operating conditions (very flexible reactor), albeit subject to the presence of carbon by-product. This suggests that this type of methane conversion system could be a good substitute for the most common hydrogen production technologies.

CFD modelling of longwall goaf atmosphere under vertical boreholes gas drainage

To effectively control and utilise large amounts of gas emissions from underground coal mining, Australia and many other countries rely heavily on a series of vertical boreholes to capture the gas during mining. This gas capture not only reduces the greenhouse gas impact but also recovers a significant amount of energy. Vacuum pumps are connected to surface boreholes to drive gas flow from the goaf and overlying fractured strata. However, applying high suction pressure to the boreholes may cause more oxygen to enter the goaf from the longwall working face. This influx of oxygen can potentially react with residual coal in the goaf, accelerating coal self-heating and possibly resulting in endogenous fires. By analysing extensive goaf gas drainage data collected from Australian longwalls, researchers have established the normal trend of goaf gas concentration and flow rate as a result of intensive goaf gas drainage. This paper further developed goaf gas flow CFD models with the operating vertical boreholes, which were then calibrated using field borehole production data under certain operating conditions. The CFD model simulated the distribution of O2 and CH4 as well as the gas flow pathways in the goaf, considering the complication of goaf gas drainage. This study found that the O2 concentration is higher on the goaf tailgate side under the influence of tailgate side boreholes compared to the maingate side. Furthermore, for the well-compacted goaf, a significant proportion of the ventilation air travels through ‘high permeability flow channels’ provided by the goaf edge on tailgate side, and then circulates back into the goaf boreholes. These CFD modelling results not only enable ventilation engineers to visualize the goaf gas flow patterns under the impact of multiple operating boreholes, but also to understand the impact on goaf atmosphere through sensitivity analysis of natural goaf characteristics, such as goaf permeability distributions and gas emission rates.

CFD modeling of flow, combustion and NOx emission in a wall-fired boiler at different low-load operating conditions

In the context of achieving carbon peaking and carbon neutrality, the implementation of flexible peak shaving techniques is of significant importance to coal-fired units. Operating coal-fired units under different low loads can result in decreased combustion efficiency, unstable combustion, and increased emissions of nitrogen oxides (NOx) during the combustion of pulverized coal. However, few studies have been carried out wall-fired boiler under low-load operation in most papers. This paper employs numerical simulation to investigate the flow, temperature, composition concentration fields, as well as combustion stability and NOx emission characteristics of a 600 MWe wall-fired under various low-load (specifically, 400, 300, 240 and 200 MWe) conditions. The simulations demonstrate that reducing the boiler load leads to decreases in the amount of filling gas and the average temperature of the furnace. Despite the overall decrease in average furnace temperature with load reduction, the central part of the furnace can reach 1400 K at low load (200 MWe), due to the strong flame stability of centrally fuel-rich burner. The NOx concentrations for 400, 300, 240, and 200 MWe were 475.9, 498.4, 361.9 and 259.7 mg/Nm3, respectively. The NOx concentration initially increases with the load reduction, and decreases as the load is further reduced. Considering the broad industrial application prospect of flexible peak shaving of coal-fired boilers, these research results provide guidance and suggestions for different load operation of wall-fired boilers, and provide theoretical support for low load stable combustion operation of wall-fired boilers.

CFD modeling of flow and local scour around submerged bridge decks

In this study, the level set method-based, multiphase hydro- and morphodynamic numerical model REEF3D is used for the simulation of the flow conditions and local scouring around submerged bridge decks. Presence of hydraulic jumps, bridge overtopping, pressurized jets and the resulting scouring make the selected test cases especially challenging from the numerical modelling point of view. The models are validated against data from laboratory experiments. The influence of the submergence ratio on the prevailing flow and scouring is investigated. The level set method showed robustness and good accuracy for the treatment of the complex free surface as well as for the tracking of the mobile bed. The submergence ratio showed no clear correlation with the prevailing erosion/deposition patterns. As the simulations offered insights into the prevailing hydrodynamics and thus the relevance of numerical modelling was emphasized for such complex sediment transport problems.

CFD modelling of powder flow in a continuous horizontal mixer

This work presents a continuum model for simulating the flow of powders inside continuous horizontal mixers. The challenge is to adopt a reliable rheological model that allows simulating granular flows accurately. We selected the μ(I)-rheology model. First, we considered a set of granular collapse experiments, showing that the model can successfully reproduce these flows, and also using the experimental results to evaluate the material properties of the powders. Then, we investigated the complex powder flow in continuous horizontal mixers. Here computational cost is a challenge. We showed that the sliding mesh technique is accurate but expensive owing to the rotation of the boundaries, making this method impractical for industrial applications. Therefore, we also employed the multiple reference frame technique, showing that its results are accurate at far lower computational cost. The results section ends with a sensitivity analysis of the mixer solid mass loading to the powder material properties.

CFD modeling of the multiphase flow in an SKS furnace—The effect of melt density and viscosity

A previously reported numerical method using the multi-fluid VOF model to simulate an SKS furnace multiphase flow was further verified to provide a good reference for the macroscopic flow field simulation of industrial vessels with similar geometry. Using the verified numerical model, CFD simulation of a full-scale SKS furnace multiphase flow was conducted, targeting the agitation performance with different melt densities and viscosities, under constant furnace operating conditions. According to this simulation, the melt density and viscosity in a common applied range in industry is not able to significantly affect the bath agitation efficiency like other parameters, such as the tuyere diameter and bath depth. More specifically, the results indicate that an increased melt density or viscosity slightly weakens the melt flow motion, and increases the wall shear stress. Since variation in melt density and viscosity is common in industry, the results from this simulation offer a good basis for the estimation of SKS furnace operating performance and the adjustment of the physical properties of the melt in SKS furnaces or other similar industrial vessels.

CFD-modeling of fluid flow in Ansys Fluent using Python-based code for automation of repeating calculations

CFD-modeling for numerical investigation is used in a wide range of applied tasks, e.g. in fluid mechanics. To better understand the effect of operational parameters on the final results, some tasks are associated with carrying out monotonous, repetitive calculations for a wide range of operational parameters such as velocity, flow direction and temperature. In this paper, a Python-based code for automation of the repeating calculations in CFD-modeling was developed and described. The automation code was tested for CFD-modeling in Ansys Fluent for two flow dynamic tasks: a simple 2D-geometry — NACA0018 airfoil, and a complex 3D-geometry — packed bed with heat transfer. Three different computers with various computational power were used for the comparison. The results of CFD-modeling were compared with the experimental data. The efficiency of using Python-based code was evaluated through comparison with the results of manual (without automation) calculation. It was established that the application of the Python-based code does not affect the accuracy of numerical results. At the same time, utilization of the Python-based code can save up to 25% of computation time for the simple 2D-geometries with a moderately low number of elements in the mesh, and up to 15% for the complex 3D-geometries with a number of elements in several millions. The compiled Python-based code is attached as supplementary material to this paper.

Use of recirculation theory and reduced dimensionality for efficient calculation of jet flow in cylindrical combustors

This work evaluates use of a dimensionally adaptive (DA) meshing technique to speed CFD modeling of non-reacting pressurized flow in a cylindrical geometry with a center jet and non-axisymmetric secondary jets. The DA-capable approach incorporates an a priori dimensional boundary location and extension of 3-D RANS flow solvers. Recirculation zone length, not flow asymmetry, was the limiting factor in placement of the dimensional boundary between 3-D and axisymmetric meshes. Boundary placement was based on confined turbulent jet theory, which suggests jet attachment is a linear function of cylinder radius, L, expressed as 5.85L. CFD results for a turbulent axial pipe flow showed that as the dimensional boundary was moved upstream, computational time dropped quadratically with the reduction in mesh cells. Further simulations of a 0.2032-m diameter, 1.5-m long reactor with turbulent center primary jet and outer radius secondary jets placed the dimensional boundary at 0.7 m. Results for pressures of 20, 10, and 5 bar and mass flow rates of 75% and 50% of baseline demonstrated two key results. First, flow similarity was preserved across all cases and the predicted jet attachment location was approximately 0.61 m, compared with the theoretical value of 0.594 m. Second, runtime reductions of 79% (pressure) and 82% (flow rate) were seen for the DA meshes compared with fully 3-D meshes. Differences in average exit axial velocities between DA and fully 3-D meshes were 2–4% for the pressure cases and 0.7–1.5% for the flow rate cases. Lastly, comparison with 3-D quarter-geometry calculations showed the DA approach to be ∼10% faster with exit axial velocities within 3–5% of 3-D velocities.

EXPERIMENTAL AND NUMERICAL EVALUATION OF AN IN-FLIGHT ANGLE OF ATTACK MEASUREMENT SYSTEM FOR HIGH POWER MODEL ROCKETS

The angle of attack (α) affects the drag, flight path, and flight stability during rocket ascent. This work proposes an in-flight α measurement system based on pressure measurements at the surface of the nosecone for low apogee rockets. An electronic micro differential pressure transducer was selected to measure the pressure difference between selected points in the rocket’s nosecone. Wind tunnel tests were performed to correlate the α with the sensor output at low Mach numbers (Ma ≃ 0.08). The experimental results were further used as a reference for the construction of CFD models of the external flow in the rocket’s nosecone with the aim of predicting the measurements in an extended Mach number range (up to Ma ≃ 0.7). The numerical results allowed for an extended model correlating α with the differential pressure transducer output (Ch). The estimate of model’s errors completes the analysis.

CFD modeling of two-phase flow with surfactant by an arbitrary Lagrangian–Eulerian method

The effects of surfactants on the motion and deformation of sinking and rising drops are studied numerically by employing the arbitrary Lagrangian-Eulerian (ALE) method. To describe the surfactant transfer in two-phase flow, the transport equations of the surfactant in the bulk fluid and the interface are solved in a coupled way which was developed in the commercial solver. The applicability of the numerical approach is verified by a series of benchmark tests and then employed to simulate the sinking drop contaminated by insoluble surfactant. The predicted drop motions and velocity profiles show good agreement with the experimental results from the literature, and the “stagnant cap” is found in the rear region, where the surface velocity nearly vanishes. Furthermore, the effects of the soluble surfactant on the drop rising in a straight tube are studied in detail, and the numerical results also agree well with the experimental data. It is found that the surfactant at the interface leads to the decrease of terminal velocity, especially in the transition region of drop shape. In addition, the Marangoni stress would inhibit the inner circulation of the drop and leads to immobilized behavior at the interface. The present method exhibits good accuracy and affordability, which can be easily used to solve the two-phase flow with surfactant.

Organic Rankine cycle turbogenerator cooling – Optimization of the generator water jacket heat exchange surface

Discharge of excess heat from the micro-turbine electric generator is an important issue for the micro-turbine operation and should be considered during the design process. The manuscript is intended to present a new tool for rapid shape optimization of the heat exchanging surface of the ORC (Organic Rankine Cycle) micro-turbine electric generator. The optimization of the water jacket geometry of a 10 kWe ORC micro-turbine generator is performed by making use of a modified, with respect to the models presented in the literature, 0D heat transfer model of the finned heat exchange surface of the cooling water jacket, and a genetic algorithm. As a result of optimization, an apparent reduction in fin size and increased fin density at the finned wall surface is achieved, yielding a significant increase of the heat transfer coefficient and a temperature decrease of the electric generator stator. The temperature at the shell surface tangential to the electric generator stator was found to decrease by over 6°C. A considerable reduction of temperature gradients around the water jacket wall is also reported.The results of optimization from the 0D model are verified by numerical simulation using a full 3D CFD model of fluid flow and conjugate heat transfer (CHT) in Ansys CFX for the original and optimized geometries. The CFD CHT model was first validated using experiment-based correlations for heat transfer in liquid flow over a circular cylinder pipe for a wide range of Reynolds numbers.The obtained temperature decrease in the optimized ORC electric generator stator for the nominal operating point of the ORC generator is found similar for both 0D and 3D models. The temperatures calculated in the 0D model at the shell surface tangential to the electric generator stator deviate from respective CFD values by 0.5–1.5°C. Another operational case beyond the nominal operating point has been analysed making use of the 3D CFD method as well, showing that the optimized geometry is characterized by an improved heat exchange performance not only for the nominal operating point.

CFD model of acceleration of thermal-hydrodynamic processes in solar air collectors

Recent studies on increasing the thermal-hydrodynamic efficiency of solar air collectors have been carried out on the installation of barriers of various shapes on the surface of the absorber, and this method ensures a significant increase in the energy efficiency of the collector. The transfer of the air flow washing the surface of the absorber from a laminar flow state to an accelerated lumped air flow is carried out by installing obstacles. Installation of barriers is the main factor in increasing the heat transfer in solar air collectors and prolongs the time of air flow in the collector. The barrier solar air collector has a high local heat transfer coefficient, and the Nusselt number value is up to 3.5 times higher than that of the flat plate solar air collector. Also, this article presents the results of CFD modeling of the air flow in the solar air collector, the results of which can be used in the theoretical research of the solar air collector.

Slurry flow characteristics through a horizontal pipeline at different Prandtl number

The settling behavior of solid particles in the slurry pipeline leads to bed formation and sedimentation at the bottom of the pipeline. This in turn causes the blockage of the pipeline resulting in more energy consumption and a pressure drop in the slurry pipeline. The present work investigates the effect of the different Prandtl numbers on the slurry flow characteristics through a horizontal pipe. Since the flow is a liquid-solid mixture, therefore, a steady-state three-dimensional Eulerian two-phase model in combination with the RNG k-ε turbulence model is implemented for the current simulation in the commercial software ANSYS FLUENT. Numerical predictions and procedures for the mixture of solid concentrations are generally in good agreement with the past experimental data available in the literature. Slurry flow features are examined at four different Prandtl numbers i.e., 2.88, 3.42, 4.62 and 5.83 for different-sized glass beads (125, 200, 275, 350 and 440 μm) slurry for the concentration ranging from 40 to 60% (by weight) at a mean flow-velocity of 5 m/s. The findings show that the pressure drop rises with the escalation in particle sizes and Prandtl number for chosen efflux concentration range. Furthermore, low Prandtl fluid demonstrates relatively higher granular pressure, temperature and wall shear stress, which further increases with raise in solid concentration and particle size. In addition, higher Prandtl number fluid demonstrates maximum specific energy consumption (SEC) for every particle and efflux concentration range. • 3D CFD modeling of slurry flow via horizontal straight pipe is investigated. • Effect of different Prandtl number on slurry flow characteristics is studied. • Effect of particle size and concentration on slurry pressure drop is presented. • At lower Prandtl number, maximum granular pressure and temperature is established. • Transportation of slurry with higher Prandtl fluid is more energy efficient.

Scaling analysis as a tool to validate CFD simulation of a lubricant flow in the bearing housing of a gas turbine

• The effects of rotor speed on the temperature of the lubricant oil are studied. • CFD model of oil flow and heat transfer in the bearing chamber is developed. • Scaling analysis is used to simplify and nondimensionalize the governing equations. • Scaling analysis is used to replace experimental data to validate CFD results. • An equation to compute viscous dissipation energy is obtained by Scaling analysis. This work concentrates on the journal bearing chamber of a gas turbine engine, to explain the impacts of the rotational speed of the rotor on the velocity, pressure and temperature distribution in the bulk oil. In the first step, a CFD model of fluid flow and heat transfer in the bulk oil of the bearing chamber was developed via COMSOL 6. Next, and in a novel approach, scaling analysis was employed to verify the CFD simulation results. Scaling analysis, as a systematic method for non-dimensionalizing a set of equations, was used to simplify the governing equations based on the specific conditions of the physics. Afterward, the velocity, pressure and temperature profiles attained from the CFD simulation were compared to this set of simplified equations. In general, it was confirmed that the CFD model developed in the current article is physically valid and follows the main descriptive equations governing the entire physics of the system. Scaling analysis was effectively used to confirm the simulation results where insufficient experimental results were available, due to the geometrical and operational restrictions in the test rig. Temperature, pressure and velocity were the factors considered in this study and the average of simulation and scaling results for each factor were compared. Additionally, the average point-to-point error between the simulation and scaling results for each factor was reported as another basis for the comparison. In summary, scaling analysis in this work is presented as a straightforward method to substitute experimental measurements in order to validate CFD simulation results.

CFD Modeling for the Influence of Fly Ash Particle Size on the Different Properties of High Concentrated Slurry Transportation in Horizontal Pipe

The disposal of fly ash from thermal power plants is becoming a serious concern for environmental engineers. This article attempts to study the influence of particle size of the fly ash on the various properties of high concentrated slurry (50 - 70 % by weight) flow through a horizontal pipe with the help of a commercial CFD code ANSYS FLUENT. Modified Herschel-Bulkley model and SST k-ω turbulence model is used for computational analysis, and the computational outcomes are validated with the available literature. In the present study, the fly ash samples were procured from different coal-based thermal power plants. Various properties: physical and rheological are obtained experimentally. The specific gravity of particles and the static settling concentration (SSC) of the slurry increases with the decrease in the particle size. The rheological properties increase as the concentration increases, and the slurry behaves like a non-Newtonian fluid at a high concentration. In addition, the particle size and concentration intensively impact on the skin friction coefficient and velocity distribution. However, no significant impact on the velocity profile at 70 % concentration (by weight).
 HIGHLIGHTS
 
 The rheological properties increase as the concentration increases, and the slurry behaves like a non-Newtonian fluid at a high concentration
 CFD modelling of the slurry flow at high concentration with modified Herschel-Bulkley model and SST k-ω turbulence model
 The particle size and concentration intensively impact on the skin friction coefficient
 
 GRAPHICAL ABSTRACT

A New, Green, Recyclable Fireproof Insulation Board for Use in Integrated Composite Structure Fire Protection Systems

A fireproof insulation board can be recycled, and the raw materials used in its production are very environmentally friendly, non-toxic and non-hazardous, and bring no harm to the human body and the surrounding environment. One practical application of fireproof insulation board is in an integrated composite structural fire protection system, which is a multidimensional comprehensive structural fire protection system proposed for the combined construction of buildings with different functions, such as horizontal and vertical, to ensure overall safety in the event of a building fire. The specific new technology of this new system includes an integrated structural fire protection system composed of a 3.00 h fire insulation board, which comes from the collection of textile scraps consisting of metals and buttons removed from clothes. To prove the effectiveness of this fireproof insulation board, its parameters were collected and put into FDS (FirG Dynamics Simulator, a CFD model of fluid flow during combustion developed by the National Institute of Standards and Technology), the fire safety goals considering the safety of building and personnel were established, and fire scene design based on the statistics of fire data and building codes was generated to test the safety of evacuation. To ensure the reliability of simulation results, an on-site physical fire test was conducted with the recycled insulation board. The result shows that the function of recycled board optimizes the phased evacuation design plan of personnel and solves the design difficulties of expanding fire zones and long evacuation distances when used in warehouses. Through the innovative design of the roof opening rate set at 30% and a hole spacing of 60 m, this underground fireproof insulation board is guaranteed to possess natural smoke exhaust conditions and can be used to improve public safety areas.

Математичне моделювання теплопередачі у повітряно-крапельному потоку камери підшипника ГТД

The gas-liquid flow in the bearing chamber (BC) of the gas turbine engine is realized due to the interaction of the sealing air and oil supplied for lubrication and cooling of friction units. The complex nature of the flow movement is determined not only by the BC geometry but also by the presence of rotating elements and the manner of oil supply and flow removal. The most important result for the engineering practice of BC flow modelling is the determination of the heat transfer coefficient to the inner wall. The variety of influencing factors causes difficulties even at the stage of an integral mathematical model of the process formation, which makes it possible to determine this coefficient. As a result, significantly different approaches are used – from three-dimensional CFD modelling of a heterogeneous flow up to the use of a criterion equation that formally considers the effect of geometric and regime parameters on a heat transfer. The first approach requires significant computational resources, and certain difficulties arise in setting the initial and boundary conditions, especially in terms of droplet parameters. Homogeneous models somewhat simplify the problem, including when formulating the boundary conditions. However, all the effects of the influence of the droplet diameter are levelled. In both cases, the computation time is long, and the results of CFD simulations require selective experimental verification. Therefore, it is problematic to use this approach solely for engineering problems, as well as when generalizing experimental data in several regime parameters. When using the criterion equation, the calculation procedures are as simple as possible. However, dimensionless complexes do not ensue from the basic equations of heterogeneous media mechanics and do not consider the effects of interfacial interaction during heat transfer in the BC. Therefore, the possibility of the application of the proposed correlations for other BC geometries and oil and air supplying conditions also needs to be experimentally confirmed. This makes it problematic to use such correlations at the design stage of the BC and the oil system as a whole. The preferred approach for engineering practice is when the thermohydraulic processes in the BC are described on the basis of the proven equations of heterogeneous media mechanics with the transition to a two-dimensional problem by averaging the phase parameters along the axis. This averaging is justified by the fact that the main heat carrier from the core to the inner wall of the BC is the radial flow of droplets. In view of the low volume fraction of droplets, the Lagrange approach is used to simulate a two-phase flow in the BC core. The droplet parameters along the trajectory are calculated considering the interfacial interaction with the air. In this regard, the air velocity field is determined by considering the geometry of the BC, the flow through the seals and the shaft speed. Here, it is possible to consider not only the droplet polydispersity but also the effects of primary droplet reflection, the formation, and movement of secondary droplets during the formation of a near-wall oil film, the thermal resistance of which directly affects the value of the internal heat transfer coefficient.

Prediction of film thickness in starved EHL point contacts using two-phase flow CFD model

In grease lubricated rolling contacts, the oil bleeding from the grease bulk forms an elastohydrodynamic lubricating (EHL) film. When the amount of bled oil at the contact inlet is insufficient, starvation occurs leading to a decrease in film thickness. Although most grease lubricated bearings operate under starvation, the correlation of starvation and film thickness is not fully understood. In this contribution, a two-phase flow CFD model is proposed. This model allows a calculation of the oil/air flow field in the vicinity of starved contacts and its effect on EHL film formation. For starvation conditions, the results show a decrease of film thickness at the center line in flow direction, while the contact sides can still remain fully supplied by replenishment.

Multiphase throttling characteristic analysis and structure optimization design of throttling valve in managed pressure drilling

As the key equipment to achieve accurate control of wellhead pressure during managed pressure drilling, the throttle valve can ensure the bottom hole pressure accurately controllable during the migration of invading gas in the annulus. At present, most of the research focuses on the throttling characteristics of single-phase fluid, and the research on the pressure regulation characteristics of throttle valve under the condition of multiphase flow is still relatively weak. In this paper, the mathematical model and CFD model of multiphase flow in the throttle valve are established, and the multiphase throttling characteristics under different hydraulic parameters are studied. The rationality of the proposed model is verified by field full-scale experiments. The results show that throttling pressure drop shows a nonlinear trend with the opening, which is not conducive to field application. Furthermore, through the sensitivity analysis of the throttle characteristic curve under multiphase flow conditions, the geometric structure of the throttle valve core is optimized to realize the fine adjustment of the wellhead back pressure under multiphase flow conditions, which is of guiding significance for wellbore pressure control under gas invasion condition.