Experimental study on simplification of Darrieus-type hydro turbine with inlet nozzle for extra-low head hydropower utilization

doi:10.1016/j.renene.2011.09.017

Renewable Energy

Volume 41, May 2012, Pages 376-382

https://doi.org/10.1016/j.renene.2011.09.017 Get rights and content

Abstract

A ducted Darrieus-type hydro turbine has been proposed for utilization of extra-low head hydropower less than 2 m. In general, the low head hydro turbine system demands the simple structure to reduce the cost of power generation. The Darrieus-type hydro turbine is cross flow type and takes larger values of generated torque with higher efficiency on the upstream path of the Darrieus blades passing in one revolution. Based on this reason, when a narrow intake at the upstream of the runner, called as “inlet nozzle”, is installed, the performance of Darrieus-type hydro turbine becomes higher than that without one. In addition, it is possible to remove the draft tube and side-walls of the runner casing keeping the turbine efficiency high. In the present paper, more simplified runner casing, composed of only the inlet nozzle and the small upper-casing, is proposed and the experimental results are shown.

Highlights

► A Darrieus hydro turbine is proposed for utilization of extra-low head hydropower. ► Installation of an inlet nozzle improves the cost of power generation. ► Simplified turbine performances are influenced by downstream water level. ► The control of water level is necessary for practical use of Darrieus turbine.

Introduction

Energy and environmental problems are related each other and needed to discuss comprehensibly. For the solution of these issues, the utilization of renewable energy becomes the target of global attention. Hydropower has been used since ancient times as one of the major renewable energy. However, the “dam type” hydropower generation is difficult to apply strongly because high head hydropower area has been already developed and makes large impact for ecological system. On the other hand, low head hydropower area, where the head takes less than 2 m, has remained as undeveloped. The utilization of low head hydropower has an advantage that the transmission loss of electricity becomes lower because it is located near the consuming area, however low energy density makes the cost of generation higher. Thereby it is demanded to improve the turbine performances and to decrease the equipment cost for achievement of “the cost-advantage” and “environmental friendly”.

The ducted Darrieus-type hydro turbine system has been proposed for extra-low head hydropower utilization [1]. The vertical axis Darrieus-type runner with the two-dimensional blades is so simple structure that it has the cost advantage. In addition, under the restriction as low head, only the radius R of rotating pitch circle or the duct height B can be changed in proportion to the available flow rate, which is another advantage of Darrieus runner. Authors have been clarified the design guideline and the characteristics of Darrieus turbine to obtain the higher performances [2], [3]. A peculiar characteristic of the Darrieus runner is variations in generated blade torque in one revolution. Matsushita et al. [4] proposed a runner casing with inlet nozzle which was optimized the torque variation, then achieved higher turbine performances. In addition, they presumed that a potency of the Darrieus turbine system without the draft tube which is generally equipped to decrease velocity at the duct outlet for head recovery, providing the inlet nozzle was installed. In response to this prediction, Shimokawa et al. [5] experimentally investigated effects on turbine performance by use of a test model without draft tube and side-walls of runner casing, and made sure as a result that the simplified system with inlet nozzle could obtain turbine efficiency as similar as that of the ducted turbine system with draft tube.

For a practical use of the extra-low head hydro turbine system, simplification of system is a key factor to improve the cost-advantage. In present paper, authors suggest a simpler structure of the runner casing, which consists of a basic inlet nozzle and exposes the rotating runner to downstream pond, and then research turbine performances experimentally. Besides, the new simplified Darrieus hydro turbine system, that is submerged in small water current directly, raises other criterion of turbine performance; that is downstream water level against the runner height. Although general ducted runners consistently operate in water, the propositional Darreius-type runner for low head sites is interfered from water surface because natural open channels cause flow and water level variations temporally and seasonally. For this reason, effects of downstream water level on turbine characteristics are also studied and discussed for performance estimation.

Section snippets

Working principle of Darrieus runner and effect of inlet nozzle

The working principle of Darrieus-type runner in parallel walls without the inlet nozzle is depicted in Fig. 1. The resultant force F with lift F_l and drag F_d varies in one revolution because the relative velocity W and the attack angle α are dependent on the rotating position θ, defined as shown in Fig. 1, in the constant operation condition of oncoming absolute velocity V and the peripheral speed of blade U. Therefore, the periodic variation of tangential force F_u and the generated power L

Experimental apparatus

Fig. 5 shows the test waterway and hydro turbine with vertical shaft. The test waterway is divided to up- and downstream ponds and the water in the upstream pond enters the runner section through the inlet nozzle with width S_in = 400 mm (S_in/D = 0.80) and height B = 300 mm. Then, the water is discharged to the downstream pond directly. There is no draft tube. The runner with diameter of pitch circle D = 500 mm is equipped with two different runner casings. One has the whole covered upper casing

Effects of runner casing simplification

Fig. 8 depicts comparison of turbine performances with different upper casings of whole and quarter covers at the velocity of runner section V* = 0.80 and 1.07 m/s, where V* is evaluated as V* = Q/(BD). The downstream water level H_d is kept enough high as 46 cm against the runner height 38 cm. The horizontal axis of Fig. 8 means the ratio of blade peripheral speed U (=Rω) to runner section velocity V* and each vertical axis expresses head coefficient C_h/Z in Fig. 8(a), power coefficient C_p/Z in

Concluding remarks

The performance of Darrieus-type hydro turbine with the inlet nozzle and simplified runner casing was examined experimentally. In addition, effect of downstream water level on turbine performances was investigated in consideration of flow rate variation at the practical use.

(1)
Provided the inlet nozzle is installed to obtain effective generated torque in the high efficiency blade rotating positions, it is possible to simplify the runner casing drastically with keeping the turbine performances

References (5)

A. Furukawa et al.
Optimum design of the Darrieus-type cross flow water turbine for low head water power. In: Proc. 2nd World enewable Energy Cong. V
(1992)
Y. Takamatsu et al.
Experimental studies on a preferable blade profile for high efficiency and the blade characteristics of Darrieus-type cross-flow water turbine
JSME Int J Ser II
(1991)

There are more references available in the full text version of this article.

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Technical noteExperimental study on simplification of Darrieus-type hydro turbine with inlet nozzle for extra-low head hydropower utilization

Abstract

Highlights

Introduction

Section snippets

Working principle of Darrieus runner and effect of inlet nozzle

Experimental apparatus

Effects of runner casing simplification

Concluding remarks

Optimum design of the Darrieus-type cross flow water turbine for low head water power. In: Proc. 2nd World enewable Energy Cong. V

Experimental studies on a preferable blade profile for high efficiency and the blade characteristics of Darrieus-type cross-flow water turbine

JSME Int J Ser II

Technical note
Experimental study on simplification of Darrieus-type hydro turbine with inlet nozzle for extra-low head hydropower utilization