Tony Arts

The Effect of Periodic Ribs on the Local Aerodynamic and Heat Transfer Performance of a Straight Cooling Channel

The local aerodynamic and heat transfer performance were measured in a rib-roughened square duct as a function of the rib pitch to height ratio. The blockage ratio of these square obstacles was 10 or 20 percent depending on whether they were placed on one single (1s) or on two opposite walls (2s). The Reynolds number, based on the channel mean velocity and hydraulic diameter, was fixed at 30,000. The aerodynamic description of the flow field was based on local pressure distributions along the ribbed and adjacent smooth walls as well as on two-dimensional LDV explorations in the channel symmetry plane and in two planes parallel to the ribbed wall(s). Local heat transfer distributions were obtained on the floor, between the ribs, and on the adjacent smooth side wall. Averaged parameters, such as friction factor and averaged heat transfer enhancement factor, were calculated from the local results and compared to correlations given in literature. This contribution showed that simple correlations derived from the law of the wall similarity and from the Reynolds analogy could not be applied for the present rib height-to-channel hydraulic diameter ratio (e/D h = 0.1). The strong secondary flows resulted in a three-dimensional flow field with high gradients in the local heat transfer distributions on the smooth side walls.

Investigation of the Unsteady Rotor Aerodynamics in a Transonic Turbine Stage

The paper focuses on the unsteady pressure field measured around the rotor midspan profile of the VKI Brite transonic turbine stage. The understanding of the complex unsteady flow field is supported by a quasi-three-dimensional unsteady Navier-Stokes computation using a k - ω turbulence model and a modified version of the Abu-Ghannam and Shaw correlation for the onset of transition. The agreement between computational and experimental results is satisfactory. They both reveal the dominance of the vane shock in the interaction. For this reason, it is difficult to identify the influence of vane-wake ingestion in the rotor passage from the experimental data. However, the computations allow us to draw some useful conclusions in this respect. The effect of the variation of the rotational speed, the stator-rotor spacing, and the stator trailing edge coolant flow ejection is investigated and the unsteady blade force pattern is analyzed.

Comparison of Turbine Tip Leakage Flow for Flat Tip and Squealer Tip Geometries at High-Speed Conditions

The tip leakage flow characteristics for flat and squealer turbine tip geometries are studied in the von Karman Institute Isentropic Light Piston Compression Tube facility, CT-2, at different Reynolds and Mach number conditions for a fixed value of the tip gap in a nonrotating, linear cascade arrangement. To the best knowledge of the authors, these are among the very few high-speed tip flow data for the flat tip and squealer tip geometries. Oil flow visualizations and static pressure measurements on the blade tip, blade surface, and corresponding endwall provide insight to the structure of the two different tip flows. Aerodynamic losses are measured for the different tip arrangements, also. The squealer tip provides a significant decrease in velocity through the tip gap with respect to the flat tip blade. For the flat tip, an increase in Reynolds number causes an increase in tip velocity levels, but the squealer tip is relatively insensitive to changes in Reynolds number.

Experimental Investigation of the Aerothermal Performance of a High Blockage Rib-Roughened Cooling Channel

The present study deals with a detailed experimental investigation of the turbulent flow inside a rib-roughened turbine blade cooling channel. The measurements are carried out in a stationary straight channel with high blockage ribs installed on one wall. The main objective is to enhance the understanding and deepen the analysis of this complex flow field with the help of highly resolved particle image velocimetry measurements. A quasi-three-dimensional view of the flow field is achieved, allowing the identification of the main time-averaged coherent structures. The combined analysis of the present aerodynamic results with available heat transfer data emphasizes the role of the mean and fluctuating flow features in the heat transfer process. In particular, the stream wise/ normal to the wall component of the Reynolds stress tensor is shown to be strictly related to the heat transfer rate on the channel surfaces. A correlation to estimate the heat transfer field from the aerodynamic data is presented for the high blockage rib roughened channel flow.

Unsteady Heat Transfer in Stator–Rotor Interaction by Two-Equation Turbulence Model

A transonic turbine stage is computed by means of an unsteady Navier-Stokes solver. A two-equation turbulence model is coupled to a transition model based on integral parameters and an extra transport equation. The transonic stage is modeled in two dimensions with a variable span height for the rotor row. The analysis of the transonic turbine stage with stator trailing edge coolant ejection is carried out to compute the unsteady pressure and heat transfer distribution on the rotor blade under variable operating conditions. The stator coolant ejection allows the total pressure losses to be reduced, although no significant effects on the rotor heat transfer are found both in the computer simulation and the measurements. The results compare favorable with experiments in terms of both pressure distribution and heat transfer around the rotor blade.

Investigation of the Flow Field Downstream of a Turbine Trailing Edge Cooled Nozzle Guide Vane

A trailing edge cooled low aspect ratio transonic turbine guide vane is investigated in the VKI Compression Tube Cascade Facility at an outlet Mach number {bar M}{sub 2,is} = 1.05 and a coolant flow rate {dot m}c/{dot m}g = 3 percent. The outlet flow field is surveyed by combined total-directional pressure probes and temperature probes. Special emphasis is put on the development of low blockage probes. Additional information is provided by oil flow visualizations and numerical flow visualizations with a three-dimensional Navier-Stokes code. The test results describe the strong differences in the axial evolution of the hub and tip endwall and secondary flows and demonstrate the self-similarity of the midspan wake profiles. According to the total pressure and temperature profiles, the wake mixing appears to be very fast in the near-wake but very slow in the far-wake region. The total pressure wake profile appears to be little affected by the coolant flow ejection.

Aerothermal Performance Measurements and Analysis of a Two-Dimensional High Turning Rotor Blade

The purpose of this contribution is to report on the aerothermal performance measurements and calculations carried out around a high-pressure gas turbine rotor blade profile mounted in a two-dimensional linear cascade arrangement. The measurements were performed in the CT-2 facility of the von Karman Institute, allowing a correct simulation of the operating conditions encountered in modern aero-engines. Independent variations of exit Mach (0.8--1.3) and Reynolds number (5 {times} 10{sup 5}--2 {times} 10{sup 6}), free-stream turbulence (1--6%) and incidence angle ({minus}14{minus} + deg) provided the definition of a detailed data base of test results. The measured quantities were the blade velocity and convective heat transfer coefficient distributions. The first objective of the paper is to open and analyze this data base, which is one of those used at SNECMA for validation purposes. The paper shows the degree of maturity and reliability SNECMA-ONERA Navier-Stokes solvers have now reached for daily use in turbine airfoil design and analysis.

Characterization of the Velocity and Heat Transfer Fields in an Internal Cooling Channel With High Blockage Ratio

The present experimental study is dealing with a detailed aero/thermal investigation of the turbulent flow inside a rib-roughened turbine blade cooling channel by means of Particle Image Velocimetry (PIV) and Liquid Crystal Thermometry (LCT). The main objectives of the paper are to provide detailed information about the behaviour of such a complicated flow, useful for its understanding, and to create a wide and reliable data base for numerical code validation. The measurements are carried out at engine representative Reynolds number within a scaled up model of a stationary straight cooling channel, with turbulent promoters (or ribs) installed on one wall. The ribs have an angle of attack of 90 deg with respect to the “mean” flow direction; their blockage ratio is equal to 30%. Detailed wall heat transfer distributions are presented. The main time-averaged flow features are identified and quantified; a number of rms characteristics are put in evidence and compared to the heat transfer distributions.Copyright

Aerodynamic Performance of a Very High Lift Low Pressure Turbine Airfoil (T106C) at Low Reynolds and High Mach Number With Effect of Free Stream Turbulence Intensity

A detailed experimental analysis of the effects of the Reynolds number and free-stream turbulence intensity on the aerodynamic performance of a very high-lift, mid-loaded low-pressure turbine blade (T106C) is presented in this paper. The study was carried out on a large scale linear cascade in the VKI S1/C high-speed wind tunnel, operating at high exit Mach number (0.65) with a range of low Reynolds numbers (80,000–160,000) and three levels of free-stream turbulence intensity (0.8–3.2%). In the first part of the paper, the overall aerodynamic performance of the airfoil is presented, based on mid-span measurements performed by means of static pressure taps, hot-film sensors and a five-hole probe traversing downstream of the cascade. Some specific features of separated flow transition are also discussed for selected cases. The second part presents the analysis of the results in terms of correlations derived for the characteristic points of boundary layer separation and transition. A comparison with some previously published prediction models is shown. The large variety of boundary conditions provides a unique database for validating codes dealing with separated flow transition in turbomachinery.

Aerodynamic Performance of a Very High Lift Low Pressure Turbine Blade With Emphasis on Separation Prediction

The present paper is based on an experimental study of a front-loaded very high lift, low pressure turbine blade designed at the VKI. The experiments have been carried out in a low-speed wind tunnel over a wide operating range of incidence and Reynolds number. The aim of the study is to characterize the flow through the cascade in terms of losses, mean outlet flow angle, and secondary flows. At low inlet freestream turbulence intensity, a laminar separation bubble is present, and a prediction model for a separated flow mode of transition has been developed.