scholarly journals The effects of free-stream turbulence intensity on the aerodynamic performance of compressor cascade

2019 ◽  
Author(s):  
Majed Etemadi ◽  
Jeff Defoe ◽  
Reza Taghavi-Zonouz
Keyword(s):  
Turbulence Intensity ◽  
Free Stream ◽  
Aerodynamic Performance ◽  
Compressor Cascade ◽  
Free Stream Turbulence

Aerodynamic Performance of a Very High Lift Low Pressure Turbine Airfoil (T106C) at Low Reynolds and High Mach Number With Effect of Free Stream Turbulence Intensity

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Jan Michálek ◽  
Michelangelo Monaldi ◽  
Tony Arts
Keyword(s):  
Mach Number ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Separated Flow ◽  
Aerodynamic Performance ◽  
Flow Transition ◽  
High Lift ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine ◽  
Very High

A detailed experimental analysis of the effects of the Reynolds number and free-stream turbulence intensity on the aerodynamic performance of a very high-lift, mid-loaded low-pressure turbine blade (T106C) is presented in this paper. The study was carried out on a large scale linear cascade in the VKI S1/C high-speed wind tunnel, operating at high exit Mach number (0.65) with a range of low Reynolds numbers (80,000–160,000) and three levels of free-stream turbulence intensity (0.8–3.2%). In the first part of the paper, the overall aerodynamic performance of the airfoil is presented, based on mid-span measurements performed by means of static pressure taps, hot-film sensors and a five-hole probe traversing downstream of the cascade. Some specific features of separated flow transition are also discussed for selected cases. The second part presents the analysis of the results in terms of correlations derived for the characteristic points of boundary layer separation and transition. A comparison with some previously published prediction models is shown. The large variety of boundary conditions provides a unique database for validating codes dealing with separated flow transition in turbomachinery.

Assessment of Transition Modeling for the Design of Controlled Diffusion Airfoil Compressor Cascades

2013 ◽  
Author(s):  
Vincent Marciniak ◽  
Marco Longhitano ◽  
Edmund Kügeler
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Bypass Transition ◽  
Compressor Cascade ◽  
Free Stream Turbulence ◽  
Wide Range ◽  
Transition Models ◽  
Transition Modeling

The aim of this paper is to investigate whether correlation-based transition models can be used for the design of CDA profiles. To this end, a CDA compressor cascade has been widely experimentally investigated at DLR Cologne. Off-design measurements have been carried out and the influence of the variation of four flow parameters has been investigated: The inlet Mach number, the incidence, the chord-based Reynolds number and the free-stream turbulence intensity. The inlet Mach number has been varied from 0.5 up to 0.8. The incidence was varied over the whole working range and beyond. Realistic values of the Reynolds number and of the free-stream turbulence intensity have been attained. Hence, the test case apt to assess the capacity of the DLR’s in-house turbomachinery specific CFD code TRACE to design modern compressor blades. In this paper, computations simulating the influence of those four parameters on the performance of the CDA profile are presented and compared to the measurements. Two transition models are used for this study: an in-house model denoted MultiMode model and the γ-ReΘ model. In addition, two turbulence models (Wilcox k-ω and Menter k-ω SST) and their turbomachinery extensions have also been used for this study. The results between the different numerical simulations and the measurements are discussed in term of loss coefficients and Mach number distributions. The computed losses are close to the experimental values and the physics of the flow is also well reproduced. Bypass transition as well as laminar separation bubbles have been simulated in accordance with the experimental observations. Hence, the TRACE code is able to predict the onset of transition over a wide range of flow conditions.

Aerodynamic Performance of a Very High Lift Low Pressure Turbine Airfoil (T106C) at Low Reynolds and High Mach Number With Effect of Free Stream Turbulence Intensity

2010 ◽  
Author(s):  
Jan Micha´lek ◽  
Michelangelo Monaldi ◽  
Tony Arts
Keyword(s):  
Mach Number ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Separated Flow ◽  
Aerodynamic Performance ◽  
Flow Transition ◽  
High Lift ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine ◽  
Very High

A detailed experimental analysis of the effects of the Reynolds number and free-stream turbulence intensity on the aerodynamic performance of a very high-lift, mid-loaded low-pressure turbine blade (T106C) is presented in this paper. The study was carried out on a large scale linear cascade in the VKI S1/C high-speed wind tunnel, operating at high exit Mach number (0.65) with a range of low Reynolds numbers (80,000–160,000) and three levels of free-stream turbulence intensity (0.8–3.2%). In the first part of the paper, the overall aerodynamic performance of the airfoil is presented, based on mid-span measurements performed by means of static pressure taps, hot-film sensors and a 5-hole probe traversing downstream of the cascade. Some specific features of separated flow transition are also discussed for selected cases. The second part presents the analysis of the results in terms of correlations derived for the characteristic points of boundary layer separation and transition. A comparison with some previously published prediction models is shown. The large variety of boundary conditions provides a unique database for validating codes dealing with separated flow transition in turbomachinery.

The interaction of free-stream turbulence with a compressor cascade

2000 ◽  
Author(s):  
Chittiappa Muthanna ◽  
Diego de la Riva ◽  
William Devenport ◽  
Stewart Glegg
Keyword(s):  
Free Stream ◽  
Compressor Cascade ◽  
Free Stream Turbulence

Free-Stream Turbulence From a Circular Wall Jet on a Flat Plate Heat Transfer and Boundary Layer Flow

1989 ◽  
Vol 111 (1) ◽  
pp. 78-86 ◽  
Author(s):  
R. MacMullin ◽  
W. Elrod ◽  
R. Rivir
Keyword(s):  
Heat Transfer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Flow Characteristics ◽  
Surface Profile ◽  
Constant Heat Flux ◽  
Length Scale ◽  
Wall Jet ◽  
Reynolds Analogy ◽  
Free Stream Turbulence

The effects of the longitudinal turbulence intensity parameter of free-stream turbulence (FST) on heat transfer were studied using the aggressive flow characteristics of a circular tangential wall jet over a constant heat flux surface. Profile measurements of velocity, temperature, integral length scale, and spectra were obtained at downstream locations (2 to 20 x/D) and turbulence intensities (7 to 18 percent). The results indicated that the Stanton number (St) and friction factor (Cf) increased with increasing turbulence intensity. The Reynolds analogy factor (2St/Cf) increased up to turbulence intensities of 12 percent, then became constant, and decreased after 15 percent. This factor was also found to be dependent on the Reynolds number (Rex) and plate configuration. The influence of length scale, as found by previous researchers, was inconclusive at the conditions tested.

Correlations for the Prediction of Intermittency and Turbulent Spot Production Rate in Separated Flows

2018 ◽  
Author(s):  
M. Dellacasagrande ◽  
R. Guida ◽  
D. Lengani ◽  
D. Simoni ◽  
M. Ubaldi ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Production Rate ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Turbine Blades ◽  
Transition Process ◽  
Separated Flows ◽  
Intensity Level ◽  
Turbulent Spot ◽  
Free Stream Turbulence

Experimental data describing laminar separation bubbles developing under strong adverse pressure gradients, typical of Ultra-High-Lift turbine blades, have been analyzed to define empirical correlations able to predict the main features of the separated flow transition. Tests have been performed for three different Reynolds numbers and three different free-stream turbulence intensity levels. For each condition, around 4000 Particle Image Velocimetry (PIV) snapshots have been acquired. A wavelet based intermittency detection technique, able to identify the large scale vortices shed as a consequence of the separation, has been applied to the large amount of data to efficiently compute the intermittency function for the different conditions. The transition onset and end positions, as well as the turbulent spot production rate are evaluated. Thanks to the recent advancements in the understanding on the role played by Reynolds number and free-stream turbulence intensity on the dynamics leading to transition in separated flows, guest functions are proposed in the paper to fit the data. The proposed functions are able to mimic the effects of Reynolds number and free-stream turbulence intensity level on the receptivity process of the boundary layer in the attached part, on the disturbance exponential growth rate observed in the linear stability region of the separated shear layer, as well as on the nonlinear later stage of completing transition. Once identified the structure of the correlation functions, a fitting process with own and literature data allowed us to calibrate the unknown constants. Results reported in the paper show the ability of the proposed correlations to adequately predict the transition process in the case of separated flows. The correlation for the spot production rate here proposed extends the correlations proposed in liter-ature for attached (by-pass like) transition process, and could be used in γ–Reϑ codes, where the spot production rate appears as a source term in the intermittency function transport equation.

The influence of background turbulence on Ahmed-body wake bistability

2021 ◽  
Vol 926 ◽  
Author(s):  
D. Burton ◽  
S. Wang ◽  
D. Tudball Smith ◽  
H. N. Scott ◽  
T. N. Crouch ◽  
...  
Keyword(s):  
Experimental Study ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Wind Tunnels ◽  
Experimental Investigations ◽  
Switching Rate ◽  
Free Stream Turbulence ◽  
Background Turbulence ◽  
Ahmed Body

The discovery of wake bistability has generated an upsurge in experimental investigations into the wakes of simplified vehicle geometries. Particular focus has centred on the probabilistic switching between two asymmetrical bistable wake states of a square-back Ahmed body; however, the majority of this research has been undertaken in wind tunnels with turbulence intensities of less than $1\,\%$ , considerably lower than typical atmospheric levels. To better simulate bistability under on-road conditions, in which turbulence intensities can easily reach levels of $10\,\%$ or more, this experimental study investigates the effects of free-stream turbulence on the bistability characteristics of the square-back Ahmed body. Through passive generation and quantification of the free-stream turbulent conditions, a monotonic correlation was found between the switching rate and free-stream turbulence intensity.

scholarly journals Effects of Free-Stream Turbulence Intensity on a Boundary Layer Recovering From Concave Curvature Effects

1993 ◽  
Author(s):  
Michael D. Kestoras ◽  
Terrence W. Simon
Keyword(s):  
Boundary Layer ◽  
Velocity Distribution ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Outer Region ◽  
Free Stream Turbulence ◽  
Flat Wall ◽  
Curvature Effects ◽  
Turbulent Eddies ◽  
Concave Wall

Experiments are conducted on a flat recovery wall downstream of sustained concave curvature in the presence of high free-stream turbulence (TI∼8%). This flow simulates some of the features of the flow on the latter parts of the pressure surface of a gas turbine airfoil. The combined effects of concave curvature and TI, both present in the flow over a turbine airfoil, have so far little been studied. Computation of such flows with standard turbulence closure models has not been particularly successful. This experiment attempts to characterize the turbulence characteristics of this flow. In the present study, a turbulent boundary layer grows from the leading edge of a concave wall then passes onto a downstream flat wall. Results show that turbulence intensities increase profoundly in the outer region of the boundary layer over the recovery wall. Near-wall turbulent eddies appear to lift off the recovery wall and a “stabilized” region forms near the wall. In contrast to a low-free-stream turbulence intensity flow, turbulent eddies penetrate the outer parts of the “stabilized” region where sharp velocity and temperature gradients exist. These eddies can more readily transfer momentum and heat. As a result, skin friction coefficients and Stanton numbers on the recovery wall are 20% and 10%, respectively, above their values in the low-free-stream turbulence intensity case. Stanton numbers do not undershoot flat-wall expectations at the same ReΔ2 values as seen in the low-TI case. Remarkably, the velocity distribution in the core of the flow over the recovery wall exhibits a negative gradient normal to the wall under high free-stream turbulence intensity conditions. This velocity distribution appears to be the result of two effects: 1) cross transport of kinetic energy by boundary work in the upstream curved flow and 2) readjustment of static pressure profiles in response to the removal of concave curvature.

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