• Title/Summary/Keyword: low head

Search Result 1,398, Processing Time 0.035 seconds

Computational Analysis of an Inverted-type Cross-flow Turbine for Ultra-low head Conditions (전산유체역학을 이용한 초저낙차 상황에서의 도립형 횡류수차의 해석 및 설계 최적화)

  • Ham, Sangwoo;Ha, Hojin;Lee, Jeong Wan
    • Journal of the Korean Society of Manufacturing Process Engineers
    • /
    • v.18 no.4
    • /
    • pp.76-86
    • /
    • 2019
  • The cross-flow turbine is a key hydraulic power system that is widely due to low costs, high efficiency, and low maintenance. In particular, the cross-flow turbine considered as the most suitable turbine for low head situations as it is known to operate down to 5 m of water head. However, the conventional cross-flow turbine is unsuitable for ultra-low head situations with less than a 3 m water head. In this study, we propose an inverted-type cross-flow turbine to overcome the limitations of conventional cross-flow turbines under ultra-low head situations. First, we described the limitations of conventional turbines and suggested a new turbine for the ultra-low head circumstances. Second, we investigated the performance of the new turbine using CFD analysis. Results demonstrated the effects of the design parameters, such as number of blades and rotor diameter ratio, on the performance of the suggested turbine. As a result, we developed an inverted-type cross-flow turbine with up to 60% efficiency under low water head conditions.

Parametric Study of a Fixed-blade Runner in an Ultra-low-head Gate Turbine

  • Mohamed Murshid Shamsuddeen;Duc Anh Nguyen;Jin-Hyuk Kim
    • New & Renewable Energy
    • /
    • v.20 no.1
    • /
    • pp.116-125
    • /
    • 2024
  • Ultra-low-head is an unexplored classification among the sites in which hydroelectric power can be produced. This is typically owing to the low power output and the economic value of the turbines available in this segment. A turbine capable of operating in an ultra-low-head condition without the need of a dam to produce electricity is developed in this study. A gate structure installed at a shallow water channel acting as a weir generates artificial head for the turbine mounted on the gate to produce power. The turbine and generator are designed to be compact and submersible for an efficient and silent operation. The gate angle is adjustable to operate the turbine at varying flow rates. The turbine is designed and tested using computational fluid dynamics tools prior to manufacturing and experimental studies. A parametric study of the runner blade parameters is conducted to obtain the most efficient blade design with minimal hydraulic losses. These parameters include the runner stagger and runner leading edge flow angles. The selected runner design showed improved hydraulic characteristics of the turbine to operate in an ultra-low-head site with minimal losses.

Low RCS Characteristics of an Elliptical Ogive Head (타원형 Ogive 형상을 가지는 헤드의 Low RCS 특성)

  • 심재륜;한대현;김효태
    • Proceedings of the IEEK Conference
    • /
    • 2000.06a
    • /
    • pp.263-266
    • /
    • 2000
  • An elliptical ogive head for a generic missile is proposed to reduce its detectable probability from a ground defense radar. Numerical RCS results of a generic missile with an elliptical ogive head are evaluated using the GTD/UTD (Geometrical Theory of Diffraction/Uniform GTD). The results are compared with those of a cylindrical ogive head. In the sense of aerodynamics, the Performance evaluation of an elliptical ogive head for a generic missile should be followed.

  • PDF

A Study on Head-Disk Interactions at Ultra-low Flying Height in Contact Start-Stop (Contact Start-Stop 방식에서의 극저부상 높이에서 Head-Disk Interface Interactions 연구)

  • 조언정
    • Tribology and Lubricants
    • /
    • v.19 no.2
    • /
    • pp.102-108
    • /
    • 2003
  • The height of laser bumps has been considered as the limit of the minimum flying height in the contact start-stop (CSS) of hard disk drives. In this paper, tribological interactions at flying height under laser bumps are investigated in a spin stand for development of ultra-low flying head-disk interface. With the reduction of the spinning speed in a spin stand, the flying height is decreased under the height of laser bumps and, then, head-disk interactions are investigated using AE and stiction/friction signals. During seek tests and 20000 cycle-sweep tests, AE and stiction/friction signals are not significantly changed and there are no catastrophic failures of head-disk interface. Bearing analysis and AFM analysis show that there are signs of wear and plastic deformation on the disks. It is suggested that flying height could be as low as and, sometimes, lower than laser bump height.

Low-Grade Fibromyxoid Sarcoma Arising in Posterior Nasal Cavity: Case Report and Review of the Literature (후비강에서 발생한 저등급의 섬유점액성 육종: 증례 보고 및 문헌 고찰)

  • Sohn, Jung Heob;Lee, Kijin;Cho, Kyoung Rai
    • Korean Journal of Otorhinolaryngology-Head and Neck Surgery
    • /
    • v.61 no.11
    • /
    • pp.624-629
    • /
    • 2018
  • Low-grade fibromyxoid sarcoma (LGFMS), a soft tissue tumor that has high recurrence and metastasizing potential, rarely occurs in the head and neck region. Therefore, the treatment for LGFMS in the facial area is challenging in terms of cosmetic and functional maintenance. The authors report a case of LGFMS in the posterior nasal cavity. It was completely removed in parallel with the nasal endoscopic and oral approach, but the lower margin was closed by preserving the soft palate. The patient is well without any recurrence or metastasis after 5 years of follow-up.

Effects of Daily Herbage Allowance on Sward Structure, Herbage Intake and Milk Production by Dairy Cows Grazing a Pure Perennial Ryegrass Sward

  • Kim, T.H.;An, K.W.;Jung, W.J.
    • Asian-Australasian Journal of Animal Sciences
    • /
    • v.14 no.10
    • /
    • pp.1383-1388
    • /
    • 2001
  • To explore the factors restricting animal performance in relation to sward structure under a strip-grazing system, measurements of sward factors, herbage intake and milk production at 3 levels of herbage allowance were made on perennial ryegrass (Latium perenne L.) sward for 3 experimental periods. About 29%, 36% and 52% of the biomass offered was removed by grazing in high $(42kg\;OM{\cdot}day^{-1}{\cdot}head^{-1})$, medium $(30kg\;OM{\cdot}day^{-1}{\cdot}head^{-1})$ and low $(18kg\;OM{\cdot}day^{-1}{\cdot}head^{-1})$ herbage allowance plots. Live leaf material was much more affected by grazing under different herbage allowance levels than dead material or leaf sheath. Grazing with a low herbage allowance decreased the proportion of live lamina by 93% and live lamina density by 96% before grazing. The density of dead material plus sheath was decreased by 17% after grazing at a low allowance, while it slightly increased or remained constant in the plots applied with high and medium allowances, respectively. The highly significant (p<0.01) correlations between herbage allowance and proportion (r=0.94) and density (r=0.91) of live lamina in residual sward after grazing were observed. Daily herbage intakes in the plots with high and medium levels of herbage allowance were not significantly different at $15.3kg\;OM{\cdot}head^{-1}$ in average, whereas with low level it decreased to $13.9kg\;OM{\cdot}head^{-1}$. Daily milk production was significantly (p<0.05) declined from $22.3kg{\cdot}head^{-1}$ (at high herbage allowance) to $19.7kg{\cdot}head^{-1}$ (at low herbage allowance). The data obtained clearly indicated that herbage intake and milk production were highly affected by the characteristics of residual sward, which were closely related to the level of herbage allowance.

Reynolds Number Effect on Regenerative Pump Performance in Low Reynolds Number Range

  • Horiguchi, Hironori;Yumiba, Daisuke;Tsujimoto, Yoshinobu;Sakagami, Masaaki;Tanaka, Shigeo
    • International Journal of Fluid Machinery and Systems
    • /
    • v.1 no.1
    • /
    • pp.101-108
    • /
    • 2008
  • The effect of Reynolds number on the performance of a regenerative pump was examined in a low Reynolds number range in experiment. The head of the regenerative pump increased at low flow rates and decreased at high flow rates as the Reynolds number decreased. The computation of the internal flow was made to clarify the cause of the Reynolds number effect. At low flow rates, the head is decreased with increasing the Reynolds number due to the decrease of the shear force exerted by the impeller caused by the increase of leakage and hence local flow rate. At higher flow rates, the head is increased with increasing the Reynolds number with decreased loss at the inlet and outlet as well as the decreased shear stress on the casing wall.

Design and Simulation of Very Low Head Axial Hydraulic Turbine with Variation of Swirl Velocity Criterion

  • Muis, Abdul;Sutikno, Priyono
    • International Journal of Fluid Machinery and Systems
    • /
    • v.7 no.2
    • /
    • pp.68-79
    • /
    • 2014
  • The type of turbine developed is based on the very low head of water potential source for the electric power production. The area of research is focused for the axial water turbine that can be applied at the simple site open channel with has a very low cost and environmental impact compared to the conventional hydro installation. High efficiency of axial turbine which applied to the very low potential head will made this type of turbine can be used at wider potential site. Existing irrigation weir and river area will be the perfect site for this turbine. This paper will compare the effects of the variation of swirl velocity criterion during the design of the blade of guide vane and rotor of the turbine. Effects of the swirl velocity criterion is wider known as a vortex conditions (free vortex, force vortex and swirl velocity constant), and the free vortex is the very popular condition that applied by most of turbine designer, therefore will be interesting to do a comparison against other criterion. ANSYS Fluent will be used for simulation and to determine the predictive performance obtained by each of design criteria.

Performance Improvement of Very Low Head Cross Flow Turbine with Inlet Open Duct (입구 개방형 덕트를 적용한 초저낙차 횡류수차의 성능향상)

  • Chen, Zhenmu;Singh, Patrick Mark;Choi, Young-Do
    • The KSFM Journal of Fluid Machinery
    • /
    • v.17 no.4
    • /
    • pp.30-39
    • /
    • 2014
  • The cross flow turbine is economical because of its simple structure. For remote rural region, there are needs for a more simple structure and very low head cross flow turbines. However, in this kind of locations, the water from upstream always flows into the turbine with some other materials such as sand and pebble. These materials will be damage to the runner blade and shorten the turbine lifespan. Therefore, there is a need to develop a new type of cross flow turbine for the remote rural region where there is availability of abundant resources. The new design of the cross flow turbine has an inlet open duct, without guide vane and nozzle to simplify the structure. However, the turbine with inlet open duct and very low head shows relatively low efficiency. Therefore, the purpose of this study is to optimize the shape of the turbine inlet to improve the efficiency, and investigate the internal flow of a very low head cross flow turbine. There are two steps to optimize the turbine inlet shape. Firstly, by changing the turbine open angle along with changing the turbine inlet open duct bottom line (IODBL) location to investigate the internal flow. Secondly, keeping the turbine IODBL location at the maximum efficiency achieved at the first step, and changing the turbine IODBL angle to improve the performance. The result shows that there is a 7.4% of efficiency improvement by optimizing turbine IODBL location (open angle), and there is 0.3% of efficiency improvement by optimizing the turbine IODBL angle.

The Study of Influence Factor of Head Restraints on the Whiplash by using DFSS (DFSS 기법을 이용한 후방 추돌 시 경부 상해 감소를 위한 머리지지대 인자의 영향성 연구)

  • Oh, Hyungjoon;Seo, Sangjin;Yoo, Hyukjin
    • Journal of Auto-vehicle Safety Association
    • /
    • v.4 no.2
    • /
    • pp.5-10
    • /
    • 2012
  • Whiplash is the most frequent injury among occupants in low speed rear-end car collision. The aim of this paper is to analyze thecorrelation between influence parameters of head restraints and whiplash injury criteria.In this paper, DFSS (Design for Six Sigma) method is used for optimum design of head restrains. Four control factors of head restraints have selected by function matrix method. The effects of the control factors have been experimentally evaluated by using a sled pulse from 16km/h relative velocity which is suggested by KNCAP (Korean New Car Assessment Program). In order to reduce the noise factors of dynamic tests, whiplash tests were repeated twice. By using DFSS, the correlation between control factors and injury criteria has been comprehended.