Wind tunnel experiments of a newly developed two-bladed Savonius-style wind turbine

Wind energy is one of the most promising renewable energy resources for power generation, and rapid growth has been seen in its acceptance since 2000. The most acceptable classification for wind turbines is by its axis of orientation: Horizontal Axis Wind Turbines (HAWT) and Vertical Axis Wind Turbines (VAWT). HAWTs are used in many countries for medium-to-large scale power projects, and most commercial installations around the globe are solely based on these turbines. On the other hand, HAWTs are not recognized as a viable option to harness the energy of the wind in urban areas, where the wind is less intense, much more chaotic and turbulent. VAWTs are suggested as a better choice for cities and isolated semi-urban areas. Several attributes have been suggested for the large-scale deployment of VAWTs, e.g., good performance under the weak and unstable wind, no noise and safety concerns, and aesthetically sound for integration in urban areas. Significant research has been published on wind turbine technology and resources assessment methodologies, and this review paper is a modest attempt to highlight some of the major developments of VAWTs, with a focus on the integration with urban infrastructure. Several recommendations have been drawn based on the state-of-the-art information on the subject for future studies and acceptance of wind turbines in the urban areas. It was concluded that further research is critical in making VAWTs a viable, dependable, and affordable power generation technology for many low and decentralized power applications.

A critical review of vertical axis wind turbines for urban applications

Blade Shape Optimization of the Savonius Wind Turbine Using a Genetic Algorithm

Energy crisis and high emission of fossil fuels are major driving forces for developing renewable energy based technologies. In order to meet growing demand for energy, hydropower can be one of the sustainable alternatives. Further, the hydrokinetic turbine is considered as one of the most emerging technologies which harness energy from flowing water. In this paper, an attempt has been made to review hydrokinetic energy theory for energy conversion system from water currents analogous to wind power system. The most widespread classes of hydrokinetic turbines are discussed in detail with respect to their benefits, drawbacks and desirable conditions for applications. It has been found that in spite of some prevailing downsides of vertical axis turbine like of self-starting and lower efficiency, vertical axis turbines are appealing for many riverine applications. One of the prominent turbines of its kind is the Savonius hydrokinetic turbine that has the capacity to self-start at a very low fluid velocity in the river, canal etc. However, Savonius type hydrokinetic turbine inherently has poor efficiency. A number of experimental and numerical studies with a large number of physical designs and parameters have been carried out in the area of Savonius rotor to enhance its efficiency. Under this study, review of different parameters affecting the performance of Savonius hydrokinetic turbine has been carried out and presented in this paper which may be useful for future studies to improve the efficiency of such turbines.

Performance parameters of Savonius type hydrokinetic turbine – A Review

Shape optimization of a Savonius wind rotor with different convex and concave sides

Numerical investigation of conventional and modified Savonius wind turbines

Aerodynamic instabilities in centrifugal compressors are dangerous phenomena affecting machine efficiency and in severe cases leading to failure of the compressing system. Quick and robust instability detection during compressor operation is a challenge of utmost importance from an economical and safety point of view. Rapid indication of instabilities can be obtained using a pressure signal from the compressor. Detection of aerodynamic instabilities using pressure signal results in specific challenges, as the signal is often highly contaminated with noise, which can influence the performance of detection methods. The aim of this study is to investigate and compare the performance of two non-linear signal processing methods—Empirical Mode Decomposition (EMD) and Singular Spectrum Analysis (SSA)—for aerodynamic instability detection. Two instabilities of different character, local—inlet recirculation and global—surge, are considered. The comparison focuses on the robustness, sensitivity and pace of detection—crucial parameters for a successful detection method. It is shown that both EMD and SSA perform similarly for the analysed machine, despite different underlying principles of the methods. Both EMD and SSA have great potential for instabilities detection, but tuning of their parameters is important for robust detection.

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Comparison of Empirical Mode Decomposition and Singular Spectrum Analysis for Quick and Robust Detection of Aerodynamic Instabilities in Centrifugal Compressors

In this paper, a thorough 2D unsteady computational fluid dynamic analysis was performed on a pitching airfoil to properly comprehend the dynamic stall and aerodynamic forces. The computational software ANSYS Fluent was used to solve the unsteady Reynolds-averaged Navier–Stokes equations. Low Reynolds number flows were modeled using the k-ω shear stress transport turbulence model. Aerodynamic forces, fluid flow structures, and flow separation delay angles were explored as a function of the Reynolds number, reduced frequency, oscillation amplitude, and mean angle of attack. The maximum aerodynamic forces, including lift, drag, and the onset of the dynamic stall, were all influenced by these variables. The critical parameters that influenced the optimum aerodynamic forces and ended up causing dynamic stall delay were oscillation amplitude and mean angle of attack. The stall angle was raised by 9° and 6°, respectively, and a large increment in the lift coefficient was also noted in both cases. Additionally, for the highest Reynolds number, a considerable rise in the maximum lift coefficient of 20% and a 28% drop in drag coefficient were observed, with a 1.5° delay in the stall angle. Furthermore, a significant increase of 33% in the lift force was seen with a rise of 4.5° in the stall angle in the case of reduced frequency.

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Two-Dimensional URANS Numerical Investigation of Critical Parameters on a Pitch Oscillating VAWT Airfoil under Dynamic Stall

Aerodynamic instabilities detection via empirical mode decomposition in centrifugal compressors


 In this paper the possibility of diagnosing the compressor flow stability by acoustic measurements is explored. A correlated acoustic signal was measured together with pressure in the flow channel. The method allowed to evaluate the applicability of acoustic measurements for simple diagnostics of machine working conditions. The advantage of acoustic study is that it can be conducted ad-hoc without installing any special equipment, does not interfere with the machine setting and does not require changing the working conditions. The biggest downside is the method accuracy, possible reflections and interference with the noise coming from another machines present in the room. Study was performed on a low speed industrial compressor. A set of acoustic measurements was conducted in 7 locations to observe the influence of possible reflections. Study included continuous voice recording made at constant flow conditions and signals gathered during continuous closure of the throttling valve - on the way to the surge. Study confirmed that the microphone noise measurement allows to distinguish the main unstable flow phenomena. It could be potentially used as an initial test of flow stability in industrial centrifugal compressor or even predict the surge proximity.

Grzegorz Liskiewicz

Papers

Numerical investigation of conventional and modified Savonius wind turbines

Comparison of Empirical Mode Decomposition and Singular Spectrum Analysis for Quick and Robust Detection of Aerodynamic Instabilities in Centrifugal Compressors

Two-Dimensional URANS Numerical Investigation of Critical Parameters on a Pitch Oscillating VAWT Airfoil under Dynamic Stall

Aerodynamic instabilities detection via empirical mode decomposition in centrifugal compressors

Acoustic Signature of Flow Instabilities Present in Industrial Centrifugal Compressor