Effects of Surface Roughness and Turbulence Intensity on the Aerodynamic Losses Produced by the Suction Surface of a Simulated Turbine Airfoil

2004 ◽  
Vol 126 (2) ◽  
pp. 257-265 ◽  
Author(s):  
Qiang Zhang ◽  
Sang Woo Lee ◽  
Phillip M. Ligrani
Keyword(s):  
Surface Roughness ◽  
Turbulence Intensity ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Intensity Level ◽  
Flow Conditions ◽  
Suction Surface ◽  
Energy Profiles ◽  
Turbine Airfoils ◽  
Aerodynamic Losses

The effects of surface roughness on the aerodynamic performance of turbine airfoils are investigated with different inlet turbulence intensity levels of 0.9%, 5.5% and 16.2%. Three symmetric airfoils, each with the same shape and exterior dimensions, are employed with different rough surfaces. The nonuniform, irregular, 3-D roughness is characterized using the equivalent sand grain roughness size. Mach numbers along the airfoil range from 0.4 to 0.7. Chord Reynolds numbers based on inlet and exit flow conditions are 0.54×106 and 1.02×106, respectively. The contributions of varying surface roughness and turbulence intensity level to aerodynamic losses, Mach number profiles, normalized kinetic energy profiles, and Integrated Aerodynamics Losses (IAL) are quantified. Results show that effects of changing the surface roughness condition on IAL values are substantial, whereas the effects of different inlet turbulence intensity levels are generally relatively small.

Effects of Surface Roughness and Turbulence Intensity on the Aerodynamics Losses Produced by a Suction Surface of a Simulated Turbine Airfoil

2003 ◽  
Author(s):  
Qiang Zhang ◽  
Sang Woo Lee ◽  
Philip M. Ligrani
Keyword(s):  
Surface Roughness ◽  
Boundary Layers ◽  
Turbulence Intensity ◽  
Turbulent Transport ◽  
Three Dimensional ◽  
Intensity Level ◽  
Suction Surface ◽  
University Of Utah ◽  
Trailing Edges ◽  
Turbine Airfoils

The effects of surface roughness on the aerodynamic performance of turbine airfoils are investigated with different inlet turbulence intensity levels of 0.9 percent, 5.5 percent and 16.2 percent using the University of Utah Transonic Wind Tunnel. Three symmetric airfoils, each with the same shape and exterior dimensions, are employed with different rough surfaces created to match the roughness which exists on operating turbine vanes and blades subject to extended operating times and significant surface particulate deposition. The non-uniform, irregular, three-dimensional roughness is characterized using the equivalent sand grain roughness size. Mach numbers along the airfoil range from 0.4 to 0.7. Chord Reynolds numbers based on inlet and exit flow conditions are 0.54×106 and 1.02×106, respectively. The contributions of varying surface roughness and turbulence intensity level to aerodynamic losses, Mach number profiles, normalized kinetic energy profiles, and Integrated Aerodynamics Losses (IAL) are quantified. Results show that effects of changing the surface roughness condition on IAL values are substantial, whereas the effects of different inlet turbulence intensity levels are generally relatively small. Relative to smooth airfoils, these variations are due to: (i) augmentations of mixing and turbulent transport in the boundary layers which develop along the roughened airfoils, (ii) thicker boundary layers at the trailing edges of roughened airfoils, (iii) separation of flow streamlines at airfoil trailing edges, and (iv) increased turbulent diffusion in the transverse direction within the wakes of roughened airfoils as they advect downstream.

Aerodynamics of a Family of Three Highly Loaded Low-Pressure Turbine Airfoils: Measured Effects of Reynolds Number and Turbulence Intensity in Steady Flow

2006 ◽  
Author(s):  
I. Popovic ◽  
J. Zhu ◽  
W. Dai ◽  
S. A. Sjolander ◽  
T. Praisner ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Turbulence Intensity ◽  
Separation Bubble ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Aerodynamic Performance ◽  
Favourable Effect ◽  
Pressure Probe ◽  
Turbine Airfoils

The steady, midspan aerodynamic performance of a family of three low pressure (LP) turbine airfoils has been investigated in a low-speed cascade wind tunnel. The baseline profile has a Zweifel coefficient of 1.08. To examine the influence of increased loading as well as the loading distribution, two additional airfoils were designed, each with 25% higher loading than the baseline version. All three airfoils have the same design inlet and outlet flow angles. The aerodynamic performance was investigated for Reynolds numbers ranging from 25,000 to 150,000 (based on the axial chord and inlet velocity) and for values of freestream turbulence intensity of 1.5% and 4%. The flow field was measured with a three-hole pressure probe. Also, detailed loading distributions were obtained for all three airfoils using surface static pressure taps. The baseline airfoil and the new aft-loaded airfoil showed a separation bubble on the suction side of the airfoil under most of the conditions examined. In addition, a sudden and intermittent stall was observed at low Reynolds numbers for the new aft-loaded airfoil. The relatively short separation bubble would abruptly “burst” and fail to reattach. As the Reynolds number was decreased over a narrow range, the percentage of time that the flow was fully-separated increased to 100%. By comparison, the separation bubble on the baseline airfoil gradually increased in size in an orderly way as the Reynolds number was decreased. The new front-loaded airfoil provided the most encouraging performance: no separation bubble was present except at the very lowest Reynolds numbers. The absence of a separation bubble also had a favourable effect on the loss behaviour of this airfoil: despite its much higher aerodynamic loading, it exhibited very similar midspan losses to those observed for the baseline airfoil.

Effects of a Realistically Rough Surface on Vane Aerodynamic Losses Including the Influence of Turbulence Condition and Reynolds Number

2010 ◽  
Author(s):  
E. L. Erickson ◽  
F. E. Ames ◽  
J. P. Bons
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Rough Surface ◽  
Reynolds Numbers ◽  
Grid Turbulence ◽  
Suction Surface ◽  
Trailing Edge ◽  
Average Roughness ◽  
Early Transition ◽  
Aerodynamic Losses

Aerodynamic loss surveys are reported for a vane with a realistically rough surface. Aerodynamic losses are investigated over a range of turbulence levels {low (0.7%), grid (8.5%), aero-combustor, (13.5%)} and a range of chord Reynolds numbers {Rec = 500,000, 1,000,000, and 2,000,000}. The realistically rough surface distribution was generated by Brigham Young University’s accelerated deposition facility. The surface is intended to represent a TBC surface which has accumulated 7500 hours of operation with a particulate concentration of 0.02 ppmw. The realistically rough surface was scaled by 11 times for consistency with the vane geometry and cast using epoxy to comply with the vane geometry. The surface was applied over the vane pressure surface and about 10% of the suction surface. The 958 by 573 point roughness array generated by Brigham Young on a 9.5 by 5.7 mm region was averaged to a 320 by 191 array for fabrication. The calculated surface roughness parameters of this scaled and averaged array included the maximum roughness, Rt = 1.99 mm, the average roughness, Ra = 0.25 mm and the average forward facing angle, αf = 3.974°. The peak to valley roughness, Rz, was determined to be 0.784 mm. The sand grain roughness of the surface (ks = 0.466 mm) was estimated using a correlation offered by Bons [1]. Based on estimates of skin friction coefficient using a turbulence correlation with the vane chord Reynolds numbers, representative values for the surface’s roughness Reynolds number are 23, 43, and 80 for the three exit condition Reynolds numbers tested. Exit survey measurements for the realistically roughened vane have been compared with the base vane geometry. Total pressure loss measurements have shown an incremental increase above the original base vane which averages 0.68% for the low turbulence, 0.48% for the grid turbulence and 0.24% for the aero-combustor turbulence conditions. A portion of this increment, about 0.20%, could be attributed to the thicker trailing edge due to the average thickness of the roughened tile applied. The roughness on the near suction surface along with the abrupt end of the roughness tiles at about 0.05 m from the stagnation region causes early transition on the suction surface. This early transition influences the comparison of the low turbulence cases much more due to laminar flow on the base vane suction surface. The grid turbulence shows an incremental loss of 0.48% and this difference is likely due to both the thicker trailing edge and the suction surface roughness. The incremental loss increase for the aero-combustor is lower suggesting that the thicker trailing edge has the largest affect on incremental losses.

An Experimental Investigation of the Effect of Freestream Turbulence on the Wake of a Separated Low-Pressure Turbine Blade at Low Reynolds Numbers

1999 ◽  
Vol 122 (2) ◽  
pp. 431-433 ◽  
Author(s):  
C. G. Murawski ◽  
K. Vafai
Keyword(s):  
Reynolds Number ◽  
Turbine Blade ◽  
Turbulence Intensity ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Freestream Turbulence ◽  
Suction Surface ◽  
Low Reynolds Numbers ◽  
Low Pressure Turbine ◽  
Flow Reynolds Number

An experimental study was conducted in a two-dimensional linear cascade, focusing on the suction surface of a low pressure turbine blade. Flow Reynolds numbers, based on exit velocity and suction length, have been varied from 50,000 to 300,000. The freestream turbulence intensity was varied from 1.1 to 8.1 percent. Separation was observed at all test Reynolds numbers. Increasing the flow Reynolds number, without changing freestream turbulence, resulted in a rearward movement of the onset of separation and shrinkage of the separation zone. Increasing the freestream turbulence intensity, without changing Reynolds number, resulted in shrinkage of the separation region on the suction surface. The influences on the blade’s wake from altering freestream turbulence and Reynolds number are also documented. It is shown that width of the wake and velocity defect rise with a decrease in either turbulence level or chord Reynolds number. [S0098-2202(00)00202-9]

Effects of Freestream Turbulence on the Losses of a Highly-Loaded Compressor Stator Blade

2003 ◽  
Author(s):  
J. W. Douglas ◽  
S.-M. Li ◽  
B. Song ◽  
W. F. Ng ◽  
Toyotaka Sonoda ◽  
...  
Keyword(s):  
Turbulence Intensity ◽  
Flow Separation ◽  
Reynolds Numbers ◽  
Freestream Turbulence ◽  
Suction Surface ◽  
Flow Losses ◽  
Oil Flow ◽  
Oil Flow Visualization ◽  
Inlet Conditions ◽  
High Reynolds

Very little published literature documents the effects of different freestream turbulence intensities on compressor flows at realistically high Reynolds numbers. This paper presents a study of these effects on a transonic, linear, compressor stator cascade. The cascade consisted of high turning stator airfoils that had the camber of 55 degrees. The effects of freestream turbulence intensities of approximately 0.1% (baseline) and 1.6% were examined. Inlet Mach numbers to the cascade were tested from 0.55 to 0.89. Reynolds numbers, based on the inlet conditions and blade chord, varied between 1.0–2.0×106. Inlet flow angles to the cascade ranged from a choking to a stall condition. For the baseline cases, at most positive incidence angles to the cascade, surface oil flow visualization and Schlieren pictures showed a significant flow separation on the suction surface of the blade. Under these conditions, the increase in freestream turbulence from 0.1% to 1.6% significantly reduced the flow losses of the cascade (by as much as 57% in some cases). In other test conditions where no evidence depicted flow separation on the blade, there were no measurable effects on the losses due to the increase in freestream turbulence intensity. In addition, the increase of freestream turbulence intensity also improved the effective operating range of the cascade significantly (e.g., by 46% or higher).

Parametric Studies on Aerodynamic Performance of Various Types of LP Turbine Airfoils for Aero-Engines Under the Influence Periodic Wakes and Freestream Turbulence

2019 ◽  
Author(s):  
Ken-ichi Funazaki ◽  
Daichi Murakami ◽  
Yasuhiro Okamura
Keyword(s):  
Estimation Method ◽  
Navier Stokes ◽  
Freestream Turbulence ◽  
Flow Conditions ◽  
Suction Surface ◽  
Aerodynamic Loss ◽  
Flow Deceleration ◽  
Aero Engines ◽  
Lp Turbine ◽  
Turbine Airfoils

Abstract This study carries out parametric investigations on aerodynamic loss of various types of LP turbine airfoils characterized with different flow deceleration rates (DR) on their suction surfaces under the realistic flow conditions such as wake inflow and freestream turbulence. The Reynolds number examined in this study ranges from 57,000 to 170,000. As for the freestream turbulence, two levels of the turbulence are used, i.e., about 1.2% and 3.5%. Stagnation pressure distributions downstream of each of the airfoil cascades are measured by use of a Pitot tube, while steady-state and unsteady boundary-layers are measured over the rear part of suction surface and pressure side near the trailing edge using a single hot-wire probe. The measured boundary-layer data are used to estimate the cascade loss along with RANS (Reynolds-Averaged Navier-Stokes) simulations by taking advantage of the momentum-theory based Denton’s method. First, relationships between the cascade loss for each flow condition and DR are examined. The estimated loss values are then compared with the measured cascade loss to check the validity of the loss estimation method, which is a derivative of Denton’s method, under the realistic flow conditions.

Air-assisted atomization of liquid jets in varying levels of turbulence

2014 ◽  
Vol 764 ◽  
pp. 95-132 ◽  
Author(s):  
A. Kourmatzis ◽  
A. R. Masri
Keyword(s):  
Turbulence Intensity ◽  
Weber Number ◽  
Intensity Level ◽  
Flow Conditions ◽  
Mean Flow ◽  
Potential Core ◽  
Droplet Sizes ◽  
The Mean ◽  
Break Up ◽  
Primary Break

AbstractAir-assisted primary atomization is investigated in a configuration where liquid is injected in a turbulent gaseous jet flow both within as well as outside of the potential core. Cases are studied where the injection point is moved within the flow to maintain a range of constant gaseous mean velocities but changing local fluctuating velocity root-mean-square (r.m.s.) levels. Over a range of mean conditions, this allows for a systematic understanding of both the effects of gas-phase turbulence and mean shear on primary break-up independently. Extensive data is obtained and analysed from laser Doppler anemometry/phase Doppler anemometry, high-speed microscopic backlit imaging and advanced image processing. It is found that the ratio of the turbulent Weber number $\mathit{We}^{\prime }$ to the mean Weber number $\mathit{We}$ is a relevant parameter as is the turbulence intensity. The primary break-up length is found to be heavily influenced not only by the mean velocity, but also by the turbulence level and the mass fuel to air ratio. Above a particular threshold intensity level the break-up time changes in proportion to the change in the integral time scale of the flow. In addition, it is found that regardless of diameter and turbulent flow conditions at the liquid jet, the final size of ligaments converges to a value which is of the order of the measured primary instability wavelength (${\it\lambda}_{1}$). In contrast, cases of different turbulence intensity show the mean of droplet sizes diverging as the spray is advected downstream and this is because droplets are generated from ligaments, the latter of which are subjected both to Rayleigh–Taylor instabilities and turbulent fluctuations. This contribution, for the first time, examines the theoretical applicability of the Rayleigh–Taylor instability in flows where the turbulence is substantial with respect to the mean flow. It is shown that for high turbulence intensities a full theoretical reconstruction of the measured final droplet size distribution is possible from a probability density function of model Rayleigh–Taylor wavelengths (${\it\lambda}_{RT}$). In agreement with the literature (Varga et al. J. Fluid Mech., vol. 497, 2003, pp. 405–434), mean droplet sizes are found to be equal to a mean theoretical Rayleigh–Taylor wavelength normalized by a particular constant value. This, however, is only true for local turbulence intensities less than ${\sim}25\,\%$, or for ratios of the turbulent Weber number to mean Weber number ($\mathit{We}^{\prime }/\mathit{We}$) of less than ${\sim}6\,\%$. Above this, the normalization value is no longer constant, but increases with $\mathit{We}^{\prime }/\mathit{We}$. Finally, the instability wavelengths can be used as part of an approximation that estimates the total number of objects formed after break-up, where the object number is found to be dictated by a balance of both mean flow conditions and local turbulence.

Heat Transfer Measurements on a Turbine Airfoil at Various Reynolds Numbers and Turbulence Intensities Including Effects of Surface Roughness

1996 ◽  
Author(s):  
A. Hoffs ◽  
U. Drost ◽  
A. Bölcs
Keyword(s):  
Heat Transfer ◽  
Liquid Crystals ◽  
Turbulence Intensity ◽  
Leading Edge ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Laminar To Turbulent Transition ◽  
Dimensional Boundary ◽  
Turbulence Length ◽  
Turbine Airfoils

This paper presents heat transfer measurements on a turbine airfoil in a linear cascade at various exit Reynolds and Mach numbers ranging from 3.2e5 to 1.6e6 and 0.2 to 0.8, respectively, which have been conducted with the transient liquid crystal technique. Two series were performed at turbulence intensities of 5.5% and 10%, the latter being created by a squared-bar mesh placed 10 meshsizes upstream of the turbine airfoils. While normally polished liquid crystals were used additional experiments were done at the high turbulence intensity with naturally rough liquid crystals. All measurements indicate a gradual increase in heat transfer and an upstream shift of the laminar-to-turbulent transition with increasing Reynolds number and turbulence intensity. The leading edge heat transfer agrees well with correlations if the turbulence length scale is taken into account. The measurements conducted with rough liquid crystals show an earlier transition on the suction side. Calculations with a two-dimensional boundary layer code agree well with the measurements.

Influence of Discrete Pin Shaped Surface Roughness (P-Pins) on Heat Transfer and Aerodynamics of Film Cooled Aerofoil

2002 ◽  
Author(s):  
S. M. Guo ◽  
M. L. G. Oldfield ◽  
A. J. Rawlinson
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Surface Roughness ◽  
Turbine Blades ◽  
Thermodynamic Characteristics ◽  
Wide Band ◽  
Reynolds Numbers ◽  
Suction Surface ◽  
Shaped Surface ◽  
Annular Cascade

The influence of localized pin-shaped surface roughness (P-Pins) on heat transfer and aerodynamics of a fully film cooled engine aerofoil has been studied in a transonic annular cascade. The “P-Pins”, present on some casting film cooled turbine blades and vanes, are the residues left in the manufacturing process. This paper investigates the effect of the P-Pins on the aerodynamic performance and measures the heat transfer consequences both for the aerofoils and the P-Pins. The effect on performance was determined independently on the pressure and suction surface of the aerofoil. For comparison, the aerofoil without P-Pins was also tested to provide baseline results. The measurements have been made at engine representative Mach and Reynolds numbers. Wide band liquid crystal and direct heat flux gauge technique were employed in the heat transfer tests. A four-hole pyramid probe was used to obtain the aerodynamic data. The aerodynamic and thermodynamic characteristics of the coolant flow have been modelled to represent engine conditions by using a heavy “foreign gas” (30.2% SF6 and 69.8% Ar by weight). The paper concludes that P-Pins as usually placed on the blade do not have detrimental effects to the heat transfer performance of film-cooled aerofoil. P-Pins, located in thick boundary layer regions of the aerofoil, such as the later portion of the suction surface, do not cause any reduction of aerofoil aerodynamic efficiency. For contrast, the P-Pins located in the thin boundary layer regions on the pressure side of the aerofoil cause noticeably more losses.

scholarly journals Observations of Wake-Induced Transition on an Axial Compressor Blade

1995 ◽  
Author(s):  
W. J. Solomon ◽  
G. J. Walker
Keyword(s):  
Reynolds Number ◽  
Axial Compressor ◽  
Reynolds Numbers ◽  
Compressor Blade ◽  
Transitional Flow ◽  
Suction Surface ◽  
Time Space ◽  
Contour Plots ◽  
Turbine Airfoils ◽  
Hot Film

A closely-spaced array of hot-film gages fully covering both suction and pressure surfaces on the outlet stator of a 1.5-stage axial compressor was used to obtain dynamic measurements of wall shear stress. Observations were made over a range of Reynolds numbers at an incidence close to the design value. Various methods of presnting the data, including time-space contour plots of ensemble-average intermittency from the film gages are analyzed: related problems of interpretation are discussed. Extensive regions of laminar flow were identified on the suction surface: at the highest Reynolds number, small laminar patches were still evident at 85% chord and transitional flow covered up to 70% of suction surface length. The influence of passing rotor wakes on transition varied markedly with Reynolds number. The behavior of wake-induced transitional strips on the suction and pressure surfaces of the compressor blade differed significantly; their propagation characteristics also varied in some respects from those observed on turbine airfoils.

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