Low-pressure Turbine Nozzle Research Articles

Energy, exergy, economic, environmental, energy based economic, exergoeconomic and enviroeconomic (7E) analyses of a jet fueled turbofan type of aircraft engine

In this study, energy, exergy, economic, environmental, energy based economic, exergoeconomic and enviroeconomic analyses (namely the 7E analysis) are performed to the gas turbine type of aero engines used in the civil and military aviation industries. The energy efficiency of the system is determined as 19.37%, and the exergy efficiency of the system is computed as 18.25%, whereas the exergetic improvement potential rate, fuel waste exergy rate, productivity lack ratio, improved exergetic efficiency and the improvement percentage of exergetic efficiency of the system are calculated as 36.456 GJ/h, 81.75%, 447.91%, 55.02% and 201.47%, respectively. Also, the exergy efficiencies of the components of the fan, fan duct nozzle, air compressor, combustion chamber, high pressure turbine, low pressure turbine and exhaust duct nozzle are estimated as 88.11%, 96.19%, 89.62%, 49.75%, 98.76% 98.42%, and 98.61%, respectively. The annual loss energy rate of the overall system is estimated to be 16010909.67 kWh/year, while the present worth of the system is 2478509.293 US$ and the energy based economic parameter is obtained to be 6.46 kWh/US$-year. The unit exergy cost rate of the overall engine’s product is calculated as 98.441 US$/GJ and the exergy cost rate of the engine is computed to be 980.111 US$/h.

Reynolds, Mach, and Freestream Turbulence Effects on the Flow in a Low-Pressure Turbine

Abstract This article presents the large-eddy simulation (LES) of a low-pressure turbine (LPT) nozzle guide vane (NGV) for different Reynolds (Re) and Mach (Ma) numbers with or without inlet turbulence prescribed. The analysis is based on a slice of an LPT blading representative of a midspan flow, where secondary flows, hub, and shroud effects are lower. The characteristic Re of the LPT can vary by a factor of four between take-off and cruise conditions. In addition, the LPT operates at different Ma values, and the incident flow can have significant levels of turbulence due to upstream blade wakes. This article investigates numerically using LES the flow around an LPT blading with three different Reynolds number Re = 175,000 (cruise), 280,000 (mid-level altitude), and 500,000 (take-off) keeping the same characteristic Mach number Ma = 0.2 and three different Mach number Ma = 0.2, 0.5, and 0.8 keeping the same Reynolds number Re = 280,000. These different simulations are performed with 0% freestream turbulence (FST) followed by inlet turbulence (6% FST). The study focuses on the influence of these three parameters (Re, Ma, and upstream turbulence) on different flow characteristics: pressure distribution around the blade, near-wall flow behavior, loss generation, and turbulent kinetic energy (TKE) budget. The results show an earlier boundary layer separation on the aft region of the blade suction side when the Re is increased, while the increase of the Ma delays separation, similar to freestream turbulence. The TKE budget led on the different cases shows the predominant effect of the turbulent production and diffusion in the wake, the axial evolution of these different terms being relatively insensitive to Re and Ma.

Unsteady flow mechanism of the integrated aggressive inter-turbine duct in low Reynolds number condition

Aggressive inter-turbine duct, which has ultra-high bypass ratio and ultra-short axial length, is widely applied in the modern turbofan engine because it can reduce engine weight and improve low-pressure rotor dynamic characteristics. However, the aggressive inter-turbine duct that has swirling flow, wake, shock, and tip clearance leakage flow of upstream high-pressure turbine, and even has structs in its flow channel, is liable to separate, especially in high-altitude low Reynolds number (Re) condition. In addition, its downstream low-pressure turbine is on the edge of separation too. In this paper, an integrated aggressive inter-turbine duct embedded with wide-chord low-pressure turbine nozzle is adopted to eliminate the aggressive inter-turbine duct's end-wall separation. Since there are many studies on suppressing the blade suction surface's separation by upstream wake, in this study inherent wake is utilized to suppress the boundary layer separation on low-pressure turbine nozzle's suction surface in the integrated aggressive inter-turbine duct. The paper studies the unsteady flow mechanisms of the integrated aggressive inter-turbine duct (especially the separation and transition mechanisms of low-pressure turbine nozzle's suction surface boundary layer) by the computatioinal simulation method.

Impact of turbulence intensity on the unsteady flow characteristics of the integrated aggressive inter-turbine duct

Aggressive inter-turbine duct (AITD) which has ultra-short axial length and ultra-large area ratio is widely applied in the modern turbofan engine to meet the demand of higher efficiency and better low pressure rotor dynamic characteristics. However, the adverse stream-wise pressure gradient in this duct is enhanced, and there are complicate upstream and downstream flow conditions. The flow field of the AITD and its downstream low pressure turbine is seriously deteriorated and prone to separate, especially in high-altitude cruise state. The integrated AITD which integrates the AITD with strut had been proved to can restrain the traditional AITD's three-dimensional flow separation. Besides, periodic wake can suppress the downstream blade suction surface's flow separation by “calmed region” effect according to former studies. The AITD of this research taken from a real engine utilizes integrated design and inherent upstream wake to suppress the flow separation of the AITD's end wall and low pressure turbine nozzle's suction surface correspondingly. In this article, the computational simulation method is used to quantify the impact of turbulence intensity ( T u) on the integrated AITD's unsteady flow characteristics, especially the separation and transition mechanism of low pressure turbine nozzle's suction surface boundary layer. Research shows that the impact of T u on the integrated AITD's flow property depends on the balance of T u's dual effect.

Analysis of Low-Pressure Turbine Nozzle Guide Vane Failure in an Aero Gas Turbine Engine: A Computational Approach

Failure of low-pressure turbine nozzle guide vane (NGV) in an aero gas turbine engine is analyzed using computational approach. Breakage in the cooling system of the nozzle guide vane reducing the cooling effectiveness is found to be the main cause of NGV failure. Microstructure analysis also shows severe oxidation due to high temperature experienced in service leading to erosion of the NGV.

Influence of Reynolds Number on the Unsteady Aerodynamics of Integrated Aggressive Intermediate Turbine Duct

The ultra-high bypass ratio turbofan engine attracts more and more attention in modern commercial engine due to advantages of high efficiency and low Specific Fuel Consumption (SFC). One of the characteristics of ultra-high bypass ratio turbofan is the intermediate turbine duct which guides the flow leaving high pressure turbine (HPT) to low pressure turbine (LPT) at a larger diameter, and this kind of design will lead to aggressive intermediate turbine duct (AITD) design concept. Thus, it is important to design the AITD without any severe loss. From the unsteady flow’s point of view, in actual operating conditions, the incoming wake generated by HPT is unsteady which will take influence on boundary layer’s transition within the ITD and LPT. In this paper, the three-dimensional unsteady aerodynamics of an AITD taken from a real engine is studied. The results of fully unsteady three-dimensional numerical simulations, performed with ANSYS-CFX (RANS simulation with transitional model), are critically evaluated against experimental data. After validation of the numerical model, the physical mechanisms inside the flow channel are analyzed, with an aim to quantify the sensitivities of different Reynolds number effect on both the ITD and LPT nozzle. Some general physical mechanisms can be recognized in the unsteady environment. It is recognized that wake characteristics plays a crucial role on the loss within both the ITD and LPT nozzle section, determining both time-averaged and time-resolved characteristics of the flow field. Meanwhile, particular attention needs to be paid to the unsteady effect on the boundary layer of LPT nozzle’s suction side surface.

Numerical investigation of the effects of ITD length on low pressure nozzle

The advantage of high efficiency, low SFC (Specific Fuel Consumption), ultra-high bypass ratio turbofan engine attracts more and more attention in modern commercial engine. The intermediate turbine duct (ITD), which connects high pressure turbine (HPT) with low pressure turbine (LPT), has a critical impact on the overall performance of turbine by guiding flow coming from HPT to LPT without too much loss. Therefore, it becomes more and more urgent to master the technique of designing aggressive, even super-aggressive ITD. Much more concerns have been concentrated on the duct. However, in order to further improve turbine, LPT nozzle is arranged into ITD to shorten low pressure axle. With such design concept, it is obvious that LPT nozzle flow field is easily influenced by upstream duct structure, but receives much less interests on the contrary. In this paper, numerical method is used to investigate the effects of length of ITD with upstream swirl blades on LPT nozzle. Nine models with the same swirl and nozzle blades, while the length of ITD is the only parameter to be changed, will be discussed. Finally, several conclusions and advices for designers are summarized. After changing axial length of ducts, inlet and outlet flow field of nozzle differs, correspondingly. On the other hand, the shearing stress on nozzle blade (suction and pressure) surface presents individual feature under various inlet flow. In addition to that, “Clocking-like effect” is described in this paper, which will contribute much to the pressure loss and should be paid enough attention.

Functional Validation of K-Type (NiCr-NiMn) Thin Film Thermocouple on Low Pressure Turbine Nozzle Guide Vane (LPT NGV) of Gas Turbine Engine

This study presents a concerted approach developed for experimental measurement of surface temperature of critical aeroengine components using a non non-intrusive sensor that is compatible with structural integrity and endurance requirements of high temperature environments. Contrary to wire type thermocouples that cause structural degradation and aerodynamic disturbance in the flow path, the present study proposes a thin film thermocouple (TFTC) that is deposited using electron beam (E-beam) evaporation process. The basic experimentation and proof-of-concept studies are carried out to suit the deposition of K-Type TFTC on a turbine nozzle guide vane that is made of nickel based super alloy. The performance of TFTC is compared to that of wire type thermocouples. The Seebeck co-efficient of the developed K-Type TFTC is found to be 42 μV/°C, with a time constant and drift of 1.11784 ms and 0.4 °C/hour respectively. Based on the feasibility studies and characterization results of prototype TFTC, the deposition of similar TFTC was carried out on low pressure turbine nozzle guide vane (LPT NGV) of an aeroengine using same optimized parameters and procedures. The results presented vindicate the application of the proposed methodology for a developmental aero gas turbine engine.

Failure Analysis of Nozzle Guide Vane of a Low Pressure Turbine in an Aero Gas Turbine Engine

Failure of low pressure turbine nozzle guide vane (NGV) in an aero gas turbine engine is analyzed to determine its root cause. Forensic and metallurgical investigations are carried out on the NGV failed as well as the failed components of the downstream modules. Failure in the cooling system in the NGV due to crack in the sealing plate was found to be the cause of NGV getting burnt. This failure has caused extensive damages in low pressure turbine modules. Remedial measures are also suggested to prevent such failures.

Modeling Techniques for a Computational Efficient Dynamic Turbofan Engine Model

A transient two-stream engine model has been developed. Individual component models developed exclusively in MATLAB/Simulink including the fan, high pressure compressor, combustor, high pressure turbine, low pressure turbine, plenum volumes, and exit nozzle have been combined to investigate the behavior of a turbofan two-stream engine. Special attention has been paid to the development of transient capabilities throughout the model, increasing physics model, eliminating algebraic constraints, and reducing simulation time through enabling the use of advanced numerical solvers. The lessening of computation time is paramount for conducting future aircraft system-level design trade studies and optimization. The new engine model is simulated for a fuel perturbation and a specified mission while tracking critical parameters. These results, as well as the simulation times, are presented. The new approach significantly reduces the simulation time.

Time-Averaged and Time-Accurate Aerodynamic Effects of Forward Rotor Cavity Purge Flow for a High-Pressure Turbine—Part I: Analytical and Experimental Comparisons

The effect of rotor purge flow on the unsteady aerodynamics of a high-pressure turbine stage operating at design corrected conditions has been investigated, both experimentally and computationally. The experimental configuration consisted of a single-stage high-pressure turbine with a modern film-cooling configuration on the vane airfoil and the inner and outer end wall surfaces. Purge flow was introduced into the cavity located between the high-pressure vane and the high-pressure disk. The high-pressure blades and the downstream low-pressure turbine nozzle row were not cooled. All of the hardware featured an aerodynamic design typical of a commercial high-pressure ratio turbine and the flow path geometry was representative of the actual engine hardware. In addition to instrumentation in the main flow path, the stationary and rotating seals of the purge flow cavity were instrumented with high frequency response flush-mounted pressure transducers and miniature thermocouples in order to measure the flow field parameters above and below the angel wing. Predictions of the time-dependent flow field in the turbine flow path were obtained using FINE/Turbo, a three-dimensional Reynolds-averaged Navier–Stokes computational fluid dynamics CFD code that had the capability to perform both a steady and unsteady analysis. The steady and unsteady flow fields throughout the turbine were predicted using a three blade-row computational model that incorporated the purge flow cavity between the high-pressure vane and disk. The predictions were performed in an effort to mimic the design process with no adjustment of boundary conditions to better match the experimental data. The time-accurate predictions were generated using the harmonic method. Part I of this paper concentrates on the comparison of the time-averaged and time-accurate predictions with measurements in and around the purge flow cavity. The degree of agreement between the measured and predicted parameters is described in detail, providing confidence in the predictions for the flow field analysis that will be provided in Part II.

Time-Averaged and Time-Accurate Aerodynamic Effects of Rotor Purge Flow for a Modern, One and One-Half Stage High-Pressure Turbine—Part II: Analytical Flow Field Analysis

The detailed mechanisms of purge flow interaction with the hot-gas flow path were investigated using both unsteady computationally fluid dynamics (CFD) and measurements for a turbine operating at design corrected conditions. This turbine consisted of a single-stage high-pressure turbine and the downstream, low-pressure turbine nozzle row with an aerodynamic design equivalent to actual engine hardware and typical of a commercial, high-pressure ratio, transonic turbine. The high-pressure vane airfoils and inner and outer end walls incorporated state-of-the-art film cooling, and purge flow was introduced into the cavity located between the high-pressure vane and disk. The flow field above and below the blade angel wing was characterized by both temperature and pressure measurements. Predictions of the time-dependent flow field were obtained using a three-dimensional, Reynolds-averaged Navier–Stokes CFD code and a computational model incorporating the three blade rows and the purge flow cavity. The predictions were performed to evaluate the accuracy obtained by a design style application of the code, and no adjustment of boundary conditions was made to better match the experimental data. Part I of this paper compared the predictions to the measurements in and around the purge flow cavity and demonstrated good correlation. Part II of this paper concentrates on the analytical results, looking at the primary gas path ingestion mechanism into the cavity as well as the effects of the rotor purge on the upstream vane and downstream rotor aerodynamics and thermodynamics. Ingestion into the cavity is driven by high static pressure regions downstream of the vane, high-velocity flow coming off the pressure side of the vane, and the blade bow waves. The introduction of the purge flow is seen to have an effect on the static pressure of the vane trailing edge in the lower 5% of span. In addition, the purge flow is weak enough that upon exiting the cavity, it is swept into the mainstream flow and provides no additional cooling benefits on the platform of the rotating blade.

Comparison of Harmonic and Time Marching Unsteady Computational Fluid Dynamics Solutions With Measurements for a Single-Stage High-Pressure Turbine

The unsteady aerodynamics of a single-stage high-pressure turbine has been the subject of a study involving detailed measurements and computations. Data and predictions for this experiment have been presented previously, but the current study compares predictions obtained using the nonlinear harmonic simulation method to results obtained using a time-marching simulation with phase-lag boundary conditions. The experimental configuration consisted of a single-stage high-pressure turbine (HPT) and the adjacent, downstream, low-pressure turbine nozzle row (LPV) with an aerodynamic design that is typical to that of a commercial high-pressure ratio HPT and LPV. The flow path geometry was equivalent to engine hardware and operated at the proper design-corrected conditions to match cruise conditions. The high-pressure vane and blade were uncooled for these comparisons. All three blade rows are instrumented with flush-mounted, high-frequency response pressure transducers on the airfoil surfaces and the inner and outer flow path surfaces, which include the rotating blade platform and the stationary shroud above the rotating blade. Predictions of the time-dependent flow field for the turbine flow path were obtained using a three-dimensional, Reynolds-averaged Navier–Stokes computational fluid dynamics (CFD) code. Using a two blade row computational model of the turbine flow path, the unsteady surface pressure for the high-pressure vane and rotor was calculated using both unsteady methods. The two sets of predictions are then compared to the measurements looking at both time-averaged and time-accurate results, which show good correlation between the two methods and the measurements. This paper concentrates on the similarities and differences between the two unsteady methods, and how the predictions compare with the measurements since the faster harmonic solution could allow turbomachinery designers to incorporate unsteady calculations in the design process without sacrificing accuracy when compared to the phase-lag method.

Turbine Airfoil Optimization Using Quasi-3D Analysis Codes

A new approach to optimize the geometry of a turbine airfoil by simultaneously designing multiple 2D sections of the airfoil is presented in this paper. The complexity of 3D geometry modeling is circumvented by generating multiple 2D airfoil sections and constraining their geometry in the radial direction using first- and second-order polynomials that ensure smoothness in the radial direction. The flow fields of candidate geometries obtained during optimization are evaluated using a quasi-3D, inviscid, CFD analysis code. An inviscid flow solver is used to reduce the execution time of the analysis. Multiple evaluation criteria based on the Mach number profile obtained from the analysis of each airfoil cross-section are used for computing a quality metric. A key contribution of the paper is the development of metrics that emulate the perception of the human designer in visually evaluating the Mach Number distribution. A mathematical representation of the evaluation criteria coupled with a parametric geometry generator enables the use of formal optimization techniques in the design. The proposed approach is implemented in the optimal design of a low-pressure turbine nozzle.

Averaged and Time-Dependent Aerodynamics of a High Pressure Turbine Blade Tip Cavity and Stationary Shroud: Comparison of Computational and Experimental Results

The unsteady aero-dynamics of a single-stage high-pressure turbine blade operating at design corrected conditions has been the subject of a thorough study involving detailed measurements and computations. The experimental configuration consisted of a single-stage high-pressure turbine and the adjacent, downstream, low-pressure turbine nozzle row. All three blade-rows were instrumented at three spanwise locations with flush-mounted, high-frequency response pressure transducers. The rotor was also instrumented with the same transducers on the blade tip and platform and the stationary shroud was instrumented with pressure transducers at specific locations above the rotating blade. Predictions of the time-dependent flow field around the rotor were obtained using MSU-TURBO, a three-dimensional (3D), nonlinear, computational fluid dynamics (CFD) code. Using an isolated blade-row unsteady analysis method, the unsteady surface pressure for the high-pressure turbine rotor due to the upstream high-pressure turbine nozzle was calculated. The predicted unsteady pressure on the rotor surface was compared to the measurements at selected spanwise locations on the blade, in the recessed cavity, and on the shroud. The rig and computational models included a flat and recessed blade tip geometry and were used for the comparisons presented in the paper. Comparisons of the measured and predicted static pressure loading on the blade surface show excellent correlation from both a time-average and time-accurate standpoint. This paper concentrates on the tip and shroud comparisons between the experiments and the predictions and these results also show good correlation with the time-resolved data. These data comparisons provide confidence in the CFD modeling and its ability to capture unsteady flow physics on the blade surface, in the flat and recessed tip regions of the blade, and on the stationary shroud.

A Classifiers Based Optimization Technique for Designing Turbine Airfoils

The primary focus of this work is in the development of an evolutionary optimization technique which gets progressively 'smarter' during the optimization process by learning from computed domain knowledge. In the approach, the influence of the design variables on the problem solution is recognized, and the knowledge learned is then generalized to dynamically create or change design rules during optimization. This technique, when applied to a constrained optimization problem, shows progressive improvement in convergence of search, as successive generations of rules evolve by learning from the environment. This method is applied to a complex aerodynamic optimization problem involving turbine airfoil design. In this investigation, the 3D geometry of an airfoil is optimized by simultaneously optimizing multiple 2D slices of the airfoil. Results from the optimization of a low pressure turbine nozzle are presented in the paper. Results obtained using standard numerical optimization techniques are also presented for comparison purposes.