Development of a small telescope like PZT and effects of vibrations of mercury surface and ground noise

© 2017, Pleiades Publishing, Ltd. A PZT type telescope for observations of gravity gradient and lunar rotation was developed, and a Bread Board Model (BBM) for ground experiments was completed. Some developments were made for the BBM such as a tripod with attitude control system, a stable mercury pool and a method for collecting the effects of vibrations. Laboratory experiments and field observations were performed from August to September of 2014, in order to check the entire system of the telescope and the software, and the results were compared to the centroid experiments which pursue the best accuracy of determination of the center of star images with a simple optical system. It was also investigated how the vibrations of mercury surface affect the centroid position on Charge Coupled Device (CCD). The results of the experiments showed that the effects of vibrations are almost common to stars in the same view, and they can be corrected by removing mean variation of the stars; and that the vibration of mercury surface can cause errors in centroid as large as 0.2 arcsec; and that there is a strong correlation between the Standard Deviation (SD) of variation of the centroid position and signal to noise ratio (SNR) of star images. It is likely that the accuracy of one (1) milli arcsecond is possible if SNR is high enough and the effects of vibrations are corrected

Development of a digital zenith telescope for advanced astrometry

Like other optical astrometric techniques, the Photographic Zenith Tube (PZT) has played a key role in the past observations of the Earth rotation, and it also has a potential to be applied to several other observations by taking advantage of automatic observations with self compensation of tilt of the tube. We here propose In-situ Lunar Orientation Measurement (ILOM) to study lunar rotational dynamics by direct observations of the lunar rotation from the lunar surface by using a small telescope like PZT with an accuracy of 1 milli-seconds of arc (1 mas) in the post-SELENE mission. Our second application is to obtain local gravity field on the Earth by combining deflection of the vertical measured by PZT and the position measured by Global Positioning System (GPS) or Global Navigation Satellite System (GNSS). The accuracy required for this purpose is not as strict as ILOM. We have already developed a Bread Board Model (BBM) of the telescope for ILOM and made some experiments in order to know the performance of the driving mechanism under a similar condition to the lunar environment showing high vacuum, large temperature change and dusty condition. We have also shown that it is possible to correct the effects of uniform temperature change upon the optical system by using a simple model with an accuracy of better than 1 mas. This model has the potential to attain the accuracy of 1 mas, based on the results of the experiments and the simulations. © 2012 Science China Press and Springer-Verlag Berlin Heidelberg

Reduction of Secondary Flow Effects in a Linear Cascade by Use of an Air Suction From the Endwall

The objective of this study is to reduce secondary flow effects in a linear cascade by sucking the working fluid from the endwall. It is widely known that the secondary flow developed in a cascade has a significant impact on the cascade loss or blade erosion in steam turbines. Therefore, a number of studies have been made on the physics of the secondary flow and several devices to control the secondary flow, such as a fence, have been examined. In this study, considering the application to nozzles in gas turbines or steam turbines, the air suction approach is investigated for reducing the secondary flow effects. A suction slit is provided on the lower endwall of the cascade and a flow rate of the sucked air is controlled by adjusting the exit pressure of the slit. The effects of the suction upon the flow nearby the endwall and the secondary flow are observed through several flow visualizing techniques, for example an oil flow method or a tuft method. Furthermore, velocity and stagnation pressure measurement are conducted by a five-hole pressure tube. This clearly demonstrates the vorticity and loss profiles downstream of the cascade with and without the endwall suction.</jats:p

2002a, “Effects of Flow Injection from Outer Casing upon Turbine Nozzle Vane Flow Field”, ASME Paper GT-2002-30598

ABSTRACT In the present paper steady three-dimensional numerical calculations were performed in order to investigate the effects of flow injection from the outer casing upon turbine nozzle vane flow field. Several test cases were analyzed by applying different nozzle vane configurations such as the blade lean, injection slot width and distance from the leading edge. Numerical simulations were conducted considering the no injection case, 5% and 10% main stream flow injection from the outer casing. The impact of the flow injection design variables and the blade lean angle on the aerodynamic loss in terms of the energy loss coefficient and the outlet flow angle were analyzed through a parametric study

A Novel Method for Improvement of Aerodynamic Performance of Highly Loaded LP Turbine Airfoils for Aeroengines

This paper proposes a novel method to improve aerodynamic performance of highly loaded Low-Pressure (LP) turbine airfoils for aeroengines over a relatively wide range of Reynolds number. This new method employs two types of approaches; one is the equipment of two-dimensional contouring with small step on the suction surface of the airfoil and the other approach is a re-shaping of the airfoil near the trailing edge. A linear cascade test facility is employed to investigate the aerodynamic performance of the newly proposed airfoils by use of a miniature Pitot probe. Suction surface boundary layers as well as airfoil wakes are also measured using a hot wire probe. In the experiment, various flow conditions, Reynolds number, wake-passing Strouhal number, are examined. Numerical simulations are carried out to have a better understanding of the flow field around the airfoil. URANS and LES are employed for this purpose. It is found that the proposed method has a capability to reduce the profile loss to some extent.</jats:p