No description available.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 121-127). Also available via the Internet.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 56-58). Also available via the Internet.

No description available.

This thesis summarizes the results of an experimental study on transonic turbine blades in the presence of ejection of coolant in the direction of the flow from slots near the trailing edge. I t presents the effect of the trailing edge coolant ejection on the turbine blade aerodynamic efficiency.¹ The objective of this work is to contribute to the design of new turbine blades by giving loss data for cooled blades. Data were taken in the Virginia Polytechnic Institute & State University wind tunnel, which includes a two-dimensional transonic turbine cascade. The tunnel simulates supersonic discharge flows of turbine rotor blading in a linear cascade with trailing edges designed for ejection of cooling flow. Two blade designs, named Baseline and ULTRE, were tested. Experiments were performed on a transonic turbine cascade designed for a deflection of approximately 68 degrees and outlet Mach number of 1.14 for the Baseline blade and 1.2 for the ULTRE blade. Tests were carried out with CO₂ as coolant in order to ensure the proper simulation of the density ratio between coolant flow and main flow. Data were obtained for both the Baseline and ULTRE cascades with a good periodicity. The content of this thesis is limited to the aerodynamic aspects of coolant ejection. Heat transfer aspects are mentioned but not developed. The first part of this thesis reports on the theoretical considerations necessary for the understanding of the work done and describes the arrangement, instrumentation, and data acquisition system of the wind tunneL The second part of the thesis presents experimental results from tests carried out on both Baseline and ULTRE blades. The cascade tests cover an exit isentropic Mach number range of M2,it = 0.72 to 1.34 and four different ejection rates. 1 The efficiency being characterized by the total pressure loss in this work / Master of Science

Externally applied loads from high winds or impacts may cause structural damage to the wind-turbine blade, and this may further affect the aerodynamic performance of the blade. Wind-turbine blades experience high vibration levels or amplitudes under high winds. Vibrations negatively affect the wind flow on the blade. This project considers the structural dynamic analysis of a small-scale wind turbine with a particular focus on the blade; it involves the finite element model development, model validation and structural analysis of the validated model. The analysis involves a small-scale wind-turbine structural response when subjected to different loading inputs. The analysis is specifically focused on on-shore systems. The use of small-scale wind-turbine systems is common however, apart from initial structural analysis during design stages, these systems have not been studied sufficiently to establish their behaviour under a variation of real-life loading conditions. On-shore wind turbines are often designed for low-wind speeds and their structural strength may be compromised. In addition, these systems experience widely-varying wind speeds from one location to another to an extent that it is extremely difficult to achieve a uniform structural performance. The main reason for solving this problem is to evaluate the structural response of the blade, with special emphasis on an 800 W Kestrel e230i. This involves the calculation of the distribution of blade deflections and stresses over the wind-turbine blade under different loading conditions. To solve the problem, a three-dimensional model of a Kestrel e230i blade was firstly developed in Autodesk Inventor Professional using geometrical measurements that were taken in the mechanical engineering laboratory. A 3D finite element model was developed in ANSYS using approximate material properties for fiberglass obtained from the literature. The model was then validated by comparing its responses with those from a number of static tests, plus a simple impact test for comparison of the first natural frequency. Finally, a number of numerical tests were conducted on the validated finite element model to determine its structural responses. The purpose of the numerical analysis was to obtain the equivalent von Mises stress and deformation produced in the blade. It was determined that under the examined different loading conditions, a higher stress contour was found to occur around the mid-span of the blade. The calculated maximum flexural stress on the blade was observed to be less than the allowable flexural stress for fiberglass which is 1,770 MPa. As expected, the highest deformation occurred at blade tip. The first critical speed of the assembled three-bladed wind turbine was found to be at 4.3 rpm. The first mode shape was observed to be in the flap-wise bending direction and for a range of rotor speeds between zero and 608 rpm, three out of a total of five mode shapes were in the flap-wise bending direction. Future studies should address issues relating blade vibrations with generated power, validation of dynamic tests, fluid-structural interaction and introduction of bio-inspired blade system. Although the performance of the bioinspired blade has not been studied in great detail, preliminary studies indicate that this system has a superior performance. / Mechanical and Industrial Engineering / M. Tech. (Electrical and Mining Engineering)

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 113-115). Also available via the Internet.

Turbine aerodynamic designers are currently focusing on unsteady passage flow to increase turbine performance. In particular, for high pressure turbine stages the effects of wakes and shocks shed from an upstream blade row on the downstream blade row need to be understood. Also, experimental data is needed for comparison with unsteady three-dimensional turbine stage calculations. Previous simulations of the unsteady shock/wake inlet flow field for a turbine rotor or stator used a rotating disk with radial bars upstream of a linear cascade. An alternate method of shock generation is developed here using a capped shock tube with multiple outlets to get a traveling system of three shock waves. Different lengths of tubing are used to get time delays between the shocks, which are then introduced at the top of a linear cascade of turbine blades and travel downwards (tangentially) along the leading edge. Advantages of this method include the absence of wakes and excellent two-dimensionality of the inlet shock waves. The period of the incoming shocks is easily adjustable to simulate different Strouhal numbers. Unsteady measurements of upstream total pressure, blade static pressures, and uncorrected downstream total pressure are made for a transonic mean flow with introduction of traveling shocks at M=1.3. An analytical solution (Bach and Lee, 1970) for the decay of cylindrical shock waves is used to estimate the behavior of flow variables other than pressure at the cascade inlet. The unsteady total pressure loss of the blade passage and the unsteady blade forces are measured with one shock passing and with three shocks passing at periods of 0.055 and 0.200 milliseconds. Loss is estimated as the normalized difference in unsteady total pressures and blade forces are integrated from seventeen unsteady surface pressure measurements. The Strouhal number for the 0.200 msec case is 2.9, which is typical of a high-pressure turbine nozzle or rotor. Periodic behavior in blade force and loss are observed for this case. Blade lift shows peak-to-peak variation of 6% and the estimated loss fluctuates by 100%. No change is observed in the average level of loss due to the incident shock waves. / Ph. D.

This thesis documents an experimental investigation of the base (trailing edge) pressure and its approximate distribution on a transonic turbine blade. Since the base pressure plays an important role in determining the profile loss on blades with thick trailing edges, both the base pressure and the blade losses are presented for a range of transonic exit Mach numbers. The overall objective of this work is to provide experimental data for improving current computer-based models used in designing turbine blades. The two-dimensional cascade was tested in the VPI&SU Transonic Cascade Wind Tunnel, a blow-down type of tunnel facility. The blade design for the cascade was based on the pitchline profile of the high-pressure turbine in a commercial jet engine with a design exit Mach number of approximately 1.2. In order to carefully instrument the thin trailing edge, the blades used in the experiment were made five times the size of the actual engine blade. With this large-scale blade, five static pressure taps were placed around the trailing edge. In addition to these taps, the rearward portion of the suction surface was also instrumented with five static pressure taps. The aerodynamic losses were quantified by a loss coefficient: the mass-averaged total pressure drop divided by the total pressure upstream of the blade row. These measured pressures were taken with a fixed total pressure probe upstream of the cascade and a pitchwise traversing probe in the downstream position. The cascade was tested for an exit Mach number ranging from 0.70 to 1.40. The results of the experiments indicate a decreasing normalized base pressure (p_B/p_t1) with increasing downstream Mach number (M₂) until the minimum value of p_B/p_t1 = 0.30 at M₂ = 1.30. The approximate base pressure distributions for all transonic downstream Mach numbers indicate nearly uniform pressure around the central 90° of the trailing edge. Results for the profile loss are displayed for exit Mach numbers between 0.70 and 1.35; the trend of increasing loss with decreasing base pressure is shown. The shadowgraph pictures taken reveal the trailing edge region of the flow for several downstream transonic Mach numbers. / Master of Science

An investigation of tip leakage flow and its effects on loss production was performed on a large-scale linear turbine cascade having a tip gap measuring 2.1% of the blade height. The Reynolds number based on axial chord and cascade exit velocity was 4.5x10⁵. The experimental work began with a visualization study of the flow in and around the tip gap. The actual flow measurements consisted of two phases, the tip gap exit plane measurements for determination of the losses incurred within the tip gap, and the downstream measurements for determination of the overall cascade losses. The downstream measurements made 140% of an axial chord downstream of the blade leading edges show the development of the leakage flow and its associated losses. Numerical analyses of the data were used to evaluate various flow properties at both the tip gap exit plane and the downstream measurement plane. Using the measured downstream flow, a mixing analysis was performed to estimate the maximum loss of the cascade. Models of the flow were developed to explain and quantify the various factors contributing to the cascade's overall loss. At a particular downstream location, the additional loss due to tip leakage was found to be the sum of the measured loss at the tip gap exit plane and the amount of tip gap secondary kinetic energy which had been dissipated by that downstream location. / M.S.