scholarly journals Experimental and CFD Analysis of Impact of Surface Roughness on Hydrodynamic Performance of a Darrieus Hydro (DH) Turbine

Energies ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 928 ◽  
Author(s):  
Mohammad Hassan Khanjanpour ◽  
Akbar A. Javadi
Keyword(s):  
Surface Roughness ◽  
Drag Coefficient ◽  
Output Power ◽  
Negative Impact ◽  
Pressure Coefficient ◽  
Turbine Blades ◽  
Roughness Height ◽  
Hydrodynamic Performance ◽  
Cfd Modeling ◽  
Wide Range

Although improving the hydrodynamic performance is a key objective in the design of ocean-powered devices, there are some factors that affect the efficiency of the device during its operation. In this study, the impacts of a wide range of surface roughness as a tribological parameter on stream flow around a hydro turbine and its power loss are studied. A comprehensive program of 3D Computational Fluid Dynamics (CFD) modeling, as well as an expansive range of experiments were carried out on a Darrieus Hydro (DH) turbine in order to measure reduction in hydrodynamic performance due to surface roughness. The results show that surface roughness of turbine blades plays an important role in the hydrodynamics of the flow around the turbine. The surface roughness increases turbulence and decreases the active fluid energy that is required for rotating the turbine, thereby reducing the performance of the turbine. The extent of the negative impact of surface roughness on the drag coefficient, pressure coefficient, torque, and output power is evaluated. It is shown that the drag coefficient of a turbine with roughness height of 1000 μm is about 20% higher than a smooth blade (zero roughness height) and the maximum percentage of reduction of output power could be up to 27% (numerically) and 22% (experimentally).

Numerical Study of Cavitation Characteristics of Profiles for Use in Marine Current Turbines

2011 ◽  
Author(s):  
Alexander Ladino
Keyword(s):  
Numerical Study ◽  
Pressure Coefficient ◽  
Turbine Blades ◽  
Design Stage ◽  
Power Performance ◽  
Trailing Edge ◽  
Free Zone ◽  
Wide Range ◽  
Marine Current ◽  
Promising Source

Kinetic energy in the oceans offers an important and promising source of renewable energy which can be exploited by marine current turbines (MCT). One of the key issues related with design of MCT’s is the cavitation inception along turbine blades. Cavitation occurrence in MCT’s blades generates erosion and poor power performance with similar effect in the hydraulic turbine case. In this work, a numerical investigation using the vorticity–stream function code XFOIL in order to study cavitation characteristics in NACA 4 series profiles was performed. The study was developed systematically starting from NACA 4415 profiles and varying independently camber percentage, camber position and thickness. Other study carried out was the effect of trailing edge deflection in the cavitation bucket. Results show a symmetrical increment in cavitation free zone for profiles with increasing thickness. Also for camber increment, the cavitation free zone is incremented, especially at high angles of attack. For variation of camber percentage, increasing camber produces the cavitation bucket moves to high lift zone which suggest that the profile could cavitate at low and negative Cl in wide range of cavitation numbers. Finally the effect of trailing edge deflection produces a slight increment in cavitation free zone which is similar to the effect of camber increment. Also, the trailing edge deflection shows that a same Cl can be achieved with lower angle of attack and lower pressure coefficient compared with the standard profile, constituting a desired behavior from the cavitation point of view. Finally, local dimensionless correlations were developed which can be used for parametric studies of cavitation performance of MCT’s in the design stage.

Effects of Surface-Roughness Geometry on Separation-Bubble Transition

2005 ◽  
Vol 128 (2) ◽  
pp. 349-356 ◽  
Author(s):  
Stephen K. Roberts ◽  
Metin I. Yaras
Keyword(s):  
Surface Roughness ◽  
Separation Bubble ◽  
Turbine Blades ◽  
Dominant Mode ◽  
Roughness Height ◽  
Height Variation ◽  
Separated Shear Layer ◽  
Roughness Elements ◽  
Negative Skewness ◽  
Typical Range

This paper presents measurements of separation-bubble transition over a range of surfaces with randomly distributed roughness elements. The tested roughness patterns represent the typical range of roughness conditions encountered on in-service turbine blades. Through these measurements, the effects of size and spacing of the roughness elements, and the tendency of the roughness pattern toward protrusions or depressions (skewness), on the inception location and rate of transition are evaluated. Increased roughness height, increased spacing of the roughness elements, and a tendency of the roughness pattern toward depressions (negative skewness) are observed to promote earlier transition inception. The observed effects of roughness spacing and skewness are found to be small in comparison to that of the roughness height. Variation in the dominant mode of instability in the separated shear layer is achieved through adjustment of the streamwise pressure distribution. The results provide examples for the extent of interaction between viscous and inviscid stability mechanisms.

scholarly journals Marine Turbine Hydrodynamics by a Boundary Element Method with Viscous Flow Correction

2018 ◽  
Author(s):  
Francesco Salvatore ◽  
Zohreh Sarichloo ◽  
Danilo Calcagni
Keyword(s):  
Viscous Flow ◽  
Numerical Models ◽  
Turbine Blades ◽  
Integral Equation Method ◽  
Boundary Integral ◽  
Operating Conditions ◽  
Hydrodynamic Performance ◽  
Numerical Predictions ◽  
Wide Range ◽  
Marine Current

A computational methodology for the hydrodynamic analysis of horizontal axis marine current turbines is presented. The approach is based on a boundary integral equation method for inviscid flows originally developed for marine propellers and adapted here to describe the flow features that characterize hydrokinetic turbines. To this purpose, semi-analytical trailing wake and viscous-flow correction models are introduced. A validation study is performed by comparing hydrodynamic performance predictions with two experimental test cases and with results from other numerical models in the literature. The capability of the proposed methodology to correctly describe turbine thrust and power over a wide range of operating conditions is discussed. Viscosity effects associated to blade flow separation and stall are taken into account and predicted thrust and power are comparable with results of blade element methods that are largely used in the design of marine current turbines. The accuracy of numerical predictions tend to reduce in cases where turbine blades operate in off-design conditions.

Assessment of Real Turbine Blade Roughness Parameters for the Design of a Film Cooling Test Rig

2017 ◽  
Author(s):  
Tobias Glasenapp ◽  
Franz Puetz ◽  
Achmed Schulz ◽  
Hans-Jörg Bauer
Keyword(s):  
Surface Roughness ◽  
Fluid Flow ◽  
Gas Turbines ◽  
Numerical Models ◽  
Suction Side ◽  
Roughness Height ◽  
Optical Measurements ◽  
Roughness Parameters ◽  
Average Roughness ◽  
Wide Range

The average roughness height Ra was used for characterizing surface roughness in many past investigations. In order to fully describe heat transfer and fluid flow over a rough surface, statistical parameters, however, are not sufficient. There is a lack of data in the literature in terms of three-dimensional real turbine roughness and the distribution of roughness parameters on the turbine airfoils. This study closes this gap and provides detailed surface roughness data of high-pressure turbine vanes that have been in service in land-based gas turbines and aero engines. Furthermore, samples of thermal barrier coatings from two different application techniques are investigated. High-resolution 3D profilometer and optical measurements are performed at various locations on both the pressure and suction side. Key parameters such as roughness shape and density are quantified. Equivalent sand grain roughness height (ks) values are obtained and related to the fluid flow by calculating the corresponding dimensionless roughness heights. The results show that roughness parameters are spread over a wide range. No correlation with position on the vane surface is found. The distribution of the roughness heights deviates from a Gaussian distribution. Roughness on the suction side is generally smaller than on the pressure side. Dimensionless roughness heights are found to be mainly in the transitional regime and not in the fully rough regime as expected. The data presented in this paper is of great importance to the design of test surfaces for laboratory experiments and as input for numerical models.

Fluid forces and vortex patterns of an oscillating cylinder pair in still water with both fixed side-by-side and tandem configurations

2021 ◽  
pp. 1-23
Author(s):  
Ang Li ◽  
Shengmin Shi ◽  
Dixia Fan
Keyword(s):  
Drag Coefficient ◽  
Oscillatory Flow ◽  
Lift Coefficient ◽  
Stokes Number ◽  
Hydrodynamic Performance ◽  
Circular Cylinders ◽  
Oscillating Cylinder ◽  
Tandem Configuration ◽  
Fluid Forces ◽  
Wide Range

Abstract Models of cylinders in the oscillatory flow can be found virtually everywhere in the marine industry, such as pump towers experiencing sloshing load in a LNG ship liquid tank. However, compared to the problem of a cylinder in the uniform flow, a cylinder in the oscillatory flow is less studied, let alone multiple cylinders. Therefore, we experimentally and numerically studied two identical circular cylinders oscillating in the still water with either a side-by-side or a tandem configuration for a wide range of Keulegan-Carpenter number and Stokes number β. The experiment result shows that the hydrodynamic performance of an oscillating cylinder pair in the still water is greatly altered due to the interference between the multiple structures with different configurations. In specific, compared to the single-cylinder case, the drag coefficient is greatly enhanced when two cylinders are placed side-by-side at a small gap ratio, while dual cylinders in a tandem configuration obtain a smaller drag coefficient and oscillating lift coefficient. In order to reveal the detailed flow physics that results in significant fluid forces alternations, the detailed flow visualization is provided by the numerical simulation: the small gap between two cylinders in a side-by-side configuration will result in a strong gap jet that enhances the energy dissipation and increase the drag, while due to the flow blocking effect for two cylinders in a tandem configuration, the drag coefficient decreases.

Investigation of Wide Range of Flow around Circular Cylinder Using Turbulence Model

2013 ◽  
Vol 664 ◽  
pp. 878-883 ◽  
Author(s):  
Kee Quen Lee ◽  
Abu Aminudin ◽  
Muhamad Pauziah
Keyword(s):  
Experimental Data ◽  
Circular Cylinder ◽  
Drag Coefficient ◽  
Strouhal Number ◽  
Turbulence Model ◽  
Pressure Coefficient ◽  
Wide Range ◽  
Flow Around Circular Cylinder ◽  
Turbulence Length ◽  
Physical Features

The purpose of present study is to identify the possibility of predicting the physical features of circular cylinder in two dimensional for a wide range of Reynolds number using a modified turbulence model. The modification is focused on the turbulence length and intensity. The drag coefficient and the Strouhal number were calculated and compared with the existing experimental data. The contour of vorticity and pressure gradient were also presented. Although variation up to 159% was noted in the drag coefficient, it was just on a particular Reynolds number.The simulated outputs of Strouhal number, pressure coefficient and vorticity contour indicated reasonable agreement with the experimental data. The modified turbulence model has showed potential in simulating the flow around the circular cylinder.

Effects of Surface-Roughness Geometry on Separation-Bubble Transition

2005 ◽  
Author(s):  
Stephen K. Roberts ◽  
Metin I. Yaras
Keyword(s):  
Surface Roughness ◽  
Separation Bubble ◽  
Turbine Blades ◽  
Dominant Mode ◽  
Roughness Height ◽  
Height Variation ◽  
Separated Shear Layer ◽  
Roughness Elements ◽  
Negative Skewness ◽  
Typical Range

This paper presents measurements of separation-bubble transition over a range of surfaces with randomly distributed roughness elements. The tested roughness patterns represent the typical range of roughness conditions encountered on in-service turbine blades. Through these measurements, the effects of size and spacing of the roughness elements, and the tendency of the roughness pattern toward protrusions or depressions (skewness), on the inception location and rate of transition are evaluated. Increased roughness height, increased spacing of the roughness elements, and a tendency of the roughness pattern toward depressions (negative skewness) are observed to promote earlier transition inception. The observed effects of roughness spacing and skewness are found to be small in comparison to that of the roughness height. Variation in the dominant mode of instability in the separated shear layer is achieved through adjustment of the streamwise pressure distribution. The results provide examples for the extent of interaction between viscous and inviscid stability mechanisms.

scholarly journals Computational Fluid Dynamics Modeling of Rotating Annular VUV/UV Photoreactor for Water Treatment

Processes ◽  
2020 ◽  
Vol 9 (1) ◽  
pp. 79
Author(s):  
Minghan Luo ◽  
Wenjie Xu ◽  
Xiaorong Kang ◽  
Keqiang Ding ◽  
Taeseop Jeong
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Water Treatment ◽  
Cfd Modeling ◽  
Flow Mode ◽  
Oh Radicals ◽  
Dynamics Modeling ◽  
Rotational Movement ◽  
Contaminant Degradation ◽  
Wide Range

The ultraviolet photochemical degradation process is widely recognized as a low-cost, environmentally friendly, and sustainable technology for water treatment. This study integrated computational fluid dynamics (CFD) and a photoreactive kinetic model to investigate the effects of flow characteristics on the contaminant degradation performance of a rotating annular photoreactor with a vacuum-UV (VUV)/UV process performed in continuous flow mode. The results demonstrated that the introduced fluid remained in intensive rotational movement inside the reactor for a wide range of inflow rates, and the rotational movement was enhanced with increasing influent speed within the studied velocity range. The CFD modeling results were consistent with the experimental abatement of methylene blue (MB), although the model slightly overestimated MB degradation because it did not fully account for the consumption of OH radicals from byproducts generated in the MB decomposition processes. The OH radical generation and contaminant degradation efficiency of the VUV/UV process showed strong correlation with the mixing level in a photoreactor, which confirmed the promising potential of the developed rotating annular VUV reactor in water treatment.

scholarly journals Treatment patterns and appropriateness of antipsychotic prescriptions in patients with schizophrenia

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Verónica Gamón ◽  
Isabel Hurtado ◽  
José Salazar-Fraile ◽  
Gabriel Sanfélix-Gimeno
Keyword(s):  
Negative Impact ◽  
Current Treatment ◽  
Treatment Patterns ◽  
Mental Condition ◽  
Comorbid Condition ◽  
Concomitant Treatment ◽  
Antipsychotic Medications ◽  
Wide Range ◽  
Schizophrenic Patients ◽  
High Level

AbstractSchizophrenia is a chronic mental condition presenting a wide range of symptoms. Although it has a low prevalence compared to other mental conditions, it has a negative impact on social and occupational functions. This study aimed to assess the appropriateness of antipsychotic medications administered to schizophrenic patients and describe current treatment patterns for schizophrenia. A retrospective cohort study was conducted in all patients over the age of 15 with an active diagnosis of schizophrenia and treated with antipsychotics between 2008 and 2013 in the Valencia region. A total of 19,718 patients were eligible for inclusion. The main outcome assessed was inappropriateness of the pharmacotherapeutic management, including polypharmacy use. Altogether, 30.4% of patients received antipsychotic polypharmacy, and 6.8% were prescribed three or more antipsychotics. Overdosage affected 318 individuals (1.6%), and 21.5% used concomitant psychotropics without an associated psychiatric diagnosis. Women and people with a comorbid condition like anxiety or depression were less likely to receive antipsychotic polypharmacy. In contrast, increased polypharmacy was associated with concomitant treatment with other psychoactive drugs, and only in user on maintenance therapy, with more visits to the mental health hospital. Overall, we observed a high level of inappropriateness in antipsychotic prescriptions. Greater adherence to guidelines could maximize the benefits of antipsychotic medications while minimizing risk of adverse effects.

scholarly journals Production of Microfibrillated Cellulose from Fast-Growing Poplar and Olive Tree Pruning by Physical Pretreatment

2021 ◽  
Vol 11 (14) ◽  
pp. 6445
Author(s):  
David Ibarra ◽  
Raquel Martín-Sampedro ◽  
Bernd Wicklein ◽  
Úrsula Fillat ◽  
María E. Eugenio
Keyword(s):  
Negative Impact ◽  
Raw Materials ◽  
Olive Tree ◽  
Barrier Properties ◽  
Microfibrillated Cellulose ◽  
Mechanical Resistance ◽  
Fast Growing ◽  
Wide Range ◽  
Pfi Refining ◽  
Tree Pruning

Motivated by the negative impact of fossil fuel consumption on the environment, the need arises to produce materials and energy from renewable sources. Cellulose, the main biopolymer on Earth, plays a key role in this context, serving as a platform for the development of biofuels, chemicals and novel materials. Among the latter, micro- and nanocellulose have been receiving increasing attention in the last few years. Their many attractive properties, i.e., thermal stability, high mechanical resistance, barrier properties, lightweight, optical transparency and ease of chemical modification, allow their use in a wide range of applications, such as paper or polymer reinforcement, packaging, construction, membranes, bioplastics, bioengineering, optics and electronics. In view of the increasing demand for traditional wood pulp (e.g., obtained from eucalypt, birch, pine, spruce) for micro/nanocellulose production, dedicated crops and agricultural residues can be interesting as raw materials for this purpose. This work aims at achieving microfibrillated cellulose production from fast-growing poplar and olive tree pruning using physical pretreatment (PFI refining) before the microfibrillation stage. Both raw materials yielded microfibrillated cellulose with similar properties to that obtained from a commercial industrial eucalypt pulp, producing films with high mechanical properties and low wettability. According to these properties, different applications for cellulose microfibers suspensions and films are discussed.

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