Development of Experimental and Numerical Methods for the Analysis of Active Clearance Control Systems

2020 ◽  
Author(s):  
Riccardo Da Soghe ◽  
Lorenzo Mazzei ◽  
Lorenzo Tarchi ◽  
Lorenzo Cocchi ◽  
Alessio Picchi ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Current Trend ◽  
Turbulence Models ◽  
Pressure Head ◽  
Test Sample ◽  
Low Pressure ◽  
Numerical Approach ◽  
Tip Clearance ◽  
Target Plate ◽  
Clearance Control

Abstract The ever increasing performance requirements of modern aero-engines necessitate the development of effective ways to improve efficiency and reduce losses. Casing temperature control is particularly critical from this point of view, since thermal expansion directly affects the blade tip clearance and thus the associated leakages. To limit the turbine tip flows, Active Clearance Control (ACC) systems have been implemented over the last decades. These systems are usually based upon impingement cooling, generated by a series of perforated manifolds enclosing the turbine casing. When dealing with aeroengine low pressure turbines, the current trend in increasing the engine by-pass ratio, so as to enhance the system propulsive efficiency, pushes the limits of ACC traditional design performance. The reduction of the pressure head at the ACC system inlet requires lower nozzle-to-target distances as well as denser impingement arrays to compensate the reduction of the jets’ Reynolds number. Literature correlations for the impingement heat transfer coefficient estimation are then out of their confidence range and also RANS numerical approaches appear not suitable for future ACC designs. In this work, methodologies for the development of accurate and reliable tools to determine the heat transfer characteristics of low pressure ACC systems are presented. More precisely, this paper describes a custom designed finite difference procedure capable of solving the inverse conduction problem on the target plate of a test sample. The methodology was successfully applied to an experimental setup for the measurement of the thermal loads on a target plate of a representative low pressure ACC impinging system. The experimental data is then used to validate a suitable numerical approach. Results show that RANS model is not able to mimic the experimental trends, while scale-resolving turbulence models provide a good reconstruction of the experimental evidences, thus allowing to obtain a correct interpretation of flow and thermal phenomena for ACC systems.

Development of Experimental and Numerical Methods for the Analysis of Active Clearance Control Systems

2020 ◽  
Author(s):  
Riccardo Da Soghe ◽  
Lorenzo Mazzei ◽  
Lorenzo Tarchi ◽  
Lorenzo Cocchi ◽  
Alessio Picchi ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Current Trend ◽  
Turbulence Models ◽  
Pressure Head ◽  
Test Sample ◽  
Low Pressure ◽  
Numerical Approach ◽  
Impingement Heat Transfer ◽  
Aero Engines ◽  
Clearance Control

Abstract To increase the performance of modern aero-engines, the control of blade tip leakages in mandatory. In the last decades, this task was performed by Active Clearance Control (ACC) systems, which manage the casing thermal deformations and the associated losses via cooling jets impinging on the casing outer surface. The current trend of increasing the engine by-pass ratio pushes the limits of ACC traditional design, since a lower pressure head is available for the generation of the jets. Therefore, denser jet patterns and lower jet-to-target distances are required to compensate the reduction of the jets' Reynolds number. Literature correlations for the estimation of impingement heat transfer are then out of their confidence range, and also RANS numerical approaches appear not to be suitable. In this work, methodologies for the development of accurate and reliable tools to determine the heat transfer characteristics of low pressure ACC systems are presented. More precisely, this paper describes a custom designed finite difference procedure capable of solving the inverse conduction problem on the target plate of a test sample. The methodology was successfully applied to an experimental setup for the measurement of the heat transfer features of a representative low pressure ACC system. The experimental data was then used to validate a suitable numerical approach. Results show that RANS is not able to mimic the experimental trends, while scale-resolving turbulence models provide a good reconstruction of the experimental evidences, thus allowing to obtain a correct interpretation of flow and thermal phenomena.

scholarly journals A Comparison of Single-Entry and Multiple-Entry Casing Impingement Manifolds for Active Thermal Tip Clearance Control

2021 ◽  
Author(s):  
Priyanka Dhopade ◽  
Benjamin Kirollos ◽  
Peter Ireland ◽  
Leo Lewis
Keyword(s):  
Heat Transfer ◽  
Numerical Approach ◽  
Tip Clearance ◽  
Advantages And Disadvantages ◽  
Entry Points ◽  
Single Entry ◽  
Current Production ◽  
Enhancing Heat Transfer ◽  
The Impact ◽  
Clearance Control

In this paper, we investigate the aerothermal performance of active clearance control (ACC) methods that use impingement as a means of enhancing heat transfer. We describe a numerical approach to compare the aerothermal performance of two circumferential impingement manifold supply designs that vary in the number of entry points to the manifold channel. For a 180°-sector, the first design has a single entry point, while the second has two. Both the single-entry and multiple-entry systems analysed in this paper are idealised version of ACC systems in current production engines. Aerothermal performance is quantitatively assessed on the basis of the HTC distribution, driving temperature difference for heat transfer between the jet and casing wall, and total pressure loss within the HPT ACC system. We conclude key advantages and disadvantages of each system based on the impact on engine efficiency, response time, ease of optimisation and implications for weight, cost and complexity of the design.

Effect of Jet-to-Jet Distance and Pipe Position on Flow and Heat Transfer Features of Active Clearance Control Systems

2021 ◽  
Author(s):  
Lorenzo Cocchi ◽  
Alessio Picchi ◽  
Bruno Facchini ◽  
Riccardo Da Soghe ◽  
Lorenzo Mazzei ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Metal Plate ◽  
Target Distance ◽  
Target Plate ◽  
Ir Camera ◽  
Supply Pipe ◽  
Heating Up ◽  
Clearance Control

Abstract The goal of the present work is to investigate the effect of supply pipe position on the heat transfer features of various active clearance control (ACC) geometries, characterized by different jet-to-jet distances. All geometries present 0.8 mm circular impingement holes arranged in a single row. The jets generated by such holes cool a flat target surface, which is replicated by a metal plate in the experimental setup. Measurements are performed using the steady-state technique, obtained by heating up the target plate thanks to an electrically heated Inconel foil applied on the side of the target opposite to the jets. Temperature is also measured on this side by means of an IR camera. Heat transfer is then evaluated thanks to a custom designed finite difference procedure, capable of solving the inverse conduction problem on the target plate. The effect of pipe positioning is studied in terms of pipe-to-target distance (from 3 to 11 jet diameters) and pipe orientation (i.e. rotation around its axis, from 0° to 40° with respect to target normal direction), while the investigated jet Reynolds numbers range from 6000 to 10000. The obtained results reveal that heat transfer is maximized for a given pipe-to-target distance, dependent on both jet-to-jet distance and target surface extension. Pipe rotation also affects the cooling features in a non-monotonic way, suggesting the existence of different flow regimes related to jet inclination.

scholarly journals Influences of Tip Cooling Injection on Tip Clearance Control at Design and Off-Design Incidences

2009 ◽  
Vol 2009 ◽  
pp. 1-12 ◽  
Author(s):  
Maosheng Niu ◽  
Shusheng Zang
Keyword(s):  
Heat Transfer ◽  
Tip Clearance ◽  
Air Injection ◽  
Turbine Cascade ◽  
Tip Clearance Flow ◽  
Clearance Flow ◽  
Blade Tip ◽  
Design Value ◽  
Tip Injection ◽  
Clearance Control

A numerical investigation has been performed to study the influences of cooling injection from the blade tip surface on controlling tip clearance flow in an unshrouded, high-turning axial turbine cascade. Emphasis is put on the analysis of the effectiveness of tip injection when the approaching flow is at design and off-design incidences. A total of three incidence angles are investigated, 7.4°, 0°, 0°, 0°, and 7.6°, 0° relative to the design value. The results indicate that even at the off-design incidences, tip injection can also act as an obstruction to the tip clearance flow and weaken the interaction between the passage flow and the tip clearance flow. It is also found that tip injection causes the tip clearance loss to be less sensitive to the incidences. Moreover, with injection, at all these incidences the heat transfer conditions are improved significantly on the blade tip surface in the middle and aft parts of blade. Thus, tip injection is proved to be an effective method of controlling tip clearance flow, even at off-design conditions. Beside that, an indirect empirical correlation is observed to be able to perform well in predicting the losses induced by tip clearance flow at design and off-design conditions, no matter whether air injection is active or not.

Technique for Adequate CFD-Modeling of the Pump With Hydro-Drive of the Low-Pressure Stage

2016 ◽  
Author(s):  
Vasilii M. Zubanov ◽  
Leonid S. Shabliy ◽  
Alexander V. Krivcov ◽  
Valeriy N. Matveev
Keyword(s):  
Rotational Speed ◽  
Cfd Simulation ◽  
Turbulence Models ◽  
Pressure Head ◽  
Low Pressure ◽  
Inlet Pressure ◽  
Cfd Modeling ◽  
Future Research ◽  
Rotor Speed ◽  
Pressure Stage

This article describes the technique for CFD-modeling of a powerful two-stage pump with the following main parameters: main rotor speed is 13,300 rpm, inlet pressure is 0.2 MPa, pressure head is more than 3,000 meters with mass flow of 250 kg/s. The main feature of investigated pump is the hydro-drive of the low-pressure stage of turbine with variable rotational speed. There are two highlights in this work in comparison with the previous ones. The first one is how to choose the rotating speed of hydro-turbine. The second one is the CFD-modeling of cavitation processes. The core part of proposed technique is the determination of rotational speed during CFD-simulation by special methodology. Another feature is the cavitation modeling to be sure that there is no cavitation in pre-pump at quite low inlet pressure and variable rotor speed. Also, recommendations about program tools (ANSYS CFX, NUMECA AutoGrid5, ANSYS ICEM CFD) are a significant part of the discussed technique, as well as modeling features (fluid domain restriction, meshing, turbulence models choosing, convergence checking, post-processing). The adequacy of CFD-model was evaluated by comparing predicted characteristics of the pump with the experimental ones derived from the test rig. The differences amounted to less than 10%. The obtained technique can be used in the future research for performance improving and efficiency increasing of pumps with hydro-drive of the low-pressure stage by CFD-tools.

Parametric Design and Optimization for Impingement Jet Heat Transfer Over Dimpled Topologies

2012 ◽  
Author(s):  
Deepchand Singh Negi ◽  
Arvind Pattamatta
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Average Nusselt Number ◽  
Parametric Design ◽  
Turbulence Models ◽  
Impinging Jet ◽  
Initial Section ◽  
Geometric Parameters ◽  
Complex Flow ◽  
Target Plate

A large number of experimental and theoretical studies investigating heat transfer of impinging jet and jet arrays exist in the literature. However, there are only a few experimental and numerical studies that consider the heat transfer performance of the impinging jet and jet array over complex impinging surface topologies. In spite of these studies, several other factors concerning the dimpled target plate configuration such as dimple height, diameter, pitch spacing between dimples, and their effects on the heat transfer coefficient have not yet been well apprehended. The purpose of the present study is to address some of these aspects through a detailed computational investigation of 3D impinging jet interaction on dimpled target plates. The initial section of the study is focused on the evaluation of different turbulence models in capturing the complex flow features associated with dimpled topology. These models are validated for Nusselt number against previous experimental data in literature. This is followed by a parametric study in which geometric parameters of the dimpled target plate such as dimple diameter, pitch spacing between dimples and dimple height are varied to understand their role on heat transfer enhancement. The final section of the study deals with the optimization of the above geometric parameters based on three factorial design of parametric space. Results from these designed simulations are used to construct a surrogate model based on response surface analysis and the optimized configuration is determined. The objective functions for optimization include maximizing the average Nusselt number, Nuavg, and minimizing the deviation of maximum Nusselt number, Numax-sd. With respect to the reference configuration there is 12% and 8.58 % increase in the average Nusselt number values for the optimized case corresponding to Reynolds number of 3000 and 8200 respectively. Enhancement in terms of Nusselt number is observed with the dimpled target plate over corresponding non dimpled target plates.

Effect of Jet-to-Jet Distance and Pipe Position On Flow and Heat Transfer Features of Active Clearance Control Systems

2021 ◽  
Author(s):  
Lorenzo Cocchi ◽  
Alessio Picchi ◽  
Bruno Facchini ◽  
Riccardo Da Soghe ◽  
Lorenzo Mazzei ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Metal Plate ◽  
Target Distance ◽  
Target Plate ◽  
Ir Camera ◽  
Supply Pipe ◽  
Heating Up ◽  
Clearance Control

Abstract The goal of the present work is to investigate the effect of supply pipe position on the heat transfer features of various active clearance control (ACC) geometries, characterized by different jet-to-jet distances. All geometries present 0.8 mm circular impingement holes arranged in a single row. The jets generated by such holes cool a flat target surface, which is replicated by a metal plate in the experimental setup. Measurements are performed using the steady-state technique, obtained by heating up the target plate thanks to an electrically heated Inconel foil applied on the side of the target opposite to the jets. Temperature is also measured on this side by means of an IR camera. Heat transfer is then evaluated thanks to a custom designed finite difference procedure, capable of solving the inverse conduction problem on the target plate. The effect of pipe positioning is studied in terms of pipe-to-target distance (from 3 to 11 jet diameters) and pipe orientation (i.e. rotation around its axis, from 0° to 40° with respect to target normal direction), while the investigated jet Reynolds numbers range from 6000 to 10000. The obtained results reveal that heat transfer is maximized for a given pipe-to-target distance, dependent on both jet-to-jet distance and target surface extension. Pipe rotation also affects the cooling features in a non-monotonic way, suggesting the existence of different flow regimes related to jet inclination.

Aircraft Engine Performance Improvement by Active Clearance Control in Low Pressure Turbines

2009 ◽  
Author(s):  
Christian Knipser ◽  
Wolfgang Horn ◽  
Stephan Staudacher
Keyword(s):  
Fuel Consumption ◽  
Performance Improvement ◽  
Engine Performance ◽  
Aircraft Engine ◽  
Low Pressure ◽  
Performance Model ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Cooling Air ◽  
Clearance Control

In order to minimize fuel consumption, resulting in reduced operating costs and lower environmental impact, turbofan engines must be of high overall efficiency. The design of the low pressure turbine (LPT) plays a significant role in the development of such engines. During a flight mission changing operating conditions (spool speeds, temperatures, pressures, etc.) cause altering magnitudes of the LPT tip clearance, leading to a decrease in LPT performance. As minimum clearances usually do not occur in steady state cruise condition — the major flight condition concerning fuel consumption — active measures to minimize radial tip clearance (ACC – active clearance control) must be incorporated to achieve a considerable reduction in fuel consumption over the whole flight mission. Actively minimizing radial tip clearance by manipulating the turbine casing requires energy in terms of cooling air (thermal ACC), electrical or hydraulical power (mechanical ACC). The cooling air or the power respectively must be provided by the engine itself, thus partly compensating the benefit gained through the improved LPT behavior. This paper investigates the potential of ACC systems from a whole engine perspective. The approach uses a performance model of a state-of-the-art high bypass turbofan engine with a thermal LPT-ACC system to assess the different benefits and detriments of an enhanced ACC. The overall benefit in TSFC for the simulated engine is compared to measured data of other engines indicating an increase of ACC effectiveness with increasing bypass ratios. To compensate deterioration losses due to single rub-in events, closed-loop controls are required. A tip clearance sensor allows the ACC to adapt to an individual engine. As thermal ACC systems show an optimum benefit with a corresponding optimum ACC cooling air flow, the additional TSFC benefit by compensating deterioration is limited. The achievable overall performance improvement is evaluated for different control loops. Mechanical ACC systems bear the highest potential of eliminating clearance losses, while only minor improvements can be made for thermal ACC systems.

scholarly journals Heat Transfer on a Film-Cooled Rotating Blade Using a Two-Equation Turbulence Model

1998 ◽  
Vol 4 (3) ◽  
pp. 201-216 ◽  
Author(s):  
Vijay K. Garg
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Leading Edge ◽  
Equation Model ◽  
Tip Clearance ◽  
Suction Surface ◽  
Pressure Surface ◽  
Rotating Blade

A three-dimensional Navier–Stokes code has been used to compare the heat transfer coefficient on a film-cooled, rotating turbine blade. The blade chosen is the ACE rotor with five rows containing 93 film cooling holes covering the entire span. This is the only filmcooled rotating blade over which experimental data is available for comparison. Over 2.278 million grid points are used to compute the flow over the blade including the tip clearance region, using Coakley'sq-ωturbulence model. Results are also compared with those obtained by Garg and Abhari (1997) using the zero-equation Baldwin-Lomax (B-L) model. A reasonably good comparison with the experimental data is obtained on the suction surface for both the turbulence models. At the leading edge, the B-L model yields a better comparison than theq-ωmodel. On the pressure surface, however, the comparison between the experimental data and the prediction from either turbulence model is poor. A potential reason for the discrepancy on the pressure surface could be the presence of unsteady effects due to stator-rotor interaction in the experiments which are not modeled in the present computations. Prediction using the two-equation model is in general poorer than that using the zero-equation model, while the former requires at least 40% more computational resources.

scholarly journals A Comparison of Single-Entry and Multiple-Entry Casing Impingement Manifolds for Active Thermal Tip Clearance Control

2021 ◽  
Vol 6 (2) ◽  
pp. 10
Author(s):  
Priyanka Dhopade ◽  
Benjamin Kirollos ◽  
Peter Ireland ◽  
Leo Lewis
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Heat Transfer Coefficient ◽  
Control System ◽  
Tip Clearance ◽  
Feed System ◽  
High Pressure Turbine ◽  
Aero Engine ◽  
Single Entry ◽  
Clearance Control

In this paper, we compare using computational fluid dynamics the aero-thermal performance of two candidate casing manifolds for supplying an impingement-actuated active tip clearance control system for an aero-engine high-pressure turbine. The two geometries are (a) single-entry: an annular manifold fed at one circumferential location; (b) multiple-entry: a casing manifold split into four annular sectors, with each sector supplied separately from an annular ring main. Both the single-entry and multiple-entry systems analysed in this paper are idealised versions of active clearance control systems in current production engines. Aero-thermal performance is quantitatively assessed on the basis of the heat transfer coefficient distribution, driving temperature difference for heat transfer between the jet and casing wall and total pressure loss within the high-pressure turbine active clearance control system. We predict that the mean heat transfer coefficient (defined with respect to the inlet temperature and local wall temperature) of the single-entry active clearance control system is 77% greater than the multiple-entry system, primarily because the coolant in the multiple-entry case picks up approximately 40 K of temperature from the ring main walls, and secondarily because the average jet Reynolds number of impingement holes in the single-entry system is 1.2 times greater than in the multiple-entry system. The multiple-entry system exhibits many local hot and cold spots, depending on the position of the transfer boxes, while the single-entry case has a more predictable aero-thermal field across the system. The multiple-entry feed system uses an average of 20% of the total available pressure drop, while the feed system for the single-entry geometry uses only 2% of the total available pressure drop. From the aero-thermal results of this computational study, and in consideration of holistic aero-engine design factors, we conclude that a single-entry system is closer to an optimal solution than a multiple-entry system.

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