Flow Boundary Layer Research Articles

Non-linear radiative second-grade nano fluid with sinusoidal magnetic force and arrhenius activation energy: A computational exploration

The goal of this work is to further improve our knowledge of the nonlinear radiative second-grade nano fluid flow boundary layer phenomena which is associated with an Arrhenius activation energy, a sinusoidal magnetic field, and a stretched peripheral with a heat source. The unsteady governing equations are transformed into a proper dimensionless arrangement, and then the explicit finite difference (EFD) method is applied to numerically calculate the equations. However, precise stability and convergence criteria have been developed to make the solution convergent. Along with the typical profile of other flow fields, the oscillatory forms of the velocity are shown. Tabular research has even demonstrated a relationship between the Nusselt number and other parameters, and graphical depiction has been used for regression and data prediction. The novel conclusions drawn from this research indicate that, in comparison to linear patterns, nonlinear radiative heat flux significantly raises (30.35 %) flow profiles with second-grade characteristics. Moreover, the heat transfer rates of second-grade Nano fluids are seen to be significantly influenced (35.14 %) by the sinusoidal magnetic component. When considering nonlinear thermal radiation, activation energy principles cause a major change (34.19 % more) in mass transmission, as high-temperature processes become an essential part of chemical reactions.

Exploring thermal buoyant flow in urban street canyons: Influence of approaching turbulent boundary layer

Turbulent boundary layer inflow is a critical factor in urban climate research, shaping canyon flow dynamics, air ventilation patterns, and heat flux distribution. In numerical simulation studies, it serves as a fundamental inflow boundary condition, profoundly influencing overall results. In this study, simultaneous Particle Image Velocimetry and Laser-Induced Fluorescence (PIV-LIF) measurements are utilized within a large closed-circuit water tunnel. This approach allows comprehensive flow data to be gathered under varied flow and thermal conditions, encompassing a spectrum of Richardson numbers ranging from 0.01 to 1.34. The investigation aims to elucidate the effects of turbulent boundary layer flows on heat transfer mechanisms and flow behaviours within a two-dimensional street canyon model with a unit aspect ratio. The analysis reveals distinct heat and fluid flow characteristics, highlighting the interplay between thermal conditions and flow dynamics. The three chosen turbulent boundary layer flows demonstrate unique influences on flow characteristics and heat removal capacity. Significant variations in ventilation rates are observed, with a maximum difference of 80% among the tested boundary layer flows. Additionally, the most pronounced variation in heat removal capacity is approximately 45%. Thicker boundary layers with lower velocities near the canyon exhibit reduced ventilation and heat removal capabilities. Furthermore, the investigation reveals that varied turbulence inlet profiles result in diverse fluctuating features at the canyon roof level, with a comparatively lesser impact on the deeper regions of the canyon.

Large Eddy Simulation of Laminar and Turbulent Shock/Boundary Layer Interactions in a Transonic Passage

Abstract Shock/boundary layer interactions (SBLI) are a fundamental fluid mechanics problem relevant in a wide range of applications including transonic rotors in turbomachinery. This paper uses wall-resolved large eddy simulation (LES) to examine the interaction of normal shocks with laminar and turbulent inflow boundary layers in transonic flow. The calculations were performed using GENESIS, a high-order, unstructured LES solver. The geometry created for this study is a transonic passage with a convergent-divergent nozzle that expands the flow to the desired Mach number upstream of the shock and then introduces constant radius curvature to simulate local airfoil camber. The Mach numbers in the divergent section of the transonic passage simulate single stage commercial fan blades. The results predicted with the LES calculations show significant differences between laminar and turbulent SBLI in terms of shock structure, boundary layer separation and transition, and aerodynamic losses. For laminar flow into the shock, significant flow separation and low-frequency unsteadiness occur, while for turbulent flow into the shock, both the boundary layer loss and the low-frequency unsteadiness are reduced. The time period of the unsteadiness was hypothesized to align with the time it takes for turbulent structures to convect from the shock to the trailing edge and acoustic disturbances to travel back from the trailing edge to the shock, and this is supported by the LES results.

Numerical investigation of acoustic streaming vortices in cylindrical tube arrays

Abstract Acoustic streaming has a significant effect on accelerating material mixing and flow field disturbance. To explore the characteristics of acoustic streaming in the cylindrical tube array field under the action of an acoustic wave, we derive the dimensionless acoustic streaming control equation and establish a numerical calculation model of acoustic streaming. The effects of acoustic incidence angle, acoustic Reynolds number, and Strouhal number on the acoustic streaming vortex flow field in the tube array were investigated. The numerical results show that with the change in acoustic parameters, the acoustic streaming in the tube array presents rich changes in the vortex flow field, and there are flow field phenomena such as shrinking, merging, tearing, and splitting of the vortex structure. Toward the walls of each tube, there is a strong acoustic streaming flow velocity. Besides, there is also a large streaming velocity on the interface of the adjacent acoustic streaming vortices. The inner streaming vortex structure in the acoustic boundary layer decreases with the increase in the acoustic Reynolds number, but the intensity of the inner streaming vortex and outer streaming vortex increases rapidly, and the disturbance effect of the flow field is enhanced. With the increase in the dimensionless acoustic frequency (or Strouhal number), although the structure and intensity of the inner streaming vortex decrease, the velocity gradient on the wall of the cylindrical tube increases, which is beneficial to destroy the flow boundary layer of the cylindrical tube wall and accelerate the instability of the wall flow field.

Spatially evolving cascades in wall turbulence with and without interface

Direct numerical simulations of channel flow and temporal boundary layer at a Reynolds number $Re_{\tau } = 1500$ are used to assess the scale-by-scale mechanisms of wall turbulence. From the peak of turbulence production embedded at the small scales of the near-wall region, spatially ascending reverse cascades are generated that move through self-similar eddies growing in size with the wall distance. These fluxes are followed by spatially ascending forward cascades through detached eddies thus reaching sufficiently small scales where eventually scale energy is dissipated. This phenomenology is shared by both boundary layer and channel flow and is recognized as a robust physical feature characterizing wall turbulence in general. Specific features related to the flow configuration are indeed identified in the outer region. In particular, the central region of channels is characterized by a generalized Richardson energy cascade where large scales are in equilibrium with small scales at different wall distances through a combined forward cascade and spatial flux. On the contrary, the interface region of boundary layers is characterized by an almost two-dimensional physics where spatially ascending reverse cascades sustain long and wide interface structures with a forward cascade that survives only in the wall-normal scales. The overall scenario consists in a variety of scale motions that while protruding from the turbulent core towards the external region, squeeze at the interface thus sustaining vertical shear in a thin layer. The observed multidimensional physics sheds light on the complex interactions between outer entrainment and near-wall self-sustaining mechanisms with possible repercussions for theories.

Significance of quadratic density variation on the heat transport phenomena in Careau dusty fluid subject to Lorentz force via stretching surface

The two-dimensional boundary layer of steady mixed convective magnetohydrodynamic Carreau dusty fluid flow across a stretched sheet was investigated in this study. The primary focus of this study is to examine the impact of Carreau nanofluid on dusty flow dynamics in the presence of the Lorentz force. The partial differential equations governing the fluid flow, temperature, and concentration fields for both the fluid and dust phases are transformed into ordinary differential equations using an appropriate set of similarity transformations. Numerical outcomes are acquired employing the Runge–Kutta technique combined with the shooting method, implemented on the MATLAB platform. The numerical outcomes are compared to previous research and confirmed to be in very good accord. Finally, the impacts of relevant factors of physical and technical importance on flow and thermal transport characteristics are visually and tabulated. The results for the linear density and the quadratic density profile, it is noted that the linear density decreases compared to the quadratic density for velocity, but the opposite behavior is observed for temperature profile. The advancement of dusty nanofluids has resulted in significant enhancements in the heat transfer mechanism, which finds application in manufacturing, industry, and nanotechnology research. Research on dusty flows benefits on is beneficial in air pollution studies, dust entrainment in a cloud formed during a nuclear, vehicle emissions of smoke and other pollutants, crude oil purification, petroleum production, combustion, industrial effluent emissions, capillary blood flow, paint sparing, and, more.

Experimental study of a separated shear layer transition under acoustic excitation

The paper discusses experimental results on the effect of broadband acoustic excitation on laminar-to-turbulent transition in a separated shear layer developing on a flat plate subjected to an adverse pressure gradient (APG) and freestream turbulence level equal to Tu ≅ 1 %. The study encompasses the influence of Reynolds number (Rex = 185 000 and 370 000) and sound pressure level (SPL). The inherent complexity of the problem is simplified by providing an acoustic excitation from a controlled source (loudspeaker), acting on the boundary layer developing on the flat plate with a given streamwise pressure gradient. Two types of instabilities were identified in the pre-transitional boundary layer in unexcited flows. One was related to the inviscid Kelvin-Helmholtz (K-H) instability, while the second one was associated with formation of streamwise-oriented Klebanoff streaks (so-called Klebanoff mode).In the low Reynolds number case (Rex = 185 000), the K-H was responsible for transition onset, while in the high Reynolds number flow (Rex = 370 000), the Klebanoff distortions dominated the turbulent breakdown with the minor effect of the K-H instability. In addition to the naturally developing boundary layer, the flow was exposed to a pink noise characterized by SPL = 125 dB and 135 dB. In the low Reynolds number case, the acoustic excitation enhanced the K-H instability. It resulted in an earlier laminar-to-turbulent transition in case with higher sound pressure level (135 dB). In the high Reynolds number flow, the acoustic excitation enhanced the mixed-type transition mechanism with dominant role of the Klebanoff streaks. Shrinking or complete suppression of the separation bubbles was observed, depending on the applied sound pressure level (125 and 135 dB).

A theoretical study of the signal enhancement mechanism of coaxial DP-LIBS

In the field of dual-pulse laser-induced breakdown spectroscopy (DP-LIBS) research, the pursuit of methods for determining pulse intervals and other parameters quickly and conveniently in order to achieve optimal spectral signal enhancement is paramount. To aid researchers in identification of optimal signal enhancement conditions and more accurate interpretation of the underlying signal enhancement mechanisms, theoretical simulations of the spatiotemporal processes of coaxial DP-LIBS-induced plasma have been established in this work. Using a model based on laser ablation and two-dimensional axisymmetric fluid dynamics, plasma evolutions during aluminum–magnesium alloy laser ablation under single-pulse and coaxial dual-pulse excitations have been simulated. The influences of factors, such as delay time, laser fluence, plasma temperature, and particle number density, on the DP-LIBS spectral signals are investigated. Under pulse intervals ranging from 50 to 1500 ns, the time evolutions of spectral line intensity, dual-pulse emission enhancement relative to the single-pulse results, laser irradiance, spatial distribution of plasma temperature and species number density, as well as laser irradiance shielded by plasma have been obtained. The study indicates that the main reason behind the radiation signal enhancement in coaxial DP-LIBS-induced plasma is attributed to the increased species number density and plasma temperature caused by the second laser, and it is inferred that the shielding effect of the plasma mainly occurs in the boundary layer of the stagnation point flow over the target surface. This research provides a theoretical basis for experimental research, parameter optimization, and signal enhancement tracing in DP-LIBS.

Mass transport in Couette flow

In this study we examine the large Péclet number, Pe, limit of a concentration boundary layer in Couette flow. The boundary layer has a thickness of order Pe−1/2. The asymptotic concentration is asymptotically obtained as an integral solution up to order Pe−1/2 using the Fourier sine transform. The asymptotic solution is found to be in good agreement with the full numerical solution for large Péclet numbers. Further, the effective diffusivity obtained from the asymptotic solution is found to be in good agreement with the effective diffusivity obtained from the full numerical solution for large Péclet numbers.

Numerical study on magnetic control of boundary layers in non-Newtonian flows over stretching cylinders using Keller box analysis

This article presents an analysis of the magnetic field’s effects on two-dimensional, two-directional, incompressible, and steady third-grade fluid flow over a stretched circular cylinder. A mathematical model describing the behavior of third-grade fluid in the cylindrical coordinate system is developed, accounting for nonlinear differential conditions. To simplify the analysis, appropriate transformations are applied to convert the fractional differential conditions into ordinary differential conditions. The resulting nonlinear differential framework is solved using the Keller Box method. The influences of several novel parameters on the velocity are depicted and examined. Furthermore, the expression for the skin-friction coefficient is computed and provided. The comparison of the obtained results with existing literature is made and found in good accordance. Through comprehensive numerical simulations and analytical derivations, this study contributes to the understanding of magnetic field control in boundary layers of third-grade fluid over stretching cylinders, with implications for a wide range of practical applications in engineering and fluid dynamics. The stronger influence of the magnetic field, indicating an increase in the Hartmann number, corresponds to suppression of thermal and solutal transport, thereby leading to a decrease in the temperature and concentration gradients. Conversely, the velocity profile exhibits an increase, indicating enhanced fluid motion under the influence of the magnetic field. This behavior is consistent with the magnetohydrodynamic effects, where the Lorentz force induced by the magnetic field alters the fluid flow, resulting in changes in the velocity distribution while impacting temperature and concentration gradients.

Wake Formation Flow Physics and Boundary Layer Analysis on the Sides of the Isosceles Triangular Cylinder with Apex Pointing Downstream

Boundary layer interaction with downstream flow structures was numerically studied to find the region of inactivity behind an 75° isosceles triangular cylinder with apex pointing downstream at intermediate Reynolds numbers (Re = 520, 640, 840 and 1040). The Standard k-ε model in OpenFOAM was used in the study. Numerical results were validated against Particle Image Velocimetry data. Results revealed the stable region of inactivity characterized by low turbulent kinetic energy and vorticity. The onset of secondary vortex and separation point, independent of Reynolds number, was identified. The onset of the secondary vortex was located at (x = 2 mm) from the base and (y = 1.5 mm) from the apex on either side of the cylinder. The ratio of modulus of absolute primary z-component of vorticity, |ω_z^1 |, to the modulus of secondary z-component of vorticity, |ω_z^2 |, was found to be approximately equal to 1.2. This ratio is invariant of the Reynolds number of the study. These findings have practical implications. The unique properties of the inactivity region forms an ideal location that can be used for injecting fluid, placing measurement probe, active flow control and drag reduction. The research problem is formulated in the introduction. Literature is reviewed next providing the background. Details about the range of parameters, governing equations, numerical study details and software used are given in the methodology section. The results section gives the numerical results, verified by mesh refinement test and validated against experimental results. The results are finally discussed in the next section.

Formulation, Implementation and Validation of a 1D Boundary Layer Inflow Scheme for the QUIC Modeling System

AbstractRecent studies have highlighted the importance of accurate meteorological conditions for urban transport and dispersion calculations. In this work, we present a novel scheme to compute the meteorological input in the Quick Urban & Industrial Complex () diagnostic urban wind solver to improve the characterization of upstream wind veer and shear in the Atmospheric Boundary Layer (ABL). The new formulation is based on a coupled set of Ordinary Differential Equations (ODEs) derived from the Reynolds Averaged Navier–Stokes (RANS) equations, and is fast to compute. Building upon recent progress in modeling the idealized ABL, we include effects from surface roughness, turbulent stress, Coriolis force, buoyancy and baroclinicity. We verify the performance of the new scheme with canonical Large Eddy Simulation (LES) tests with the GPU-accelerated FastEddy"Equation missing" solver in neutral, stable, unstable and baroclinic conditions with different surface roughness. Furthermore, we evaluate QUIC calculations with and without the new inflow scheme with real data from the Urban Threat Dispersion (UTD) field experiment, which includes Lidar-based wind measurements as well as concentration observations from multiple outdoor releases of a non-reactive tracer in downtown New York City. Compared to previous inflow capabilities that were limited to a constant wind direction with height, we show that the new scheme can model wind veer in the ABL and enhance the prediction of the surface cross-isobaric angle, improving evaluation statistics of simulated concentrations paired in time and space with UTD measurements.

Enhanced heat transfer study of microchannel heat sink with periodically arranged triangular cavities and arc‐shaped ribs

AbstractThe microchannel heat sink with periodically arranged triangular cavities and arc‐shaped ribs (MC‐ARTC) is investigated numerically under the conditions of Reynolds number 147–736. The effects of triangular cavities and arc‐shaped ribs on velocity, pressure, and temperature distribution in the channel are analyzed in comparison with a rectangular microchannel heat sink, microchannel heat sink with arc‐shaped ribs, and microchannel heat sink with triangular cavities. The results show that the triangular cavity and the arc‐shaped rib have important effects on the flow and heat transfer characteristics in the microchannel heat sink. Both rib and cavity can cause a change in fluid flow direction and disturb the development of the flow boundary layer. The fluid flow and heat transfer characteristics of microchannels are improved. Among the four microchannels, the MC‐ARTC has the optimum comprehensive performance for the combined effect of the rib and cavity. Relative cavity width () and relative rib height () are also defined to study the effects of cavity width ( = 89–200 μm) and rib height ( = 8.9–28.9 μm) on the flow and heat transfer characteristics. It is found that the heat transfer of MC‐ARTC is enhanced with increasing and , while lead to higher pressure drop. When and are 252 and 249 μm, respectively, the comprehensive performance factor () of MC‐ARTC reaches 1.76.

Dielectric barrier discharge actuators: Momentum injection into co-flow and counter-flow freestream

In a quiescent environment, dielectric barrier discharge (DBD) plasma actuators generate a wall jet through the interaction of ionized and neutral molecules in an electric field. In external flow, the coupling between electrohydrodynamic (EHD), turbulence, inertial, and viscous effects in the flow boundary layer is more complex and requires additional investigation. We experimentally study momentum injection by DBD actuators into the free stream flow with Re = 35,000 and 75,000 in co-flow and counter-flow scenarios over a range of VAC = 12 kV–19.5 kV peak-to-peak at a frequency of 2 kHz. In co-flow, the momentum injection leads to boundary layer thinning and fluid entrainment from the freestream into the DBD forcing region, while in the counter-flow configuration, flow separation can occur. A separation bubble is observed at Re = 35,000 for the tested condition. The momentum difference in the counter-flow configuration is six times greater than the EHD jet momentum in a quiescent environment. Both co-flow and counter-flow momentum injections show diminishing effects with higher Re. We show that the resulting flow pattern is not a superposition of the EHD jet and the free stream but is determined by the coupling and competition of inertial, viscous, and Coulombic effects between the EHD-driven forcing and the external flow. The proposed non-dimensional momentum ratio (M*) of EHD jet momentum to momentum in the external flow boundary layer can be used to predict the onset of separation; however, additional experimental and numerical studies are required to generalize this concept to other flow scenarios. The velocity profiles and momentum measurements presented here can be used to validate numerical models and inform the design of DBD actuators for active flow control.

Evaluation of Streamline on Aerofoil with Suction Hole in Wind Tunnel

This study looks into the impact of pressure suction holes in the NACA 0012 airfoil on aerodynamic performance. The goal is to use wind tunnel tests to compute the lift and drag forces for the NACA 0012 airfoil with suction holes at various air speeds and angles of attack. The relationship between air speed, angle of attack, drag coefficient, and lift coefficient will be determined by analysing the obtained data. The goal of the research is to better understand the flow patterns and variations in streamlines of the NACA 0012 airfoil at different velocity and attack angles. The test model will use the NACA 0012 airfoil, which is recognised for its symmetrical shape. Suction holes, varying from one to four, will be installed to provide insight into the influence of pressure suction on the boundary layer and streamline behaviour of the airfoil. The study will be carried out in a low-speed wind tunnel within the Fluid Mechanics laboratory, with the streamlines visualised using a smoke generator. This study is significant because it contributes to our understanding of flow characteristics, pressure distributions, and boundary layer control in aerodynamic design. It also provides excellent exposure to wind tunnel testing procedures, aviation industry practises, and continuing airfoil design research. This study adds to the body of knowledge on optimising airfoil performance by evaluating the effect of pressure suction holes on the NACA 0012 airfoil. The findings will be useful to researchers, aerodynamic enthusiasts, and aviation experts, allowing them to further investigate the potential benefits of pressure suction techniques in improving airfoil efficiency and performance.

Wall-modeled large eddy simulation in the immersed boundary-lattice Boltzmann method

This work presents the wall-modeled large eddy simulation (WMLES) in the immersed boundary-lattice Boltzmann method (IB-LBM). Here, the wall model with both diffusive- and sharp-interface immersed boundary methods (IBMs) is incorporated into the IB-LBM to handle the turbulent boundary layer in high Reynolds number turbulent flows. To maintain the numerical stability, two collision models, i.e., multiple-relaxation-time (MRT) and recursive regularized (RR), are implemented. The performance of these models in the WMLES is examined and compared in the simulation of internal and external flows by considering four benchmarks, i.e., turbulent flow in a channel, flow around a hull of submarine, flow around an Ahmed car model, and flow around a circular cylinder. It is found that a diffusive-interface IBM with wall model is capable to achieve excellent results for the simulation of external flows around bluff objects but fails in the simulation of internal flows of underestimating the wall shear stress due to its extra dissipation. The sharp-interface IBM with the wall model predicts the internal flow very well but fails in some simulations of external flow around bluff bodies due to the failure in the separation flow modeling. It is also found that the MRT-LBM is less dissipative than the RR-LBM, but it generates spurious nonphysical noise in the turbulent flows and tends to be unstable at high Reynolds numbers. Therefore, the diffusive-interface IBM with the wall model is more suitable for the external turbulent flow modeling, while its sharp-interface counterpart is more suitable for the internal turbulent flow modeling. The RR-LBM outperforms the MRT-LBM for the better stability and less nonphysical noise.

Multi‐Platform Observations of Severe Typhoon Koinu

AbstractSevere Typhoon Koinu passed south of Hong Kong on 8 and 9 October 2023, triggering the issuance of the Increasing Gale or Storm Signal No. 9, the second highest tropical cyclone (TC) warning signal in Hong Kong. Koinu was a difficult case for TC warning service due to its compact size and rather erratic movement over the coastal waters of Guangdong. To monitor Koinu's movement and wind structure, the Hong Kong Observatory utilized various observational platforms, including meteorological aircraft, ocean radar, and synthetic aperture radar on polar orbiting satellites. The paper presents major observations derived from these measurements. The aircraft probe and dropsonde data suggested boundary layer inflow, warm core structure, eyewall updraft, and high turbulence in the eyewall of the typhoon. The weather radar observations indicated the occurrence of a waterspout in the vicinity of the typhoon. Additionally, the study highlights the forecasting performance of the AI‐based Pangu‐Weather model, which could outperform the conventional global numerical weather prediction models in forecasting TC track in the region. The documentation of these observations aims to provide valuable references for weather forecasters and stimulate further research on forecasting this type of tropical cyclone.

Numerical investigation on flow and heat transfer of the rotating spherical particle in a supercritical water crossflow environment

The supercritical water gasification reactor provides a green and efficient method for the utilization of organic resources such as coal and biomass. It is important to note that collision-induced particle rotation in the reactor will affect the flow and heat transfer characteristics between the particles and the fluid. At present, there is a lacking consideration of particle rotation in the supercritical water environment. The purpose of this paper is to investigate the effects of dimensionless rotation rate (Ω∗) and particle Reynolds number (Rep) on drag coefficient (Cd), lift coefficient (Cl) and average Nusselt number (Nu) for the single particle in a supercritical water crossflow under two rotation modes, with rotation axes parallel and perpendicular to the jet direction. The flow field, temperature field, boundary layer, and surface pressure coefficient (Cp) were analyzed to interpret the variation of the particle dimensionless coefficients (Cd, Cl and Nu). It was found that the value of ∣Cp∣ on the particle surface rose at different locations for the two rotation modes, leading to an increase in the pressure drag and dominating the total drag force. However, the two rotation modes produced different deviating effects on the average Nusselt number. Ultimately, new correlation formulas of Cd, Cl and Nu for a rotating spherical particle in a supercritical water environment were proposed based on the results of numerical simulations, with a maximum deviation of 8.52%.

Ionizing Waves in Surface Dielectric Barrier Discharges Plasma Actuators

Plasma actuators have been proposed as a tool to produce hydrodynamical effects in the boundary layer of aerodynamical flows. We have analyzed some properties of these systems using suitable plasma diagnostics based on the emissivity characteristics of such plasmas. The direction and the velocity of propagation of the ionizing wave spreading on the dielectric surface were measured (in the 100–200 km/s range), and it was demonstrated that it behaves like a cathode-directed streamer. The averaged electron temperature (4–5 eV) and the reduced field strength (E/N ≈ 6 × 1019 V·m2) of the ionizing wave switching the discharges on were measured, too.

Island‐Induced Eyewall Replacement in a Landfalling Tropical Cyclone: A Model Study of Super Typhoon Mangkhut (2018)

AbstractAn unconventional, island‐induced eyewall replacement (IER) occurred in Super Typhoon Mangkhut (2018) when it crossed Luzon Island. Upon landfall, its original compact eyewall broke down and dissipated rapidly. As Mangkhut exited Luzon and entered the South China Sea, a much larger new eyewall formed at a radius of 150–200 km from the storm center, three times larger than the original one. Unlike the eyewall replacement cycle in intense tropical cyclones, the breakdown of the original eyewall preceded the formation of the new eyewall (NEF) in Mangkhut. This evolution was reproduced reasonably well in a control experiment using the Weather Research and Forecasting Model. Two sensitivity experiments showed that the IER was triggered by Luzon Island, whose terrain is essential for not only the destruction of the original eyewall but also the NEF. In an axisymmetric framework, it is demonstrated for the first time that the NEF was preceded by the following processes: (a) an increase in the outward‐directed agradient force in the boundary layer (BL) inflow region after landfall due to differential rates of weakening between the radial pressure gradient and the tangential wind, (b) creation of a BL deceleration zone, (c) localized reinforcement of BL inflow deceleration within the NEF region when Mangkhut re‐entered the ocean, following an exisiting framework of an unbalanced dynamical pathway, and (d) strengthening of the BL convergence and uplift which initiated and sustained the deep convection of the new eyewall.