Irregular Roughness Research Articles

The Properties of Xylan Extracted from Corncob Using Deep Eutectic Solvent

Abstract Corncob is an abundant agricultural biomass that is generally underutilized and discarded. It has potential to be a resource for high-value products due to its cellulose and hemicellulose content. Xylan, which is the primary constituent of hemicellulose, can serve as a raw material or intermediary in both non-food and food industry. This research aims to study the extraction of xylan from corncob using deep eutectic solvent (DES) for clean processing and analyzes the characteristics of corncob xylan. DES comprises choline chloride and acetic acid with a molar ratio of 1:2. Xylan was extracted from corncobs by immersion in aqueous DES (70% and 90%) and heating using an autoclave at 105°C for 15 minutes. FT-IR and NMR characterized the chemical structures of xylan, while FE-SEM observed the surface. The FT-IR result showed that xylan had a peak range of 1041 cm−1, which is attributed to the glycosidic bond. A delignification process seems to have occurred as indicated by the absorption peak at 1475-1477 cm−1, indicating the presence of lignin in xylan and solid residue. Both types of extracted xylan had similar NMR spectra in the 3-4.3 ppm range, which indicates that they contained xylose. The solid residue structure obtained from extracting two DES concentrations shows the difference in the extraction process. However, the surface morphology of the two types of extracted xylan had a similar irregular shape and roughness. The use of the DES choline chloride-acetic acid could lead to the extraction and separation of xylan from lignocellulosic corncob.

Physicochemical properties and fractal characterizations of the functionalized porous clinoptilolites for controlling alginate delivery in growing cauliflower and leaf mustard

Using natural clinoptilolite (NCP) as a carrier and alginate (Alg)-calcium as an active species, the porous silicon calcium alginate nanocomposite (Alg-Ca-NCP) was successfully fabricated via adsorption-covalence-hydrogen bond. Its structural features and physicochemical properties were detailed investigated by various characterizations. The results indicated that Alg-Ca-NCP presented the disordered lamellar structures with approximately uniform particles in size of 300–500 nm. Specially, their surface fractal evolutions between the irregular roughness and dense structures were demonstrated via the SAXS patterns. The results elucidated that the abundant micropores of NCP were beneficial for unrestricted diffusing of Alg-Ca, which was conducive to facilitate a higher loading and sustainable releasing. The Ca content of leaf mustard treated with Alg-Ca-NCP-0.5 was 484.5 mg/100g on the 21st day, higher than that by water (CK) and CaCl2 solution treatments, respectively. Meanwhile, the prepared Alg-Ca-NCPs presented the obvious anti-aging effects on peroxidase drought stress of mustard leaves. These demonstrations provided a simple and effective method to synthesize Alg-Ca-NCPs as delivery nanocomposites, which is useful to improve the weak absorption and low utilization of calcium alginate by plants.

Adhesion Behavior of Underground Coal Dust with Fused Silica: Effects of Relative Humidity and Particle Size

Coal dust particles adhering to a camera lens reduce its light transmittance, which deteriorates the performance of the camera and may lead to serious problems with mining equipment that requires visual ability. Aiming at improving coal dust removal and cleaning technologies, the adhesion behavior of coal dust with fused silica is studied here. Experiments were conducted from microscopic and statistical points of view. The adhesion force between a single coal dust particle and fused silica is tested using atomic force microscopy (AFM), and the number and size distribution of large amounts of coal dust particles on fused silica are tested using a home-made adhesion experimental platform and image processing method. The results show that the adhesion force increases at high relative humidity (RH); it is dominated by van der Waals forces at low RH and capillary forces at high RH. The fused silica glass surface is predominantly covered by small-sized coal dust particles, and the total number of particles as well as the proportion of large-sized particles increases with RH. The theoretical values of van der Waals and capillary forces are significantly larger than the experimental values, owing to the irregular shape and roughness of the surface of the coal dust.

Numerical Investigation of Thermo-Flow Characteristics of Tubes with Transverse Micro-Fins

The article presents the results of numerical studies of heat transfer and pressure drops in a channel with transverse micro-fins. The main aim of the study was to prepare the thermal and flow characteristics of such a channel for a variable longitudinal spacing of micro-fins. For the tested pipe with an internal diameter of D = 12 mm, the absolute height of the micro-fins was e = 0.243 mm, which is 2% of its diameter. The tests were carried out for turbulent flow in the range of Reynolds numbers of 5000–250,000 with the variable spacing of micro-ribs in the range of L = 0.28–13.52 mm, which corresponds to their dimensionless longitudinal distance, L/D = 0.023–1.126. For the studied geometries, the characteristics of the friction factor, ft(Re), and the Nusselt number, Nu(Re), are shown in the graphs. The highest values of Nu were observed for a spacing of L/D = 0.092 in the range of Re = 5000–60,000, while the lowest were observed for a geometry of L/D = 0.035 for Re = 60,000–250,000. The friction factors, however, were the highest for the two geometries L/D = 0.161 and L/D = 0.229 over the entire range of the tested Re numbers. A large discrepancy was observed between the friction factors calculated from the Colebrook–White equation (for irregular relative roughness depicted in the Moody diagram) and those obtained from simulations (for pipes with the same roughness height but regular geometry created by micro-fins). An analysis of the heat transfer efficiency of the tested geometries was also presented, taking into account the criterion of equal pumping power, i.e., the PEC (performance evaluation criteria) coefficient. The highest values of the PEC coefficient, up to 1.25–1.28, were obtained for micro-fin spacings of L/D = 0.069 and L/D = 0.092 in the Re number range of 20.000–30.000.

The role of the areal parameters on turbulent flow over 2D Gaussian roughness

In the past decades, numerous efforts have been dedicated to establishing a direct correlation between a geometric parameter that represents wall roughness and the corresponding velocity reduction, known as the Roughness Function ΔU+. This reduction is influenced by various statistical measures of roughness height, including average roughness height, peak-to-valley roughness distance, roughness root mean square, and Effective Slope, among others. It has been demonstrated that a singular measure of roughness height cannot sufficiently predict the Roughness Function across all turbulent regimes. Consequently, many studies have concentrated on identifying a universal correlation between roughness geometry and the downward shift of the mean velocity profile. In this study, we investigated the correlation between various geometrical parameters and the Roughness Function using Large Eddy Simulation (LES) techniques in channel flows at a friction Reynolds number of Reτ=400. Given the complexity introduced by the random nature of irregular roughness, we explored specific aspects of the relationship between wall irregularities and the roughness function by studying 2D geometries. This approach allowed us to systematically investigate the impact of geometrical properties on the roughness function and isolate the effects of roughness density and coverage area. Several irregular rough surfaces, characterized by different average oscillations height, different distributions and different densities, were designed throughout 2D Gaussian functions. With the aim to find a universal correlation between the roughness geometry and the Roughness Function, new geometrical quantities were investigated, based on the global area occupied by the roughness A∗. The prediction of the roughness function can be thus obtained using apriori data. To predict the roughness function, we introduced a parameter called Effective Area (EA), which is derived from the correlation between the Effective Slope (ES) and the roughness area A∗. Our findings indicate that a single geometric parameter, whether ES or Area A, is insufficient to predict the roughness effect. Conversely, combining these two parameters enhances predictive accuracy, at least for the proposed roughness model. This improvement can be attributed to the ability of ES to interpret the roughness distribution and height, while the coverage area is effective in predicting roughness density over a flat plate.

Direct Numerical Simulation of Transitional and Turbulent Flows Over Multi-Scale Surface Roughness—Part I: Methodology and Challenges

Abstract High-fidelity simulation of transitional and turbulent flows over multi-scale surface roughness presents several challenges. For instance, the complex and irregular geometrical nature of surface roughness makes it impractical to employ conforming structured grids, commonly adopted in large-scale numerical simulations due to their high computational efficiency. One possible solution to overcome this problem is offered by immersed boundary methods, which allow wall boundary conditions to be enforced on grids that do not conform to the geometry of the solid boundary. To this end, a three-dimensional, second-order accurate boundary data immersion method (BDIM) is adopted. A novel mapping algorithm that can be applied to general three-dimensional surfaces is presented, together with a newly developed data-capturing methodology to extract and analyze on-surface flow quantities of interest. A rigorous procedure to compute gradient quantities such as the wall shear stress and the heat flux on complex non-conforming geometries is also introduced. The new framework is validated by performing a direct numerical simulation (DNS) of fully developed turbulent channel flow over sinusoidal egg-carton roughness in a minimal-span domain. For this canonical case, the averaged streamwise velocity profiles are compared against results from the literature obtained with a body-fitted grid. General guidelines on the BDIM resolution requirements for multi-scale roughness simulation are given. Momentum and energy balance methods are used to validate the calculation of the overall skin friction and heat transfer at the wall. The BDIM is then employed to investigate the effect of irregular homogeneous surface roughness on the performance of an LS-89 high-pressure turbine blade at engine-relevant conditions using DNS. This is the first application of the BDIM to realize multi-scale roughness for transitional flow in transonic conditions in the context of high-pressure turbines. The methodology adopted to generate the desired roughness distribution and to apply it to the reference blade geometry is introduced. The results are compared to the case of an equivalent smooth blade.

Prediction of equivalent sand-grain size and identification of drag-relevant scales of roughness – a data-driven approach

Despite decades of research, a universal method for prediction of roughness-induced skin friction in a turbulent flow over an arbitrary rough surface is still elusive. The purpose of the present work is to examine two possibilities; first, predicting equivalent sand-grain roughness size $k_s$ based on the roughness height probability density function and power spectrum (PS) leveraging machine learning as a regression tool; and second, extracting information about relevance of different roughness scales to skin-friction drag by interpreting the output of the trained data-driven model. The model is an ensemble neural network (ENN) consisting of 50 deep neural networks. The data for the training of the model are obtained from direct numerical simulations (DNS) of turbulent flow in plane channels over 85 irregular multi-scale roughness samples at friction Reynolds number $Re_\tau =800$ . The 85 roughness samples are selected from a repository of 4200 samples, covering a wide parameter space, through an active learning (AL) framework. The selection is made in several iterations, based on the informativeness of samples in the repository, quantified by the variance of ENN predictions. This AL framework aims to maximize the generalizability of the predictions with a certain amount of data. This is examined using three different testing data sets with different types of roughness, including 21 surfaces from the literature. The model yields overall mean error 5 %–10 % on different testing data sets. Subsequently, a data interpretation technique, known as layer-wise relevance propagation, is applied to measure the contributions of different roughness wavelengths to the predicted $k_s$ . High-pass filtering is then applied to the roughness PS to exclude the wavenumbers identified as drag-irrelevant. The filtered rough surfaces are investigated using DNS, and it is demonstrated that despite significant impact of filtering on the roughness topographical appearance and statistics, the skin-friction coefficient of the original roughness is preserved successfully.

Direct numerical simulation of turbulent flow in pipes with realistic large roughness at the wall

We carry out direct numerical simulation (DNS) of turbulent flow in rough pipes. Two types of irregular roughness are investigated, namely a grit-blasted and a graphite surface. A wide range of Reynolds numbers is tested, from the laminar up to the fully rough regime, attempting to replicate Nikuradse's pioneering study. Despite the large relative roughness, outer-layer similarity is achieved at high Reynolds number as hypothesised by Townsend, with deviations from the smooth wall case of 4 % for the grit-blasted surface and 13 % for the graphite surface. This makes it possible to define a roughness function and the equivalent sand-grain roughness. The results are compared with those obtained in plane channels, with small differences pointing to the residual influence of the duct cross-sectional shape in the presence of relatively large roughness. The computed friction factors behave similar to those Nikuradse's chart, with differences in terms of the friction factor in the laminar region and of the critical Reynolds number, which are partly absorbed by using the hydraulic radius as reference length scale. The distributions of the velocity fluctuations intensities point to a isotropisation of turbulence in the near-wall region resulting from the roughness, with influence of the roughness geometry. Comparison of the computed equivalent sand-grain roughness height suggest that existing correlations suffer from poor predictive power, at least for surfaces with large relative roughness.

Impact of calcium addition on the characteristics of hyaluronic acid-based oral films for vitamin D supplementation

An orally disintegrating film (ODF) was developed using hyaluronic acid as a base material, along with incorporation of vitamin D and varying amounts of calcium citrate. Increasing calcium amount within ODF resulted in higher opacity of the film, and stiffer texture. Microscopic examination of calcium-added films revealed consistently rough surfaces and cross-sections with irregular roughness. The moisture content and water vapor permeability were found to be higher in calcium-added films than in control films, however there was no significance by calcium amount. The content analysis indicated a loss of 32.66–46.16% of vitamin D and 8.05–13.53% of calcium in a sheet of ODF, which could be attributed to the formation of new chemical bonds among HA, vitamin D and calcium based on the result of FT-IR. In this study, it was successfully developed an ODF containing both vitamin D and calcium. However, unlike vitamin D, which can be added in recommended quantities within a single ODF, the addition of the insoluble bulk mineral, calcium, is limited, indicating that addition of plasticizer or technologies may be required to achieve an adequate amount of calcium incorporation into the ODF.

A comparison of RANS models used for CFD prediction of turbulent flow and heat transfer in rough and smooth channels

CFD of convective heat transfer remains a challenge, especially in channels with irregular rough walls due to the complex fluid dynamics over and between these roughness elements. This study investigates the performance of four commonly utilised RANS CFD models, namely Spalart-Allmaras (SA), Realisable k-ε, SST k-ω, and Reynolds Stress Model (RSM) in estimating the velocity and temperature profile as well as the skin friction coefficient and Nusselt number in smooth and rough channels. The CFD results were compared with DNS and experimental data in the literature. The roughness-resolving approach was used for all models to resolve the realistic geometry of irregular roughness in channel flows. The smooth-channel flow study was conducted at Reτ = 500, 1000, 2000, and 5000 and Pr = 0.71. Over this range, compared to smooth-wall DNS data from literature, the RSM showed consistent and satisfactory performance in estimating the velocity and temperature profiles within 2.54% and 4.21%, respectively; leading to the skin friction coefficient and Nusselt number in the smooth channels being predicted very well within 1.94% and 2.03%, respectively. The rough-channel flow study was performed at Reτ = 240, 360, 540, 720, 1000 and Pr = 1, with computational cells 7.8 times that of the smooth channel to resolve the irregular roughness geometry. Over this range, the Realisable k-ε showed the best performance in estimating the roughness function within 6.85%, while the results of the other models were wider at uncertainty levels of up to 36.9%. Similarly, the Realisable k-ε demonstrated the best performance in estimating the skin friction and Nusselt number in rough channels within 2.76% and 9.50%, respectively, while the performance of the other models was to a wider latitude ranging between 15.62% to 26.34%. In the present study, the Realisable k-ε with enhanced wall treatment showed the best capabilities in capturing the mean flow characteristics of both smooth and rough channels; however, its usage should be approached with caution in flows at higher Reynolds numbers. RANS models are also discussed for forced convection heat transfer at high Reynolds numbers. The results of this study should be useful in CFD studies on the effects of roughness in complex geometries without the need for LES and DNS.

A generalized theory of flow forcing by rough topography

An analytical model is developed which explores the impact of irregular sea-floor roughness on large-scale oceanic flows. The previously reported asymptotic ‘sandpaper’ theory of flow-topography interaction represents relatively swift currents and exhibits singular behaviour in the weak flow limit. The present investigation systematically spans a wider parameter space and identifies the principal dissimilarities in the topographic regulation of slow and fast currents. The fast flows are controlled by the Reynolds stresses produced by topographically generated eddies. In contrast, relatively weak flows are more affected by the eddy-induced bottom form drag. The asymptotic models for fast and slow currents are then combined to arrive at a concise description of flow forcing by small-scale topography in homogeneous and multilayer models. The proposed closure is validated by comparing corresponding topography-resolving and parametric simulations.

Direct numerical simulation of vertically heated natural convection over 3D irregular roughness

Natural convection in a cavity having an aspect ratio of 4 with irregular roughness on vertical isothermal sidewalls is investigated through compressible direct numerical simulation at a Rayleigh number of 1 × 1010. The compressible solver combined with the immersed boundary adopted in this paper is validated. The profiles of probability density functions of the thermal and hydrodynamic quantities show that at this Rayleigh number, the roughness increases the instability of the nearby fluid. In the instantaneous results, the isosurfaces of the Q-criterion reveal that a vortex is generated near roughness peaks and increases the local heat transfer, but in the valley regions, it is difficult to find vortex structures like in the peak regions. Results for the quasi-steady state show that the cavity with rough sidewalls has a lower Nusselt number on the hot wall than the smooth cavity. In other words, the roughness adversely affects the wall heat transfer. This indicates that the hot sidewall with roughness conveys less energy than the smooth wall. As a consequence, the fluid in the cavity with rough sidewalls has lower wall shear stress than that with smooth sidewalls. However, the results of the eddy heat flux show that turbulent flows generated by roughness enhance the heat transfer near the sidewalls. As the mixing effects of turbulent flows strengthen, the disparity of the average Nusselt number at the sidewall between rough and smooth cases reduces.

The effects of irregular roughness with different surface power spectrums on the heat transfer of natural convection in enclosures

The effects of irregular roughness with different surface power spectrums on the heat transfer of natural convection in enclosures

An experimental and numerical study of turbulent oscillatory flow over an irregular rough wall

The hydrodynamics of turbulent oscillatory flow over a gravel-based irregular rough wall is investigated using laser-Doppler anemometry measurements of velocities in a large oscillatory flow tunnel and direct numerical simulation (DNS) of the Navier–Stokes equations. The same periodic irregular roughness was used for both experiments and DNS. Four flow shapes are investigated: sinusoidal, skewed, asymmetric and combined skewed–asymmetric. The experiments were conducted for target Reynolds numbers (based on the Stokes length and standard deviation of free-stream velocity) of$R_{\delta,\sigma }=800$and$R_{\delta,\sigma }=1549$; DNS was conducted for flows with target$R_{\delta,\sigma }=800$. Boundary layer thickness, bottom phase lead and friction factor are in good agreement with previous studies. For the first time, evidence of Prandtl's secondary flows of the second kind in oscillatory flow is presented. Turbulence structure is visualised using isosurfaces of$\lambda _{2}$(Jeong & HussainJ. Fluid Mech., vol. 285, 1995, pp. 69–94), revealing densely packed structures that grow stronger and weaker in correspondence with the free-stream velocity. Reynolds and dispersive stresses peak just below the highest roughness crest, with dispersive stress vanishing a short distance above the roughness. Bursts of turbulence kinetic energy and wake kinetic energy are generated each flow half-cycle, with variable behaviour depending on flow shape. Non-Gaussian turbulence statistics are observed that originate near the wall, becoming increasingly non-Gaussian far from the wall. Probability density functions of turbulence statistics can be closely approximated by a fourth-order Gram–Charlier distribution at most phases and elevations, though when statistics deviate more strongly from Gaussian, streamwise and wall-normal (spanwise) statistics are better described by a Pearson type IV (VII) distribution.

Anisotropic property of turbulent flow control through multiple stenosed microtubes

Rapid development in micro-scale systems and devices for drug delivery and biotechnical analysis has been scurrying. Microtube or microchannel roughness is another challenging factor in microfabrication technology. Moreover, the irregular roughness occurs due to the multiple depositions of cholesterol and other substances in the endothelium of the arterial wall. To investigate those issues, the effect of the irregular roughness of the wall on the anisotropy of the turbulent blood flow through an atherosclerotic artery has been analyzed. The flow through a stenosed microtube has been numerically simulated to understand the blood flow phenomenon through arterial stenosis and different turbulent states. The Reynolds stress components are estimated and plotted an invariant map and Eigen map to examine the turbulent states. The comparison results have been studied to show the nature of turbulent flow in low Reynolds numbers due to irregular roughness. The turbulent kinetic energy and turbulent viscous dissipation rate are also examined. Due to wall shear stress, the flow deserves the turbulence flow characteristic downstream of the abnormally narrowed regions of the microtube. The nature of the wall shear rate and the high viscosity of blood impact the disturbance in the flow velocity in microtubes.

Surface Topography Description of Threads Made with Turning on Inconel 718 Shafts

The technology of producing threads, especially in materials that are difficult to cut, is a rare subject of research and scientific publications. The requirements for the production of these elements apply not only to the geometry, but also to the quality of the surface obtained. This is particularly important in the aviation industry, where the durability of the threaded connection affects passenger safety. Due to the design of the thread, the quality of its surface is assessed visually in industrial practice. The authors of this study decided to examine the surface topography of external threads made by turning on Inconel 718 shafts in order to confirm the visual evaluation, as well as to investigate the influence of such factors as cutting speed, turning direction and type of profile. Three types of contours were cut for the research: triangular, trapezoidal symmetrical and trapezoidal asymmetrical. Turning of each was carried out twice at cutting speeds vc = 17 m/min and vc = 30 m/min. On each of the threads, the side surface of the profile made in the direction of the insert feed and the opposite surface were examined. The surface texture parameters Sa, Sq, Sp, Sv, Sz, Ssk and Sku were determined and compared. It was noticed that the thread surfaces show a tendency to irregular roughness, which was confirmed by the analysis of the Sku and Ssk coefficients. The sides of the contours made in the direction of the insert feed are characterized by a higher roughness in relation to the opposite sides, which may result from high cutting forces and difficulties with chip evacuation. With the cutting speed being considered, lower values of Sa and Sq were obtained for vc = 17 m/min, which differed from the visual assessment, proving its high subjectivity.

Spin-down of a baroclinic vortex by irregular small-scale topography

This study explores the impact of small-scale variability in the bottom relief on the dynamics and evolution of broad baroclinic flows in the ocean. The analytical model presented here generalizes the previously reported barotropic ‘sandpaper’ theory of flow–topography interaction to density-stratified systems. The multiscale asymptotic analysis leads to an explicit representation of the large-scale effects of irregular bottom roughness. The utility of the multiscale model is demonstrated by applying it to the problem of topography-induced spin-down of an axisymmetric vortex. We find that bathymetry affects vortices by suppressing circulation in their deep regions. As a result, vortices located above rough topography tend to be more stable than their flat-bottom counterparts. The multiscale theory is validated by comparing corresponding topography-resolving and parametric simulations.

Quantitative Measurement Method for Ice Roughness on an Aircraft Surface

When an aircraft passes through clouds containing supercooled water droplets, the leading edge’s surface will gradually accumulate ice. Ice surface roughness is an important parameter affecting the local convective heat transfer coefficient and the water collection coefficient, which in turn affect the ice’s shape. However, because the surface roughness of aircraft icing is a transient value varying in time and space, it is extremely difficult to measure with existing methods in real time. In this study, a noncontact ultrasonic pulse-echo (UPE) technique is applied to characterize the ice roughness of an airfoil model’s surface. A multilayer model with equivalent bead-like roughness profiles is established to study the effects of changes in ice roughness on ultrasonic echo signals. A series of simulations indicated that ice roughness can be measured quantitatively and effectively in the range of [11.6, 120] μm. Based on these simulations, an experimental UPE device was developed to measure echo signals on top of the ice corresponding to surface roughness. The results show that for both the regular and irregular surface roughness samples, the maximum relative error in the roughness is less than 15%. Meanwhile, we designed and supplemented the experiment with the NACA-0012 airfoil model to realize the online measurement of ice roughness in an icing research tunnel.

Insights into the micromechanical response of adhesive joint with stochastic surface micro-roughness

Micro-roughness at adhesion surface yields significant influences on the structural behaviour of adhesive joints. Investigations into the micromechanical mechanism are extremely limited. This works developed a novel particle-based model of joints with stochastic microstructural features of roughness, which can capture refined multi-scale responses as first of this kind. Aluminium adherends with mechanical surface treatments were firstly scanned using 3D laser scanning microscope. The statistical features and reconstruction method of micro-roughness profiles were determined. Single lap shear tests on joints made of epoxy adhesive (Loctite EA 9497) and treated aluminium adherends were performed to provide testing data and observations on failure modes. The refined numerical models were subsequently developed to examine the influences of the actual micro-roughness on the micromechanical behaviors and failure mechanism. The mechanical interlocking, mitigation on crack propagation due to the irregular roughness were investigated. It is followed by introducing the reconstructed roughness of various magnitudes and further numerically examining the micromechanical responses by key stochastic parameters such as root mean square roughness and correlation length. The results indicate that the mechanical interlocking contribute more to enhancing the joint strength than the increase of adhesion area by micro-roughness. A rougher surface in either horizontal or vertical directions does not exhibit a consistent improvement of joint strength, which also depends on the threshold of roughness and the surface skewness triggering the transition of failure modes.

Flame acceleration process and detonation transition in a channel with roughness elements on a wall

We experimentally investigated the effect of small roughness elements, which could be regarded as the wall roughness, on flame acceleration and deflagration-to-detonation transition (DDT). Our previous experiments (Maeda et al., 2019) using the sandpaper-like irregular roughness indicated that the flame acceleration and the associated DDT were greatly enhanced by the roughness. In this study, CH* chemiluminescence imaging as well as schlieren imaging was conducted in parallel with pressure measurements using an ethylene-oxygen combustion in the channel (486 mm long, 10 mm square cross-section) with the regular roughness (square pyramid elements with a base length and a height of 1 mm) in order to directly link the interference between the flow-field affected by the roughness and the propagating flame surface resulting the enhancement of chemical reactions, whereas the schlieren imaging alone could not allow to discuss the chemical reaction field in the previous study. After the leading shock wave was formed by the initial finger flame acceleration process, multiple interactions were observed on the flame front with the flow-field and pressure disturbances of the unreacted gas near the roughness elements. The results provided clear evidence that the roughness emphasized the effect of boundary layer, and the region where the disturbance layer and the flame were interacting coincided with the strong chemical reaction in the chemiluminescence image, indicating increase of the flame surface area caused by the turbulence on the flame front, which was also validated by the rough estimation of the burning velocity. The detonation onset was observed at the flame surface near the wall with the roughness elements. The possible factors of the final detonation transition were deduced to be the hot spot formation based on the multiple interactions of pressure waves with the roughness elements and entrainment of the unreacted gas of the highly turbulent flame front.