Experimental Study of the Effect of Periodic Unsteady Wake Flow on Boundary Layer Development, Separation, and Reattachment Along the Surface of a Low Pressure Turbine Blade

Schobeiri, Meinhard T.; Rk, B

doi:10.1115/1.1791646

Cited by 19 publications

(5 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Similarly, wake turbulence induced transition over a separation bubble has been found to happen in a quasi-steady way [35]. Again the local velocity scale is used.…”

Section: Equation For Near-wall Intermittency Factor γmentioning

confidence: 99%

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

“…Similarly, wake turbulence induced transition over a separation bubble has been found to happen in a quasi-steady way [35]. Again the local velocity scale is used.…”

Section: Equation For Near-wall Intermittency Factor γmentioning

confidence: 99%

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 calmed region D is then also a zone of increased resistance against separation. That the transition evolution with a separated boundary layer, for paths under wakes and in between wakes, can be similar to the evolution under a statistically steady mean flow was further demonstrated by Schobeiri et al [32,33] for unsteady wake passages from cylindrical rods along the suction side of a low-pressure turbine profile. Turbulent spots generated by the wake impact suppress or reduce periodically the size and height of the separation bubble.…”

Section: Wake-induced Transitionmentioning

confidence: 86%

Transition Models for Turbomachinery Boundary Layer Flows: A Review

Dick

Kubacki

2017

IJTPP

View full text Add to dashboard Cite

Current models for transition in turbomachinery boundary layer flows are reviewed. The basic physical mechanisms of transition processes and the way these processes are expressed by model ingredients are discussed. The fundamentals of models are described as far as possible, with a common structure of the equations and with emphasis on the similarities between the models. Tests of models reported in the literature are summarized and our own test is added. A conclusion on the performance of models is formulated.Keywords: turbomachinery flows; transition models; boundary layers; bypass transition; separationinduced transition; wake-induced transition; Reynolds-averaged Navier-Stokes; intermittency; laminar kinetic energy Transition MechanismsWith the objective of modelling with Reynolds-averaged Navier-Stokes (RANS) or URANS (unsteady or time-accurate RANS) description of a flow, generally, four types of transition from laminar state to turbulent state in turbomachinery boundary layer flows are distinguished [1,2]. These are: natural transition in attached boundary layer state, bypass transition in attached boundary layer state under a statistically steady mean flow, separation-induced transition in the free shear layer formed by separation of a boundary layer under a statistically steady mean flow, and wake-induced transition due to periodically unsteady impact of wakes on boundary layers in attached or separated state. Despite the vast amount of studies on these transition types during the last 4 or 5 decades, understanding of the mechanisms is still not complete, although large progress has been made in the last decade thanks to direct numerical simulation (DNS) and large-eddy simulation (LES). Hereafter, we summarise the mean mechanisms, taking into account the inherent limitations of modelling with Reynolds-averaged Navier-Stokes description of a flow. This means that secondary effects, which mostly are the least understood and sometimes still are a matter of controversy, are not discussed, because, anyhow these features cannot be represented by RANS or URANS. Natural TransitionUnder a statistically steady mean flow of low turbulence level, transition in an attached boundary layer is initiated by 2D viscosity-dependent Tollmien-Schlichting instability waves, followed by a 3D instability, leading to formation of spanwise periodic hairpin vortices, which, farther downstream, cause breakdown of the laminar layer with generation of turbulent spots. These spots finally merge resulting in the formation of a turbulent boundary layer [1,2]. This type of transition is called natural transition. It is a rather slow process and, under a very low mean-flow turbulence level, as in external Int.

show abstract

“…The study also indicated that increasing the free-stream turbulence intensity constrains separation but is not as helpful as increasing the reduced frequency. Schobeiri 6 concluded that the reduced frequency does not significantly affect the initiation and reattachment position of the separation bubble but that increasing the reduced frequency reduces the maximum thickness of the separation bubble. Mahallati and Sjolander 17 studied several working conditions, including different turbulence intensities, flow coefficients, and reduced frequencies of incoming flow.…”

Section: Overviewmentioning

confidence: 99%

“…Curtis et al 3 reported that suction surface boundary layer loss accounts for 60% of profile loss, which is important for reducing the loss. Mayle, 4 Halstead, 5 and Schobeiri 6 showed that the main part of a boundary layer comprises laminar flow and that the local adverse pressure gradient allows the boundary layer to easily separate, resulting in a significant decrease in efficiency, especially at high altitudes and low Reynolds numbers. This problem restricts the wide application of high-lift low-pressure turbines.…”

Section: Overviewmentioning

confidence: 99%

Study of the influence of multiple factors on the boundary layer of a high-lift LPT with the RBF-GA method

Sun,

Huang,

Kang

et al. 2023

Proceedings of the Institution of Mechanical Engineers, Part G:

View full text Add to dashboard Cite

In a high-altitude cruising state, boundary layer separation exists in high-lift low-pressure turbines, and inflow conditions corresponding to different blade designs can directly affect the working efficiency of low-pressure turbines. In particular, the reduced frequency of wake and free-stream turbulence intensity in an inlet flow can greatly influence boundary layer separation and transition development. In this paper, the influence of different inflow turbulence intensities and reduced wake frequencies on the development of suction surface boundary layers in high-lift low-pressure turbines under the influence of upstream wakes is studied by numerical simulations and experiments. Due to the combination of inflow free-stream turbulence intensity and reduced wake frequency, many inflow conditions can be chosen in the design process, and the unsteady influence of upstream wakes complicates the boundary layer flow. In this paper, an RBF (radial basis function)-GA (genetic algorithm) machine learning method is used to explore the optimal inlet conditions corresponding to the minimum profile loss of the Pak-B profile. The search region of the free-stream turbulence intensity is 2%–4%, and the reduced frequency of the wake is changed by changing the flow coefficient, whose variation range is 0.7–1.3. It is found that the RBF-GA machine learning method can attain an inflow condition with a lower profile loss while using the same amount of computation and effort.

show abstract

Experimental Study of the Effect of Periodic Unsteady Wake Flow on Boundary Layer Development, Separation, and Reattachment Along the Surface of a Low Pressure Turbine Blade

Cited by 19 publications

References 23 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

Transition Models for Turbomachinery Boundary Layer Flows: A Review

Study of the influence of multiple factors on the boundary layer of a high-lift LPT with the RBF-GA method

Contact Info

Product

Resources

About