Flow Conditions Research Articles

Zeolite intervention in soil nitrate dynamics: insights from column experiments and modelling

This study aims to address the harmful effects of excessive nitrogen fertilizer by investigating the mobility-retardance effect of zeolite on nitrate movement in loam soil columns. Disturbed and undisturbed soil columns, treated with zeolite as well as control soil columns, were analysed over a span of three years. Breakthrough curves generated from the experiments were evaluated using the HYDRUS-1D code with mobile–immobile water (MIM) and dual-permeability (DP) models. Our findings highlight that zeolite application significantly reduced nitrate mobility, with recovery rates decreasing by 8% in disturbed and 11% in undisturbed columns. The DP model, which accurately reflects real soil water flow conditions, outperformed the MIM model in predictive accuracy. This research offers a novel long-term perspective on the benefits of zeolite in enhancing soil properties and mitigating nitrate leaching, recommending the DP model for superior prediction of contaminant transport in structured soils within the vadose zone.

A Practical, Adaptive, and Scalable Real-Time Control Approach for Stormwater Storage Systems

Traditionally, urban stormwater infrastructure systems consist of passive infrastructure that is not actively controlled in response to rainfall events. Recently, real-time control (RTC) has been considered as a means to significantly increase the capacity and lifespan of these systems. This paper introduces the target flow control systems (TFCS) approach, which can use real-time control of systems of storages to achieve the desired flow conditions at the locations of interest. The first distinctive feature of this approach is that it does not require calibration to catchment-specific data, unlike existing approaches. This means that the TFCS approach is generally applicable to different catchments and is able to respond to future changes in runoff due to land use and/or climate change. The second distinctive feature is that the approach only requires storage-level information measured in real time with the aid of low-cost pressure sensors. This means that the approach is practical and relatively easy to implement. In addition to the introduction of the novel TFCS approach, a key innovation of this study is that the approach is tested on three case studies, each with different physical configurations and stormwater management objectives. Another key innovation is that the TFCS approach is compared to five RTC approaches, including three of the best-performing advanced approaches from the literature. Comparisons of multiple RTC approaches that consider both performance and practicality across multiple case studies are rare. Results show that the TFCS approach is the only one of the five control approaches analysed that has both the best overall performance and the highest level of practicality. The outcomes highlight the potential of the TFCS approach as a practical RTC approach that is applicable to a wide range of catchments with different stormwater management objectives. By maximizing the performance of existing stormwater storages, the TFCS approach can potentially extend the lifespan of existing infrastructure and avoid costly upgrades due to increased runoff caused by land use and climate change.

Research on the Influence of Particles and Blade Tip Clearance on the Wear Characteristics of a Submersible Sewage Pump

A submersible sewage pump is designed for conveying solid–liquid two-phase media containing sewage, waste, and fiber components, through its small and compact design and its excellent anti-winding and anti-clogging capabilities. In this paper, the computational fluid dynamics–discrete element method (CFD-DEM) coupling model is used to study the influence of different conveying conditions and particle parameters on the wear of the flow components in a submersible sewage pump. At the same time, the energy balance equation is used to explore the influence mechanism of different tip clearance sizes on the internal flow pattern, wear, and energy conversion mechanism of the pump. This study demonstrates that increasing the particle volume fraction decreases the inlet particle velocity and intensifies wear in critical areas. When enlarging the tip clearance thickness from 0.4 mm to 1.0 mm, the leakage vortex formation at the inlet is enhanced, leading to increased wear rates in terms of the blade and volute. Consequently, the total energy loss and turbulent kinetic energy generation increased by 3.57% and 2.25%, respectively, while the local loss coefficient in regard to the impeller channel cross-section increased significantly. The findings in this study offer essential knowledge for enhancing the performance and ensuring the stable operation of pumps under solid–liquid two-phase flow conditions.

Analysis of Local Scour around Double Piers in Tandem Arrangement in an S-Shaped Channel under Ice-Jammed Flow Conditions

The stability of bridge foundations is affected by local scour, and the formation of ice jams exacerbates local scour around bridge piers. These processes, particularly the evolution of ice jams and local scour around piers, are more complex in curved sections than in straight sections. This study, based on experiments in an S-shaped channel, investigates how various factors—the flow Froude number, ice–water discharge rate, median particle diameter, pier spacing, and pier diameter—affect the maximum local scour depth around double piers in tandem and the distribution of ice jam thickness. The results indicate that under ice-jammed flow conditions, the maximum local scour depth around double piers in tandem is positively correlated with the ice–water discharge rate, pier spacing, and pier diameter and negatively correlated with median particle diameter. The maximum local scour depth is positively correlated with the flow Froude number when it ranges from 0.1 to 0.114, peaking at 0.114. Above this value, the correlation becomes negative. In curved channels, the arrangement of double piers in tandem substantially influences ice jam thickness distribution, with increases in pier diameter and spacing directly correlating with greater ice jam thickness at each cross-section. Furthermore, ice jam thickness is responsive to flow conditions, escalating with higher ice–water discharge rates and decreasing flow Froude numbers.

Assessing the feasibility of mapping channel bathymetry of long river corridors from hyperspectral data across a range of flow conditions

ABSTRACT Hyperspectral imagery is a promising tool for bathymetric retrieval because that might be more robust than traditional imagery. However, in fluvial sciences, this approach has only been applied to short reaches for which sparse bathymetric information is available and studies extrapolating such models to longer reaches are lacking. In this paper, we use linear regression and random forest (RF) regression to derive bathymetric estimates from hyperspectral data acquired under two different flow conditions: an unmanned aerial vehicle (UAV) acquisition at 27 m3.s−1 (base flow) and an airplane acquisition at 127 m3.s−1 (mean flow) for reaches of 0.35 km and 20 km, respectively. Using a 2D bathymetric model based on a green LiDAR acquisition, we generate calibration and validation data for the 20 km reach and the two flow conditions. First, we show that the airplane dataset is able to retrieve base flow bathymetry with a similar accuracy to the UAV acquisition (5–10 cm) despite having been acquired at a higher discharge. Then, we show that we can extrapolate bathymetric models calibrated on a smaller reach to the 20 km study reach with a loss in accuracy compared to an RF model calibrated on the study reach (20–30 cm vs. 5–10 cm). By analysing the errors from our models, we show that the accuracy of the extrapolated models dropped due to an underprediction of deep pool areas and changes in the optical properties of the water column and substratum across the study reach, with some spectral bands performing more poorly. The better performance of the random forest calibrated on the study reach led us to suggest using multi-band machine learning models when attempting bathymetric predictions over long river corridors, and highlights the need to cover the range of environmental conditions in the target reach when acquiring field data.

Effects of Solidification Thermal Variables on the Microstructure and Hardness of the Silicon Aluminum Bronze Alloy CuAl6Si2

The properties of the final product obtained by solidification directly result from the thermal variables during solidification. This study aims to analyze the influence of thermal solidification variables on the hardness, microstructure, and phases of the CuAl6Si2 alloy. The material was solidified using unidirectional solidification equipment under non-stationary heat flow conditions, where heat extraction is conducted through a water-cooled graphite base. The thermal solidification variables were extracted using a data acquisition system, and temperature was monitored at six different positions, with cooling rates ranging from 217 to 3 °C/min from the nearest to the farthest position from the heat extraction point. An optical microscope, scanning electron microscope (SEM), and X-ray diffraction (XRD) were used to verify the fusion structure and determine the volumetric fraction of the formed phases. The XRD results showed the presence of β phases, α phases, and possible Fe3Si2 and Fe5Si3 intermetallics with different morphologies and volumetric fractions. Positions with lower cooling rates showed an increased volume fraction of the α phase and possible intermetallics compared to positions with faster cooling. High cooling rates increased the Brinell hardness of the alloy due to the refined and equiaxed β metastable phase, varying from 143 HB to 126 HB for the highest and lowest rates, respectively.

Sound source characteristics of heat exchanger under flow conditions

Heat exchangers are the most important equipment in ship cooling system, which generate vibration and noise due to flow excitation during operation, affecting structural safety and having a significant impact on acoustic stealth performance. Mastering the characteristics of sound source has guiding significance for noise reduction design. The acoustic signal directly obtained from the hydrophone inside the pipe including reflected sound wave, which cannot accurately characterize the sound radiation energy from heat exchanger into pipe. In order to accurately evaluate the sound source characteristics of heat exchanger under flow conditions, experimental method was used to test the sound source characteristics of heat exchanger which are not affected by connected pipelines based on the two-port sound source theory. The main factors affecting the sound source characteristics of heat exchanger were analyzed, such as flow rate, background pressure, and temperature. The research can provide reference for the vibration and noise reduction design of heat exchangers.

Hydrodynamic optimization and performance verification of fairings for round-ended cofferdams using dam-break wave experiments and numerical simulations

Round-ended cofferdams are crucial for large-scale marine projects but are vulnerable to the complex marine environment, including waves, tides, and storms. Enhancing the hydrodynamic performance of these cofferdams is essential for improving safety and efficiency in marine construction. This study introduces a novel fairing design aimed at reducing water flow resistance during the quasi-stable stage of a tsunami. The flow field is analyzed using computational fluid dynamics (CFD) simulations, and an adaptive surrogate model is employed to optimize the parameterized fairing shape. The results demonstrate that the optimized shape significantly suppresses vortex shedding, leading to a 16.59 % reduction in the drag coefficient and a 44.3 % reduction in the lift coefficient under flow conditions. Experimental and numerical simulations of dam-break waves are conducted for two designs, R1 and R0. By comparing their flow field and force characteristics, it is found that R1 effectively separates waves during the impulse stage, reduces wave climb height, and decreases impact loads. In the quasi-stable stage, R1 mitigates the blockage effect, reducing the liquid level difference between the front and back, and thus lowering flow forces. Experimental data further reveals that when the downstream is a dry riverbed, R1′s load reduction is particularly notable, with maximum reductions of 45.62 % in the impulse stage and 28.75 % in the quasi-stable stage. When the riverbed is wet, the maximum load reduction rates are 18.04 % and 8.72 %, respectively. Therefore, R1 not only reduces the resistance of round-end cofferdams under water currents but also under extreme wave forces, providing valuable insights for advancing ocean engineering design.

Calcium Carbonate Deposition Model Supporting Multiple Operating Conditions Based on the Phase-Field Method for Free-Surface Flows

The drainage systems of tunnels situated in limestone regions frequently encounter crystallization blockages. Numerous studies have addressed this issue, and their findings identified factors such as the flow velocity and temperature as influencing the crystallization process. However, these studies could not predict the occurrence of crystallization. Regarding theoretical approaches, most studies have focused on full-pipe operations or have solely considered flow-field dynamics without including simulations of the chemical reactions and mass transfers. This study introduces a mass-transfer model for drainage pipes based on a two-phase flow (water and air) with a free surface and non-full pipe flow that simulates the crystallization deposition process in drainage pipes. This model can predict the deposition conditions at varying flow velocities and intuitively visualize the crystallization process under the influence of various factors. The impact of flow velocity on the overall crystallization deposition process can be directly analyzed through simulations developed using this model. The results show that under conditions of incomplete pipe flow with no pressure at the outlet, the weight of the deposition first increases and then decreases within a certain velocity. This model can depict the variations within a 30 d period.

Aeroacoustic analysis of flow induced resonance in a gas pipeline

Flow induced noise and vibration in the pipework of gas production platforms can lead to fatigue failures of attached small-bore pipes, and this can constrain the operating conditions of the platform. Typically such problems comprise a source of turbulence in the flow, an aeroacoustic feedback mechanism due to acoustic resonances inside the pipework, and mechanical resonances which amplify the resulting vibration. The problem described here occurred in the gas metering system of the platform, with the source located in the header which comprised a bifurcation into two metering lines and a number of sharp bends. Because of the cost of rectifying the problem an in-depth study was carried out to analyse the flow and induct acoustic conditions. The predictions will support recommendations for an efficient redesign of the entire system to control the problem at source. Various levels of CFD modelling (RANS and URANS) were carried out using the Openfoam code to predict the exact location and mechanism of the vortex shedding. The acoustic response of the complex ductwork was then modelled using the ACTRAN code to understand the feedback mechanism which led to resonance and high levels of response.

Multiphysical design for optimised ventilation and noise attenuation in ducts: an approach using metamaterials

Noise generation and propagation through mechanical ventilation and air conditioning (MVAC) ducts have been increasingly investigated since commercial solutions allow sensible noise attenuation while reducing the duct section. So, a commercial silencer forces the MVAC power to rise to overcome the flow resistance, increasing the noise source. For this reason, this study focuses on soundproofing ventilation ducts through acoustic metamaterials with no inner duct section decreasing. A crucial part of this study falls into the multiphysical interaction between acoustics and fluid dynamics, which is a phenomenon that may result in a challenging analytical model. In conditions of flowing motion, the wave vector has been modelled according to the Lighthill model: the component of the velocity rotor potential becomes significant, influencing the soundproofing performance due to the metamaterial placed at the edge of the inner surface of the duct. FEM analysis helped design a series of samples which then have been tested experimentally in static conditions. Once the numerical method is calibrated, further multiphysical numerical analysis are used to implement the sound insulation properties of the metamaterial-based filter through dynamic flow conditions. Guidelines for multiphysical setup for wave-based simulation are drawn, and preliminary experimental results are presented.

Relation between measured noise levels and traffic flow

Road-traffic flow parameters are a critical input to urban noise pollution evaluation frameworks such as CNOSSOS-EU. The accuracy and resolution of the traffic flow improves the quality of the noise exposure assessment. Highly resolved traffic flow within an urban network is difficult to reliably measure or predict. The quality and availability of such traffic information may be improved using data from low-cost noise sensors that are mounted beside representative segments of the road network. A model is presented, which relates the noise levels measured at a single noise sensor with the local traffic flow conditions. The noise data is obtained from a noise sensor mounted alongside a road, which is part of a test-bed in Stockholm, Sweden. The local traffic flow is obtained from commercial vehicle-counting sensors mounted alongside the noise sensor. Effect of seasonality is observed when comparing models trained on different subsets of the training data. The effect of seasonality on the noise levels is investigated.

Fuel blend combustion for decarbonization

The utilization of fossil fuels is currently transforming to low-carbon or zero-carbon fuels, which is one of the solutions to global warming. Hydrogen and ammonia are regarded as promising zero-carbon fuels in power supply and transportation scenarios but the availability of hydrogen and their distinctly different chemical activity constrain their large-scale direct utilizations. Fuel blends with physical and chemical complementary are considered as the effective approaches in the utilization of hydrogen and ammonia because no significant modification to the existing end-user infrastructures is needed. This paper reports recent progress in the fundamental combustion behaviors of fuel blends, focusing on hydrogen-hydrocarbon blends and ammonia-hydrocarbon blends. Firstly, laminar flame behaviors, auto- and forced-ignition characteristics, and pollutant emissions of binary fuels containing hydrogen are reviewed, all of which are supplemented with a discussion on the governing hydrogen-enriched combustion chemistry. Subsequently, the hydrogen-enriched flame responses to the flow conditions are discussed, including the turbulent burning velocity and statistical structures, the flashback swirl flames, thermoacoustic instabilities, and the jet ignition characteristics; Furthermore, with the increasing concern over ammonia as a zero carbon fuel and its extremely weak reactivity, recent progress on combustion of fuel blends containing ammonia are also reviewed. The fundamental combustion chemistry studies including laminar burning velocity, the ignition delay times data collection, as well as the attempts for chemical kinetic modeling development for fuel blend with ammonia are presented. The literature reported ammonia containing blends of turbulent flame characteristics are presented. Finally, from an engineering point of view, examples using hydrogen blends in practical internal combustion engines and in gas turbines are introduced, including the topic of engine efficiency performance and pollutant emissions and different combustors for gas turbines. It is suggested that fuel blends with hydrogen or ammonia that potentially monitors the overall reactivity will be one realistic solution to de-carbonization, on the basis of current transportation and power generation systems.

Air-Stable Membrane-Free Magnesium Redox Flow Batteries.

Membrane-free biphasic self-stratified batteries (MBSBs) utilizing aqueous/nonaqueous electrolyte systems have garnered significant attention owing to their flexible manufacturing and cost-effectiveness. In this study, we present an ultrastable high-voltage Mg MBSB based on an aqueous/nonaqueous electrolyte system. The engineered aqueous electrolyte had a wide electrochemical stability window of 3.24 V. The Mg metal anode features a Mg2+-conductive protective coating. Two metal-free redox compounds, 2,2,6,6-tetramethylpiperdinyl oxy (TEMPO) and N-propyl phenothiazine (C3-PTZ), were used as catholytes. The Mg||TEMPO and Mg||C3-PTZ MBSBs exhibited high cell voltages of 2.07 and 2.12 V, respectively, and were studied under static, stirred, and flow conditions. The Mg MBSBs were initially evaluated at different catholyte concentrations (0.1, 0.3, and 0.5 M) under static conditions. Notably, the Mg||TEMPO (0.5 M) and Mg||C3-PTZ (0.5 M) static batteries maintained exceptional performances over 500 cycles at 8 mA/cm2, with capacity retention rates of 97.84% and 98.87%, Coulombic efficiencies of 99.17% and 99.12%, and capacity utilization of 70.2% and 71.3%, respectively. Under stirred and flow conditions, the Mg||TEMPO (0.5 M) and Mg||C3-PTZ (0.5 M) batteries cycled 500 times at 12 mA/cm2 demonstrated capacity retention rates of 99.82% and 99.88% (stirred), 93.58% and 92.16% (flow), respectively. Under flow conditions, the Mg||TEMPO (0.5 M) and Mg||C3-PTZ (0.5 M) batteries demonstrated power densities of 195 and 191 mW/cm2, respectively, surpassing those of 139 and 144 mW/cm2 under static conditions. These cost-effective Mg MBSBs exhibit remarkable performance and advance the application of Mg chemistry in organic flow batteries.

Heat transfer and entropy generation characteristics of nanofluid flow over bluff bodies under steady and unsteady flow: A two-phase approach

Owing to higher thermal conductivity, nanofluids have the potential to be the coolant for various applications ranging from internal to external flows. A two-phase model is implemented to model the interaction between nanoparticles and base fluid to obtain accurate results. Heat transfer and entropy generation characteristics of nanofluid (Al2O3 and water) flow over bluff bodies such as circular and square cylinders for steady (20 < Re < 100) and unsteady (Re = 150 and 300) flow conditions have been carried out for various volume fractions (0.5–2 %). The same has been expressed in quantitative and qualitative aspects with parameters such as mean Nusselt number, surface Nusselt number, heat transfer enhancement ratio, and entropy generation. Heat transfer rate increases with an increase in flow rate and volume fraction for both steady and unsteady flow. Heat transfer enhancement in steady flow ranges from 1.10 to 1.35. For unsteady flow (Re = 150 & Re = 300), nanofluid's heat transfer enhancement ratio is higher than water in the range of 1.10–1.8. This is attributed to the early separation of flow and the presence of large recirculatory regions. With the increase in Re, the entropy generation decreases for circular and square cylinders. Compared to nanofluid, the entropy generation is higher for water.

Tuning metal-support interactions in nickel–zeolite catalysts leads to enhanced stability during dry reforming of methane

Ni-based catalysts are highly reactive for dry reforming of methane (DRM) but they are prone to rapid deactivation due to sintering and/or coking. In this study, we present a straightforward approach for anchoring dispersed Ni sites with strengthened metal-support interactions, which leads to Ni active sites embedded in dealuminated Beta zeolite with superior stability and rates for DRM. The process involves solid-state grinding of dealuminated Beta zeolites and nickel nitrate, followed by calcination under finely controlled gas flow conditions. By combining in situ X-ray absorption spectroscopy and ab initio simulations, it is elucidated that the efficient removal of byproducts during catalyst synthesis is conducted to strengthen Ni–Si interactions that suppress coking and sintering after 100 h of time-on-stream. Transient isotopic kinetic experiments shed light on the differences in intrinsic turnover frequency of Ni species and explain performance trends. This work constructs a fundamental understanding regarding the implication of facile synthesis protocols on metal-support interaction in zeolite-supported Ni sites, and it lays the needed foundations on how these interactions can be tuned for outstanding DRM performance.

Enhancing LSPIV accuracy in low-speed flows and heterogeneous seeding conditions using image gradient

Flow measurement in rivers and channels is crucial for water resource management and infrastructure planning, especially under the context of climate change. However, traditional methods like mechanical current meters and hydroacoustic instruments face limitations in terms of cost, intrusiveness, and accessibility. In recent years, image-based velocimetry techniques have emerged as promising alternatives due to their non-contact nature and cost-effectiveness. Nevertheless, persistent challenges remain, particularly concerning the uniform distribution of surface tracers necessary for precise measurements. These challenges are particularly pronounced in cases involving artificial seeding, where ensuring uniform distribution poses a significant obstacle. To address this issue, this study presents a novel methodology for filtering Large Scale Particle Image Velocimetry (LSPIV) data based on indicators of pixel intensity gradients. The methodology was evaluated across various field measurements under low flow conditions, encompassing a wide range of seeding characteristics. The evaluations demonstrated improvements in mean surface velocity profile estimation, showing reductions of up to 70 % in normalized root mean square error compared to not using filters. Additionally, the results were compared with filters typically employed by experienced LSPIV users, such as background subtraction and cross-correlation coefficient thresholds, showing improvements with the proposed filter. Implementation of the proposed strategy reduces the subjectivity in LSPIV implementation, particularly for users with limited knowledge of the technique, but also require minimal post-processing efforts. The methodology is anticipated to be integrated into existing software tools, thereby enhancing the accessibility of LSPIV for individuals with limited expertise in image velocimetry. Overall, this methodology facilitates cost-effective expansion of hydrological information availability, particularly in resource-constrained regions.

Novel dopamine-derived carbon modified fe-based metal–organic framework enhanced aptasensor rendering ultrasensitive electrochemical detection of oxytetracycline

In the present work, an aptasensor with dual binding sites based on Au NPs modified with self-polymerized polydopamine (PDA) and Fe-MOF is successfully constructed. In terms of standard electron transfer, the cyclic voltammetry (CV) analysis showcases a rate constant (ks) of 96.0 s−1, signifying an exceptional electron transfer rate of oxytetracycline at the sensor interface of Apt/Au@PDA@NH2-MIL-101(Fe)/GCE. Further deepening the investigation into electrochemical kinetics using chronoamperometry (CA), we investigated the electrocatalytic parameters (Kcat) of Au@PDA@NH2-MIL-101(Fe) in relation to oxytetracycline. The results divulged an impressive average Kcat value of 3.06 × 105 M−1 S-1. This evidence robustly suggests the superior electrocatalytic activity of Au@PDA@NH2-MIL-101(Fe) when it comes to oxytetracycline oxidation. A custom-designed portable rapid detection platform was developed, achieving detection limits of 6.88 nM under static water flow conditions and 5.56 nM under dynamic conditions. Remarkably, the self-polymerization of PDA on Au NPs not only refines their size but also boosts their interaction with biomolecules, thereby promising excellent biocompatibility. Moreover, the abundance of –COOH groups and unsaturated Fe3+ sites on the NH2-MIL-101(Fe) surface furnishes a considerable number of grafting sites for the aptamer. More importantly, the redox interplay between Au@PDA and NH2-MIL-101(Fe) accelerates electron movement, thus amplifying the electrochemical signal and the detection sensitivity for oxytetracycline.

Barrier-free, open-top microfluidic chip for generating two distinct, interconnected 3D microvascular networks

Developing microphysiological cell culture platforms with a three-dimensional (3D) microenvironment has been a significant advancement from traditional monolayer cultures. Still, most of the current microphysiological platforms are limited in closed designs, i.e. are not accessible after 3D cell culture loading. Here, we report an open-top microfluidic chip which enables the generation of two sequentially loaded 3D cell cultures without physical barriers restricting the nurture, gas exchange and cellular communication. As a proof-of-concept, we demonstrated the formation of two 3D vasculatures, one in the upper and the other in the lower compartment, under three distinct flow conditions: asymmetric side-to-center, symmetric side-to-center and symmetric center-to-side. We used computational modelling to characterize initial flow pressures in cell culture compartments. We showed prominent vessel formation and branched vasculatures in upper and lower cell culture compartments with interconnecting, lumenized vessels with in vivo-relevant diameter in all flow conditions. With advanced image processing, we quantified and compared the overall vascular network volume and the total length formed in asymmetric side-to-center, symmetric side-to-center and symmetric center-to-side flow conditions. Our results indicate that the developed chip can house two distinct 3D cell cultures with merging vessels between compartments and by providing asymmetric side-to-center or symmetric center-to-side flow vascular morphogenesis is enhanced in terms of overall network length. The developed open-top microfluidic chip may find various applications in generation of tissue-specific 3D-3D co-cultures for studying cellular interactions in vascularized tissues and organs.

Drag reduction utilizing a wall-attached ferrofluid film in turbulent channel flow

This study explores the application of a wall-attached ferrofluid film to decrease skin-friction drag in turbulent channel flow. We conduct experiments using water as a working fluid in a turbulent channel flow set-up, where one wall is coated with a ferrofluid layer held in place by external permanent magnets. Depending on the flow conditions, the interface between the two fluids is observed to form unstable travelling waves. While ferrofluid coating has been previously employed in laminar and moderately turbulent flows (Reynolds number $Re&lt;4000$ ) to reduce drag by creating a slip condition at the fluid interface, its effectiveness in fully developed turbulent conditions, particularly when the interface exhibits instability, remains uncertain. Our primary objective is to assess the effectiveness of ferrofluid coating in reducing turbulent drag with particular focus on scenarios when the ferrofluid layer forms unstable waves. To achieve this, we measure flow velocity using two-dimensional particle tracking velocimetry (2D-PTV), and the interface contour between the fluids is determined using an interface tracking algorithm. Our results reveal the significant potential of ferrofluid coating for drag reduction, even in scenarios where the interface between the surrounding fluid and ferrofluid exhibits instability, with observed drag reduction rates up to 95 %. In particular, waves with an amplitude significantly smaller than a viscous length scale positively contribute to drag reduction, while larger waves are detrimental, because of induced turbulent fluctuations. However, for the latter case, slip outcompetes the extra turbulence so that drag is still reduced.