Abstract:The effect of stator clocking has been experimentally and computationally investigated using a low-speed, two-stage, low-pressure turbine (LPT) which was specifically designed to maximize the clocking potential by aligning the stator 1 wake segments with the stator 2 leading edge along the span. It was verified that the wake segments are aligned to within 10% of stator pitch across the span. The measured clocking effect on the work extraction is 0.12% and on efficiency is 0.08%. Although the effect of clocking… Show more
“…The total pressure loss C pt is defined in the following where P 1t is a total pressure measured at the cascade inlet; P 2t and P 2 , respectively, denotes total and static pressures measured at the cascade outlet. Note that the total pressure at cascade inlet and outlet are taken in averaged mass, since in the current investigations, the flow inside the vane passage is compressible (Evans and Longley 25 ). Figure 11.Effects of different vane tips on mixed-out total pressure loss coefficients downstream of the cascade at an exit Mach number of 0.44.…”
Section: Resultsmentioning
confidence: 99%
“…where P 1t is a total pressure measured at the cascade inlet; P 2t and P 2 , respectively, denotes total and static pressures measured at the cascade outlet. Note that the total pressure at cascade inlet and outlet are taken in averaged mass, since in the current investigations, the flow inside the vane passage is compressible (Evans and Longley 25 ). It is shown from Figure 11 that the total pressure loss is reduced significantly by the WT and CWT designs due to the reduced leakage flow and losses, while the CT and PTI designs have a slight reduction in the total pressure loss.…”
Section: Specific Flow Features Of the Various Clearance Designsmentioning
Variable geometry turbine exists in small mobile gas turbines or some marine gas turbines to enhance the part-load performance. However, there are efficiency penalties associated with the vane partial gap, which is needed for the movement of variable vanes. This paper investigates the vane-end clearance leakage flow for a flat tip, a cavity tip, a winglet tip, a tip with passive injection, and a cavity-winglet tip to assess the possibility of minimizing vane-end clearance losses in a variable geometry turbine cascade. First, calculations were done at the test rig conditions for comparison with measured data, and they were used for validation of computational fluid dynamics model. Then, numerical calculations were done for turbine typical conditions. Specific flow structures of the various clearance designs of variable vanes are described, and then the effects of vane turning, including exit Mach numbers of 0.34, 0.44, and 0.54 as well as turning angles of –6°, 0°, and 6° on total pressure losses and outflow yaw angle for different vane tips are shown. In addition, the sensitivity of aerodynamic losses to vane tip gap height is evaluated. Results show that the strong interactions near the tip endwall region change the near-tip loading distribution significantly. With winglet and cavity-winglet tip designs, the loading distribution becomes very similar to the typical fixed vane, and the total loading is reduced, thus reducing the vane-end losses. Among the different vane tips presented, the cavity-winglet tip achieves the best aerodynamic performance, and the cavity tip has the lowest sensitivity to vane tip gap height. Overall, the cavity-winglet tip is found to be the best choice for variable vanes. The research results can provide useful reference for the vane design in a real high endwall-angle variable geometry turbine.
“…The total pressure loss C pt is defined in the following where P 1t is a total pressure measured at the cascade inlet; P 2t and P 2 , respectively, denotes total and static pressures measured at the cascade outlet. Note that the total pressure at cascade inlet and outlet are taken in averaged mass, since in the current investigations, the flow inside the vane passage is compressible (Evans and Longley 25 ). Figure 11.Effects of different vane tips on mixed-out total pressure loss coefficients downstream of the cascade at an exit Mach number of 0.44.…”
Section: Resultsmentioning
confidence: 99%
“…where P 1t is a total pressure measured at the cascade inlet; P 2t and P 2 , respectively, denotes total and static pressures measured at the cascade outlet. Note that the total pressure at cascade inlet and outlet are taken in averaged mass, since in the current investigations, the flow inside the vane passage is compressible (Evans and Longley 25 ). It is shown from Figure 11 that the total pressure loss is reduced significantly by the WT and CWT designs due to the reduced leakage flow and losses, while the CT and PTI designs have a slight reduction in the total pressure loss.…”
Section: Specific Flow Features Of the Various Clearance Designsmentioning
Variable geometry turbine exists in small mobile gas turbines or some marine gas turbines to enhance the part-load performance. However, there are efficiency penalties associated with the vane partial gap, which is needed for the movement of variable vanes. This paper investigates the vane-end clearance leakage flow for a flat tip, a cavity tip, a winglet tip, a tip with passive injection, and a cavity-winglet tip to assess the possibility of minimizing vane-end clearance losses in a variable geometry turbine cascade. First, calculations were done at the test rig conditions for comparison with measured data, and they were used for validation of computational fluid dynamics model. Then, numerical calculations were done for turbine typical conditions. Specific flow structures of the various clearance designs of variable vanes are described, and then the effects of vane turning, including exit Mach numbers of 0.34, 0.44, and 0.54 as well as turning angles of –6°, 0°, and 6° on total pressure losses and outflow yaw angle for different vane tips are shown. In addition, the sensitivity of aerodynamic losses to vane tip gap height is evaluated. Results show that the strong interactions near the tip endwall region change the near-tip loading distribution significantly. With winglet and cavity-winglet tip designs, the loading distribution becomes very similar to the typical fixed vane, and the total loading is reduced, thus reducing the vane-end losses. Among the different vane tips presented, the cavity-winglet tip achieves the best aerodynamic performance, and the cavity tip has the lowest sensitivity to vane tip gap height. Overall, the cavity-winglet tip is found to be the best choice for variable vanes. The research results can provide useful reference for the vane design in a real high endwall-angle variable geometry turbine.
“…The aerodynamic design of the turbine is listed in Table 3. The geometrical arrangement of the working section and the instrumentation are not necessary for this paper but they are described in [5] and [6].…”
Section: Turbine Facilitymentioning
confidence: 99%
“…For long timescale variations which occur between runs, e.g. seasonal ambient conditions, which cannot be directly eliminated by choice of the facility operating point, Evans & Longley [5,6] developed the Accounting Methodology (where multiple runs are best-fit correlated to a common datum).…”
The accuracy with which experimental investigations of turbine performance need to be undertaken require either a semi- or fully-automated control of the operating point as any variation can compromise the reliability of the measurements. Fundamentally, both the mass flow rate through the turbine and the applied brake torque need to be adjusted in real-time so that the required operating point is maintained.
This paper describes the development of a time accurate computational simulation of the unsteady dynamics of a largescale, low-speed turbine facility when its operating point is determined by a full-authority control system. The motivation for the development of the computational simulation was to be able to safely undertake parametric studies to refine the control system and to investigate the cause of monotonic excursions of the operating point which were observed after a major rebuild.
The monotonic excursions of the turbine operating point could only be reproduced by the computational simulation after an unsteady aerodynamic coupling between the turbine exit flow and the downstream centrifugal fan had been incorporated. Based on this observation a honeycomb was installed upstream of the fan in the turbine facility. This eliminated the monotonic excursions and the fractional noise of the operating point was reduced by 37%. When combined with an earlier refinement of the control system the factional noise was reduced by a factor of three. This enables the number of repeated measurements to be reduced by nine and still obtain the same quality of data.
“…The blade loading distribution of the second stage stator and the rotor rows are typical of current aero-engine technology for low pressure turbines. The Datum blading used in this investigation had been designed for an investigation of clocking [13] so the stator blade stacking had been chosen to align the wakes across the span and no endwall geometry features had been included. The Peregrine facility has two controls: the motor and the eddy-current brake.…”
An experimental and computational investigation has been undertaken into the effects of deterioration of the first stage rotor shroud knife-edge seal clearance in a two-stage turbine which has engine representative cavity geometries. Four values of deterioration were investigated which cover the new-condition to old-condition knife-edge seal clearance.Measurements within the first stage rotor shroud cavity show that whilst the leakage mass flow rate increases with deterioration, the angle at which the leakage flow approaches the downstream stator is essentially fixed and independent of the flow coefficient. This is in agreement with a simple over-tip leakage model. Because of the engine representative cavity geometry, the over-shroud leakage flow undergoes little mixing when it re-enters the mainstream and approaches the downstream stator at more than 60° negative incidence.Detailed measurements at the exit of the second stage stator identified two large positive vortices which were not consistent with the horseshoe vortex model for secondary flow. A computational investigation revealed that one vortex originates from the rolling-up within the stator passage of the streamwise vorticity sheet associated with the first stage rotor over-shroud leakage. This roll-up vortex cannot be eliminated. The second vortex is generated within the stator passage by the separation of the over-shroud leakage flow at the leading-edge due to the large negative incidence. It was hypothesised that this separation vortex might be eliminated by locally redesigning the stator.A new stator was designed, manufactured and tested. As predicted, the roll-up vortex was still present but the separation vortex was eliminated. For all the values of deterioration tested the entropy loss coefficient of the new stator and the unchanged second stage rotor were reduced. It is estimated that the new stator would improve the lifetime average efficiency by 0.5% compared to the original.
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