Heat Transfer Measurements Using Liquid Crystals in a Preswirl Rotating-Disk System

2005 ◽  
Vol 127 (2) ◽  
pp. 375-382 ◽  
Author(s):  
Gary D. Lock ◽  
Youyou Yan ◽  
Paul J. Newton ◽  
Michael Wilson ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Gas Turbines ◽  
Fluid Dynamic ◽  
Turbine Blades ◽  
Rotating Disk ◽  
Impinging Jets ◽  
Viscous Effects ◽  
Scaled Model ◽  
Flow Rates

Preswirl nozzles are often used in gas turbines to deliver the cooling air to the turbine blades through receiver holes in a rotating disk. The distribution of the local Nusselt number, Nu, on the rotating disk is governed by three nondimensional fluid-dynamic parameters: preswirl ratio, βp, rotational Reynolds number, Reϕ, and turbulent flow parameter, λT. A scaled model of a gas turbine rotor–stator cavity, based on the geometry of current engine designs, has been used to create appropriate flow conditions. This paper describes how a thermochromic liquid crystal, in conjunction with a stroboscopic light and digital camera, is used in a transient experiment to obtain contour maps of Nu on the rotating disk. The thermal boundary conditions for the transient technique are such that an exponential-series solution to Fourier’s one-dimensional conduction equation is necessary. A method to assess the uncertainty in the measurements is discussed and these uncertainties are quantified. The experiments reveal that Nu on the rotating disk is axisymmetric except in the region of the receiver holes, where significant two-dimensional variations have been measured. At the higher coolant flow rates studied, there is a peak in heat transfer at the radius of the preswirl nozzles. The heat transfer is governed by two flow regimes: one dominated by inertial effects associated with the impinging jets from the preswirl nozzles, and another dominated by viscous effects at lower flow rates. The Nusselt number is observed to increase as either Reϕ or λT increases.

Influence of Fluid Dynamics on Heat Transfer in a Preswirl Rotating-Disk System

2004 ◽  
Vol 127 (4) ◽  
pp. 791-797 ◽  
Author(s):  
Gary D. Lock ◽  
Michael Wilson ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Gas Turbines ◽  
Fluid Dynamic ◽  
Rotating Disk ◽  
Impinging Jets ◽  
Coolant Flow ◽  
Viscous Effects ◽  
Scaled Model ◽  
Flow Rates

Modern gas turbines are cooled using air diverted from the compressor. In a “direct-transfer” preswirl system, this cooling air flows axially across the wheel space from stationary preswirl nozzles to receiver holes located in the rotating turbine disk. The distribution of the local Nusselt number Nu on the rotating disk is governed by three nondimensional fluid-dynamic parameters: preswirl ratio βp, rotational Reynolds number Reϕ, and turbulent flow parameter λT. This paper describes heat transfer measurements obtained from a scaled model of a gas turbine rotor-stator cavity, where the flow structure is representative of that found in the engine. The experiments reveal that Nu on the rotating disk is axisymmetric except in the region of the receiver holes, where significant two-dimensional variations have been measured. At the higher coolant flow rates studied, there is a peak in heat transfer at the radius of the preswirl nozzles associated with the impinging jets from the preswirl nozzles. At lower coolant flow rates, the heat transfer is dominated by viscous effects. The Nusselt number is observed to increase as either Reϕ or λT increases.

Influence of Fluid-Dynamics on Heat Transfer in a Pre-Swirl Rotating-Disc System

2004 ◽  
Author(s):  
Gary D. Lock ◽  
Michael Wilson ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Gas Turbines ◽  
Fluid Dynamic ◽  
Impinging Jets ◽  
Coolant Flow ◽  
Viscous Effects ◽  
Rotating Disc ◽  
Scaled Model ◽  
Flow Rates

Modern gas turbines are cooled using air diverted from the compressor. In a “direct-transfer” pre-swirl system, this cooling air flows axially across the wheel-space from stationary pre-swirl nozzles to receiver holes located in the rotating turbine disc. The distribution of the local Nusselt number, Nu, on the rotating disc is governed by three non-dimensional fluid-dynamic parameters: pre-swirl ratio, βp, rotational Reynolds number, Reφ, and turbulent flow parameter, λT. This paper describes heat transfer measurements obtained from a scaled model of a gas turbine rotor-stator cavity, where the flow structure is representative of that found in the engine. The experiments reveal that Nu on the rotating disc is axisymmetric except in the region of the receiver holes, where significant two-dimensional variations have been measured. At the higher coolant flow rates studied, there is a peak in heat transfer at the radius of the pre-swirl nozzles, associated with the impinging jets from the pre-swirl nozzles. At lower coolant flow rates, the heat transfer is dominated by viscous effects. The Nusselt number is observed to increase as either Reφ or λT increases.

Heat Transfer Measurements Using Liquid Crystal in a Pre-Swirl Rotating-Disc System

2003 ◽  
Author(s):  
Gary D. Lock ◽  
Youyou Yan ◽  
Paul J. Newton ◽  
Michael Wilson ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Liquid Crystal ◽  
Gas Turbines ◽  
Fluid Dynamic ◽  
Turbine Blades ◽  
Impinging Jets ◽  
Viscous Effects ◽  
Rotating Disc ◽  
Flow Rates

Pre-swirl nozzles are often used in gas turbines to deliver the cooling air to the turbine blades through receiver holes in a rotating disc. The distribution of the local Nusselt number, Nu, on the rotating disc is governed by three non-dimensional fluid-dynamic parameters: pre-swirl ratio, βp, rotational Reynolds number, Reφ, and turbulent flow parameter, λT. A scaled model of a gas turbine rotor-stator cavity, based on the geometry of current engine designs, has been used to create appropriate flow conditions. This paper describes how thermochromic liquid crystal (TLC), in conjunction with a stroboscopic light and digital camera, is used in a transient experiment to obtain contour maps of Nu on the rotating disc. The thermal boundary conditions for the transient technique are such that an exponential-series solution to Fourier’s one-dimensional conduction equation is necessary. A method to assess the uncertainty in the measurements is discussed and these uncertainties are quantified. The experiments reveal that Nu on the rotating disc is axisymmetric except in the region of the receiver holes, where significant two-dimensional variations have been measured. At the higher coolant flow rates studied, there is a peak in heat transfer at the radius of the pre-swirl nozzles. The heat transfer is governed by two flow regimes: one dominated by inertial effects associated with the impinging jets from the pre-swirl nozzles, and another dominated by viscous effects at lower flow rates. The Nusselt number is observed to increase as either Reφ or λT increases.

Physical Interpretation of Flow and Heat Transfer in Preswirl Systems

2006 ◽  
Vol 129 (3) ◽  
pp. 769-777 ◽  
Author(s):  
Paul Lewis ◽  
Mike Wilson ◽  
Gary Lock ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Turbulent Flow ◽  
Gas Turbines ◽  
Flow Parameter ◽  
Rotating Disk ◽  
Turbine Rotor ◽  
Scaled Model ◽  
Flow Rates

This paper compares heat transfer measurements from a preswirl rotor–stator experiment with three-dimensional (3D) steady-state results from a commercial computational fluid dynamics (CFD) code. The measured distribution of Nusselt number on the rotor surface was obtained from a scaled model of a gas turbine rotor–stator system, where the flow structure is representative of that found in an engine. Computations were carried out using a coupled multigrid Reynolds-averaged Navier-Stokes (RANS) solver with a high Reynolds number k-ε∕k-ω turbulence model. Previous work has identified three parameters governing heat transfer: rotational Reynolds number (Reϕ), preswirl ratio (βp), and the turbulent flow parameter (λT). For this study rotational Reynolds numbers are in the range 0.8×106<Reϕ<1.2×106. The turbulent flow parameter and preswirl ratios varied between 0.12<λT<0.38 and 0.5<βp<1.5, which are comparable to values that occur in industrial gas turbines. Two performance parameters have been calculated: the adiabatic effectiveness for the system, Θb,ad, and the discharge coefficient for the receiver holes, CD. The computations show that, although Θb,ad increases monotonically as βp increases, there is a critical value of βp at which CD is a maximum. At high coolant flow rates, computations have predicted peaks in heat transfer at the radius of the preswirl nozzles. These were discovered during earlier experiments and are associated with the impingement of the preswirl flow on the rotor disk. At lower flow rates, the heat transfer is controlled by boundary-layer effects. The Nusselt number on the rotating disk increases as either Reϕ or λT increases, and is axisymmetric except in the region of the receiver holes, where significant two-dimensional variations are observed. The computed velocity field is used to explain the heat transfer distributions observed in the experiments. The regions of peak heat transfer around the receiver holes are a consequence of the route taken by the flow. Two routes have been identified: “direct,” whereby flow forms a stream tube between the inlet and outlet; and “indirect,” whereby flow mixes with the rotating core of fluid.

Physical Interpretation of Flow and Heat Transfer in Pre-Swirl Systems

2006 ◽  
Author(s):  
Paul Lewis ◽  
Mike Wilson ◽  
Gary Lock ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Turbulent Flow ◽  
Gas Turbines ◽  
Flow Parameter ◽  
Swirl Flow ◽  
Rotating Disc ◽  
Scaled Model ◽  
Flow Rates

This paper compares heat transfer measurements from a pre-swirl rotor-stator experiment with 3D steady state results from a commercial CFD code. The measured distribution of Nusselt number on the rotor surface was obtained from a scaled model of a gas turbine rotor-stator system, where the flow structure is representative of that found in an engine. Computations were carried out using a coupled multigrid RANS solver with a high-Reynolds-number k-ε/k-ω turbulence model. Previous work has identified three parameters governing heat transfer: rotational Reynolds number (Reφ), pre-swirl ratio (βp) and the turbulent flow parameter (λT). For this study rotational Reynolds numbers are in the range 0.8×106 &lt; Reφ &lt; 1.2×106. The turbulent flow parameter and pre-swirl ratios varied between 0.12 &lt; λT &lt; 0.38 and 0.5 &lt; βp &lt; 1.5, which are comparable to values that occur in industrial gas turbines. At high coolant flow rates, computations have predicted peaks in heat transfer at the radius of the pre-swirl nozzles. These were discovered during earlier experiments and are associated with the impingement of the pre-swirl flow on the rotor disc. At lower flow rates, the heat transfer is controlled by boundary-layer effects. The Nusselt number on the rotating disc increases as either Reφ or λT increases, and is axisymmetric except in the region of the receiver holes, where significant two-dimensional variations are observed. The computed velocity field is used to explain the heat transfer distributions observed in the experiments. The regions of peak heat transfer around the receiver holes are a consequence of the route taken by the flow. Two routes have been identified: “direct”, whereby flow forms a stream-tube between the inlet and outlet; and “indirect”, whereby flow mixes with the rotating core of fluid. Two performance parameters have been calculated: the adiabatic effectiveness for the system, Θb,ab, and the discharge coefficient for the receiver holes, CD. The computations show that, although Θb,ab increases monotonically as βp increases, there is a critical value of βp at which CD is a maximum.

scholarly journals Effect of Rotation Number on Heat Transfer Characteristics of a Row of Impinging Jets in Confined Channel

2020 ◽  
Vol 77 (1) ◽  
pp. 161-171
Author(s):  
Thantup Nontula ◽  
Natthaporn Kaewchoothong ◽  
Wacharin Kaew-apichai ◽  
Chayut Nuntadusit
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rotation Number ◽  
Turbine Blades ◽  
Jet Impingement ◽  
Impinging Jets ◽  
Internal Cooling ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Impingement Surface

Jet impingement has been applied for internal cooling in gas turbine blades. In this study, heat transfer characteristics of impinging jets from a row of circular orifices were investigated inside a flow channel with rotations. The Reynolds number (Re) based on the jet mean velocity was fixed at 6,700. Whereas, the rotation number (Ro) of a channel was varied from 0 to 0.0099. The jet-to-impingement distance ratio (L/Dj) and jet pitch ratio (P/Dj) were respective 2 and 4, Dj is a jet diameter of 5 mm. The thermochromic liquid crystals (TLCs) technique was used to measure the heat transfer coefficient distributions on an impingement surface. The results show that heat transfer enhancement on a jet impingement surface depended on the effects of crossflow and Coriolis force. The local Nusselt number at X/Dj?20 on the leading side (LS) was higher than on the trailing side (TS) while heat transfer on the LS at 20?X/Dj?40 gained the lowest, compared to on the TS. The average Nusselt number ratios ( ) on the TS at Ro = 0.0049 gave higher than on the LS of around 2.17%. On the other hand, the on the TS at Ro = 0.0099 was less than the LS of about 0.08%.

Rib Turbulated Pin Fin Array for Trailing Edge Cooling

2017 ◽  
Author(s):  
Marcel Otto ◽  
Erik Fernandez ◽  
Jayanta S. Kapat ◽  
Mark Ricklick ◽  
Shantanu Mhetras
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Gas Turbines ◽  
Reynolds Numbers ◽  
Hydraulic Diameter ◽  
Low Flow ◽  
Trailing Edge ◽  
Flow Rates ◽  
Pin Fin ◽  
Pin Fin Array

Increasing the firing temperatures in gas turbines require better, and highly efficient means of heat removal of turbine blades so that metal temperatures stay within the limit of safe operation with respect to metal properties. This study focuses on the trailing edge region of a turbine blade. Ribs were added into a pin fin array in order to achieve better heat transfer compared to pin fin arrays without additional ribs as they are commonly used. Heat transfer measurements are obtained using the thermochromic liquid crystal technique (TLC) in a trapezoidal duct with pin fins and rib turbulators representing endwall cooling. The blockages due to pins are 35%, 50% and 65%. There are a total of 15 rows of pins in the streamwise direction, and 5 columns in the spanwise direction. The non-dimensional rib heights are 0, 0.27, 0.7 and 0.1. The minor angle of the trapeze is 14 degrees, the hydraulic diameter of the duct is 21 mm. The Reynolds Numbers tested, based on free stream velocity and the hydraulic diameter of the experiment, are 40,000 60,000 and 106,000. The test matrix for this study contains all possible blockage and rib height combinations for all three Reynolds Numbers tested. Streamwise averaged and spanwise averaged Nusselt number augmentations are compared to the Dittus-Boelter baseline case, and are presented for the endwalls together with heat transfer results for the pins. A pitot probe was traversed at the inlet and exit of the wind tunnel in order to measure the inlet and exit velocity profiles. For the endwall heat transfer, it was found for all configurations, that a local maxima occurs around one pin diameter downstream of the pin and a local heat transfer minima occurs near two pin diameters downstream of the pin. Nusselt number augmentation is generally higher closer to the longer side of the trapeze. The same trend is seen for the pin heat transfer which is in the columns closer to the long side of the duct larger than on the short edge of the duct. This claim can be supported with the results from the velocity profile measurements. Through the length of the duct, the flow shifts from the nose region to the larger opening on the opposite wall. This effect is weaker at higher flow rates, higher blockages, and larger ribs since more flow resistance exists, and this resistance hinders the flow to move sideward. Also, it is observed that increasing the blockage ratio as well as increasing the rib height, has a positive impact on heat transfer. It is also observed that increasing the Reynolds number causes a reduction in Nusselt number augmentation. At higher flow rates, the flow has higher momentum, and tends to be less impacted by the inclusion of the ribs, which results in the ribs being more effective at lower flow velocities. However, for low flow rates, the ribs only act as an extended surface, for higher flowrates though, the ribs act as turbulators as well which causes better mixing and a more evenly distributed heat transfer on the endwall. In order to interpret the presented measurements correctly, a comprehensive uncertainty analysis was conducted, and all heat transfer results are reported accurately within 12.3%. Repeatability tests show a maximum difference of 6%.

Heat Transfer Enhancement for Turbine Blade Internal Cooling

2013 ◽  
Author(s):  
Lesley M. Wright ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Gas Turbines ◽  
Critical Role ◽  
Turbine Blades ◽  
Internal Heat ◽  
Impinging Jets ◽  
Industrial Applications ◽  
Internal Cooling ◽  
Heat Transfer Augmentation

Gas turbines are used extensively for aircraft propulsion, land-based power generation, and industrial applications. The turbine inlet temperatures are far above the permissible metal temperatures. Therefore, there is a need to cool the blades for safe operation. Modern developments in turbine cooling technology play a critical role in increasing the thermal efficiency and power output of advanced gas turbine designs. Turbine blades and vanes are cooled internally and externally. This paper focuses on heat transfer augmentation of turbine blade internal cooling. Internal cooling is typically achieved by passing the cooling air through rib-enhanced serpentine passages inside the blades. Impinging jets, pin fins and dimples are also used for enhancing internal cooling heat transfer. In the past 10 years, there has been considerable progress in turbine blade internal cooling research and this paper is emphasized on reviewing selected publications to reflect recent developments in this area. In particular, this paper focuses on the newly developed design concepts as well as the combination of existing cooling techniques for turbine airfoil internal heat transfer augmentation. Rotation effects on the turbine blade leading-edge, triangular-shaped channel, mid-chord multi-pass channel and trailing-edge, wedge-shaped channel with coolant ejection are also considered.

Investigating Gas Turbine Internal Cooling Using Supercritical CO2 at High Reynolds Numbers for Direct Fired Cycle Applications

2021 ◽  
Author(s):  
Matthew Searle ◽  
Arnab Roy ◽  
James Black ◽  
Doug Straub ◽  
Sridharan Ramesh
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Gas Turbines ◽  
Cfd Simulation ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Process Conditions ◽  
Internal Cooling ◽  
Air Breathing

Abstract In this paper, experimental and numerical investigations of three variants of internal cooling configurations — dimples only, ribs only and ribs with dimples have been explored at process conditions (96°C and 207bar) with sCO2 as the coolant. The designs were chosen based on a review of advanced internal cooling features typically used for air-breathing gas turbines. The experimental study described in this paper utilizes additively manufactured square channels with the cooling features over a range of Reynolds number from 80,000 to 250,000. Nusselt number is calculated in the experiments utilizing the Wilson Plot method and three heat transfer characteristics — augmentation in Nusselt number, friction factor and overall Thermal Performance Factor (TPF) are reported. To explore the effect of surface roughness introduced due to additive manufacturing, two baseline channel flow cases are considered — a conventional smooth tube and an additively manufactured square tube. A companion computational fluid dynamics (CFD) simulation is also performed for the corresponding cooling configurations reported in the experiments using the Reynolds Averaged Navier Stokes (RANS) based turbulence model. Both experimental and computational results show increasing Nusselt number augmentation as higher Reynolds numbers are approached, whereas prior work on internal cooling of air-breathing gas turbines predict a decay in the heat transfer enhancement as Reynolds number increases. Comparing cooling features, it is observed that the “ribs only” and “ribs with dimples” configurations exhibit higher Nusselt number augmentation at all Reynolds numbers compared to the “dimples only” and the “no features” configurations. However, the frictional losses are almost an order of magnitude higher in presence of ribs.

scholarly journals The Effects of Incident Turbulence and Moving Wakes on Laminar Heat Transfer in Gas Turbines

1992 ◽  
Author(s):  
K. Dullenkopf ◽  
R. E. Mayle
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Gas Turbines ◽  
Free Stream ◽  
Cross Flow ◽  
Turbulence Parameter ◽  
Constant Acceleration ◽  
Free Stream Turbulence ◽  
Laminar Boundary Layers ◽  
Good Agreement

The effect of free-stream turbulence and moving wakes on augmenting heat transfer in accelerating laminar boundary layers is considered. First, the the effect of free-stream turbulence is re-examined in terms of a Nusselt number and turbulence parameter which correctly account for the free-stream acceleration and a correlation for both cylinders in cross flow and airfoils with regions of constant acceleration is obtained. This correlation is then used in a simple quasi-steady model to predict the effect of periodically passing wakes on airfoil laminar heat transfer. A comparison of the predictions with measurements shows good agreement.

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