Numerical Investigation Of Flow Research Articles

Numerical Investigation of Flow and Thermal Fields in Heat Exchanger with Two Porous Vertical Baffles

Numerical Investigation of Flow and Thermal Fields in Heat Exchanger with Two Porous Vertical Baffles

Numerical Investigation of flow and combustion process in a hydrogen direction injection rotary engine

The high power-to-weight ratio and zero carbon emission hydrogen rotary engine (HRE) is an attractive development direction of hydrogen-powered systems, which is of great significance in expanding the hydrogen energy diversified utilization and promoting greenhouse gas (GHG) emission reduction. In this paper, a direct injection HRE simulation model coupling chemical reaction kinetics is constructed. The flow and combustion processes are visually presented using computational fluid dynamics (CFD) means, and the effect of the air intake method and hydrogen injection timing on the mixture formation and combustion performance are analyzed. Research finds that the combustion pressure, peak pressure, indicated work and indicated power of the HRE are larger when using methods of the compound or side intake or delaying hydrogen injection strategy. Due to the forward flame propagation characteristics, the combustion process mainly occurs in the front part of the combustion chamber, and the mixture distribution in this area and aggregation near the ignition chamber are more favorable to improving the combustion performance. More gas fuel gathered in the leading or end regions of the chamber will affect the burn rate in the later combustion stage. The preferred scheme is compound AIM with HIT at the early compression stage (CAIM-190), and its peak pressure, indicated work and indicated power improve by 30.9%, 25.5% and 26.6% respectively while combustion duration shortens by 15.3% when comparing to the scheme of minimum peak pressure (PAIM-286). This study can offers basic data to promote the HRE achieving efficient combustion and zero carbon emissions.

Numerical investigation of flow and heat transfer on turbine guide vane leading edge slot film cooling

As the demand for enhanced turbine cooling performance grows, the optimization of traditional discrete film hole is becoming increasingly complex. Compared with discrete holes, slot cooling is considered one of the most effective forms of film cooling, which effectively improves cooling performance while retaining a relatively simple structure. In order to explore the flow and heat transfer properties of leading-edge slot film cooling in turbine vanes, this paper analyzes the AGTB guide vane profile to examine the properties of the slot structure under different slot pitch-to-width ratios and blowing ratios (M), deeply investigates the evolution and underlying mechanism of the secondary flow downstream the slot and within the vane passage, comparisons are also made with standard cylindrical hole and inclined hole. The results show that the development of the counter-rotating vortex pairs on the pressure surface lags and extends over a longer distance downstream of the slot. Reducing the slot spacing can enhance the mutual interference between the vortex pairs, significantly improving the cooling performance on the pressure surface. On the suction side, the coolant streams remain largely independent, and both increasing M and reducing slot spacing adversely affect cooling performance. Under the same M, the slot structure achieves an average cooling effectiveness 2–3 times higher than the hole structure, accompanied by a 25 % increase in total pressure loss. At the same coolant mass flow, the cooling effectiveness on the pressure surface increases by approximately 30 %, and on the suction surface, it is three times greater than that of the hole structure, while the total pressure loss remains similar.

Numerical investigation of flow and particles contamination in reticle mini environment for extreme ultraviolet lithography

Numerical investigation of flow and particles contamination in reticle mini environment for extreme ultraviolet lithography

Experimental and numerical investigation of flow and heat transfer characteristics of teardrop and circular pin fins in a wedge channel

ABSTRACT Pin fin arrays, which have a high heat transfer capacity and minimal pressure loss, are currently being used as the primary cooling technique for the turbine trailing edge cooling channel used in modern gas turbines. To enhance the heat transmission efficiency of the channel, this study proposes the use of a circular-shaped pin and a teardrop pin, through both experimental and numerical investigations. The numerical simulations conducted in the Reynolds number range of 10,000 to 80,000 are used to investigate and compare the flow and heat transfer parameters of a wedge channel which has three rows of staggered circular-shaped and teardrop-shaped pin fins with a diameter of 12 mm. The experiment showed that teardrop pin fns with staggered arrangement has different effect on flow pattern and heat transfer characteristics. Heat transfer is increased by 10.45% when compared to the circular pin fins and the pressure drop of teardrop pin fins is reduced by 54.6%.Therefore thermal performance factor exhibits a 25.4% increase when compared to circular fins.

Numerical investigation of flow around the injector of a Pelton turbine due to eroded needle

Abstract Injectors of Pelton turbines are prone to both sediment erosion and cavitation. This causes degradation of the surface morphology, which aggravates the quality of the jet, lowering the turbine’s performance. The study focuses on CFD analysis of a groove-shaped erosion pattern on the needle and analyses its influence on the quality of the jet at the three stages of erosion. The numerical model comprises of a nozzle with a cylindrical passage for modelling the jet. The research used the SST turbulence model and boundary conditions defined according to the turbine’s data, from which the model was obtained. This study explores the impact of silt erosion on pressure signals around the injector of a Pelton turbine. Needle pressure distribution curves were plotted at various erosion levels and openings, revealing that pressure deviation increases with increase in erosion. The effect turns out to be minimal during high opening levels but becomes substantial as opening levels decrease. Operating in part load conditions leads to a significant pressure drop due to the reduction in flow rate. The pressure distribution tends to become more uniform at full load, achieving optimal flow rates. However, a noticeable pressure drop is observed in the eroded region, reaching a minimum at the deepest eroded area. The pressure drop is further amplified with an increase in the level of erosion, indicating erosion’s disruptive impact on fluid flow. The findings highlight the complex interplay between erosion, needle pressure distribution, and jet diffusion.

Numerical investigation of flow boiling characteristics in narrow rectangular channels using two-fluid Eulerian CFD model covering a wide range of pressures

Narrow channel heat exchange technology is one of the key technologies for the development of integrated small modular reactors (SMR). The ‘wall heat flux partitioning’ (WHFP) model in conjunction with an Eulerian–Eulerian Multiphase Flow (EEMF) method is found to be an important tool for two-phase hydrothermal analysis. In this paper, the accuracy of the EEMF-WHFP method with various sub-models is systemically evaluated over a large database of boiling flows in narrow rectangular channels. Prediction results using a total of 9 model combinations, are compared with data from 22 experimental conditions covering a range of the mass flux of 134.2 to 2200 kgm-2s-1, the inlet fluid subcooling of 7.2 to 74.2 K, the pressure of 0.1 to 14 MPa and the heat flux of 9.54 to 1700 kWm-2 in narrow rectangular channels with gaps of 1.0 to 3.0 mm. The evolution of distributions of void fraction, wall temperature and the net vapor generation (NVG) point along the flow channel is simulated and compared with experimental data. It is found that due to the limitation of the range of applicability of sub-models, certain models produced better prediction results under different pressure ranges than others, and the recommended combinations are given according to the quantitative assessments. In addition, the ability of the model combinations to predict the NVG point, as well as the flow structure and boiling process in narrow channels is investigated. The critical local void fraction near the wall at the NVG point is quantitatively estimated based on numerical results. The research conclusions in this paper can be used in thermal–hydraulic calculations in a wide range of operating pressures covering the applications of compact heat exchangers, flat plate fuels, climbing/falling film plate evaporators and the cooling of microelectronics, among other applications.

Numerical investigation of flow and heat transfer characteristics of special-shaped fuel

Helical cruciform fuel, a relatively new type of fuel element, has garnered significant interest due to its distinctive attributes, such as transverse mixing characteristics and self-supporting properties. However, helical cruciform fuel still faces numerous challenges. To address the issue of high central temperatures, an annular helical cruciform fuel is introduced, and its internal flow and heat transfer characteristics are evaluated through numerical simulation in comparison to helical cruciform fuel. The results indicate that fuel elements with a helical structure exhibit lower maximum temperatures and higher convective heat transfer coefficients. Specifically, the maximum temperature of helical cruciform fuel at a power density of 200 WM/m3 is 712.26 K, whereas for annular helical cruciform fuel under the same heat generation rate, the maximum temperature is only 686.34 K. Regarding convective heat transfer, the annular helical cruciform fuel element demonstrates an improvement of approximately 20% compared to the helical cruciform fuel element. Consequently, annular helical cruciform fuel contributes more to the safety of the reactor core and the miniaturization of nuclear power devices. This study could serve as a reference for the subsequent design and enhancement of reactor cores.

Numerical investigation of flow boiling characteristics of R134A in a smooth horizontal tube

Three-dimensional transient simulations using ANSYS Fluentʼs mixture multiphase model was conducted to investigate the impact of heat flux, mass flux, and saturation temperature variations on pressure drop behaviour and heat transfer characteristics during flow boiling of R134a refrigerant in smooth horizontal tubes of different diameters. The simulations employ an implicit numerical method to solve the governing equations, with relevant source terms for mass and energy transfer, incorporating the continuum surface force (CSF) and shear stress transport (SST) κ-ω models to account for surface tension and flow turbulence respectively. The results are presented in both dimensional (heat transfer coefficient and pressure drop) and non-dimensional (Nusselt number and two-phase frictional factor) forms. The Nusselt number shows a direct relationship with the Reynolds number, while the two-phase friction factor exhibits different behaviour. At higher vapor quality, mass flux significantly affects heat transfer performance and pressure drop. Heat flux plays a crucial role in heat transfer, but its impact on pressure drop is negligible. Higher saturation temperatures enhance heat transfer while reducing pressure gradients. The obtained results demonstrate good agreement with existing correlations, with mean absolute deviations (MAD) as low as 1.2 % for the heat transfer coefficient and 23.7 % for the pressure drop behaviour. This highlights the model's accuracy in predicting flow boiling behaviour of R134a in smooth horizontal channels, providing valuable insights for thermal analysis. The findings contribute to the understanding of flow boiling processes and aid in designing and optimizing efficient heat exchangers for various engineering applications.

Numerical investigation of flow past a cylinder using cumulant lattice Boltzmann method

This paper presents simulations of flow past a circular cylinder within the subcritical Reynolds number (Re) range from 3900 to 2 × 105, utilizing the parameterized cumulant lattice Boltzmann model. In this study, a three-dimensional characteristic boundary condition for incompressible flow has been integrated into the lattice Boltzmann method at the outflow boundary to minimize spurious reflection. The flow field, wake statistics, hydrodynamic force, and power spectra results of Re = 3900 from the cumulant lattice Boltzmann model are exhaustively compared with the laboratory data and other numerical models. Relative to other numerical models employing turbulence closure, the cumulant lattice Boltzmann simulations demonstrate enhanced agreement with the experimental data even with relatively coarser grid resolution. The resolution-spanning feature for the cumulant lattice Boltzmann model in turbulent flows, without using explicit turbulence model, aligns with the previous benchmark case studies. The stability-preserving regularization process in the present model is analyzed. Results indicate that the influence of the regularization parameter is mitigated with improved grid resolution. A specific regularization parameter for flow around cylinder simulations is recommended. Variations in flow properties and hydrodynamic forces within the subcritical Reynolds number range of 3900 to 2 × 105 are analyzed. The results confirm that the parameterized cumulant lattice Boltzmann model can accurately simulate practical engineering flows, characterized by complex separation and recirculation, within the subcritical range. Moreover, the computational efficiency and parallel scalability are compared with other numerical methods.

Numerical investigation of flow boiling behavior in a vertical tube of a shell‐and‐tube phase change heat storage unit

AbstractPhase Change Materials (PCMs) demonstrate significant potential as latent heat storage systems for direct steam generation. This investigation explores the heat transfer dynamics of an upward‐flowing heat transfer fluid (HTF) boiling within a vertical tube, concurrently examining the solidification process of PCM outside the tube. A two‐dimensional model of a shell and tube heat storage device is established for this purpose. The simulation employs the Volume of Fluid (VOF) model coupled with the Lee model to simulate HTF boiling inside the tube. Concurrently, the enthalpy‐porosity model is utilized to analyze the PCM solidification process. The findings reveal that PCM solidification and heat discharge are influenced by the temperature and thermal conductivity of the HTF, leading to uneven solidified PCM thickness along the tube's length over time. Additionally, variations in tube length, inlet velocity, and inlet temperature impact both the vapor quality of HTF and the thickness of solidified PCM. Tube length correlates with boiling time, affecting the accumulation of steam quality throughout the coupling process. Inlet velocity dictates the heat transfer of HTF with PCM within a limited distance, and insufficient heat exchange resulting in the cessation of HTF boiling. Inlet temperature determines the appropriate device size, lower inlet temperatures necessitate longer tubes to extend the heat charging duration until boiling initiation.

Numerical investigation of forced convection flow of a complex Bingham–Papanastasiou fluid between two concentric

This research presents a numerical investigation of the flow field and heat transfer of a Visco-plastic fluid, The Bingham-Papanastasiou model is used to examine the flow field and forced convection heat transfer of a Viscoplastic fluid between two concentric cylinders with a wavy inner surface. By focusing on this particular configuration (wavy inner cylinder shape), where the inner surface exhibits as the hot wall while the outer surface is considered as the cold wall. This investigation is numerically achieved by using the Comsol Multiphysics, which is based on the finite‐volume method, employing Galerkin’s method for solving the governing equations. The parameters studied in this research are expressed with the following values: r/ R=1/3, Reynolds number (Re=1, 10, 50), and undulation number (nu=0, 6, 12, 24). Increasing the inertia parameter results in a higher intensity of thermal buoyancy, positively influencing heat transfer, particularly at Re=50. Furthermore, the acceleration of flow within the investi-gated space improves the hydrodynamic behavior, facilitating the exchange of thermal energy between the hot and cold walls. Additionally, it has been discovered that an undulating shape with a specific number of undulations (nu=6) maximizes hydrothermal performance within the investigated volume. The presence of these undulations enhances fluid mixing and dis-rupts the formation of stagnant regions ,which leading to improved heat transfer.

Numerical investigation of flow and heat transfer characteristics in a fluidized bed solar particle receiver

Numerical investigation of flow and heat transfer characteristics in a fluidized bed solar particle receiver

Resolution assessment of Reynolds stress model-based DES methods for high-lift device flow over 30P30N configuration

Flows over high-lift devices (HLD) contain abundant complex physical characteristics such as flow separation, free shear layer transition, and turbulent vortex evolution, which cause challenges to the numerical prediction of unsteady flow characteristics over the HLD. The recently developed detached-eddy simulation (DES) based on the Reynolds-stress model (RSM) is expected to resolve the complex flow characteristics with high fidelity due to the RSM model holding fewer modeling assumptions than classical eddy-viscosity models (EVM). To assess the flow resolution performance of the RSM-based DES method and its dynamic version on the HLD, they are adopted in the numerical investigation of flow over a 30P30N multielement airfoil, a canonical HLD configuration with sufficient experiment measurements. The widely used EVM-based DES method, the shear-stress transport (SST)-based DES method, is also applied for the numerical investigation as the benchmark DES method for the flow resolution performance assessment of RSM-based DES methods. The results are compared with the available experimental data and the benchmark DES method, including average quantities, fluctuation quantities, and instantaneous flow field. It is found that RSM-based DES methods can overcome the prediction delay matter of free-shear layer instability appearing in the SST-based DES method. The dynamic RSM-based DES method can predict the fluctuation flow characteristics in the slat cove of 30P30N configuration more exactly than the other two methods and resolve finer vortex structures in the flow field.

Numerical Investigation of Flow and Scour around Complex Bridge Piers in Wind–Wave–Current Conditions

A sea-crossing bridge is typically constructed in a marine environment with complex piers, and is susceptible to severe scour at the foundation. This study presents a numerical investigation on flow and scour around a complex pier, specifically focusing on a real-world sea-crossing bridge in China. A comprehensive CFD model incorporating hydrodynamic, free surface, sediment transport, and morphological models is employed for numerical modeling. Additionally, a wind shear stress model is considered to accurately simulate wind generation. The validation of the CFD model is achieved through comparison with experimental data of scour around a cylinder, demonstrating its capability to accurately replicate scour morphology and the temporal evolution of scour depth. Subsequently, the validated model is utilized for full-scale simulation of scour around the complex bridge pier under different wind, wave, and current conditions. The results indicate that compared to single piers with uniform cross-sectional shapes, flow patterns around complex piers are much more complicated. Scour predominantly occurs around the first row of group piles, while downstream piles experience less scour due to the sheltering effect from upstream piles. Furthermore, it becomes evident that the current exerts greater influence on pier scour than waves and wind, while the latter two factors primarily influence the superstructure of the bridge.

Numerical investigation of flow past a triangular cylinder at various Reynolds numbers

Numerical simulation of flow around a triangular cylinder placed both in left and right position at Reynolds number Re = 80–200 is presented in this study. The single relaxation time lattice Boltzmann method is used. The results are obtained in terms of vorticity contour visualization, drag and lift coefficients, and force statistics. Regular vortex shedding is observed for both cases, but the vortices generated for a triangular cylinder placed in the right position move toward the top downstream position as the range of Reynolds number increases due to effect of pressure (effect of thrust). The drag coefficient is constant, and lift coefficient is containing negative values from Re = 80–150 for that case, but negative Cdmean values are not observed for a triangular cylinder placed in the left position. In that case, it is due to the reason that the effect of thrust diminishes. The maximum value of Cdmean is obtained at Re = 200, that is, 1.5006 for the left triangular cylinder, but the value of the mean drag coefficient for the right triangular cylinder is zero throughout the cases for Re = 80–200. No fluid forces are produced for right triangular case. The Strouhal number (St) values increased by increasing the Reynolds number, i.e., Re = 80–200, for the right triangular cylinder, and it has a mixed trend for the left triangular cylinder. In literature, a lot of work has been found on rectangular and square cylinders, but triangular cylinder has not been studied much.

Numerical investigation of flow across three co-rotating cylinders in side-by-side arrangement

Flow across three side-by-side co-rotating cylinders is investigated at a Reynolds number of 100 and non-dimensional rotation rates varied from 0 to 8, for spacing ratios of L/D=1.5, 2, and 4 through two-dimensional numerical simulations, where D and L are cylinder diameter and the center-to-center spacing between the cylinders, respectively. For L/D=1.5 and 2, the wakes are classified into regime FF (flip-flopping) at smaller rotation rates and regime SB (single-body) at higher rotation rates. Each regime can be further divided into sub-regimes based on the wake patterns. Regime FF is a regime where the flow switches between two patterns intermittently. The three sub-regimes of SB at L/D=1.5: vortex shedding (SB-VS), steady state (SB-SS), and secondary instability (SB-SI) are the same as those of a single rotating cylinder as the flow through the gap is too weak to have effect on global wake. A new sub-regime single-body quasi-steady (SB-QS) is found for L/D=2, where the two shear layers in the wake of the three cylinders interact weakly with each other but do not form strong vortices. For L/D=4, two new regimes are found: regime 3V-to-3S (transition from three vortex shedding wake to three steady wake), where the vortex shedding from the three cylinders are suppressed consecutively one by one with the increase in the rotation rate, and regime TB (two-body) where two of the three cylinders behave as a single body. Regime TB for L/D=4 has two sub-regimes: steady state (TB-SS) and secondary instability (TB-SI). The effects of the flow regimes on the force coefficients are quantified. For all the spacing ratios L/D=1.5, 2, and 4, the standard derivation drag and lift coefficients are significantly greater than that of a single cylinder when vortex shedding occurs.

Numerical investigation of flow and heat transfer behavior on vortex cooling with an optimal convergent coolant chamber for different nozzle aspect ratio arrangement mode

A computational model including convergent coolant chamber, nozzles and vortex chamber is established. The vortex cooling flow and thermal exchange features are investigated under different nozzle aspect ratio arrangement mode based on an optimal convergent coolant chamber. The nozzle aspect ratio arrangement mode consists of two parts, namely eight nozzle aspect ratio sizes and three kinds of nozzle aspect ratio axial variations. Results indicate that the erosion velocity increases due to the smaller windward area with the increasing nozzle size. The convergent coolant chamber makes the mass flow and pressure increases, the reflux phenomenon appears. And the increasing nozzle size leads to the first increase and then decrease with high pressure and Nusselt number area. For the nozzle aspect ratio arranged from high to low, the airflow stiffness and turbulent kinetic energy at the sixth nozzle are the largest, the thermal transfer feature enhances. For the nozzle aspect ratio arranged from low to high, the airflow impact strength and heat exchange characteristic decreases. But the drag coefficient is minimal that has a positive effect on flow features. The thermal exchange capacity is the highest with the nozzle aspect ratio 2.0. Consequently, this study can provide reference for gas turbine design.

Three-dimensional numerical investigation of flow and heat transfer performances of novel straight microchannel heat sinks

Four-type novel single crystal diamond (SCD) straight microchannel heat sinks with different shapes (symmetrically inclined, turned symmetrically inclined, V-shaped, and X-shaped) are designed and investigated by the three-dimensional computational fluid dynamics method. These four-type microchannel heat sinks are evaluated in terms of fluid flow and heat transfer capabilities compared to the conventional rectangular straight microchannel (RSMC) heat sink. Our research indicates that the newly designed novel SCD microchannel heat sinks can enhance the heat dissipation effect in comparison to the conventional RSMC heat sink, thereby substantiating its potential for enhancing thermal management in electronic devices. Each V-shaped and X-shaped straight microchannel heat sink has a higher heat transfer capacity than the RSMC heat sink. Among the heat sinks involved in this work, the V-shaped SCD heat sink has the best surface temperature uniformity. The symmetrically inclined heat sink shows the lowest pumping power, with 14.1 % lower than that of the RSMC heat sink. The X-shaped SCD heat sink exhibits a significantly lower thermal resistance, with an 8.5 % reduction compared to the RSMC heat sink. Additionally, it demonstrates a substantially higher Nusselt number, with a 27.6 % increase relative to the RSMC heat sink. The X-shaped SCD heat sink has the highest heat transfer coefficient of up to 1.08 × 105 W/(m2·K), which is 20.4 % higher than that of RSMC heat sink. Owing to the highest performance evaluation criterion of 1.22, the X-shaped straight microchannel heat sink is the most optimal of the designed heat sinks.

Numerical Investigation of Flow and Heat Transfer in Vane Impingement/Effusion Cooling with Various Rib/Dimple Structure

Numerical Investigation of Flow and Heat Transfer in Vane Impingement/Effusion Cooling with Various Rib/Dimple Structure