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

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.

Performance of a large partial-depth guide wall to divert downstream migrating Atlantic salmon smolts at Tuilières dam, Dordogne River

From 2010 to 2016, an evaluation of the performance of a partial-depth guide wall associated with three surface bypasses to ensure the safe downstream migration of Atlantic salmon smolts was conducted at the Tuilières power plant on the Dordogne River in southwestern France. The objectives of this study, during which 603 smolts were monitored using radio telemetry, were (i) to determine their escapement rate (passage through routes other than turbines), (ii) to analyse their behaviour faced with the structure and (iii) to assess the permeability of the guide wall as a function of turbine and spilling flows. The rate of escapement through the surface bypass routes varied from approximately 15% to 85%. The turbine flow was the main factor influencing the guide wall efficiency. The contribution of secondary bypasses, while significant for low flows, decreased rapidly with the increase in turbine flows. The vast majority of fish arrived on the two downstream bays of the wall or directly in the area of the main bypass, with the guiding effect of the guide wall becoming less noticeable with the increase of turbine flow. A modification of the depth of the guide wall in 2014 slightly improved its efficiency (by 5–10%) for low turbine flows. Logistic regression models were used to describe the evolution of the efficiency of the facilty as a function of the turbine flow and the probability of direct passage under a bay as a function of average velocity under this bay.

Research on the water level in a bending channel using a guide wall

In order to study the water level at the convex and concave banks after installing a guide wall in a spillway chute bend, with the original condition that the Fr at the entrance of the channel bend is larger than 1.0 (supercritical flow) when there is no the guide wall, systematic experiments with the guide wall were conducted for three radii (2.4B, 3.2B and 4B; B is the width of the channel), bottom slopes (0.01, 0.005 and 0.02), and discharges (50, 100 and150 m3 h−1). Results show that, firstly, after installing a guide wall, the Fr becomes smaller and even lower than 1.0, which means the flow status changes from supercritical to subcritical in some conditions with the help of the guide wall. Secondly, the water depth at the convex bank decreases with the increase of the relative axial radius while this presents to be adverse at the concave bank. Thirdly, for water surface differences in cross-sections, the maximum value decreases with the increase of the relative axial radius, and increases with the increase of the discharge per unit width or the bottom slope. Additionally, a novel formula for calculating the maximum water surface difference was obtained in this article.

Analysis for the Vibration Mechanism of the Spillway Guide Wall Considering the Associated-Forced Coupled Vibration

During the flood discharge in large-scale hydraulic engineering projects, intense flow-induced vibrations may occur in hydraulic gates, gate piers, spillway guide walls, etc. Furthermore, the vibration mechanism is complicated. For the spillway guide wall, existing studies on the vibration mechanism usually focus on the vibrations caused by flow excitations, without considering the influence of dam vibration. According to prototype tests, the vibrations of the spillway guide wall and the dam show synchronization. Thus, this paper presents a new vibration mechanism of associated-forced coupled vibration (AFCV) for the spillway guide wall to investigate the dynamic responses and reveal coupled vibrational properties and vibrational correlations. Different from conventional flow-induced vibration theory, this paper considers the spillway guide wall as a lightweight accessory structure connected to a large-scale primary structure. A corresponding simplified theoretical model for the AFCV system is established, with theoretical derivations given. Then, several vibrational signals measured in different structures in prototype tests are handled by the cross-wavelet transform (XWS) to reveal the vibrational correlation between the spillway guide wall and the dam. Afterwards, mutual analyses of numeral simulation, theoretical derivation, and prototype data are employed to clarify the vibration mechanism of a spillway guide wall. The proposed mechanism can give more reasonable and accurate results regarding the dynamic response and amplitude coefficient of the guide wall. Moreover, by changing the parameters in the theoretical model through practical measures, the proposed vibration mechanism can provide benefits to vibration control and structural design.

Dwarfing and the underlying morphological changes of Poa alpigena plants in response to overgrazing conditions

Poa alpigena as the research object on alpine meadow in this paper,analyzed the change characteristics of the stem and leaf anatomical structures of Poa alpigena plants under the overgrazing and enclosed conditions aims to revealed the dwarfing of morphological mechanism in overgrazing.the results show that that leaf thickness, leaf epidermal thickness, epidermal cell area, and phloem thickness increased with increasing grazing intensity (p < 0.05). In contrast, xylem thickness, mesophyll cell area, and guide wall thickness decreased with increasing grazing intensity (p < 0.05). Mesophyll cell density was relatively unaffected by grazing intensity. Additionally, the plasticity indices were high (i.e., greater than 0.5) for leaf area, upper epidermal cutin layer thickness, and leaf xylem thickness. The plasticity indices were greater than 0.4 for stem tube diameter, epidermal cell size, and epidermal cuticle thickness. These results reflected the Poa alpigena stem and leaf structural changes induced by the water and mechanical stresses caused by grazing livestock. Thus, plateau plants adapt to grazing stress by increasing the thickness of their leaves, cuticles, and phloem. The Poa alpigena mesophyll cell area as well as the stem epidermal cell area and density decrease in response to minor changes in grazing intensity, which ultimately result in the shortened leaves and stems of dwarf plants.