Detached Shear Layer Research Articles

Influence of gap ratios on wake dynamics of two rectangular 5:1 cylinders placed inline

The present study explores the impact of gap ratio (G) on the wake dynamics of two rectangular 5:1 cylinders placed inline at a fixed Reynolds number (Re) = 250. The lattice Boltzmann method is used for numerical simulations, and the gap ratio is varied in the range of 0.25–10. After validating the code for flow around a single square cylinder, the simulations are further carried out to explore the impact of gap ratio on the fluid flow past two inline cylinders with a similar aspect ratio = 5:1. Both the cylinders are found to face the reattachment of detached shear layers from front edges on to the side surfaces before the final separation. These reattached shear layers generate vortices on the upper and lower surface of cylinders exhibiting the reverse flow. For G < 4.5, the surface vortices appear on the first cylinder only, while for G ≥ 4.5, the surface vortices appear at both cylinders upper and lower sides. The reattachment point on the surface of the first cylinder is found to move downstream till G = 3, but after that, reverse phenomena occur with an increase in the gap ratio. The enhancement of flow induced lift results due to such separating and reattaching flow. Four distinct flow patterns appear at different gap ratios range: (a) single slender body, (b) non-fully developed duplex shedding, (c) fully developed duplex shedding, and (d) unpredictable vortex shedding. The root mean square value of drag coefficient for the first cylinder is mostly found less as compared to the second cylinder for all G. Negative pressure is observed at the upper, lower, and wake region of both bodies. However, the pressure appears to be positive at the foremost surface of second body when the flow pattern changed from fully developed duplex shedding to unpredictable vortex shedding. Strouhal of both cylinders shows distinct values corresponding to dual frequency at small gap ratios but becomes consistent at higher ones.

Numerical approach for the simulation of flow-induced noise around a structure with complex geometry: High-speed train bogie in a cavity

The bogie region is a significant source of aerodynamic noise on high-speed trains. Owing to its complex geometry and flow field, numerical simulations using computational fluid dynamics are especially challenging. The main challenge is to achieve a grid with adequate resolution, especially in the boundary layer, while ensuring computational affordability. This challenge is addressed here by employing a hybrid grid, integrating a structured hexahedral mesh near solid surfaces with an unstructured polyhedral mesh in the remaining volume. To limit the number of cells in the boundary layer region, the delayed detached eddy simulation method is adopted. Additionally, to achieve a further reduction in the cell count, the Reynolds number of the model is decreased by scaling down the model size and lowering the inflow speed. The hybrid grid generation and numerical settings are guided by validated simulations of flow over cylinders. A grid sensitivity study, conducted with a simplified half-width bogie model, reveals the meshing requirements for the full-width model. Aerodynamic results highlight the rear section of the cavity and bogie as primary noise sources, emphasizing the critical role of the detached shear layer from upstream components. Time-resolved surface pressure data are input into the Ffowcs Williams–Hawkings equation for far-field noise calculation. The results indicate that the sound energy is concentrated below 200 Hz in the full-scale model, with the cavity contributing more than the bogie. This study provides a practical numerical approach for simulating a structure with complex geometry, offering insights for realistic model simulations.

Reynolds number effects in shock-wave/turbulent boundary-layer interactions

We investigate Reynolds number effects in strong shock-wave/turbulent boundary-layer interactions (STBLI) by leveraging a new database of wall-resolved and long-integrated large-eddy simulations. The database encompasses STBLI with massive boundary-layer separation at Mach $2.0$ , impinging-shock angle $40^{\circ }$ and friction Reynolds numbers ${\textit {Re}}_\tau$ $355$ , $1226$ and $5118$ . Our analysis shows that the shape of the reverse-flow bubble is notably different at low and high Reynolds number, while the mean-flow separation length, separation-shock angle and incipient plateau pressure are rather insensitive to Reynolds number variations. Velocity statistics reveal a shift in the peak location of the streamwise Reynolds stress from the separation-shock foot to the core of the detached shear layer at high Reynolds number, which we attribute to increased pressure transport in the separation-shock excursion domain. Additionally, in the high Reynolds case, the separation shock originates deep within the turbulent boundary, resulting in intensified wall-pressure fluctuations and spanwise variations associated with the passage of coherent velocity structures. Temporal spectra of various signals show energetic low-frequency content in all cases, along with a distinct peak in the bubble-volume spectra at a separation-length-based Strouhal number $St_{L_{sep}}\approx 0.1$ . The separation shock is also found to lag behind bubble-volume variations, consistent with the acoustic propagation time from reattachment to separation and a downstream mechanism driving the shock motion. Finally, dynamic mode decomposition of three-dimensional fields suggests a Reynolds-independent statistical link among separation-shock excursions, velocity streaks and large-scale vortices at low frequencies.

Experimental investigations on the effect of upstream-edge rounding on the BARC configuration

We experimentally investigate the influence of upstream-edge roundness on the flow around a 5:1 rectangular cylinder. We examine various values of edge curvature radius, ranging from nearly sharp edges to r/D=0.1104 at Reynolds number Re=40000, based on the freestream velocity and the crossflow dimension of the cylinder. Additionally, we explore the combined effects of edge roundness and (i) Reynolds number (Re=20000−80000) and (ii) angle of attack (|α|≤2deg). For all examined Re and α, limited sensitivity to upstream-edge rounding is observed up to r/D=0.0360, with results close to those obtained for nominally sharp edges. For r/D≥0.0781, and fixed Re and α=0deg, a noticeable decrease in the size of the mean recirculation region alongside the rectangular cylinder, lr, is observed with increasing r/D. For r/D≥0.0781, the flow features are also sensitive to Re, with a reduction in the length of the mean recirculation with increasing Re. The reduction of lr with increasing r/D and Re is due to the detached shear layer becoming more tilted towards the cylinder. Finally, for r/D≥0.0781, the effect of α, that is the increase of lr on the leeward side surface and the opposite on the windward side, is more important than for small r/D values.

Development of a Framework for Cost–Benefit Analysis of I-Head and T-Head Groynes Based on Scour and Turbulent Flow Characteristics

River bank protection is a vital component of sustainable development. This study investigates and compares the scour and flow features around two different types of groynes, an unsubmerged I-head groyne (IHG) and T-head groyne (THG), to provide insights into their performance and efficiency in river reaches. Experiments were conducted to examine the scouring pattern, mean and turbulent flow characteristics including 3D mean flow velocity distribution, Reynolds stresses, turbulent kinetic energy, and bed shear stress near the bed region around the groynes under similar flow conditions. The results indicated that THG had a maximum equilibrium scour depth over three-fold greater than IHG. For both the IHG and THG cases, it was observed that there is a direct correlation between the location of maximum negative vertical velocity and its magnitude to the region of maximum local scour and its depth. All the stresses of high magnitude are found along the propagation of the detached shear layer profile, which turns back sharply downstream towards the bank containing the IHG while remaining mostly away from the bank in the case of THG. The effective bank protection length was estimated to be two-fold the groyne length in the case of IHG and three-fold the groyne transverse length in the case of THG. Cost–benefit analysis of the two groyne types shows IHG as the more cost-efficient groyne with respect to bank protection lengths. This study provides valuable insights for developing design methodologies aimed at promoting the wider utilization of different head-shape groynes in river reaches and aids in selecting appropriate groyne head configurations that align with specific field requirements.

Numerical investigation of a Mach 6 laminar shock-wave/boundary-layer interaction on a two-dimensional ramp with 3D controlled surface roughness

Direct Numerical Simulations (DNS) are performed to investigate roughness effects on a Mach 6 hypersonic compression-corner flow. Different variants of a roughness patch placed upstream of the ramp are considered in order to study their impact on the steady base flow characterized by a large separation bubble. The patches consist of sinusoidal elements, with modifications in position and spanwise extent of the roughness. Under adiabatic-wall conditions, compared to a smooth-wall case, the rough cases where the patch is upstream of the smooth-separation point cause a delayed boundary-layer separation and hence a smaller recirculation bubble. Moreover, the roughness-induced streamwise vorticity convected downstream by the detached shear layer generates mushroom-like structures once the flow reattaches on the ramp. The properties of such structures, although similar, reflect the character of the patch upstream of the bubble. The roughness inducing the largest local flow distortion is responsible for the widest structure on the ramp, characterized by the highest increase in wall-temperature. The patch occupying the entire width of the domain instead generates the weakest vortices on the ramp. No noticeable effects on the recirculation region can be noticed if the patch is placed downstream of the separation point for smooth conditions. Regarding the cold-wall case, the patch increases the heat-transfer rate on the ramp downstream of the roughness location, but with minimal effects on the bubble length. The analysis of the shear magnitude in the mushroom-shaped structures at reattachment suggests that, under adiabatic-wall conditions, the most upstream patch might have the highest transition potential.

Cross flow over two heated cylinders in tandem arrangements at subcritical Reynolds number using large eddy simulations

This study analyses the heat transfer and flow characteristics of cross-flow over two heated infinite cylinders in a tandem (in-line) configuration. Non-isothermal Large Eddy Simulations (LES) using the dynamic Smagorinsky model were conducted at a fixed Reynolds number of 3,000 (based on the free stream velocity and the cylinder diameter). A range of cylinder gap ratios (1.0≤L/D≤5.0) was investigated (in increments of 0.25) with two different Prandtl numbers Pr=0.1 and 1.0. Results show that the flow structures vary according to the order of the patterns: (i) Extended body regime: without attachment for low L/D (1.0-1.25) where cylinders behave as a single bluff body with top–bottom vortex shedding, (ii) Shear layer reattachment regime: with reattachment for moderate L/D (1.5-3.75) where the detached shear layer from the upstream cylinder reattaches to the downstream cylinder, and (iii) Co-shedding regime: for high gap ratios (3.75≤L/D≤5.0) a phenomenon called “jumping”, where the two cylinders behave as isolated bluff bodies. Furthermore, it was observed that the average Nusselt number of both cylinders experience a drastic variation at a critical spacing ratio (between 3.75≤L/D≤4.0). For L/D≤3.0, the average Nusselt number of the upstream cylinder was found to be higher than that of the downstream one. However, for spacing ratios L/D>3.0, the average Nusselt number was similar for both cylinders. For the downstream cylinder, the maximum Nusselt number was located at the separation angle and was found to be independent of the spacing ratio.

Numerical Investigation of Flow Structure and Turbulence Characteristic around a Spur Dike Using Large-Eddy Simulation

Spur dikes provide significant control for flow regimes in river regulation engineering, which can help in the regeneration of stream habitats. However, the narrowing of the flow by spur dike changes the turbulence characteristics. To clarify the turbulence characteristics around the spur dike, the method of large eddy simulation (LES) was used to investigate the horizontal turbulence structure around spur dikes with different discharges in an open-channel flume. The simulations were an exact reproduction of large-scale laboratory experiments, which showed agreement with the experimental results. The distributions of time-averaged streamwise velocity, bed shear stress, and second-order turbulence statistics obtained from the LES were analyzed. An examination of the time series of velocity fluctuation as the probability density function, quadrant analysis, the power density spectra, flow instability, and the vortex separation created in the detached shear layer were estimated. The results accurately revealed the flow field under flow separation, the turbulence statistics inside the separated shear layer, and the vortex structure and emphasized the variation in the different water depths. The results demonstrated that the form of turbulence was not significantly affected by discharge. Moreover, vortex and energy transmission displayed the same periodicity, despite variances in the structural form of turbulence at different water depths. Overall, the results of the study provide an efficient basis for understanding the turbulence around spur dikes, which is crucial for their safe design.

Hilbert–Huang Spectral Analysis of Cavity Flows Incorporating Fluidic Spoilers

Numerical aeroacoustic analysis was conducted on an M219 cavity geometry, incorporating signature suppression features and leading-edge fluidic spoilers. The numerical model was validated against existing experimental data. The palliative properties of fluidic spoilers were investigated at Mach numbers of 0.85, 1.20, and 1.80 with blowing coefficients of 0.03 and 0.06. The results are presented for the acoustic spectrum, and further analysis was conducted using the Hilbert–Huang methodology. The fluidic spoilers were able to considerably reduce the overall level of acoustic noise and to reduce and/or suppress the resonant modes typical of cavity flows. The effectiveness of the spoilers was a direct consequence of their effect on the detached shear layer, of which the trajectory and coherence were altered. The Hilbert–Huang spectral analysis provided an enhanced understanding of the complex nature of the aeroacoustic behavior of the cavity. Acoustic modes were identified that, together with the Rossiter–Heller tones, governed the behavior of the spectrum. This demonstrated how the generated tones, appearing inside the cavity, were a result of complex nonlinear interactions between shear-layer acoustic instabilities and centrifugal instabilities originating in the flow recirculating in the internal part of the cavity. This also demonstrated that the fundamental frequencies had frequency and amplitude modulation characteristics that spread the energy in a wide bandwidth. This is not captured by classical Fourier analysis.

On the Characteristics of the Super-Critical Wake behind a Circular Cylinder

The flow topology of the wake behind a circular cylinder at the super-critical Reynolds number of Re=7.2×105 is investigated by means of large eddy simulations. In spite of the many research works on circular cylinders, there are no studies concerning the main characteristics and topology of the near wake in the super-critical regime. Thus, the present work attempts to fill the gap in the literature and contribute to the analysis of both the unsteady wake and the turbulent statistics of the flow. It is found that although the wake is symmetric and preserves similar traits to those observed in the sub-critical regime, such as the typical two-lobed configuration in the vortex formation zone, important differences are also observed. Owing to the delayed separation of the flow and the transition to turbulence in the attached boundary layer, Reynolds stresses peak in the detached shear layers close to the separation point. The unsteady mean flow is also investigated, and topological critical points are identified in the vortex formation zone and the near wake. Finally, time-frequency analysis is performed by means of wavelets. The study shows that in addition to the vortex shedding frequency, the inception of instabilities that trigger transition to turbulence occurs intermittently in the attached boundary layer and is registered as a phenomenon of variable intensity in time.

Flow transitions on a cambered airfoil at moderate Reynolds number

A combined experimental and numerical study is performed to investigate the flow field and associated aerodynamic forces on a cambered airfoil. The Reynolds number is low enough to ensure importance of viscous dynamics, and high enough so that instability and transition to turbulence can occur. The flow fields are complex and their correct description is essential in understanding the nonlinear curves describing the variation of lift and drag coefficients with angle of attack, α. As α is increased from 0, the flow states go through a number of qualitatively distinct phases. At low to moderate α, the laminar boundary layer separates before the trailing edge, and as the separation point moves forward, instabilities of the detached shear layer form coherent vortices over the upper (suction) surface. At a critical angle, αcrit, instabilities in the shear layer grow fast enough to transition to turbulence, which then leads to reattachment before the trailing edge. In this flow state, lift is increased and drag decreases. Hence, in order to understand the aerodynamics at this scale, we need to understand the viscous dynamics of the boundary layer, as elegantly described and analyzed by Frank White.

Numerical Analysis of Side-loads Reduction in a Sub-scale Dual-bell Rocket Nozzle

A calibrated delayed detached eddy simulation of a sub-scale cold-gas dual-bell nozzle flow at high Reynolds number and in sea-level mode is carried out at nozzle pressure ratio NPR = 45.7. In this regime the over-expanded flow exhibits a symmetric and controlled flow separation at the inflection point, that is the junction between the two bells, leading to the generation of a low content of aerodynamic side loads with respect to conventional bell nozzles. The nozzle wall-pressure signature is analyzed in the frequency domain and compared with the experimental data available in the literature for the same geometry and flow conditions. The Fourier spectra in time and space (azimuthal wavenumber) show the presence of a persistent tone associated to the symmetric shock movement. Asymmetric modes are only slightly excited by the shock and the turbulent structures. The low mean value of the side-loads magnitude is in good agreement with the experiments and confirms that the inflection point dampens the aero-acoustic interaction between the separation-shock and the detached shear layer.

Flow dynamics and wall-pressure signatures in a high-Reynolds-number overexpanded nozzle with free shock separation

A delayed detached eddy simulation of an overexpanded nozzle flow with shock-induced separation is carried out at a Reynolds number of , based on nozzle throat diameter and stagnation chamber properties. In this flow, self-sustained shock oscillations induce local unsteady loads on the nozzle wall as well as global off-axis forces. Despite several studies in the last few decades, a clear physical understanding of the factors driving this unsteadiness is still lacking. The geometry under investigation is a subscale truncated ideal contour nozzle, which was experimentally tested at the University of Texas at Austin at a nozzle pressure ratio of 30. Under these conditions, the nozzle operates in a highly overexpanded state and comprises a conical separation shock that merges to form a Mach disk at the nozzle centre. The delayed detached eddy simulation model agrees well with the experimental results in terms of mean and fluctuating wall-pressure statistics. Wall-pressure spectra reveal a large bump at low frequencies associated with an axisymmetric (piston-like) motion of the shock system, followed by a broad and high-amplitude peak at higher frequencies associated with the Mach waves produced by turbulent eddies convecting through the detached shear layer. Moreover, a distinct peak at an intermediate frequency ( ) persists in the wall-pressure spectra downstream of the separation shock. A Fourier-based analysis performed in both time and space (azimuthal wavenumber) reveals that this intermediate-frequency peak is associated with the (non-symmetric) pressure mode and is thus related to the generation of aerodynamic side loads. It is then shown how the unsteady Mach disk motion is characterized by an intense vortex shedding activity that, together with the vortical structures of the annular shear layer, contributes to the sustainment of an aeroacoustic feedback loop occurring within the nozzle.

Experimental study of the near wake of a circular cylinder and its detached shear layers

The near wake of a cylinder (x < 1.6D) and its detached shear layers are studied at Re = 3.5 × 104 through phase averaging of 2D-PIV snapshots using as trigger the pressure at φ=90°. The shedding cycle is examined at 8 time instants as well as at 16 time instants based on POD analysis. In the shear layer region, the flow becomes fully turbulent at x ~ 0.45D according to the momentum thickness spatial variation, whereas based on the velocity profile shapes there is a transition from convective to absolute type of instabilities at the same x - station. The Karman vortices once formed at (0.8D, ±0.5D),accelerate streamwise towards the wake centre line following curved trajectories with speeds much smaller than those at the distant field. The Reynolds stresses and the turbulent kinetic energy production of each phase exhibit peaks downstream of the vortex centres in contrast to the spanwise vorticity, swirling strength and turbulent kinetic energy which maximize at the vortex centres, seen from a moving frame of reference. In the wake, normally v'2¯ > u'2¯ in contrast to the shear layer region in which u'2¯ > v'2¯. The Reynolds shear u'v'¯ being the smallest of the Reynolds stresses in the wake, shows two peaks of opposite sign, one being close to the vortex. The pressure at φ=90° (which might be related to the lift applied on the cylinder) takes its peak values with a time delay after the Karman vortex formation and particularly when the latter passes through x ~ 1.05D, its fluctuations being high or low according to the size of the vortex.

Incident shock wave and supersonic turbulent boundarylayer interactions near an expansion corner

Direct numerical simulations of incident shock wave and supersonic turbulent boundary layer interactions near an expansion corner are performed at Mach number M∞ = 2.9 and Reynolds number Re∞ = 5581 to investigate the expansion effect on the characteristic features of this phenomenon. Four expansion angles, i.e. α = 00 (flat-plate), 20, 50 and 100 are considered. The nominal impingement point of the oblique shock wave with a flow deflection angle of 120 is fixed at the onset of the expansion corner, and flow conditions are kept the same for all cases. The numerical results are in good agreement with previous experimental and numerical data. Various flow phenomena, including the flow separation, the post-shock turbulent boundary layer and the flow unsteadiness in the interaction region, have been systematically studied. Analysis of the instantaneous and mean flow fields indicates that the main effect of the expansion corner is to significantly decrease the size and three-dimensionality of the separation bubble. A modified scaling analysis is proposed for the expansion effect on the interaction length scale, and a satisfactory result is obtained. Distributions of the mean velocity, the Reynolds shear stress and the turbulent kinetic energy show that the post-shock turbulent boundary layer in the downstream region experiences a faster recovery to the equilibrium state as the expansion angle is increased. The flow unsteadiness is studied using spectral analysis and dynamic mode decomposition, and dynamically relevant modes associated with flow structures originated from the incoming turbulent boundary layer are clearly identified. At large expansion angle (α=100), the unsteadiness of the separated shock is dominated by medium frequencies motions, and no low frequency unsteadiness is observed. The present study confirms that the driving mechanism of the low frequency unsteadiness is strongly related to the separated shock and the detached shear layer.

Hypersonic Transitional Shock-Wave–Boundary-Layer Interaction on a Flat Plate

This work presents an experimental and numerical study of hypersonic transitional shock-wave–boundary-layer interaction, wherein transition occurs between separation and reattachment in the detached shear layer. Experiments were conducted in a free-piston compression-heated Ludwieg tube that provided a Mach 5.8 flow at a freestream Reynolds number of . A shock generator deflected the flow by 10°, resulting in an oblique shock impinging on a flat plate. The shock triggered transition in the boundary layer and the formation of Görtler-like vortices downstream of reattachment. Heat flux and pressure distributions on the plate were measured globally using infrared thermography and pressure-sensitive paint. Oil film visualization was employed to evaluate the boundary-layer reattachment. Numerical results consist of Reynolds-averaged Navier–Stokes and fully laminar steady-state three-dimensional simulations. Shock-induced transition is considered to be the cause of the overshoot in peak pressure and peak heating of approximately 15%, in agreement with previous studies. Görtler instability, triggered by the concave nature of the bubble at separation, is identified as the main mechanism leading to boundary-layer transition, resulting in heat-flux variations of less than 30%. By comparing numerical results against thermographic values it is possible to delineate the extent of transition. Within this region, the disturbance amplification factor was estimated to be approximately between 6 and 10, in reasonable agreement with other relevant numerical and experimental data.

Heat transfer and flow field features between surface mounted trapezoidal-ribs

Present work is an experimental study of flow over array of trapezoidal-ribs transversely placed on the wider bottom surface of the rectangular passage. It is intended to study the profound impact of taper angle variation (0 to 20°) on the flow mechanism, and subsequently on heat transfer improvement. The local and augmentation heat transfer patterns have been investigated using liquid crystal thermography (LCT). Further, the aerodynamic characteristics, in a module between seventh and eight ribs, have been obtained using particle image velocimetry (PIV) for understanding the flow physics. Existence of large- and small-scale coherent structures within the detached shear layer zone have been confirmed and further explained by means of critical points. As compared to square rib, trapezoidal rib provides higher heat transfer rate just downstream of the rib, which is observed to be in line with the fluid flow results.

Raymond Hide. 17 May 1929—6 September 2016

Raymond Hide was a physicist who worked at the interfaces between fundamental hydrodynamics, magnetohydrodynamics (MHD), the geophysics of the Earth's interior, atmosphere and oceans and those of other planets. He received his PhD from the University of Cambridge, and spent the majority of his career at the Met Office and then the University of Oxford. In laboratory studies of sloping thermal convection carried out at Cambridge in the early 1950s he discovered various regimes of vacillation and other multiply-periodic intransitive flows as well as aperiodic flows, now recognized as a form of geostrophic turbulence. These findings influenced seminal mathematical studies of what came to be known as deterministic chaos, and provided a paradigm for interpreting large-scale flows in the atmospheres of the Earth and other planets. Related contributions include general theoretical results tested by crucial laboratory experiments on boundary layers, Taylor columns and detached shear layers. His contributions to MHD include the concepts of potential magnetic field and magnetic superhelicity. He also initiated research on the dynamo origin of the magnetic fields of Jupiter and other major planets and its implications for their internal structure and dynamics. His extensive research on fluctuations of the Earth's rotation led to new developments in areas as diverse as meteorology and climatology and studies of the structure and dynamics of the Earth's deep interior.

An investigation on mechanisms of equilibrium-stage scour and deposition process around a submerged L-head groyne

ABSTRACT A numerical model based on large eddy simulation code supported with a laboratory experiment was used to explore the mechanism of scour and deposition process around a submerged L-head groyne at equilibrium stage of flow. The numerical model used the equilibrium bathymetry, which was obtained from an experiment conducted in the laboratory. The components of Horse Shoe vortex system (HV) including the presence of aperiodic oscillatory motions between back flow and zero flow modes near the groyne faces junction are explored. Formations of elliptical-shaped vortex tubes along detached shear layer (DSL) and their merging phenomenon at different time scales of flow are also investigated. Increase in vorticity magnitude towards bottom as compared to upper planes for instantaneous and mean flow field is identified. Near bed region, concentration of DSL profile towards submerged mound situated in the wake region emerges as dominating factor over HV system for the production of larger vorticity magnitude. Transportation of DSL eddies, their interaction with wake vortices and flow within reattachment zone are also focussed. To emphasize, this innovative study was conducted first time to fulfil the gap of exploring mechanism of scour and deposition process around such a complex geometry under submerged condition over scoured bed.

Near-bed turbulence around an unsubmerged L-head groyne

ABSTRACT L-head groynes are widely used in river training, thereby motivating the present study of the near-bed turbulence around an unsubmerged L-head groyne. Near-bed turbulence characteristics are required to understand the fluctuations of turbulent structures to ensure the safety of such groynes for bank protection work. In this study, the mean and turbulent flow characteristics such as time-averaged three-dimensional velocity distribution, Reynolds stresses, turbulent kinetic energy, and bed shear stress have been investigated experimentally at a channel Reynolds number of 3.9 × 104 and Froude number of 0.34. The maximum positive streamwise velocity along detached shear layer (DSL) and negative velocity within the wake zone are found as 1.51 and 0.60 times the mean flow velocity, respectively. Amplified transverse velocity caused by horseshoe vortex and the increased vertical velocity caused by downflow are observed in the upstream recirculation region. From the Reynolds stress variation, stronger horizontal turbulent mixing than the vertical turbulent mixing is observed. Amplified normal stresses and kinetic energy are observed along the DSL, which represents the intense turbulent fluctuations because of the presence of high shear instability therein. The bed shear stress at the junction of the groyne faces increases by 4.78 times the approach bed shear stress.