Showing papers on "Tip clearance published in 1988"
06 Jun 1988
TL;DR: In this paper, the tip clearance region of an annular turbine cascade with a rotating outer casing was simulated to simulate the relative motion at the tip of an axial rotor and microscopic static pressure measurements were done in the tip clearing region.
Abstract: Flow visualisation and microscopic static pressure measurements were done in the tip clearance region of an annular turbine cascade with a rotating outer casing to simulate the relative motion at the tip of an axial rotor. The effect of relative motion did not have a significant effect on the blade gap pressure distributions. As in previous studies the narrow deep pressure depression on a sharp pressure edge was seen. It was confirmed that the width of the gap separation bubble depends on clearance and a correlation with flow visualisation showed that at the reattachment line there is the expected slight pressure peak. The separation bubble, which is thought to contribute a major part of the leakage loss, was shown to disappear when the pressure surface tip is give a radius of 2.5 gap widths.Copyright © 1988 by ASME
46 citations
Patent•
02 May 1988
TL;DR: In this article, a method for periodically restoring the blade tip to annular seal clearance in a gas turbine engine was proposed, based on incrementing (42a, 42b) the flow of external cooling air responsive only to an accumulated engine use parameter.
Abstract: A method for periodically restoring the blade tip to annular seal clearance in a gas turbine engine (10) includes incrementing (42a, 42b) the flow of external cooling air responsive only to an accumulated engine use parameter (58).
30 citations
Patent•
27 Apr 1988TL;DR: In this paper, an axially extending electrode (16) is provided on a casing liner such that a capacitor is formed, with rotor blades constituting the other electrode, and the tip clearance therebetween forming a dielectric.
Abstract: An axially extending electrode (16) is provided on a casing liner (10) such that a capacitor is formed, with rotor blades constituting the other electrode, and the tip clearance therebetween forming a dielectric. The axial length of the electrode (16) exceeds that swept by the rotor blade tips and is sufficient for any axial movement of the rotor blades under operating conditions not to affect the capacitance of the sensor.
24 citations
06 Jun 1988
TL;DR: In this article, the axial clearance between the tip of the blades of an unshrouded impeller and its stationary shroud has been varied to study its effect on overall compressor performance.
Abstract: The axial clearance between the tip of the blades of an unshrouded impeller and its stationary shroud has been varied to study its effect on overall compressor performance. The compressor under investigation consisted of an inlet nozzle, a 3D open impeller with full inducer, a parallel-wall vaneless diffuser and a collector. High-accuracy overall performance data were obtained for this compressor.The experiments were carried out in a closed-loop centrifugal compressor test rig with the impeller running at a rotational Mach number u2/a0 = 1.39. The impeller tip diameter was 0.516 m, its tip width 0.021 m and the impeller blade exit angle was 30 degrees from radial.Assuming a linear relationship, the experimental data indicates a pressure ratio decrease of 0.77 percent, an efficiency loss of 0.31 points, an input head reduction of about 0.25 percent and an output head reduction of about 0.65 percent for each percent increase in clearance ratio. However, the data seems to indicate a non-linear effect showing stronger performance sensitivity at smaller clearances.The test data are compared against a clearance loss model. Improved performance prediction is obtained by including the effect of clearance on impeller work input.Copyright © 1988 by ASME
20 citations
TL;DR: In this paper, the rotor tip clearance flow is aerothermodynically analyzed and a loss model is presented that includes the above-mentioned effects, and the discharge coefficient and the stage loading factor are taken as modeling parameters.
Abstract: Tip clearance flow is a major contributor to the losses in axial flow turbines. Tip shrouding reduces the extent of this loss at the expense of more structural complexity and increased centrifugal blade stresses. Recent technological advance in the area of active clearance control promises to minimize the tip clearance loss without the adverse tip shrouding effects. Due to complexity of rotor tip flows, a comprehensive tip clearance loss model that accounts for the tip shape, relative wall motion, tip loading, and stage characteristics has not yet been developed. In the present paper, the rotor tip clearance flow is aerothermodyn amically analyzed and a loss model is presented that includes the above-mentioned effects. Tip leakage discharge coefficient and the stage loading factor are taken as modeling parameters. Finally, earlier tip clearance loss models are reviewed and comparisons are drawn with the present work.
17 citations
Patent•
26 Aug 1988TL;DR: In this article, the authors present a turbine blade tip clearance control system using a rub tolerant, high-temperature seal material coating on a turbine shroud and a turbine blades made of at least two materials.
Abstract: The turbine blade tip clearance control system presently used with existing turbine blade uses an abradable seal material with a conventional squealer tip. Others use a thin, coating added to the tip of the blade. The present turbine blade tip control system minimizes the problem of controlling the clearance between the blade and the shroud and ovecomes the problem of wearing away of the thin coating added to the tip by using a rub tolerant, high-temperature seal material coating on a turbine shroud and a turbine blade made of at least two materials. The combination of the coating and an outer tip being of a different material than the metallic body also minimizes the problems associated with the burning of dirty fuels. The blade has a metallic body of high strength and the outer tip has a strength less than the strength of the body and made of a material resistant to oxidation, sulfidation and thermal fatigue at operating temperatures. The outer tip has a radial length "L" at least 1 mm in length.
16 citations
TL;DR: In this article, the authors derived three-dimensional spanwise pressure loss and flow angle deviation variations from NASA, university, and industrial sources from middle-stage research compressors operating near design point.
Abstract: Three-dimensional spanwise pressure loss and flow angle deviation variations have been deduced from NASA, university, and industrial sources from middle-stage research compressors operating near design point. These variations are taken as the difference above or below that predicted by blade element theory at any spanwise location. It was observed that the magnitude of the three-dimensional loss and deviation in the endwall regions is affected by hub and casing boundary layer thickness, camber, solidity, and blade channel aspect ratio for stators and rotor hubs. Rotor tip variations were found to depend on casing boundary layer thickness and tip clearance. Simple design point loss models derived from these data can aid in the design of axial compressor middle stages.
14 citations
Patent•
11 May 1988
TL;DR: In a turbojet engine of the kind having a fan, the face of the radially outer tip of each rotor blade of the fan has a radiussed profile centered at a point R situated in a position displaced on the concavely curved side of the blade relative to its radial axis and beyond the rotational axis of the engine relative to the blade as discussed by the authors.
Abstract: In a turbojet engine of the kind having a fan, the face of the radially outer tip of each rotor blade of the fan has a radiussed profile centered at a point R situated in a position displaced on the concavely curved side of the blade relative to its radial axis and beyond the rotational axis of the engine relative to the blade
14 citations
01 Jun 1988
TL;DR: In this article, a simple and more universal approach for the estimation of tip clearance losses in centrifugal impellers, the possibility of correlation through specific speed is examined, and a tip clearance loss sensitivity factor is introduced and its likely dependence on specific speed.
Abstract: Results of a continious effort at such a correlation, involving the most important effects of tip clearance on overall efficiency deterioration, are presented. The term tip clearance refers to the clearance between the vane tips of a half shrouded impeller and the front casing. In an attempt to develop a simple and more universal approach for the estimation of tip clearance losses in centrifugal impellers, the possibility of correlation through specific speed is examined. A tip clearance loss sensitivity factor is introduced and its likely dependence on specific speed presented. The weakness and ambiguity of the correlcation are discussed.Copyright © 1988 by ASME
7 citations
06 Jun 1988
TL;DR: In this paper, a simple and more universal approach for the estimation of tip clearance losses in centrifugal impellers, the possibility of correlation through specific speed is examined, and a tip clearance loss sensitivity factor is introduced and its likely dependence on specific speed.
Abstract: Results of a continious effort at such a correlation, involving the most important effects of tip clearance on overall efficiency deterioration, are presented. The term tip clearance refers to the clearance between the vane tips of a half shrouded impeller and the front casing. In an attempt to develop a simple and more universal approach for the estimation of tip clearance losses in centrifugal impellers, the possibility of correlation through specific speed is examined. A tip clearance loss sensitivity factor is introduced and its likely dependence on specific speed presented. The weakness and ambiguity of the correlcation are discussed.Copyright © 1988 by ASME
7 citations
15 Nov 1988-JSME international journal. Series 2, Fluids engineering, heat transfer, power, combustion, thermophysical properties
01 Jun 1988
TL;DR: The efficiency of gas turbine engines is strongly affected by the clearance between the rotating compressor or turbine blades and the stationary annulus around them as discussed by the authors, and the current trend is towards unshrouded blades, the efficiency of which is more strongly influenced by tip clearance as the absence of the shroud creates overtip leakage.
Abstract: The efficiency of gas turbine engines is strongly affected by the clearance between the rotating compressor or turbine blades and the stationary annulus around them. The most critical area is the high pressure turbine which, unfortunately, is the area where it is most difficult to make measurements, as the turbine blades run at temperatures in the region of 1000°C with hot gases containing unburnt fuel, soot etc., flowing over them at high pressure and speeds approaching sonic. The current trend is towards unshrouded blades, the efficiency of which is more strongly affected by tip clearance as the absence of the shroud creates overtip leakage (figure 1).
Patent•
28 Mar 1988
TL;DR: In this paper, a ribbed rotor was used to make a tip clearance smaller without entailing any rotational cushioning, and a combination clearance between both outer and inner rotors was kept in almost constant.
Abstract: PURPOSE:To aim at improvement in sealability and pump performance (volumetric efficiency), by making form of a plastic rotor into a ribbed form, while forming it into a specific tooth profile in order to make a tip clearance smaller without entailing any rotational cushioning. CONSTITUTION:Among trochoidal items, when a base circle diameter is set down to Amm, an eccentric quantity to emm, eccentricity to fe=e/B, and a base circle ratio to n=A/B, respectively, these trochoidal items are selected so as to make fe satisfy 0 DELTAc), and thereby an outer rotor curve is corrected. With this constitution, a combination clearance between both outer and inner rotors is kept in almost constant.
15 May 1988-JSME international journal. Series 2, Fluids engineering, heat transfer, power, combustion, thermophysical properties
06 Jun 1988
TL;DR: In this paper, the effects of tip clearance changes on efficiency in axial compressors are typically established experimentally and an analysis of this sensitivity range in terms of the blade and stage design parameters was initiated.
Abstract: The effects of tip clearance changes on efficiency in axial compressors are typically established experimentally. The ratio of change of efficiency with change of clearance gap varies significantly for different compressors in the published data. An analysis of this sensitivity range in terms of the blade and stage design parameters was initiated. The analysis revealed that the sensitivity range largely resulted from a derivation at constant flow of the efficiency decrement. It was also found that a generalized loss method of generating the sensitivities produced a much improved correlation of the change in efficiency with change in clearance over a variety of machines, configurations and speeds.Copyright © 1988 by ASME
01 Jan 1988
TL;DR: In this paper, two recent electronic advances at NASA-Lewis that meet the blade tip clearance needs of a wide class of fans, compressors, and turbines are described, including a frequency modulated (FM) oscillator that requires only a single low cost ultrahigh frequency operational amplifier.
Abstract: Two recent electronic advances at NASA-Lewis that meet the blade tip clearance needs of a wide class of fans, compressors, and turbines are described. The first is a frequency modulated (FM) oscillator that requires only a single low cost ultrahigh frequency operational amplifier. Its carrier frequency is 42.8 MHz when used with a 61 cm long hermetically sealed coaxial cable. The oscillator can be calibrated in the static mode and has a negative peak frequency deviation of 400 kHz for a typical rotor blade. High temperature performance tests of the probe and 13 cm of the adjacent cable show good accuracy up to 600 C, the maximum which produces a clearance error of + or - 10 microns at a clearance of 500 microns. In the second advance, a guarded probe configuration allows a longer cable capacitance. The capacitance of the probe is part of a small time constant feedback in a high speed operational amplifier. The solution of the governing differential equation is applied to a ramp type of input. The results show an amplifier output that contains a term which is proportional to the derivative of the feedback capacitance. The capacitance is obtained by subtracting a balancing reference channel followed by an integration stage.
Patent•
28 Jun 1988
TL;DR: In this paper, a segment-form shroud is set up in a turbine case and the turbine case is connected to the shroud by two links via pins 4 and 5, and the shroud is automatically displaced in the radial direction by differential thermal expansion.
Abstract: PURPOSE:To simplify a structure, by setting up a shroud in a turbine case, and coupling them together so as to cause the shroud to be displaced in the radial direction by differential thermal expansion between the turbine case and the shroud CONSTITUTION:A segment-form shroud 1 is set up in a turbine case 3 Both ends of the shroud 1 are connected each to the turbine case 3 by two links 2 via pins 4 and 5 The shroud 1 is automatically displaced in the radial direction by differential thermal expansion between the turbine case 3 and the shroud 1, thereby optimizing a blade tip clearance With this constitution, an optimization mechanism for this clearance is simplifiable
TL;DR: In this paper, the effect of the tip clearance between the blade tip and the fan casing on the noise generated by a diagonal flow fan is examined over a wide range of the flow rate of a fan and discussed in relation to the characteristics of flow measured at a cross section behind the fan rotor.
Abstract: The effect of the tip clearance between the blade tip and the fan casing on the noise generated by a diagonal flow fan is examined over a wide range of the flow rate of a fan and discussed in relation to the characteristics of flow measured at a cross section behind the fan rotor. Wake width, which controls the fan noise level, increases with decreasing the flow rate of the fan, which results in the increase in the noise level. The increase in the tip clearance causes the increase in the wake width especially in the tip region of a fan blade. A method to estimate the wake width by the known quantity of the deviation angle of the flow is proposed and verified experimentally to be useful, which enable us to estimate the noise level even in the low fan flow rate region.
Journal Article•
Patent•
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23 Jun 1988
TL;DR: In this paper, a tip clearance unit for removing tips of bulk material from storage has a discharge apparatus which discharges the bulk material laterally and in which discharge means (8) are connected to at least one plate link chain revolving in a vertical plane.
Abstract: A tip clearance unit for removing tips of bulk material from storage has a discharge apparatus which discharges the bulk material laterally and in which discharge means (8) are connected to at least one plate link chain revolving in a vertical plane. In the deflection region of the discharge apparatus around the drive star wheel (4) lying on the discharge side, a metal sheet (10) connected to the bridge (1) closes the discharge means (8), so that no bulk material can emerge during the deflection. Immediately after the deflection the discharge means (8) are exposed, so that the bulk material slides out onto a conveying means (1) lying below and in front of the return strand, this conveying means conveying the bulk material onwards laterally and transferring it to a lengthwise conveyor lying parallel to the tip.