Bottom Boundary Layer Research Articles

Bubble characteristics affecting air-water exchange in open-channel flow with a jet forming over a sudden bottom drop

Entrainment of air bubbles into flowing water increases significantly the interfacial area between the two phases hence enhancing the air-water mass transfer. The air bubble characteristics are thus of direct relevance to the waterbody aeration and oxygenation, which should be understood in the context of bubbly-flow turbulence development. In this paper, we studied experimentally a canonical aerated flow featured by a two-dimensional jet over a sudden bottom drop followed by a sloping open-channel flow. This is a representative scenario of open-channel flow with simultaneous free-surface air-water exchange and bottom aeration into the deep water. In addition to the air concentration and air flux evolutions upstream and downstream of the jet impact on the channel bed as well as from bottom to the free-surface, the local and accumulative bubble count rate distributions were depicted. The air-water flow structures were revealed at bubble scales with the aid of a further characterisation of the bubble chord length spectrum and mean bubble size distributions, indicating intense bubble breakups following the jet impact and next to the bottom boundary layer. Although the jet impact on the dry bottom was responsible for a substantial air loss, an increasing number of smaller bubbles were produced and prevented drastic drop in the air-water interfacial area. The mean bubble size and specific interfacial area were predicted under some rough assumption for the deep-water mass transfer. An insight into the bubble-turbulence interplay was presented based on a statistic bubble clustering analysis.

A Regional, Early Spring Bloom of Phaeocystis pouchetii on the New England Continental Shelf

AbstractThe genus Phaeocystis is distributed globally and has considerable ecological, biogeochemical, and societal impacts. Understanding its distribution, growth and ecological impacts has been limited by lack of extensive observations on appropriate scales. In 2018, we investigated the biological dynamics of the New England continental shelf and encountered a substantial bloom of Phaeocystis pouchetii. Based on satellite imagery during January through April, the bloom extended over broad expanses of the shelf; furthermore, our observations demonstrated that it reached high biomass levels, with maximum chlorophyll concentrations exceeding 16 µg L−1 and particulate organic carbon levels > 95 µmol L−1. Initially, the bloom was largely confined to waters with temperatures <6°C, which in turn were mostly restricted to shallow areas near the coast. As the bloom progressed, it appeared to sink into the bottom boundary layer; however, enough light and nutrients were available for growth. The bloom was highly productive (net community production integrated through the mixed layer from stations within the bloom averaged 1.16 g C m−2 d−1) and reduced nutrient concentrations considerably. Long‐term coastal observations suggest that Phaeocystis blooms occur sporadically in spring on Nantucket Shoals and presumably expand onto the continental shelf. Based on the distribution of Phaeocystis during our study, we suggest that it can have a significant impact on the overall productivity and ecology of the New England shelf during the winter/spring transition.

Cohesive Sediment Erosion in a Combined Wave‐Current Boundary Layer

AbstractWe conducted field work on the shoals of South San Francisco Bay to elucidate the mechanisms driving cohesive sediment erosion in a shallow, wave‐ and current‐driven flow. Compiling data from three deployments, including measurements taken within the combined wave‐current boundary layer, we found that wave shear stress was strongly correlated to turbulent sediment fluxes across all seasons and a range of deployment depths. Tidal turbulence was only correlated to turbulent sediment fluxes for larger relative depths, or when a wave‐driven sediment flux in the bottom boundary layer allowed the tidal shear stress to transport sediment into the overlying flow. Despite the dominance of waves in eroding sediment, we found favorable agreement between in situ boundary layer erosion measurements and laboratory erosion measurements conducted in a steady flume. Results were analyzed in the context of two benthic surveys which provided insight into the sediment bed properties.

A Two‐Layer Turbulence‐Based Model to Predict Suspended Sediment Concentration in Flows With Aquatic Vegetation

AbstractTraditional bed shear stress‐based models (e.g., Rouse model) derived from the classic parabolic profile of eddy viscosity in open‐channel flows fail to accurately predict suspended sediment concentration (SSC) in flows with aquatic vegetation. We developed a two‐layer, turbulence‐based model to predict SSC profiles in emergent vegetated flows. Turbulence generated from vegetation, bed, and coherent structures caused by stem‐bed‐flow interaction are considered into the near‐bed turbulent kinetic energy (TKE) to calculate the effective bed shear velocity, . The model, validated by experimental data, further showed that the thickness height of the near‐bed layer (effective bottom boundary layer), Hb, varies with flow velocity and canopy density. Two additional models are provided to estimate Hb and . The model is expected to provide critical information to future studies on sediment transport, landscape evolution, and water quality management in vegetated streams, wetlands, and estuaries.

Seasonal Variability in Near-bed Environmental Conditions in the Vazella pourtalesii Glass Sponge Grounds of the Scotian Shelf

The Scotian Shelf harbors unique aggregations of the glass sponge Vazella pourtalesii that provides an important habitat for benthic and pelagic fauna. Recent studies have shown that these sponge grounds have persisted in the face of strong inter-annual and multi-decadal variability in temperature and salinity. However, little is known of these environmental characteristics on hourly-seasonal time scales. This study presents the first hydrodynamic observations and associated (food) particle supply mechanisms for the Vazella sponge grounds, highlighting the influence of natural variability in environmental conditions on sponge growth and resilience. Near-bottom environmental conditions were characterized by high temporal resolution data collected with a benthic lander, deployed during a period of 10 months in the Sambro Bank Sponge Conservation Area. The lander was equipped with temperature and oxygen sensors, a current meter, a sediment trap and a video camera. In addition, water column profiles of temperature and salinity were collected in an array across the sponge grounds from high to lower sponge presence probability. Over the course of the lander deployment, temperature fluctuated between 8.8–12°C with an average of 10.6 ± 0.4°C. Dissolved oxygen concentration was on average 6.3 mg l–1, and near-bottom current speed was on average 0.12 m s–1, with peaks up to 0.47 m s–1. Semi-diurnal tidal currents promoted constant resuspension of particulate matter in the benthic boundary layer. Surface storm events episodically caused extremely turbid conditions on the seafloor that persisted for several days, with particles being resuspended to more than 13 m above the seabed. The carbon flux in the near-bottom sediment trap peaked during storm events and also after a spring bloom in April, when fresh phytodetritus was observed in the bottom boundary layer. While resuspension events can represent a major stressor for sponges, limiting their filtration capability and remobilizing them, episodes of strong currents and lateral particle transport likely play an important role in food supply and the replenishment of nutrients and oxygen. Our results contextualize human-induced threats such as bottom fishing and climate change by providing more knowledge of the natural environmental conditions under which sponge grounds persist.

Flow around a surface-mounted finite circular cylinder completely submerged within the bottom boundary layer

This paper presents a detailed investigation on the flow characteristics and the bed-shear-stress distribution around a finite circular cylinder at a fixed Reynolds number (Re= 2 ×104) and seven aspect ratios (AR= 0.5∼6) by solving the Reynolds Averaged Navier–Stokes (RANS) equations. It is found that, for a moderate Reynolds number and a relatively large boundary-layer thickness, the time-averaged streamwise vortex structure will be transformed from the ‘Dipole Type’ at AR≤3 to the ‘Three-Pairs Type’ at AR≥4. It is the first time that the ‘Three-Pairs Type’ vortex structure has been reported, which consists of Time-Mean Streamwise Tip Vortices, Time-Mean Streamwise Base Vortices and Time-Mean Streamwise Bottom Vortices. Besides, this study indicates that, with increasing AR, the maximum time-averaged bed-shear-stress amplification magnitude upstream of the cylinder will first decrease and then increase, with the minimum occurring at approximately AR= 3.0, due to the influence of AR on the horseshoe vortices. Additionally, this study manifests that different critical AR values can be obtained for various flow variables. For instance, in terms of the total lift coefficient of the cylinder and the transverse fluctuating velocity in the symmetry plane at the mid-height of the cylinder, the critical AR is equal to ARc=3.0 and ARc=2.0, respectively.

Using Tracer Variance Decay to Quantify Variability of Salinity Mixing in the Hudson River Estuary

AbstractThe salinity structure in an estuary is controlled by time‐dependent mixing processes. However, the locations and temporal variability of where significant mixing occurs is not well‐understood. Here we utilize a tracer variance approach to demonstrate the spatial and temporal structure of salinity mixing in the Hudson River Estuary. We run a 4‐month hydrodynamic simulation of the tides, currents, and salinity that captures the spring‐neap tidal variability as well as wind‐driven and freshwater flow events. On a spring‐neap time scale, salinity variance dissipation (mixing) occurs predominantly during the transition from neap to spring tides. On a tidal time scale, 60% of the salinity variance dissipation occurs during ebb tides and 40% during flood tides. Spatially, mixing during ebbs occurs primarily where lateral bottom salinity fronts intersect the bed at the transition from the main channel to adjacent shoals. During ebbs, these lateral fronts form seaward of constrictions located at multiple locations along the estuary. During floods, mixing is generated by a shear layer elevated in the water column at the top of the mixed bottom boundary layer, where variations in the along channel density gradients locally enhance the baroclinic pressure gradient leading to stronger vertical shear and more mixing. For both ebb and flood, the mixing occurs at the location of overlap of strong vertical stratification and eddy diffusivity, not at the maximum of either of those quantities. This understanding lends a new insight to the spatial and time dependence of the estuarine salinity structure.

Hydrodynamics and sediment dynamics in Barataria Bay, Louisiana, USA

Barataria Bay is a receiving basin for a large Mid-Barataria Sediment Diversion scheme in Louisiana, USA. In this region, data on sediment transport and hydrodynamics are scarce but essential for the design and planning of future sediment diversion and marsh creation. Four months of bottom boundary layer observations were conducted to study winter and spring hydrodynamics and sediment dynamics in this coastal bay. Hourly waves, tides, currents, and bottom suspended sediment concentrations were measured using multiple optical and acoustic sensors attached to two tripod platforms. High temporal resolution data indicated that the salinity in the northern bay was mainly controlled by northerly winds, and tidal currents kept the salinity high in the southern bay during the winter cold front season. In spring, frequent, pervasive southerly winds and the westward shelf transport of less saline water emerging from the Mississippi River Delta lowered the salinity in the southern bay. Spectral analysis showed that wave-current combined shear stress played the most critical role in triggering sediment resuspension. The Style-Glenn 1-D bottom boundary layer model was applied in sediment flux calculations, and showed that net sediment transport mainly occurred during cold front passages. During two 3-day cold-front events, southward sediment fluxes accounted for 56% of the total sediment flux during the 35-day winter period, revealing their nonlinear, event-driven, and episodic nature. The direction of the sediment transport generally rotated, and its magnitude changed considerably, when southeasterly winds shifted to intensified northwesterly winds. Long-duration southerly pre-frontal winds facilitated wetland sedimentation by transporting sediment to the northern bay during high water level conditions impacted by flooding spring tides or southerly winds. Conversely, northerly winds during cold fronts dominated bidirectional tidal currents and led to southward net sediment transport and possible escape of sediment from the bay. The timing of diversion openings, the orientation of receiving basins, and dominant wind directions in relation to fetch, as well as the dynamic water levels should be considered in the planning and management of future diversion operations in coastal areas.

Direct Numerical Simulations of the Pulsating Flow over a Plane Wall

The results of direct numerical simulations of the flow generated in a plane duct by a pressure gradient which is the sum of two terms are described. The first term of the pressure gradient is constant in space but it oscillates in time whereas the second term is constant both in space and in time. Therefore, a pulsating flow is generated, similar to that generated at the bottom of a monochromatic propagating surface wave when nonlinear effects are taken into account. The simulations are carried out for values of the parameters similar to those considered in previous investigations. It is shown that even a small constant pressure gradient influences the flow regime in the bottom boundary layer. In particular, turbulence strength is damped when the steady velocity component has the direction opposite to the oscillating velocity component whereas turbulence strength increases when the steady and oscillating components point in the same direction. Even though the flow is not exactly equal to that generated at the bottom of sea waves, where second order effects in the wave steepness induce a steady streaming in the direction of wave propagation, our results provide information on the interaction of the steady streaming with the oscillatory flow and are also relevant for investigating the dynamics of sediment close to the sea bottom. Indeed, since the turbulent eddies tend to pick-up the sediment from the bottom, it can be inferred that the triggering of turbulence enhances sediment transport towards the shore.

Predicting mean velocity profiles inside urban canyons

Knowledge of mean wind profiles is important for applications in wind engineering and air quality modeling. Yet despite advances in our ability to simulate winds on street scales, existing theoretical predictions do not apply to the important limit of tall, closely packed buildings or generalize to realistic geometries. We present an alternative strategy based on the existence of intense layers of vorticity at solid boundaries and the roof level. Following the approach in vortex dynamics, wherein the velocity field is modelled by approximating the vorticity field, spatially and temporally averaged vertical profiles of the horizontal velocity components are derived from the numerical Green's functions for the three-dimensional Poisson equation and vortex sheets located at the top and bottom of an urban canyon; mean profiles of the spanwise velocity along the canyon axis are obtained similarly. The method is applied to skimming flow for idealised and realistic canyons and tested against building-resolving simulations. Good agreement is obtained for a wide range of external wind directions, including winds that are parallel to the canyon axis. For a unit-aspect-ratio street canyon, the relative error in the streamwise velocity is 30−50% over the entire canyon, but 10−20% when the top and bottom boundary layers are excluded; the errors in the spanwise velocity are smaller. It is shown that the model can be successfully calibrated from single-point measurements taken above the urban canopy.

Diapycnal Transport near a Sloping Bottom Boundary

AbstractThe diapycnal motion in the stratified ocean near a sloping bottom boundary is studied using analytical solutions from one-dimensional boundary layer theory. Bottom-intensification of the diapycnal mixing intensity ensures that in the stratified mixing layer (SML), where isopycnals are relatively flat, the diapycnal motion is downward toward denser fluid. In contrast, convergence of the diffusive buoyancy flux near the seafloor drives diapycnal upwelling in what we define as the bottom boundary layer (BBL). Much of the one-dimensional BBL is characterized by a stratification only slightly reduced from that in the SML because the maximum in the buoyancy flux at the top of the BBL, where the diapycnal velocity changes sign, must occur in well-stratified fluid. The diapycnal upwelling in the BBL is determined by variations not only in the magnitude of the buoyancy gradient but also in the curvature of isopycnals. The net diapycnal upwelling is concentrated in the bottom half of the BBL where the magnitude of the buoyancy gradient changes most rapidly. The curvature effect drives upwelling near the seafloor that only makes a significant contribution to the net upwelling for steep slopes. The structure of the diapycnal velocity in this stratified BBL differs from the case of a turbulent well-mixed BBL that has been assumed in some recent theoretical studies on bottom-intensified mixing. This work therefore extends recent theories in a way that should be more applicable to abyssal ocean observations where well-mixed BBLs are not common.

Sources and scales of near-bottom turbulent mixing in large meromictic Lake Iseo

Mixing dynamics in the bottom boundary layer (BBL) of lakes is of primary importance for mediating mass and heat fluxes across the upper sediment. In lakes with depth of several hundred meters, the BBL mixing is often suggested to be low; however, quantitative information from these depths is extremely rare. We assessed the mixing conditions in the BBL of Lake Iseo, a 256 m deep, meromictic Italian lake, where anoxia and accumulation of phosphorus is a major issue. High-resolution temperature and currents measurements demonstrated regular development of turbulence at 220 m depth, with dissipation rates of the turbulent kinetic energy up to 10−7 W kg−1, characteristic of a shear boundary layer. Analysis of temperature and oxygen dynamics revealed a direct link between the turbulence intensification in the BBL and the passage of a 90-h period basin-scale internal wave. This slow oscillatory motion was attributed to lake-wide internal waves of second vertical mode, whose effect in the upper part of the water column was much less profound. The wave passages were able to increase hypolimnetic velocities above 1 cm s−1, to produce thermal instability across the BBL and to significantly enhance turbulent mixing in the deepest waters. During periods of high velocity bursts, the chemical stratification in the BBL was effectively eroded while direct sediment resuspension was unlikely. The new results reveal the turbulent character of the bottom boundary mixing in deep lakes, highlighting the direct link to wind-driven motions and important effects on the water–sediment exchange of solutes.

Heat transfer enhancement of wall with a near wall cylinder in a channel at low and middle Reynolds number ranges

This paper investigated the flow performance around a near-wall cylinder and its effect on heat transfer enhancement in the laminar and early transitional flow region. The numerical model is resolved by finite volume method through FORTRAN code. The results show that the flow field becomes a transitional flow state when Re = 100 due to the insertion of a cylinder. In the transitional flow sate, the heat transfer enhancement is regional, mainly concentrating in the region of –2 ≤ x/D≤ 10, and the region increases with the increase of Re; There are three or four peaks in the distribution of instantaneous local Nusselt number. The first peak is caused by the acceleration of the fluid between the cylinder and the bottom wall. The other peaks are caused by the interaction between the cylinder wake and the bottom wall boundary layer. The vortical structure induced by the periodic instability of the fluid in the transitional flow is the main factor for explaining the local heat transfer enhancement of the cylinder downstream wall. Re has a direct impact on the vortical structure in the flow field. The greater Re, the greater the heat transfer enhancement of the cylinder downstream wall. Under the same blocking ratio of D/H, the greater Re, the smaller the optimal clearance ratio of C/D. The guidelines are suggested for the design on heat dissipation of electronic equipment.

Numerical Study of Swash Driven by a Breaking Wave Over a Permeable Sandy Beach

We present a new methodology that is able to resolve wavefield and bottom boundary layer processes throughout the water column over a permeable beach. An Eulerian two-phase model for sediment phase, SedFoam, and a surface wave solver, InterFoam/olaFlow, are integrated in the OpenFOAM framework. The new model, called SedWaveFoam, is validated with two laboratory datasets for swash driven by a plunging solitary wave over a permeable and immobile sandy beach. Results demonstrate that surface elevation and depth-averaged velocity are well predicted during uprush. To better match the model results with the measured data during backwash, sand beds with different porosities are tested. It is suggested that significant vertical pore pressure gradient can be induced due to infiltration and exfiltration processes that affects stabilizing force of sand particles.

Self-sustained instability, transition, and turbulence induced by a long separation bubble in the footprint of an internal solitary wave. I. Flow topology

Using a high-accuracy-and-resolution implicit Large Eddy Simulation we study the development of the bottom boundary layer (BBL) driven by the long separation bubble which forms under an internal solitary wave (ISW) of depression propagating against a barotropic background current. We obtain insights on the structure of the initial instability in the form of a global mode with a distinct transverse structure, and that of the self-sustained transition and resulting fully developed turbulence along the bed. Comparisons are made to similar flow features previously found in shorter separation bubbles typical of applications in aerodynamics.

An analysis of the stabilization of fire whirls

Stabilization of the flame base at the bottom Ekman boundary layer of the fire whirl under strong circulation is analytically and numerically studied. The problem is relevant for fire safety and the associated understanding of the generation mechanism of the newly discovered whirling flame, the so-called blue whirl. Based on the dynamic balance of the triple flame propagation speed and the local flow velocity at the bottom boundary layer, theoretical solutions of the liftoff position, rf, and the critical blowout limit represented by its Ekman number, EkBt, are derived. The theoretical results agree well with the numerical results both qualitatively and quantitatively. It is shown that the response of rf to the system Damköhler number, Da, forms a typical C-shaped curve and there are two solutions of rf for relatively large Da, with the one closer to the edge of the fuel pool being stable while the other being unstable. Explicit solution of the blowout limit shows that EkBt∝(SLS)4/3, where SLS is the stoichiometric planar flame speed. This is because not only the triple flame propagation speed linearly increases as SLS increases, but the flame front can also reach a position closer to the edge of the fuel pool where the flow velocity is lower. The effect of the transversal radial velocity gradient (TVG) at the Ekman boundary layer on the stabilization of the fire whirl is also investigated. The TVG makes the flame harder to liftoff and blowout and the effect of which can be described by a non-dimensional parameter, λ, which represents the ratio of the flame curvature and the TVG. The TVG normally plays a secondary role in the triple flame propagation due to the relatively large flame curvature of the triple flame.

Stabilized RANS simulation of surf zone kinematics and boundary layer processes beneath large-scale plunging waves over a breaker bar

This paper presents numerical simulations of a bichromatic wave group propagating and breaking over a fixed breaker bar. The simulations are performed using a newly stabilized Reynolds-averaged Navier–Stokes (RANS) two-equation turbulence closure, which solves the longstanding problem of over-production of turbulence beneath surface waves in the nearly potential flow region prior to breaking. This model has previously been tested on small-scale spilling breaking regular waves, whereas in this work focus is on full (rather than model) scale application, wave groups (rather than regular waves) and plunging (rather than spilling) breakers. Additionally this paper has novel emphasis on bottom boundary layer dynamics which are very important for cross-shore sediment transport predictions. The model is validated by comparing with results from a previous experimental campaign. The model is shown to predict the surface elevations, velocities and turbulence well in the shoaling and outer surf-zone, avoiding turbulence over-production and incorrect undertow structure typical of standard turbulence closures. Comparison with detailed boundary layer measurements in the shoaling position reveals that the model is able to accurately capture the temporal dynamics of the entire wave boundary layer, including evolution of the boundary layer thickness, velocity overshoot and phase-shifts. Comparison in the surf zone additionally reveals that the model is able to accurately capture the transport of breaking-induced turbulence into the wave boundary layer. The performance of the model indicates that it can be used directly in the simulation of cross-shore sediment transport and morphology and also be used to study important hydrodynamic processes, which can help improve the predictive skill of morphodynamic profile models applied in coastal engineering.

Comparison of Turbulence Models in the Turbulent Wave Boundary Layer for Cnoidal Waves

Turbulent structures in the bottom boundary layer beneath the wave motion have an important role in the nearshore sediment transport modeling and its analyses. Cnoidal waves can be used as a representative of asymmetry waves in the ocean. This paper is aimed to observe the structure of turbulent boundary layer under cnoidal waves as a representative of asymmetry waves in which the effect of asymmetric is actualized along wave cycle related with the wave asymmetric parameter, Ni. The turbulent boundary layer characteristics beneath cnoidal waves motion (i.e. mean velocity and turbulent intensity) are given in the results of experimental results and turbulent numerical models (i.e. the k-ε, the k-ω, the BSL k-ω and the SST k-ω model). Turbulent properties prediction of cnoidal waves from each turbulence model is compared among them and that of experimental results. A laser Doppler velocimeter (LDV) is used to measure the profiles of velocity distribution in the tunnel of oscillating wind over rough bed beneath cnoidal waves motion. From the comparison of the average velocity distribution between all the models of turbulence and the results of experimental for the cases of cnoidal waves in general, it has been obtained that the model of BSL k-ω is superior to predict which is followed by the model of k-ε, the model of k-ω and the model of SST k-ω.

Large Eddy Simulation of Near-Bed Flow and Turbulence over Roughness Elements in the Shallow Open-Channel

Turbulent flows in rough open-channels have complex structures near the channel-bed. The near-bed flow can cause bed erosion, channel instability, and damages to fish habitats. This paper aims to improve our understanding of the structures. Transverse square bars placed at the channel-bed form two-dimensional roughness elements. Turbulent flows over the bars are predicted using large eddy simulation (LES). The predicted flow quantities compare well with experimental data. The LES model predicts mean-flow velocity profiles that resemble those in the classic turbulent boundary layer over a flat plate and profiles that change patterns in the vicinity of roughness elements, depending on the pitch-to-roughness height ratio λ/k. The relative turbulence intensity and normalized Reynolds shear stress reach maxima of 15% and 1.2%, respectively, at λ/k = 8, compared to 9% and 0.2% at λ/k = 2. The predicted bottom boundary layers constitute a large portion of the total depth, indicating roughness effect on the flow throughout the water column. Fluid exchange between the roughness cavity and outer region occurs due to turbulence fluctuations. The fluctuations increase in intensity with increasing λ/k ratio. This ratio dictates the number of eddies in the cavity as well as their locations and shapes. It also controls turbulence stress distributions. LES can be used to explore strategies for erosion control, channel restoration, and habitat protection.

Direct Numerical Simulation of the Pulsed Arc Discharge in Supersonic Compression Ramp Flow

Direct numerical simulation (DNS) of shock wave/turbulent boundary layer interaction (SWTBLI) with pulsed arc discharge is carried out in this paper. The subject in the study is a Ma=2.9 compression flow over a 24-degree ramp. The numerical approaches were validated by the experimental results in the same flow conditions. The heat source model was added to the Navier-Stokes equation to serve as the energy deposition of the pulsed arc discharge. Four streamwise locations are selected to apply energy deposition. The effect of the pulsed arc discharge on the ramp-induced flow separation has been studied in depth. The DNS results demonstrate the incentive locations play a dominant role in suppressing the separated flow. Results show that pulsed heating is characterized by a thermal blockage, which leads to streamwise deflection. The incentive locations upstream the interaction zone of the base flow have a better control effect. The separation bubble shape shows as “spikes”, and the downstream flow of the heated region is accelerated due to the momentum exchange between the upper boundary layer and the bottom boundary layer. The high-speed upper fluid is transferred to the bottom, and thus enhances its ability to resist the flow separation. More stripe vortex structures are also generated at the edge of the flat-plate. Furthermore, the turbulent kinetic disturbance energy is increased in the flow filed. The disturbances that originate from the pulsed heating are capable of increasing the turbulent intensity and then diminishing the trend of flow separation.