Tip clearance

About: Tip clearance is a research topic. Over the lifetime, 2637 publications have been published within this topic receiving 32671 citations.

Monitoring blade passage in turbomachinery through the engine case (no holes)

Abstract: It is possible to detect passage of turbomachinery blades without penetrating the engine case. This "look through the wall" eddy current sensor eases the addition of a PHM system to an engine. This paper introduces this sensing concept, summarizes the physics, and presents results of preliminary tests. Blade material and geometry, case material, thickness and temperature, blade tip clearance, sensor detail and design and blade tip velocity all affect the strength and quality of the signal detected.

Three-dimensional separations in compressors.

Abstract: A lack of understanding of the nature and characteristics of three-dimensional (3D) separation, which is inherent in compressor blade passages and tip clearance dominated 3D flow in the rotor tip region, has limited the success of 3D blade design. This dissertation is therefore aimed at contributing to compressor design process by exploring the formation of 3D separations. Detailed measurements in compressor cascades, tests in a low-speed single stage Deverson compressor rig and considerable use of Denton multi-stage Reynolds averaged Navier-Stokes (RANS) solver MULTIP have provided better understanding and improved predictive capability of this important phenomenon. An attempt has also been made to clarify the role of different flow mechanisms. Tests carried out to determine the effect of surface roughness in the single-stage axial compressor show that stage performance, even at design point is extremely sensitive to roughness around the leading edge and peak suction regions because of the effect on 3D separations. A numerical model to simulate the effect of roughness was formulated and incorporated into MULTIP and this showed good agreement with measurements. A method of estimating the thickness of the 3D separated layer has been developed, which was used in a parametric study to assess the sensitivity of 3D separations to key flow and design parameters in axial compressors. Investigation into endwall flow control methods was undertaken, based on the understanding of the formation of 3D separation. These include clearance flows, endwall fences and endwall dividing streamline suction. The latter was demonstrated to be the most effective method of control. The knowledge gained in predicting 3D separation was then used to explore the 3D nature of the flow around rotor tip sections and how this is influenced by key 3D design techniques. The performance of the existing 3D rotor and the modified version with tip chord extension was analysed using detailed CFD, with carefully refined mesh especially in the blade tip/clearance region. This approach enabled key problems with the oliginal 3D design to be diagnosed. The lesson learned from the performance of the 3D rotor therefore guided a re-design of the rotor tip. It was found that a more modest amount of blade lean is enough to achieve improved performance improvement in the tip region. Suggested future work that will aid further understanding of 3D separations in terms of flow mechanism, unsteadiness and control are also presented.

Study of tip clearance effects in centrifugal fans with unshrouded impellers using computational fluid dynamics

Abstract: Performance of centrifugal fans with unshrouded impellers strongly depends upon complex configuration of the asymmetrical flowfield in the axial direction, which is highly unsteady. The flowfield, in turn, is considerably affected by the design parameters of both scroll and impeller geometry, for which tip clearance is of particular interest. This article presents a three-dimensional computational fluid dynamics (CFD) simulation of the flowfield in three different unshrouded centrifugal fan impellers with varying tip clearances. A commercial CFD code, namely, Fluent V6.2.16 with a k-ɛ two-equation turbulence model was utilized in order to study the effects of tip clearance on the overall performance of each fan with the tip clearances ranging from 5 to 30 mm. The numerical results were compared with the experimental data reported previously in the literature by the present author and his colleagues, and excellent agreements were observed for each fan.

Capacitive Measurement of Compressor and Turbine Blade Tip to Casing Running Clearance

Abstract: It is an established fact that the efficiency of a gas turbine engine has an inverse relationship with the clearance between the rotor blades and the casing (Tip Clearance, or TC). TC is an essential measurement during the testing of development engines. While commercial TC measurement systems are available, their applicability to an engine is dictated by engine size, geometry, physical accessibility, and temperature distribution around the measurement region. This paper describes the development of a TC measurement system, based on the capacitive measurement principle, which was undertaken to satisfy the application requirements of a specific class of gas turbine engines. The requirements included a relatively long and flexible cable to route the electrical signals out of the engine. The TC measurement system was successfully used during engine testing and valuable data were obtained.