Transitional Flow Research Articles

Flow-induced high frequency vascular wall vibrations in an arteriovenous fistula: a specific stimulus for stenosis development?

Hemodialysis is the lifeline for nearly three million end stage renal disease patients worldwide. Native arteriovenous fistula (AVF) is the preferred vascular access, but 40% fail within 1 year. We recently demonstrated that AVFs harbour transitional flows and the goal of the present study was to investigate whether the associated high-frequency pressure fluctuations could promote vibrations within the vascular wall. We acquired MRI images and flow rates immediately after surgery in one patient and generated a 3D patient-specific model. High-fidelity fluid structure interaction simulations revealed the presence of wall vibrations in distinct frequency bands up to 200 Hz and amplitude of 200 μm. A sensitivity analysis to assess the impact of flow rates, and vascular wall stiffness and thickness, changes that typically occur during AVF maturation, confirmed the robustness of the results. Interestingly, the vibrations were always predominant at the anastomosis floor and on the inner venous side, which correlates with typical stenotic regions. As studies seeking to correlate aberrant stresses and vascular remodelling have been largely inconclusive, the focal colocalization between vibrations and stenosis may suggest an unknown mechanobiological process between high-frequency mechanical stresses within the vascular wall and adverse vascular remodelling.

Modeling large-scale bioreactors with diffusion equations. Part I: Predicting axial dispersion coefficient and mixing times.

Bioreactor scale-up is complicated by dynamic interactions between mixing, reaction, mass transfer, and biological phenomena, the effects of which are usually predicted with simple correlations or case-specific simulations. This two-part study investigated whether axial diffusion equations could be used to calculate mixing times and to model and characterize large-scale stirred bioreactors in a general and predictive manner without fitting the dispersion coefficient. In this first part, a resistances-in-series model analogous to basic heat transfer theory was developed to estimate the dispersion coefficient such that only available hydrodynamic numbers and literature data were needed in calculations. For model validation, over 800 previously published experimentally determined mixing times were predicted with the transient axial diffusion equation. The collected data covered reactor sizes up to 160 m3 , single- and multi-impeller configurations with diverse impeller types, aerated and non-aerated operation in turbulent and transition flow regimes, and various mixing time quantification methods. The model performed excellently for typical multi-impeller configurations as long as flooding conditions were avoided. Mixing times for single-impeller and few nonstandard bioreactors were not predicted equally well. The transient diffusion equation together with the developed transfer resistance analogy proved to be a convenient and predictive model of mixing in typical large-scale bioreactors.

Ultrasound Particle Image Velocimetry to Investigate Potential Hemodynamic Causes of Limb Thrombosis After Endovascular Aneurysm Repair With the Anaconda Device.

To identify potential hemodynamic predictors for limb thrombosis (LT) following endovascular aneurysm repair with the Anaconda endograft in a patient-specific phantom. A thin-walled flow phantom, based on a patient's aortic anatomy and treated with an Anaconda endograft, that presented with a left-sided LT was fabricated. Contrast-enhanced ultrasound particle image velocimetry was performed to quantify time-resolved velocity fields. Measurements were performed in the same phantom with and without the Anaconda endograft, to investigate the impact of the endograft on the local flow fields. Hemodynamic parameters, namely vector complexity (VC) and residence time (RT), were calculated for both iliac arteries. In both limbs, the vector fields were mostly unidirectional during the peak systolic and end-systolic velocity phases before and after endograft placement. Local vortical structures and complex flow fields were observed at the diastolic and transitional flow phases. The average VC was higher (0.11) in the phantom with endograft, compared to the phantom without endograft (0.05). Notably, in both left and right iliac arteries, the anterior wall regions corresponded to a 2- and 4-fold increase in VC in the phantom with endograft, respectively. RT simulations showed values of 1.3 to 6 seconds in the phantom without endograft. A higher RT (up to 25 seconds) was observed in the phantom with endograft, in which the left iliac artery, with LT in follow-up, showed 2 fluid stasis regions. This in vitro study shows that unfavorable hemodynamics were present mostly in the limb that thrombosed during follow-up, with the highest VC and longest RT. These parameters might be valuable in predicting the occurrence of LT in the future. This in-vitro study aimed to identify potential hemodynamic predictors for limb thrombosis following EVAR using ultrasound particle image velocimetry (echoPIV) technique. It was shown that unfavorable hemodynamic norms were present mostly in the thrombosed limb. Owing to the in-vivo feasibility of the echoPIV, future efforts should focus on the evaluation of these hemodynamic norms in clinical trials. Thereafter, using echoPIV as a bedside technique in hospitals becomes more promising. Performing echoPIV in pre-op phase may provide valuable insights for surgeons to enhance treatment planning. EchoPIV is also applicable for follow-up sessions to evaluate treatment progress and avoid/predict complications.

Impacts of Mask Wearing and Leakages on Cyclic Respiratory Flows and Facial Thermoregulation

Elevated face temperature due to mask wearing can cause discomfort and skin irritation, making mask mandates challenging. When thermal discomfort becomes intolerable, individuals instinctively or unknowingly loosen or remove their facemasks, compromising the mask’s protective efficacy. The objective of this study was to numerically quantify the microclimate under the mask and facial thermoregulation when wearing a surgical mask with different levels of misfit. An integrated ambient–mask–face–airway computational model was developed with gaps of varying sizes and locations and was validated against complementary experiments. The low Reynolds number (LRN) k-ω turbulence model with porous media was used to simulate transient respiratory flows. Both skin convective heat transfer and tissue heat generation were considered in thermoregulation under the facemask, besides the warm air exhaled from the body and the cool air inhaled from the ambient. The results of this study showed that when wearing a surgical mask with a perfect fit under normal breathing, the temperature at the philtrum increased by 4.3 °C compared to not wearing a mask. A small gap measuring 0.51 cm2 (gap A) at the nose top resulted in 5.6% leakage but reduced the warming effect by 28% compared to zero gap. Meanwhile, a gap of 4.3 cm2 (R1L1) caused 42% leakage and a 62% reduction in the warming effect. Unique temporospatial temperature profiles were observed at various sampling points and for different gap sizes, which correlated reasonably with the corresponding flow dynamics, particularly close to the gaps. The temperature change rate also exhibited patterns unique to the gap site and sampling point, with distinctive peaks occurring during the inspiratory–expiratory flow transitions. These results have the significant implications that by using the temporospatial temperature profiles at several landmark points, the gap location can potentially be pinpointed, and the gap size and leakage fractions can be quantified.

Opportunities for Kazakhstan exports in the Southeast Asian region in the context of current geopolitical upheavals

This article discusses the main current processes of trade and economic cooperation between Kazakhstan and the region of Southeast Asia, in the current geopolitical conditions of the formation of the latest model of trade and economic interaction in the world. According to the available world trade forecasts, in the medium term, the large volumes of all world trade will move specifically to the region of Southeast Asia. This is due to several factors, including changing geopolitical conditions, changing delivery routes and increased interest from international investors. Kazakhstan, given the lack of access to the World Ocean, have to make significant efforts to build accessible logistics in the direction of the European Union – Southeast Asia, which will increase transit flows through Kazakhstan territory. In addition, it is necessary to carry out more active work to promote domestic enterprises to the market of Southeast Asian countries. Particular emphasis in the course of this research work was placed on the opportunities and potential for increasing Kazakhstani exports to Southeast Asian countries, using the Comparative Advantage Index. As a result,the main categories of goods that have a certain competitiveness in the market of the Southeast Asian countries are determined, considering imports to the region from third countries. In general, Kazakhstan can increase its trade with Southeast Asia through improving transportation infrastructure, improving the legislative framework, and increasing its presence at events in the region.This work will be of interest both to representatives of the diplomatic corps of Kazakhstan and representatives of the business community interested in selling their products to the markets of the countries of Southeast Asia.

Characterization of the transitional boundary layer flow on a marine propeller blade through Under-resolved Direct Numerical Simulation

In this paper, the full boundary layer flow on a C-series marine propeller is investigated through Under-resolved Direct Numerical Simulation (U-DNS). The simulated Reynolds number of 600,000 corresponds to experimental conditions for which a lab-scale propeller was designed and tested at MARIN’s towing tank in the late 1970s. The operating conditions of the simulations are set by matching the experimental advance ratio of 0.73. The simulation uses the high-order spectral element code Nek5000 to solve the boundary layer flow accurately. A specific computational domain is set to simulate the flow in the near-wall region of one of the propeller blades. The results are validated using experimental data on the propeller’s performances and the boundary layer regimes obtained from previous paint test measurements. The detailed boundary layer flow analysis provides new insights into understanding the transition mechanisms on both sides of the blade. Results suggest that centrifugal instabilities occur at the blade’s surface, inducing laminar-to-turbulent transition. A new flow map of the boundary layer regime is then discussed. The laminar cross-flow vortice inception and breakdown are studied in detail to characterize the transition dynamics.

Numerical model development for critical region flow and thermodynamic transitions of CO2 fluids in microchannel

Dramatic changes of thermophysical properties in the vicinity of critical point brings significant accelerating effect on the thermodynamic transitions of fluid. This study performs a confined geometric design with CO2 fluids passing through the critical zone in microchannel. Such a problem formulation combines the compressible Navier-Stokes equations with different property formulations to obtain critical anomaly effects at complex critical transport coefficients. Three equations of state (van der Waals (vdW), Redlich-Kwong (R-K) and Peng-Robinson (P-R) state equations) and their corresponding thermodynamic relations are derived in solving the governing equations of flow and heat transfer equations. Basic results are found to be consistent with theoretical asymptotic analysis, with linearly curves of pressure and a sudden shift of density (425 kg/m3–502 kg/m3) and velocity (0.82 m/s to 0.97 m/s) profiles when the microchannel flow across the critical region. The cascade effect between weakened radial thermal conductivity (λ ∼ (ρ – 1)-1/2, cp ∼ (ρ - 1)−2) and enhanced fluid expansion (βp ∼ (ρ - 1)−2) in the critical region is also shown to cause a sharp negative transition in temperature. In addition, the simulations demonstrate a qualitative comparison for three state equations, and the distinctions in quantitative terms (negative temperature value are −0.1 (vdW), −0.17 (R-K), and − 0.23(P-R)) are found to originate from stronger divergence characteristics (the specific heat cp and thermal expansion coefficients βp) in P-R gases than vdW and R-K gases.

Effects of the Wall Temperature on Rarefied Gas Flows and Heat Transfer in a Micro-Nozzle.

When the satellite is in orbit, the thruster will experience drastic temperature changes (100-1000 K) under solar radiation, which will affect the rarefied gas flow state in the micro-nozzle structure of the cold gas micro-thruster. In this study, the effect of different wall temperatures on the rarefied flow and heat transfer in the micro-nozzle is investigated based on the DSMC method. The micro-nozzle structure in this paper has a micro-channel with a large length-to-diameter ratio of 10 and a micro-scale needle valve displacement (maximum needle valve displacement up to 4 μm). This leads to more pronounced multiscale flow characteristics in the micro-nozzle, which is more influenced by the change in wall temperature. At wall temperatures ranging from 100 K to 1000 K, the spatial distribution of local Kn distribution, slip velocity distribution, temperature, and wall heat flux distribution in the micro-nozzle were calculated. The slip flow region is located in the flow channel and transforms into transition flow as the slip velocity reaches approximately 50 m/s. The spatial distribution of the flow pattern is dominated by the wall temperature at small needle valve opening ratios. The higher the wall temperature, the smaller the temperature drop ratio in the low-temperature region inside the micro-nozzle. The results of the study provide a reference for the design of temperature control of micro-nozzles in cold gas micro-thrusters.

Influence of Reynolds number and rotational number on the features of a transitional flow in short Taylor-Couette cavity

The paper reports on the DNS results of the flow in co- and counter-rotating coaxial cylinders of aspect ratios Γ = H/(R2 − R1) between 3.8 and 4.05, and radius ratio η = R1/R2 = 0.5, with the end-walls rotating with the angular velocity of the inner cylinder Ω1. The computations are performed for a wide range of rotational number RΩ = (1 − η)(Re1 + Re2)/(ηRe2 − Re1), from − 1.069 to 0.0, which includes both the linearly unstable flows and the Rayleigh stable flows. The considered Reynolds numbers of the inner cylinder Re1 = Ω1R1(R2 − R1)/ν are up to 3000 (Re2 = Ω2R2(R2 − R1)/ν). The obtained flow structures appearing at various stages of the laminar-turbulent transition and the radial profiles of statistical parameters are discussed in the light of the data published by other authors. The critical bifurcation lines are determined as functions of the inner and outer cylinder Reynolds numbers. Many interesting phenomena have been found.

Influences of geometry configurations on the performance of micro-nozzles

Micro-nozzles play a critical role in various applications, such as micro-/nano-satellites in aerospace and heat dissipation and cooling in microelectronic systems (MEMS). The flows inside micro-nozzles can experience both continuum and rarefied flow due to their small size. In this research, we explore the optimal geometry configuration of micro-nozzles to achieve comprehensive performance and size, as well as background pressure compensation. Using classical computational fluid dynamics (CFD) and direct simulation Monte Carlo methods (DSMC), we investigate the effects of the expansion ratio, cross-profile shape, and plug on the performance of micro-nozzles operating over a wide range of pressures (0.5−100kPa). The results reveal that micro-nozzle performance is influenced by the interplay between flow expansion and viscous loss induced by the subsonic layer next to the micro-nozzle wall. The findings show that micro-nozzle performance improves with increasing expansion ratio in slip and continuum flow regimes, but decreases in the transition flow regime. Additionally, the results indicate that the axisymmetric micro-nozzle (with a circular cross-profile) outperforms the linear micro-nozzle (with a rectangular cross-profile) in terms of both performance and size when subject to the same conditions, making it the recommended choice for practical applications. We also find that plugs designed at the throat decrease performance, but increase stability under diverse background pressures. This study provides valuable insights for the design of high-efficiency micro-nozzles in applications such as nanosats and MEMS heat dissipation units.

A comprehensive study with high-speed camera assisted visualizations of HFO-1234ze(E) condensation inside an enhanced tube

Flow condensation of HFO-1234ze(E) inside a helical micro-finned tube of 4.28 mm ID underwent experimentation. Flow patterns were visualized with a high-speed camera while varying vapor qualities from 0.01 to 0.95 and mass fluxes from 100 to 400 kg m−2 s1, at saturation temperature of 30 °C. Intermittent, stratified-wavy, transitional, and annular flow pattern types were identified. The flow pattern map of Doretti et al. (validated by Cavallini et al.) accurately predicted the flow patterns. Heat transfer coefficients (HTCs) and frictional pressure drops (FPDs) were also measured for mass fluxes ranging from 100 to 600 kg m−2 s−1 at saturation temperatures of 30 °C and 40 °C. Both HTC and FPD elevated with higher mass fluxes and vapor qualities which stemmed from the presence of observed shear stress-driven annular flow patterns. HTC and FPD are generally higher at lower saturation temperatures. Experimental HTC and FPD have been compared against values estimated with empirical models. Furthermore, the average enhancement factor of the micro-finned tube was 2.94 with an area enhancement factor of 2.39. Plotting enhancement factor versus non-dimensional gas velocity provided detailed insight into the augmentation effect of micro-finned tubes under different operating conditions.

Assessment of Socio-Economic Benefits from the Construction of Bypasses of Transport Infrastructure

The aim of the study is to analyse the feasibility of the second phase of the construction of the Rožaje (Montenegro) bypass project. The objectives of the construction of this bypass are to eliminate or reduce existing problems by redirecting transit flows to the bypass. Based on the observed economic costs of construction and the expected economic benefits from the project in a 20-year period, by applying Cost-Benefit Analysis (CBA), the indicators of the project economic feasibility were determined. As part of the socio-economic analysis of the project feasibility, the expected benefits for transport users (savings in travel time and savings in the vehicle exploitation costs), as well as external impacts (impacts on safety and impacts on the environment) were assessed. The analysis showed the dominant savings are in travel time and vehicle exploitation costs. The economic net present value (ENPV) of this project is positive and amounts to EUR 55 054 502, the economic internal rate of return (EIRR) is 26.88% (with a discount rate of 5%), while the benefit-cost ratio (B/CR) is 4.96. All scenarios developed within the Project Sensitivity Analysis have confirmed that this project has satisfactory economic justification.

Performance characterization of a slotted wind turbine airfoil featuring passive blowing

Renewable energy is crucial for a sustainable future, and wind energy holds significant potential as a viable solution to meet global demands. The current study employs high-fidelity Computational Fluid Dynamics (CFD) simulations to investigate the unsteady aerodynamics of an S809 wind turbine airfoil carved with an inclined contracting curved slot at the mid-chord location. The numerical analyses cover a wide range of angles of attack, α = 0°− 20°, at a chord-based Reynolds number of Rec = 5 × 105. The slotted airfoil exhibits superior aerodynamic performance over moderate-to-high angles of attack (α > 6°), with increased lift, reduced drag, and enhanced glide ratio of up to 1.3×, 0.5×, and 3.7× respectively, compared to the baseline. The slot-induced flow control significantly suppresses flow transition and separation across the airfoil surfaces. The attached-flow regime impedes the formation of flow anomalies, resulting in enhanced aerodynamic performance. Comparative analyses reveal significant reductions in velocity fluctuations, Reynolds shear, vorticity, and turbulent kinetic energy, across the slotted airfoil surface and wake region. The aeroacoustic analysis of the slotted airfoil exhibits substantial reduction in the far-field noise over moderate-high angles of attack, with an overall noise level reduction of approximately 14 decibels recorded at α = 17°. Overall, this study highlights the potential of slot-induced flow control as an effective strategy for enhancing the aerodynamic performance of wind turbines.

Wall-Normal Focused Laser Differential Interferometry

A new approach for measuring boundary-layer disturbances with focused laser differential interferometry (FLDI) for planar models is presented. By integrating a glass window into a flat plate, the optical axis was aligned normal to the model surface, and the focal plane was set inside the boundary layer. By determining the extent of the sensitive volume along the optical axis and calculating the analytical transfer function of the setup, the implications of the FLDI properties on the measured data are analyzed. Measurements performed on a flat plate at Mach 6 are used to demonstrate the effects of the laminar–turbulent transition on the spectral distribution of the power density and to explicitly verify the detectability of the expected second-mode instabilities. Advantages and disadvantages of the proposed setup compared to the conventional one are discussed.

Subcritical transition of the Stokes layer induced by wall surface roughness

Wall defect is an important reason for the Stokes layer transition. The present study investigates the transition of the Stokes layer induced by wall surface roughness under subcritical Reynolds numbers, which is lower than the critical Reynolds number of the global neutral curve. A pseudo-spectral numerical method is utilized to simulate the interactive effects of different parameters related to surface roughness. Based on the cycle-average pulsation energy, a critical roughness height is defined for the flow transition. A characteristic curve, termed as the transition curve, is discovered to relate the most critical roughness height with the Reynolds number for a given wave number in the span-wise direction. This curve can provide a quantitative criterion to predict the transition of the Stokes layer caused by the surface roughness. The result demonstrates that the critical roughness height is lower for three-dimensional than for two-dimensional roughness. It is also shown that when the Reynolds number is close to the critical Reynolds number of the global neutral curve (R=600), even a roughness height in the order of one nanometre could significantly interact with the flow and causes the transition. Moreover, when the Reynolds number is around 300, the order of 1 roughness height could be sufficient for the transition. This offers a possible explanation as to why the transitions observed in most of the experimental findings usually occur when the Reynolds number is around 275.

Boundary layer transition due to distributed roughness: effect of roughness spacing

The influence of roughness spacing on boundary layer transition over distributed roughness elements is studied using direct numerical simulation and global stability analysis, and compared with isolated roughness elements at the same Reynolds number $Re_h=U_eh/\nu$ ( $U_e$ is the boundary layer edge velocity, h is roughness height and $\nu$ is the kinetic viscosity of the fluid). Small spanwise spacing ( $\lambda _z=2.5h$ ) inhibits the formation of counter-rotating vortex pairs (CVP) and, as a result, hairpin vortices are not generated and the downstream shear layer is steady. For $\lambda _z=5h$ , the CVP and hairpin vortices are induced by the first row of roughness, perturbing the downstream shear layer and causing transition. The temporal periodicity of the primary hairpin vortices appears to be independent of the streamwise spacing. Distributed roughness leads to a lower critical roughness Reynolds number for instability to occur and a more significant breakdown of the boundary layer compared with isolated roughness. When the streamwise spacing is $\lambda _x=5h$ , the high-momentum fluid barely moves downward into the cavities and the wake flow has little impact on the following roughness elements. The leading unstable varicose mode is associated with the central low-speed streaks along the aligned roughness elements, and its frequency is close to the shedding frequency of hairpin vortices in the isolated case. For larger streamwise spacing ( $\lambda _x=10h$ ), two distinct modes are obtained from global stability analysis. The first mode shows varicose symmetry, corresponding to the primary hairpin vortex shedding induced by the first-row roughness. The high-speed streaks formed in the longitudinal grooves are also found to be unstable and interact with the varicose mode. The second mode is a sinuous mode with lower frequency, induced as the wake flow of the first-row roughness runs into the second row. It extracts most energy from the spanwise shear between the high- and low-speed streaks.

The Experiments and Stability Analysis of Hypersonic Boundary Layer Transition on a Flat Plate

Experimental and linear stability theory (LST) investigation of boundary layer transition on a flat plate was conducted with a flow of Mach number 5. The temperature distributions and second-mode disturbances on the flat plate surface at different unit Reynolds number (Reunit) values were captured by infrared thermography and PCB technology, respectively, which revealed the transition location of the flat-plate boundary layer. The PCB sensors successfully captured the second-mode disturbances within the boundary layer initially at a frequency of about 100 kHz, with a gradually expanding frequency range as the distance travelled downstream increased. The evolution characteristics of the second-mode instabilities were also investigated by LST and obtained for the second mode, ranging from 100 to 250 kHz. The amplitude amplification factor (N-factor) of the second-mode instabilities was calculated by the eN method. The N-factor of the transition location in the wind tunnel experiment predicted by LST is about 0.98 and 1.25 for Reunit = 6.38 × 106 and 8.20 × 106, respectively.

The role of a low-level jet for stirring the stable atmospheric surface layer in the Arctic

Abstract. In this study, we analyze the transition of a stable atmospheric boundary layer (ABL) with a low-level jet (LLJ) to a traditional stable ABL with a classic Ekman helix in the late-winter central Arctic. Vertical profiles in the ABL were measured with a hot-wire anemometer on a tethered balloon during a 15 h period in March 2018 in northeast Greenland. The tethered balloon allows high-resolution turbulence observations from the ground to the top of the ABL. The core of the LLJ was observed at about 150 m altitude, and its height and strength were associated with the temperature inversion. Increased turbulence was observed in the vicinity of the LLJ, but most of the turbulence does not reach down to the surface, thus decoupling the LLJ from the surface. Only when the LLJ collapses and the ABL again exhibits a more classical Ekman spiral is a coupling to the surface re-established. The LLJ might enhance both advective and turbulent vertical transport of passive tracers such as aerosol particles or moisture in the often stably stratified Arctic ABL.

DEVELOPMENT OF THE "ONE BELT, ONE ROAD" PROJECT AT THE PRESENT STAGE: TRANSFORMATION OF GOALS AND OBJECTIVES

The article examines a new period in the development of the “One Belt, One Road” (OBOR) initiative, of which Kazakhstan is a significant participant. It is noted that over the decade since the initiative was launched, key external and internal factors that directly influence it have undergone major changes. A conceptual analysis of these factors was carried out, including the goals and objectives set by the PRC, as the initiator and main driving force of the initiative, as well as other countries taking part. The adjustment of the attitude of third countries not participating in the OBOR, which have moved from a position of observation to open and active competition, is considered. The consequences of changes in the economic conditions in which the BRI is being implemented are studied, including the processes of transformation of regional transport flows and the redesign of Eurasian communications. Despite the profound changes in these factors, the strategic focus of the OBOR remains as a transcontinental long-term investment program. It is concluded that an adequate assessment of the new stage of development of the OBOR is important for Kazakhstan and the importance of developing its own participation strategy is increasing. It should be aimed not only at increasing competitive advantages in the field of competition for transit flows, but also at using the opportunities of the OBOR to ensure the modernization of the domestic economy.

Effects of Riblet Dimensions on the Transitional Boundary Layers Over High-Lift Turbine Blades

Abstract Substantial research exists in the literature on reducing the profile loss of transitional boundary layers over low-pressure turbine (LPT) blades via different mechanisms such as freestream turbulence, upstream wakes, and surface roughness. These mechanisms have proven to be beneficial in mitigating the separation bubble-related losses in ultra-high-lift blade designs, despite an increase in the loss due to increased turbulent wetted area (TWA). In this work, we adopt a strategy of employing surface roughness in the transitional regime to minimize the separation bubble-related losses and flush-mounted riblets downstream to further mitigate the skin-friction drag and boundary layer losses due to an increase in the TWA. Several high-fidelity scale-resolving simulations are performed on this “rough-ribbed blade surface” to discern the effect of varying the riblet spacing (s+) and height (h+). The streamwise evolution of skin-friction coefficient, boundary layer integral parameters, and shape factor are compared and contrasted among riblets of different dimensions. The instantaneous flow features and second-order statistics such as the Reynolds stress, turbulent kinetic energy, and its production are analyzed for different test cases to determine the impact of riblets on these quantities. When compared to the roughness alone configuration, the scalloped shape riblets with s+ = 17 and h+ = 22 reduced the net skin-friction drag by 7.3% and the trailing edge momentum thickness by 14.5%, thereby demonstrating the efficacy of riblets in reducing the mixing losses under adverse pressure gradients. Through an analysis of flow blockage introduced by the application of riblets, the deleterious effects of increasing the riblet height along with the necessity of optimizing the riblet ramp are highlighted.