Propeller Jet Research Articles

Technical Note: Analytical Estimate of Rotor Controls Required for a Propeller Wake Disturbance Rejection

During helicopter air-to-air refueling, the aircraft propeller’s jet can engage with the helicopter rotor. The impact on the helicopter rotor thrust and aerodynamic hub moments is solved analytically for the first time, based on blade element momentum theory. The collective and cyclic blade pitch controls needed for disturbance rejection are computed for a typical air-to-air refueling scenario. A propeller jet affecting the retreating side of the rotor requires much more pilot controls to retrim than an impingement on the advancing side.

Experimental Studies of the Impact of Ship Propeller Jet Flow on Scour Protection with Gabions

Experimental Studies of the Impact of Ship Propeller Jet Flow on Scour Protection with Gabions

How Fluid Pseudoplasticity and Elasticity Affect Propeller Flows in Biogas Fermenters

AbstractMixing in biogas fermenters is complex due to the non‐Newtonian rheology of biogenic substrates, which exhibit both pseudoplasticity and elasticity. It is yet unclear how these non‐Newtonian properties affect propeller flows and the mixing behavior in fermenters. Therefore, propeller flows in Newtonian as well as shear‐thinning inelastic and elastic fluids are compared numerically and validated against particle image velocity (PIV) data. Elastic normal stresses lead to an increase of pumping rates in the laminar regime and a suppression of the formation of a propeller jet in the transitional regime. Thus, flow rates are severely overestimated by the inelastic, shear‐thinning model in this regime. The results indicate that elasticity is critical for an accurate modeling of flows of biogenic substrates.

Ship-Forced Sediment Transport: A New Model for Propeller Jet Flow

A numerical model is presented for ship-induced sediment transport, focusing on the fundamental role of propeller jet flow. The new module has been implemented in the open-source numerical model FUNWAVE in order to reproduce the effect of the propeller on sediment transport. Numerical simulations have been performed for both stationary and moving vessel cases, as well as for different values of propeller revolution speed. Numerical results are presented for the propeller-induced velocity field and the resulting morphological evolution of the seabed. Qualitative similarities are observed between the numerical results and literature experimental findings, showing the ability of the model to mimic complex morphodynamic processes induced by ship propellers. Compared to stationary vessel cases, smaller scour depths are generated in moving vessel cases. It is concluded that the effect of the propeller provides a major contribution to the mobilization and suspension of seabed sediment, and it should not be neglected in numerical models for ship-induced sediment transport.

Physical Modelling Of Propeller Jet Induced Scour Near Quay Walls

Ship propellers cause high flow velocities near quay walls, jetties, locks and other hydraulic structures which can lead to scour of the bed near these structures and potentially result in instabilities of the construction. Bed protection is commonly applied as a measure to prevent damage and increase the life span of such hydraulic structures. When designing bed protection, the existing guidelines e.g. (PIANC 2015, BAW 2010) may not always result in optimal designs due to simplifications made in jet-flow schematizations and uncertainty of propeller-induced loads. To improve these design guidelines and optimize bed protection, a working group led by CROW and the Dutch Government was formed, and a joint research programme was initiated aiming at developing knowledge on propeller jet-induced scour by combining field measurements (Tukker 2021), scale model tests (Deltares 2023), and numerical modelling. The objective of the presentation during the Coastlab24 conference is to provide an overview of the various measurement techniques applied in the present research.

Experiment investigation on the local scour around circular and square piles in open wharf

Open wharves often rely on pile structures for stability, but these can cause local scouring, risking structural integrity and safety. Understanding scour mechanisms induced by propeller jet flow is crucial for effective scour protection, yet research on square piles and double piles is limited. This study presents a series of flume tests to investigate the local scour mechanisms around square piles and circular piles under propeller jet flow. The experiments consist of seven different configurations, including single square piles, double square piles, single circular piles, double circular piles, and a control case without any piles. The main focus of this research is to understand the development and variations of scour depth and scour pit dimensions induced by propeller jet flow. Additionally, the scour mechanisms of square piles are compared with those of circular piles, and the influence of double piles and pile spacing is examined. It can be found that substituting circular piles with square piles in practical engineering will generally lead to an increase in the overall scouring range of the foundation. The horizontal scouring range of double piles is significantly influenced by the pile spacing, resulting in a larger range with increased spacing. However, the variation in pile spacing has minimal impact on the vertical scouring range of the double piles. The shape of piles significantly impacts scour depth in both single and double-pile setups, with square piles resulting in deeper scour. Furthermore, increased pile numbers and narrower spacing contribute to higher scour depths. The results of this study enhance understanding of scour characteristics and offer valuable insights for designing and maintaining pile-supported open wharves, ensuring the safety and durability of waterfront structures through effective scour protection measures.

Technical Note: Analytical Estimate of Rotor Controls Required for a Propeller Wake Disturbance Rejection

During helicopter air-to-air refueling, the aircraft propeller's jet can engage with the helicopter rotor. The impact on the helicopter rotor thrust and aerodynamic hub moments is solved analytically for the first time, based on blade element momentum theory. The collective and cyclic blade pitch controls needed for disturbance rejection are computed for a typical air-to-air refueling scenario. A propeller jet affecting the retreating side of the rotor requires much more pilot controls to retrim than an impingement on the advancing side.

Effect of wave motion on the scouring caused by a marine propeller jet: An experimental and numerical study

Bathymetry changes induced by marine propeller jets on movable beds are a crucial issue in harbors, especially in the maneuvering zone. The knowledge of the scour hole and deposition mound dimensions, due to propeller jets, is important in the context of sediment management.Although the presence of waves is well known in harbor environments, propeller jet scours are usually investigated under still water conditions neglecting the effect of wave interaction. Moreover, the interaction between waves and propeller jets can also occur in mooring out of harbors. For these cases, the interaction of wave induced hydrodynamics and propeller jets is a crucial issue that is still an open and challenging problem. This paper aims to address, for the first time, the knowledge gap by investigating the influence of waves on propeller jets in unconfined conditions, which in turn can lead to alterations in scour and deposition patterns. The study relies on a specific experimental investigation. The selection of the parameters of the experimental tests is based on the results of prior analyses aimed to investigate the propeller jets induced scour and deposition in still water conditions and in the presence of a current. Hence, regular waves with different parameters (i.e. wave height and wave period) have been then reproduced in a wave flume where a propeller jet has been installed. The experimental tests aimed to get insight on the scour profiles as well as scour hole bathymetry induced by propeller jets under the influence of regular wave propagation. Numerical simulations have been also performed to investigate the effects of the wave-induced velocity acting on the propeller jets hydrodynamics. Spectral analysis has been then applied to characterize the complex scoured form and bedforms on the bathymetry configuration induced by the tested propeller jet and waves.

Development of clustered machine learning technique for the modeling of scour profile induced by propeller jets

In this study novel clustered machine learning (CML) models were developed by applying different base learners including multi linear regression (MLR), adaptive neuro-fuzzy inference system (ANFIS), classification and regression trees (CART), least-squares boosting (LSBoost), and random forest (RF) to predict scour profile induced by the jet of a propeller. Moreover, the results of CML models were compared with regular ML algorithms. The results show that the tree-based ensemble models, RF and LSBoost, are more accurate than CART. The ANIFS has the worst performance compared with other regular nonlinear methods, RMSE = 17.414 mm. The performance of MLR is also weak, RMSE = 35.63 mm and R2 = 0.088. However, the implementation of CML drastically increases the performance of MLR, RMSE = 15.053 mm, and R2 = 0.871. The CANFIS with RMSE = 8.757 mm, R2 = 0.976, and SI = 0 is ranked as the most accurate model. The results show that CLM enhances the performance of regular ML by up to 59.90%. The application of clustered ML is recommended for other complex problems. Finally, the results show that the derived models trained by other datasets very well predict measured scour profiles which datasets were not used in the training process.

Cloud-based system for monitoring loads generated on the quay wall by ship propeller jets

The paper presents a cloud-based system for monitoring loads generated on the quay wall by ship propeller jets during berthing and unberthing maneuvers. The system provides online measurements of the dynamic pressure generated loads by propellers and warns of exceeding the permissible jet velocities over the seabed protection along the berth. The system has a modular structure consisting of a network of pressure sensors, information mapping server, communication module and web server. The suitability of the system was confirmed during two years of operation in Port of Gdynia. The open architecture of the system allows for its further extension with additional berths and integration with the smart port system.

Comparative molecular dynamics study of liquid hydrogen annular jets in subcritical and supercritical environments

In this paper, the injection characteristics of a liquid hydrogen propellant jet under subcritical and supercritical operating conditions are comparatively studied at the molecular scale using molecular dynamics methods in the context of spacecraft propulsion systems. To control the temperature and pressure within the environment and nozzle respectively, two sub-computational domains are set up for separate modeling. The sub-computational domain merging process eliminates the broken molecular bonds by using the computational domain reduction in the x-direction. The jet velocity, density and other physical property distributions at different temperatures and pressures were comparatively studied. It is found that the rate of change of the radial density of the jet under supercritical conditions is small. Based on this, the surface area and volume of the liquid phase region of the jet were extracted and calculated. Compared to result of subcritical case, the volume of the liquid hydrogen jet in the supercritical environment is reduced by 1.9%, while the surface area is increase by 6.7%. To explain the variation in the surface area due to molecular diffusion, the molecular stress results revealed that the stress in the hydrogen jet in supercritical environment is only 88.9% of that in subcritical environment.

Predicting propeller jet scour in silty and sandy marine environments

The propeller jet generated by a ship's propeller during berthing and unberthing from quays initiates sediment transport and causes scouring around the quay structures. Investigating the flow area caused by ship propeller jets at quays and piers is important in terms of determining the local scour at the seabed. In this study, the water jet formed by ship's propellers and sediment movements on the seabed were investigated. While medium sand is typically used as the sediment type in literature, fine-grained sand and silt were used as base materials in this study. As a result of the experiments conducted with a three-dimensional flow velocity measuring device (ADV), the measured three-dimensional velocity components and the propeller efflux velocity coefficients were redefined. By examining the time dependent scour graphs of silt and sand, their scour rates were compared, and time scales were obtained from graphs. Silt was observed to have a significantly slower scour rate compared to sand. Contrary to the findings in the literature, despite silt having a smaller median particle diameter than sand, the maximum scour depths of silt were found to be less than those of sand under the same experimental conditions. Based on the results of this study and previous studies, two equations were proposed to quantify the scour depth for sand material, and silt and sand-clay mixtures.

Propeller-Induced Jet Impact on Vegetated Flow Fields: Complex Coupled Effect towards the Velocity Profile

The failure of swirling ship propellers in marine environments can lead to huge repair costs. One of the main causes of such failure is when propellers tangle with vegetation, especially in shallow flow environments like ports, harbours, or shipyards. In order to understand the above-mentioned issue, this study proposes an analytical approach to explore efficient predictions and provide a flow guideline with respect to the co-existence of vegetation and propeller swirling effects. More specifically, we intend to investigate the full-depth theoretical velocity profile to represent propeller-induced flow under submerged vegetation conditions. This paper first investigates the modified logarithmic law approach to determine its suitability to represent the regional vegetated flow zone before implementing it into a three-layer analytical model. It was found, using the benchmark of literature measurements, that the modified log law improved the near-bed velocity calculation by nearly 70% when compared to an existing model. A propeller jet impact computation coupled into the vegetation analytical model was then investigated in different locations within the vegetated flow, i.e., at free-flow, water–vegetation interface, and vegetation-hindered zones, to study their complex velocity distribution patterns. The results demonstrate adequate validation with the vegetated flow and measured propeller jet data from the literature. This proves the potential of the proposed analytical approach in representing a real-world propeller jet event submerged in water flow with the existence of vegetation. The proposed novel method allows costless computation, i.e., as compared to conventional numerical models, in representing the complex interaction of the propeller jet and vegetated flow.

Minimisation of Propeller-Induced Sediment Resuspension with Rip-Rap System

Sediment resuspension caused by the movement of propellers during manoeuvring is a major problem in daily port operations. Negative impacts include: Marine flora and fauna, sediment erosion that weakens berth structures, sediment deposits that require dredging. Later, this leads to delays in port operations. Several authors have proposed different methods to cope with this problem. This paper presents methods and tools to determine the critical propeller jet velocities, which are the most important parameter to determine the size of the bank stabilisation system. The tool is a bridge simulator that can be used to simulate the intrusive departure manoeuvre of a ship. The ship motion data are analysed to determine the critical shear stress of the sediment particles. The critical velocity induced by the propeller jet is determined using the German method.

Mechanisms of propeller jet-induced migration, release, and distribution of perfluoroalkyl acids in sediment–water systems

Perfluoroalkyl acids (PFAAs) are continuously accumulated in surface sediments due to extensive and long-term application. However, the mechanisms through which disturbances induced by ship propeller jets at the riverbed cause secondary release of PFAAs from sediments remain unclear. In this study, the effects of different propeller rotational speeds on PFAA migration, release, and distribution in multiphase media were investigated by performing indoor flume experiments combined with particle tracking velocimetry. Moreover, key factors influencing PFAA migration and distribution were identified, and partial least squares regression (PLS) method was applied to develop quantitative prediction models of relationships among hydrodynamics, physicochemical parameters, and PFAA distribution coefficients. The total PFAA concentrations (ΣPFAAs) in overlying water under propeller jet action exhibited transient characteristics and hysteresis with time after the disturbance. In contrast, the ΣPFAAs in suspended particulate matter (SPM) exhibited an upward trend throughout the process with consistent characteristics. The spatial distribution trends of PFAAs in overlying water and SPM at different propeller rotational speeds featured vertical variability and axial consistency. Furthermore, PFAA release from sediments was driven by axial flow velocity (Vx) and Reynolds normal stress Ryy, while PFAA release from porewater was inextricably linked to Reynolds stresses Rxx, Rxy, and Rzz (p < 0.05). PLS regression models showed that variations in Vorticity, dissolved organic carbon, and pH influenced the decreases in PFAA distribution coefficients between SPM and overlying water (KD-SW) as propeller rotational speed increased, except for very long-chain PFAAs (C > 10). The increases in PFAA distribution coefficients between sediment and porewater (KD-SP) were mainly determined by physicochemical parameters of sediments, and the direct effect of hydrodynamics was relatively weak. Our study provides valuable information regarding the migration and distribution of PFAAs in multiphase media under propeller jet disturbance (both during and after disturbance).

Physically based formula for the maximum scour depth induced by a propeller jet

In the last two decades, many studies have been dedicated to the employment of predictive formulas able to assess the maximum scour depth produced by propeller jets. Owing to the complexity of the phenomenon, most of the literature formulas were built on empirical arguments, making them susceptible to scale issues and not fully coherent with the physics underpinning the scouring problem. Recent studies exploited the phenomenological theory of turbulence and the paradigms of sediment incipient-motion theory to derive a predictive formula of the maximum equilibrium scour depth in different cases: scour produced by jet, scour at bridge piers, and scour downstream of hydrokinetic turbines. In the present study, using the same considerations of the aforementioned works, we propose a new model that allows the derivation of a predictive physically based formula that includes all the relevant parameters controlling the scouring process induced by the propeller rotation. The theory is validated at the laboratory scale with experimental published data: a good agreement between theoretical predictions and literature data is shown. The proposed design formula clearly indicates that, when tested against experimental data, it leads to lower scattering levels than those obtained with empirical literature formulas.

Improved formulation for the geometric characteristics of the scour hole and deposition mound caused by a rotating propeller jet on a mobile bed

The densimetric Froude number, F0, which depends on the propeller rotational speed, n, and on the median diameter of bed sediments, d50, is the main parameter considered by researchers for analysing the propeller-induced scouring process. Common literature equations for evaluating the three-dimensional (3D) geometric characteristics of the scour hole and deposition mound are functions of F0. In this paper, the agreements among the data and these literature equations are critically discussed, demonstrating that the use of other two dimensionless parameters (the propeller Froude number, F0p, and d50/Dp where Dp is the propeller diameter), which are separately dependent on n and d50, returns more satisfying results than using F0 solely.Also, the influence of the water depth, h, on the scour hole and the deposition mound is here analysed. Researchers commonly neglected the effects of h, because the ratio between it and Dp was large enough. This is reasonably true when h/Dp is considerably high, but no clear cut-off value was found in the literature. For the first time, by investigating a larger range of h, the present study underlines that the effects of h on the scour hole and the deposition mound are negligible for h/Dp ≥ 2.44.

Unconfined propeller jet scour on clay/sand mixtures

In this study, scour due to an unconfined propeller water jet on homogeneous clay-sand mixtures was investigated experimentally. A total of 9 tests were conducted for the sand bed and 18 tests were carried out for the sand-clay mixture bed. Since clay contents (p) of 0, 5 and 10% by weight were used in the experiments, scour in poorly cohesive sand-clay mixture bed was taken into account. Propeller diameters (Dp) were 0.06 and 0.09 m. Dimensionless propeller heights (y0/Dp) were defined as 1.67, 1.11, 1.0. The increase in clay content causes a decrease in the scour depth and changes the formation of scour profiles. The parameters y0/Dp, F0 (densimetric Froude number), p were found to have significant effects on the behavior of clay-sand mixtures. Considering the test results, equations were proposed to estimate the maximum depth and length of the scour hole formed in the equilibrium condition. In addition, by modifying the equation proposed by Hong et al. (2013), a new equation is proposed for the estimation of temporal maximum scour depth due to the propeller water jet on the sand and weakly cohesive sand-clay mixture beds.

Unconfined propeller scour in waterways: The role of flow intensity

Flow intensity represents an important input to be investigated in the ship propeller jet scouring process in ship maneuvering areas, waterways path, and mooring in navigation channels. Although the still water condition is not realistic, since it induces modifications in the canonical propeller jet scouring process in waterways, several studies were based on this assumption and only a few papers focused on the influence of the flow intensity are present in the technical literature. In this work, an experimental campaign aimed at exploring the flow intensity effects on the propeller jet and related scour was carried out. In particular, three flow intensities combined with different propeller submergence depths were tested. The experimental results are shown in terms of longitudinal and cross-sectional scoured bed profiles, and empirical equations to compute the main scour hole dimensions are proposed. Moreover, scour hole bathymetries were analyzed by spectral analysis to estimate characteristics length scales. In order to increase the detail on the fluid mechanics analysis to explain the influence of the flow intensity on the evolution of the scour hole and obtain an insight into the influence of the boundary effect on the flow field, Reynolds-Averaged Navier–Stokes simulations were performed over the three-dimensional scoured bathymetry, acquired at the equilibrium stage, and over the horizontal boundary, representing the earliest stages of the scouring process. The good agreement between the numerical results and the measured velocities at the equilibrium stage allowed also the simulations over a flat bed in the same hydraulic conditions. These represent the beginning of the scour process in the case in which the propeller blades are close to the bottom. As to the authors' knowledge, the last configurations were never simulated before, owing to the difficulties in managing the computation of a moving mesh close to a solid boundary. The results show, for the first time numerically, the plane boundary effects on the characteristics of propeller jets with and without an incoming flow.

Improved mixing of viscoelastic fluids by the use of hysteresis effect

A non-conventional mixing strategy utilizing the hysteresis effect of propeller jets in viscoelastic xanthan gum solutions was evaluated through decolorization mixing time experiments. The experiments consisted of capturing and analyzing the images of the flow patterns illustrated by a fast acid-base indicator reaction in a rectangular tank equipped with a side-entering propeller. A non-subjective image processing method using average color was compared with the literature. The steady operation using the axial flow pattern was found more effective than the one using the semi-radial flow pattern. The time-periodic operations with appropriate combinations of both flow patterns significantly enhanced mixing, whereas an inappropriate combination extended the mixing time. The unsteady mixing concept using the hysteresis effect shortened the mixing time, even when the propeller was operated at a reduced rotational speed. Hence, the mixing strategy utilizing the hysteresis effect can reduce mixing time and power consumption simultaneously.