Flow Coefficient and Reduced Frequency Effects on Wake-Boundary Layer Interaction in Highly Accelerated LPT Cascade

Canepa, Edward; Lengani, Davide; Nilberto, Alessandro; Petronio, Daniele; Simoni, Daniele; Ubaldi, Marina; Zunino, Pietro

doi:10.3390/ijtpp6030032

Cited by 5 publications

(4 citation statements)

References 15 publications

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“…Since more wake-induced turbulence is present in the passage, increasing the effect of the wake-induced effects is expected. Similarly, an inverse relationship between the profile losses and flow coefficient was reported in previous studies [6,11,18]. This is suggested in the presented data by the higher difference between the losses at M 6,is = 0.70 (between steady and unsteady cases) than the difference at M 6,is = 0.90.…”

Section: Cascade Outlet Flowsupporting

confidence: 89%

“…This result has been related in the literature to the migration of the incoming wakes towards the blade SS. The interaction of the incoming wake with the boundary layer on the blade SS is associated with high levels of turbulent kinetic energy [7,18] and increased downstream turbulent mixing [11]. At Re 6,is = 70k (see Figure 7), the effect of the wakes seems to be opposite between the low exit Mach number and the high Mach number (M 6,is = 0.90 and 0.95) cases (B, B ).…”

Section: Cascade Outlet Flowmentioning

confidence: 97%

“…The location of this optimum varied with Reynolds number and freestream turbulence intensity, demonstrating that the effect of the incoming wakes on the blade depends on the specific pre-existing conditions of the boundary layer. Mahallati and Sjolander [2], and Canepa et al [18], also considered the influence of the flow coefficient. Higher negative incidence of the wake on the suction surface is determined as the flow coefficient decreases, which at low Reynolds numbers was associated to earlier reattachment and, consequently, to a larger surface portion occupied by turbulent boundary layer, thus resulting in larger profile losses.…”

Section: Introductionmentioning

confidence: 99%

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Effects of Periodic Incoming Wakes on the Aerodynamics of a High-Speed Low-Pressure Turbine Cascade

Simonassi,

Lopes,

Lavagnoli

2023

IJTPP

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The influence of unsteady wakes incoming from the upstream stages is of high relevance in modern high-speed, low-pressure turbines (LPT) operating at transonic exit Mach numbers and low Reynolds numbers for their potential to trigger transition and influence the separation of the boundary layer on the blade suction side. The aim of this paper is the experimental characterization of the influence of incoming wakes on the 2D aerodynamics of a high-speed LPT cascade operating at a low Reynolds number and transonic exit Mach number. A detailed analysis of the status of the flow along the blade under investigation and its impact on the profile loss are presented for a range of Mach numbers from 0.70 to 0.95 and Reynolds numbers from 70k to 120k under steady and unsteady inflow conditions. Tests were conducted at on- and off-design engine realistic conditions in the VKI S-1/C wind tunnel on the SPLEEN C1 transonic cascade. The wakes incoming from an upstream blade row have been replicated using a set of rotating bars, which shed wakes at an engine-representative reduced frequency (f+=0.95) and flow coefficient (Φ=0.80). A set of densely instrumented traversable blades were used to sample the surface pressure distributions. The development of the boundary layers along the blade suction side is examined through quasi-wall shear stress obtained with surface-mounted hot-film sensors. Wake traverses were carried out downstream of the cascade with a miniaturized L-shaped five-hole probe to characterize the blade losses. The introduction of periodic incoming wakes promotes variations in the flow topology over the blade. The effect on the suction side separation bubble is shown to depend on the exit flow conditions. At low Mach numbers, the incoming wakes determine a reduction in the size of the bubble; in contrast, this effect is not registered as the exit Mach number increases. Consistently, a high dependence of the unsteady wake effect on the profile loss on the exit Reynolds and Mach numbers is demonstrated.

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Section: Cascade Outlet Flowsupporting

confidence: 89%

Section: Cascade Outlet Flowmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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Effects of Periodic Incoming Wakes on the Aerodynamics of a High-Speed Low-Pressure Turbine Cascade

Simonassi,

Lopes,

Lavagnoli

2023

IJTPP

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“…There are several studies dealing with PIV measurements in linear and annular turbine cascades. However, the Reynolds numbers investigated are relatively high (Re out > 200 k) [20] or the outlet Mach number is subsonic (M out < 0.6) [21][22][23].…”

Section: Introductionmentioning

confidence: 99%

PIV Measurements in a High-Speed Low-Reynolds Low-Pressure Turbine Cascade

Okada,

Simonassi,

Lopes

et al. 2023

Volume 13B: Turbomachinery — Axial Flow Turbine Aerodynamics

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Particle image velocimetry (PIV) measurements in the blade-to-blade (B2B) plane and cascade outlet plane (COP) of a high-speed low-pressure turbine (LPT) cascade were performed. The measurements were performed at engine-representative outlet Mach number (0.70–0.95), and Reynolds number (70k–120k) under steady flow conditions. The freestream turbulence characteristics were imposed by means of a passive turbulence grid. The PIV results on the B2B plane were compared against five-hole probe (5HP) and Reynolds-averaged Navier-Stokes (RANS) computations to assess the validity of measurement and simulation techniques in the engine-relevant LPT cascade flows. The PIV captured the wake depth and width measured by the 5HP whereas the RANS displayed an overprediction of the wake Mach number deficit. The 5HP was found to impose sinewave fluctuations of the measured flow angle downstream. The variation of fluctuation captured by the PIV was around three times lower. In addition, PIV provided an estimation of the turbulence intensity (TI) in the cascade passage, displaying a decay along a streamline following the passage curvature. For the highest Mach number investigated, a peak in the TI was measured past a shock wave. Measurements of the outlet flow field highlighted a high TI in the secondary flow region whereas high degree of anisotropy (DA) was registered in the boundary of the secondary flow and freestream regions. The contribution of the streamwise fluctuation component was found to be less than the crosswise and radial components in the freestream region. Increasing the cascade outlet Mach number, the contribution of streamwise fluctuation to the DA was observed to decrease.

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Effects of Reynolds number on the flow field in a low-pressure turbine with incoming wakes

Zhao,

Wang,

et al. 2023

J Mech Sci Technol

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Flow Coefficient and Reduced Frequency Effects on Wake-Boundary Layer Interaction in Highly Accelerated LPT Cascade

Cited by 5 publications

References 15 publications

Effects of Periodic Incoming Wakes on the Aerodynamics of a High-Speed Low-Pressure Turbine Cascade

Effects of Periodic Incoming Wakes on the Aerodynamics of a High-Speed Low-Pressure Turbine Cascade

PIV Measurements in a High-Speed Low-Reynolds Low-Pressure Turbine Cascade

Effects of Reynolds number on the flow field in a low-pressure turbine with incoming wakes

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