Analysis Of Internal Flow Research Articles

CFD numerical simulation, verification with experimental results and internal flow analysis of bristle turbines

In industrial facilities, a considerable amount of waste heat is often generated. However, due to the high costs associated with traditional methods of recovery, which do not align with the economic interests of enterprises, this waste heat is frequently wasted. With technological advancements, the bristle turbine has been proposed as a solution capable of effectively managing waste gases and providing added value to enterprises. Its advantages lie in its simple structure, easy installation, low rotational speed, and high reliability, offering a new option for waste heat recovery and utilization. Despite its potential, no previous research has conducted a detailed simulation of the bristle turbine, particularly focusing on internal flow dynamics, energy loss mechanisms, drag forces, and entropy generation. This study is the first to explore these critical aspects, making a novel contribution to the field. The paper presents the computational fluid dynamics (CFD) simulation of a 20 kW bristle turbine. The numerical simulation results are in good agreement with experimental results. Subsequently, the isentropic efficiency of the turbine at different speeds is simulated, and the performance of the turbine under off-design conditions is analyzed. By investigating the energy loss mechanisms within the turbine, optimization designs are proposed.

The impact of a variable-camber inlet guide vane on the performance of a highly loaded counter-rotating fan under variable working conditions

In this research, a variable-camber inlet guide vane (VIGV) is applied to a highly loaded counter-rotating fan for the first time at variable working conditions. Additionally, internal flow analysis of the highly loaded counter-rotating fan is performed to reveal the essential flow mechanism and determine its impact on overall performance. It is found that the through-flow capacity is improved with a decrease in the camber angle. At −10°VIGV, the through-flow capacity increases by 3.1% at the design speed, while the through-flow capacity is only increased by 0.7% at the low corrected speed. The main reason for this is that the through-flow capacity along the blade span of the high-pressure rotor can be increased at the design speed, while only part of the blade span can be increased at the low corrected speed. At the low corrected speed, with the increase in the camber angle, the isentropic efficiency can be effectively improved by the counter-rotating fan, and the isentropic efficiency increases by 1.43% at +20°VIGV. This is mainly due to the decrease in the camber angle reducing the low-pressure rotor's incidence angle along the blade span, which suppresses the flow separation of the low-pressure rotor's suction surface.

Computationally cost-efficient analysis of the flow behavior of twin-fluid atomizers using computational fluid dynamics

In industrial-scale operations, wet electrostatic precipitators (WESPs) are used to minimize particulate matter, employing atomizers such as single-fluid and twin-fluid atomizers (TFAs). While TFAs provide several benefits over single-fluid atomizers, quantifying their spray characteristics is more complex, necessitating comprehensive case studies to design the internal structure of the spray and achieve desired properties. This study employed computational fluid dynamics (CFD) to simulate the internal and external flow phenomena of TFAs in industrial-scale WESPs, aiming to facilitate various parametric studies by reducing the high computational costs associated with analyzing high-speed internal flows and particle dynamics within the spray system. To decrease computational costs, the simulation was divided into two parts using stepwise segregated scenarios: Part I focused on the high-cost internal flow analysis, examining the spatiotemporal evolution of internal flow until it is fully developed, followed by droplet size distribution estimation at the nozzle. Part II computed the external flow of the spray, assessed potential cost reductions by examining the interactions between dispersed droplets, and validated the spray angle, penetration, and coverage against experimental data. The segregated strategy employed mapping techniques to integrate the two parts seamlessly. The simulation results closely matched the experimental benchmarks for spray angle, penetration, and coverage within a minimal error margin (< 5 %), demonstrating the model’s accuracy in capturing actual spray phenomena in TFAs. This approach significantly reduced the computational cost by more than twentyfold compared to conventional one-step solvers, offering a viable method for conducting various case studies in spray CFD simulations.

Internal flow analysis and design optimization of a membrane oxygenator

Abstract The membrane oxygenator is an essential component in the Extracorporeal Membrane Oxygenation (ECMO) system to offer temporary support to the respiratory system. This study aims to optimize the hemodynamic performance and reduce the thrombosis risk of a membrane oxygenator prototype using computational fluid dynamics. Numerical simulations of steady laminar flow in a full-scale oxygenator prototype (model 1) and two optimized structure Models 2 and 3 at flow rates of 5∼7L/min are carried out using the porous media model. Flow-field-based hydraulic performance indicators and the thrombus risk indicator of the three models are compared extensively. Detailed internal flow analysis revealed that adverse flow states such as insufficient flow circulation in the inlet shunt cone zone, large flow separations at the top corners of heat exchangers, and intensive flow impingement at the exit elbow tube are notably improved in the optimized model 2 and 3. The improvement is more significant at high flow rates. Performance parameters quantitatively validate the effect of optimized configurations. Specifically, at a flow rate of 7L/min, the flow uniformity indexes for the original model at the shunt cone exit increase from 0.884 to 0.923 and 0.890 in the two modified models. The total pressure loss is reduced by over 14%, and maximum wall shear stress is notably reduced from 241.46Pa to 135.9Pa. Additionally, the optimized models exhibited lower thrombus risk. The optimized designs emphasize the importance of smooth transitions between cross-sections and minimizing abrupt changes in flow direction. The employment of flow-field-based parameters allows for the establishment of the relationship between geometric and performance parameters to guide effective design optimization and ensure the safe clinical operation of oxygenator prototypes.

Investigation into the Energy Loss Mechanism of Pump Turbine During the Runaway Process Based on Entropy Production Theory

Abstract The power-trip of the pump under certain conditions leads to the runaway of the unit, causing dangerous transitional process in pumped storage power stations. This process is characterized by transient hydraulic features like flow separation and vortex structures, which increase hydraulic losses significantly and severely impact unit efficiency and stability. This paper aims to elucidate the mechanism of energy loss due to unstable flow during pump turbine runaway. It focuses on a high-head model pump turbine, examining the transient flow process from pump conditions to runaway conditions. It conducts quantitative analysis of energy loss using entropy production theory, besides, further clarifies the location and causes of hydraulic losses by integrating with internal flow analysis. The results show that a significant high-entropy production zone is captured in the pump braking condition, indicating extremely chaotic internal flow in this area during the runaway transition process. Additionally, throughout the transition process, turbulent entropy production initially increases, then decreases. Turbulent entropy production accounts for more than 80% of total entropy production, indicating that turbulent entropy production dominates throughout the entire transition process. The energy of the water is primarily dissipated within the runner during the runaway process. The maximum proportion is 87%, which is in the pump braking condition. Correlation analysis between flow and hydraulic losses reveals that vortex structure induced by flow separation under off-design conditions is the primary contributor to increased hydraulic losses.

Analysis of internal flow and energy loss in a LNG cryogenic submerged pump

Analysis of internal flow and energy loss in a LNG cryogenic submerged pump

Effect of free and compound vortex designs on the energy characteristics and operational stability of mixed flow pumps

The effectiveness of the inverse design method has been widely proven in previous studies, but research on the effect of different vortex designs on the performance of mixed flow pumps is relatively scarce. In this paper, the performances of models I1 and I2, which were designed with free and compound vortex designs, respectively, are compared to study the effect of different vortex designs on the energy characteristics and operational stability of mixed flow pumps. The results show that the efficiency of the compound vortex design at 0.8Qdes, 1.0Qdes, and 1.2Qdes is improved by 0.54%, 0.95%, and 5.91%, respectively, compared to that of the free vortex design, and the velocity and pressure pulsations under the design conditions are also significantly reduced. The internal flow analysis shows that the increased efficiency in the compound vortex design is mainly related to the reduction in the local entropy production from the hub to the mid-span and the wall entropy production from the mid-span to the shroud within the diffuser due to the improvement in the jet-wake structure near the hub. The increased operational stability is mainly related to the suppression of low-momentum fluid aggregation and H-S secondary flow caused by the increase in axial velocity near the hub and the spanwise uniformity of the total pressure.

Research of VDT scheme for porous media thermal-hydraulics analysis of plate-type fuel assembly

Thermal-hydraulics analysis of nuclear reactor core is crucial for the safe operation of nuclear power plants. Porous media models in computational fluid dynamics (CFD) code are commonly used to simulate flow and heat transfer in nuclear reactor cores because they simplify geometry and reduce computational cost. However, their low spatial resolution limits detailed analysis of internal flow and temperature fields. This research develops a Virtual Domain Technology (VDT) scheme to improve the resolution of porous media models without increasing mesh density. VDT sets localized resistance coefficients to create virtual solid and fluid domains within the porous core representation. The flow and thermal effects of these virtual domains mimic real structural effects. VDT was verified on a cylinder flow case and showed excellent agreement with CFD for velocity and pressure fields. Application to a plate-type research reactor core demonstrated VDT’s ability to capture detailed temperature profiles and flow traces consistent with CFD, using only 6% as many mesh cells. By improving spatial resolution, VDT enhances porous media-based modeling of reactor cores to provide more accurate thermal-hydraulics analysis, while maintaining computational efficiency. This will aid optimization and safety analysis for advanced reactor designs.

Unsteady behaviour and plane blade angle configurations' effects on pressure fluctuations and internal flow analysis in axial flow pumps

Pumps play a crucial role in various applications, and this study employs the CFD method to simulate the internal flow of an axial pump. Utilizing a three-dimensional model with real clearances, our investigation focuses on the pump's internal flow and pressure pulsation under diverse operating conditions. Specifically, we operated an axial pump at varying blade angles (30°, 45°, 60°, and 75°) to determine transient flow fields, aiming to identify both qualitative and quantitative characteristics. In line with current research practices, we present a comparison between numerical calculations and experimental results, revealing reasonable agreement. The simulation results highlight the influence of flow rate and plane blade angle on key parameters such as static pressure, dynamic pressure, total pressure, velocity magnitude fluctuations, and shear stress. Notably, pressure increases near or at the blade tip, and hydraulic flow becomes more evident under different blade angles and conditions. The highest pressure and velocity are observed on the blade with a 45-degree plane angle. These findings provide valuable insights for enhancing the hydraulic performance of axial pumps. To ascertain the model's accuracy and reliability, our research establishes a side-by-side comparison between numerical predictions and experimental data, demonstrating a satisfactory level of agreement. The CFD simulations yield critical insights into the pump's performance, emphasizing the profound sensitivity of parameters to variations in flow rate and blade angle, crucial for understanding and optimizing the pump's behavior.

Research on the thermal flow characteristics of viscosity oil in hydrodynamic torque converter

The increase in power density of hydrodynamic torque converters (HTCs) leads to a sharp rise in temperature within flow channels, affecting the reliability. In order to accurately predict the thermal effect and temperature distribution characteristics of the HTC internal viscosity oil, a multi-physics computational fluid dynamics (CFD) model is proposed. A specialized test bench was established, and the macro and internal flow temperature data were obtained. HTCs with different working conditions and wheel sets were studied. The results indicate that CFD model considering energy equation can accurately predict the overall hydrodynamic performance and the flow field temperature characteristics under different rotating conditions. The prediction error of the overall temperature rise is within 4.92%, and the flow field temperature prediction error of the stator is under 14.3%. The hydraulic characteristics is improved by 6.02%. The analysis of internal flow and energy exchange characteristics indicates the thermal effects and temperature distribution mechanisms caused by energy loss in the flow field within the HTC. The study provides an effective computational model for the prediction and control of the heat generation of the HTC and enhances the depth of research on the flow mechanism of inhomogeneous flow fields caused by thermal effects.

Refill friction stir spot welding tool plunge depth effects on shear, peel, and fatigue properties of Alclad coated AA7075 aluminum joints

This study investigates the impact of refill friction stir spot welding (RFSSW) on Alclad-coated AA7075 aluminum alloy, specifically exploring the effects of two plunge depths (g = 1.55 mm and g = 1.9 mm) on the mechanical and fatigue properties. The influence of the Alclad layer on the final joint properties is assessed. Internal flow analysis reveals a concentration of the Alclad layer at the corners of the stir zone for an increased plunge depth. Notably, the sample using a plunge depth of 1.55 mm exhibits a 32 % increase in pure shear strength compared to the sample executed with a plunge depth of 1.9 mm, emphasizing the significance of the plunge depth for achieving superior mechanical performance. SEM analysis of the fracture surface highlights deformation and dimples in the g = 1.55 mm sample, while EDS confirms the Alclad layer's presence, indicating its positive influence on mechanical resilience. Additionally, peel tests demonstrate a 41 % strength increase for the g = 1.9 mm sample. Low and high cycle fatigue tests reveal superior fatigue performance in the g = 1.55 mm sample, supported by SEM analysis illustrating crack initiation and fracture mechanisms. These findings contribute to a nuanced understanding of the interaction between plunge depth, Alclad ldistribution and resulting mechanical and fatigue properties.

A comparative analysis of internal flow and spray characteristics in triangular orifices with diesel and biodiesel

This paper presents an inquiry into the internal flow and spray behavior of diesel and biodiesel in a triangular orifice, using experimental and numerical methods. The inner flow was analyzed through the implementation of Large Eddy Simulation model. Furthermore, two high-speed cameras were utilized to capture spray images of the major and minor axes of the triangle-shaped nozzle simultaneously. The investigation revealed that, in comparison to diesel, biodiesel exhibited a higher discharge coefficient. Additionally, the vorticity magnitudes and turbulence vortex structures for biodiesel were consistently lower than those for diesel. The use of biodiesel can hinder the occurrence of cavitation. Moreover, it was observed that the triangular spray cone angle displayed axis-switching phenomena for both fuels. The axis-switching phenomenon is suppressed by using biodiesel. The research also discovered that the triangular biodiesel spray has a longer spray tip penetration and a smaller angle in all view planes. This could be attributed to the higher viscosity and surface tension of biodiesel, as well as the inhibition of the spray axis-switching during the injection, leading to an increase in the spray tip penetration and a decrease in the spray cone angle for biodiesel.

Investigation of the complex 3D flow structure within a selective catalytic reduction (SCR) reactor of a coal-fired power plant

A selective catalytic reduction (SCR) reactor is commonly used to remove nitrogen oxides (NOx) from coal-fired boilers. Uniformity of the flow passing through the catalyst layer is important for increasing denitrification (de-NOx) efficiency. In order to examine flow uniformity, this study conducted an experimental and numerical analysis of the complex internal flow within a realistic SCR model. Magnetic resonance velocimetry (MRV) was utilized to obtain non-invasive measurements of three-dimensional three-component average velocity and validate Reynolds-averaged Navier-Stokes (RANS) numerical simulations. The computational results showed similar overall flow structure compared with the MRV results. Parameters representing flow quality such as relative standard deviation (RSD) and recirculation zone strength (RZS) were calculated by integrating the flow field. These parameters have the largest value after the straightener area and decrease towards the catalyst reactor, and are not significantly affected by Reynolds number upstream of the catalyst layer. The recirculation zone size was analyzed using spanwise uniformity and skewness indicators. As the recirculation zone induces biased flow, the non-reacted NOx concentration was more prominent in the outlet zone opposite of the recirculating area in the corresponding actual on-site SCR reactor. Based on this finding, a meaningful correlation between flow maldistribution and de-NOx reaction could be deduced.

Structural optimization of multistage centrifugal pump via computational fluid dynamics and machine learning method

Abstract To implement energy savings in multistage centrifugal pumps, a return channel is utilized to replace the origin inter-stage flow channel structure, and then a single-objective optimization work containing high-precision numerical simulation, design variable dimensionality reduction, and machine learning is conducted to obtain the optimal geometric parameters. The variable dimensionality reduction process is based on the Spearman correlation analysis method. The influence of 15 design variables of the impeller and return channel is investigated, and seven of them with high-impact factors are selected as the final optimization variables. Thereafter, a genetic algorithm-backpropagation neural network (GA-BPNN) model is used to create a surrogate model with a high-fitting performance by employing a GA to optimize the initial thresholds and weights of a BPNN. Finally, a multi-island genetic algorithm (MIGA) is employed to maximize hydraulic efficiency under the nominal condition. The findings demonstrate that the optimized model’s efficiency is increased by 4.29% at 1.0Qd, and the deterioration of the pump performance under overload conditions is effectively eliminated (the maximum efficiency increase is 14.72% at 1.3Qd). Furthermore, the internal flow analysis indicates that the optimization scheme can improve the turbulence kinetic energy distribution and reduce unstable flow structures in the multistage centrifugal pump.

Performance Analysis of Internal Ballistic Multiphase Flow of Composite Charge Structure

Different charge structures have different interior ballistic performance. Existing research is based on experimental measurements or the lumped parameter method to obtain limited ballistic characteristics, which indirectly impacts the analysis of the parameters’ distribution, requiring a complex modeling solution process. Besides this, the ignition performance of different charge structures needs to be further explored. The disadvantages of previous studies have limited the feasibility of further optimization of the composite charge structure. In this paper, we apply a two-dimensional two-phase flow method based on the Eulerian–Lagrangian model to study the performance of different composite charge structures. First, we establish the mathematical model of different particle types based on interior ballistics, which is directly related to the research foundation of subsequent ballistic performance. Next, we investigate the multi-scale reaction flow of complex charge structures by the two-phase flow method and obtain the distribution of parameters in the chamber. Finally, we conduct a study with different particle charge parameters to explore the sensitivity of ballistic characteristics to structural parameters. The results show that the tubular propellant has good ignition performance in different charge structures, and the ignition consistency can be improved by charging tubular propellant in the center of the chamber. However, more tubular propellants are ineffective at significantly improving ignition performance, and result in a decrease in combustion chamber pressure. These results may be promising for the optimization of various charge structures.

A Multifidelity Simulation Method for Internal and External Flow of a Hypersonic Airbreathing Propulsion System

As hypersonic vehicles are highly integrated, a multifidelity simulation method based on a commercial solver is developed to reduce simulation time for such vehicles and their propulsion systems. This method is characterized by high-level fidelity numerical analysis of external flow and low-level fidelity numerical analysis of internal flow. The external flow of a propulsion system is solved by RANS equations. The internal flow is modeled by a quasi-one-dimensional equation. The interaction between external and internal flow is governed by a CFD solver through a user-defined function (UDF). The static pressure distribution acquired from the multifidelity simulation method is in agreement with the experimental data, indicating that this simulation method can be used to study the flow physics of hypersonic propulsion systems at a reasonable cost. From a design perspective, the results indicate that the horizontal force increases with the fuel equivalence ratio, and the thrust balance is realized at φ = 0.35. The positive net thrust is maintained throughout the flight regime from Ma 4 to Ma 7, whether the combustor operates in ramjet or scramjet mode.

Optimization Design and Internal Flow Analysis of Prefabricated Barrel in Centrifugal Prefabricated Pumping Station with Double Pumps

In order to improve the hydraulic performance of the centrifugal prefabricated pumping station and improve its internal flow pattern, this paper optimizes the geometric model of the centrifugal prefabricated pumping station based on the orthogonal optimization method. Through the subjective analysis method and range analysis method, it is concluded that the primary and secondary order affecting the hydraulic performance of the prefabricated pumping station is: center distance Y, pump spacing S, inlet radius R, suspension height Z, inlet height H, and the optimal parameter combination is pump spacing 550 mm (5.5 d), The suspension height is 300 mm (3.0 d), the center distance is 100 mm (1.0 d), the inlet height is 700 mm (7.0 d), and the inlet radius is 75 mm (0.75 d). The orthogonal optimization results show that under the design condition (Qd = 33.93 m3/h), the efficiency of the centrifugal prefabricated pumping station is 64.69%, which is increased by 0.70%, compared with the initial scheme. The head is 8.76 m, which is increased by 0.10 m, compared with the initial scheme. After optimization, the recirculation vortex at the water inlet of the prefabricated pumping station is smaller than that before optimization, the flow velocity uniformity in the prefabricated barrel is improved, and the flow field is more stable. The research results of this paper can provide theoretical guidance and engineering reference value for the same type of prefabricated pumping stations.

Optimization and Internal Flow Analysis of Inlet and Outlet Horn of Integrated Pump Gate

In order to improve the hydraulic performance of the integrated pump gate, the flow pattern of the inlet and outlet of the pump gate is improved. This paper adopts the SST k-ω turbulence model to numerically calculate the initial scheme of the integrated pump gate, verifies its internal flow pattern through experiments, then adds and optimizes the design of the inlet and outlet horn pipes of the integrated pump gate through orthogonal optimization. The research results conclude that the hydraulic performance of the integrated pump gate is significantly improved after adding the inlet and outlet horn. Under the design flow condition (Qd = 11.5 L/s), the efficiency of the pump gate increased from 60.50% to 67.19%, the head increased from 2.7569 m to 3.1178 m, the hydraulic loss in the inlet channel decreased from 0.064 m to 0.027 m, and the hydraulic loss in the outlet channel decreased from 1.337 m to 1.027 m. The optimized trumpet pipe can improve the inlet conditions of the pump while weakening the vortices in the outlet channel, thus improving the efficiency and safety of the integrated pump gate. The research results of this paper are of reference value for similar projects.

Simulation of the secondary air system of turbofan engines: Insights from 1D-3D modeling

Focusing on the internal flow and heat transfer analysis, a platform for the performance evaluation of the Secondary Air System (SAS) is developed. A multi-fidelity modeling technique has been developed in a turbofan engine model under different flight conditions. A turbine blade cooling model which integrates external heat transfer calculations and coolant side modeling with common components is proposed. In addition, the Computational Fluid Dynamics (CFD) method is selected to capture the complex flow field structure in the preswirl system. The validity of the SAS models is compared with publicly available data. An elaborately designed cooling system for the AGTF30 engine is analyzed through three main branches. It is found that the 1D-3D modeling technique can provide more accurate predictions of the SAS for the AGTF30 engine. The results demonstrate the versatility and flexibility of the SAS models, thereby indicating the capacity of meeting most of the demands of flow and thermal analysis of the SAS.

Analysis of Internal Flow and Wear Characteristics of Binary Mixture Particles in Centrifugal Pump Based on CFD-DEM

Solid-liquid two-phase flow centrifugal pumps are widely used in many fields closely related to economic development, such as energy exploitation, and the petrochemical industry. Many scholars have studied the influence of solid particles with different parameters on the transportation performance of centrifugal pumps but have mainly focused on the study of low-concentration single-component particles, and the research on the transportation of high-concentration binary mixture particles in centrifugal pumps is insufficient. In this paper, two kinds of glass beads (0.4 mm and 2 mm) were mixed as a solid phase medium, representing small particles and large particles, respectively. The effects of a high concentration (Cv = 10%) of binary mixture particles on the transport and wear characteristics of a solid-liquid centrifugal pump were analyzed by simulation and experiment. Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) and Archard wear model were used for simulation, realized by Fluent software and EDEM software. The results show that the large particles have a greater effect on the performance decline than the small particles, and the increase of the proportion of large particles has a greater effect on the efficiency decline than the head decline. The wear degree of the flow channel in the pump changes obviously with the particle ratio, and the overall wear is small when the particle ratio is 1:2.