Thesis (M.S.)--Rochester Institute of Technology, 1981. / Typescript. Includes bibliographical references (leaves 147-149).

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This thesis documents an experimental investigation into the effect of trailing edge Injection on the aerodynamic performance of turbine blades conducted at Virginia Polytechnic Institute and State University (VPl&SU). A brief description of the arrangement, instrumentation and data acquisition system of the VPl&SU Transonic Cascade Wind Tunnel is given. Testing was conducted under a number of test conditions. Baseline data was obtained for the blades with no trailing edge injection. The blades were then tested for two different blowing rates to test the effect of blowing rate on the total pressure loss coefficient, L. Tests were conducted at a variety of save cascade exit Mach numbers ranging from 0.79 to 1.36. Measurements were taken at three locations downstream of the cascade blade trailing edges. The algorithm used to calculate the L from the measured data is discussed. Results of the testing indicate that trailing edge injection has a negligible effect on the total pressure loss coefficient. Correlations of cascade exit Mach number to L are given. The development of L downstream of the blade trailing edge is discussed. / Master of Science

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The necessary clearance at the tip of unshrouded rotors of axial turbines allows fluid to leak from the pressure to the suction side of the blade and produces an important component of loss that is ultimately responsible for approximately 25 % of the total turbine rotor losses. Leakage fluid can pass through the tip clearance gap with either high or low loss generation. It has been customary in turbine design to employ high loss designs since it is only by the creation of loss that the gap mass flow rate can be restricted. The present work, however examined the effect of streamlined tips that have low entropy generation within the tip and high leakage flows. An axial turbine followed by a second stage nozzle (ie one and a half stages) was designed, built and instrumented and used to evaluate performance with particular reference to the understanding of tip clearance effects in a real machine and possible benefits of streamlined low loss rotor tips. A radiused pressure edge was found to improve the performance of a single stage and of a one and a half stage turbine at the selected tip clearances. This was in contrast to previous cascade results where mixing losses reduced the benefits of such tips. Clearance gap flow appears to be similar to other turbine flow where the loss mechanism of separation must be avoided. Loss formation within and downstream of a rotor is more complex than previously realized and does not appear to obey the simple rules used to design for minimum tip clearance loss. For example, approximately 48 % of the tip leakage mass flow within a rotor may be a flat wall-jet rather than a vortex. Second stage nozzle efficiency was significantly higher than first stage nozzle efficiency, and even increased with tip clearance. This was a surprising result since it means that not only was there a reduction in secondary flow loss but also that rotor leakage and rotor secondary flows did not generate significant downstream mixing loss. The manner in which the second nozzle responds to the complex leakage flows presented to it and how it completes the formation of tip clearance loss for various rotor tip clearances was identified. The tangentially averaged relative rotor flow in the tip clearance region differed radically from that found in cascades which was seen to be underturned with a high axial velocity. There was evidence rather of overturning presumably caused by secondary flow. Axial velocity followed an almost normal endwall boundary layer pattern with almost no leakage jet effect. Cascade tip clearance models are therefore not accurate in predicting leakage flows of real rotors. The reduction in second stage nozzle loss was seen to occur near the hub and tip confirming a probable reduction in secondary flow loss. Nozzle exit loss contours showed that the leakage flow suppressed the formation of the classical secondary flow pattern and that a new tip clearance related loss phenomenon existed on the suction surface. The second stage nozzle reduced the hub endwall boundary layer below that of both the first nozzle and that behind the rotor. It also appeared to rectify the secondary and tip clearance flows to the extent that a second stage rotor would experience no greater flow distortion than the first stage rotor would. Radial flow angles behind the second stage nozzle were found to be much smaller than those measured in a previous study of low aspect ratio, untwisted blades. / Thesis (Ph.D.)-University of Natal, Durban, 1993.

On unshrouded axial flow turbine rotors, the tip clearance, required for thermal expansion and manufacturing limitations, allows fluid to leak from the pressure side to the suction side of the blade. This flow across the blade tip causes a large proportion of the overall rotor loss. In this work, the flow was visualized, microscopic static pressures taken and flow field measurements were done in the blade tip region to investigate the complex nature of tip clearance flows. An annular turbine cascade with a rotating outer casing was used to simulate the relative motion at the tip of an axial rotor. It was found that relative motion did not have a significant effect on the basic structure of the micro-flow, even though it reduced the leakage mass flow rate which is important as far as mixing loss formation is concerned. The existence of a narrow, very low pressure depression, caused by the flow remaining attached around the sharp pressure corner edge, was confirmed. The width and pressure of the separation bubble were found to be strongly dependent on gap size but the relationship was not linear. The point at which the separation bubble reattaches was seen to coincide with a slight rise in static pressure. The separation bubble which caused the majority of the internal gap loss, and which was thought to contribute to the mixing loss, was shown to disappear when the pressure corner was given a radius of 2,5 gap widths.A linear cascade was used to evaluate the performance of two blade tip shapes that substantially reduced internal gap loss and to compare them to a standard sharp or flat tip blade. A method whereby linear cascade data was analyzed as if it were a rotor with work transfer, was used to evaluate the performance of the various blade tip geometries. It was found that both modified tips increased the mixing loss due to the extra leakage mass flow rate. The first tip with the radiused pressure corner was seen to have a lower efficiency than the flat tip blade. A second tip that was contoured to shed flow in a radial direction and thus decrease the leakage mass flow rate through the gap was seen to significantly increase the overall efficiency. / Thesis (M.Sc.)-University of Natal, Durban, 1989.

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No description available.

In a previous work of a similar nature, the performance of a low speed axial turbine with a second stage nozzle was examined with respect to the effect of the variation of tip clearance for various tip shapes. Present findings suggest some interesting phenomena, including the effect of tip clearance on the flow within the rotor and show that poor resolution from a transducer and insufficient data points in the critical tip region, where a high velocity peak was found, were responsible for a number of incorrect conclusions in the original study. In terms of blade tip geometry, a standard flat tip shape was found to deliver only a marginally better performance when compared to a double squealer tip and the two streamlined shapes previously investigated. Although contemporary opinion suggests that a streamlined tip should increase the leakage flow and hence cause greater mixing losses, the machine efficiency was not significantly reduced. This is an exciting result since it suggests that a streamlined tip shape can be used to alleviate the problem of blade tip burnout without significantly reducing machine efficiency. When the single stage performance in the absence of a second nozzle was examined, slightly different trends were obtained. The low entropy tips produced slightly lower mixing loss, suggesting that the internal gap loss is an important parameter in determining the rate at which the leakage jet mixes downstream of the rotor. The flow behind the rotor (ie time averaged) was found to be in remarkable agreement with linear cascade data when time averaged even though the latter did not include any effects of relative motion. An increase in clearance was seen to reduce the Euler work and also to cause a deficit of mass flow across the remainder of the blade right down to the hub. The leakage flow was also seen to induce a flow blockage which resulted in a higher driving pressure across the rotor for the same mass flow rate. As in the previous study, the second stage nozzle efficiency was seen to be independent of tip clearance or tip shape and was moderately better than that of the first nozzle. However, the improvement was not found to be as large, due to a previously undetected very thin ring of high energy leakage fluid. When this is taken into account, the efficiency of the second stage nozzle is comparable to the first. The second nozzle was seen to have a flow straightening effect on the poorly deflected, high energy leakage flow, causing a rapid mixing process within these downstream blade passages. The growth of secondary flow was reduced at both the hub and the tip and this is believed to result in a slight decrease in loss. The outlet flow was closer to design conditions than that of the first stage nozzle. / Thesis (Ph.D.)-University of Natal, Durban, 1996.

A 2-D plain strain CFD/FEM model to simulate thermal shocks and stresses in a turbine blade has been set up using the commercially available software FLUENT and NASTRAN. The model was validated against the experimental data of Bohn et. al. and used to simulate real test cases. The steady state numerical model was set up for a single Mark II nozzle guide vane using the correct boundary conditions to resolve the flow field. A combined laminar and turbulent model was developed in FLUENT that was used to highly accurately predict the pressure, temperature and heat transfer coefficient distribution on the blade surface as well as the temperature distribution on the cooling holes inside the blade. The resulting temperature profiles on the blade and cooling holes were used as boundary conditions for the FEM analysis to resolve the internal temperature and stress profiles. The pressure, temperature and heat transfer distribution on the blade, from FLUENT, were compared to those from Bohn et. al. The predicted pressure distribution was exact with the experimental results and the predicted temperature distribution had an average overprediction of 1.4 % on both the pressure and suction side. The internal temperature profile predicted by NASTRAN was correctly predicted with an average over-prediction of 2 %. The stress contours were accurately predicted with the stress magnitude varying by 17 % to that of Bohn et. al. The reason for the difference between the MSC.NASTRAN and Bohn et. al. stress results is believed to be purely solver related. Bohn et al. used a FEM package called MSC.MARClMentat. With the steady state model validated, transient test cases were simulated that represent typical operational data. The mission profile was obtained for the T-56 engine found on the C130 cargo plane. The model was used to simulate the test case where the turbine inlet temperature (TIT) varied with time. The simulation results showed that stress was proportional to TIT, where changes in the TIT were seen later in the stress curve, due to conduction in the blade. Steep TIT changes, such as shock loads affected stress later than gentler TIT changes. Thus, the FLUENT / NASTRAN model was successfully validated, and used to simulate a flight mission profile. The goal to calculate quality unsteady stress profiles was achieved and forms the boundary conditions for thermal fatigue calculations. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2005.