Enhanced Turbulence Intensity Research Articles

Exploration of heat transfer and entropy generation in an irregular wall cavity filled with Al2O3-water nanofluid

This study investigates 2-D natural convection heat transfer within an irregular wall cavity filled with nanofluid, employing a computational approach. The rough profile of the cavity surface is generated using the Weierstrass-Mandelbrot (W-M) function, and various parameters such as Rayleigh number ( 10 3 ≤ Ra ≤ 10 6 ), Knudsen number ( 0 ≤ Kn ≤ 1.5 ), solid volume fraction ( 0 ≤ ϕ ≤ 0.15 ), and amplitude of the irregular rough wall ( 0 ≤ A 1 ≤ 0.1 ) are varied. The nanofluid consists of water as the base fluid and aluminum oxide (Al2O3) nanoparticles. Heat transfer characteristics are analyzed using the Nusselt number (Nu), while entropy generation is quantified to optimize thermal system efficiency. Grid sensitivity analysis and validation against existing literature are conducted to ensure the accuracy of the numerical methodology. Notably, the study demonstrates that increasing the slip velocity at the cavity wall enhances convection within the cavity, leading to a substantial increase in Nu. At Ra = 106, the Nu increases by 53.52% when Kn changes from 0 to 1. Furthermore, the study highlights the significant influence of nanoparticle volume fraction on Nu, showing that as the volume fraction increases, Nu also increases, indicating improved convective heat transfer performance. The Nu for a cavity with an amplitude of 0.1 is roughly 2.5 times higher compared to a smooth-walled cavity at Ra = 106. Increased surface irregularity enhanced turbulence intensity and mixing, leading to stronger convective currents. The novelty of this study lies in examining natural convection in irregular shaped cavities with wall-slip conditions, which are common in practical applications such as solar collectors, microelectronic devices, energy storage units, industrial furnaces, etc. This study offers valuable insights into the thermal behavior of rough enclosures filled with nanofluids, which will facilitate the optimization of heat transfer systems to minimize energy losses.

Study on Additive Effect of Film Cooling Effectiveness in Two Rows of Fan-Shaped Holes

Abstract The coolant jet interaction has a great influence on the superposition prediction of multirow film cooling. Although there have been many efforts to reveal the mechanics of additive effect in multirow film cooling, the available knowledge about developing the superposition method is still limited. The present work examines the film cooling effectiveness in two rows of fan-shaped holes by pressure sensitive paint technique, at the blowing ratios of 0.5–2.0 and the density ratio of 1.0. It is found that the impact of upstream flow on the downstream cooling film is reflected in the variation of turbulence intensity. The enhanced turbulence intensity is detrimental to the downstream film cooling effectiveness especially at the far away region. The mixing of upstream flow and coolant ejection starts at the leading edge of the hole exit. Thus, the streamwise width of the hole exit should be taken into consideration for better predicting the film cooling effectiveness around the holes. The cause of additive effect is that the coolant ejection at the second row affects the local mainstream entrainment. Then, a new correction factor, which characterizes the influence of coolant ejection on the mainstream entrainment of the upper row, is proposed for improving the classical Sellers method. The final result shows a good agreement with experimental data.

Influence of Upstream Sweeping Wake Number on the Unsteady Flow Mechanism in an Integrated Aggressive Intermediate Turbine Duct

This paper focuses on the dynamic internal flow in the integrated aggressive intermediate turbine duct (AITD) with different HPT wake numbers, using CFX Solver with dynamic Reynolds-averaged Navier–Stokes equations (RANS), the shear stress transmission κ-ω turbulence model (SST) and the γ-θ transition model. The HPT wakes are simulated using sweeping rods, with the number of rods ranging from 14 to 56 and a reduced frequency of 1.07. The increasing wake number reduces the radial pressure gradient in the integrated AITD, and then decelerates the radial migration and dissipation of wake vortices, so that some residual wakes can reach the integrated low-pressure turbine guide vane (LPT-GV) to enhance the suppression of flow separation to a certain extent. On the other hand, the increase in wake number can also weaken the skewness and stretching of the wake, thereby increasing the duration of flow separation suppression. When there are too many wakes, the mixing between adjacent wakes accelerates the dispersion of wake vortices, leading to increased total pressure loss and an enhanced turbulence intensity. This enhanced turbulence intensity promotes bypass transition on the suction surface of the LPT-GV in advance, thereby completely eliminating flow separation on the LPT-GV in the entire spatiotemporal domain, which is beneficial for reducing separation loss, but also increasing turbulent viscous loss. When N ≤ 28, the gross loss of the integrated AITD studied in this paper reaches a minimum value (around 0.22), as the benefits brought by the wake suppression of flow separation can offset the wake dissipation loss and the turbulent viscous loss caused by the wake-induced transition. Considering that wake loss is inherently present, using sweeping wakes to inhibit the flow separation on the integrated LPT-GV can bring certain aerodynamic benefits when the wake number is less than 28.

Influence of Wake Sweeping Frequency on the Unsteady Flow Characteristics of an Integrated Aggressive Interturbine Duct

A dynamic simulation was launched to research the influence of high-pressure turbine (HPT) rotor wake passing frequency on the flow mechanism in an integrated aggressive interturbine duct (AITD). Sweeping rods were adopted to replace the HPT rotors to decouple the influence of its wake from those of other secondary flows. The diameter of the rods (d/s, nondimensionalized by the pitch (s) of the integrated struts at midspan) was 0.10, and their reduced frequency (f) ranged from 0.49 to 1.61. The k–ω SST turbulence model and γ–θ transition model were adopted for the turbulence closure. A 6.3-million-node structured grid was used to meet the grid dependency. Along with increasing f, the intensified circumferential motion of the wake (1) enhances the wake vortex stretching and exhaustion near the hub; (2) promotes the radial inclination of wakes and elongates and narrows the wake vortex band, resulting in increased spacing between the adjacent wake vortices and the weakened vortex interaction. In the high-f cases, the enhanced turbulence intensity in the interval between the adjacent wakes could suppress the separation bubble on LPT-GV in advance, but the elongated and narrowed wake vortices resulted in a substantial reduction in the radial extent and duration of their suppression on the separation bubble. Therefore, the influence of f on the integrated AITD and its parts was bidirectional, and adjusting the sweeping frequency to balance its positive and negative effects could minimize the total loss in the integrated AITD.

Evaluation on the flow characteristics of helium working fluid in generation Ⅳ nuclear power station

This paper investigates the fundamental flow behaviors of helium, aiming at supporting the helium turbomachinery design optimization in generation Ⅳ nuclear power station. The applicability of hydrodynamics theory to helium has been discussed from many aspects including continuous medium, Newtonian fluid, Stokes hypotheses, and perfect gas state. The Reynolds average N-S method (RANS) with the γ-θ transition model is used for solving the compressible helium boundary layer. The influence of the Reynolds number on the helium boundary layer transition is explored. With the increasing Reynolds number, the transition of boundary layer occurs in advance on the plate. On the other side, the boundary layers under different Reynolds numbers have uniformity in the comparison of dimensionless parameters. The free stream turbulence (FST) is a main influence factor on the transition. Both the enhanced turbulence intensity and the large turbulence scale can make the transition be triggered in advance and reduce the onset Reynolds number. For the fluids with different specific heat ratios, the helium transition lags behind the air under the same Mach number. When under the same Reynolds number, the helium boundary layer is identical to the air. They share the same mean velocity profile and agree with the theory solution and experimental data simultaneously.

Linear instability and resonance effects in large-scale opposition flow control

Opposition flow control is a robust strategy that has been proved effective in turbulent wall-bounded flows. Its conventional set-up consists of measuring wall-normal velocity in the buffer layer and opposing it at the wall. This work explores the possibility of implementing this strategy with a detection plane in the logarithmic layer, where control could be feasible experimentally. We apply control on a channel flow at $Re_\tau = 932$ , only on the eddies with relatively large wavelengths ( $\lambda / h > 0.1$ ). Similarly to the buffer layer opposition control, our control strategy results in a virtual-wall effect for the wall-normal velocity, creating a minimum in its intensity. However, it also induces a large response in the streamwise velocity and Reynolds stresses near the wall, with a substantial drag increase. When the phase of the control lags with respect to the detection plane, spanwise-homogeneous rollers are observed near the channel wall. We show that they are a result of a linear instability. In contrast, when the control leads with respect to the detection plane, this instability is inactive and oblique waves are observed. Their wall-normal profiles can be predicted linearly as a response of the turbulent channel flow to a forcing with the advection velocity of the detection plane. The linearity, governing the flow, opens a possibility to affect large scales of the flow in a controlled manner, when enhanced turbulence intensity or mixing is desired.

Numerical Investigation on the Effects of Impeller Structures in Hot Metal Desulfurization Processes by Mechanical Stirring

With the increasing demand for high-quality steel, the requirements for the efficiency and stability of deep desulfurization are increasing too. The Kanbara Reactor (KR) is widely accepted around the world because of its high efficiency and economy. In order to destroy the rigid motion of molten iron in this area, two kinds of blade structures are designed and compared with traditional blades. In this study, a three-dimensional transient coupling mathematical model was established by using volume of fluid (VOF) and discrete phase model (DPM) to simulate the KR desulfurization process. The turbulence intensity of the molten iron, main vortex size and desulfurizing agent (DA) particle distributions for the three impeller models were investigated in detail. Model results showed that the staggered blade structure may improve the desulfurization efficiency of the KR process, and the desulfurization rate increases from 95.7% to 97.1% when compared with ordinary blades. The main reason for this can be attributed to the enhanced turbulence intensity of the molten iron, larger main vortex size and more uniform DA particle distributions. Plant tests also showed that the desulfurizer consumption per 1 ppm sulfur for the staggered blades was reduced by approximately 8.6%.

Spray evolution and thermal pyrolysis of low sulfur heavy fuel oils under high temperatures

The spray evolution and thermal pyrolysis of the heavy fuel oil (HFO) and its blends with #2 diesel were firstly investigated. First, the gas chromatography was performed to analyze their molecular distributions. The low sulfur HFOs with different viscosities show similar molecular distributions, and the content of light-end C9 – C17 alkanes and polyaromatics is reduced compared with the high sulfur HFOs. Then, the spray experiments were conducted. The increase of ambient temperature has little effects on the HFO sprays. However, the blends spray of HFOs and #2 diesel penetrates faster and produces some opaque products under high-temperature conditions, probably due to the enhanced turbulence intensity, potential thermal pyrolysis and polymerization. Finally, the thermogravimetric analysis coupled with the isothermal gas chromatography and mass spectrometry were conducted, and the apparent activation energy of thermal pyrolysis for various HFOs were obtained. The results revealed that the HFO undergoes four stages in the inert gas, namely the endothermic evaporation, mixed evaporation-pyrolysis, violent exothermic pyrolysis, and high-temperature polymerization, producing large amounts of residues. However, in the oxygen-containing condition, the combustion occurs instead of the high-temperature polymerization, and the residual quality is prominently reduced. The high ambient pressure is proved to have a significant effect on the pyrolysis and polymerization processes for the low sulfur HFO, the residual mass significantly increases under high pressures. For the blended HFO, due to the volatile components trapped inside the viscous shell generated by polymerization or asphaltene fractions, the residual weight of the blended HFOs increases.

Turbulent flow and heat flux analysis from validated large eddy simulations of flow past a heated cylinder in the near wake region

We conduct non-isothermal large eddy simulations (LESs) of flow past a heated cylinder (Re = 3900) to investigate flow physics throughout the wake region and develop a foundation upon which future heat flux wall models can be built (both for wall-modeled LES and other lower fidelity models) for mathematical closure of the energy equation. A rigorous validation of the mesh is made under isothermal conditions with results showing a closer match to experimental data than any other LES studies to date. The insights gained into the mesh design and approach are discussed. Simulation of non-isothermal flow is performed on the validated mesh for temperature differences between the cylinder surface and the freestream of 25 K and 300 K. The mesh design and realistic (temperature-dependent) thermodynamic property variations play key roles in predicting delayed separation, larger re-circulation zones, and enhanced turbulence intensity for the higher temperature difference case. The effect of both temperature differences on the flow is analyzed, and a new scaling of the flow domain is proposed to gain further insight into non-isothermal flow physics. Key scaling variables, friction temperature and friction velocity, are able to reduce nearly all of the temperature dependence of first and second order flow statistics, including turbulent heat fluxes. This leads to the finding that the turbulent heat flux in the wake region scales with the wall heat flux irrespective of the temperature difference in the flow.

On the Wind Energy Resource above High-Rise Buildings

One of the main challenges of urban wind energy harvesting is the understanding of the flow characteristics where urban wind turbines are to be installed. Among viable locations within the urban environment, high-rise buildings are particularly promising due to the elevated height and relatively undisturbed wind conditions. Most research studies on high-rise buildings deal with the calculation of the wind loads in terms of surface pressure. In the present paper, flow pattern characteristics are investigated for a typical high-rise building in a variety of configurations and wind directions in wind tunnel tests. The aim is to improve the understanding of the wind energy resource in the built environment and give designers meaningful data on the positioning strategy of wind turbines to improve performance. In addition, the study provides suitable and realistic turbulence characteristics to be reproduced in physical or numerical simulations of urban wind turbines for several locations above the roof region of the building. The study showed that at a height of 10 m from the roof surface, the flow resembles atmospheric turbulence with an enhanced turbulence intensity above 10% combined with large length scales of about 200 m. Results also showed that high-rise buildings in clusters might provide a very suitable configuration for the installation of urban wind turbines, although there is a strong difference between the performance of a wind turbine installed at the centre of the roof and one installed on the leeward and windward corners or edges, depending on the wind direction.

Effects of Channel Geometries and Acceleration on Heat Transfer of Hydrocarbon Fuel

The convective heat transfer enhancement and deterioration of the supercritical hydrocarbon fuel in the regenerative cooling channels of a scramjet were investigated numerically. This study focused on the heat transfer enhancement and deterioration suppression of the spiral rectangular channels with enhanced heat transfer effects resulting from the enhanced turbulence intensity and induced spiral flow. As a result, compared with the straight rectangular channel, the maximum temperature of the spiral rectangular channel with a pitch of 20 mm was reduced by 31.3%. Although the cross-sectional shape and heat transfer area of the rectangular channel and the spiral rectangular channel were the same, the spiral rectangular channel with a short pitch had significant effects of heat transfer enhancement and deterioration suppression. Furthermore, the influence mechanisms of the acceleration field on the convective heat transfer were explored. Results indicate that acceleration has a significant effect on the heat transfer of the supercritical hydrocarbon fuel in the straight rectangular channel, but has little influence on the heat transfer of the spiral rectangular channel with a pitch of 20 mm.

Numerical investigations on the effects of turbulence intensity on knocking combustion in a downsized gasoline engine

In this work, the influence of turbulence intensity on knocking characteristics was studied. Different levels of initial swirl ratio inside cylinder were firstly performed to investigate the effect of turbulence intensity on combustion process. The results show that the enhanced turbulence intensity with increasing initial swirl ratio accelerates the spark-ignited flame (main flame) propagation, resulting in a shortage of combustion phasing (or an advance combustion phasing) and a faster flame speed. Under low turbulence intensity, the faster flame propagation can facilitate knocking combustion because of the enhanced compression of SI flame on the improvement of end-gas thermodynamic conditions. However, further increases in turbulence intensity and flame speed suppress the knocking combustion due to the insufficient time for end-gas autoignition occurrence. Further analysis shows that knock intensity mainly depended on the Unburned Mass Fraction (UBMF). Under lower levels of initial swirl ratios, the enhanced compression of SI flame with the increase of turbulence intensity induces an advanced knock onset, which leads to a larger UBMF and heavier knock intensity. However, under higher swirl ratio scenarios, UBMF and knock intensity exhibited an opposite trend because the consumption of end-gas by the fast main flame played a dominating role.

Effects of jet in crossflow on flame acceleration and deflagration to detonation transition in methane–oxygen mixture

The fluidic jet turbulator has been a novel perturbation generator in the pulse-detonation engines research field for the past few years. In this paper, an experiment is performed to study the deflagration to detonation transition (DDT) process in a detonation chamber with a reactive transverse methane–oxygen mixture jet in crossflow (JICF). The jet injection arrangement is fundamentally investigated, including single jet and various double jets patterns. Corresponding two-dimensional direct numerical simulations with a multistep chemical kinetics mechanism are employed for analyzing details in the flow field, and the interaction between the vortex and flame temporal evolution is characterized. Both the experiments and simulations demonstrate that the JICF can distinctly accelerate flame propagation and shorten the DDT time and distance. The vortex stream induced by the jet distorts and wrinkles the flame front resulting in local flame acceleration. Moreover, the double jet patterns enhance flame acceleration more than the single jet injection because of the intrinsic counter-rotating vortex pairs and enhanced turbulence intensity.

Effect of photocatalytic surface roughness on reactors effectiveness for indoor air cleaning

Photocatalysis is a promising technique for remediation of indoor air pollution. This study focuses on the enhancement of the effectiveness of the photocatalytic process by the introduction of artificial roughness on the interior reactor surface. Artificial roughness elements on the catalytic surface could enhance the turbulence intensity close to the catalytic surface. The enhanced turbulence intensity would translate to an increased in the mass transfer of airborne contaminants to the catalyst surface, improving the efficiency of photocatalysis.Air flow properties in a model photoreactor channel with transverse rib roughness on the wall are investigated by the “realizable k–epsilon (k–ε)” model. The investigation includes different shapes, sizes, and arrangements of the roughness elements for determining the maximum enhancement of turbulence intensity in the photoreactor channel. The optimum roughness has been determined to be an isosceles triangle shape with the bottom angle (α) equal to 75°, the relative height (e/h) equal to 0.05, and the pitch ratio (p/e) equal to 10. An experimental study was also carried out, which verified that the photocatalytic reactor performance for indoor air cleaning is significantly improved by a roughness pattern on catalyst surface compared to a reactor with a smooth catalyst surface.

Effects of Thermal Stability and Incoming Boundary-Layer Flow Characteristics on Wind-Turbine Wakes: A Wind-Tunnel Study

Wind-tunnel experiments were carried out to study turbulence statistics in the wake of a model wind turbine placed in a boundary-layer flow under both neutral and stably stratified conditions. High-resolution velocity and temperature measurements, obtained using a customized triple wire (cross-wire and cold wire) anemometer, were used to characterize the mean velocity, turbulence intensity, turbulent fluxes, and spectra at different locations in the wake. The effect of the wake on the turbulence statistics is found to extend as far as 20 rotor diameters downwind of the turbine. The velocity deficit has a nearly axisymmetric shape, which can be approximated by a Gaussian distribution and a power-law decay with distance. This decay in the near-wake region is found to be faster in the stable case. Turbulence intensity distribution is clearly non-axisymmetric due to the non-uniform distribution of the incoming velocity in the boundary layer. In the neutral case, the maximum turbulence intensity is located above the hub height, around the rotor tip location and at a distance of about 4–5.5 rotor diameters, which are common separations between wind turbines in wind farms. The enhancement of turbulence intensity is associated with strong shear and turbulent kinetic energy production in that region. In the stable case, the stronger shear in the incoming flow leads to a slightly stronger and larger region of enhanced turbulence intensity, which extends between 3 and 6 rotor diameters downwind of the turbine location. Power spectra of the streamwise and vertical velocities show a strong signature of the turbine blade tip vortices at the top tip height up to a distance of about 1–2 rotor diameters. This spectral signature is stronger in the vertical velocity component. At longer downwind distances, tip vortices are not evident and the von Karman formulation agrees well with the measured velocity spectra.

Experimental Study of Flow Structures of Circular Pulsating Air Jet

Problem Statement: Applications of impingement jets in industry for heating and cooling purposes requires a high convective heat transfer coefficient. Numerous studies have been conducted to improve the convective heat transfer coefficient for a steady impinging jet. A pulsating jet has a very high potential in replacing steady jet after it been found able to increase the heat transfer coefficients at certain pulsating frequencies. The objectives of this study were to; (i) determine the velocity profile of a circular pulsating air jet at different pulse frequencies and Reynolds Number using a rotating valve pulse jet system and (ii) to compare the normalized steady and pulsed jet velocity at highest Reynolds number of 32 000 and highest pulsating frequency of 80Hz. Approach: Pulsation of the air jet was produced by a rotating cylinder valve mechanism at frequencies between 10-80 Hz. Flow structures of the heated steady and pulse single circular axisymmetric air jet velocity were measured using a calibrated hot-wire anemometer and presented in non-dimensional form. The measurements were carried out at three different Reynolds numbers which was set at 16000, 23300 and 32000. The jet exit velocity profile for all the test frequency is determined by plotting the graph of radial distance against the non-dimensional jet exit velocity. Results: The corresponding Reynolds number in this test is based on time-averaged centerline velocity. The results of the velocity measurement were plotted side by side using non-dimensional parameters in order to make direct comparison of the velocity profile at different frequencies and Reynolds numbers. Stagnation point velocities are the same for steady and pulsating jet for all pulse frequencies. As the radial distance from the stagnation point increases, pulsating velocity increases between 20-30% from radial distance of 2-22 mm. Conclusion: Results of the flow structures plotted show a distinctive exit air jet profile which can affect the impingement heat transfer characteristics. This was the result of enhanced turbulence intensity due to pulsating jet produced by the rotating cylinder. From the jet exit velocity profile obtained, it is found that mass flow rate for different test frequencies are slightly different due to the difference in the local velocity measurement affected by the pulses. The jet exit velocity profile data will be used to form a correlation between the pulsating jet velocity and heat transfer data.

An investigation and evaluation of variable-valve-timing and variable-valve-actuation strategies in a diesel homogeneous charge compression ignition engine using three-dimensional computational fluid dynamics

A three-dimensional computational fluid dynamics modelling was carried out to investigate effects of variable valve timing (VVT) and variable valve actuation (VVA) on gas exchange and fuel-air mixing processes in a diesel homogeneous charge compression ignition (HCCI) engine with early fuel injection. Four VVT or VVA strategies were conducted for this study: first, a negative valve overlap (NVO) strategy with fixed exhaust-valve-opening (EVO) and intake-valve-closing (IVC) timings but variable valve lifts, referred to as the NVO strategy; second, the NVO strategy with fixed valve profiles but variable EVO and IVC timings, referred to as the EVO strategy; third, the NVO strategy with fixed valve lifts and fixed EVO and IVC timings but variable exhaust-valve-closing (EVC) and intake-valve-opening timings, referred to as the EVC strategy; fourth, VVA with just variable valve lifts, referred to as the VMAX strategy. The results indicate that suitable NVO settings will enhance in-cylinder tumble and then increase turbulence intensity before compression end, although the increased NVO has a negative contribution to swirl ratio. It was found that reducing valve lifts alone is not an efficient way to retain the residual gas, but the function of reduced valve lifts will become significantly obvious by combining it with increasing NVO. For the effect of NVO on in-cylinder temperature, longer NVO not only will increase in-cylinder temperature because of the higher residual gas rate but also will improve the in-cylinder temperature homogeneity. On lowering the maximum valve lift or increasing the NVO, the unmixed region of the in-cylinder charge shrinks. The fuel-rich region expands because of the high intake velocity and enhanced turbulence intensity. This is beneficial to the forming of a global homogeneous charge. It has been noted from the current study that, as the droplet distribution may be influenced more by the in-cylinder air motion caused by NVO when the average droplet size is smaller, it is recommended that future studies explore the effects of VVT and VVA on diesel HCCI mixing and combustion with various advanced fuel injection strategies.

Effect of Pulsating Circular Hot Air Jet Frequencies on Local and Average Nusselt Number

The study was carried out to determine the effect of pulsating frequencies on the local and average heat transfer characteristic of a heated circular air jet. The velocity profile of a heated circular pulsating air jet was measured in the first part of the study. The same set-up was used to measure the heat flux of the pulsating jet impinging on a wall. The heat flux of the heated air jet impinging on the plate was measured using a heat flux microsensor at different radial positions. Measurement of the heat flux was used to calculate the average and local Nusselt Number for different pulsating frequencies and at different flow Reynolds Number. The pulsating frequencies were between 10-80 Hz and the Reynolds number used were 16 000, 23 300 and 32 000. Results obtained show that the local Nusselt number calculated were higher at all radial position away from the stagnation point. The pulsed jet Nusselt number was higher than the average steady jet Nusselt number for all values of frequencies due to the higher localised heat transfer. The higher Nusselt number obtained at localized radial positions can be due to the higher instantaneous velocity as was shown from the velocity profile plotted in the first part of the experiment. Enhanced turbulence intensity found was due to the pulsed jet.

Experimental Studies on Wake-Induced Bypass Transition of Flat-Plate Boundary Layers under Favorable and Adverse Pressure Gradients

This study investigates wake-induced bypass transition of boundary layers on a flat plate which is subjected to favorable and adverse pressure gradients. Inlet free-stream turbulence level is controlled with a turbulence grid. Detailed boundary layer measurements are executed by use of a single hot-wire probe. The main focus of this paper is on how and to what extent the wake-induced bypass transition of a flatplate boundary layer can be affected by favorable - adverse pressure gradient as well as enhanced turbulence intensity. A spoked-wheel-type wake generator creates periodic wakes in front of the flat plate. Two types of the wakes are generated by altering the direction of the movement of the wake-generating bars. Instantaneous velocity signals successfully reveal the flow events associated with the wake passage happening inside the boundary layer, such as the emergence of turbulent spots and calmed regions behind them. Noticeable differences in the transitional behavior due to the wake passage also appear between these two types of the wakes.