EXPERIMENTAL INVESTIGATION OF TIP DESIGN EFFECTS ON THE UNSTEADY AERODYNAMICS AND HEAT TRANSFER OF A HIGH SPEED TURBINE

2021 ◽  
pp. 1-15
Author(s):  
Bogdan C. Cernat ◽  
Sergio Lavagnoli
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Thermal Field ◽  
New Technologies ◽  
Unsteady Aerodynamics ◽  
Secondary Flows ◽  
Tip Leakage Flow ◽  
Adiabatic Wall ◽  
The Impact ◽  
Transfer Mechanisms

Abstract While modern engine manufacturers devote significant efforts to the development of reliable and efficient machines, the introduction of novel, optimized components in the hot gas path represents a risky opportunity. Accurate experimental and numerical data are critical to assess the impact of new technologies on the harsh engine environment. The present study addresses the impact of a selection of high-performance rotor blade tips on the aerodynamic and heat flux field of a high pressure turbine (HPT) stage. A combined numerical and experimental approach is employed to characterize the interaction of the tip leakage flow with the rotor secondary flows and the casing heat transfer mechanisms for each individual tip geometry. The turbine stage is tested at engine-scaled conditions in the rotating turbine facility of the von Karman Institute. For the present study, the turbine rotor is operated in rainbow configuration to allow the simultaneous testing of multiple blade tip geometries. RANS simulations are employed to predict the aerodynamic and thermal field of the individual profiles using test-calibrated boundary conditions. Isothermal computations are performed at different wall temperatures to compute the tip-dependent adiabatic wall temperature and heat transfer coefficient. Low-order models are developed to represent the over-tip thermal field and the driving heat transfer mechanisms. The time-resolved outlet flow is characterized using a vortex tracking technique and high frequency aerodynamic measurements to identify the rotor secondary flow structures.

Experimental Investigation of Tip Design Effects on the Unsteady Aerodynamics and Heat Transfer of a High Speed Turbine

2020 ◽  
Author(s):  
Bogdan Cernat ◽  
Sergio Lavagnoli
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Thermal Field ◽  
New Technologies ◽  
Unsteady Aerodynamics ◽  
Secondary Flows ◽  
Tip Leakage Flow ◽  
Adiabatic Wall ◽  
The Impact ◽  
Transfer Mechanisms

Abstract While modern engine manufacturers devote significant efforts to the development of reliable and efficient machines, the introduction of novel, optimized components in the hot gas path represents a risky opportunity. Accurate experimental and numerical data are critical to assess the impact of new technologies on the harsh engine environment. The present study addresses the impact of a selection of high-performance rotor blade tips on the aerodynamic and heat flux field of a high pressure turbine (HPT) stage. A combined numerical and experimental approach is employed to characterize the interaction of the tip leakage flow with the rotor secondary flows and the casing heat transfer mechanisms for each individual tip geometry. The turbine stage is tested at engine-scaled conditions in the rotating turbine facility of the von Karman Institute. For the present study, the turbine rotor is operated in rainbow configuration to allow the simultaneous testing of multiple blade tip geometries. RANS simulations are employed to predict the aerodynamic and thermal field of the individual profiles using test-calibrated boundary conditions. Isothermal steady computations are performed at different wall temperatures to compute the adiabatic wall temperature and heat transfer convective coefficient. Low-order models are used to represent the over-tip thermal field and the driving heat transfer mechanisms. The time-resolved outlet flow is characterized using a vortex tracking technique and high frequency aerodynamic measurements to identify the rotor secondary flow structures.

Experimental and Numerical Investigation of Optimized Blade Tip Shapes—Part II: Tip Flow Analysis and Loss Mechanisms

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Marek Pátý ◽  
Bogdan C. Cernat ◽  
Cis De Maesschalck ◽  
Sergio Lavagnoli
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Thermal Stresses ◽  
Flow Analysis ◽  
Vortical Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Blade Tip ◽  
The Impact ◽  
Blade Tip Geometry

The leakage flows within the gap between the tips of unshrouded rotor blades and the stationary casing of high-speed turbines are the source of significant aerodynamic losses and thermal stresses. In the pursuit for higher component performance and reliability, shaping the tip geometry offers a considerable potential to modulate the rotor tip flows and to weaken the heat transfer onto the blade and casing. Nevertheless, a critical shortage of combined experimental and numerical studies addressing the flow and loss generation mechanisms of advanced tip profiles persists in the open literature. A comprehensive study is presented in this two-part paper that investigates the influence of blade tip geometry on the aerothermodynamics of a high-speed turbine. An experimental and numerical campaign has been performed on a high-pressure turbine stage adopting three different blade tip profiles. The aerothermal performance of two optimized tip geometries (one with a full three-dimensional contoured shape and the other featuring a multicavity squealer-like tip) is compared against that of a regular squealer geometry. In the second part of this paper, we report a detailed analysis on the aerodynamics of the turbine as a function of the blade tip geometry. Reynolds-averaged Navier-Stokes (RANS) simulations, adopting the Spalart–Allmaras turbulence model and experimental boundary conditions, were run on high-density unstructured meshes using the numecafine/open solver. The simulations were validated against time-averaged and time-resolved experimental data collected in an instrumented turbine stage specifically setup for the simultaneous testing of multiple blade tips at scaled engine-representative conditions. The tip flow physics is explored to explain variations in turbine performance as a function of the tip geometry. Denton's mixing loss model is applied to the predicted tip gap aerodynamic field to identify and quantify the loss reduction mechanisms of the alternative tip designs. An advanced method based on the local triple decomposition of relative motion is used to track the location, size and intensity of the vortical flow structures arising from the interaction between the tip leakage flow and the main gas path. Ultimately, the comparison between the unconventional tip profiles and the baseline squealer tip highlights distinct aerodynamic features in the associated gap flow field. The flow analysis provides guidelines for the designer to assess the impact of specific tip design strategies on the turbine aerodynamics and rotor heat transfer.

Experimental and Numerical Investigation of Optimized Blade Tip Shapes: Part II — Tip Flow Analysis and Loss Mechanisms

2018 ◽  
Author(s):  
Marek Pátý ◽  
Bogdan Cernat ◽  
Cis De Maesschalck ◽  
Sergio Lavagnoli
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Thermal Stresses ◽  
Flow Analysis ◽  
Vortical Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Blade Tip ◽  
The Impact ◽  
Blade Tip Geometry

The leakage flows within the gap between the tips of unshrouded rotor blades and the stationary casing of high-speed turbines are the source of significant aerodynamic losses and thermal stresses. In the pursuit for higher component performance and reliability, shaping the tip geometry offers a considerable potential to modulate the rotor tip flows and to weaken the heat transfer onto the blade and casing. Nevertheless, a critical shortage of combined experimental and numerical studies addressing the flow and loss generation mechanisms of advanced tip profiles persists in the open literature. A comprehensive study is presented in this two-part paper that investigates the influence of blade tip geometry on the aerother-modynamics of a high-speed turbine. An experimental and numerical campaign has been performed on a high-pressure turbine stage adopting three different blade tip profiles. The aerothermal performance of two optimized tip geometries (one with a full three-dimensional contoured shape and the other featuring a multi-cavity squealer-like tip) is compared against that of a regular squealer geometry. In the second part of this paper, we report a detailed analysis on the aerodynamics of the turbine as a function of the blade tip geometry. Reynolds-averaged Navier-Stokes simulations, adopting the Spalart-Allmaras turbulence model and experimental boundary conditions, were run on high-density unstructured meshes using the Numeca FINE/Open solver. The simulations were validated against time-averaged and time-resolved experimental data collected in an instrumented turbine stage specifically set up for the simultaneous testing of multiple blade tips at scaled engine-representative conditions. The tip flow physics is explored to explain variations in turbine performance as a function of the tip geometry. Denton’s mixing loss model is applied to the predicted tip gap aerodynamic field to identify and quantify the loss reduction mechanisms of the alternative tip designs. An advanced method based on the local triple decomposition of relative motion is used to track the location, size and intensity of the vortical flow structures arising from the interaction between the tip leakage flow and the main gas path. Ultimately, the comparison between the unconventional tip profiles and the baseline squealer tip highlights distinct aerodynamic features in the associated gap flow field. The flow analysis provides guidelines for the designer to assess the impact of specific tip design strategies on the turbine aerodynamics and rotor heat transfer.

The Influence of Boundary Conditions on Tip Leakage Flow

2013 ◽  
Author(s):  
John D. Coull ◽  
Nicholas R. Atkins
Keyword(s):  
High Pressure ◽  
Boundary Conditions ◽  
High Speed ◽  
Secondary Flows ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
High Pressure Turbine ◽  
Tip Leakage ◽  
Inlet Condition ◽  
The Impact

Most of the current understanding of tip leakage flows has been derived from detailed cascade experiments. However, the cascade model is inherently approximate since it is difficult to simulate the boundary conditions present in a real machine, particularly the secondary flows convecting from the upstream stator row and the relative motion of the casing and blade. This problem is further complicated when considering the high pressure turbine rotors of aero engines, where the high Mach numbers must also be matched in order to correctly model the aerodynamics and heat transfer. More realistic tests can be performed on high-speed turbines, but the experimental fidelity and resolution achievable in such set-ups is limited. In order to examine the differences between cascade models and real-engine behavior, the influence of boundary conditions on the tip leakage flow in an unshrouded high pressure turbine rotor is investigated using RANS calculations. This study examines the influence of the rotor inlet condition and relative casing motion. A baseline calculation with a simplified inlet condition and no relative endwall motion exhibits similar behavior to cascade studies. Only minor changes to the leakage flow are induced by introducing either a more realistic inlet condition or relative casing motion. However when both of these conditions are applied simultaneously the pattern of leakage flow is very different, with ingestion of flow over much of the early suction surface. The paper explores the physical processes driving this change and the impact on leakage losses and modeling requirements.

Aerodynamic and Heat Transfer Measurements on an Intermediate Turbine Duct Vane

2014 ◽  
Author(s):  
Martin Johansson ◽  
Thomas Povey ◽  
Kam Chana ◽  
Fredrik Wallin ◽  
Hans Abrahamsson
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Test Facility ◽  
Tip Leakage Flow ◽  
Current Configuration ◽  
Speed Test ◽  
Intermediate Turbine Duct ◽  
Dimensional Parameters ◽  
Film Heat Transfer ◽  
The Impact

Flow in a turbine duct is highly complex, influenced by the upstream turbine stage flow structures, including tip leakage flow and non-uniformities originating from the upstream HP vane and rotor. The complexity of the flow makes the prediction using CFD methods difficult, hence there exists a need for experimental validation. This paper presents a new design of an intermediate turbine duct with a structural vane that has been designed, manufactured and integrated into the Oxford Turbine Research Facility. This is a short duration high speed test facility enabling the use of an engine sized turbine, operating at the correct non-dimensional parameters relevant for aerodynamic and heat transfer measurements. The current configuration consists of a HP stage and a downstream duct including a low-aspect ratio vane, representative for a counter rotating turbine configuration. Aerodynamic and heat transfer measurements are conducted to generate a database with which current CFD methods can be validated. The instrumentation presented here includes static pressure tappings and thin film heat transfer gauges on the ITD vane surface and endwalls. The time averaged measurements show the impact of different clocking positions of the ITD vane with respect to the up-stream HP vane. This demonstrates the requirements of addressing the influence of vane counts and stator-stator clocking when designing new components. The measurements are compared with CFD predictions.

scholarly journals Investigation of aerodynamics and heat transfer of the modular jet recuperator

2021 ◽  
Vol 2039 (1) ◽  
pp. 012001
Author(s):  
P D Alekseev ◽  
Yu L Leukhin
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Annular Channel ◽  
Secondary Flows ◽  
Cocurrent Flow ◽  
Outlet Section ◽  
Entire Cross Section ◽  
Staggered Arrangement ◽  
Perforated Pipe ◽  
The Impact

Abstract A study of the aerodynamics and heat transfer of a jet modular recuperator with a change in its geometric characteristics has been carried out. The influence of the in-line and staggered arrangement of the blowing holes, as well as the diameter of the perforated pipe is considered. In all considered variants, the number of holes, their diameter and gas flow rate through the recuperator remained unchanged. Numerical modeling of the problem was carried out in a three-dimensional setting using the ANSYS Fluent 15.0 software package. It was found that with the in-line arrangement of the blowing holes, secondary flows are formed between their longitudinal rows in the form of swirling jets of opposite rotation directed towards the outlet section of the recuperative device, through which the main part of the heated air flows out. With the staggered arrangement of the blowing holes, the formation of spiral vortices is disturbed, the air flow is carried out along the entire cross section of the annular channel, increasing the drift effect of the flow on the impact jets, which leads to a decrease in the intensity of heat transfer and its uniformity along the length of the working surface. An increase in the diameter of the inner perforated pipe leads to a decrease in the drift effect of the cocurrent flow on the jets, an increase in the distribution uniformity of the heat flux along the length of the heat transfer surface, and an increase in the heat transfer coefficient.

Interfacial Heat Transfer During Droplet Impact on a Solid Surface: Comparison of High-Resolution Laser Measurements With Finite-Element Simulations

2007 ◽  
Author(s):  
Rajneesh Bhardwaj ◽  
Jon P. Longtin ◽  
Daniel Attinger
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Finite Element ◽  
High Speed ◽  
Element Model ◽  
Deposition Process ◽  
Interfacial Heat Transfer Coefficient ◽  
Interfacial Heat Transfer ◽  
Laser Measurements ◽  
The Impact

The objective of this work is to understand the coupling of fluid dynamics and heat transfer during the impact of a millimeter-size water droplet on a flat, solid glass substrate. In this work, a finite-element model is presented which simulates the transient fluid dynamics and heat transfer during the droplet deposition process, considering Laplace forces on the liquid-gas boundary, and the dynamics of wetting. A novel, experimental laser-based method is used to measure temperatures at the solid-liquid interface. This method is based on a thermoreflectance technique and provides unprecedented temporal and spatial resolutions of 1 microsecond and 20 micrometer, respectively. Matching between simulations, temperature measurements and high-speed visualization allows the determination of the interfacial heat transfer coefficient.

Thermal Investigation of Integrated Combustor Vane Concept Under Engine-Realistic Conditions

2016 ◽  
Author(s):  
Simon Jacobi ◽  
Budimir Rosic
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Gas Turbines ◽  
High Speed ◽  
Secondary Flows ◽  
Experimental Measurements ◽  
Thermal Investigation ◽  
Nozzle Guide ◽  
The Heat Transfer Coefficient

This paper presents a thermal investigation of the Integrated Combustor Vane concept for power generation gas turbines with individual can combustors. This concept has the potential to replace the high-pressure turbine’s first vanes by prolonged combustor walls. Experimental measurements are performed on a linear high-speed cascade consisting of two can combustors and two integrated vanes. The modularity of the facility allows for the testing at engine-realistic high turbulence levels, as well as swirl strengths with opposing swirl directions. The heat transfer characteristics of the integrated vanes are compared to conventional nozzle guide vanes. The experimental measurements are supported by detailed numerical simulations using the inhouse CFD code TBLOCK. Experimental as well as numerical results congruently indicate a considerable reduction of the heat transfer coefficient (HTC) on the integrated vanes surfaces and endwalls caused by a differing state of boundary layer thickness. The studies furthermore depict a slight, non-detrimental shift in the heat transfer coefficient distributions and the strength of the integrated vanes secondary flows as a result of engine-realistic combustor swirl.

scholarly journals The Simultaneous Analysis of Droplets’ Impacts and Heat Transfer during Water Spray Cooling Using a Transparent Heater

Water ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 2730
Author(s):  
Vladimir Serdyukov ◽  
Nikolay Miskiv ◽  
Anton Surtaev
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Spray Cooling ◽  
Capillary Waves ◽  
Heat Fluxes ◽  
Small Scale ◽  
Unsteady Temperature ◽  
The Impact

This paper demonstrates the advantages and prospects of transparent design of the heating surface for the simultaneous study of the hydrodynamic and thermal characteristics of spray cooling. It was shown that the high-speed recording from the reverse side of such heater allows to identify individual droplets before their impact on the forming liquid film, which makes it possible to measure their sizes with high spatial resolution. In addition, such format enables one to estimate the number of droplets falling onto the impact surface and to study the features of the interface evolution during the droplets’ impacts. In particular, the experiments showed various possible scenarios for this interaction, such as the formation of small-scale capillary waves during impacts of small droplets, as well as the appearance of “craters” and splashing crowns in the case of large ones. Moreover, the unsteady temperature field during spray cooling in regimes without boiling was investigated using high-speed infrared thermography. Based on the obtained data, the intensity of heat transfer during spray cooling for various liquid flow rates and heat fluxes was analyzed. It was shown that, for the studied regimes, the heat transfer coefficient weakly depends on the heat flux density and is primarily determined by the flow rate. In addition, the comparison of the processes of spray cooling and nucleate boiling was made, and an analogy was shown in the mechanisms that determine their intensity of heat transfer.

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