Prediction of the Influence of Upstream Wake Passing on Downstream Blade Row External Heat Transfer Coefficient: A New Physically-Based Method

2010 ◽  
Author(s):  
K. S. Chana ◽  
B. R. Haller
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Gas Turbines ◽  
Cooling System ◽  
Guide Vane ◽  
External Heat ◽  
Test Facility ◽  
Internal Cooling ◽  
External Heat Transfer

For gas turbines, accurate prediction of the external heat transfer coefficient on the high pressure (HP) turbine rotor blades is of immense importance, as this component is critical and operates at material limits. Furthermore the external heat load is the governing boundary condition for the design of the internal cooling system of the blade. There is a continuous drive to increase the turbine entry temperature to increase the cycle efficiency, whilst developing blade cooling systems with higher efficiency (i.e. using less cooling air). A new systematic procedure has been developed and validated to predict the external heat transfer to a blade surface. The procedure allows for the unsteady effects caused by the passing of upstream nozzle guide vane (NGV) wakes. The early part of the suction surface was shown to have a pessimistic prediction of external heat transfer coefficient which resulted in unnecessary over-cooling of the blade in this region. The heat transfer aspect is found from the well-known TEXSTAN differential boundary layer method, developed by Mike Crawford at Texas University from the original approach of Spalding & Patankar. The method is validated against the MT1 turbine tested in the QinetiQ Turbine Test Facility. Predictions and comparisons have also been carried out on the VKI turbine stage. The level of agreement with the test data is shown to be good.

scholarly journals Turbine Airfoil External Heat Transfer Measurement in a Hot-Cascade

1997 ◽  
Author(s):  
Luzeng J. Zhang ◽  
Boris Glezer
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
External Heat ◽  
Operating Conditions ◽  
Test Facility ◽  
High Heat Flux ◽  
Transfer Coefficients ◽  
External Heat Transfer ◽  
Heat Transfer Coefficients

Detailed knowledge of local external heat transfer around a turbine airfoil is critical for an accurate prediction of metal temperature and component life. This paper discusses the results of measurements of the local gas side heat transfer coefficient distribution which were performed in an annular gas turbine vane hot-cascade test facility and provides comparisons with analytical predictions. The steady state tests were performed at simulated engine operating conditions. The tests were conducted on an internally cooled airfoil with the intent to provide close to uniform coolant temperature at the mid-span of the airfoil and also to obtain a high heat flux through the wall, minimizing uncertainty. Internal coolant side heal transfer coefficients were measured through calibration tests outside the cascade by a wire heater. A calibrated infrared pyrometer was used to provide detailed airfoil surface local temperatures and the corresponding external heat transfer coefficients. The airfoil was instrumented with a number of thermocouples for both calibration and temperature measurement. A 12% freestream turbulence was generated by a turbulence grid upstream of the test cascade. The static pressure measured over the test vane agreed well with invicid predictions. Heat transfer coefficients were measured and compared to a TEXSTAN boundary layer code prediction. The influence of Reynolds number and Mach number on the airfoil external heat transfer coefficient were also studied and is presented in the paper.

scholarly journals Numerical Investigation of Influence of Entropy Wave on the Acoustic and Wall Heat Transfer Characteristics of a High-Pressure Turbine Guide Vane

Acoustics ◽  
2020 ◽  
Vol 2 (3) ◽  
pp. 524-538
Author(s):  
Keqi Hu ◽  
Yuanqi Fang ◽  
Yao Zheng ◽  
Gaofeng Wang ◽  
Stéphane Moreau
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Flow Field ◽  
Transfer Coefficient ◽  
Gas Turbines ◽  
Guide Vane ◽  
Turbulence Models ◽  
Local Pressure ◽  
Maximum Heat ◽  
Turbine Guide Vane

As an indirect noise source generated in the combustion chamber, entropy waves are widely prevalent in modern gas turbines and aero-engines. In the present work, the influence of entropy waves on the downstream flow field of a turbine guide vane is investigated. The work is mainly based on a well-known experimental configuration called LS89. Two different turbulence models are used in the simulations which are the standard k-ω model and the scale-adaptive simulation (SAS) model. In order to handle the potential transition issue, Menter’s ð-Reθ transition model is coupled with both models. The baseline cases are first simulated with the two different turbulence models without any incoming perturbation. Then one forced case with an entropy wave train set at the turbine inlet at a given frequency and amplitude is simulated. Results show that the downstream maximum Mach number is rising from 0.98 to 1.16, because the entropy waves increase the local temperature of the flow field; also, the torque of the vane varies as the entropy waves go through, the magnitude of the oscillation is 7% of the unforced case. For the wall (both suction and pressure side of the vane) heat transfer, the entropy waves make the maximum heat transfer coefficient nearly twice as the large at the leading edge, while the minimum heat transfer coefficient stays at a low level. As for the averaged normalized heat transfer coefficient, a maximum difference of 30% appears between the baseline case and the forced case. Besides, during the transmission process of entropy waves, the local pressure fluctuates with the wake vortex shedding. The oscillation magnitude of the pressure wave at the throat is found to be enhanced due to the inlet entropy wave by applying the dynamic mode decomposition (DMD) method. Moreover, the transmission coefficient of the entropy waves, and the reflection and transmission coefficients of acoustic waves are calculated.

42 COMPARISON OF COOLING RATES IN OOCYTE VITRIFICATION SYSTEMS USING A NUMERICAL SIMULATION

2012 ◽  
Vol 24 (1) ◽  
pp. 133 ◽  
Author(s):  
M. Sansinena ◽  
M. V. Santos ◽  
N. Zaritzky ◽  
J. Chirife
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cooling Rate ◽  
External Heat ◽  
Experimental Comparison ◽  
The Finite Element Method ◽  
Cooling Rates ◽  
External Heat Transfer

Interest in oocyte cryopreservation has increased due to the application of assisted reproductive technologies and the need for the establishment of ova/gene banks worldwide. In order to maintain cell viability, biological functions must be halted, inducing a suspended animation state by cooling it into a solid phase. Compared to cryopreservation of male gametes, oocytes represent a greater challenge due to their low surface area:volume. Vitrification, the solidification into an amorphous, glassy state while maintaining absence of intra- and extracellular ice crystals, requires high concentrations of cryoprotectants and extremely rapid cooling rates. Several vitrification devices such as open pulled straws (OPS), ultra fine pipette tips, nylon loops and polyethylene films have been introduced to manipulate minimal volumes and achieve high cooling rates. However, experimental comparison of cooling rates presents difficulties mainly because of the reduced size of these systems. To circumvent this limitation, a numerical simulation of cooling rates of various vitrification systems immersed in liquid nitrogen was conducted, solving the non-stationary heat transfer partial differential equation using the finite element method. Three external heat transfer coefficients (h = 200, 1000 and 2000 W m–2 K) were considered. The Cryotip® and OPS were approached as 2 concentric finite cylinders; differential equations representing heat transfer in cylindrical coordinates were described considering radial and axial coordinates and were numerically solved as a 1-dimensional heat conduction problem in an infinite cylinder. The Cryoloop® was approximated as a 1-dimensional heat flow system in Cartesian coordinates and Cryotop® was numerically described as an irregular bi-dimensional axial-symmetric problem. All differential equations were numerically solved using the finite element method in COMSOL Multiphysics 3.4. The domain was discretized in triangular (Cryotip®, OPS and Cryotop®) and linear elements (Cryoloop®) in order to obtain accurate numerical approximations. In each case, the warmest point of the system was identified to determine the time-temperature curve that allows the evaluation of the slowest cooling rate (worst condition). Results indicate the nylon loop (Cryoloop®) is the most efficient heat transfer system analysed, with a predicted cooling rate of 180 000°C min–1 for an external heat transfer coefficient h = 1000 W m–2 K when cooling from 20 to –130°C; in contrast, the pipette tips (Miniflex® showed the lowest performance with a cooling rate of 6164°C min–1 at same value of external heat transfer coefficient. Predicted cooling rates of OPS and Cryotop® (polyethylene film) were 40 909 and 37 500°C min–1, respectively for the same heat transfer coefficient. It can be concluded that in oocyte cryopreservation systems, in which experimental comparison of cooling rates presents difficulties due to the reduced size of the vitrification devices, the numerical simulations and the analysis of the predicted thermal histories could contribute to determine the performance of the different techniques.

A new experimental approach for heat transfer coefficient and adiabatic wall temperature measurements on a Nozzle Guide Vane with inlet temperature distortions

2021 ◽  
pp. 1-33
Author(s):  
Tommaso Bacci ◽  
Alessio Picchi ◽  
Bruno Facchini ◽  
Simone Cubeda
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Wall Temperature ◽  
Gas Turbines ◽  
Experimental Approach ◽  
Guide Vane ◽  
Adiabatic Wall ◽  
Nozzle Guide Vane ◽  
Nozzle Guide

Abstract Modern gas turbines lean combustors are used to limit NOx pollutant emissions; on the other hand, their adoption presents other challenges, especially concerning the combustor-turbine interaction. Turbine inlet conditions are generally characterized by severe temperature distortions and swirl degree, which is responsible for very high turbulence intensities. Past studies have focused on the description of the effects of these phenomena on the behavior of the high pressure turbine. Nevertheless, very limited experimental results are available when it comes to evaluate the heat transfer coefficient (HTC) on the nozzle guide vane surface, since relevant temperature distortions present a severe challenge for the commonly adopted measurement techniques. The work presented in this paper was carried out on a non-reactive, annular, three-sector rig, made by a combustor simulator and a NGV cascade. It can reproduce a swirling flow, with temperature distortions at the combustor-turbine interface plane. This test apparatus was exploited to develop an experimental approach to retrieve heat transfer coefficient and adiabatic wall temperature distributions simultaneously, to overcome the known limitations imposed by temperature gradients on state-of-the-art methods for HTC calculation from transient tests. A non-cooled mockup of a NGV doublet, manufactured using low thermal diffusivity plastic material, was used for the tests, carried out using IR thermography with a transient approach. In the authors' knowledge, this presents the first experimental attempt of measuring a nozzle guide vane heat transfer coefficient in the presence of relevant temperature distortions and swirl.

Experimental Survey on Heat Transfer in a Trailing Edge Cooling System: Effects of Rotation in Internal Cooling Ducts

2012 ◽  
Author(s):  
L. Bonanni ◽  
C. Carcasci ◽  
B. Facchini ◽  
L. Tarchi
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Gas Turbine ◽  
Cooling System ◽  
Internal Cooling ◽  
Test Rig ◽  
Trailing Edge ◽  
Tip Mass

The high thermal loads, the heavy structural stresses and the small thickness required for aerodynamic performances make the trailing edge cooling (TE) cooling of high pressure gas turbine blades a critical challenge. The presented paper point out an experimental study focusing the aerothermal performance of a TE internal cooling system of a high pressure gas turbine blade, evaluated under stationary and rotating conditions. The investigated geometry consists of a 30:1 scaled model reproducing the typical wedge shaped discharge duct with one row of enlarged pedestals. The airflow pattern inside the device simulates a highly loaded rotor blade cooling scheme with a 90° turning flow from the radial hub inlet to the tangential TE outlet. Two different tip configurations were tested, the first one with a completely closed section, the second one with 5 holes on the tip outlet surfaces discharging at ambient pressure. To investigate the rotation effects on the trailing edge cooling system performance, a rotating test rig was purposely developed and manufactured. The test rig is composed by a rotating arm that holds the PMMA TE model and the instrumentation. A thin Inconel heating foil and wide band Thermo-chromic Liquid Crystals are used to perform steady state heat transfer measurements. A rotary joint ensures the pneumatic connection between the blower and the rotating apparatus, moreover several slip rings are used for both instrumentation power supply and thermocouple connection. Heat transfer coefficient measurements were made with fixed Reynolds number close to 20k in the hub inlet section and with variable rotating speed in order to set the Rotation number from 0 (non rotational test) up to 0.3. Six different configurations were tested: two different tip mass flow rates (the first one with a completely closed tip, the second one with the 12.5% of the inlet flow discharged from the tip) and three different surface conditions: the first one consists in the flat plate case and the others in two ribbed cases, with different angular orientation (60° and −60° respect to the radial direction). Results are reported in terms of detailed heat transfer coefficient 2D maps on the suction side surface as well as span-wise profiles inside the pedestal ducts. The reported work has been supported by the Italian Ministry of Education, University and Research (MIUR).

Effect of Rotation on a Gas Turbine Blade Internal Cooling System: Numerical Investigation

2016 ◽  
Author(s):  
E. Burberi ◽  
D. Massini ◽  
L. Cocchi ◽  
L. Mazzei ◽  
A. Andreini ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Flow Field ◽  
Transfer Coefficient ◽  
Numerical Investigation ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Cooling System ◽  
Leading Edge ◽  
Internal Cooling

Increasing turbine inlet temperature is one of the main strategies used to accomplish the demands of increased performance of modern gas turbines. As a consequence, optimization of the cooling system is of paramount importance in gas turbine development. Leading edge represents a critical part of cooled nozzles and blades, given the presence of the hot gases stagnation point and the unfavourable geometry for cooling. This paper reports the results of a numerical investigation aimed at assessing the rotation effects on the heat transfer distribution in a realistic leading edge internal cooling system of a high pressure gas turbine blade. The numerical investigation was carried out in order to support and to allow an in-depth understanding of the results obtained in a parallel experimental campaign. The model is composed of a trapezoidal feeding channel which provides air to the cold bridge system by means of three large racetrack-shaped holes, generating coolant impingement on the internal concave leading edge surface, whereas four big fins assure the jets confinement. Air is then extracted through 4 rows of 6 holes reproducing the external cooling system composed of shower-head and film cooling holes. Experiments were performed in static and rotating conditions replicating the typical range of jet Reynolds number (Rej) from 10000 to 40000 and Rotation number (Roj) up to 0.05, for three crossflow cases representative of the working condition that can be found at blade tip, midspan and hub, respectively. Experimental results in terms of flow field measurements on several internal planes and heat transfer coefficient on the LE internal surface have been performed on two analogous experimental campaigns at University of Udine and University of Florence respectively. Hybrid RANS-LES models were used for the simulations, such as Scale Adaptive Simulation (SAS) and Detached Eddy Simulation (DES), given their ability to resolve the complex flow field associated with jet impingement. Numerical flow field results are reported in terms of both jet velocity profiles and 2D vector plots on symmetry and transversal internal planes, while the heat transfer coefficient distributions are presented as detailed 2D maps together with radial and tangential averaged Nusselt number profiles. A fairly good agreement with experimental measurements is observed, which represent a validation of the adopted computational model. As a consequence, the computed aerodynamic and thermal fields also allow an in-depth interpretation of the experimental results.

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