Large-scale Loop Research Articles

Heating manifestations at the onset of the 29 June 2012 flare

Analysis of GOES data for the SOL2012-06-29T04:09 flare, class C4.6, shows a thermal character of the energy release for several minutes before the impulsive stage. Plasma heating to temperatures above 10 MK leads to the appearance of plasma jets along open field lines and in large loops. This work examines the relationship between the heated plasma and the flare structure and its dynamics, using observations in the X-ray, extreme ultraviolet (EUV), and radio-wave ranges. Particular attention is drawn to the detection of narrow-band fine temporal structures of radio emission before and after the impulsive stage of the flare in dynamic spectra. In the initial stage, broadband pulses in the decimeter range are observed which can be associated with the formation of thermal fronts in the jets. A series of super-bright drifting bursts in the centimeter range occurs after the end of the impulsive energy release in the flare kernel. Using data from the Siberian Solar Radio Telescope (5.7 GHz), we managed to localize the position of the source of the fine structure of drifting bursts at the remote footpoint of the large-scale flare loop.

Проявления нагрева в начале вспышки 29 июня 2012 г.

Analysis of GOES data for the SOL2012-06-29T04:09 flare, class C4.6, shows a thermal character of the energy release for several minutes before the impulsive stage. Plasma heating to temperatures above 10 MK leads to the appearance of plasma jets along open field lines and in large loops. This work examines the relationship between the heated plasma and the flare structure and its dynamics, using observations in the X-ray, extreme ultraviolet (EUV), and radio-wave ranges. Particular attention is drawn to the detection of narrow-band fine temporal structures of radio emission before and after the impulsive stage of the flare in dynamic spectra. In the initial stage, broadband pulses in the decimeter range are observed which can be associated with the formation of thermal fronts in the jets. A series of super-bright drifting bursts in the centimeter range occurs after the end of the impulsive energy release in the flare kernel. Using data from the Siberian Solar Radio Telescope (5.7 GHz), we managed to localize the position of the source of the fine structure of drifting bursts at the remote footpoint of the large-scale flare loop.

PC-Kriging-powered parallelizing Bayesian updating for stochastic vehicle-track dynamical system with contact force measurements and Gaussian process discrepancy model

High-precision vehicle-track coupled dynamical models play a vital role in assessing the running safety of the vehicle, tracking fatigue behavior, and establishing a digital twin for high-speed railways. This study established a high-fidelity vehicle-track coupled dynamical model as a forward solver, which was then updated in a Bayesian inference framework based on the field tests of rail irregularities and wheel/rail normal contact forces. The prediction errors corresponding to different time steps were represented through a Gaussian process (GP) model characterized by a covariance function with the Gaussian kernel to incorporate the correlation between different time steps. To cope with the considerable expense of the likelihood function calculations with large-scale loop operations and the computational burden due to the large batch of repetitive evaluations of the high-fidelity forward model involved in the stochastic sampling from the posterior probability distribution, a metamodel-powered parallelizing stochastic sampling scheme was adopted. The posterior distribution could be formulated by replacing the expensive explicit model evaluation involved in the likelihood function with a Polynomial-Chaos-Kriging (PC-Kriging) predictor providing a surrogate mapping between the wheel/rail normal contact forces and physical parameters. Finally, a parallelizing computing scheme running across multiple CPU cores on high-performance computers was realized to sample from the vectorized formula of the emulator-powered posterior distribution. Field test data from a high-speed railway in China was adopted to demonstrate that the Bayesian inference scheme can quantify the uncertainties of the core physical parameters of the high-fidelity vehicle-track coupled dynamical system by efficiently trading off accuracy and computational efficiency.

Source Region and Launch Characteristics of Magnetic-arch-blowout Solar Coronal Mass Ejections Driven by Homologous Compact-flare Blowout Jets

We study the formation of four coronal mass ejections (CMEs) originating from homologous blowout jets. All of the blowout jets originated from NOAA Active Region (AR) 11515 on 2012 July 2, within a time interval of ≈14 hr. All of the CMEs were wide (angular widths ≈ 95°–150°), and propagated with speeds ranging between ≈300 and 500 km s−1 in LASCO coronagraph images. Observations at various EUV wavelengths in Solar Dynamics Observatory/Atmospheric Imaging Assembly images reveal that in all the cases, the source region of the jets lies at the boundary of the leading part of AR 11515 that hosts a small filament before each event. Coronal magnetic field modeling based on nonlinear force-free extrapolations indicates that in each case, the filament is contained inside of a magnetic flux rope that remains constrained by overlying compact loops. The southern footpoint of each filament is rooted in the negative polarity region where the eruption onsets occur. This negative polarity region undergoes continuous flux changes, including emergence and cancellation with opposite polarity in the vicinity of the flux rope, and the EUV images reveal brightening episodes near the filament’s southeastern footpoint before each eruption. Therefore, these flux changes are likely the cause of the subsequent eruptions. These four homologous eruptions originate near adjacent feet of two large-scale loop systems connecting from that positive polarity part of the AR to two remote negative polarity regions, and result in large-scale consequences in the solar corona.

Estimating the Critical Velocity of the Incipient Motion of Particles on the Cuttings Bed Surface: An Experimental and Theoretical Analysis

During the drilling of highly deviated and horizontal wells, a pump shutdown causes drill cuttings to settle and form a cuttings bed in the annulus. This study investigated the incipient motion law of the particles on the cuttings bed surface when the drilling fluid starts circulating again. This work could help field engineers to determine a reasonable incipient pump displacement to improve hole-cleaning efficiency. In this study, the effects of the well inclination angle, cuttings size, and different cuttings densities on the critical velocity of particle motion are analyzed experimentally, using a large-scale flow loop. Next, based on a stress analysis of the particles on the cutting bed surface and on the boundary layer flow around the particles, an analytical formula for the surface shear force of the drilling fluid on particles is derived and a critical velocity model for incipient motion is established. Verification is then carried out and combined with the experimental results. This study has important implications for the design of drilling operations and for the management of cuttings transport in oil and gas wells. It can guide the setting and prediction of pump discharge to improve hole-cleaning efficiency.

Secondary structure of the human mitochondrial genome affects formation of deletions

BackgroundAging in postmitotic tissues is associated with clonal expansion of somatic mitochondrial deletions, the origin of which is not well understood. Such deletions are often flanked by direct nucleotide repeats, but this alone does not fully explain their distribution. Here, we hypothesized that the close proximity of direct repeats on single-stranded mitochondrial DNA (mtDNA) might play a role in the formation of deletions.ResultsBy analyzing human mtDNA deletions in the major arc of mtDNA, which is single-stranded during replication and is characterized by a high number of deletions, we found a non-uniform distribution with a “hot spot” where one deletion breakpoint occurred within the region of 6–9 kb and another within 13–16 kb of the mtDNA. This distribution was not explained by the presence of direct repeats, suggesting that other factors, such as the spatial proximity of these two regions, can be the cause. In silico analyses revealed that the single-stranded major arc may be organized as a large-scale hairpin-like loop with a center close to 11 kb and contacting regions between 6–9 kb and 13–16 kb, which would explain the high deletion activity in this contact zone. The direct repeats located within the contact zone, such as the well-known common repeat with a first arm at 8470–8482 bp (base pair) and a second arm at 13,447–13,459 bp, are three times more likely to cause deletions compared to direct repeats located outside of the contact zone. A comparison of age- and disease-associated deletions demonstrated that the contact zone plays a crucial role in explaining the age-associated deletions, emphasizing its importance in the rate of healthy aging.ConclusionsOverall, we provide topological insights into the mechanism of age-associated deletion formation in human mtDNA, which could be used to predict somatic deletion burden and maximum lifespan in different human haplogroups and mammalian species.

Study of Temperature on the Corrosion Behavior of Antibacterial Steel by a Large-Scale Multiphase Flow Corrosion Test Loop.

The System #2 flow loop used in this study is a 4-inch-diameter, high-temperature, high-pressure system. In situ corrosion and electrochemical measurements were performed using a homemade flat corrosion specimen and a three-electrode probe. The experiment results show that temperature has an accelerated influence on the corrosion of antibacterial alloy steel. With the increase of temperature and the presence of O2 in the environment, a loose and porous corrosion product film was formed on the surface of the resistant steel, which made it easier for the corrosion medium to enter the corrosion product film from the pore, thus accelerating the corrosion.

Effect of Fluid Viscosity and Fiber Length on the Performance of Fibrous Fluid in Horizontal Well Cleanout

SummaryDuring drilling, completion, and intervention operations, solids can deposit in the wellbore. Innovative cleanout fluids reduce the problems associated with inadequate hole cleaning. Various methods have been developed to improve hole cleaning, but their effectiveness decreases as the wellbore inclination increases. One way to solve this issue is to add fibers to the drilling fluid and reduce the settling velocity of the solids to improve the fluid’s lifting capacity.The purpose of this study is to evaluate the cleanout performance of fibrous fluids in horizontal wells using a large-scale flow loop. Thus, flow loop experiments were conducted to assess the impact of fiber on equilibrium bed height. The experiment measures equilibrium bed height and pressure loss in an eccentric annular test section. During the investigation, the flow rate and apparent viscosity of the fluid and fiber length were varied.The results demonstrate the effectiveness of long fiber (length = 0.5 in.) in improving hole cleanout in horizontal wellbores. When a small amount (0.04% wt.) of long fiber was added, the cleanout performance of the high-viscosity fluid did not show a noticeable change. In contrast, the performance of the low-viscosity fluid improved. Even though adding fiber has minimal impact on the apparent viscosity of the fluids, the long fiber improved the cleaning performance of the low-viscosity fluid.Hole cleaning is challenging in operations such as coiled tubing (CT) in which rotating the drillstring is impossible. Hence, this study focuses on cleanout operations in horizontal wellbores without drillstring rotation. The novelty of this work lies in demonstrating how the adjustment of fluid viscosity can positively impact the hole cleaning performance of fibrous fluids in the absence of pipe rotation. The study also presents a new approach to modeling the effects of solids bed irregularity on wellbore pressure loss and equivalent circulating density (ECD).

White-light QFP wave train and the associated failed breakout eruption

Quasi-periodic fast-propagating (QFP) magnetosonic wave trains are commonly observed in the low corona at extreme ultraviolet wavelength bands. Here, we report the first white-light imaging observation of a QFP wave train propagating outwardly in the outer corona ranging from 2 to 4 R⊙. The wave train was recorded by the Large Angle Spectroscopic Coronagraph on board the Solar and Heliospheric Observatory (SOHO), and was associated with a GOES M1.5 flare in NOAA active region AR12172 at the southwest limb of the solar disk. Measurements show that the speed and period of the wave train were about 218 km s−1 and 26 min, respectively. The extreme ultraviolet imaging observations taken by the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory reveal that in the low corona the QFP wave train was associated with the failed eruption of a breakout magnetic system consisting of three low-lying closed loop systems enclosed by a high-lying large-scale one. Data analysis results show that the failed eruption of the breakout magnetic system was mainly because of the magnetic reconnection that occurred between the two lateral low-lying closed-loop systems. This reconnection enhances the confinement capacity of the magnetic breakout system because the upward-moving reconnected loops continuously feed new magnetic fluxes to the high-lying large-scale loop system. For the generation of the QFP wave train, we propose that it could be excited by the intermittent energy pulses released by the quasi-periodic generation, rapid stretching, and expansion of the upward-moving, strongly bent reconnected loops.

Harmonic Electron Cyclotron Maser Emission along the Coronal Loop

Efficient radiation at second and/or higher harmonics of Ωce has been suggested to circumvent the escaping difficulty of the electron cyclotron maser emission mechanism when it is applied to solar radio bursts, such as spikes. In our earlier study, we developed a three-step numerical scheme to connect the dynamics of energetic electrons within a large-scale coronal loop structure with the microscale kinetic instability energized by the obtained nonthermal velocity distribution and found that direct and efficient harmonic X-mode (X2 for short) emission can be achieved due to the strip-like features of the distribution. That study only considered the radiation from the loop top at a specific time. Here we present the emission properties along the loop at different locations and timings. We found that, in accordance with our earlier results, few to several strip-like features can appear in all cases, and the first two strips play the major role in exciting X2 and Z (i.e., the slow extraordinary mode) that propagate quasi-perpendicularly. For the four sections along the loop, significant excitation of X2 is observed from the upper two sections, and the strongest emission is from the top section. In addition, significant excitation of Z is observed for all loop sections, while there is no significant emission of the fundamental X mode. The study provides new insight into coherent maser emission along the coronal loop structure during solar flares.

Oscillatory reconnection and waves driven by merging magnetic flux ropes in solar flares

ABSTRACT Oscillatory reconnection is a process that has been suggested to underlie several solar and stellar phenomena, and is likely to play an important role in transient events such as flares. Quasi-periodic pulsations in flare emissions may be a manifestation of oscillatory reconnection, but the underlying mechanisms remain uncertain. In this paper, we present 2D magnetohydrodynamic simulations of two current-carrying magnetic flux ropes with an out-of-plane magnetic field undergoing oscillatory reconnection in which the two flux ropes merge into a single flux rope. We find that oscillatory reconnection can occur intrinsically without an external oscillatory driver during flux rope coalescence, which may occur both during large-scale coronal loop interactions and the merging of plasmoids in fragmented current sheets. Furthermore, we demonstrate that radially propagating non-linear waves are produced in the aftermath of flux rope coalescence, due to the post-reconnection oscillations of the merged flux rope. The behaviour of these waves is found to be almost independent of the initial out-of-plane magnetic field. It is estimated that the waves emitted through merging coronal loops and merging plasmoids in loop-top current sheets would have a typical phase speed of 90 and 900 km s−1, respectively. It is possible that the properties of the waves emitted during flux rope coalescence could be used as a diagnostic tool to determine physical parameters within a coalescing region.

A novel prediction model for cuttings bed height in horizontal and deviated wells

A better understanding of cuttings accumulation in the wellbore and ensuring favorable hole-cleaning conditions are crucial for successful oil and gas drilling operations. Considering the limited ability of existing critical velocity models to predict the cuttings bed height, and these models only consider the rolling transport mode of drill cuttings, improvement and development of new models are needed. This paper presents a new model for predicting the cuttings bed height over three possible transport modes of the target bed particle: sliding, rolling, and lifting. A mechanical equilibrium relationship of the particle in the critical condition is established and to calculate the bed-friction velocity of different transport modes. The transport mode can be judged by comparison among the minimum calculated values. The mean annular velocity and cuttings bed height can be calculated according to the borehole geometry information and eccentricity. The model can be applied to drilling fluids with different flow patterns (laminar, turbulent) and different rheological models (Newtonian fluid such as water, non-Newtonian fluid conforming to Power-Law or Herschel-Bulkley models). The effects of inclination angle, cuttings size, circulation velocity, rheological parameters, eccentricity, and hole size on mean annular velocity and cuttings bed height were analyzed. Cuttings transportation experiments were carried out on a large-scale flow loop to validate the theoretical analysis results by comparison against the experimental results. This work has certain guiding significance for predicting the hole cleaning degree in the annulus, as well as the subsequent optimization of hydraulic parameters and the implementation of hole-cleaning measures.

Vectorization and distributed parallelization of Bayesian model updating based on a multivariate complex-valued probabilistic model of frequency response functions

This study was devoted to investigating stochastic model updating in a Bayesian inference framework based on a frequency response function (FRF) vector without any post-processing such as smoothing and windowing. The statistics of raw FRFs were inferred with a multivariate complex-valued Gaussian ratio distribution. The likelihood function was formulated by embedding the theoretical FRFs that contained the model parameters to be updated in the class of the probability model of the raw FRFs. The Transitional Markov chain Monte Carlo (TMCMC) used to sample the posterior probability density function implies considerable computational toll because of the large batch of repetitive analyses of the forward model and the increasing expense of the likelihood function calculations with large-scale loop operations. The vectorized formula was derived analytically to avoid time-consuming loop operations involved in the likelihood function evaluation. Furthermore, a distributed parallel computing scheme was developed to allow the TMCMC stochastic simulation to run across multiple CPU cores on multiple computers in a network. The case studies demonstrated that the fast-computational scheme could exploit the availability of high-performance computing facilities to drastically reduce the time-to-solution. Finally, parametric analysis was utilized to illustrate the uncertainty propagation properties of the model parameters with the variations of the noise level, sampling time, and frequency bandwidth.

Transverse oscillation of a coronal loop induced by a flare-related jet

Context. Kink oscillations in coronal loops are ubiquitous, and we apply the observed parameters of oscillations to estimate the magnetic field strength of the loops. Aims. In this work, we report our multiwavelength observations of the transverse oscillation of a large-scale coronal loop with a length of ≥350 Mm. The oscillation was induced by a blowout coronal jet, which was related to a C4.2 circular-ribbon flare (CRF) in active region 12434 on 2015 October 16. We aim to determine the physical parameters in the coronal loop, including the Alfvén speed and the magnetic field strength. Methods. The jet-induced kink oscillation was observed in extreme ultraviolet (EUV) wavelengths by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). Line-of-sight magnetograms were observed by the Helioseismic and Magnetic Imager (HMI) on board the SDO. We took several slices along the loop to assemble time-distance diagrams and used an exponentially decaying sine function to fit the decaying oscillation. The initial amplitude, period, and damping time of kink oscillations were obtained. Coronal seismology of the kink mode was applied to estimate the Alfvén speed and the magnetic field strength in the oscillating loop. In addition, we measured the magnetic field of the loop through nonlinear force-free field (NLFFF) modeling using the flux rope insertion method. Results. The oscillation is most pronounced in AIA 171 and 131 Å. The oscillation is almost in phase along the loop with a peak initial amplitude of ∼13.6 Mm, meaning that the oscillation belongs to the fast standing kink mode. The oscillation lasts for ∼3.5cycles with an average period of ∼462 s and an average damping time of ∼976 s. The values of τ/P lie in the range of 1.5–2.5. Based on coronal seismology, the Alfvén speed in the oscillating loop is estimated to be ∼1210 km s−1. Two independent methods are applied to calculate the magnetic field strength of the loop, resulting in 30–43 G using coronal seismology and 21–23 G using NLFFF modeling. Conclusions. The magnetic field strength estimated using two different approaches are on the same order of magnitude, which confirms the reliability of coronal seismology by comparing with NLFFF modeling.

Combining Virtual Reality Visualization with Ensemble Molecular Dynamics to Study Complex Protein Conformational Changes.

Molecular dynamics (MD) simulations are increasingly used to elucidate relationships between protein structure, dynamics, and their biological function. Currently, it is extremely challenging to perform MD simulations of large-scale structural rearrangements in proteins that occur on millisecond timescales or beyond, as this requires very significant computational resources, or the use of cumbersome "collective variable" enhanced sampling protocols. Here, we describe a framework that combines ensemble MD simulations and virtual reality visualization (eMD-VR) to enable users to interactively generate realistic descriptions of large amplitude, millisecond timescale protein conformational changes in proteins. Detailed tests demonstrate that eMD-VR substantially decreases the computational cost of folding simulations of a WW domain, without the need to define collective variables a priori. We further show that eMD-VR generated pathways can be combined with Markov state models to describe the thermodynamics and kinetics of large-scale loop motions in the enzyme cyclophilin A. Our results suggest eMD-VR is a powerful tool for exploring protein energy landscapes in bioengineering efforts.

Solar Flare–CME Coupling throughout Two Acceleration Phases of a Fast CME

Abstract Solar flares and coronal mass ejections (CMEs) are closely coupled through magnetic reconnection. CMEs are usually accelerated impulsively within the low solar corona, synchronized with the impulsive flare energy release. We investigate the dynamic evolution of a fast CME and its associated X2.8 flare occurring on 2013 May 13. The CME experiences two distinct phases of enhanced acceleration, an impulsive one with a peak value of ∼5 km s−2, followed by an extended phase with accelerations up to 0.7 km s−2. The two-phase CME dynamics is associated with a two-episode flare energy release. While the first episode is consistent with the “standard” eruption of a magnetic flux rope, the second episode of flare energy release is initiated by the reconnection of a large-scale loop in the aftermath of the eruption and produces stronger nonthermal emission up to γ-rays. In addition, this long-duration flare reveals clear signs of ongoing magnetic reconnection during the decay phase, evidenced by extended hard X-ray bursts with energies up to 100–300 keV and intermittent downflows of reconnected loops for >4 hr. The observations reveal that the two-step flare reconnection substantially contributes to the two-phase CME acceleration, and the impulsive CME acceleration precedes the most intense flare energy release. The implications of this non-standard flare/CME observation are discussed.

Effect of Particle Size and Surface Properties on the Sandbed Erosion with Water Flow in a Horizontal Pipe

Summary An experimental study was conducted to investigate the transport of sand particles over the sand bed deposited in a horizontal conduit by using turbulent flow of water. The main objectives were to determine the near-wall turbulence characteristics at the onset of bed erosion (i.e., near-wall velocity profile, Reynolds shear stresses, and axial-turbulent intensity); to determine critical velocity required for particle removal from the bed deposits; and more specifically, to determine how the sand-particle size and surface characteristics would influence the critical velocity required for the onset of bed erosion and the near-wall turbulence characteristics. A large-scale horizontal flow loop equipped with a nonintrusive laser-based particle-image velocimetry (PIV) system has been used for the experiments. The effect of sand-particle surface characteristics (i.e., wettability) on the critical velocity and the near-wall turbulence characteristics were investigated by using treated and untreated industrial sands of four different mesh sizes (i.e., 20/40, 30/50, 40/70, 100). The PIV technique was used to determine instantaneous local velocity distribution near the stationary sandbed fluid interface under subcritical and critical flow conditions. The near-wall velocity distribution measured directly at the sand bed/fluid interface together with the measured frictional pressure-loss values were then used for the evaluation of the Reynolds shear stresses and axial turbulent intensities acting at the bed/fluid interface. The results indicated that critical velocity for the onset of particle removal from sand beds increased with the increasing particle size. When sands with special surface treatment were used, it was observed that the critical velocity required for the onset of the bed erosion was significantly lower than that of required for the untreated sands. The degree of reduction in critical velocity varied between 14 and 40% depending on the particle size. In this study, by conducting experiments under controlled conditions, we provided much-needed fundamental data that can be used for the development of improved solid-transport design criteria and suitable mitigation technologies. In particular, we have shown the proof of concept that the surface-treated sand particles might have great potential for improving the transport efficiency of proppants used for hydraulic-fracturing operations.

Perspective of S−CO2 power cycles

In this perspective paper, the research and development of S-CO2 cycles are analyzed from two aspects: (i) the system design and analysis and (ii) energy transfer/conversion mechanisms and key components development. Based on the analysis, barriers for further promotion of S-CO2 cycles are summarized, including the lack of system design and analysis methodology, not well understood mechanisms of energy transfer/conversion, and technic barriers such as seal, leakage and roto-dynamics stability of key components. To overcome these issues, perspectives on three aspects are proposed. First, S-CO2 cycle adapting to the distinct characteristic of a heat source should be optimized to promote the global system efficiency. Second, new theoretical/numerical works are suggested emphasizing the real gas effect of S-CO2 to improve the accuracy, convergence and stability of numerical simulations, fine experiments should be expanded to verify the correctness of the numerical simulations. Third, the integrated solution strategies for key components such as intermediate heat exchanger, recuperator heat exchanger and turbomachines should be developed and verified in large-scale test loop for reliable and efficient operation. This critical review is hopefully to present readers a clue to promote the development of S-CO2 cycles driven by nuclear energy, renewable energy and fossil energy.

Parallel loop cluster quantum Monte Carlo simulation of quantum magnets based on global union-find graph algorithm

A large-scale parallel loop cluster quantum Monte Carlo simulation is presented. On 24,576 nodes of the K computer, one loop cluster Monte Carlo update of the world-line configuration of the S=1∕2 antiferromagnetic Heisenberg chain with 2.6×106 spins at inverse temperature 3.1×105 is executed in about 8.62 s, in which global union-find cluster identification on a graph of about 1.1 trillion vertices and edges is performed. By combining the nonlocal global updates and the large-scale parallelization, we have virtually achieved about 1013-fold speed-up from the conventional local update Monte Carlo simulation performed on a single core. We have estimated successfully the antiferromagnetic correlation length and the magnitude of the first excitation gap of the S=4 antiferromagnetic Heisenberg chain for the first time as ξ=1.040(7)×104 and Δ=7.99(5)×10−4, respectively.

Effect of Sand Bed Deposits on the Characteristics of Turbulent Flow of Water in Horizontal Annuli

An experimental program was conducted to investigate turbulent flow of water over the stationary sand bed deposited in horizontal annuli. A large-scale horizontal flow loop equipped with the state-of-the-art particle image velocimetry (PIV) system has been used for the experiments. Experiments were conducted to measure the instantaneous local velocity profiles during turbulent flow and examine the impact of the presence of a stationary sand bed deposits on the local velocity profiles, Reynolds shear stresses and turbulence intensities. Results have shown that the existence of a stationary sand bed causes the volumetric flow to be diverted away from the lower annular gap. Increasing the sand bed height causes further reduction of the volumetric flow rate in the lower annulus. Velocity profiles near the surface of the bed deposits showed a downward shift from the universal law in wall units indicating that the flow is hydraulically rough near the sand bed. The equivalent roughness height varied with flow rates. At flow rates less than the critical flow rate, the Reynolds stress profile near the bed interface had slightly higher peak values than that of the case with no sand bed. At the critical flow rate, however, the peak Reynolds stress values for the flow over the sand bed was lower than that of the case with no bed. This behavior is attributed to the bed load transport of sand particles at the critical flow rate.