Aerodynamic Comparison of Straight Edge and Swept Edge Wind Turbine Blade

Recently there has been an increase in the demand for the utilization of clean renewable energy sources. This is a direct result of a rise in oil prices and an increased awareness of human induced climate change. Wind energy has been shown to be one of the most promising sources of renewable energy. With current technology, the low cost of wind energy is competitive with more conventional sources of energy such as coal. This however is only true in areas of high wind density. These areas are not as abundant and therefore the number of profitable sites is limited. This paper explores the possibility increasing the number of profitable sites by optimizing wind turbine blade design for low wind speed areas. The two methods of optimization that are investigated are first, optimizing the angle of attack and chord length for a given airfoil cross section at different positions along the blade and second implementing a swept blade profile. The torque generated from a blade using only the first optimization technique is compared to that generated from a blade using both techniques as well as that generated by NTK500/41 turbine using LM19.1 blades. Performance will be investigated using the CFD solver FLUENT.

Development of Nomograms for the Calculation of the Temperature Distribution in a Membrane Wall

The present paper deals with one of the most important structural component in combustion chambers of modern steam generators — the membrane wall. The design of the membrane wall is depending on the operation pressure and the heat flux to the wall. For a correct design the knowledge of the temperature distribution and in this connection the points with the highest temperatures at the membrane wall surface is necessary. In this paper nomograms for the calculation of the surface metal temperature at selected points of the membrane wall are presented. The investigation was done for the two heat transfer mechanisms radiation and convection, different tube diameters, bar thickness and tube pitches. The nomograms are based on a dimensionless temperature and dimensionless membrane bar lengths. One result of the analysis is that the nomograms can be used independent from the tube dimensions. For a fast computer-assisted design of the membrane wall correlations are developed to calculate the dimensionless temperature for the selected points as a function of the dimensionless membrane bar lengths and bar thickness.

Computational Modeling and Experimental Investigation of Static Straight-Through Labyrinth Seals

To design highly efficient and stable turbomachines, engineers require accurate methods to model seal flows and calculate clearance-excitation forces generated by the eccentric position of the rotor. One of the most widely used methods to predict leakage flow and dynamic coefficients is the use of computer codes developed based on bulk flow theory. In recent years, computational fluid dynamics (CFD) modeling is increasingly being recognized as an accurate assessment tool for flow parameters and dynamic coefficients evaluation as compared to the bulk flow codes. This paper presents computational and experimental investigations that were carried out to calculate flow parameters in a stationary straight-through model labyrinth seal. The main objective of this study is to explore the capabilities of Ansys-CFX, a commercially available state of the art 3D numerical code, to accurately model compressible flow through the seals. The flow behavior is analyzed using CFD and the flow parameters calculated by CFD are validated against experimental data taken for the same seal configuration. The integrated values of leakage flow rates estimated from the computational results agree with the experimental data within 7.6%. This study serves as a benchmark case that supports further efforts in applying CFD analysis in conjunction with automatic design optimization techniques for seals used for compressible media. It was shown that optimization algorithms combined with CFD simulations have good potential for improving seal design.

A New Design Concept of Highly-Loaded Axial Flow Compressor by Applying Boundary Layer Suction and 3D Blade Technique

A new design concept of highly-loaded axial flow compressor by applying boundary layer suction and 3D blade technique was proposed in this paper. The basic idea of this design concept was that low reaction was adopted as while as increasing the rotor’s geometry turning angle, so that the boundary layer separation of a rotor could be eliminated and the rotor was kept working in high efficiency. This design concept would greatly increase the stator’s geometry turning angle, so boundary layer suction on stator cascades was adopted in order to restrain the boundary layer separation. In some situations, 3D blade technique was also applied in order to control the boundary layer separation more efficiently. The advantages of the above design concept were: the compressor’s pressure ratio was increased remarkably; boundary layer suction was only adopted in stator cascades so as to reduce the complexity of boundary layer suction structure. The key techniques of the new design concept were also explained in this paper. In order to increase the compressor’s pressure ratio, the geometry turning angle of rotor was increased greatly, and the rotor inlet was prewhirled to reduce the rotor’s reaction so as to restrain the rotor’s boundary separation. Boundary layer suction was carried out in the stator cascades (mainly on suction side), hub and shroud in order to control the flow separation. 3D blade technique could be adopted if necessary. The limitation of the application of this design concept was also pointed out through the analysis of the Mach number at rotor inlet, the prewhirl angle of rotor, the work distribution along span wise and the control method of stator separation. Numerical simulation was carried out on a single low-reaction compressor stage with IGV in order to demonstrate the new design concept. By using boundary layer suction and 3D blade technique, the energy loss in stator cascades was greatly reduced and the whole stage’s isentropic efficiency was about 90%. The low-reaction stage’s aerodynamic load was double than conventional design. The boundary layer separation could be effectively controlled by proper combination of boundary layer suction and bowed or twisted blade. The numerical result proved that the new design concept was feasible and had a wide application area.

The Potential of Using CFD in Order to Design Better Centrifugal Pumps

Recent advances in CFD made it capable of producing fairly realistic predictions of the flow-patterns within the passages of centrifugal pumps. This raises the possibility that CFD might also be capable of assisting the pump engineer to come up with better designs. Success, however, is still very elusive. This paper discusses the reason for that state of affairs, and how to cope with it. As such, this paper can be regarded as a supplement to the discussions presented in References [1] and [2]. It has been demonstrated in Refs. [1] and [2], that the main cause for that lack of success is due to the present explosion of information. It prevents the CFD specialist from acquiring the necessary in-depth knowledge of the practical aspects of a problem, which a pump engineer has to solve. At the same time, this explosion of information makes it impossible for the pump specialist to become adequately familiar with the potentials and with the limitations of CFD. It has been demonstrated in Ref.[2] that certain problems related to centrifugal pumps can be solved easier, faster and more successfully with the aid of more conventional logical tools, than with the aid of CFD. This paper will discuss, among others, problems, which only CFD might be capable to solve.

Assessment of Loss Correlations for Performance Prediction of Low Reaction Gas Turbine Stages

In spite of the remarkable advances in the field of the Computational Fluid Dynamics, algebraic models built upon empirical loss and deviation correlations are still one of the most reliable and effective tools to predict the performance of gas turbine stages with reasonable accuracy, especially when low-reaction, multi-stage architectures are considered. This paper deals with a comparison among some of the most popular loss correlations used by gas turbine manufacturers; such comparison is performed on a two-stage low-reaction turbine for which detailed experimental data are available. An overall assessment on the validity of loss correlations is carried out to help the designer/analyst using the most accurate model when both on- and off-design are to be carried out.

Natural Frequencies of Centrifugal Compressor Impellers for High Density Gas Applications

Characteristics of natural frequencies of an impeller and an equivalent disc were investigated in high-density gas to develop a method for predicting natural frequencies of centrifugal compressor impellers for high-density gas applications. The equivalent disc had outer and inner diameters equal to those of the impeller. We expected that natural frequencies would decrease with increasing the gas density because of the added-mass effect. However, we found experimentally that some natural frequencies of the impeller and the disc in high-density gas decreased but others increased. Moreover, we observed, under high-density condition, some resonance frequencies that we did not observe under low-density condition. These experimental results cannot be explained by only the added-mass effect. For simplicity, we focused on the disc to understand the mechanism of the behavior of natural frequencies. We developed a theoretical analysis of fluid-structure interaction considering not only the mass but also stiffness of gas. The analysis gave a qualitative explanation of the experimental results. In addition, we carried out a fluid-structure interaction analysis using the finite element method. The behavior of natural frequencies of the disc in high-density gas was predicted with errors less than 6%.

A Hardware-in-the-Loop Simulation Testbed for Emulating Hydraulic Loads Representing the Complete Dig Cycle of a Construction Machine

A hardware-in-the-loop (HIL) simulation testbed is designed to be capable of emulating the entire domain of hydraulic workport loads incident on a test valve during normal work cycle operations of a certain hydraulic construction machine, such as a backhoe or excavator. The HIL testbed is a useful tool during rapid prototyping of control algorithms for the test valve, and for performing controlled experiments with the valve in the context of developing valve control algorithms to improve the overall energy efficiency of hydraulic systems. This paper discusses four key topics: the architecture of the real-time simulation and testbed control process, the modeling and validation of the emulated machine dynamics, the controller development for the HIL testbed, and some initial performance testing of the HIL testbed.

Sensorless Detection and Isolation of Faults in Motor-Pump Systems

Induction motors are the workhorses of industry and a lot of effort has been invested in detecting and diagnosing induction motor faults through the analysis of the motor electrical signals. However, in many industrial applications, electric motors are used to drive dynamic loads such as pumps, fans, blowers etc. Failure of either the motors or the driven loads is associated with operational disruption. Consequently it would be beneficial if the entire motor-pump system is monitored and diagnosed. The large costs associated with production losses can be avoided if system degradation can be detected at early stages prior to failure. Moreover, downtime can be further reduced if the faulty component within the drive power system can be isolated thereby aiding plant personnel to be better prepared with spares and repair kits. Hence there is not only a strong need for cost-effective detection schemes to assess the condition of the drive power system as a whole, but also a strong need for efficient isolation schemes to identify the component within the system that is faulty. This paper describes a sensorless approach to detect and isolate induction motor and/or centrifugal pump faults. Motor and pump bearing degradation is considered to validate the performance effectiveness of the proposed scheme. No add-on sensors, on either the motor or the pump, are used in the development of the proposed method to avoid any reduction in overall system reliability and prevent increased costs. In fact, motor and/or pump bearing degradation is detected and isolated using only the motor line voltages and phase currents. The proposed technique is insensitive to electric power supply fluctuations and mechanical load variations and it does not require prior knowledge of either the motor or the pump design parameters. Hence this approach can be easily ported to motor-pump systems of varying manufacturers and sizes. The developed algorithm has been tested on accelerated fault data collected from a centrifugal pump fluid loop driven by a 3-φ, 3 hp induction motor. Results from these experiments indicate that the proposed fault detection and isolation scheme successfully detects and classifies bearing degradation in the motor and/or the pump without false positives or misclassification.

Shape Optimization of Power Plant Ducting Using CFD

Power plant ducting generally designed with simple shapes has to undergo many changes of shape to accommodate interfacing equipment associated with plant operation leading to higher pressure drop, higher power consumption and flow maldistribution zones having higher or lower velocities. To redress this situation, baffles, guide vanes and other internals are used to streamline the flow through ducts, especially in bends. A basic disadvantage in coal fired plants of using baffles is that they get punctured / eroded due to impact of high velocity ash particles in flue gas ducting, and the effectiveness of baffles is lost in short duration. To overcome the above disadvantages, a new method is developed to change the shape of the duct in such a way that a more streamlined flow is maintained across any cross section. The velocity profile, obtained using computational fluid dynamics (CFD) calculations, across the cross-section is examined at several locations along the duct. Wherever high velocity compared to average velocity is found, the cross-section is increased and where the velocity is low, the cross-section is reduced. A new grid is created through the revised cross-section and a fresh CFD analysis is made to identify zones of flow maldistribution. The flow simulation is done in an iterative manner, alternately calculating the flow domain and modifying the local cross-section based on the local velocity distribution. The method has been found to be more robust and led, after a few iterations, to a shape of the duct which resulted in a significant reduction in the pressure drop without using any baffles or inserts.