Roughness Configurations Research Articles

Film Cooling Performances Under Various Upstream Roughness Conditions: Experimental Investigations and Similarity Hypothesis

Abstract Roughness caused by deposition, erosion, and additive manufacturing can significantly affect gas turbine efficiency. Previous research has often examined film cooling performance under limited roughness configurations, resulting in inconclusive findings. In this study, film cooling performances under various upstream roughness conditions were investigated to simulate the roughness-affected film cooling performance of the suction side and the endwall. Three roughness heights (k/D = 0.1, 0.2, and 0.4) and shapes (ks/k = 0.17, 0.67, and 1.95) were selected to cover a wide range of surface roughness characteristics. Three blowing ratios were examined (M = 0.5, 1.0, and 1.5). The weakly roughened surfaces showed improved cooling effectiveness as k/D increased. Meanwhile, the moderately and severely roughened surfaces showed a decrease in cooling effectiveness with increasing k/D at M = 0.5 and 1.0 but an increase at M = 1.5. Cases with shallower and higher roughness elements at M = 1.5 outperformed the smooth plate. Subsequently, a similarity hypothesis for film cooling effectiveness was proposed. At all blowing ratios, the scaled cooling effectiveness profiles converged around the smooth plate results for ks/D < 0.391, encompassing common turbine roughness scales, including irregularly roughened surfaces. Deviations emerged at ks/D = 0.782, and they were correlated with the deteriorated regions observed at various blowing ratios. Ensemble-averaged scaled cooling effectiveness exponentially grew with increasing roughness scale for all blowing ratios, and empirical expressions based on smooth plate result and roughness scale were proposed.

Advancing Rock-Socketed Pile Design with a Unified Interface Shear Strength Framework for Soft Rocks

The shaft resistance of rock-socketed piles (RSPs) is primarily influenced by the interactions between the pile, rock and any soft interface materials. This study presents a fundamental experimental and numerical investigation to predict the shaft resistance of model RSPs in soft rocks through a comprehensive shear strength framework incorporating the major variables such as roughness and smear fabric. By calibrating the Discrete Element Method (DEM) results with the experimental outcomes, this study evaluates the load-resistance attributes of RSPs in three different soft rocks for a wide range of roughness and smear configurations. The interface roughness effect of the RSPs in terms of the friction coefficient was correlated with the ultimate shaft resistances, uniaxial compressive strength and Young’s modulus of the rock. The study then incorporated the effect of smear fabric (placement, thickness and area proportion) in the shear strength framework of clean shafts. Comprehensive review of the DEM results revealed that the socket roughness effect diminishes at a critical roughness factor (RF)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$({\ ext{RF}})$$\\end{document} of 0.4, beyond which the smear predominantly influences the shaft capacity. Following this, the effects of roughness and smear fabric were incorporated into a single equation representing the interface shear strength of RSPs, where the existence of smear results in a maximum reduction of up to 75% of the ultimate shaft resistance. The distinctive feature of this unified interface shear strength framework lies in its integration of the new smear fabric parameter and the linkage to the mechanical properties of soft rocks, which is the limitation of the earlier studies. It thereby sets a strong base for future studies aimed at advancing the pile-rock interface models.

Latent heat energy storage using nanomaterials as a heat sink for the prevention of thermal runaway: A study in conjugate heat dissipation

Phase change material (PCM) based heat sinks are the passive cooling technologies that achieve required thermal management. PCM increases the energy storage capacity, and adding nanomaterial to the PCM improves the heat sink capacity. However, there are very few studies on the effect of heat load on thermal performance in this field. This research focuses on the experimental investigation of the thermal characteristics of Nano-PCM-based heat sinks with varying base roughness and load. To enhance the heat transfer characteristics of paraffin PCM, two distinctive nanoparticles, i.e., graphene and Silver Titanium Dioxide (Ag-TiO2), are used. Two different heat sinks containing one of the nanoparticles mixed PCM were tested. However, one more heat sink containing only PCM was also used in the study. Scanning electron microscope analysis, thermogravimetric analysis, differential scanning calorimetry, and energy dispersive X-ray analysis were performed, and the performance was measured at various heat loads (25 W, 35 W, and 45 W), and different roughness configurations (R1, R2, and R3) with PCM and Nano-PCM. The study's findings indicate that the R3 configuration containing graphene-PCM performs better than the others. It had a longer charging time (heating), a shorter discharging time (cooling), and a more constant temperature during discharging. Comparing the discharging cycles of AgTiO2-PCM, graphene-PCM reveals a minor difference. The cooling rate depends on the heat load and a heat load of 45 W results in a faster cooling rate.

Effect of isothermal rough boundaries on the statistics of velocity and temperature fluctuations in turbulent Rayleigh–Bénard convection

Using direct numerical simulations, we investigate the effect of surface roughness on the statistics of fluctuations in a 2D rectangular cell of aspect ratio Γ = 2 with air as the working fluid. We consider roughly two decades of Rayleigh number, 108≤Ra≤4.64×109, with three roughness configurations of R1, R2, and R3 characterized by their maximum heights of 5%, 10%, and 20% of the cell height, respectively. We show that roughened cells trigger stronger fluctuations, which further gets augmented with increasing Ra. Vertical variations of velocity and temperature fluctuations show different trends. While the temperature fluctuation becomes homogeneous in the bulk, it exhibits strong inhomogeneous vertical velocity fluctuations. The comparison of global heat flux with smooth case shows a significant increment beyond Ra=2.15×108. Surface roughness impacts local heat flux through augmented plumes, which is qualitatively ascertained by instantaneous temperature field. Furthermore, probability distribution functions reveal no particular trend for the taller roughness configurations, though the magnitude is amplified. Through identification of plumes and background regions, we show their behavior as a function of Ra for different rough cases. Finally, we decompose the shear production into its three components (based on the nature of mechanical forces) to understand the energy interaction between the mean flow and fluctuating flow field.

Numerical investigation of rocket engine cooling channel heat transfer for different LNG under trans-critical conditions

Hydrocarbon impurities in Liquified Natural Gas LNG may produce undesired phenomena such as pseudo boiling and two-phase flow. This can be an issue for rocket engine cooling channels. This study investigates the impacts of hydrocarbon impurities on LNG thermophysical and transport properties. It estimates the required relative roughness to improve the cooling capabilities with appropriate pressure drops for different LNG mixtures flowing in the rocket engine cooling channel. The Reynolds-averaged-Navier–Stokes equations are numerically solved for a straight cooling channel with a circular cross-section and uniform heat flux. LNG’s thermophysical and transport properties are calculated using the GERG equation of state and extended corresponding states, respectively. The turbulent models are validated numerically for supercritical LNG, vapor methane, and supercritical hydrogen. The results show that hydrocarbon compositions play a significant role in cricondenbar pressure. When the hydrocarbon impurities increase, the phase envelope develops, and cricondenbar pressure increases. The impacts of various relative wall roughness configurations on the cooling capabilities and pressure drops are sensitive under transcritical processes and hydrocarbon compositions. This study provides a systematic understanding of the relationships between cooling channel surface roughness, Nusselt Number, and LNG composition, offering designers the ability to optimize heat transfer in rocket engine cooling systems.

Experimental study on wind characteristics and prediction of mean wind profile over complex heterogeneous terrain

This study investigates the impact of complex heterogeneous terrain on mean wind speed and turbulence intensity, highlighting the significance of terrain configuration in the wind loading on buildings and airflow over urban areas. Extensive wind tunnel tests were conducted for 60 different roughness configurations, obtained by processing aerial images across the United States. The study makes two main contributions. First, a model was proposed to predict mean wind profiles, using the morphological information of complex heterogeneous terrain. The Deaves and Harris model was utilized along with a novel algorithm for the automatic characterization of roughness transitions. The proposed model exhibited less than 2% average prediction error compared to the measured wind speed. Second, the study investigated the impact of terrain complexity on near-surface wind characteristics. By comparing the experimental results with those obtained from a homogeneous terrain with a similar roughness length, we quantified the potential errors that may arise when assuming a homogeneous terrain for wind speed assessment. It was observed that increasing variability in roughness length led to a decrease in mean wind speed and an increase in turbulence intensity. The influence of terrain complexity, however, was found to be secondary compared to roughness length. Consequently, the relationships between terrain complexity and wind characteristics were quantified, and a simplified model was proposed.

Roughness effect on hypersonic second mode instability and transition on a cone

Recent studies by Fong et al. [“Finite roughness effect on modal growth of a hypersonic boundary layer,” AIAA Paper No. 2012-1086, 2012; “Stabilization of hypersonic boundary layer waves using 2-D surface roughness,” AIAA Paper No. 2013-2985, 2013; “Numerical simulation of roughness effect on the stability of a hypersonic boundary layer,” Comput. Fluids 96, 350–367 (2014); and “Second mode suppression in hypersonic boundary layer by roughness: Design and experiments,” AIAA J. 53, 1–6 (2015)] have shown that finite roughness can attenuate Mack's second mode instability when placed at the discrete mode synchronization location for two-dimensional planar flow over a flat plate. However, more practical hypersonic flows are non-planer conical flows, and the roughness effect phenomenon in conical flows has not been extensively investigated. For that reason, this investigation research the ability of finite roughness strips to attenuate the second mode instability on a Mach 8 straight blunt cone with a freestream unit Reynolds number of 9 585 000. Two roughness configurations are studied: a single roughness strip and an array of six sequential strips. N-factor calculations determine the second mode frequency most likely to lead to turbulent transition, and the linear stability theory is used to determine the mode's synchronization location. In the unsteady simulations of the roughness configurations, a blowing-suction actuator introduces an upstream broadband Gaussian pulse. Fourier decomposition of the pulse's history shows that the single roughness strip attenuates frequencies higher than 208 kHz while lower frequencies are amplified. Likewise, the roughness array exhibits similar results, attenuating frequencies higher than 164 kHz and amplifying lower frequencies downstream. The results show that both configurations can delay second mode instability growth on a hypersonic blunt cone and possibly delay turbulent transition. However, investigations of the roughness effect's behavior downstream of the roughness configurations show that disturbance growth resumes and becomes more destabilizing to the boundary layer.

Assessment of solar air heater performance using a variety of artificially roughened components

For the past 40 years, many researchers have been studying solar collection devices with artificial roughness. Estimation of transfer of heat and fluid flowing properties is well acquired by an experimental, computational, and theoretical approach. This review provides an authentic overview of the topic's current growth., contemplates the previous growths, and focuses on the future presuppositions of the roughened SAH. Finally, this article shows a comprehensive study of several roughness configurations employed on heated wall to rise of heat transfer rate of SAH passage. Correlation’s discovered for HT & FF by different authors have also been reported.

Island scan length effect on processability, microstructure, and mechanical property of laser powder bed fusion processed nickel matrix composites

Nickel matrix composites (NMCs) reinforced with WC particles were manufactured by laser powder bed fusion (LPBF) using island strategy with the variation of island scan length. The processability, microstructural evolution, and mechanical property were investigated. The results indicated that all samples showed high densification, while the surface morphology, molten pool geometry, and microstructures were distinct. With increasing scan length from 0.5 to 1 mm, the grain size was similar, while the high angle grain boundaries (HAGBs) decreased from 68.1% to 50.4%. With further increasing scan length, the residual stress increased from 206.3 to 308.8 MPa, the surface roughness and molten pool configurations were enlarged, and columnar/cellular dendrites became irregular. This change was related to the large temperature gradient and unstable thermal behaviors resulting from the weakened preheat effect under long scan length. Thus, the superior mechanical properties with wear rate of 4.09 × 10−5 mm3/N·m, ultimate tensile strength of 1132 MPa, and elongation of 16.1% were obtained at the moderate scan length of 1 mm. The high performance was related to smaller residual stress, fewer HAGBs and dislocation-carbides interactions along the columnar/cellular boundary.

An experimental investigation on pressure loss and local heat transfer characteristics in additively manufactured ribbed cooling configurations

Pressure loss and transient heat transfer measurements are performed on real-scale turbine cooling configurations at engine-relevant flow conditions. To determine the influence of rib turbulators and surface roughness on heat transfer and pressure loss, five additively manufactured models and one milled model were investigated, which distinguish in their manufacturing-related surface roughness and/or rib turbulator configurations. The experimentally determined friction factors are compared with data from a computed tomography (CT) scan, which was carried out for one of the additively manufactured models. An inverse discrete volume approach is applied, where the temperature response of the accessible outer wall caused by a sudden change in the temperature of the fluid flowing through the channel is measured. This allows the determination of locally resolved heat transfer coefficients on the non-accessible inner surface and provides information about the internal heat transfer processes. From the variety of experiments performed on the six models, the influence of surface roughness, one-sided high-blockade ribs, combination of these two, and the Reynolds number on friction factor and heat transfer coefficient is determined. The effects of roughness and rib configuration are separated from each other, and the expected measurement uncertainties are estimated by means of a sensitivity analysis.

Empirical Model for Low-Speed Rough-Wall Turbulent Boundary Layer Pressure Spectra

An empirical model for estimating surface pressure spectra in high Reynolds number rough-wall turbulent boundary layers in the low-speed regime is presented. The model is based on the low-frequency mean velocity defect scaling [1] and the high-frequency shear friction velocity scaling [2]. This model satisfactorily predicts surface pressure spectra measured over a wide range of roughness configurations in high Reynolds number flows free of transitional effects. These data also provide insights into the characteristics of the turbulent scales which are on the order of the roughness size and comprise the mid-frequency region. The slope of this region is highly dependent on roughness element density and element-relative measurement location. This contradicts the premise of an overlap region with slope . An evanescent pressure decay model provides evidence that the slope changes are due to a roughness-dependent pressure decay within the interstitial flow and suggests that a traditional mid-frequency similarity law may not be possible.

Evaluation of the tau-omega model over bare and wheat-covered flat and periodic soil surfaces at P- and L-band

It has been over ten years since the successful launch of the first-ever dedicated satellite for global soil moisture monitoring; Soil Moisture and Ocean Salinity (SMOS). Looking towards the future, P-band (0.3–1 GHz) is a promising technique to replace or enhance the L-band (1.4 GHz) SMOS and SMAP (Soil Moisture Active Passive) missions because of an expected reduction in roughness and vegetation impact, leading to an improved soil moisture accuracy over rougher soil surfaces and more densely vegetated areas. Accordingly, this investigation evaluated the tau-omega model at P-band (0.75 GHz) using a tower-based experiment in Victoria, Australia, where brightness temperature observations were collected concurrently at P- and L-band over bare and wheat-covered flat and periodic soil surfaces. The potential to retrieve soil moisture without discriminating periodic and flat surfaces was investigated by applying the roughness and vegetation parameters calibrated for flat soil to retrieve the moisture of periodic soil. Results showed that P-band had a comparable RMSE across different roughness configurations (variations less than 0.016 m3/m3) for both bare and wheat-covered soil, while the L-band RMSE was only comparable for wheat-covered soil, indicating that periodic surfaces did not need to be discriminated in such scenarios. Conversely, a difference of 0.022 m3/m3 was observed for L-band with bare soil. A reduced vegetation impact was also demonstrated at P-band, with an RMSE of 0.029 m3/m3 achieved when completely ignoring the wheat existence with under 4-kg/m2 vegetation water content, whereas at L-band the RMSE increased to 0.063 m3/m3. This study therefore paves the way for a successful P-band radiometer mission for obtaining more accurate global soil moisture information.

Amplitude and wavelength scaling of sinusoidal roughness effects in turbulent channel flow at fixed

Direct numerical simulations are performed for incompressible, turbulent channel flow over a smooth wall and different sinusoidal wall roughness configurations at a constant$Re_\tau = 720$. Sinusoidal walls are used to study the effects of well-defined geometric features of roughness-amplitude,$a$, and wavelength,$\lambda$, on the flow. The flow in the near-wall region is strongly influenced by both$a$and$\lambda$. Establishing appropriate scaling laws will aid in understanding the effects of roughness and identifying the relevant physical mechanisms. Using inner variables and the roughness function to scale the flow quantities provides support for Townsend's hypothesis, but inner scaling is unable to capture the flow physics in the near-wall region. We provide modified scaling relations considering the dynamics of the shear layer and its interaction with the roughness. Although not a particularly surprising observation, this study provides clear evidence of the dependence of flow features on both$a$and$\lambda$. With these relations, we are able to collapse and/or align peaks for some flow quantities and, thus, capture the effects of surface roughness on turbulent flows even in the near-wall region. The shear-layer scaling supports the hypothesis that the physical mechanisms responsible for turbulent kinetic energy production in turbulent flows over rough walls are greatly influenced by the shear layer and its interaction with the roughness elements. Finally, a semiempirical model is developed to predict the contribution of pressure and skin friction drag on the roughness element based purely on its geometric parameters and the corresponding shear-layer velocity scale.

Turbulent plane Couette flow with a roughened wall

Using direct numerical simulations, we studied the effects of roughness in a turbulent plane Couette flow where one wall is rough and the other one is smooth. Two different roughness configurations are simulated, and the results are compared with the case where both walls are smooth. Upon roughening a wall, roughness would generate vortical structures near the vicinity of the roughness elements and enhance turbulence locally. In the current study, however, we report that turbulence is enhanced near both the rough and the smooth walls.

Velocity Structure of Density Currents Propagating over Rough Beds

In most practical cases, density-driven currents flow over surfaces that are not smooth; however, the effects of bottom roughness on these currents have not been fully understood yet. Hence, this study aims to examine the velocity structure of density currents while propagating over rough beds. To this end, alterations in the vertical velocity profiles within the body of these currents were investigated in the presence of different bottom roughness configurations. Initially, laboratory experiments were carried out for density currents flowing over a smooth surface to provide a baseline for comparison. Thereafter, seven bottom roughness configurations were tested, encompassing both dense and sparse bottom roughness. The bottom roughness consisted of repeated arrays of square cross-section beams covering the full channel width and perpendicular to the flow direction. The primary results indicate that the bottom roughness decelerated the currents and modified the shape of velocity profiles, particularly in the region close to the bed. Additionally, a critical spacing of the roughness elements was detected for which the currents demonstrated the lowest velocities. For the spacings above the critical value, increasing the distance between the roughness elements had little impact on controlling the velocity of these currents. Moreover, using dimensional analysis, equations were developed for estimating the mean velocities of the currents flowing over various configurations of the bottom roughness. The findings of this research could contribute towards better parameterization and improved knowledge of density currents flowing over rough beds. This can lead to a better prediction of the evolution of these currents in many practical cases as well as improved planning and design measures for the control of such currents.

The low-frequency pressure fluctuations of near-equilibrium turbulent boundary layers

The low-frequency pressure fluctuations generated by a range of roughness configurations are explored for flows of roughness Reynolds numbers over 200 and blockage ratios above 73. Two-point analysis of the pressure fluctuations reveals that surfaces with high frontal solidity, $$\lambda$$ , and/or complex shear layer interactions near the elements, have structures which persist longer than structures on the smooth wall. A low-frequency pressure spectrum scaling based on the broadband convection velocity defect, $$U_{\text{e}}-{\overline{U}}_{\text{c}_{\text{b}}}$$ , is proven effective for all rough surfaces and the smooth wall. Here $$U_{\text{e}}$$ is the boundary layer edge velocity, and $${\overline{U}}_{\text{c}_{\text{b}}}$$ is the mean broadband convection velocity. A second scaling, which is more appropriate for a priori predictions, is also proposed. It uses the mean velocity defect, $$U_{\text{e}}-{\overline{U}}$$ (where $${\overline{U}}$$ is the mean boundary layer velocity), first proposed for velocity profiles by Zagarola and Smits (J Fluid Mech 373:33–79, 1998). Both scalings are effective because they are based on velocity defects proportional to the outer-layer shear stress which generates the pressure fluctuations. A re-examination of the outer-layer wall-similarity in the context of these new findings suggests that this concept is limited to a narrow range of turbulent boundary layer flows.

Effect of biofouling roughness on a marine propeller's performance including cavitation and underwater radiated noise (URN)

This study aims to investigate the effects of biofouling-related roughness on a propeller's hydrodynamic and underwater radiated noise (URN) performance. Selected benchmark INSEAN E779A propeller operated in uniform & open water flow under non-cavitating and cavitating conditions. The hydrodynamic flow field around the propeller was first solved using RANS (Reynolds-averaged Navier Stokes) solver. The Schnerr-Sauer cavitation model, based on reduced Rayleigh-Plesset equation, was used to model the sheet cavitation on the propeller blades and tip vortex cavitation (TVC) in the propeller's slipstream. A vorticity-based Adaptive Mesh Refinement (AMR) technique was employed for the observation of TVC. The porous form of the Ffowcs-Williams Hawkings (P-FWH) equation, which is coupled with the RANS solver, was used to predict the URN (or hydroacoustic performance) of the propeller. The propeller performance characteristics, including cavitation, were validated with the available experimental data. Following that, the roughness functions representing the different roughness configurations obtained from the literature were employed using wall function model of Computational Fluid Dynamics (CFD) solver. The results showed that roughness has detrimental impacts on the propeller's performance characteristics. That is to say that the propeller's thrust decreases while the torque increases with increasing severity of the roughness. Hence, the efficiency loss of the propeller at the most severe roughness condition can be as high as 30% and 25% at J = 0.795 and J = 0.71 & σ=1.763, respectively. Unlike its detrimental effects on the hydrodynamic performance, the roughness had some positive effects by reducing the cavitation volume, especially for the TVC and hence on the propeller underwater radiated noise (URN). The results also indicated that the URN levels might be reduced up to 10 dB between 1 kHz and 2 kHz. Besides, 2nd and 3rd BPF values decrease between 1 and 7 dB under varying roughness configurations in comparison to the smooth case. The study reported the effect of a particular biofouling roughness on the URN levels of a propeller for the first time in model-scale and using the CFD simulations.

Influence of grain boundaries, interface roughness and non-collinear magnetic configurations in the AF layer on the exchange bias properties of F/AF nanodots: A numerical investigation

Motivated by the insufficient understanding of the drastic effects of the disordered interfacial phases at the interface in F/AF bilayers on the exchange bias properties, we consider a realistic model for F/AF nanodots which accounts for roughness at the interface, grain boundaries (GB) and magnetic frustration in the AF layer. Then, we investigate the effect of the magnetic disorder at the F/AF interface on the exchange field by means of Monte Carlo simulations. First, using a simplified model based on a perfect crystal structure (without GB) and with an ideal interface, our results indicate that non-collinear ordered magnetic configuration at the F/AF interface (due to frustration) causes a small decrease of the exchange field (about few dozen percent). Including GB in the model, we show that this kind of structural disorder produces disordered magnetic configurations with domains at the F/AF interface. This magnetic disorder does not lead to a decrease of the exchange field compared to the perfect crystal but makes the AF layer more stable. Our study also reveals that adding roughness in the form of a percentage of mixed F and AF moments in the interfacial layer results in a more significant decrease of the exchange field (two orders of magnitude) leading to values which are comparable to experimental values.

Analysis of the different sources of stress acting in fully rough turbulent flows over geometrical roughness elements

The discrete element roughness method is considered in this article for the prediction of turbulent flows over rough walls. This approach is derived by ensemble- and volume-averaging the Navier–Stokes equations, providing double-averaged Navier–Stokes equations, and yielding three unknown terms in the momentum equation: the Reynolds stress and dispersive stress tensors and the average drag force acting on the roughness elements. This work aims at analyzing these different terms, quantifying their respective contributions to the near-wall momentum budget, and providing guidance for their modeling. For this purpose, relevant data of turbulent flows are required. Roughness-resolved Reynolds-averaged Navier–Stokes simulations of transitionally and fully rough channel flows over academic roughness configurations are performed at high friction Reynolds numbers ranging from 3500 to 8000. Comparisons with existing and new velocity measurements performed in rough-wall turbulent boundary layers provide support to the simulation results, a particular emphasis being given on the validity of the numerical results in the wake of the roughness elements. These numerical results highlight the influence of roughness elements geometry and density on the roughness drag coefficient and the dispersive stress. It is particularly suggested that the standard roughness drag closure model should be revisited for double-averaged flows. Furthermore, the dispersive stress is shown to mainly originate from the wake of the roughness elements, an observation that could be leveraged for its modeling. However, since this stress contributes only marginally to the global stress and to the skin friction coefficient, such a modeling may not be critical at first order.

Investigations of tip vortex mitigation by using roughness

The application of artificial roughness to mitigate tip vortex cavitation inception is analyzed through numerical and experimental investigations carried out on an elliptical foil. Different roughness configurations and sizes are tested, and effects on cavitation inception, drag, and lift are studied. Implicit Large Eddy Simulation is employed to conduct the simulation on a proper grid resolution having the tip vortex spatial resolution as fine as 0.062 mm. Two different approaches including using a rough wall function and resolving the flow around roughness elements are evaluated. New experiments, performed in the cavitation tunnel at Kongsberg Hydrodynamic Research Center, for the rough foil are presented. The vortical structures and vorticity magnitude distributions are employed to demonstrate how different roughness patterns and configurations contribute to the vortex roll-up and consequently on the tip vortex strength. It is found that the application of roughness on the leading edge, tip region, and trailing edge of the suction side is acceptable to mitigate the tip vortex and also to limit the performance degradation. This is regarded to be in close relation with the way that the tip vortex forms in the studied operating condition. The boundary layer characteristics show that roughness separation line is the reason for a more even distribution of vorticity over the tip compared to the smooth foil condition, leading to a reduction in vortex strength. For the optimum roughness pattern, both the numerical results and experimental measurements show a decrease in the tip vortex cavitation inception as large as 33% compared to the smooth foil condition with a drag force increase observed to be less than 2%.