Journal of Turbomachinery

Journal: Journal of Turbomachinery

Abbreviation

J. Turbomach

Publisher

American Society of Mechanical Engineers

ISSN

0889-504X
1528-8900

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Publications1 - 10 of 53

Three-Dimensional Flow Prediction and Improvement of Holes Arrangement of a Film-Cooled Turbine Blade Using a Feature-Based Jet Model
Burdet, André; Abhari, Reza S. (2007)
Journal of Turbomachinery
Experimental Investigation of Conjugate Heat Transfer in a Rib-Roughened Trailing Edge Channel With Crossing Jets
Coletti, Filippo; Scialanga, Manfredi; Arts, Tony (2011)
Journal of Turbomachinery
The present contribution is devoted to the experimental study of the conjugate heat transfer in a turbine blade cooling cavity located near the trailing edge. The cooling scheme is characterized by a trapezoidal cross-section, one rib-roughened wall, and slots along two opposite walls. The Reynolds number, defined at the inlet of the test section, is set at 67,500 for all the experiments. The values of all the important nondimensional parameters characterizing the experiment, including the solid-to-fluid conductivity ratio, are engine-representative. Uniform heat flux is imposed along the outer side of the rib-roughened wall. The measurements are performed using three different ribbed walls, with thermal conductivities ranging from 1 W m−1 K−1 to 18 W m−1 K−1. Highly resolved distributions of nondimensional temperature and Nusselt number over the rib-roughened wall are obtained by means of infrared thermography and finite element analysis. The impact of the conduction through the wall on the thermal performance is demonstrated by comparison with purely convective results, previously published by the authors on the same configuration.
Investigation of an inversely designed centrifugal compressor stage - Part I: Design and numerical verification
Zangeneh, Mehrdad; Schleer, Matthias; Pløger, F.; et al. (2004)
Journal of Turbomachinery
Improving Efficiency of a High Work Turbine Using Nonaxisymmetric Endwalls - Part II: Time-Resolved Flow Physics
Schüpbach, Peter; Abhari, Reza S.; Rose, Martin G.; et al. (2010)
Journal of Turbomachinery
This paper is the second part of a two part paper that reports on the improvement of efficiency of a one and a half stage high work axial flow turbine. The first part covered the design of the endwall profiling, as well as a comparison with steady probe data; this part covers the analysis of the time-resolved flow physics. The focus is on the time-resolved flow physics that leads to a total-to-total stage efficiency improvement of 1.0%±0.4%. The investigated geometry is a model of a high work (Δh/U2=2.36), axial shroudless HP turbine. The time-resolved measurements have been acquired upstream and downstream of the rotor using a fast response aerodynamic probe (FRAP). This paper contains a detailed analysis of the secondary flow field that is changed between the axisymmetric and the nonaxisymmetric endwall profiling cases. The flowfield at the exit of the first stator is improved considerably due to the nonaxisymmetric endwall profiling and results in reduced secondary flow and a reduction in loss at both hub and tip, as well as a reduced trailing shed vorticity. The rotor has reduced losses and a reduction in secondary flows mainly at the hub. At the rotor exit, the flow field with nonaxisymmetric endwalls is more homogenous due to the reduction in secondary flows in the two rows upstream of the measurement plane. This confirms that nonaxisymmetric endwall profiling is an effective tool for reducing secondary losses in axial turbines. Using a frozen flow assumption, the time-resolved data are used to estimate the axial velocity gradients, which are then used to evaluate the streamwise vorticity and dissipation. The nonaxisymmetric endwall profiling of the first nozzle guide vane show reductions in dissipation and streamwise vorticity due to the reduced trailing shed vorticity. This smaller vorticity explains the reduction in loss at midspan, which is shown in the first part of the two part paper. This leads to the conclusion that nonaxisymmetric endwall profiling also has the potential of reducing trailing shed vorticity.
Modeling of Film Cooling
Burdet, André; Abhari, Reza S.; Rose, Martin G. (2007)
Journal of Turbomachinery
Computational fluid dynamics (CFD) has recently been used for the simulation of the aerothermodynamics of film cooling. The direct calculation of a single cooling hole requires substantial computational resources. A parametric study, for the optimization of the cooling system in real engines, is much too time consuming due to the large number of grid nodes required to cover all injection holes and plenum chambers. For these reasons, a hybrid approach is proposed, based on the modeling of the near film-cooling hole flow, tuned using experimental data, while computing directly the flow field in the blade-to-blade passage. A new injection film-cooling model is established, which can be embedded in a CFD code, to lower the central processing unit (CPU) cost and to reduce the simulation turnover time. The goal is to be able to simulate film-cooled turbine blades without having to explicitly mesh inside the holes and the plenum chamber. The stability, low CPU overhead level (1%) and accuracy of the proposed CFD-embedded film-cooling model are demonstrated in the ETHZ steady film-cooled flat-plate experiment presented in Part I (Bernsdorf, Rose, and Abhari, 2006, ASME J. Turbomach., 128, pp. 141–149) of this two-part paper. The prediction of film-cooling effectiveness using the CFD-embedded model is evaluated.
An additively manufactured four-sensor fast response aerodynamic probe
Chasoglou, Alexandros; Tsirikoglou, Panagiotis; Kalfas, Anestis; et al. (2021)
Journal of Turbomachinery
This study describes the design, development, and testing of a miniature fast response aerodynamic probe (FRAP) with four sensors (4S), which are able to perform measurements in the unsteady three-dimensional flow field. Moreover, the calibration and first results with the newly developed probe are provided. The miniature FRAP-4S demonstrates a 3 mm tip diameter, offering a 25% reduction in diameter size, in comparison to a first-generation FRAP-4S, without any loss in terms of measurement bandwidth. The 3 mm outer casing of the probe is additively manufactured with a high-precision binder jetting technique. In terms of aerodynamic performance, the probe demonstrates high angular sensitivity up to ±18 deg incidence angle in both directions. To evaluate the measurement accuracy of the newly developed FRAP-4S, measurements are performed at the Laboratory for Energy Conversion (LEC) in both a round axisymmetric jet and an one-and-a-half stage, unshrouded and highly loaded axial turbine configuration. Turbulence measurements performed with the miniature FRAP-4S are compared against hot-wire studies in round freejets found in the literature. Good agreement in both trends but also absolute values is demonstrated. Moreover, the performance of the probe is compared against traditional instrumentation developed at LEC, namely, miniature pneumatic and FRAP-2S probes. The results indicate that the FRAP-4S, despite its larger size in comparison to the other probes tested, can resolve the main flow patterns, with the highest deviations occuring in the presence of highly skewed and sheared flow. Furthermore, the additively manufactured probe was proven to be robust after more than 50 hours of testing in the representative turbine environment configuration. Finally, it should be highlighted that the newly developed FRAP reduces measurement time by a factor of three in comparison to FRAP-2S, which directly translates to reduced development time and thus cost during the turbomachinery development phase.
Experimental and Numerical Investigation of the Unsteady Flow Field in a Vaned Diffuser of a High-Speed Centrifugal Compressor
Vogel, Klemens; Abhari, Reza S.; Zemp, Armin (2015)
Journal of Turbomachinery
Fluid dynamics and performance of partially and fully shrouded axial turbines
Porreca, L.; Behr, T.; Schlienger, J.; et al. (2005)
Journal of Turbomachinery
A unique comparative experimental and numerical investigation carried out on two test cases with shroud configurations, differing only in the labyrinth seal path, is presented in this paper. The blade geometry and tip clearance are identical in the two test cases. The geometries under investigation are representative of an axial turbine with a full and partial shroud, respectively. Global performance and flow field data were acquired and analyzed. Computational simulations were carried out to complement the investigation and to facilitate the analysis of the steady and unsteady flow measurements. A detailed comparison between the two test cases is presented in terms of flow field analysis and performance evaluation. The analysis focuses on the flow effects reflected on the overall performance in a multi-stage environment. Strong interaction between the cavity flow and the blade tip region of the rotor blades is observed up to the blade midspan. A marked effect of this interaction can be seen in the downstream second stator where different vortex structures are observed. Moreover, in the partial shroud test case, a strong tip leakage vortex is developed from the first rotor and transported through the downstream blade row. A measurable change in the second stage efficiency was observed between the two test cases. In low aspect ratio blades within a multi-stage environment, small changes in the cavity geometry can have a significant effect on the mainstream flow. The present analysis has shown that an integrated and matched blade-shroud aerodynamic design has to be adopted to reach optimal performances. The additional losses resulting from small variations of the sealing geometry could result in a gain of up to one point in the overall stage efficiency.
Turbine Hub Cavity Modes and Their Impact on Efficiency
Iranidokht, Vahid; Purwar, Naman; Kalfas, Anestis I.; et al. (2021)
Journal of Turbomachinery
Non-synchronous pressure and temperature fluctuations at the hub cavity of a turbine stage are the main focus of this study. Cavity modes are unsteady fluctuations generated at the cavity exit due to instabilities in this region. The cavity modes carried into the main flow impose an unsteady flow field in the rotor passages, which varies the passage-wise flow parameters considerably. A two-stage axial turbine was designed and tested in the "LISA"test facility at ETH Zurich. A reference case with baseline geometry and a modified case with an axial deflector at the hub cavity exit were tested. Comprehensive unsteady pressure and temperature measurements were performed using fast response aerodynamic (FRAP) and entropy probes (FENT), respectively. In addition, 12 fast response unsteady pressure transducers were mounted on the stationary wall of the cavity exit to measure the main characteristic parameters of the cavity modes. Full annular unsteady simulations were also carried out for both cases to support the experiments. Computational fluid dynamics (CFD) successfully predicted the effect of cavity modes on both frequency and amplitude of the fluctuations. The cavity modes indicated fluctuation amplitudes up to eight times of the blade passing fluctuations at the cavity exit. The analysis shows that the convected cavity modes alter the efficiency of different rotor passages by redistributing the mass flow and the losses resulting in a drop in overall efficiency. This work suggests that implementing a small axial deflector at the hub cavity exit would completely eliminate the cavity modes leading to a reduced pressure unsteadiness and enhanced efficiency
Clearance Effects on the Evolution of the Flow in the Vaneless Diffuser of a Centrifugal Compressor at Part Load Condition
Schleer, Matthias Wolfgang; Abhari, Reza S. (2008)
Journal of Turbomachinery
This work reports on flow measurements taken within the vaneless diffuser of a scaled-up model of a small-scale, highly loaded unshrouded compressor with large relative tip clearance. The aims are to describe and to analyze the influence of the clearance flow on the flow structure at the impeller exit in part load operation. The kind of compressor described herein is widely used in distributed power applications and automotive turbocharging. It demands further enhancement of the operation range, as well as a high head rise and an improved efficiency. Therefore, the understanding of flow features and their interaction is crucial. The interaction and mixing of the flow pattern downstream of the impeller are shown using spatially and temporally resolved 3D-velocity data. The measurements have been obtained by using a 3D laser Doppler anemometry system throughout the vaneless parallel wall diffuser. This unique data set provides insight into the development of the flow within the diffuser and allows conclusions on the mixing and migration of the three-dimensional pattern. The flow structure in part load condition is strongly affected by the flow across the large relative tip gap. Due to the large relative tip clearance, a low momentum zone is formed as an additional pattern at the shroud. This clearance flow is highly vortical and interacts with the channel wake structure but remains stable throughout the vaneless diffuser. At the pressure side hub corner, a jet structure is formed, which interacts rapidly with the blade wake. This flow behavior does not comply with the classical jet-wake pattern. It is proposed that in a centrifugal compressor with large relative tip clearance, a modified flow model that includes tip leakage is more appropriate to describe the flow structure at part load condition.

Publications1 - 10 of 53

Journal: Journal of Turbomachinery

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