Reynolds Number Effects in a Low Pressure Turbine

2012 ◽  
Author(s):  
Harjit S. Hura ◽  
John Joseph ◽  
Dave E. Halstead
Keyword(s):  
Reynolds Number ◽  
Boundary Layer Separation ◽  
Low Pressure ◽  
Lapse Rate ◽  
Low Pressure Turbine ◽  
Rate Analysis ◽  
Flow Capacity ◽  
Turbulence Transition ◽  
Viscous Losses ◽  
Reynolds Number Effects

This paper reports the results of an experimental and analytical study of Reynolds number (Re) effect on Low Pressure Turbine (LPT) performance. LPTs suffer both a loss in efficiency and flow capacity at altitude due to thicker boundary layers and higher viscous losses. Boundary layer separation can occur in highly loaded and/or high lift designs. The magnitude of the effect is stronger for smaller engines being designed for regional jets which may have cruising altitudes above 50K feet. There is a general lack of knowledge about performance degradation in commercial LPTs under these conditions. A test program was undertaken in a low pressure 3 stage axial turbine to quantify the effect of low Re on efficiency and flow lapse rate. Rig inlet pressures were varied from 0.27E+5 N/m2 (4 psia) to 4.40E+5 N/m2 (65 psia) to achieve over a 15 fold variation in Re. The chord based average Re varied from 30000 to 500000. Efficiency and flow function lapse of over 5% was measured. The fall off was non-linear with a rapid loss occurring at Re below 100000. 3D CFD analysis was conducted in parallel to predict overall performance but also understand loss details within the blade rows. Measured inlet profiles of total pressure, temperature and air angle, and exit static pressure were used as boundary conditions. Leakages and purge flows were modeled as source terms. A turbulence transition model and wall integration grids was used. The CFD results corroborate the test findings on the overall efficiency and flow capacity lapse rate. Analysis of blade row performance at high and low Re shows a sharp increase in profile loss at low Re.

Prediction of Lapse Rate in Low Pressure Turbines With and Without Modeling of the Laminar-Turbulent Transition

2007 ◽  
Author(s):  
Mahmoud L. Mansour ◽  
S. Murthy Konan ◽  
Shraman Goswami
Keyword(s):  
Reynolds Number ◽  
Turbulence Model ◽  
Test Data ◽  
Low Pressure ◽  
Lapse Rate ◽  
Test Cases ◽  
Low Pressure Turbine ◽  
Turbulent Transition ◽  
Transition Modeling ◽  
Laminar Turbulent Transition

Although turbo-machinery main stream flows are predominantly turbulent, the low pressure turbine airfoil surface boundary layer may be either laminar or turbulent. When boundary layer flow is laminar and passes through a zone of adverse pressure gradient, bypass or separation transition can occur via the Tollmien-Schlichting or Kelvin-Helmholtz instabilities. As the gas turbine’s low pressure turbine operating condition changes from sea level take-off to the altitude cruise, Reynolds number is significantly lowered and the turbine’s performance loss increases significantly. This fall-off in performance characteristic is known as lapse rate. Ability to accurately model such phenomenon is a prerequisite for reliable loss prediction and essential for improving low pressure turbine designs. Establishing such capability requires the validation and evaluation of existing low Reynolds number turbulence models, with laminar-turbulent transition modeling capability, against test cases with measured data. This paper summarizes the results of evaluating and validating two 3D viscous “RANS” Reynolds-Averaged Navier-Stokes programs for two test cases with test data. The first test case is the ERCOFTAC’ flat plate with and without pressure gradient, and the second is a Honeywell three-and-half-stage low pressure turbine with available test data at high and low Reynolds number operations. In addition to evaluating the CFD codes against test data, the flat plate test cases were used to establish the meshing and modeling best practice for each code before performing the validation for the Honeywell multistage low pressure turbine. The RANS CFD programs are Numeca’s Fine Turbo and ANSYS/CFX. Numeca’s Fine Turbo employs a two-equation K-ε turbulence model without laminar-turbulent transition modeling capability and the one-equation Spallart-Allmaras turbulence model with laminar-turbulent transition modeling capability. The ANSYS/CFX, on the other hand, employs a two-equation K-ω turbulence model (AKA SST or shear stress transport) with ability to model laminar-turbulent transition. Predictions of the CFD codes are compared with test data and the impact of modeling the laminar-turbulent transition on the prediction accuracy is assessed and presented. Both CFD codes are commercially available and the evaluation presented here is based on users’ prospective that targets the applicability of such predictive tools in the turbine design process.

Separated Flow Measurements on a Highly Loaded Low-Pressure Turbine Airfoil

2008 ◽  
Author(s):  
Ralph J. Volino
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Separation Bubble ◽  
Boundary Layer Separation ◽  
Low Pressure ◽  
Transition To Turbulence ◽  
Suction Surface ◽  
Airfoil Surface ◽  
Flow Measurements ◽  
Low Pressure Turbine

Boundary layer separation, transition and reattachment have been studied on a new, very high lift, low-pressure turbine airfoil. Experiments were done under low freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Velocity profiles were acquired in the suction side boundary layer at several streamwise locations using hot-wire anemometry. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) ranging from 25,000 to 330,000. In all cases the boundary layer separated, but at high Reynolds number the separation bubble remained very thin and quickly reattached after transition to turbulence. In the low Reynolds number cases, the boundary layer separated and did not reattach, even when transition occurred. This behavior contrasts with previous research on other airfoils, in which transition, if it occurred, always induced reattachment, regardless of Reynolds number.

An Investigation of Reynolds Lapse Rate for Highly Loaded Low Pressure Turbine Airfoils With Forward and Aft Loading

2011 ◽  
Author(s):  
M. Eric Lyall ◽  
Paul I. King ◽  
Rolf Sondergaard ◽  
John P. Clark ◽  
Mark W. McQuilling
Keyword(s):  
Reynolds Number ◽  
Eddy Viscosity ◽  
Low Pressure ◽  
Lapse Rate ◽  
Freestream Turbulence ◽  
Number Range ◽  
Low Pressure Turbine ◽  
Turbine Airfoils ◽  
Hot Film ◽  
Highly Loaded

This paper presents an experimental and computational study of the midspan low Reynolds number loss behavior for two highly loaded low pressure turbine airfoils, designated L2F and L2A, which are forward and aft loaded, respectively. Both airfoils were designed with incompressible Zweifel loading coefficients of 1.59. Computational predictions are provided using two codes, Fluent (with k-k1-ω model) and AFRL’s Turbine Design and Analysis System (TDAAS), each with a different eddy-viscosity RANS based turbulence model with transition capability. Experiments were conducted in a low speed wind tunnel to provide transition models for computational comparisons. The Reynolds number range based on axial chord and inlet velocity was 20,000 < Re < 100,000 with an inlet turbulence intensity of 3.1%. Predictions using TDAAS agreed well with the measured Reynolds lapse rate. Computations using Fluent however, predicted stall to occur at significantly higher Reynolds numbers as compared to experiment. Based on triple sensor hot-film measurements, Fluent’s premature stall behavior is likely the result of the eddy-viscosity hypothesis inadequately capturing anisotropic freestream turbulence effects. Furthermore, rapid distortion theory is considered as a possible analytical tool for studying freestream turbulence that influences transition near the suction surface of LPT airfoils. Comparisons with triple sensor hot-film measurements indicate that the technique is promising but more research is required to confirm its utility.

scholarly journals Reynolds, Mach and free-stream turbulence effects on the flow in a low-pressure turbine

2021 ◽  
pp. 1-17
Author(s):  
Maxime Fiore ◽  
Nicolas Gourdain
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Free Stream ◽  
Guide Vane ◽  
Flow Behavior ◽  
Suction Side ◽  
Boundary Layer Separation ◽  
Low Pressure ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine

Abstract This paper presents the Large Eddy Simulation of a Low-Pressure Turbine Nozzle Guide Vane for different Reynolds (Re) and Mach numbers (Ma) with or without inlet turbulence prescribed. The analysis is based on a slice of a LPT blading representative of a midspan flow. The characteristic Re of the LPT can vary by a factor of four between take-off and cruise conditions. In addition, the LPT operates at different Ma and the incident flow can have significant levels of turbulence due to upstream blade wakes. The paper investigates numerically using LES the flow around a LPT blading with three different Reynolds number Re = 175'000 (cruise), 280'000 (mid-level altitude) and 500'000 (take-off) keeping the same characteristic Mach number Ma = 0.2 and three different Mach number Ma = 0.2, 0.5 and 0.8 keeping the same Reynolds number Re= 280'000. These different simulations are performed with 0% Free Stream Turbulence (FST) followed by inlet turbulence (6% FST). The study focuses on different flow characteristics: pressure distribution around the blade, near-wall flow behavior, loss generation and Turbulent Kinetic Energy budget. The results show an earlier boundary layer separation on the aft of the blade suction side when the Re is increased while the free-stream turbulence delays separation. The TKE budget shows the predominant effect of the turbulent production and diffusion in the wake, the axial evolution of these different terms being relatively insensitive to Re and Ma.

An Investigation of Reynolds Lapse Rate for Highly Loaded Low Pressure Turbine Airfoils With Forward and Aft Loading

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
M. Eric Lyall ◽  
Paul I. King ◽  
Rolf Sondergaard ◽  
John P. Clark ◽  
Mark W. McQuilling
Keyword(s):  
Reynolds Number ◽  
Eddy Viscosity ◽  
Low Pressure ◽  
Lapse Rate ◽  
Freestream Turbulence ◽  
Number Range ◽  
Low Pressure Turbine ◽  
Turbine Airfoils ◽  
Hot Film ◽  
Highly Loaded

This paper presents an experimental and computational study of the midspan low Reynolds number loss behavior for two highly loaded low pressure turbine airfoils, designated L2F and L2A, which are forward and aft loaded, respectively. Both airfoils were designed with incompressible Zweifel loading coefficients of 1.59. Computational predictions are provided using two codes, Fluent (with k-kl-ω model) and AFRL’s Turbine Design and Analysis System (TDAAS), each with a different eddy-viscosity RANS based turbulence model with transition capability. Experiments were conducted in a low speed wind tunnel to provide transition models for computational comparisons. The Reynolds number range based on axial chord and inlet velocity was 20,000 < Re < 100,000 with an inlet turbulence intensity of 3.1%. Predictions using TDAAS agreed well with the measured Reynolds lapse rate. Computations using Fluent however, predicted stall to occur at significantly higher Reynolds numbers as compared to experiment. Based on triple sensor hot-film measurements, Fluent’s premature stall behavior is likely the result of the eddy-viscosity hypothesis inadequately capturing anisotropic freestream turbulence effects. Furthermore, rapid distortion theory is considered as a possible analytical tool for studying freestream turbulence that influences transition near the suction surface of LPT airfoils. Comparisons with triple sensor hot-film measurements indicate that the technique is promising but more research is required to confirm its utility.

Reynolds Number Effects on the Performance of a Turbofan Engine

1989 ◽  
Author(s):  
Masao Kozu ◽  
Satoshi Yashima
Keyword(s):  
Reynolds Number ◽  
Gas Flow ◽  
Pressure Ratio ◽  
Engine Performance ◽  
Low Pressure ◽  
Aerodynamic Characteristics ◽  
Turbofan Engine ◽  
Low Pressure Turbine ◽  
Reynolds Number Effects ◽  
The Difference

Reynolds Number effects on the matching performance of a small twin-spool turbofan engine were investigated through the altitude tests of the F3-30 engine which was developed to power the Japan Air Self Defence Force’s T-4 intermediate trainer. Analyzing the test results made it clear that the change of the aerodynamic characteristics of the low pressure turbine due to Reynolds Number effects is as significant as these of fan and compressor, and it caused the difference between the predicted and measured engine performance at high altitudes. Correlation factors on the Reynolds Number for each of the component characteristics (pressure ratio, airflow and efficiency of fan and compressor, and gas flow and efficiency of low pressure turbine) were obtained, and simulation of the engine performance using these factors coincided well with the test data which were obtained from the altitude tests of the F3-30 at Arnold Engineering Development Center of U. S. Air Force.

The Effect of FSTI to the Combined Separation Control Strategy of Surface Roughness With Upstream Wakes

2016 ◽  
Author(s):  
Sun Shuang ◽  
Lei Zhi-jun ◽  
Lu Xin-gen ◽  
Zhang Yan-feng ◽  
Zhu Jun-qiang
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Reynolds Number ◽  
Transition Region ◽  
Boundary Layer Separation ◽  
Low Pressure ◽  
Suction Surface ◽  
High Lift ◽  
Number Range ◽  
Low Pressure Turbine

Boundary layer separation can lead to partial loss of lift and higher aerodynamic losses on low-pressure turbine airfoils at low Reynolds number in high bypass ratio engines. The combined effects of upstream wakes and surface roughness on boundary layer development have been investigated experimentally to improve the performance of ultra-high-lift low-pressure turbine (LPT) blades. The measurement was performed on a linear cascade with an ultra-high-lift aft-loaded LP turbine profile named IET-LPTA with Zweifel loading coefficient of about 1.37. The wakes were simulated by the moving cylindrical bars upstream of the cascade. The time-mean aerodynamic performance and the boundary layer behavior on suction surface had been measured with two 3-hole probes and a hot-wire probe. Three roughness heights ranging from 8.8–20.9μm combined with three roughness deposit positions ranging from 5.2%–39.5% suction surface length formed a large measurement matrix. The roughness with height of 8.8μm (1.05×10−4 chord length) covering 5.2% suction surface reduced the profile loss across the whole Reynolds number range. Under the effect of roughness associated with upstream wakes, the freestream turbulence intensity (FSTI) is responsible in part for the development of the wake-induced transition region, calmed region and natural transition region of the boundary layer. The transition length and the transition onset of the boundary layer were also affected by the FSTI.

Separated Flow Measurements on a Highly Loaded Low-Pressure Turbine Airfoil

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
Ralph J. Volino
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Separation Bubble ◽  
Boundary Layer Separation ◽  
Low Pressure ◽  
Transition To Turbulence ◽  
Suction Surface ◽  
Airfoil Surface ◽  
Flow Measurements ◽  
Low Pressure Turbine

Boundary layer separation, transition, and reattachment have been studied on a new, very high lift, low-pressure turbine airfoil. Experiments were done under low freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Velocity profiles were acquired in the suction side boundary layer at several streamwise locations using hot-wire anemometry. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) ranging from 25,000 to 330,000. In all cases, the boundary layer separated, but at high Reynolds number the separation bubble remained very thin and quickly reattached after transition to turbulence. In the low Reynolds number cases, the boundary layer separated and did not reattach, even when transition occurred. This behavior contrasts with previous research on other airfoils, in which transition, if it occurred, always induced reattachment, regardless of Reynolds number.

Sign in / Sign up

Export Citation Format

Share Document