Academic literature on the topic 'Freestream turbulence intensity'
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Journal articles on the topic "Freestream turbulence intensity"
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Chen, Yongxin, Kamal Djidjeli, and Zheng-Tong Xie. "Freestream Turbulence Effects on the Aerodynamics of an Oscillating Square Cylinder at the Resonant Frequency." Fluids 7, no. 10 (October 16, 2022): 329. http://dx.doi.org/10.3390/fluids7100329.
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Flow past a bluff body in freestream turbulence can substantially change the flow behaviour compared to that in smooth inflow. This paper presents the study of wake flow and aerodynamics of an oscillating square cylinder at the resonant frequency in freestream turbulence, with the integral length not greater than the cylinder side and the turbulence intensity not greater than 10%. Large eddy simulations (LES) in the Cartesian grid using the Immersed Boundary Method (IBM) technique embedded in a FVM solver, together with an efficient synthetic turbulent inflow generator implemented in an in-house parallel FORTRAN code (Chen et al, 2020, Journal of Fluids and Structures 2020) are used for the study. The results are compared with those for smooth inflow, and relevant data published in the literature. The key findings are: the freestream turbulence conditions evidently reduces the local turbulent scales and fluctuations in the shear layer compared to in smooth flow, as small scale freestream turbulence breaks down cylinder-generated larger scale eddies and weakens them; but does not evidently affect the vortex shedding frequency, or the length of the recirculation region behind the cylinder. This suggests negligible change of drag coefficient compared to in smooth inflow. Moreover, this is because the vortex shedding is dominated by the forced oscillation at the resonance frequency, and the turbulence intensity is small.
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Murawski, C. G., and K. Vafai. "An Experimental Investigation of the Effect of Freestream Turbulence on the Wake of a Separated Low-Pressure Turbine Blade at Low Reynolds Numbers." Journal of Fluids Engineering 122, no. 2 (December 20, 1999): 431–33. http://dx.doi.org/10.1115/1.483281.
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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]
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Nix, A. C., T. E. Diller, and W. F. Ng. "Experimental Measurements and Modeling of the Effects of Large-Scale Freestream Turbulence on Heat Transfer." Journal of Turbomachinery 129, no. 3 (October 5, 2006): 542–50. http://dx.doi.org/10.1115/1.2515555.
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The influence of freestream turbulence representative of the flow downstream of a modern gas turbine combustor and first stage vane on turbine blade heat transfer has been measured and analytically modeled in a linear, transonic turbine cascade. High-intensity, large length-scale freestream turbulence was generated using a passive turbulence-generating grid to simulate the turbulence generated in modern combustors after passing through the first stage vane row. The grid produced freestream turbulence with intensity of approximately 10–12% and an integral length scale of 2cm(Λx∕c=0.15) near the entrance of the cascade passages. Mean heat transfer results with high turbulence showed an increase in heat transfer coefficient over the baseline low turbulence case of approximately 8% on the suction surface of the blade, with increases on the pressure surface of approximately 17%. Time-resolved surface heat transfer and passage velocity measurements demonstrate strong coherence in velocity and heat flux at a frequency correlating with the most energetic eddies in the turbulence flow field (the integral length scale). An analytical model was developed to predict increases in surface heat transfer due to freestream turbulence based on local measurements of turbulent velocity fluctuations and length scale. The model was shown to predict measured increases in heat flux on both blade surfaces in the current data. The model also successfully predicted the increases in heat transfer measured in other work in the literature, encompassing different geometries (flat plate, cylinder, turbine vane, and turbine blade) and boundary layer conditions.
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Öztürk, Buğrahan, Abdelrahman Hassanein, M. Tuğrul Akpolat, Anas Abdulrahim, Mustafa Perçin, and Oğuz Uzol. "Effects of freestream turbulence on the wake growth rate of a model wind turbine and a porous disc." Journal of Physics: Conference Series 2265, no. 2 (May 1, 2022): 022042. http://dx.doi.org/10.1088/1742-6596/2265/2/022042.
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Abstract This study presents the results of an experimental investigation that focuses on quantifying the differences between the spreading rates of a model wind turbine wake and a porous disc wake at different freestream turbulence intensity levels. Two-dimensional two-component particle image velocimetry (2D2C PIV) measurements are performed within the wakes of a model wind turbine and a porous disc (up to 7D downstream) of the same diameter and a matching thrust coefficient. The wind turbine is operated at a Tip Speed Ratio (TSR) of 2 in order to have matching thrust coefficient conditions for a consistent wake comparison. The results show that the mean wake flow field (both near and far wake) is significantly different for the wind turbine compared to the porous disc even if they are operating at similar, high or low, freestream turbulence levels. The wake of the wind turbine recovers much faster than that of a porous disc with a matching thrust coefficient especially in the far wake region at both low and high freestream turbulence levels. On the other hand, the data shows that the far wake of the turbine operating at low freestream turbulence is very similar to that of the disc operating at high freestream turbulence. This suggests caution and stresses the importance in choosing the freestream turbulence intensity level when using porous discs to represent wind turbines in wind tunnel studies.
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Zhang, Qiang, and Phillip M. Ligrani. "Wake Turbulence Structure Downstream of a Cambered Airfoil in Transonic Flow: Effects of Surface Roughness and Freestream Turbulence Intensity." International Journal of Rotating Machinery 2006 (2006): 1–12. http://dx.doi.org/10.1155/ijrm/2006/60234.
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The wake turbulence structure of a cambered airfoil is studied experimentally, including the effects of surface roughness, at different freestream turbulence levels in a transonic flow. As the level of surface roughness increases, all wake profile quantities broaden significantly and nondimensional vortex shedding frequencies decrease. Freestream turbulence has little effect on the wake velocity profiles, turbulence structure, and vortex shedding frequency, especially downstream of airfoils with rough surfaces. Compared with data from a symmetric airfoil, wake profiles produced by the cambered airfoils also have significant dependence on surface roughness, but are less sensitive to variations of freestream turbulence intensity. The cambered airfoil also produces larger streamwise velocity deficits, and broader wakes compared to the symmetric airfoil.
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Tangermann, Eike, and Markus Klein. "Controlled Synthetic Freestream Turbulence Intensity Introduced by a Local Volume Force." Fluids 5, no. 3 (August 7, 2020): 130. http://dx.doi.org/10.3390/fluids5030130.
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Generating freestream turbulence within the computational domain instead of applying it as a boundary condition requires a method to introduce the turbulent fluctuations at a specific location. A method based on applying local volume forces has been adapted and supplemented with a control loop in order to compensate for alterations of the turbulence structure resulting from the numerical treatment and physical reasons. The criteria for the tuning of the controller have been developed and the performance of the approach has been assessed. The capabilities of the method are demonstrated for the flow around an airfoil at high angle of attack and with massive flow separation.
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Yokoyama, Hiroshi, Hiroshi Odawara, and Akiyoshi Iida. "Effects of Freestream Turbulence on Cavity Tone and Sound Source." International Journal of Aerospace Engineering 2016 (2016): 1–16. http://dx.doi.org/10.1155/2016/7347106.
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To clarify the effects of freestream turbulence on cavity tones, flow and acoustic fields were directly predicted for cavity flows with various intensities of freestream turbulence. The freestream Mach number was 0.09 and the Reynolds number based on the cavity length was 4.0 × 104. The depth-to-length ratio of the cavity,D/L, was 0.5 and 2.5, where the acoustic resonance of a depth-mode occurs forD/L= 2.5. The incoming boundary layer was laminar. The results for the intensity of freestream turbulence of Tu = 2.3% revealed that the reduced level of cavity tones in a cavity flow with acoustic resonance(D/L=2.5)was greater than that without acoustic resonance(D/L=0.5). To clarify the reason for this, the sound source based on Lighthill’s acoustic analogy was computed, and the contributions of the intensity and spanwise coherence of the sound source to the reduction of the cavity tone were estimated. As a result, the effects of the reduction of spanwise coherence on the cavity tone were greater in the cavity flow with acoustic resonance than in that without resonance, while the effects of the intensity were comparable for both flows.
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Oo, Aung N., and Chan Y. Ching. "Stagnation Line Heat Transfer Augmentation Due to Freestream Vortical Structures and Vorticity." Journal of Heat Transfer 124, no. 3 (May 10, 2002): 583–87. http://dx.doi.org/10.1115/1.1471526.
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An experimental study has been performed to investigate the effect of freestream vortical structures and vorticity on stagnation region heat transfer. A heat transfer model with a cylindrical leading edge was tested in a wind tunnel at Reynolds numbers ranging from 67,750 to 142,250 based on leading edge diameter of the model. Grids of parallel rods were placed at several locations upstream of the heat transfer model in orientations where the rods were perpendicular and parallel to the stagnation line to generate freestream turbulence with distinct vortical structures. All three components of turbulence intensity, integral length scale and the spanwise and transverse vorticity were measured to characterize the freestream turbulence. The measured heat transfer data and freestream turbulence characteristics were compared with existing empirical models for the stagnation line heat transfer. A new correlation for the stagnation line heat transfer has been developed that includes the spanwise fluctuating vorticity components.
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Zhang, Qiang, and Phillip M. Ligrani. "Aerodynamic Losses of a Cambered Turbine Vane: Influences of Surface Roughness and Freestream Turbulence Intensity." Journal of Turbomachinery 128, no. 3 (January 23, 2006): 536–46. http://dx.doi.org/10.1115/1.2185125.
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The effects of surface roughness and freestream turbulence level on the aerodynamic performance of a turbine vane are experimentally investigated. Wake profiles are measured with three different freestream turbulence intensity levels (1.1%, 5.4%, and 7.7%) at two different locations downstream of the test vane trailing edge (1 and 0.25 axial chord lengths). Chord Reynolds number based on exit flow conditions is 0.9×106. The Mach number distribution and the test vane configuration both match arrangements employed in an industrial application. Four combered vanes with different surface roughness levels are employed in this study. Effects of surface roughness on the vane pressure side on the profile losses are relatively small compared to suction side roughness. Overall effects of turbulence on local wake deficits of total pressure, Mach number, and kinetic energy are almost negligible in most parts of the wake produced by the smooth test vane, except that higher freestream losses are present at higher turbulence intensity levels. Profiles produced by test vanes with rough surfaces show apparent lower peak values in the center of the wake. Integrated aerodynamic losses and area-averaged loss coefficient YA are also presented and compared to results from other research groups.
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Zhang, Meihong, Shengyang Nie, Xiaoxuan Meng, and Yingtao Zuo. "The Application of the γ-Reθt Transition Model Using Sustaining Turbulence." Energies 15, no. 17 (September 5, 2022): 6491. http://dx.doi.org/10.3390/en15176491.
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The freestream turbulence intensity is an important parameter for Tollmien–Schlichting waves and is also used as one of the key variables for the local- and transport-equation-based transition model in the simulations. To obtain the similar turbulence level in the vicinity to the aircraft as the turbulence intensity measured in a wind tunnel or in free-flight conditions, the sustaining turbulence term can be used for the transition model. It is important to investigate the model behavior when the sustaining turbulence is coupled with the frequently used SST-variants for transitional flows. Additionally, it is essential to obtain a nearly independent solution using the same transition model for different users on different meshes with similar grid resolution for purposes of verification and validation. So far, the relevant work has not been performed sufficiently and the sustaining turbulence technology introduces non-independent results into the freestream values. Thus, a modified sustaining turbulence approach is adopted and investigated in several test cases, including a computational effort on NACA0021 test case at 10 angles of attack. The results indicate that the modified sustaining turbulence in conjunction with the SST-2003 turbulence model yields results nearly independent to the freestream value of ω for the prediction of both streamwise and crossflow transition for two-dimensional flows without increasing computational effort too much. For three-dimensional flow, the sensitivity to initial value of ω is reduced significantly as well in comparison to the SST-based transition model, and it is highly recommended to use present sustaining turbulence technology in conjunction with the SST-2003-based transition model for engineering applications.
Dissertations / Theses on the topic "Freestream turbulence intensity"
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Nix, Andrew Carl. "Effects of High Intensity, Large-Scale Freestream Combustor Turbulence On Heat Transfer in Transonic Turbine Blades." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/27451.
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The influence of freestream turbulence representative of the flow downstream of a modern gas turbine combustor and first stage vane on turbine blade heat transfer has been measured and analytically modeled in a linear, transonic turbine cascade. Measurements were performed on a high turning, transonic turbine blade. The facility is capable of heated flow with inlet total temperature of 120ºC and inlet total pressure of 10 psig. The Reynolds number based on blade chord and exit conditions (5x106) and the inlet and exit Mach numbers (0.4 and 1.2, respectively) are representative of conditions in a modern gas turbine engine. High intensity, large length-scale freestream turbulence was generated using a passive turbulence-generating grid to simulate the turbulence generated in modern combustors after it has passed through the first stage vane row. The grid produced freestream turbulence with intensity of approximately 10-12% and an integral length scale of 2 cm near the entrance of the cascade passages, which is believed to be representative of the core flow entering a first stage gas turbine rotor blade row. Mean heat transfer results showed an increase in heat transfer coefficient of approximately 8% on the suction surface of the blade, with increases on the pressure surface on the order of two times higher than on the suction surface (approximately 17%). This corresponds to increases in blade surface temperature of 5-10%, which can significantly reduce the life of a turbine blade. The heat transfer data were compared with correlations from published literature with good agreement.
Time-resolved surface heat transfer and passage velocity measurements were performed to investigate and quantify the effects of the turbulence on heat transfer and to correlate velocity fluctuations with heat transfer fluctuations. The data demonstrates strong coherence in velocity and heat flux at a frequency correlating with the most energetic eddies in the turbulence flow field (the integral length-scale). An analytical model was developed to predict increases in surface heat transfer due to freestream turbulence based on local measurements of turbulent velocity fluctuations (u'RMS) and length-scale (Lx). The model was shown to predict measured increases in heat flux on both blade surfaces in the current data. The model also successfully predicted the increases in heat transfer measured in other work in the literature, encompassing different geometries (flat plate, cylinder, turbine vane and turbine blade) as well as both laminar and turbulent boundary layers, but demonstrated limitations in predicting early transition and heat transfer in turbulent boundary layers. Model analyses in the frequency domain provided valuable insight into the scales of turbulence that are most effective at increasing surface heat transfer.Ph. D.
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LIN, ZHI-LONG, and 林志隆. "Freestream turbulence intensity effect on the film cooling performance on a inclined film-cooled surface." Thesis, 1991. http://ndltd.ncl.edu.tw/handle/07790760785036523805.
Full textConference papers on the topic "Freestream turbulence intensity"
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Laroche, E. "Influence of Freestream Turbulence Intensity on Cooling Effectiveness." In ASME Turbo Expo 2001: Power for Land, Sea, and Air. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/2001-gt-0139.
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The objective of the study is to evaluate the potential of various turbulence models to simulate satisfactorily the influence of freestream turbulence intensity on the development of a cooling film, via a coupled computation, i.e. taking into account the full geometry (plenum, hole and main channel). Isotropic as well as anisotropic turbulence models (for the velocity as well as for the temperature fields) are tested, and an insight on the best suited closure is expected. The question of the respective influences of the various flow parameters (boundary layer characteristics, turbulent length scales, mass blowing ratios…) is also addressed. A low Reynolds number approach gives a correct estimation of the cooling effectiveness after approximately 10 hole diameters, for high or small blowing ratios, and using a k-ε model. The standard k-1 model largely underestimates the mixing in the injection region. The prediction of the injection region still needs to be improved for most configurations, but qualitatively the computation seems more than acceptable, as it exhibits the classically identified counter-rotating vortices that drive the heat transfer phenomena. The study also showed that predicting the influence of the freestream turbulence intensity requires taking into account thermal anisotropies, using an EARSMt (Explicit Algebraic Reynolds Stress Model, t being for Thermal) type model. An increase in freestream turbulence intensity was then shown to diminish the cooling effectiveness for all blowing ratios. The magnitude of the drop has still to be satisfactorily captured.
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Boyle, Robert J., and Ali A. Ameri. "Effects of Turbulence Intensity and Scale on Turbine Blade Heat Transfer." In ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-43597.
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The effects of turbulence intensity and length scale on turbine blade heat transfer and aerodynamic losses are investigated. The importance of freestream turbulence on heat transfer increases with Reynolds number and turbulence intensity, and future turbine blade Reynolds numbers are expected to be higher than in current engines. Even when film cooling is used, accurate knowledge of baseline heat transfer distributions are needed. Heat flux reductions due to film cooling depend on the ratio of film cooled-to-solid blade heat transfer coefficients. Comparisons are made between published experimental data and published correlations for leading edge heat transfer. Stagnation region heat transfer rates of vanes and blades of high pressure turbines can be nearly double those predicted when predictions neglect freestream turbulence effects. Correlations which included the scale of turbulence gave better agreement with data. Two-dimensional Navier-Stokes analysis were done for several existing test cases where measures of the turbulence scale are available. The test cases had significant regions where the flow was not fully turbulent. Freestream turbulence increases laminar heat transfer, but has little influence on turbulent heat transfer. The Navier-Stokes analysis included a model for the effects of high freestream turbulence on laminar or transitioning boundary layers. Comparisons were made with vane and rotor blade data, as well as with high Reynolds number test data that simulated the favorable pressure gradient regions seen in the forward portions of turbine blades. Predictions of surface heat transfer showed the appropriate trends in heat transfer with turbulence intensity and turbulence scale. However, the absolute level of agreement indicated that further verification of approaches to predicting turbulence intensity and scale effects is needed. Significant increases in losses were calculated for vane and rotor blade geometries as inlet turbulence increased.
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Schroeder, Robert P., and Karen A. Thole. "Thermal Field Measurements for a Shaped Hole at Low and High Freestream Turbulence Intensity." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-56967.
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Shaped holes are increasingly selected for airfoil cooling in gas turbines due to their superior performance over that of cylindrical holes, especially at high blowing ratios. The performance of shaped holes is regarded to be result of the diffused outlet which slows and laterally-spreads coolant, causing coolant to remain close to the wall. However, few thermal field measurements exist to verify this behavior at high blowing ratio or to evaluate how high freestream turbulence alters the coolant distribution in jets from shaped holes. The present study reports measured thermal fields, along with measured flowfields, for a shaped hole at blowing ratios up to 3 at both low and high freestream turbulence intensities of 0.5% and 13.2%. Thermal fields at low freestream turbulence intensity showed that the coolant jet was initially attached, but far downstream of the hole the jet lifted away from the surface due to the counter-rotating vortex pair. Elevated freestream turbulence intensity was found to cause strong dilution of the coolant jet and also increased dispersion, almost exclusively in the lateral as opposed to the vertical direction. Dominance of lateral dispersion was due to the influence of the wall on freestream eddies, as indicated from changes in turbulent shear stress between the low and high freestream turbulence cases.
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Murawski, Christopher G., Rolf Sondergaard, Richard B. Rivir, Kambiz Vafai, Terrence W. Simon, and Ralph J. Volino. "Experimental Study of the Unsteady Aerodynamics in a Linear Cascade With Low Reynolds Number Low Pressure Turbine Blades." In ASME 1997 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/97-gt-095.
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Low pressure turbines in aircraft experience large changes in flow Reynolds number as the gas turbine engine operates from takeoff to high altitude cruise. Low pressure turbine blades are also subject to regions of strong acceleration and diffusion. These changes in Reynolds number, strong acceleration, as well as elevated levels of turbulence can result in unsteady separation and transition zones on the surface of the blade. An experimental study was conducted in a two-dimensional linear cascade, focusing on the suction surface of a low pressure turbine blade. The intent was to assess the effects of changes in Reynolds number, and freestream turbulence intensity. Flow Reynolds numbers, based on exit velocity and suction surface 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 slightly rearward movement of the onset of separation and shrinkage of the separation zone. Increasing the freestream turbulence intensity, without changing Reynolds number resulted in a shrinkage of the separation region on the suction surface. Increasing both flow Reynolds numbers and freestream turbulence intensity compounded these effects such that at a Reynolds number of 300,000 and a freestream turbulence intensity of 8.1%, the separation zone was almost nonexistent. The influences on the blade’s wake from altering freestream turbulence and Reynolds number are also documented. The width of the wake and velocity defect rise with a decrease in either turbulence level or chord Reynolds number. Numerical simulations were performed in support of experimental results. The numerical results compare well qualitatively with the low freestream turbulence experimental cases.
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Nix, A. C., A. C. Smith, T. E. Diller, W. F. Ng, and K. A. Thole. "High Intensity, Large Length-Scale Freestream Turbulence Generation in a Transonic Turbine Cascade." In ASME Turbo Expo 2002: Power for Land, Sea, and Air. ASMEDC, 2002. http://dx.doi.org/10.1115/gt2002-30523.
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Heat transfer predictions in gas turbine engines have focused on cooling techniques and on the effects of various flow phenomena. The effects of wakes, passing shock waves and freestream turbulence have all been of primary interest to researchers. The focus of the work presented in this paper is to develop a turbulence grid capable of generating high intensity, large-scale turbulence for use in experimental heat transfer measurements in a transonic facility. The grid is desired to produce freestream turbulence characteristic of the flow exiting the combustor of advanced gas turbine engines. A number of techniques are discussed in this paper to generate high intensity, large length-scale turbulence for a transonic facility. Ultimately, the passive grid design chosen is capable of producing freestream turbulence with intensity of approximately 10–12% near the entrance of the cascade passages with an integral length-scale of 2 cm.
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Kanani, Yousef, Sumanta Acharya, and Forrest Ames. "Simulations of Slot Film-Cooling With Freestream Acceleration and Turbulence." In ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/gt2017-65050.
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Slot film cooling in an accelerating boundary layer with high free-stream turbulence is studied numerically using Large Eddy Simulations (LES). Recent cooling designs of turbine airfoils (such as double-wall cooling) enable slot cooling configurations that are known to provide improved cooling effectiveness over discrete hole cooling systems. Calculations are done for a symmetrical leading edge geometry with the slot fed by a plenum populated with pin fins. To generate the inflow turbulence, the Synthetic Eddy Method (SEM) is used by which the turbulence intensity and length scales in each direction can be specified at the inflow. Different levels of turbulence are imposed at the inflow cross-plane. For the inflow at the plenum, an a priori simulation has been performed in the plenum with pin fins, and the velocity signals are stored at a plane downstream of the pin fins over a sufficient period of time, and are used as the inflow boundary condition in the plenum. Calculations are done for a Reynolds number of 250,000 and freestream turbulence levels of 0.7%, 3.5%, 7.8% and 13.7% are reported. These conditions correspond to the experimental measurements of Busche and Ames (2014). Numerical results show good agreement with experiment data and show the observed decay of thermal effectiveness with turbulence intensity. The turbulence and non-uniformity exiting the slot are shown to play an important role in the cooling effectiveness distributions downstream of the slot. To provide a better understanding of the flow physics and heat transfer, the mean flowfield and turbulence statistics are studied. Generation of freestream structures is observed at the leading edge, and the amplification of the corresponding fluctuations downstream is identified as one of the parameters influencing the slot cooling performance. Predictions show the higher growth rate of the thermal boundary layer with increasing turbulence which is a clear indication of the increase in turbulent thermal diffusivity and reduction of the effective turbulence Prandtl number. The self-similar temperature profiles deviate from those measured under low freestream turbulence condition.
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Wright, Lesley M., Stephen T. McClain, and Michael D. Clemenson. "PIV Investigation of the Effect of Freestream Turbulence Intensity on Film Cooling From Fanshaped Holes." In ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/gt2011-46127.
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The coolant jet structure of fanshaped film cooling holes is experimentally investigated using two-dimensional particle image velocimetry (PIV). These results are coupled with detailed film cooling effectiveness distributions to directly relate the jet structure to surface phenomena. The cooling performance of simple angle, fanshaped holes (θ = 35°, α = 10°) is considered. The results from these shaped holes are compared to those from a traditional simple angle, cylindrical hole (θ = 35°). The flow measurements were performed in a low speed wind tunnel where the freestream turbulence intensity was varied up to 12.5%. The blowing ratio was varied from 0.5–1.5 to compare the jet structure of relatively low and high momentum cooling flows. Time averaged velocity maps of the coolant flow (in the streamwise direction) were obtained on three planes spanning a single hole: the centerline of the hole, the edge of the cylindrical section of the hole (0.5D), and the edge of the shaped portion of the hole (0.94D). From the seeded jets, time averaged, mean velocity distributions of the film cooling jets were obtained near the cooled surface. In addition, turbulent fluctuations were obtained for each flow condition. Combining the detailed flow field measurements obtained using PIV with detailed film cooling effectiveness distributions on the surface (PSP), provides a more complete view of the coolant jet – mainstream flow interaction. Due to the reduced momentum of the coolant, the shaped holes provide improved protection of the flat plate compared to the cylindrical holes. With the reduced velocity of the coolant from the shaped holes, additional turbulent mixing between the freestream and the coolant occurs. However, the increased turbulence does not induce significant changes to the jet structure nor to the surface protection offered by the coolant. Furthermore, the robustness of the fanshaped design is demonstrated through the presentation of time averaged turbulence quantities across the span of the cooling jet.
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Repko, Timothy W., Andrew C. Nix, and James D. Heidmann. "A Parametric Numerical Study of the Effects of Freestream Turbulence Intensity and Length Scale on Anti-Vortex Film Cooling Design at High Blowing Ratio." In ASME 2013 Heat Transfer Summer Conference collocated with the ASME 2013 7th International Conference on Energy Sustainability and the ASME 2013 11th International Conference on Fuel Cell Science, Engineering and Technology. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/ht2013-17255.
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An advanced, high-effectiveness film-cooling design, the anti-vortex hole (AVH) has been investigated by several research groups and shown to mitigate or counter the vorticity generated by conventional holes and increase film effectiveness at high blowing ratios and low freestream turbulence levels. [1, 2] The effects of increased turbulence on the AVH geometry were previously investigated and presented by researchers at West Virginia University (WVU), in collaboration with NASA, in a preliminary CFD study [3] on the film effectiveness and net heat flux reduction (NHFR) at high blowing ratio and elevated freestream turbulence levels for the adjacent AVH. The current paper presents the results of an extended numerical parametric study, which attempts to separate the effects of turbulence intensity and length-scale on film cooling effectiveness of the AVH. In the extended study, higher freestream turbulence intensity and larger scale cases were investigated with turbulence intensities of 5, 10 and 20% and length scales based on cooling hole diameter of Λx/dm = 1, 3 and 6. Increasing turbulence intensity was shown to increase the centerline, span-averaged and area-averaged adiabatic film cooling effectiveness. Larger turbulent length scales were shown to have little to no effect on the centerline, span-averaged and area-averaged adiabatic film-cooling effectiveness at lower turbulence levels, but slightly increased effect at the highest turbulence levels investigated.
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Bangert, B. A., A. Kohli, J. H. Sauer, and K. A. Thole. "High Freestream Turbulence Simulation in a Scaled-Up Turbine Vane Passage." In ASME 1997 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/97-gt-051.
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Quantifying high freestream turbulence effects on surface heat transfer and on blade boundary layer development is important for improving predictions of the thermal loading and aerodynamic losses for gas turbine blades, vanes, and endwalls. To improve our physical understanding as well as improve CFD capabilities, detailed flow and thermal field data is needed in addition to surface data. This paper discusses the development of a turbulence generator that is capable of generating turbulence intensities as high as 20% and yet allow an independent control on the turbulent length scale. The integral length scale at a turbulence intensity of TI = 20% ranged from 2.1 cm to 5.5 cm. The development of the turbulence generator took place in a wind tunnel having a large, constant area, test section. After this development, the turbulence generator was placed upstream of a scaled-up turbine vane. This paper also describes the development of the turbine vane test section that has a central first stage stator vane that was scaled up by a factor of nine. Finally, turbulence measurements, turbulent length scales, and energy spectra measured inside the turbine vane passage are presented and compared to measurements that were made in the constant area test section. The results indicate that in the first 40% of the stator vane passage, the turbulence levels rapidly decrease by a factor of four with the integral length scales having a rapid growth.
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Schroeder, Robert P., and Karen A. Thole. "Effect of High Freestream Turbulence on Flowfields of Shaped Film Cooling Holes." In ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-43339.
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Shaped film cooling holes have become a standard geometry for protecting gas turbine components. Few studies, however, have reported flowfield measurements for moderately-expanded shaped holes and even fewer have reported on the effects of high freestream turbulence intensity relevant to gas turbine airfoils. This study presents detailed flowfield and adiabatic effectiveness measurements for a shaped hole at freestream turbulence intensities of 0.5% and 13%. Test conditions included blowing ratios of 1.5 and 3 at a density ratio of 1.5. Measured flowfields revealed a counter-rotating vortex pair and high jet penetration into the mainstream at the blowing ratio of 3. Elevated freestream turbulence had a minimal effect on mean velocities and rather acted by increasing turbulence intensity around the coolant jet, resulting in increased lateral spreading of coolant.
Reports on the topic "Freestream turbulence intensity"
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Nix, Andrew C., Thomas E. Diller, and Wing F. Ng. Effects of High Intensity, Large-Scale Freestream Combustor Turbulence on Heat Transfer in Transonic Turbine Blades. Fort Belvoir, VA: Defense Technical Information Center, December 2003. http://dx.doi.org/10.21236/ada419523.
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