Roughness Locations Research Articles

Experimental Investigation of Biofouled Ship Control Surface Performance

Abstract Marine biofouling threatens ship safety by causing unexpected control surface performance. To explore these adverse biofouling effects, this paper presents the results of wind tunnel testing using a model-scale, low aspect ratio NACA 0018 control surface. Simulated calcareous biofouling was introduced as coarse-grit sandpaper, and, uniquely, roughness locations and sandpaper grits were varied to better understand any resulting degradation in hydrodynamic performance. Direct experimentation at high (turbulent) chord Reynolds number values suggests that leading-edge biofouling with 36-grit sandpaper results in worst-case performance, with the control surface's average lift-to-drag ratio reduced by 63%. Additional findings are presented, and recommendations for future experimental work are also provided.

Experimental Investigations on the Effects of Surface Roughness for Compressor Cascades With Different Roughness Magnitude and Location

Abstract Blade surface roughness could significantly affect the aerodynamic performance of compressors. To explore the influence of roughness magnitude and location on blade performance, experiments were conducted in a low-speed linear compressor cascade with controlled diffusion airfoils (CDA). A part-span roughness method was employed in the experiment to maintain the axial velocity–density ratio (AVDR) during the change of blade roughness magnitudes and locations. Five blade surface local roughness schemes, including the leading-edge, the fore- and aft-part of the suction surface, and the pressure surface, which were determined based on geometry sensitivity analysis, were investigated with the variation of the surface roughness magnitude between Ra = 3.1 μm to 18.8 μm. Cascade inlet and outlet flowfields and the blade surface static pressure distributions were measured, which could help to distinguish the change of blade performance characteristics and even blade surface boundary layer development state. A critical roughness effect was found, and significant blade loss increment and available incidence range reduction appear at super-critical roughness states. At the measured maxi-roughness condition, 28.4% loss increase and 41.2% incidence range reduction were reached.

Retention and release of black phosphorus nanoparticles in porous media under various physicochemical conditions

Black phosphorus nanosheets/nanoparticles (BPNs) are widely applied in many fields. However, the transport of BPNs in the subsurface still has not yet been reported and there is increasing concern about potential adverse impacts on ecosystems. Roles of median grain size and surface roughness, BPN concentration, and solution chemistries (pH, ionic strength, and cation types) on the retention and release of BPNs in column experiments were therefore investigated. The mobility of BPNs significantly increased with increasing grain size and decreasing surface roughness due to their influence on the mass transfer rate, number of deposition sites and retention capacity, and straining processes. Transport of BPNs was enhanced with an increase in pH and a decrease in ionic strength because of surface deprotonation and stronger repulsion that tends to reduce aggregation. The BPN transport was significantly sensitive to ionic strength, compared with other engineered nanoparticles. Additionally, charge heterogeneity and cation-bridging played a critical role in the retention of BPNs in the presence of divalent cations. Higher input concentrations increased the retention of BPNs, probably because collisions, aggregation at pore throat locations, and hydrodynamic bridging were more pronounced. Small fractions of BPNs can be released under decreasing IS and increasing pH due to the expansion of the electrical double layer and increased repulsion at convex roughness locations. A mathematical model that includes provisions for advective dispersive transport and time-dependent retention with blocking or ripening terms well described the retention and release of BPNs. These findings provide fundamental information that helps to understand the transport of BPNs in the subsurface environments.

Influence of Surface Roughness on a Highly Loaded Axial Compressor Stage Performance at Low Reynolds Number

In the present study, a numerical simulation was conducted to investigate the influence of surface roughness on the aerodynamic performance of a 1.5-stage highly loaded axial compressor at low Reynolds number. It was especially considered how the roughness Reynolds number ( k + ) affected the change of the inlet and outlet conditions, the growth of the separation bubble (LSB), the status of the limiting streamline, and the patterns of the wake. Regarding the roughness settings, five roughness magnitudes and four roughness locations were mainly studied. The results showed that at low Re, surface roughness mainly improved the stage performance by reducing the length and width of the LSB as well as the rotor tip vorticity, delaying the occurrence of three-dimensional flow separation and increasing the turbulence level near the wall. However, it also aggravated the incoordination between the subsequent stages to a certain extent, which limited further improvement of the overall aerodynamic performance. Generally, with k + increasing, the compressor aerodynamic performance improved and achieved the best at k + = 137.8 . The maximum increases in the total pressure ratio, peak efficiency, and chocked mass flow were approximately 4.01%, 5.34%, and 2.24%, respectively. In addition, for all the four roughness locations, the roughness covering from the leading edge to 50% of the axial chord length on the suction surface had a relatively evident advantage in improving the compressor peak efficiency because of the better control of the LSB and wall shear stress.

Effects of surface roughness on the aerodynamic performance of a high subsonic compressor airfoil at low Reynolds number

The aerodynamic performance of compressor airfoil is significantly affected by the surface roughness at low Reynolds number (Re). In the present study, numerical simulations have been conducted to investigate the impact of surface roughness on the profile loss of a high subsonic compressor airfoil at Re = 1.5 × 105. Four roughness locations, covering 10%, 30%, 50% and 100% of the suction surface from the leading edge and seven roughness magnitudes (Ra) ranging from 52 to 525 μm were selected. Results showed that the surface roughness mainly determined the loss generation process by influencing the structure of the Laminar Separation Bubble (LSB) and the turbulence level near the wall. For all the roughness locations, the variation trend for the profile loss with the roughness magnitude was similar. In the transitionally rough region, the negative displacement effect of the LSB was suppressed with the increase of roughness magnitude, leading to a maximum decrease of 14.6%, 16.04%, 16.45% and 10.20% in the profile loss at Ra = 157 μm for the four roughness locations, respectively. However, with a further increase of the roughness magnitude in the fully rough region, the stronger turbulent dissipation enhanced the growth rate of the turbulent boundary layer and increased the profile loss instead. By comparison, the leading edge roughness played a dominant role in the boundary layer development and performance variation. To take fully advantage of the surface roughness reducing profile loss at low Re, the effects of roughness on suppressing LSB and inducing strong turbulent dissipation should be balanced effectively.

Vehicle-induced fatigue damage prognosis of orthotropic steel decks of cable-stayed bridges

Orthotropic steel deck (OSD) in a long-span cable-stayed bridge is vulnerable to fatigue damage at the deck-to-rib (DTR) joints due to excessive vehicle-induced dynamic stresses. A framework for fatigue damage prognosis of OSD in long-span cable-stayed bridges is thus presented in this paper. The main features of the framework include hourly traffic loading simulation and prediction, multi-scale finite element bridge model, coupled vehicle-bridge system, mesh-insensitive equivalent stress responses at a DTR joint, response surface models for equivalent stress responses, OSD and pavement interaction, asphalt pavement temperature effect, fatigue test-generated S-N curve, and fatigue damage prognosis. To evaluate the feasibility of the proposed framework and to manifest the effects of pavement roughness, asphalt temperature, and vehicle transverse locations on fatigue damage accumulation, a real long span cable-stayed bridge is investigated as a case study. The results indicate that the developed framework is applicable and that the fatigue damage of a DTR joint is underestimated if the time-variant temperature of asphalt pavement and road surface condition are not considered but the fatigue damage is overestimated without consideration of variable transverse locations of vehicles.

Transition effect on aerodynamic performance of compressor profile

PurposeThe purpose of this paper is to study experimentally the effect of transition and also the roughness height on the flow structure of the shock wave boundary layer interaction in the blades passage of a compressor cascade.Design/methodology/approachA model of a turbine compressor passage was designed and assembled in a transonic wind tunnel. In the experiment, the distributed roughness with different heights and locations was used to induce transition upstream of the shock wave.FindingsRecommendation regarding the roughness parameters for the application depends on what is more important as goal, whether the reduction of losses or unsteadiness. In case if more important are the losses reduction, a good choice for the roughness location seems to be the one close to the shock wave position.Research limitations/implicationsThe knowledge gained by this paper will enable the implementation of an effective laminar flow technology for engines in which the interaction of a laminar boundary layer with a shock wave takes place in the propulsion system and causes severe problems.Originality/valueThe paper focuses on the influence of the boundary layer transition induced by different roughness values and locations on aerodynamic performance of a compressor cascade. Very valuable results were obtained in the roughness application for the boundary layer transition control, demonstrating a positive effect in changing the nature of the interaction and also some negative influence in case of oversized roughness height, which cannot be found in the existing literature.

Effects of Bio-Inspired Surface Roughness on a Swept Back Tapered NACA 4412 Wing

This paper presents the overall pros and cons of the effect of surface roughness elements over a NACA 4412 tapered, swept back half wing with a sweep angle of 30º and a dihedral angle of 5º. The tests were conducted at a Reynolds number of 4 × 105 in the IIUM Low Speed wind tunnel. Different roughness sizes and roughness locations were tested for a range of angle of attack. Lift, drag and pitching moment coefficients were measured for the smooth wing and with roughness elements. Surface roughness delays the stall angle and decreases the lift. The wing with the roughness elements located at 75% to 95% of mean chord from leading edge shows minimum drag and maximum lift compared to other locations. Significant increase in the pitching moment coefficient was found for flexible roughness elements. In case of rigid surface roughness, the effect on pitching moment is small.

Roughness effect on shock wave boundary layer interaction area in compressor fan blades passage

The main objective of this research is to study experimentally the effect of transition on the flow structure of the shock wave boundary layer interaction in the blades passage of a compressor cascade. For this purpose a model of a turbine compressor passage was designed and assembled in a transonic wind tunnel. In the experiment the distributed roughness with different heights and locations was used to induce transition upstream of the shock wave. Three locations of distributed roughness in form of standard sandpaper strips were chosen to apply on the blade. The average roughness height comprised in a range of 8 to 16 μm. All together 8 different flow cases were investigated. The paper focuses on the influence of the boundary layer transition induced by different roughness values and locations on the flow pattern in the blades passage of a compressor cascade. Very promising results were obtained in the roughness application for the boundary layer transition control, demonstrating a positive effect in changing the nature of the interaction.

Unraveling the complexities of the velocity dependency of E. coli retention and release parameters in saturated porous media

Escherichia coli transport and release experiments were conducted to investigate the pore-water velocity (v) dependency of the sticking efficiency (α), the fraction of the solid surface area that contributed to retention (Sf), the percentage of injected cells that were irreversibly retained (Mirr), and cell release under different (10–300mM) ionic strength (IS) conditions. Values of α, Sf, and Mirr increased with increasing IS and decreasing v, but the dependency on v was greatest at intermediate IS (30 and 50mM). Following the retention phase, successive increases in v up to 100 or 150mday−1 and flow interruption of 24h produced negligible amounts of cell release. However, excavation of the sand from the columns in excess electrolyte solution resulted in the release of >80% of the retained bacteria. These observations were explained by: (i) extended interaction energy calculations on a heterogeneous sand collector; (ii) an increase in adhesive strength with the residence time; and (iii) torque balance consideration on rough surfaces. In particular, α, Sf, and Mirr increased with IS due to lower energy barriers and stronger primary minima. The values of α, Sf, and Mirr also increased with decreasing v because the adhesive strength increased with the residence time (e.g., an increased probability to diffuse over the energy barrier) and lower hydrodynamic forces diminished cell removal. The controlling influence of lever arms at microscopic roughness locations and grain-grain contacts were used to explain negligible cell removal with large increases in v and large amounts of cell recovery following sand excavation. Results reveal the underlying causes (interaction energy, torque balance, and residence time) of the velocity dependency of E. coli retention and release parameters (ksw, α, and Sf) that are not accounted for in colloid filtration theory.

Do Goethite Surfaces Really Control the Transport and Retention of Multi-Walled Carbon Nanotubes in Chemically Heterogeneous Porous Media?

Transport and retention behavior of multi-walled carbon nanotubes (MWCNTs) was studied in mixtures of negatively charged quartz sand (QS) and positively charged goethite-coated sand (GQS) to assess the role of chemical heterogeneity. The linear equilibrium sorption model provided a good description of batch results, and the distribution coefficients (KD) drastically increased with the GQS fraction that was electrostatically favorable for retention. Similarly, retention of MWCNTs increased with the GQS fraction in packed column experiments. However, calculated values of KD on GQS were around 2 orders of magnitude smaller in batch than packed column experiments due to differences in lever arms associated with hydrodynamic and adhesive torques at microscopic roughness locations. Furthermore, the fraction of the sand surface area that was favorable for retention (Sf) was much smaller than the GQS fraction because nanoscale roughness produced shallow interactions that were susceptible to removal. These observations indicate that only a minor fraction of the GQS was favorable for MWCNT retention. These same observations held for several different sand sizes. Column breakthrough curves were always well described using an advective-dispersive transport model that included retention and blocking. However, depth-dependent retention also needed to be included to accurately describe the retention profile when the GQS fraction was small. Results from this research indicate that roughness primarily controlled the retention of MWCNTs, although goethite surfaces played an important secondary role.

Detecting and Correcting Localized Roughness Features

Data collected by inertial profilers on new asphalt pavements in Colorado in 2012 were used to analyze the effectiveness of the localized roughness specification in Colorado. For the analyzed projects, data were collected before any corrections were made as well as after diamond grinding had been performed to remove areas of localized roughness. The data indicated that localized roughness features having a half-car roughness index (HRI) lower than 175 in./mi were rarely addressed during correction. However, about half the localized roughness features that had an HRI of 175 to 200 in./mi were successfully addressed during correction. Localized roughness features having an HRI greater than 200 in./mi appeared to be successfully addressed during correction. The analysis indicated a significant difference in the localized roughness locations identified by AASHTO R 54 and the Colorado Department of Transportation (DOT) method of detecting localized roughness. The Colorado DOT procedure specifies a minimum length for a roughness feature that is to be corrected, but AASHTO R 54 does not. This paper shows that collecting accurate profile data and analyzing the data to determine localized roughness locations are not enough. The identified locations must be correctly marked on the pavement in the field so that the feature does not cause localized roughness. This paper presents a procedure not only for collecting accurate data but also for accurately marking the roughness features in the field. It is shown that it is possible to locate and correct localized roughness accurately to the current thresholds as set by AASHTO R 54.

A Theoretical Analysis of Colloid Attachment and Straining in Chemically Heterogeneous Porous Media

A balance of applied hydrodynamic (T(H)) and resisting adhesive (T(A)) torques was conducted over a chemically heterogeneous porous medium that contained random roughness of height h(r) to determine the fraction of the solid surface area that contributes to colloid immobilization (S(f)*) under unfavorable attachment conditions. This model considers resistance due to deformation and the horizontal component of the adhesive force (F(AT)), spatial variations in the pore scale velocity distribution, and the influence of hr on lever arms for T(H) and T(A). Values of S(f)* were calculated for a wide range of physicochemical properties to gain insight into mechanisms and factors influencing colloid immobilization. Colloid attachment processes were demonstrated to depend on solution ionic strength (IS), the colloid radius (r(c)), the Young's modulus (K), the amount of chemical heterogeneity (P+), and the Darcy velocity (q). Colloid immobilization was also demonstrated to occur on a rough surface in the absence of attachment. In this case, S(f)* depended on IS, r(c), the roughness fraction (f0), h(r), and q. Roughness tended to enhance T(A) and diminish T(H). Consequently, the effect of IS on S(f)* was enhanced by h(r) relative to attachment. In contrast, the effects of r(c) and q on S(f)* were diminished by hr in comparison to attachment. Colloid immobilization adjacent to macroscopic roughness locations shares many similarities to grain-grain contact points and may be viewed as a type of straining process. In general, attachment was more important for higher IS and variance in the secondary minimum, and for smaller r(c), q, and K, but diffusion decreased these values. Conversely, straining was dominant for the opposite conditions. Discrepancies in the literature on mechanisms of colloid retention are likely due to a lack of consideration of all of these factors.

Effects of Reynolds Number and Surface Roughness Magnitude and Location on Compressor Cascade Performance

An experimental investigation has been conducted to characterize the influence of Reynolds number and surface roughness magnitude and location on compressor cascade performance. Flow field surveys have been conducted in a low-speed, linear compressor cascade. Pressure, velocity, and loss have been measured via a five-hole probe, pitot probe, and pressure taps on the blades. Four different roughness magnitudes, Ra values of 0.38 μm (polished), 1.70 μm (baseline), 2.03 μm (rough 1), and 2.89 μm (rough 2), have been tested. Furthermore, various roughness locations have been examined. In addition to the as manufactured (baseline) and entirely rough blade cases, blades with roughness covering the leading edge, pressure side, and 5%, 20%, 35%, 50%, and 100% of suction side from the leading edge have been studied. All of the tests have been carried out for Reynolds numbers ranging from 300,000 to 640,000. For Reynolds numbers under 500,000, the tested roughnesses do not significantly degrade compressor blade loading or loss. However, loss and blade loading become sensitive to roughness at Reynolds numbers above 550,000. Cascade performance is more sensitive to roughness on the suction side than pressure side. Furthermore, roughness on the aft 2/3 of suction side surface has a greater influence on loss. For a given roughness location, there exists a Reynolds number at which loss begins to significantly increase. Finally, increasing the roughness area on the suction surface from the leading edge reduces the Reynolds number at which the loss begins to increase.

Prediction of Optimal Cutting States during Inward Turning: An Experimental Approach

This article proposes a neurogenetic based optimization scheme for predicting localized stable cutting parameters in inward turning operation. A set of cutting experiments are performed in inward orthogonal turning operation. The cutting forces, surface roughness, and critical chatter locations are predicted as a function of operating variables including tool–overhang length. Radial basis function neural network is employed to develop the generalization models. Optimum cutting parameters are predicted from the model using binary-coded genetic algorithms (Gas). Results are illustrated with the data corresponding to four work materials, i.e., EN8 steel, EN24 steel, mild steel, and aluminium operated over a high speed steel (HSS) tool.

Dust Effect on the Performance of Wind Turbine Airfoils

The full two-dimensional Navier-Stokes algorithm and the SST k-? turbulence model were used to investigate incom-pressible viscous flow past the wind turbine two-dimensional airfoil under clean and roughness surface conditions. The NACA 63-430 airfoil is chosen to be the subject, which is widely used in wind turbine airfoil and generally located at mid-span of the blade with thickness to chord length ratio of about 0.3. The numerical simulation of the airfoil under clean surface condition has been done. As a result, the numerical results had a good consistency with the experimental data. The wind turbine blade surface dust accumulation according to the operational periods in natural environment has been taken into consideration. Then, the lift coefficients and the drag coefficients of NACA 63-430 airfoil have been computed under different roughness heights, different roughness areas and different roughness locations. The role that roughness plays in promoting premature transition to turbulence and flow separation has been verified by the numeri-cal results. The trends of the lift coefficients and the drag coefficients with the roughness height and roughness area increasing have been obtained. What’s more, the critical values of roughness height, roughness area, and roughness location have been proposed. Furthermore, the performance of the airfoil under different operational periods has been simulated, and an advice for the period of cleaning wind turbine blades is proposed. As a result, the numerical simula-tion method has been verified to be economically available for investigation of the dust effect on wind turbine airfoils.

Effect of Surface Roughness on the Aerodynamic Characteristics of a Symmetrical Airfoil

The objective of this study is to investigate the effect of surface roughness by varying the roughness size and location on the aerodynamic characteristics of the airfoil. Tests were conducted on the symmetrical airfoil models NACA 0012 on which the nature of the surface was varied from smooth to very rough and at a chord Reynolds number of 1.5*105. Different airfoil models with various roughness sizes and roughness locations were tested for different angles of attack. Lift, drag and pressure coefficients were measured and velocity profiles were determined for the smooth and grit 36 roughened models. It is shown that as the surface roughness increases, the minimum drag also increases due to the increase of the skin friction and the lift decreases. Surface roughness is seen to delay the stall angle and also increase the lift in the stall region. The airfoil model with the roughness located at the trailing edge shows minimum drag and maximum lift up to the stall angle compared to the other cases of different roughness locations. It is confirmed that, for the rough surface, a turbulent boundary layer exists where the laminar boundary layer is encountered for the smooth surface at the same Reynolds number. The measured skin friction for the rough surface is larger than that for the smooth surface.