This paper presents extensive results of an ongoing study on internal blade cooling concepts. A new test rig has been designed, built and commissioned, allowing fast comparison of different cooling schemes as well as surface temperature measurements for different cooling concepts. By scaling the test specimen, full aerothermal similarity was achieved at high measurement accuracy and resolution. Surface temperature (and thus total cooling effectiveness) is measured using high resolution, high dynamic range infrared thermography with an improved data evaluation method. Results for a conventional multi-pass cooling design are presented as a baseline case. Several new internal cooling concepts are then assessed for their relative cooling performance to the conventional design as well as their absolute cooling effectiveness. Those designs include various internal swirl concepts (cyclone cooling). The results show that great care has to be taken when designing advanced internal cooling concepts with complex flow structures, since the effects of internal crossflow, internal pressure loss, internal heat transfer coefficient, and film cooling effectiveness strongly interact with each other and the hot gas flow and hence affect the resulting total cooling effectiveness.
Focusing on the experimental analysis of the effect of variable inlet flows on aerodynamics, efficiency and heat transfer of a modern high pressure turbine, the Large Scale Turbine Rig (LSTR) at Technische Universität Darmstadt has been extensively redesigned. The LSTR is a full annular, rotating low speed turbine test rig carrying a scaled 1.5-stage (NGV1 - Rotor - NGV2) axial high-pressure turbine geometry designed by Rolls-Royce Deutschland to match engine-realistic Reynolds numbers. To simulate real turbine inflow conditions, the LSTR is equipped with a combustor simulator module including exchangeable swirlers. Other inflow conditions include axial or turbulent inflow as well as altered relative positions of swirl cores and NGVs by traversing. To investigate combustor-turbine interaction, the LSTR offers a large variety of optical and physical access ports as well as high flexibility to the application of measurement techniques. An elaborate secondary air system enables the simulation of various cooling air flows. The turbine section is equipped with film-cooled NGVs, a hub side seal air injection between NGVs and rotor, as well as a hub side RIDN cooling air injection module designed to provide realistic turbine flow conditions. Exchangeable hub side RIDN-plates allow for investigation of different coolant injection geometries. Measurement capabilities include 5-hole-probes, Pitot and total temperature rakes, as well as static pressure taps distributed along NGV radial sections and at the hub side passage endwall. The NGV passage flow can be visualized by means of Particle Image Velocimetry (PIV). Hot Wire Anemometry (HWA) will be used for time-resolved measurements of the turbulence level at several positions. The distributions of heat transfer and film cooling effectiveness are acquired using infrared thermography and CO2-gas tracing.
This paper presents a new approach for assessing rotor blade cooling concepts. A new test rig has been designed, built and commissioned, allowing fast comparison of different cooling schemes as well as absolute surface temperature measurements for different cooling concepts. By scaling the test specimen, full aerothermal similarity was achieved at high measurement accuracy and resolution. This similarity however poses high demand on the employed measurement techniques. Surface temperature (and thus cooling effectiveness) is measured using high resolution, high dynamic range infrared thermography with an improved calibration method for in-situ radiation correction. Furthermore, an improved image evaluation algorithm is presented, allowing angle-of-view dependent emissivity correction and full 3D-evaluation of image data. Those improvements enable the measurement on strongly cooled and strongly curved surfaces, and thus the use of scaled rotor blades with true geometry. First results are presented comparing total cooling effectiveness of a conventionally cooled blade with internal ribs to the effectiveness of an internal swirl design blade. They show the feasibility of the measurements and the importance of the presented correction method.
In the drive for higher cycle efficiencies in gas turbine engines, turbine blades are seeing an increasingly high heat load. This in turn demands improvements in the internal cooling system and a better understanding of both the level and distribution of the internal heat-transfer. A typical approach to enhance the internal cooling of the turbine blade is by casting angled 'low blockage' ribs on the walls of the cooling channels. The objective of the present paper is to determine the detailed Nusselt number distribution in rectangular internal channels with ribs. This knowledge can be used to guide the overall design e.g. to achieve high levels of heat-transfer where required. The effects of rotation as well as the interaction effects of the position and direction of ribs on opposite walls of the cooling channel have been investigated.Numerical calculations have been carried out using the commercial CFD code Fluent to investigate the local Nusselt number enhancement factor in rectangular ducts of different aspect ratios (0.5, 1 and 2) which have 45° or 90° angled ribs located on two opposite walls. This has been studied for different Rotation number Ro (0-0.45) and with a Reynolds number >30000.The first series of studies has been carried out with the same experimental setup as by Han [1]. The geometry was slightly changed to avoid the effect of high heat transfer at the entry.This study identifies important vortical structures, which are dependent on the direction and the position of the ribs. This has a profound effect on the distribution of heat-transfer within the passage. It is shown that the two smooth walls of the duct have different average Nusselt number ratio Nu/Nu FD enhancement depending on the rib angle.In addition, based on numerical investigations, simple correlations have been developed for the rotational influence of the internal Nusselt number distribution. A major finding is that the effect of rotation is dominant for low aspect ratio channels and the local enhancement due to the rib position and angle is more dominant for high aspect ratio channels.
An experimental study has been conducted to investigate the aerothermal performance of a shrouded high pressure turbine blade in a large scale rotating rig. The rotor blade and the associated shroud and casing geometry have been modelled in a large scale low speed turbine rig that was designed to investigate a novel passive shroud cooling methodology. The objective of the present paper is to provide a detailed description of the flow field around the rotor blade shroud. The improved physical understanding of the shroud flow gained from this study will be used to analyse the aerothermal performance of the shroud cooling strategy as reported in a companion paper, Lehmann et al. [1]. Experiments have been carried out using endoscopic PIV to identify and understand salient flow features that exist upstream and downstream of the shroud as well as within the shroud cavities. The measurements are complemented by steady and unsteady numerical computations of the turbine stage. The study identifies the existence of important vortical structures within the shroud cavities that not only interact with the main passage flow but also modify the amount and distribution of the shroud leakage flow in a manner that has major implications for shroud cooling and heat transfer. A detailed shroud flow model is derived and used to elucidate the causes and consequences of the flow pattern observed. The model emphasises the circumferentially asymmetric nature of the cavity flow structures caused by the presence of the inter shroud gap that in turn influences the production, interaction and dissipation of such vortical structures.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.