Paul F. Beard

Turbine Efficiency Measurement System for the QinetiQ Turbine Test Facility

A turbine efficiency measurement system has been developed and installed on the turbine test facility (TTF) at QinetiQ Farnborough. The TTF is an engine-scale short-duration (0.5s run time) rotating transonic facility, which can operate as either single stage (HP vane and rotor) or 112 stage (HP stage with IP or LP vane). The current MT1 HP stage is highly loaded and unshrouded and is therefore relevant to current design trends. Implementation of the efficiency measurement system forms part of the EU Turbine Aero-Thermal External Flows (TATEF II) program. The following aspects of the efficiency measurement system are discussed in this paper: mass-flow rate measurement, power measurement by direct torque measurement, turbine inlet and exit area traverse measurement systems, computation of efficiency by mass weighting, and uncertainty analysis of the experimentally determined turbine efficiency. The calibration of the mass-flow rate and torque measurement systems are also discussed. Emphasis was placed on the need for a low efficiency precision uncertainty, so that changes in efficiency associated with turbine inlet temperature distortion and swirl can be resolved with good accuracy. Measurements with inlet flow distortion form part of the TATEF II program and will be the subject of forthcoming publications.

Unsteady Flow Phenomena in Turbine Rim Seals

While turbine rim sealing flows are an important aspect of turbomachinery design, affecting turbine aerodynamic performance and turbine disc temperatures, the present understanding and predictive capability for such flows is limited. The aim of the present study is to clarify the flow physics involved in rim sealing flows and to provide high quality experimental data for use in evaluation of CFD models. The seal considered is similar to a chute seal previously investigated by other workers, and the study focuses on the inherent unsteadiness of rim seal flows, rather than unsteadiness imposed by the rotating blades. Unsteady pressure measurements from radially and circumferentially distributed transducers are presented for flow in a rotor-stator disc cavity and the rim seal without imposed external flow. The test matrix covered ranges in rotational Reynolds number, Re∅, and non-dimensional flow rate, , of 2.2 –3.0x106 and 0 – 3.5x103 respectively. Distinct frequencies are identified in the cavity flow and detailed analysis of the pressure data associates these with large scale flow structures rotating about the axis. This confirms the occurrence of such structures as predicted in previously published CFD studies and provides new data for detailed assessment of CFD models.

Effect of Combustor Swirl on Transonic High Pressure Turbine Efficiency

This paper presents an experimental and computational study of the effect of inlet swirl on the efficiency of a transonic turbine stage. The efficiency penalty is approximately 1%, but it is argued that this could be recovered by correct design. There are attendant changes in capacity, work function, and stage total-to-total pressure ratio, which are discussed in detail. Experiments were performed using the unshrouded MT1 high-pressure turbine installed in the Oxford Turbine Research Facility (OTRF) (formerly at QinetiQ Farnborough): an engine scale, short duration, rotating transonic facility, in which M, Re, Tgas=Twall, and N= ffiffiffiffiffiffiffi T01 p are matched to engine conditions. The research was conducted under the EU Turbine Aero-Thermal External Flows (TATEF II) program. Turbine efficiency was experimentally determined to within bias and precision uncertainties of approximately 61.4% and 60.2%, respectively, to 95% confidence. The stage mass flow rate was metered upstream of the turbine nozzle, and the turbine power was measured directly using an accurate strain-gauge based torque measurement system. The turbine efficiency was measured experimentally for a condition with uniform inlet flow and a condition with pronounced inlet swirl. Full stage computational fluid dynamics (CFD) was performed using the Rolls-Royce Hydra solver. Steady and unsteady solutions were conducted for both the uniform inlet baseline case and a case with inlet swirl. The simulations are largely in agreement with the experimental results. A discussion of discrepancies is given. [DOI: 10.1115/1.4024841]

Impact of Severe Temperature Distortion on Turbine Efficiency

This paper presents an experimental and computational study of the effect of severe inlet temperature distortion (hot streaks) on the efficiency of the MT1 HP turbine, which is a highly-loaded unshrouded transonic design. The experiments were performed in the Oxford Turbine Research Facility (OTRF) (formerly the TTF at QinetiQ Farnborough): an engine scale, short duration, rotating transonic facility, in which M, Re, Tgas/Twall and N/T01 are matched to engine conditions. The research formed part of the EU Turbine Aero-Thermal External Flows (TATEF II) program. An advanced second generation temperature distortion simulator was developed for this investigation, which allows both radial and circumferential temperature profiles to be simulated. A pronounced profile was used for this study. The system was novel in that it was designed to be compatible with an efficiency measurement system which was also developed for this study. To achieve low uncertainty (bias and precision errors of approximately 1.5% and 0.2% respectively, to 95% confidence), the mass flow rate of the hot and cold streams used to simulate temperature distortion were independently metered upstream of the turbine nozzle using traceable measurement techniques. Turbine power was measured directly with an accurate torque transducer. The efficiency of the test turbine was evaluated experimentally for a uniform inlet temperature condition, and with pronounced temperature distortion. Mechanisms for observed changes in the turbine exit flow field and efficiency are discussed. The data are compared in terms of flow structure to full stage computational fluid dynamics (CFD) performed using the Rolls Royce Hydra code.

Experimental and computational fluid dynamics investigation of the efficiency of an unshrouded transonic high pressure turbine

This article presents an experimental and computational study of the efficiency of an unshrouded transonic turbine. This research formed part of the EU Turbine Aero-Thermal External Flows II programme. The experiments were performed in the Oxford Turbine Research Facility (previously the Turbine Test Facility at QinetiQ, Farnborough). This facility is an engine scale, short duration, rotating transonic facility, in which M, Re, T gas / T wall , and N / T 01 are matched to engine conditions. For these experiments, the MT1 turbine stage was installed. Historically, turbine efficiency measurements are conducted in steady state adiabatic facilities. However, short-duration facilities allow simultaneous aerodynamic and heat transfer measurements with a significant reduction in cost. An efficiency measurement system was developed for this investigation, and this is briefly described. The system allows efficiency to be evaluated to bias and precision errors of approximately ±1.45 per cent and ±0.16 per cent, respectively, to 95 per cent confidence. The results of accurate area surveys of the turbine inlet and exit flows are presented and discussed. At the turbine exit, data were taken at two traverse planes, approximately 0.5 and 4.5 rotor axial chords downstream of the rotor. The turbine efficiency was experimentally evaluated based on the data at both planes, using a number of mixing models, which are discussed and compared. The experimental result of turbine efficiency is also compared to that estimated from a mean-line prediction. Full-stage steady and unsteady computational fluid dynamics of the experiment using the Rolls-Royce HYDRA code was conducted and is also presented. The predicted and measured rotor exit flow-fields are compared at both downstream traverse planes.

Numerical Studies of Turbine Rim Sealing Flows on a Chute Seal Configuration

This paper presents CFD (computational fluid dynamics) modelling of a chute type rim seal that has been previously experimentally investigated. The study focuses on inherent large-scale unsteadiness rather than that imposed by vanes and blades or external flow. A large-eddy simulation (LES) solver is validated for a pipe flow test case and then applied to the chute rim seal rotor/stator cavity. LES, Reynolds-averaged Navier-Stokes (RANS) and unsteady RANS (URANS) models all showed reasonable agreement with steady measurements within the disc cavity, but only the LES shows unsteadiness at a similar distinct peak frequency to that found in the experiment, at 23 times the rotational frequency. However, there are some significant differences between unsteadiness predicted and the measurements, and possible causes of these are discussed.

Advanced Numerical Simulation of Turbine Rim Seal Flows and Consideration for RANS Turbulence Modelling

This paper reports large-eddy simulations (LES) and unsteady Reynolds-averaged Navier-Stokes (URANS) calculations of a turbine rim seal configuration previously investigated experimentally. The configuration does not include any vanes, blades or external flows, but investigates inherent unsteady flow features and limitations of CFD modelling identified in engine representative studies. Compared to RANS and URANS CFD models, a sector LES model showed closer agreement with mean pressure measurements. LES models also showed agreement with measured pressure frequency spectra, but discrepancies were found between the LES and experiment in the speed and the circumferential lobe number of the unsteady flow structures. Sensitivity of predictions to modelling assumptions and differences with experimental data are investigated through CFD calculations considering sector size, interaction between the rim cavity and the inner cavity, outer annulus boundary conditions, and the coolant mass flow. Significant sensitivity to external flow conditions, which could contribute to differences with measurements, is shown, although some discrepancies remain. Further detailed analysis of the CFD solutions is given illustrating the complex flow physics. Possible improvement of a steady RANS model using a priori analysis of LES was investigated, but showed a rather small improvement in mean pressure prediction.