Fluidic devices are of interest with turbomachinery internal air systems for modulation of cooling air and other applications. Generally, the flow states within a fluidic device are switched by control flow or flows. For most fluidic devices the switching procedure is almost instantaneous and hence it is difficult to characterize the performance of a device experimentally. The objective of this research is to numerically investigate the dynamic characteristics of a control flow operated fluidic device. In this study the dynamic characteristics of a nozzle during switching is considered. The simulations considered the unsteady interaction of the control flow with the nozzle jet for two different switching scenarios namely, switching of high to low flow state and vice versa. The magnitude of static pressure applied at the control port was identified as a controlling parameter and had to be below a critical value to achieve stable switching. The CFD solutions show that this is related to the flow physics and critical momentum flux ratios for switching are calculated for the present device.

This paper presents transient aero-thermal analysis for a gas turbine disk and the surrounding air flows through a transient slam acceleration/deceleration “square cycle” engine test, and compares predictions with engine measurements. The transient solid–fluid interaction calculations were performed with an innovative coupled finite element (FE) and computational fluid dynamics (CFD) approach. The computer model includes an aero-engine high pressure turbine (HPT) disk, adjacent structure, and the surrounding internal air system cavities. The model was validated through comparison with the engine temperature measurements and is also compared with industry standard standalone FE modelling. Numerical calculations using a 2D FE model with axisymmetric and 3D CFD solutions are presented and compared. Strong coupling between CFD solutions for different air system cavities and the FE solid model led to some numerical difficulties. These were addressed through improvement of the coupling algorithm. Overall performance of the coupled approach is very encouraging giving temperature predictions as good as a traditional model that had been calibrated against engine measurements.

The quantity of cooling air delivered by the secondary air system to various engine components is usually fixed by cooling requirements at the most arduous operating condition in the flight cycle. Modulation of cooling air would allow optimization of cooling supply at different flight cycle conditions, giving significant performance benefits. Switched vortex valves (SVV) have been proposed for control of air systems [1]. An important characteristics of this device is the absence of any moving part. This offers advantages compared to other systems. This report discusses the numerical study of a typical SVV. The study includes comparison of predicted results with available experimental data and prediction of switching characteristics of the device. In this study two turbulence models namely the Spalart-Allmaras model (SA) and Reynolds stress model (RSM) were used. The RSM showed a good agreement with measured mass flow rate and qualitative agreement with other experimental observations.

The prediction of the preswirl cooling air delivery and disk metal temperature are important for the cooling system performance and the rotor disk thermal stresses and life assessment. In this paper, standalone 3D steady and unsteady computation fluid dynamics (CFD), and coupled FE-CFD calculations are presented for prediction of these temperatures. CFD results are compared with previous measurements from a direct transfer preswirl test rig. The predicted cooling air temperatures agree well with the measurement, but the nozzle discharge coefficients are under predicted. Results from the coupled FE-CFD analyses are compared directly with thermocouple temperature measurements and with heat transfer coefficients on the rotor disk previously obtained from a rotor disk heat conduction solution. Considering the modeling limitations, the coupled approach predicted the solid metal temperatures well. Heat transfer coefficients on the rotor disk from CFD show some effect of the temperature variations on the heat transfer coefficients. Reasonable agreement is obtained with values deduced from the previous heat conduction solution.

The prediction of the pre-swirl cooling air delivery and disc metal temperature are important for the cooling system performance and the rotor disc thermal stresses and life assessment. In this paper, standalone 3D steady and unsteady CFD, and coupled FE-CFD calculations are presented for prediction of these temperatures. CFD results are compared with previous measurements from a direct transfer pre-swirl test rig. The predicted cooling air temperatures agree well with the measurement, but the nozzle discharge coefficients are under predicted. Results from the coupled FE-CFD analyses are compared directly with thermocouple temperature measurements and with heat transfer coefficients on the rotor disc previously obtained from a rotor disc heat conduction solution. Considering the modelling limitations, the coupled approach predicted the solid metal temperatures well. Heat transfer coefficients on the rotor disc from CFD show some effect of the temperature variations on the heat transfer coefficients. Reasonable agreement is obtained with values deduced from the previous heat conduction solution.

The prediction of the pre-swirl cooling air delivery and disc metal temperature are important for the cooling system performance and the rotor disc thermal stresses and life assessment. In this paper, standalone 3D steady and unsteady CFD, and coupled FE-CFD calculations are presented for prediction of these temperatures. CFD results are compared with previous measurements from a direct transfer pre-swirl test rig. The predicted cooling air temperatures agree well with the measurement, but the nozzle discharge coefficients are under predicted. Results from the coupled FE-CFD analyses are compared directly with thermocouple temperature measurements and with heat transfer coefficients on the rotor disc previously obtained from a rotor disc heat conduction solution. Considering the modelling limitations, the coupled approach predicted the solid metal temperatures well. Heat transfer coefficients on the rotor disc from CFD show some effect of the temperature variations on the heat transfer coefficients. Reasonable agreement is obtained with values deduced from the previous heat conduction solution.

De-swirl nozzles are sometimes used in turbomachinery to reduce the pressure drop when air is drawn radially inwards through a rotating cavity. However, this can lead to non-unique steady state solutions with operating conditions achieved depending on how the steady point is approached. In the present study, a transient, 1D model of flow in a rotating cavity has been created. The model allows the vortex.profile to change with through flow rate, and links "this to estimates of disk windage, tangential velocity and, consequently, the vortex pressure gradient. The model was applied to the simulation of de-swirl nozzle fed, rotating cavities with radial inflow. The steady vortex flow characteristics (non-dimensional flow versus pressure ratio) predicted by the model were validated for 2 distinct cases. For a smooth rectangular cavity the flow characteristic was predicted using the model's default parameters. For an engine-representative case with non-axisymmetric geometric features, the flow characteristic of the cavity was reproduced with some alignment of the model.The transient model reproduced experimentally observed hysteresis, discontinuity in operating characteristics, and regions where no steady-state solution could be found. A transient model is required as a steady state model would choose one of the possible solutions without physical justification. In the case of the engine-representative rig, part of the flow characteristic could not be obtained in testing. This is determined to be due to the interaction of the negative resistance region of the vortex and the flow modulating valve characteristic. Measures that allow the full capture of the flow characteristic in rig testing are identified.

Design of pre-swirl systems is important for the secondary air cooling system of gas turbine engines. In this paper, three pre-swirl nozzles, a cascade vane and two drilled nozzles are analysed and their performances are compared. The two drilled nozzles considered are a straight drilled nozzle and an aerodynamically designed nozzle. CFD analyses are presented for stand-alone and pre-swirl system 3D sector models at engine operating conditions near to engine maximum power condition rotational Reynolds number (Re-phi) up to 4.6 ! 10(7). Nozzle performance is characterised by the nozzle discharge coefficient (C-D), nozzle velocity coefficient (eta) and cooling air delivery temperature. Two commonly used eddy viscosity models are employed for the study, the standard k-epsilon and Spalart-Allmaras models with wall functions. Both models give very similar results for C-D and eta and are in reasonable agreement with available experimental data. Effects of nozzle or vane number and sealing flow have been analysed. The cascade vanes perform slightly better than the aerodynamically designed drilled nozzles but the final design choice will depend on other component and manufacturing costs. An elementary model is presented to separate temperature losses due to the nozzle, stator drag and sealing flow.

Gas turbine engine performance requires effective and reliable internal cooling over the duty cycle of the engine. Life predictions for rotating components subject to the main gas path temperatures are vital. This demands increased precision in the specification of the internal air system flows which provide turbine stator well cooling and sealing. This in turn requires detailed knowledge of the flow rates through rim seals and interstage labyrinth seals. Knowledge of seal movement and clearances at operating temperatures is of great importance when prescribing these flows. A test facility has been developed at the University of Sussex, incorporating a two stage turbine rated at 400 kW with an individual stage pressure ratio of 1.7:1. The mechanical design of the test facility allows internal cooling geometry to be rapidly reconfigured, while cooling flow rates of between 0.71 CW, ENT and 1.46 CW, ENT, may be set to allow ingress or egress dominated cavity flows. The main annulus and cavity conditions correspond to in cavity rotational Reynolds numbers of 1.71 × 106< Reϕ<1.93 × 106. Displacement sensors have been used to establish hot running seal clearances over a range of stator well flow conditions, allowing realistic flow rates to be calculated. Additionally, gas seeding techniques have been developed, where stator well and main annulus flow interactions are evaluated by measuring changes in gas concentration. Experiments have been performed which allow rim seal and re-ingestion flows to be quantified. It will be shown that this work develops the measurement of stator well cooling flows and provides data suitable for the validation of improved thermo-mechanical and CFD codes, beneficial to the engine design process.

Unsteady flow dynamics in turbine rim seals are known to be complex and attempts accurately to predict the interaction of the mainstream flow with the secondary air system cooling flows using computational fluid dynamics (CFD) with Reynolds-averaged Navier–Stokes (RANS) turbulence models have proved difficult. In particular, published results from RANS models have over-predicted the sealing effectiveness of the rim seal, although their use in this context continues to be common. Previous studies have ascribed this discrepancy to the failure to model flow structures with a scale greater than the one which can be captured in the small-sector models typically used. This article presents results from a series of Large-Eddy Simulations (LES) of a turbine stage including a rim seal and rim cavity for, it is believed by the authors, the first time. The simulations were run at a rotational Reynolds number Reθ = 2.2 × 106 and a main annulus axial Reynolds number Rex = 1.3 × 106 and with varying levels of coolant mass flow. Comparison is made with previously published experimental data and with unsteady RANS simulations. The LES models are shown to be in closer agreement with the experimental sealing effectiveness than the unsteady RANS simulations. The result indicates that the previous failure to predict rim seal effectiveness was due to turbulence model limitations in the turbine rim seal flow. Consideration is given to the flow structure in this region.

This paper describes the numerical optimisation of a high pressure turbine stage using non-axisymmetric endwall profiling. The aim of the work has been to use the endwall profiling to optimise not only the stage performance, but also the effectiveness of the rim seal in preventing mainstream gas ingestion. Any improvement in rim seal effectiveness may allow a lower coolant flow rate, and hence increased performance due to the lower bleed requirement from the compressor and the lower aerodynamic losses re-introducing the coolant flow into the turbine. To this end, the objective functions used in the optimisation have included the pressure asymmetry above the rim seal, which acts a driver for mainstream gas ingestion, as well as traditional measures of stage performance. Separate steady state optimisations have been carried out for the nozzle guide vane passage and the rotor passage with these objectives and good improvements in the figures of merit have been obtained. Since mainstream gas ingestion is a strongly unsteady phenomenon, unsteady CFD calculations have then been carried out for the datum and optimised stage geometries. These calculations show that the reduction in pressure asymmetry in the steady state calculations is maintained in the unsteady calculation and does indeed reduce predicted mainstream gas ingestion. However, the improvements in stage performance predicted by the steady state CFD are only partially obtained in the unsteady CFD calculations.

Results of fully unsteady numerical simulations of the flow in a direct transfer pre-swirl system are presented and compared with previously published experimental data from an aero-engine representative rig. The conditions considered include those where strong unsteady effects were observed experimentally. Two different rig builds are considered, with the main difference being in the design of the pre-swirl nozzles. The agreement between calculation and experiment is very good in terms of nozzle and receiver hole discharge coefficients and in identifying significant unsteady effects at certain conditions. Predicted cooling air delivery temperatures are lower than those measured. This may be due to heat transfer and other effects in the rig which have not been modelled. Present unsteady results also show agreement, where appropriate, with earlier steady CFD and an elementary model. Both calculations and measurements show similar performance in terms of delivery temperature for the two different builds studied, despite significant difference in pre-swirl nozzle discharge coefficients for the two builds. The calculations indicate that this is associated with the nozzle velocity coefficient being considerably higher than the discharge coefficient in one case.

CFD methods are increasingly being used in gas turbine secondary flow system analysis and design to establish flow distribution and convective heat transfer in internal cavities. A key area of concern is the complex flows adjacent to turbine disc rims, where undesirable levels of hot annulus gas would be ingested were it not for the cooling air supplied to limit its effects on disc rim and blade fixing temperature levels. This paper presents results from a study to investigate the practicality of applying this method to the flow distribution and heat transfer in the disc rim sealing cavity between two adjacent turbine stages, referred to here as a turbine stator well. Also described is the test facility designed to validate the CFD analysis and some preliminary results from comparisons of 3D flow solutions, with measured test data.

A simple method, for both estimating circumferential pressure variation in a turbine, and using this method to calculate the annulus flow ingested across a rim seal into the disc cavity, is presented. This method is compared with test data from 2 separate experimental programmes. The model is shown to collapse the majority of the test data well; with calibration it could form the basis of a preliminary design methodology. The model does not collapse data where unsteady pressure fluctuations were measured in the cavity, suggesting these fluctuations, when present, play an important role in determining how much annulus gas is ingested into the cavity.

Measurements and analysis for a pre-swirl cooling air delivery system are reported here. The experimental rig used is representative of aero-engine conditions, having 18 pre-swirl nozzles, 72 receiver holes, capable of speeds up to 11 000 rpm, and giving differences between total temperature upstream of the pre-swirl nozzles and relative total temperature measured in the receiver holes of up to 26K. Pressure and temperature measurements are reported. An elementary model is developed for calculation of the cooling air delivery temperature. This accounts for the pre-swirl nozzle velocity coefficient, moments on the stationary and rotating surfaces in the pre-swirl chamber, and flows through the inner and outer seals to the chamber. The model is shown to correlate the measurements well for a range of disc speeds and pre-swirl velocity to disc speed ratios.