Boundary Layer Studies on Highly Loaded Cascades using Heated Thin Films and a Traversing Probe

1981 ◽  
Vol 103 (1) ◽  
pp. 237-246 ◽  
Author(s):  
M. L. G. Oldfield ◽  
R. Kiock ◽  
A. T. Holmes ◽  
C. G. Graham
Keyword(s):  
Boundary Layer ◽  
Transfer Rate ◽  
High Speed ◽  
Blade Profile ◽  
Aerodynamic Loading ◽  
Turbine Efficiency ◽  
Surface Transition ◽  
Turbine Vanes ◽  
Constant Temperature Anemometer ◽  
Highly Loaded

In the continuing quest for increased turbine efficiency, the part played by blade profile shape remains crucial. Three turbine vanes with successively increased aerodynamic loading were tested in the High Speed Cascade Wind Tunnel at DFVLR Braunschweig. In addition to wake traverses, measurements of the boundary layer behavior were made. These consisted of (1) use of a constant temperature anemometer to measure the fluctuating heat transfer rate on an array of thin film platinum thermometers deposited on the vanes and (2) a flattened, traversing pitot probe held against the vane surface. Transition measurement by these techniques is described.

scholarly journals Boundary Layer Studies on Highly Loaded Cascades Using Heated Thin Films and a Traversing Probe

1980 ◽  
Author(s):  
M. L. G. Oldfield ◽  
R. Kiock ◽  
A. T. Holmes ◽  
C. G. Graham
Keyword(s):  
Boundary Layer ◽  
Transfer Rate ◽  
High Speed ◽  
Blade Profile ◽  
Aerodynamic Loading ◽  
Turbine Efficiency ◽  
Surface Transition ◽  
Turbine Vanes ◽  
Constant Temperature Anemometer ◽  
Highly Loaded

In the continuing quest for increased turbine efficiency, the part played by blade profile shape remains crucial. Three turbine vanes with successively increased aerodynamic loading were tested in the High Speed Cascade Wind Tunnel at DFVLR Braunschweig. In addition to wake traverses, measurements of the boundary layer behavior were made. These consisted of: a) use of a constant temperature anemometer to measure the fluctuating heat transfer rate on an array of thin film platinum thermometers deposited on the vanes and b) a flattened, traversing pitot probe held against the vane surface. Transition measurement by these techniques is described.

A Low Reynolds Number Experimental Evaluation of Tubercles on a Low-Pressure Turbine Cascade

2019 ◽  
Author(s):  
Stephen A. Pym ◽  
Asad Asghar ◽  
William D. E. Allan ◽  
John P. Clark
Keyword(s):  
Boundary Layer ◽  
Turbine Blade ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Blade Profile ◽  
Suction Surface ◽  
Low Reynolds Numbers ◽  
Low Pressure Turbine ◽  
Low Reynolds ◽  
Highly Loaded

Abstract Aircraft are operating at increasingly high-altitudes, where decreased air density and engine power settings have led to increasingly low Reynolds numbers in the low-pressure turbine portion of modern-day aeroengines. These operating conditions, in parallel with highly-loaded blade profiles, result in non-reattaching laminar boundary layer separation along the blade suction surface, increasing loss and decreasing engine performance. This work presents an experimental investigation into the potential for integrated leading-edge tubercles to improve blade performance in this operating regime. A turn-table cascade test-section was constructed and commissioned to test a purpose-designed, forward-loaded, low-pressure turbine blade profile at various incidences and Reynolds numbers. Baseline and tubercled blades were tested at axial chord Reynolds numbers at and between 15 000 and 60 000, and angles of incidence ranging from −5° to +10°. Experimental data collection included blade surface pressure measurements, total pressure loss in the blade wakes, hot-wire anemometry, surface hot-film measurements, and surface flow visualization using tufts. Test results showed that the implementation of tubercles did not lead to a performance enhancement. However, useful conclusions were drawn regarding the ability of tubercles to generate stream-wise vortices at ultra-low Reynolds numbers. Additional observations helped to characterize the suction surface boundary layer over the highly-loaded, low-pressure turbine blade profile when at off-design conditions. Recommendations were made for future work.

Aerodynamic Loading Distribution Effects on Off-Design Performance of Highly Loaded LP Turbine Cascades Under Steady and Unsteady Incoming Flows

2016 ◽  
Author(s):  
Marco Berrino ◽  
Daniele Simoni ◽  
Marina Ubaldi ◽  
Pietro Zunino ◽  
Francesco Bertini
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Incidence Angle ◽  
Reynolds Numbers ◽  
Angle Variation ◽  
Aerodynamic Loading ◽  
Profile Losses ◽  
Unsteady Inflow ◽  
The Impact ◽  
Highly Loaded

The present work is part of a continuous cooperation between GE AvioAero and the University of Genova aimed at understanding the detailed flow physics of efficient highly loaded LPT blades for aeroengine applications. In this paper the effects of the aerodynamic loading distribution on the performances of three different cascades with the same Zweifel number have been experimentally investigated under steady and unsteady incoming flow conditions. Measurements have been carried out for several Reynolds numbers (in the range 70000<Re<300000) with an incidence angle variation of ±9°, in order to cover the typical realistic LP aeroengine turbine working range on design and off-design conditions. Profile aerodynamic loadings and total pressure loss coefficients have been evaluated for the different cases. Efficiency data clearly highlight that at nominal incidence an aft loaded cascade provides the lowest profile losses when the boundary layer is attached to the wall, as it occurs in the unsteady case or at high Reynolds numbers. Only at the lowest Reynolds number in the steady case, a front loaded profile is preferable since it helps to prevent a laminar boundary layer separation. Moreover, the aft loaded profile has also shown a better robustness to incidence angle variation, both for the steady and the unsteady inflow conditions. Indeed, the growth of profile losses with incidence is weaker for the aft loaded cascade with respect to the front and the mid loaded ones. However, irrespective of the loading distribution the loss trend vs incidence angle has been found to be completely different between the steady and the unsteady operations. Results in the paper give a clear overview of the impact of the loading distribution on profile losses as a function of Reynolds number, as well as a detailed view of the influence due to the loading characteristics on incidence robustness under the realistic unsteady inflow case.

Development of Blade Profiles for Low Pressure Turbine Applications

1996 ◽  
Author(s):  
E. M. Curtis ◽  
H. P. Hodson ◽  
M. R. Banieghbal ◽  
J. D. Denton ◽  
R. J. Howell ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Pressure ◽  
Low Pressure ◽  
Blade Profile ◽  
Suction Surface ◽  
Number Range ◽  
Low Pressure Turbine ◽  
Pressure Distributions ◽  
Wide Range ◽  
Highly Loaded

This paper describes a programme of work, largely experimental, which was undertaken with the objective of developing an improved blade profile for the low-pressure turbine in aero-engine applications. Preliminary experiments were conducted using a novel technique. An existing cascade of datum blades was modified to enable the pressure distribution on the suction surface of one of the blades to be altered. Various means, such as shaped inserts, an adjustable flap at the trailing edge, and changing stagger were employed to change the geometry of the passage. These experiments provided boundary layer and lift data for a wide range of suction surface pressure distributions. The data was then used as a guide for the development of new blade profiles. The new blade profiles were then investigated in a low-speed cascade that included a set of moving bars upstream of the cascade of blades 10 simulate the effect of the incoming wakes from the previous blade row in a multistage turbine environment. Results are presented for two improved profiles that are compared with a datum representative of current practice. The experimental results include loss measurements by wake traverse, surface pressure distributions, and boundary layer measurements. The cascades were operated over a Reynolds Number range from 0.7 × 105 to 4.0 × 105. The first profile is a “laminar flow” design that was intended to improve the efficiency at the same loading as the datum. The other is a more highly loaded blade profile intended to permit a reduction in blade numbers. The more highly loaded profile is the most promising candidate for inclusion in future designs. It enables blade numbers to be reduced by 20%, without incurring any efficiency penalty. The results also indicate that unsteady effects must be taken into consideration when selecting a blade profile for the low-pressure turbine.

Detailed Analysis of Boundary Layer Control by Fluidic Oscillators on a Highly Loaded Profile

2018 ◽  
Author(s):  
Julia Kurz ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Flow Separation ◽  
High Speed ◽  
Active Flow Control ◽  
Suction Side ◽  
Transition Process ◽  
Frequency Spectra ◽  
Active Flow ◽  
Highly Loaded

One application method of active flow control is the exploitation of the interaction between transition and flow separation on a profile. As turbulent flows are able to withstand higher adverse pressure gradients the enforcement of the transition process can be utilized to prevent or to reduce flow separation. This paper focuses on gaining a better understanding of high frequency active flow control (AFC) by fluidic oscillators and its influence on the transition process for a separated boundary layer. Flow control is applied on a highly loaded turbine exit case (TEC) profile which was in particular designed for this application. The profile is investigated in the high-speed cascade wind tunnel at the Bundeswehr University Munich. Significant loss reduction by AFC could be observed by total pressure loss determination in the low Reynolds number regime. In order to gain a better understanding of development of the suction side boundary layer, several boundary layer profiles are determined by hot-wire measurements at six axial positions on the suction side of the profile. Differences between the boundary layer development and the extent of the separation can be detected. Furthermore, a stability analysis of the boundary layer upstream of separation is conducted and compared to the measured frequency spectra.

scholarly journals High-speed flow with discontinuous surface catalysis

2000 ◽  
Vol 420 ◽  
pp. 325-359 ◽  
Author(s):  
S. R. AMARATUNGA ◽  
O. R. TUTTY ◽  
G. T. ROBERTS
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Gas Phase ◽  
Heat Transfer Rate ◽  
Recombination Rate ◽  
Transfer Rate ◽  
High Speed ◽  
Speed Flow ◽  
Surface Catalysis ◽  
Catalytic Recombination

In a reacting gas flow both gas-phase chemical activity and surface catalysis can increase the rate of heat transfer from the gas to a solid surface. In particular, when there is a discontinuous change in the catalytic properties of the surface, there can be a very large increase in the local heat transfer rate. In this study numerical simulations have been performed for the laminar high-speed flow of a high-temperature, non-equilibrium reacting gas mixture over a flat plate. The surface of the plate is partly catalytic, with the leading region non-catalytic, and a discontinuous change in the catalytic properties of the surface at the catalytic junction. The surface is assumed to be isothermal, and cold relative to the free stream. The gas is assumed to be a mixture of molecular and atomic forms of a diatomic gas in an inert gas forming a thermal bath, giving a three-species mixture with dissociation and recombination of the reactive species. The calculations are performed for a gas with atomic and molecular oxygen in an argon bath, but a full range of gas-phase chemical and surface catalytic effects is considered. Kinetic schemes with frozen gas-phase chemistry, and partial or full recombination of atomic oxygen in the boundary layer are investigated. The catalytic nature of the surface material is given by a catalytic recombination rate coeffcient, which varies from zero (non-catalytic) to one (fully catalytic), and the effects on the flow and the surface heat transfer of materials which are non-, partially, or fully catalytic are considered. A self-similar thin-layer analytical model of the change in the gas composition downstream of the catalytic junction is developed. For physically realistic (O(10−2)) values of the catalytic recombination rate coeffcient, the predictions from this model of the surface values of the atomic oxygen mass fraction and the catalytic surface heat transfer rate are excellent when the only change in the composition of the gas comes from the surface catalysis, and reasonable when there is partial recombination of the gas in the boundary layer due to the gas-phase chemistry. In contrast, when the surface is fully catalytic, the streamwise diffusion terms play a significant role, and the model is not valid. These results should apply to other situations with an attached boundary layer with recombination reactions. A comparison is made between the calculated and experimental measurements of the heat transfer rate at the catalytic junction. With a kinetic scheme which allows partial recombination in the boundary layer, good agreement is found between the experimental and predicted values for surface materials which are essentially non-catalytic. For a catalytic material (platinum), the experimental and numerical heat transfer rates are matched to estimate the value of the catalytic recombination rate coeffcient. The values obtained show a considerable amount of scatter, but are consistent with those found in the literature.

Numerical Study of Transitional Rough Wall Boundary Layer

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Witold Elsner ◽  
Piotr Warzecha
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Flat Plate ◽  
Turbine Blade ◽  
Numerical Study ◽  
Rough Wall ◽  
Blade Profile ◽  
Modeling Approach ◽  
Wall Boundary ◽  
Highly Loaded

This paper presents the verification of the boundary layer modeling approach, which relies on a γ-Reθt model proposed by Menter et al. (2006, “A Correlation-Based Transition Model using Local Variables—Part I: Model Formation,” J. Turbomach., 128(3), pp. 413–422). This model was extended by laminar-turbulent transition correlations proposed by Piotrowski et al. (2008, “Transition Prediction on Turbine Blade Profile with Intermittency Transport Equation,” Proceedings of the ASME Turbo Expo, Paper No. GT2008-50796) as well as Stripf et al.'s (2009, “Extended Models for Transitional Rough Wall Boundary Layers with Heat Transfer—Part I: Model Formulation,” J. Turbomach., 131(3), 031016) correlations, which take into account the effects of surface roughness. To blend between the laminar and fully turbulent boundary layer over rough wall, the modified intermittency equation is used. To verify the model, a flat plate with zero and nonzero pressure gradient test cases as well as the high pressure turbine blade case were chosen. Furthermore, the model was applied for unsteady calculations of the turbine blade profile as well as the Lou and Hourmouziadis (2000, “Separation Bubbles Under Steady and Periodic-Unsteady Main Flow Conditions,” J. Turbomach., 122(4), pp. 634–643) flat plate test case, with an induced pressure profile typical for a suction side of highly-loaded turbine airfoil. The combined effect of roughness and wake passing were studied. The studies proved that the proposed modeling approach (ITMR hereinafter) appeared to be sufficiently precise and enabled for a qualitatively correct prediction of the boundary layer development for the tested simple flow configurations. The results of unsteady calculations indicated that the combined impact of wakes and the surface roughness could be beneficial for the efficiency of the blade rows, but mainly in the case of strong separation occurring on highly-loaded blade profiles. It was also demonstrated that the roughness hardly influences the location of wake induced transition, but has an impact on the flow in between the wakes.

Simulations of Shock/Boundary-Layer Interactions Over Highly Loaded Turbine Blades

2003 ◽  
Author(s):  
Yi Liu
Keyword(s):  
Boundary Layer ◽  
Stokes Equations ◽  
Computing Time ◽  
Turbine Blades ◽  
Navier Stokes ◽  
Flux Vector ◽  
Compressibility Effect ◽  
Turbine Vanes ◽  
Flux Vector Splitting ◽  
Highly Loaded

Transonic viscous flow over highly loaded turbine blades, where the interaction of a shock wave and a boundary layer often leads to extremely complicated flow phenomena, has been studied numerically in this paper. A Modified Implicit Flux Vector Splitting solver of the Navier-Stokes equations, which has been well established though combining a unique implicit formulation with a Flux Vector Splitting, has been extended to simulate a transonic cascade flow. A low Reynolds number k-ε turbulence model, with the compressibility effect considered, and a transition model have been implemented to predict heat transfer, flow patterns in the high loaded transonic turbine vanes and turbine vanes and blades. Numerical investigations show it has obvious superiority in terms of accuracy, robustness, convergence and computing time.

Development of Blade Profiles for Low-Pressure Turbine Applications

1997 ◽  
Vol 119 (3) ◽  
pp. 531-538 ◽  
Author(s):  
E. M. Curtis ◽  
H. P. Hodson ◽  
M. R. Banieghbal ◽  
J. D. Denton ◽  
R. J. Howell ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Pressure ◽  
Low Pressure ◽  
Blade Profile ◽  
Suction Surface ◽  
Number Range ◽  
Low Pressure Turbine ◽  
Pressure Distributions ◽  
Wide Range ◽  
Highly Loaded

This paper describes a program of work, largely experimental, which was undertaken with the objective of developing an improved blade profile for the low-pressure turbine in aero-engine applications. Preliminary experiments were conducted using a novel technique. An existing cascade of datum blades was modified to enable the pressure distribution on the suction surface of one of the blades to be altered. Various means, such as shaped inserts, an adjustable flap at the trailing edge, and changing stagger were employed to change the geometry of the passage. These experiments provided boundary layer and lift data for a wide range of suction surface pressure distributions. The data were then used as a guide for the development of new blade profiles. The new blade profiles were then investigated in a low-speed cascade that included a set of moving bars upstream of the cascade of blades to simulate the effect of the incoming wakes from the previous blade row in a multistage turbine environment. Results are presented for two improved profiles that are compared with a datum representative of current practice. The experimental results include loss measurements by wake traverse, surface pressure distributions, and boundary layer measurements. The cascades were operated over a Reynolds number range from 0.7 × 105 to 4.0 × 105. The first profile is a “laminar flow” design that was intended to improve the efficiency at the same loading as the datum. The other is a more highly loaded blade profile intended to permit a reduction in blade numbers. The more highly loaded profile is the most promising candidate for inclusion in future designs. It enables blade numbers to be reduced by 20 percent, without incurring any efficiency penalty. The results also indicate that unsteady effects must be taken into consideration when selecting a blade profile for the low-pressure turbine.

Influence of Blade Profile on Secondary Flow in Ultra-Highly Loaded Turbine Cascades at Off-Design Incidence

2013 ◽  
Author(s):  
Hoshio Tsujita
Keyword(s):  
Secondary Flow ◽  
Turbine Blade ◽  
Gas Turbines ◽  
Incidence Angle ◽  
Horseshoe Vortex ◽  
Blade Profile ◽  
Suction Surface ◽  
Turbine Efficiency ◽  
Oil Flow ◽  
Highly Loaded

An increase of aerodynamic loading of turbine blade leads to the reductions of the numbers of blade and stage. As a result, the size and the weight of gas turbines could be reduced. However, the secondary flow becomes much stronger because of the steeper pressure gradient across the cascade passage, and consequently deteriorates the turbine efficiency. Therefore, it is very important to minimize the loss generation increased by the increase of loading. In the present study, the influences of blade profile on the secondary flow structure in a linear ultra-highly loaded turbine cascade (UHLTC) at off-design incidence were investigated in detail by using a numerical method. The computations were performed for the flow in three types of UHLTC at zero and off-design incidences. The present three types of turbine blade are same in the inlet and the outlet metal angles but different in the length of the blade suction surface. The verification of the computed results was performed by comparing with the experimental oil flow visualizations and the measured static pressure on the blade surface. The decrease of the length of blade suction surface increased both the profile loss and the secondary loss according to the increase of incidence angle in the positive range. The positive incidence not only strengthened the horseshoe and the passage vortices but also induced a new vortex along the blade suction surface on the end-wall. The incidence angle at which the newly formed vortex appeared was influenced by the blade profile. Moreover, the newly formed vortex affected the strength of the pressure side leg of horseshoe vortex.

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