Effect of Unsteady Wake Passing Frequency on Boundary Layer Transition, Experimental Investigation, and Wavelet Analysis

Schobeiri, Meinhard T.; Read, K.; Lewalle, Jacques

doi:10.1115/1.1537253

Cited by 34 publications

(9 citation statements)

References 41 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Indeed, there is a lot of experimental evidence that wake turbulence induced bypass transition happens in a quasi-steady way. We refer to the work of Addison and Hodson [2,3], Orth [28], Liu, Rodi and co-workers [7,18], Schobeiri et al [36]. In these experimental works, it is shown that bypass transition caused by wake impingement begins at the same location, independent of the wake passing frequency.…”

Section: Equation For Near-wall Intermittency Factor γmentioning

confidence: 93%

Modelling of Unsteady Transition in Low-Pressure Turbine Blade Flows with Two Dynamic Intermittency Equations

Lodefier

Dick

2006

Flow Turbulence Combust

View full text Add to dashboard Cite

A transition model for describing wake-induced transition is presented based on the SST turbulence model by Menter and two dynamic equations for intermittency: one for near-wall intermittency and one for free-stream intermittency. In the Navier-Stokes equations, the total intermittency factor, which is the sum of the two, multiplies the turbulent viscosity computed by the turbulence model. The quality of the transition model is illustrated on the T106A test cascade for two Reynolds numbers, using experimental results by Stieger and Hodson for transition mainly due to kinematic wake impact on a separation bubble. The quality of the model is also revealed on the T106D test cascade using experimental results from Hilgenfeld, Stadtmuller and Fottner for wake turbulence induced transition. The test cases differ in pitch to chord ratio, Reynolds number and inlet free-stream turbulence intensity, causing different transition mechanisms. The unsteady results are presented in space-time diagrams of shape factor and wall shear stress on the suction side. The results show the capability of the model to capture the physics of unsteady transition in separated state. Inevitable shortcomings are revealed as well.Nomenclature F s = starting function for intermittency U = local velocity (m/s) U ∞ = free-stream velocity (m/s) γ = near-wall intermittency factor ζ = free-stream intermittency factor τ = turbulence weighting factor μ = molecular viscosity (Pa s) μ t = turbulent viscosity (Pa s) θ = momentum thickness Re θ = momentum thickness Reynolds number ρ ∞ U ∞ θ/μ

show abstract

Section: Equation For Near-wall Intermittency Factor γmentioning

confidence: 93%

Modelling of Unsteady Transition in Low-Pressure Turbine Blade Flows with Two Dynamic Intermittency Equations

Lodefier

Dick

2006

Flow Turbulence Combust

View full text Add to dashboard Cite

show abstract

“…The wake recovery was complete at low Strouhal numbers but reduced with increase in the wake passing frequency. Another similar study by Shobeiri et al [29] conducted tests on a concave plate with an upstream squirrel cage type wake generator. Such a setup is shown to have realizable multi-stage wake replications due to opposing directions of moving wakes, though too large a wake Strouhal number will cause the opposing wakes to combine and increase free-stream turbulence intensity.…”

Section: Review Of Literaturementioning

confidence: 93%

Heat Transfer and Film Effectiveness Study on a Pitchwise Curved Surface with Unsteady Wake Interaction

Mahadevan¹,

Kutlu²,

Golsen³

2012

48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

View full text Add to dashboard Cite

Experiments were performed to measure the heat transfer augmentation and film cooling effectiveness on a film-cooled annular surface subjected to unsteady passing wakes. The wakes can have a profound influence on the effectiveness of film cooling and heat transfer characteristics and it is the objective of an ongoing study to quantify that influence. As part of the study, three blowing ratios (M=0.25, 0.5, 0.75) were tested with discrete film injection (p/D=3) in this paper. The tests were performed for two wake Strouhal numbers (S=0.15, 0.3). The baseline cases involved a steady mainstream flow (S=0). Heat transfer augmentation was measured with passing wakes and with film cooling separately and then with combination of both. A numerical model replicating the annular geometry was used to predict film cooling effectiveness for the steady mainstream cases (S=0) and one transient case was attempted (M=0.5,S=0.3). The computations were performed with pressure-based Reynolds-Averaged Navier-Stokes solver and the realizable k-ε turbulence model. The results from the experiment and computations are compared with relevant published literature. The uncertainties in the experimental values are calculated to be ± 0.03 (absolute) for film cooling effectiveness, ± 3% for velocity measurements, and ± 6.5% for heat transfer coefficient ratio respectively. The passing wakes increased the heat transfer coefficients as high as 11% for the highest wake passing frequency for no film injection (M=0, S=0.3). The influence of the passing wakes was more significant with film injection with a heat transfer augmentation of 37% approximately for M=0.75,S=0.3. The displacement thickness to the film hole diameter ratio at the injection location was observed to be a pertinent parameter that dictates the heat transfer augmentation for the film injection experiments. The centerline film cooling effectiveness was greatly affected by the passing wakes with a maximum decrease of 15% observed for M=0.5,S=0.3. NomenclatureA = area (m 2 ) D = film cooling hole diameter (8mm) D = wake rod diameter (19mm) h = heat transfer coefficient (W/m 2 K) I = momentum flux ratio k = thermal conductivity (W/mK) M = blowing ratio (mass flux ratio) N = angular velocity of wake generator (RPM) n = number of wake generator rods p = pitch (mm) q′′ = heat flux (W/m 2 ) R = resistance of foil heater (ohm) Re = Reynolds number based on entry length; film hole diameter S = wake Strouhal number T = temperature (°C/K) Tu = turbulence intensity U = mean velocity (m/s) V = voltage (V) VR = velocity ratio w = width of heater strip (31 mm)Greek letters α = streamwise inclination angle of film hole (35°) β = compound angle of film hole (0°) δ = disturbance/boundary layer thickness (mm) ε = emissivity η = film cooling effectiveness θ = pitchwise distance θ * = momentum thickness (mm) ρ = density (kg/m 3 ); resistivity of heater material ߢ = ratio of specific heats (c p /c v )

show abstract

“…Schobeiri and his co-workers also extended the theoretical work by Schobeiri et al (1995a) to a relative frame of reference to explain the development and decay of unsteady wakes. Schobeiri et al (1995b) experimentally investigated the effects of periodic unsteady wake passing frequency on the boundary layer transition and its development along the concave surface of a constant curvature plate at zero pressure gradient. In a continuing effort, Schobeiri et al (1998) presented a detailed experimental study of the behavior of the unsteady boundary layer of a turbine cascade with a chord length of c = 281.8 mm.…”

Section: Background: Unsteady Boundary Layer Transitionmentioning

confidence: 99%

Aerodynamic and Performance Behavior of a Three-Stage High Efficiency Turbine at Design and Off-Design Operating Points

Schobeiri¹,

Gilarranz²,

Johansen³

2004

The International Journal of Rotating Machinery

View full text Add to dashboard Cite

This article deals with the aerodynamic and performance behavior of a three-stage high pressure research turbine with 3-D curved blades at its design and off-design operating points. The research turbine configuration incorporates six rows beginning with a stator row. Interstage aerodynamic measurements were performed at three stations, namely downstream of the first rotor row, the second stator row, and the second rotor row. Interstage radial and circum-ferential traversing presented a detailed flow picture of the middle stage. Performance measurements were carried out within a rotational speed range of 75% to 116% of the design speed. The experimental investigations have been carried out on the recently established multi-stage turbine research facility at the Turbomachinery Performance and Flow Research Laboratory, TPFL, of Texas A&M University. Keywords Development in the field of turbomachinery computational fluid dynamics (CFD) has reached an advanced level that allows a detailed computation of the complex three-dimensional viscous flow field through a turbomachinery stage using Navier-Stokes codes. Numerous published cases demonstrate the capability of different CFD-methods to calculate various flow quantities in a remarkably detailed fashion. The efficiency and loss calculations, however, reveal noticeable disagreement between the experimental and computational results. The detailed 3-D flow pictures delivered by viscous flow solvers display the source and location of the total pressure losses and entropy distribution within the blade channel, particularly at the blade hub and tip regions. Based on these results, the turbine aerodynamicist is able to reconfigure the blade geometry to reduce the profile and the secondary flow losses. The latter is especially relevant for high pressure (HP) turbine design with relatively small aspect ratios where the secondary flow losses significantly contribute to the reduction of the stage efficiency. In recent years, the power generation turbine manufacturers have been increasingly focus-ing their efforts on reducing the secondary flow losses of HP-turbine blades by implementing the information obtained from the Navier-Stokes flow simulations. To account for the discrepancy mentioned above, the Navier-Stokes codes are frequently calibrated. The calibration process may provide a temporary matching solution for cases in which experimental results are available. However, it is not appropriate for a priori predicting of the efficiency of new designs. The disagreement between the Navier-Stokes based efficiency calculations and the measurements , however, does not allow the engine manufacturer to issue efficiency and performance guaranty without thoroughly testing their new design. Considering the physical aspects of the computation , among other things, two major issues may be considered primarily responsible for the above discrepancy, namely the turbulence modeling and the modeling of the laminar-turbulent boundary layer transition process. The latter directly impacts the a...

show abstract

Effect of Unsteady Wake Passing Frequency on Boundary Layer Transition, Experimental Investigation, and Wavelet Analysis

Cited by 34 publications

References 41 publications

Modelling of Unsteady Transition in Low-Pressure Turbine Blade Flows with Two Dynamic Intermittency Equations

Modelling of Unsteady Transition in Low-Pressure Turbine Blade Flows with Two Dynamic Intermittency Equations

Heat Transfer and Film Effectiveness Study on a Pitchwise Curved Surface with Unsteady Wake Interaction

Aerodynamic and Performance Behavior of a Three-Stage High Efficiency Turbine at Design and Off-Design Operating Points

Contact Info

Product

Resources

About