Separation Vortex Research Articles

Study of driving force characteristics in the formation of dominant unstable flow events in water jet propulsion pumps

Unstable flow events are pivotal in influencing water jet propulsion pumps' safe and stable operation. However, a notable research gap exists in systematically investigating the underlying driving force characteristics responsible for the formation of predominant unstable flow events in the impeller. To address this gap, we conducted experimental and numerical simulation studies, yielding the following results. As the flow rate decreases, a significant rise in the peak-to-peak value of pressure fluctuations and rigid vorticity occurs on both the blade outlet hub and inlet shroud sides. Two distinct unstable flow events emerge at these locations: the leading-edge separation vortex on the blade inlet shroud side and the horn-like vortex on the blade outlet hub side. To elucidate these phenomena, we conducted an analysis of the driving force characteristics employing the momentum equation of relative motion. Our analysis revealed that, as the flow rate decreases, there is a notable increase in the potential rothalpy gradient (PRG, or the reduced static pressure gradient) at these positions, surpassing the influence of the Coriolis force. Based on these findings, we have constructed the fundamental topological structures of these unstable flow events.

Numerical Investigations of Synthetic Jet Control Effects on Iced Airfoils

Based on the numerical method, the effects of synthetic jet control (SJC) on the aerodynamic characteristics of iced airfoils are systematically analyzed for the first time. First, an analysis method for the airfoil flowfield under SJC in icing conditions is developed, which contains the CFD method, the icing prediction method, and the boundary conditions of the synthetic jet. Then, the variation in the aerodynamic characteristics of different iced airfoils under the SJC are analyzed, and the flow separation near the ice shape is discussed in detail. Finally, parameters, such as the jet position and angle, are quantified, and conclusions are obtained. The synthetic jet can reduce the separation area on the upper surface induced by the ice accretion. When the energy of the jet is sufficient, it interacts with the mainstream, reducing the separation vortex downstream of the jet orifice and greatly improving the aerodynamic characteristics of the iced airfoil. These results provide valuable insights for the application of synthetic jet technology in mitigating the adverse effects of ice accretion on the airfoil’s aerodynamic characteristics.

Roles of Air–Sea Interactions in the Predictability of Typhoon Mawar and Remote Heavy-Rainfall Events after Five Days

This study investigated the relationship between the predicted track of Typhoon Mawar (2023) and the quasi-stationary front along the southern coast of Japan where heavy rainfall occurred. Also, the role of ocean coupling was explored by using global model predictions and numerical simulations conducted by a regional atmosphere–wave–ocean coupled model. The track predictions by four major global models showed that the prediction errors became significantly larger after the recurvature. One of the global models could reasonably predict both the track and the location of the front, even after five days. The results of numerical simulations of which the initial and boundary conditions were based on the successful predictions suggest that ocean coupling contributes to the improvement of central pressure simulations compared with fixed oceanic conditions. More northward translation of Mawar after the recurvature simulated by the coupled model could be explained by the separation of the inner-core vortex into two parts in the upper and lower troposphere. However, the predictability of the Subtropical High was more important in determining not only the track but also environmental southerly flow over the moisture road formed between Mawar and the Subtropical High and in accurately predicting the location of the front.

Analysis of the results of the study of vibrations the supporting structure of the gates of spillway structures during the operation of hydroelectric power plants

The article discusses the features of the operation of the main gates of spillway structures during the operation of the HPP. As it is known, the main spillway gates are installed at the outlet of the spillway openings into the downstream of the hydroelectric power station. The gates serve to block the openings of the spillway structure, which is opened to discharge water into a flood, as well as in the event of a disaster with an overlying hydroelectric power plant, thereby ensuring reliable operation of the entire water supply path of the hydroelectric power plant. Using the example of the Zhigulevskaya HPP, during the operation of the gates of the spillway structures, stresses in the gate structures, vibrations of the gate elements and the magnitude of the forces in the gate rod during lifting and lowering operations were determined, which made it possible to identify defects in their operation and determine recommendations for their elimination. In addition, the article discusses the results of the study of vibrations of the supporting structure of the gates of the hydroelectric power plant, which could be obtained only after identifying the features of the main gates on the spillway structures during the operation of the hydropower plant. Regarding the nature and origin of the measured oscillations, it can be said that it is not possible to give a clear explanation of the causes and physical nature of the gate oscillations at the HPP, therefore, the article considers two cases as a result of which periodic undamped gate oscillations may occur. Since it has been established that the periodic undamped oscillations registered on the gate could only be caused by a periodic disturbing force, the cause of such oscillations may be the periodic separation of vortices from the lower face of the gate. As a result, the analysis of the study of vibrations, the supporting structure of the shutter showed that the main disturbing forces for the shutter could be: pulsation of the flow pressure on the upper and lower surfaces of the shutter; dynamic forces arising when the vortices are detached from the lower face of the shutter when water flows out from under it. The article provides recommendations for avoiding vibration of the shutter in subsequent periods of operation.

TRANSPORTATION OF CUTTINGS BY DRILLING MUD IN HORIZONTAL WELLS. PART 1. MODELING THE STRUCTURE OF DISPERSED CURRENTS

Link for citation: Kharlamov S.N., Mehran Janghorbani, Zaykovskiy V.V. Transportation of cuttings by drilling mud in horizontal wells. Part 1. Modeling the structure of dispersed currents. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 10, рр. 34-48. In Rus. The relevance of the research is associated with the development of technical solutions for drilling wells with horizontal endings, in which cleaning the annulus from particles of drilled cuttings in hydraulic transport conditions seems technologically and economically efficient compared to other, for example, mechanical methods. The purpose of the article is to develop a computational methodology/approach to a detailed forecast and deep understanding of the physical mechanism of the influence of hydraulic transport on the well cleaning intensity. Moreover, the strategy of such a study is focused on the choice of flow conditions/rheological parameters of the model, in which the obtained detailed theoretical information on the evolution of the dynamic flow structure should be used in the development of design methods and the formulation of recommendations to engineering personnel for emergency warnings. The object of this study is a new class of viscous currents of dispersed media induced by external and internal forces, characteristic of the functioning of special equipment that ensures the movement of drilling mud with complex rheology in the well through an eccentric annular annulus. Results. The given article is the first part of the study devoted to solving complex problems accompanying the hydraulic transfer of rheologically complex mixtures through wells with an extended horizontal section and their cleaning from drilling cuttings. The first part presents the data on reasonable modeling of hydrodynamics of viscous dispersed mixture within the framework of reference to full equations describing laws of mass conservation, impulse for detection of peculiarities, determination of flow regularities in eccentric area of annular annulus, as well as search for ways of intensification of cleaning under conditions of real drilling. It is assumed that the viscous-inertial-gravitational flow of a liquid of the Herschel–Bulkly type with solid particles (sand) is carried out in conditions of laminar-turbulent, straight-flow and twisted (by the method of a movable wall) flow developing in the space. It is noted that the formation of modes with active and conservative action of external and internal forces allows efficient cleaning of the annulus. System of defining equations of mathematical model of hydrodynamics and mass transfer is analyzed for possibility of taking into account changes in nonlinearity of thermophysical properties, resistance to disturbances at boundaries of flow area and phase separation. It is noted that the prediction of molar processes is carried out within the framework of modern statistical models of the RANS method and the Euler–Lagrangian approach to describing the movement of heterogeneous media implemented in the ANSYS CFD software. It was shown that at the real drilling conditions, the mathematical model is successful in determining the spectrum of local and integral parameters of hydrodynamics and mass transfer in a wide range of changes in drilling conditions, which make it possible to understand the effects of particle sedimentation on the lower wall, the dynamics of vortex separation and the transfer of particles to the low-Reynolds region with a suspended state of the mixture structure and the inertial zone of the flow core. It is noted that the intensity of hydraulic transport downstream is significantly influenced by the conditions of phase entry, rheological characteristics of the mud. The calculations established the flow areas with satisfactory agreement of dynamic characteristics of the flow according to the proposed model with available experimental data, for example, shear stress at the wall, radial distributions of the components of the fluid velocity vector along the length of the well at different angles of deviation of its borehole from the vertical. Moreover, the results of this article should be taken into account when describing the data of the second part, as an addition to the study of hydraulic transport according to the proposed technique of real drilling of horizontal wells with optimal rheological properties of the mud.

The Effects of Negative Pressure Induced by Flow Separation Vortices on Vocal Fold Dynamics during Voice Production.

This study used a two-dimensional flow-structure-interaction computer model to investigate the effects of flow-separation-vortex-induced negative pressure on vocal fold vibration and flow dynamics during vocal fold vibration. The study found that negative pressure induced by flow separation vortices enhances vocal fold vibration by increasing aeroelastic energy transfer during vibration. The result showed that the intraglottal pressure was predominantly negative after flow separation before gradually recovering to zero at the glottis exit. When the negative pressure was removed, the vibration amplitude and flow rate were reduced by up to 20%, and the closing speed, flow skewness quotient, and maximum flow declination rate were reduced by up to 40%. The study provides insights into the complex interactions between flow dynamics, vocal fold vibration, and energy transfer during voice production.

Influence of Six-Degree-of-Freedom Motion of a Large Marine Data Buoy on Wind Speed Monitoring Accuracy

In order to quantitatively analyze the data measurement accuracy of ocean buoys under normal and extreme sea conditions, in this study, we simulated the six-degree-of-freedom motion response of self-designed ocean buoys under different sea conditions based on a separated vortex simulation and the fluid volume method and analyzed the impact of the unsteady motion of buoys on data measurement. The results indicate that under normal sea conditions, the deviation between the numerical method used in this paper and the experimental results is less than 10%. The heaving motion of a buoy is most sensitive to changes in wave conditions. The fluctuation intensity of buoy motion is modulated by the height and wavelength of waves. When the wave height and wavelength are similar to the overall geometric size of a buoy, the wave characteristics of the buoy’s heave, yaw, and pitch motion are significant. In addition, under extreme sea conditions, the movement of the buoy can also cause a deviation in the measured velocity in the transverse flow direction, but the overall deviation is less than 10%. In extreme sea conditions, the wind speed measurement results should be corrected to improve the measurement accuracy of a buoy.

A method proposed to predict particle deposition based on critical viscosity model and roughness height prediction in a turbine cascade

Abstract Particle deposition is a common phenomenon in a turbine cascade. It can change the surface condition, which influences the flow and heat transfer. It is very important to accurately predict the particle deposition and surface condition changes. In this study, a combined particle deposition algorithm is proposed based on the critical viscosity deposition model and roughness height prediction. It couples the influence of surface roughness into the particle deposition. The combined model newly developed is employed for the particle deposition. Its effects in a turbine cascade with the combine model is discussed. The results show the deposition is mainly concentrated on the leading edge of the cascade and the pressure side. Small diameter particles are mainly deposited on the suction side and the large are mainly deposited on the pressure side due to inertial effect. The deposition number increases with the particle diameter. As time goes by, more particles deposit on the wall, which builds roughness height and shows a spreading characteristic. Heat transfer is enhanced by the surface roughness and flow characteristics including separation vortex and leakage vortex, in which flow pattern may dominate the effect. In addition, the separation vortex and leakage vortex have a significant effect on the deposition distribution, especially for smaller diameter particles

Four-dimensional particle tracking velocimetry measurements of unsteady three-dimensional vortex onset and progression for 5415 straight ahead, static drift, and pure sway

Large-scale towed system four-dimensional particle tracking velocimetry (4DPTV) implementation and measurements are presented for towing tank tests for a naval combatant 5415 ship model for straight ahead, static drift β = 10°, and pure sway βmax = 10° conditions. The results, for the first time, provide instantaneous volumetric flow field data around the ship model including near the hull surface, and a complete description of the sonar dome 3D unsteady vortex separation onset and progression due to the 4DPTV larger measurement volume and higher data rates in comparison with previous results using tomographic particle image velocimetry (TPIV); thereby, providing the essential data required for the assessment of current hybrid Reynolds-averaged Navier–Stokes/large eddy simulation turbulence modeling capabilities and guidance for the necessary modeling improvements. The 4DPTV system is summarized and compared with the previous TPIV, including the camera calibration procedures, trigger systems, and synchronization with the sway motion. Analysis procedures, including data reduction procedures and the 3D vortex core detection and voxel labeling techniques, are described. The identification of the complex vortex separations and breakdown is aided using complementary detached eddy simulations. The vortex–vortex interaction process is visualized from instantaneous volumetric datasets. The pros and cons of the 4DPTV vs TPIV, the comparison between the second- and third-generation vortex visualization technique, and the statistical convergence error analysis of sonar dome port vortex for β = 10° are discussed. Plans for increased spatial resolution of the 4DPTV system and additional data reduction techniques for detailed turbulence analysis are also discussed.

Non-Fickian solute transport in three-dimensional crossed shear rock fractures at different contact ratios

Solute transport in fractured rocks plays a crucial role in many subsurface processes, such as geothermal resource extraction and carbon capture and storage. This study conducted simulations of non-Fickian solute transport at varying contact ratios and voids in crossed shear fractures. Results indicated that increasing the contact ratio of the crossed fractures intensified the “tailing” phenomenon of non-Fickian solute transport, and has a negative relationship with the solute outflow concentration. Additionally, the anisotropy of intersections and the variations in their void structure both influence the redistribution and mixing of fluid and solute, therefore, we propose a method to determine the solute mixing patterns at the intersection. Ultimately, while the volume and magnitude of the separated vortex domain in the flow field can influence the non-Fickian solute transport, the “tailing” phenomenon is more significantly affected by its magnitude.

A comparative analysis of intraglottal geometry and velocity flow fields: Excised human, canine, and synthetic vocal fold models

Synthetic vocal fold models imitate the characteristics of human vocal folds and offer advantages over tissue models, such as accessibility and prolonged lifespan, all while producing comparable vibration frequencies to those in humans. Nonetheless, due to their simplified design, they may not fully capture the intricate behavior observed in tissue models like the canine larynx model. Canine larynges, like human’s, exhibit a vertical mucosal wave, which yields a phase delay between the inferior and superior edges of the vocal folds free margin. Consequently, a divergent glottis forms during closing, producing intraglottal flow separation vortices (FSVs) that increase voice loudness and intelligibility. To bridge the knowledge gap between silicone and tissue vocal fold models, we compared the intraglottal geometry and velocity flow fields during phonation of these three models. At low subglottal pressures, the synthetic model displayed small divergence angles and no flow separation, where both tissues models exhibited FSVs. At higher pressures, FSVs observed in tissue models were correlated with increased glottal flow waveform skewing and higher MFDR values. These findings highlight why the excised canine larynx model should be the preferred choice over synthetic vocal fold models for studying the aerodynamics and fluid-structure interaction during phonation.

Anterior-posterior characterization of intraglottal flow fields in excised canine larynges

It has been espoused that intraglottal flow separation vortices (FSVs) play a critical role in the rapid closure of the vocal fold vibrations by acting as an additional pulling force that affects the maximum flow declination rate (MFDR). Clinically, MFDR is important because studies showed it highly correlates with loudness, intelligibility, and vocal efficiency. Previous studies that aimed to characterize the influence of FSVs were focused on their role in the mid-coronal plane. In the current study, particle imaging velocimetry was used to measure the intraglottal flow, specifically the FSVs, in the anterior–posterior aspects of the glottis during the closing phase of the vocal fold vibrations. The results show that the FSVs are extending along the length of the vocal fold in the anterior–posterior direction and that there is a direct relation between the size of FSVs and the magnitudes of the glottal divergence angles. The results also show that the centroid of FSVs occurs towards the anterior direction, where larger divergence angles are observed. These findings suggest that the FSVs in the anterior aspect have a more significant effect on the aerodynamic force acting on the glottal wall than the FSVs in the posterior aspect.

Analysis of hydrodynamic characteristics and loss mechanism of hydrofoil under high Reynolds number

Hydrofoil is widely used in hydraulic machinery, the complex shear flow and wake vortex with it can cause energy dissipation of system, affecting the stable operation of the unit. This paper takes the guide vane of a Francis turbine as the research object, and adopts the SST k−ω turbulence model to simulate the complex unsteady flow in a three-dimensional hydrofoil-channel. Entropy production theory is introduced to evaluate the energy dissipation. The effects of attack angle, gap ratio and Reynolds number on the flow loss are studied. The results show that: (1) In the hydrofoil-channel, the dissipation caused by the velocity gradient always dominates the irregular flow of fluid field. So the loss caused by the turbulent dissipation term is the main source of the loss in mainstream zone, accounting for more than 95%, while the loss caused by the viscous dissipation term accounts for only about 2% of the total loss, which can be almost ignored; (2) Changing the attack angle have a significant effect on the flow separation of the suction surface and the shear effect in the wake vortex zone, causing the energy loss to fluctuate accordingly. And 2.5° is the optimal attack angle. On this working condition, the loss decreases to the minimum value of 2.2714W/K and 0.1432 m, a decrease of 57% compared to the initial value; (3) The bottom boundary of channel suppress the development of wing tip vortex, reducing gap ratio will reduce the loss caused by wake vortex to some extent. Among them, S = 0.3 is the optimal gap ratio. Under this operating condition, the loss is 2.2941W/K and 0.1447m, a decrease of 56% compared to the initial value; (4) Affected by flow separation and wake vortexes, more than 80% of energy loss occurs in the middle and downstream zones. The effects of attack angle, gap ratio and Reynolds number on the fluid field are different. Increasing attack angle and flow velocity significantly exacerbate the flow separation and shear flow, while reducing gap ratio would inhibit the adverse flow in downstream wing tip vortex zone.

On lift enhancement and noise reduction in serrated gurney flap airfoil of wind turbines using proper orthogonal decomposition

Based on the steady simulation results obtained by the SST k-ω turbulence model, large eddy simulation (LES) and proper orthogonal decomposition (POD) are used to examine the static pressure and vorticity modes of the wind turbine airfoil with serrated Gurney flaps (SGFs) and the baseline at α = 12° and 20°. The effect of SGF on the aerodynamic performance and radiated noise is investigated, and the influence of serration's span structure on the vorticity mode distribution is discussed. By analyzing the main modes and mode coefficients of the flow field, the mechanism of lift enhancement and noise reduction of SGF is explained. The results indicate that an airfoil with a SGF(ASGF) of 6.7%c width and 0.8%c height can effectively improve the lift coefficient within the investigated attack angles, delay stall by about 3°, and reduce the radiated noise of the airfoil by 0.51 and 4.40 dB, respectively, at 12° and 20°. Static pressure distribution analysis reveals that the SGF can significantly widen the positive pressure zone of the pressure surface, improve the ultra-low pressure regime of the suction surface, and make the pressure distribution on the suction surface more uniform, which increase the lift-drag ratio of ASGF. The POD method effectively extracts the most relevant mode of the airfoil surface radiated noise. The unsteady feature of the main flow of the airfoil is the vortices on the suction surface. The ASGF can effectively restrain the vortex separation on the suction surface and reduce the vorticity, delaying the stall and reducing the radiated noise of the airfoil surface.

Intracycle Control Sensitivity of Cross-Flow Turbines

Intracycle control for cross-flow turbines employs sinusoidal perturbations in rotational speed to affect turbine power output and loads. This technique is explored for one- and two-bladed turbines with experiments that combine performance measurements with in-rotor flow-field measurements using non-intrusive particle image velocimetry. Performance enhancement is demonstrated for a wide range of control parameters but is found to be more sensitive to the sinusoidal phase offset than amplitude. Optimal performance is observed under conditions which maintain constant nominal blade angle of attack and consistently high blade-relative velocities once the static stall angle is exceeded during the power stroke. This maintains high lift and delays vortex separation. Perhaps most significantly, kinematics are also identified which decrease peak turbine loading by 12% while still producing marginally higher power output, highlighting the utility of intracycle control for load mitigation. The range of control parameters that produce these beneficial loading properties is relatively narrow and flow-fields are similar to operation at a constant rotation rate. We hypothesize that reductions in maximum loading are achieved by smoothing the changes in angle of attack and blade relative velocity profiles throughout the cycle.

Flow structure and vortex dynamics of blade surface transitional flow in the near-tip region of a compressor cascade

The mean flow topology and vortex dynamics of the blade surface transitional flow in the near-tip region of a C4 compressor blade were investigated using particle image velocimetry measurements with two configurations. The experiment was conducted in a compressor cascade at a chord Reynolds number of 24 000 and an incidence angle of 0°, and a laminar separation bubble was detected on the aft portion of the blade. In the half-span region of the blade, the separation is essentially two-dimensional without reattachment. The vortex dynamics are dominated by the periodic shedding of separated shear layer vortices and their interaction with the trailing edge vortices. The progressive spanwise evolution in the flow structures and vortex dynamics occur near the blade tip (70%–80% blade height), leading to an advanced, thinner separation. In contrast, the tip leakage vortex dominated region is restricted to approximately 20% of blade height from the blade tip. In this region, secondary flow effects are intensive enough to prevent laminar separation. Between the above two regions, there is a transition region (90% blade height), where the influence of the tip flow on the blade surface flow is relatively slight that merely suppresses the vortex shedding of the separated boundary layer, nor the whole shear layer. In the transition region, the velocity fluctuations are significantly reduced.

Machine learning-based optimization of a pitching airfoil performance in dynamic stall conditions using a suction controller

Flow separation control on oscillating airfoils is crucial for enhancing the efficiency of turbine blades. In this study, a genetic algorithm was employed to optimize the configuration of a pure suction jet actuator on an oscillating airfoil at a Reynolds number of 1.35×105. Neural networks based on multilayer perceptrons were used to train the aerodynamic coefficients as functions of the control parameters and reduce the number of simulations. The objective function was the mean performance coefficient, defined as the ratio of the average lift to the average drag during an oscillation period. The control parameters were location, velocity, opening length, and suction jet angle relative to the airfoil surface. The optimal jet had the maximum velocity and opening length and was normal to the airfoil surface. The optimal jet location was near the leading edge vortex (LEV) (between 3% and 6% of the chord). The optimum jet can increase the average performance coefficient (average ratio of lift to drag during a period) by about 24 times. The major part of this improvement is related to reducing drag force. The average lift coefficient increases from about 0.58 to about 0.92 using this jet, while the average drag coefficient decreases from about 0.23 to about 0.02. The optimal jet suppressed the dynamic stall vortex, which resulted from the combination of two clockwise vortices: LEV and turbulent separation vortex. Suppressing this vortex prevented the counterclockwise trailing edge vortex from growing at the end of the airfoil.

Large eddy simulation of tip-leakage cavitating flow around twisted hydrofoil with effects of tip clearance and skew angle

Tip-leakage cavitating flow around hydrofoils has attracted much research interest, but the complex structures of tip separation vortex (TSV) and tip-leakage vortex (TLV) have not been clearly resolved and discussed with the effects of tip clearance and skew angle yet. In the present work, large eddy simulation (LES) with multi-level octree grid refinement is used to investigate the tip-leakage flows around a series of twisted hydrofoils with various skew angle and tip clearance. High resolution is guaranteed by the normalized grid sizes of y+<1, Δx+∼50 and Δz+∼10, through which the predicted flow meets the criterion that at least 80% of the turbulent kinetic energy is resolved. The TSVs are identified to grow from the entire lower edge of the tip and twine with the TLV into a primary vortex tube, which leads to counter-rotating induced vortices (IV) strongly twisted around the primary vortex in the case of medium tip clearance but weakened for small one. Cavitation effect significantly accelerates the roll-up process of the vortices so that the primary vortex is formed earlier. The tip-leakage flow turns from wake-like to jet-like when the clearance is reduced, but the jet velocity diminishes markedly for extremely small clearance. The hydrofoil skewness barely makes a lift on the vortex tube, distinctive from the effect of tip clearance variation. The adverse pressure gradient induced by the skew angle has significant effect on the laminar–turbulent​ transition of the flow. The tip vortex flow induces strongly characterized laminar ant turbulent flow regions on the suction side, which continuously changes with the variation of the skewness.

Critical State Calculation of Saddle-Shaped Unstable Region of the Axial-Flow Pump Based on Bifurcation SST k–ω Model

This study aims to investigate the critical state of the saddle-shaped unstable region of the axial-flow pump and propose a suitable criterion for identifying this state. The bifurcation SST k–ω model considered the rotation effect is used in the present work and verified in the numerical calculation of a water jet pump. Then, it is used to simulate the critical state of the axial-flow pump. Results show that the leading-edge separation vortex generates at 0.6Qd, while the head declines only at 0.55Qd. Therefore, using the inflection point of the head-flow curve as the critical state criterion is unsuitable. In addition, the fixed monitoring point is unsuitable for identifying the critical state due to the insensitivity to the amplitude, main frequency, and periodicity changes at the critical state. Finally, to identify the critical state, it is essential to arrange a monitoring point at the leading edge of the blade suction near the shroud, which should rotate with the impeller. The critical state criterion is that the main frequency position of the pressure fluctuation signal is offset at the monitoring point, and the amplitude is increased by 10 times.

Numerical Study of Flow and Particle Deposition in a Block Duct

The primary of this study is to evaluate the characteristics of airflow organization and particle deposition in blocked ducts with various subgrid models. Five popular sublattice models are chosen to conduct this and the LES method is utilized to simulate the flow field and particle deposition properties of the duct. The results demonstrate that the features of the flow field varied amongst the different sub-grid models. The Smagorinsky and WALE models provide comparable findings, with only one pair of separated vortices in the leeward region. With small separated vortices and a small vortex structure near the wall in the leeward region, the WALES model, the WALES-Omega model, and the KET model are more informative. Simultaneously, a large number of particle groups with particle sizes ranging from 1nm to 50μm were selected for particle phase analysis. It was discovered that the deposition velocity of ultrafine particles below 1μm steadily reduced as particle size grew, whereas the deposition velocity of particles larger than 1μm rose as particle size increased.