An Experimental Investigation of Cross-Flow Turbine Efficiency

1994 ◽  
Vol 116 (3) ◽  
pp. 545-550 ◽  
Author(s):  
Venkappayya R. Desai ◽  
Nadim M. Aziz
Keyword(s):  
Experimental Investigation ◽  
Angle Of Attack ◽  
Cross Flow ◽  
Water Entry ◽  
Diameter Ratio ◽  
Geometric Parameters ◽  
Maximum Efficiency ◽  
Outer Diameter ◽  
Turbine Efficiency ◽  
The Cross

An experimental investigation was conducted to study the effect of some geometric parameters on the efficiency of the cross-flow turbine. Turbine models were constructed with three different numbers of blades, three different angles of water entry to the runner, and three different inner-to-outer diameter ratios. Nozzles were also constructed for the experiments to match the three different angles of water entry to the runner. A total of 27 runners were tested with the three nozzles. The results of the experiments clearly indicated that efficiency increased with increase in the number of blades. Moreover, it was determined that an increase in the angle of attack beyond 24 deg does not improve the maximum turbine efficiency. In addition, as a result of these experiments, it was determined that for a 24 deg angle of attack 0.68 was the most efficient inner-to-outer diameter ratio, whereas for higher angles of attack the maximum efficiency decreases with an increase in the diameter ratio from 0.60 to 0.75.

Performance Improvement of Cross-Flow Turbine with a Cylindrical Cavity and Guide Wall

2021 ◽  
Author(s):  
Naoto Ogawa ◽  
Mirei Goto ◽  
Shouichiro Iio ◽  
Takaya Kitahora ◽  
Young-Do Choi ◽  
...  
Keyword(s):  
Performance Improvement ◽  
Performance Test ◽  
Guide Vane ◽  
Cross Flow ◽  
Maximum Efficiency ◽  
Small Hydropower ◽  
Turbine Efficiency ◽  
Partial Load ◽  
Guide Wall ◽  
The Cross

Abstract The cross-flow turbine has been utilizing the development of small hydropower less than about 500kW in the world. The turbine cost is lower than the other turbines because of its smaller assembled parts and more straightforward structures. However, the maximum efficiency of the cross-flow turbine is lower than that of traditional turbines. Improving the turbine efficiency without increasing manufacturing costs is the best way to develop small hydropower in the future. This study is aiming to improve the turbine efficiency at the design point and partial load. The runner's outflow angle varies with turbine speed and guide vane opening in the typical cross-flow turbine. The tangential velocity component remains in the outflow in these conditions; thus, change the outflow direction along the runner's radial direction is helpful for performance improvement. The authors experimentally change the desirable outflow angle by attaching a cavity and a guide wall at the outside casing tip. The turbine performance test was conducted for various turbine speeds and guide vane opening. Next, flow visualization around the runner was performed. As a result, the effect of the cavity and the guide wall can be revealed. The outlet flow fields are different by attaching the cavity and the guide wall, especially between the partial and optimum load conditions.

An Experimental Investigation of the Dynamics of a Loosely Supported Tube Array

2017 ◽  
Author(s):  
Amro Elhelaly ◽  
Marwan Hassan ◽  
Atef Mohany ◽  
Soha Moussa
Keyword(s):  
Experimental Investigation ◽  
Impact Force ◽  
Cross Flow ◽  
Open Loop ◽  
Diameter Ratio ◽  
Force Level ◽  
Steam Generators ◽  
Flow Induced Vibration ◽  
System Integrity ◽  
Tube Bundles

The integrity of tube bundles is very important especially when dealing with high-risk applications such as nuclear steam generators. A major issue to system integrity is the flow-induced vibration (FIV). FIV is manifested through several mechanisms including the most severe mechanism; fluidelastic instability (FEI). Tube vibration can be constrained by using tube supports. However, clearances between the tube and their support are required to allow for thermal expansion and for other manufacturing considerations. The clearance between tubes may allow frequent impact and friction between tube and support. This in turn may cause fatigue and wear at support and potential for catastrophic tube failure. This study aims to investigate the dynamics of loosely supported tube array subjected to cross-flow. The work is performed experimentally in an open-loop wind tunnel to address this issue. A loosely-supported single flexible tube in both triangle and square arrays subjected to cross-flow with a pitch-to-diameter ratio of 1.5 and 1.733, respectively were considered. The effect of the flow approach angle, as well as the support clearance on the tube response, are investigated. In addition, the parameters that affect tube wear such as impact force level are presented.

Experimental Investigation of Vortex-Induced Vibrations of a Flexibly Mounted Circular Cylinder in Combined Current and Wave Flows

2021 ◽  
Author(s):  
Pierre-Adrien Opinel ◽  
Narakorn Srinil
Keyword(s):  
Experimental Investigation ◽  
Circular Cylinder ◽  
Cross Flow ◽  
Wave Flow ◽  
Regular Wave ◽  
Regular Waves ◽  
Vortex Induced Vibrations ◽  
Flow Frequency ◽  
The Cross ◽  
Wave Flows

Abstract This paper presents the experimental investigation of vortex-induced vibrations (VIV) of a flexibly mounted circular cylinder in combined current and wave flows. The same experimental setup has previously been used in our previous study (OMAE2020-18161) on VIV in regular waves. The system comprises a pendulum-type vertical cylinder mounted on two-dimensional springs with equal stiffness in in-line and cross-flow directions. The mass ratio of the system is close to 3, the aspect ratio of the tested cylinder based on its submerged length is close to 27, and the damping in still water is around 3.4%. Three current velocities are considered in this study, namely 0.21 m/s, 0.29 m/s and 0.37 m/s, in combination with the generated regular waves. The cylinder motion is recorded using targets and two Qualisys cameras, and the water elevation is measured utilizing a wave probe. The covered ranges of Keulegan-Carpenter number KC are [9.6–35.4], [12.8–40.9] and [16.3–47.8], and the corresponding ranges of reduced velocity Vr are [8–16.3], [10.6–18.4] and [14–20.5] for the cases with current velocity of 0.21 m/s, 0.29 m/s and 0.37 m/s, respectively. The cylinder response amplitudes, trajectories and vibration frequencies are extracted from the recorded motion signals. In all cases the cylinder oscillates primarily at the flow frequency in the in-line direction, and the in-line VIV component additionally appears for the intermediate (0.29 m/s) and high (0.37 m/s) current velocities. The cross-flow oscillation frequency is principally at two or three times the flow frequency in the low current case, similar to what is observed in pure regular waves. For higher current velocities, the cross-flow frequency tends to lock-in with the system natural frequency, as in the steady flow case. The inline and cross-flow cylinder response amplitudes of the combined current and regular wave flow cases are eventually compared with the amplitudes from the pure current and pure regular wave flow cases.

An Experimental Investigation on Cylinder VIV Trajectories Under Different Model Scale

2014 ◽  
Author(s):  
Zh. Kang ◽  
Yunhe Zhai ◽  
Ruxin Song ◽  
Liping Sun
Keyword(s):  
Experimental Investigation ◽  
Vibration Frequency ◽  
Degrees Of Freedom ◽  
Natural Vibration ◽  
Cross Flow ◽  
Small Scale ◽  
Natural Vibration Frequency ◽  
Test Results ◽  
The Cross ◽  
Initial Research

In this paper, model tests were carried out to investigate two degrees of freedom VIV of horizontally-laid cylinders with diameters of 5cm, 11cm, 20cm and length 120cm and compared their vibration trajectories. The test results showed that the in-line and cross-flow vibration frequency of different scale cylinders demonstrate “multi frequency” phenomenon, that is, the in-line vibration frequency is not only twice but also once or four times as much as the cross-flow vibration frequency in some scale, natural frequency and reduced velocity conditions. Also, the cross-flow multi-frequency vibration phenomenon occurred. The trajectory of the vibration cylinder differentiated from the traditional “8” shape accordingly. The vibration trajectory, especially of small-scale cylinder, changed in most conspicuous manner. Through the initial research and analysis, it was found that in addition to in-line and cross-flow natural vibration frequency and the flow velocity, the shape of cylinders was also one of the main causes leading to different vibration trajectory forms.

scholarly journals Conjugate Heat Transfer CFD Predictions of Impingement Jet Array Flat Wall Cooling Aerodynamics With Single Sided Flow Exit

2013 ◽  
Author(s):  
Abubakar M. El-Jummah ◽  
Gordon E. Andrews ◽  
John E. J. Staggs
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Conjugate Heat Transfer ◽  
Cross Flow ◽  
Diameter Ratio ◽  
Significant Feature ◽  
Axial Distance ◽  
Impingement Jet ◽  
The Cross

Conjugate heat transfer CFD studies were undertaken on impingement square jet arrays with self induced crossflow in the impingement gap with a single sided exit. The aim was to understand the aerodynamic interactions that result in the deterioration of heat transfer with axial distance, whereas the addition of duct flow heat transfer would be expected to lead to an increase in heat transfer with axial distance. A square array of impingement holes was investigated for a common geometry investigated experimentally, pitch to diameter ratio X/D of 5 and impingement gap to diameter ratio Z/D of 3.3 for 11 rows of holes in the crossflow direction. A metal duct wall was used as the impingement surface with an applied heat flux of 100kW/m2, which for a gas turbine combustor cooling application operating at steady state with a temperature difference of ∼450K corresponds to a convective heat transfer coefficient of ∼200 W/m2K. A key feature of the predicted aerodynamics was recirculation in the plane of the impingement jets normal to the cross-flow, which produced heating of the impingement jet wall. This reverse flow jet was deflected by the cross flow which had its peak velocity in the plane between the high velocity impingement jets. The cross-flow interaction with the impingement jets reduced the interaction between the jets on the surface, with lower surface turbulence as a result and this reduced the surface convective heat transfer. A significant feature of the predictions was the interaction of the cross-flow aerodynamics with the impingement jet wall and associated heat transfer to that wall. The results showed that the deterioration in heat transfer with axial distance was well predicted, together with predictions of the impingement wall surface temperature gradients.

The Effect of Angle of Attack on the Fluidelastic Instability of Tube Bundle Subjected to Two-Phase Cross-Flow

2009 ◽  
Author(s):  
T. F. Joly ◽  
N. W. Mureithi ◽  
M. J. Pettigrew
Keyword(s):  
Tube Bundle ◽  
Angle Of Attack ◽  
Cross Flow ◽  
Diameter Ratio ◽  
Test Results ◽  
Two Phase ◽  
Void Fractions ◽  
Fluidelastic Instability ◽  
Flexible Tubes ◽  
Existing Data

Tests were done to study the effect of angle of attack on the fluidelastic instability of a fully flexible tube bundle subjected to two-phase (Air-Water) cross-flow. A test array having nineteen flexible tubes in a rotated triangular configuration with a pitch-to-diameter ratio of 1.5 was tested. Four different angles of attack ranging for 0 degree (inline flexibility) through 30 and 60 degrees to 90 degrees (transverse flexibility) were studied. For each angle of attack several homogeneous void fractions have been tested (70%, 80%, 90%, and 95%). Stability test results show that the angle of attack strongly affect the tube bundle dynamic behavior. The different mechanisms underlying the fluidelastic instability are highlighted and the results compared to existing data on fluidelastic instability.

Limits of the Turbine Efficiency for Free Fluid Flow

2001 ◽  
Vol 123 (4) ◽  
pp. 311-317 ◽  
Author(s):  
Alexander N. Gorban’ ◽  
Alexander M. Gorlov ◽  
Valentin M. Silantyev
Keyword(s):  
Wind Power ◽  
Three Dimensional ◽  
Cross Flow ◽  
Free Water ◽  
Accurate Estimate ◽  
Maximum Efficiency ◽  
Free Fluid ◽  
Two Dimensional ◽  
Turbine Efficiency ◽  
Tidal Streams

An accurate estimate of the theoretical power limit of turbines in free fluid flows is important because of growing interest in the development of wind power and zero-head water power resources. The latter includes the huge kinetic energy of ocean currents, tidal streams, and rivers without dams. Knowledge of turbine efficiency limits helps to optimize design of hydro and wind power farms. An explicitly solvable new mathematical model for estimating the maximum efficiency of turbines in a free (nonducted) fluid is presented. This result can be used for hydropower turbines where construction of dams is impossible (in oceans) or undesirable (in rivers), as well as for wind power farms. The model deals with a finite two-dimensional, partially penetrable plate in an incompressible fluid. It is nearly ideal for two-dimensional propellers and less suitable for three-dimensional cross-flow Darrieus and helical turbines. The most interesting finding of our analysis is that the maximum efficiency of the plane propeller is about 30 percent for free fluids. This is in a sharp contrast to the 60 percent given by the Betz limit, commonly used now for decades. It is shown that the Betz overestimate results from neglecting the curvature of the fluid streams. We also show that the three-dimensional helical turbine is more efficient than the two-dimensional propeller, at least in water applications. Moreover, well-documented tests have shown that the helical turbine has an efficiency of 35 percent, making it preferable for use in free water currents.

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