Freestream Turbulence Intensity Research Articles

Free stream turbulence intensity effects on the flow over a circular cylinder at [formula omitted]: bifurcation, attractors and Lyapunov metric

Varying the free-stream turbulence intensity (Ti= 0%, 5%, 10%) the flow over a circular cylinder for Re=3900 is examined using high fidelity eddy-resolving simulations. Results show that with growth of the turbulence intensity, the drag coefficient increases and the pressure base coefficient drops, as well as the flow bifurcation in the near wake occurs, when the length of the separation zone is reduced by about two, and the stream velocity profile is reshaped from U-shaped to V-shaped. The flow transformation is accompanied by the separation of the wall stress scales. At the same time, dynamics of the vortex shedding (Strouhal number) remains unchanged. The flow bifurcation, confirmed experimentally in practice, and the phase transition are examined using the Lyapunov metric (predictability time and phase-space diagrams). The predictability times, i.e. the phase transition between the two states Ti = 0% → 5% and Ti = 0% → 10% are estimated at one half and one of the characteristic convective time, after which the saturation occurs when both dynamical systems reach a statistical stationary state. Finally, phase-space states are visualized in 2D and 3D, and shown that related attractors can be bounded by simple geometrical ellipsoids.

The influence of free stream turbulence on the development of a wind turbine wake

The wake of an isolated model-scale wind turbine is analysed in a set of inflow conditions having free stream turbulence intensity between 3 % and 12 %, and integral time scales in the range of 0.1–10 times the convective time scale based on the turbine diameter. It is observed that the wake generated by the turbine evolves more rapidly, with the onset of the wake evolution being closer to the turbine, for high turbulence intensity and low integral time scale flows, in accordance with literature, while flows at higher integral time scales result in a slow wake evolution, akin to that generated by low-turbulence inflow conditions despite the highly turbulent ambient condition. The delayed onset of the wake evolution is connected to the stability of the shear layer enveloping the near-wake, which is favoured for low-turbulence or high-integral time scale flows, and to the stability of the helical vortex set surrounding the wake, as this favours interaction events and prevents momentum exchange at the wake boundary which hinder wake evolution. The rate at which the velocity in the wake recovers to undisturbed conditions is instead analytically shown to be a function of the Reynolds shear stress at the wake centreline, an observation that is confirmed by measurements. The rate of production of Reynolds shear stress in the wake is then connected to the power harvested by the turbine to explain the differences between flows at equivalent turbulence intensity and different integral time scales. The wake recovery rate, and by extension the behaviour of the turbine wake in high-integral time scale flows, is seen to be a linear function of the free stream turbulence intensity for flows with Kolmogorov-like turbulence spectrum, in accordance with literature. This relation is seen not to hold for flows with different free stream turbulence spectral distribution; however, this trend is recovered if the contributions of low frequency velocity components to the turbulence intensity are ignored or filtered out from the computation.

Flow Characterization of the UTSA Hypersonic Ludwieg Tube

The characterization of a hypersonic impulse facility is performed using a variety of methods including Pitot probe scans, particle image velocimetry, and schlieren imaging to verify properties such as the velocity, Mach number, wall boundary layer thickness, and freestream turbulence intensity levels. The experimental results are compared to the numerical simulations of the facility performed with Ansys Fluent to compare the design and operational conditions. The presentation of results in this manuscript is prefaced by a description of the facility and its capabilities. The UTSA Ludwieg tube facility can produce a hypersonic freestream flow with a Mach number of 7.2 ± 0.2 and unit Reynolds numbers of up to 200 × 106 m−1. The Pitot probe profiles of the 203-mm-square test section indicate a 152 ± 10 mm square freestream core with turbulence intensity values ranging from 1% to 2%. Schlieren imaging of the oblique shockwaves on a 15° wedge model provided an alternate means of verifying the Mach number. Particle image velocimetry and previous molecular tagging velocimetry results showed a good agreement with the Pitot probe data and numerical simulations in the key parameters including freestream velocity, wall boundary layer velocity profiles, and wall boundary layer thickness.

On the wake characteristics of a model wind turbine and a porous disc: Effects of freestream turbulence intensity

Porous discs are the experimental counterparts of the numerical actuator disc concept and are frequently used in wind tunnel studies to reproduce the far-wake characteristics of wind turbines. The potential of using porous discs instead of wind turbines comes with the benefits such as operational easiness and design simplicity. This paper presents the results of an experimental study focusing on the wake development characteristics of a single porous disc and a single wind turbine under different freestream turbulence intensities but at similar Reynolds number conditions. The measurements are performed using two-dimensional two-component particle image velocimetry (2D2C PIV) technique up to seven diameters downstream distance in the wake of the models. The wake flows are analyzed in terms of the development of mean wake velocity deficit, wake decay, and wake turbulence characteristics. The results show that the wake recovery occurs faster for both the porous disc and the turbine with increasing freestream turbulence intensity. The wake width increases with the freestream turbulence intensity, indicating faster diffusion of the wake for both models. On the other hand, the wake width of the porous disc and the turbine is similar at the same turbulence intensity conditions, although they operate with slightly different thrust coefficients. Turbulent kinetic energy profiles in the far wake of the porous disc and the turbine, which are significantly different for the low turbulence intensity conditions, become similar for the high turbulence intensity case. The comparison of the turbulent kinetic energy, decay rate and production characteristics points to different turbulence mechanisms in the wake of the porous disc and the turbine. In the near wake, the wake decay rate and turbulent kinetic energy levels are higher in the porous disc case due to enhanced mixing levels associated with the grid-generated turbulence. In the far wake, the decay rate of the turbine wake is higher, most probably due to the breakdown of the tip vortices. When the freestream turbulence is increased, the differences in the turbulent wake flow characteristics diminish in the far wake, particularly after a 4.5-diameter downstream distance.

Proper Orthogonal Decomposition (POD) of the Wake Flow Field of a Model Wind Turbine and a Porous Disc under Different Freestream Turbulence Intensity Conditions

The effects of freestream turbulence intensity on the wake development of a model wind turbine and a porous disc are investigated through Proper Orthogonal Decomposition (POD) analysis. The capability of porous discs for reproducing far-wake characteristics of a model wind turbine is examined through coherent structures both in the near-wake and far-wake regions. Instantaneous velocity fields are obtained through wake measurements using two-dimensional two-component particle image velocimetry (2D2C PIV). These velocity fields are considered snapshots of the spatial domain. Results show inherent differences between coherent structures of a model wind turbine and porous disc in the near-wake region, especially when the freestream turbulent intensity level is low. However, these differences reduce, and coherent structures become more comparable when the freestream turbulence intensity level is higher. It is shown that the first five streamwise components of POD modes are paired for the model wind turbine and the porous disc cases under high freestream turbulence intensity conditions in the far-wake region.

An algebraic transition model for fluid flows

An algebraic (zero-equation) transition model is developed to capture multiple transition mechanisms. The newly devised algebraic transition model is parameterized using “flow-structure-adaptive” variables and coupled with the truncated Spalart-Allmaras (SA) turbulence model. The intermittency factor γ relies on “local flow information” and is directly linked to the “vorticity-based production” term of the SA model. Splitting γ into lower and higher regimes of the “free-stream turbulence intensity” enhances the model coefficient calibration and predictions of various phenomena (“natural, bypass, separation-induced, wake-induced”, etc.) encountered in transitional flows. Simulations approve that the new formulation provides good correspondence with other transition models, available in the literature.

Performance of the porous disk wind turbine model at a high Reynolds number: Solidity distribution and length scales effects

A new design methodology for porous disk wind turbine modeling is proposed, where a disk is matched to a horizontal axis wind turbine (HAWT) on (i) thrust coefficient, (ii) radial solidity distribution, and (iii) length scale criteria. Three disk designs are tested, allowing for isolation of the effects of each criterion, with performance evaluated through experimental wake comparisons with a model HAWT at a diameter-based Reynolds number of 4 × 106 and free-stream turbulence intensity of 1.2%. Wake velocity measurements reveal excellent agreement on mean profiles in the near wake (as early as 112 diameters downstream) when the rotor’s radial solidity distribution is incorporated into the disk design. Higher order velocity statistics can also be matched farther downstream (312 diameters). To match the higher order moments, the disk must generate near wake turbulence of similar characteristics to the rotor, since this turbulence dominates the development of the wake in a high Reynolds number, low free-stream turbulence environment. This is achieved by the third design criterion, where physical features that match the rotor length scales are incorporated. Thus, including all three criteria in a single porous disk yields a model that performs well at field-relevant Reynolds numbers, is not performance dependent on the free-stream turbulence intensity, and does not require iterative tuning.

Uncertainty Quantification of Laminar–Turbulent Transition on Airfoil and Fuselage

The effect of uncertainty in Reynolds-averaged Navier–Stokes (RANS) simulations is determined through the application of uncertainty quantification (UQ). In this study, the sensitivity of aerodynamic coefficients to uncertainty in the freestream turbulence intensity (FSTI) and surface roughness is computed for an airfoil (SC1095) and a rotorcraft fuselage model (Rotor-Body-Interaction-Mod7). A laminar–turbulent transition model has been extended to consider roughness-induced transition by incorporating an existing roughness-induced transition model. The current UQ analysis is based on the Monte Carlo method with the Gaussian distributions of uncertain input parameters. A surrogate model allows for incorporating the results of intensive RANS simulations into the Monte Carlo method. The surrogate model is generated using a cubic interpolation for a single-uncertain parameter or a radial basis function for multiple-uncertain parameters. The stochastic standard deviation is measured using combined FSTI and roughness uncertainties. The standard deviation of each aerodynamic coefficient depends on flow conditions (angle of attack, mean FSTI, and mean roughness) and the transition type (natural or separation-induced). The main source of output uncertainty is identified between the unknown FSTI and roughness under various flow conditions.

Disturbance growth in a laminar separation bubble subjected to free-stream turbulence

Experiments were conducted to study the transition and flow development in a laminar separation bubble (LSB) formed on an aerofoil. The effects of a wide range of free-stream turbulence intensity ( $0.15\,\%< Tu<6.26\,\%$ ) and streamwise integral length scale ( $4.6\ {\rm mm}<\varLambda _{u}<17.2\ {\rm mm}$ ) are considered. The co-existence of modal instability due to the LSB and non-modal instability caused by streaks generated by free-stream turbulence is observed. The flow field is measured using hot-wire anemometry, which showed that the presence of streaks in the boundary layer modifies the mean-flow topology of the bubble. These changes in the mean flow field result in the modification of the convective disturbance growth, where an increase in turbulence intensity is found to dampen the growth of the modal instability. For a relatively fixed level of $Tu$ , the variation of $\varLambda _{u}$ has modest effects. However, a slight advancement of the nonlinear growth of disturbances and eventual breakdown with the decrease in $\varLambda _{u}$ is observed. The data show that the streamwise growth of the disturbance energy is exponential for the lowest levels of free-stream turbulence and gradually becomes algebraic as the level of free-stream turbulence increases. Once a critical turbulence intensity is reached, there is enough energy in the boundary layer to suppress the laminar separation bubble, resulting in the non-modal instability taking over the transition process. Linear stability analysis is conducted in the fore position of the LSB. It accurately models incipient disturbance growth, unstable frequencies and eigenfunctions for configurations subjected to turbulence intensity levels up to 3 %, showing that the mean-flow modification due to the non-modal instability dampens the modal instability.

Effect of environmental disturbances on crossflow instability

Wind tunnel experiments on the receptivity of three-dimensional boundary layers were performed in a range of freestream turbulence intensities, Tu, from 0.01%—the lowest level ever achieved in this type of work—up to 0.41%. This work confirms that for Tu=0.01%, and presumably below this level, the transition process is dominated by stationary modes. These are receptive to surface roughness and generate Type-I and Type-II secondary instabilities that eventually cause the transition to turbulence. The saturation amplitude of these stationary waves is highly sensitive to the level of environmental disturbances; the former is here recorded to be the highest in the literature, with the latter being the lowest. Travelling modes are still present; however, their influence on the transition process is marginal. At matched surface roughness levels, when the level of environmental disturbance is enhanced to Tuge 0.33%, the travelling modes acquire more importance, strongly influencing the laminar/turbulent transition process, whilst the initial amplitude and growth of the stationary modes are hindered. For this level of Tu, is the interaction of steady and unsteady disturbances that produces highly amplified waves (Type-III), that quickly lead to nonlinear growth and anticipated turbulence. Finally, a simple rule of thumb is proposed, where the transition front was found to move forward by roughly 10% chord for an increase in one order of magnitude in the Tu levels.Graphical abstract

DNS Study on Turbulent Transition Induced by an Interaction between Freestream Turbulence and Cylindrical Roughness in Swept Flat-Plate Boundary Layer

Laminar-to-turbulent transition in a swept flat-plate boundary layer is caused by the breakdown of the crossflow vortex via high-frequency secondary instability and is promoted by the wall-surface roughness and the freestream turbulence (FST). Although the FST is characterized by its intensity and wavelength, it is not clear how the wavelength affects turbulent transitions and interacts with the roughness-induced transition. The wavelength of the FST depends on the wind tunnel or in-flight conditions, and its arbitrary control is practically difficult in experiments. By means of direct numerical simulation, we performed a parametric study on the interaction between the roughness-induced disturbance and FST in the Falkner–Skan–Cooke boundary layer. One of our aims is to determine the critical roughness height and its dependence on the turbulent intensity and peak wavelength of FST. We found a suppression and promotion in the transition process as a result of the interaction. In particular, the immediate transition behind the roughness was delayed by the long-wavelength FST, where the presence of FST suppressed the high-frequency disturbance emanating from the roughness edge. Even below the criticality, the short-wavelength FST promoted a secondary instability in the form of the hairpin vortex and triggered an early transition before the crossflow-vortex breakdown with the finger vortex. Thresholds for the FST wavelengths that promote or suppress the early transition were also discussed to provide a practically important indicator in the prediction and control of turbulent transitions due to FST and/or roughness on the swept wing.

Algebraic modifications of the [formula omitted] and Spalart–Allmaras turbulence models to predict bypass and separation-induced transition

Many reliable and robust turbulence models are nowadays available for the Reynolds-Averaged Navier–Stokes (RANS) equations to accurately simulate a wide range of engineering flows. However, turbulence models are not suited to correctly described flows with low to moderate Reynolds numbers, which are characterized by strong transitional phenomena. Therefore, numerical models able to accurately predict transitional flows are mandatory to overcome the limits of turbulence models for the efficient design of many industrial applications. The only ways to describe transition are Direct Numerical Simulation (DNS), Large Eddy Simulation (LES), and transition models, where the computational cost of DNS and LES is still too high for their routine use in industry. A modified version of the k-ω̃ and Spalart–Allmaras turbulence models is here proposed to predict transition due to the bypass and separation-induced modes. The modifications are based on the γk-ω̃ and the SA-BCM models and avoid complex formulations of transport equations ad-hoc defined for transition. Both the transition models are correlation-based algebraic models that rely only on local flow information and an intermittency function, which damps the turbulent production according to some transition onset requirements. The proposed transition models are implemented in a high-order discontinuous Galerkin (dG) solver and validated on benchmark cases from the ERCOFTAC suite to the Eppler 387 airfoil, with different transition mode, freestream Reynolds number and turbulent intensity, and pressure gradient.

Effect of the free-stream turbulence on the bi-modal wake dynamics of square-back bluff body

The effect of a free-stream turbulence intensity level on the wake dynamics of a square-back Ahmed body is modeled using the improved delayed detached eddy simulation at Re=9.6×104. The center of pressure, pressure gradient on the base surface, and the barycenter of the momentum deficit on the wake plane are analyzed to characterize the wake bi-modality dynamics. Given that different flow dynamics have different dominant frequencies, the spectral proper orthogonal decomposition is utilized to separate the wake bi-stability, pumping motion of the whole recirculation region, the Von Kármán vortex shedding and the shear layer instability. The results show that entrainment of the oncoming flow into the wake is enhanced, the vorticity thickness is thickened and the length of the wake recirculation region is decreased with the increasing free-stream turbulence, resulting in a lower base suction pressure and a higher level of shear stress. The frequency of the pumping motion is increased with the increase in the oncoming turbulence intensity, while the frequency of Von Kármán vortex shedding is irrespective of the level of the background turbulence. Though the correlation between the switching rate and the oncoming turbulence intensity cannot be put forward due to the relatively short numerical simulation time compared with the wind tunnel experiment, it is still known that the turbulence intensity has a positive effect on the wake bi-stability switching.

Influence of free-stream turbulence intensity on static and dynamic stall of a NACA 0018 aerofoil

In many engineering applications, aerofoils experience elevated free-stream turbulence levels. The present work experimentally investigates the effect of free-stream turbulence on the aerodynamic characteristics of a sinusoidally pitching NACA 0018 aerofoil at the transitional Reynolds number of 2.8×105. Wind tunnel tests are conducted in quasi-static and dynamic conditions at different turbulence intensities between 0.3% and 8.2%, considering reduced frequencies up to 0.1. The dynamic experiments investigate multiple angle-of-attack ranges in order to quantify the influence of free-stream turbulence in the attached-flow regime, in the stalled regime, and in-and-out of stall. The study demonstrates that high free-stream turbulence drastically changes the flow physics over the aerofoil for both static and dynamic conditions, producing large deviations in the lift and moment coefficients. The quasi-static experiment performed at low free-stream turbulence features a large stall hysteresis linked to the breakdown of the leading-edge laminar separation bubble, whereas static hysteresis is not present at higher turbulence levels. Moreover, dynamic experiments at high angles of attack show a strong dependency on the incoming turbulence intensity, which is found to delay flow separation during the upstroke and enhance reattachment during the downstroke. The work also reveals the intrinsic difficulty of predicting the dynamic stall behaviour under different turbulence conditions, and gives insight into why the existing empirical dynamic stall models are unlikely to succeed in accurately predicting the aerodynamic loads across different onset turbulence intensities.

Investigation and Design of the Transonic Laminar Flow Characteristics in a Laminar Aircraft

Reducing drag is critical to aircraft design. In recent years, laminar technology has become one of the most important feasible technologies for civil aircraft drag reduction design under many design constraints. However, various factors have a certain impact on the laminar flow characteristics in the state of transonic flight. Therefore, it is necessary to deeply understand the specific effects of various flight parameters on the characteristics of laminar flow. In this paper, a parameter sensitivity analysis for a central experimental wing in a special layout aircraft was carried out to investigate its transonic laminar characteristics. Then, the airfoil of the central experimental wing of the aircraft was designed for real flight. The RANS (Reynold-averaged Navier–Stokes) method combined with the γ−Reθ transition model based on local variables was used. The computational approach was validated by the wind tunnel tests and analyzed by the grid independence analysis. The sensitivity mainly focuses on the transition location and the length of the laminar flow zone of the central experiment under different boundary conditions. The transonic transition was affected by a variety of interacting factors that include FSTI (free stream turbulence intensity), pressure gradient, Re (Reynolds number), Ma (Mach number) and α (angle of attack, degree). The essence of the transition is the disruption of flow stability caused by the increase in flow entropy. Among these factors, FSTI directly affects global flow stability, and the pressure gradient affects local flow stability. Ma and α can indirectly affect the flow stability by changing the pressure gradient. Re can control the boundary layer properties to change the flow stability, whereas its effect is easily determined by the pressure gradient. Finally, the improved design of the airfoil with the central experimental wing was conducted. The design of weak shock wave and aerodynamic load on the rear part of the airfoil can improve the aerodynamic characteristics (CL, lift coefficient, increases by 0.28) of the airfoil, which can reduce the load burden on the outboard wing without affecting the laminar flow characteristics of the airfoil. In the next step, cross-flow instability will be considered.

Simulations of Hypersonic Boundary-Layer Transition over a Flat Plate with the Spalart-Allmaras One-Equation BCM Transitional Model

Transitional flow has a significant impact on vehicles operating at supersonic and hypersonic speeds. An economic way to simulate this problem is to use computational fluid dynamics (CFD) codes. However, not all CFD codes can solve transitional flows. This paper examines the ability of the Spalart–Allmaras one-equation BCM (SA-BCM) transitional model to solve hypersonic transitional flow, implemented in the open-source CFD code Eilmer. Its performance is validated via existing wind tunnel data. Eight different hypersonic flow conditions are applied. A flat plate model is built for the numerical tests. The results indicate that the existing SA-BCM model is sensitive to the freestream turbulence intensity and the grid size. It is not accurate in all the test cases, though the transitional length can be matched by tuning the freestream intensity. This is likely due to the intermittency term of the SA-BCM model not being appropriately calibrated for high-velocity flow, though if the model can be recalibrated it may be able to solve the general high-velocity flows. Although the current SA-BCM model is only accurate under certain flow conditions after one calibration process, it remains attractive to CFD applications. As a one-equation model, the SA-BCM model runs much faster than multiple-equation flow models.

Experimental Investigation Into the Effect of a Ceramic Matrix Composite Surface on Film Cooling

Abstract Ceramic matrix composite (CMC) components enable high turbine entry temperatures, which can lead to improved efficiencies in gas turbines. Implementing film cooling over CMC components, similar to how it is employed for conventional metal components, can extend part life and push operating temperatures beyond the temperature capabilities of CMCs alone. However, CMCs have a unique surface topology that can influence film cooling performance. Often this topology takes the form of an irregular wavy pattern due to the weave of the fibers that make up the strengthening component of the composite. In this study, shaped 7–7–7 film cooling holes are embedded in a five-harness-satin weave pattern representative of a CMC, at two orientations of the pattern. Detailed adiabatic film effectiveness measurements are obtained in a wind tunnel using an infrared camera while near-wall flowfield measurements are obtained with a high-speed particle image velocimetry system. A range of blowing ratios between one and three are investigated at a density ratio of 1.5 and freestream turbulence intensities of 0.5% and 13%. Across the majority of the tested conditions, the CMC surfaces result in lower film cooling performance than a smooth surface. At a freestream turbulence intensity of 0.5%, the adiabatic film effectiveness is moderately insensitive to the blowing ratio for both weave orientations. The boundary layer over the CMC surfaces increases the mixing between the coolant and the mainstream through a combination of increased turbulence, reduced near-wall velocities, and a thicker boundary layer.

The Application of the γ-Reθt Transition Model Using Sustaining Turbulence

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.

Impact of turbulence on flame brush development of acoustically excited rod-stabilized flames

Coherent structures, such as those arising from hydrodynamic instabilities or excited by thermoacoustic oscillations, can significantly impact flame structure and, consequently, the nature of heat release. The focus of this work is to study how coherent oscillations of varying amplitudes can impact the growth of the flame brush in a bluff-body stabilized flame and how this impact is influenced by the free stream turbulence intensity of the flow approaching the bluff body. We do this by providing external acoustic excitation at the natural frequency of vortex shedding to simulate a highly-coupled thermoacoustic instability, and we vary the in-flow turbulence intensity using perforated plates upstream of the flame. We use high-speed stereoscopic particle image velocimetry to obtain the three-component velocity field and we use the Mie-scattering images to quantify the behavior of the flame edge. Our results show that in the low-turbulence conditions, presence of high-amplitude acoustic excitation can cause the flame brush to exhibit a step-function growth, indicating that the presence of strong vortical structures close to the flame can suppress flame brush growth. This impact is strongly dependent on the in-flow turbulence intensity and the flame brush development in conditions with higher levels of in-flow turbulence are minimally impacted by increasing amplitudes of acoustic excitation. These findings suggest that the sensitivity of the flow and flame to high-amplitude coherent oscillations is a strong function of the in-flow turbulence intensity.

Türbülans Yoğunluğunun Geçiş Yer Tahminine Etkisinin Bölgesel Korelasyon Geçiş Modeli ile İncelenmesi

Aerodynamic parameters are among the most important parameters in flight performance analyses of air/sea vehicles. Free stream turbulence intensity has significant importance on aerodynamic parameters obtained with computational fluid dynamic analyses and wind tunnel tests measurements. In this study, the effect of free stream turbulence intensity on the transition locations of spheroid geometry using with the widely accepted local correlation transition model. The computations are performed at 6.5 x 106 Reynolds number with 0 and 5 degree angle of attacks. The computations at 5 degree angle of attack are compared with an available experimental study. The effect of free stream turbulence intensity is investigated with axial force coefficient, normal force coefficient, and surface friction coefficient distributions. It is seen that axial and normal force coefficients increase with increasing free stream turbulence intensity. The differences in force coefficients obtained with the free stream intensity range used in the study shall create noteworthy effects in flight performance analyses. When surface friction coefficients are investigated, the transition model estimates the transition locations earlier while free stream turbulence intensity increases as expected. However, the transition front geometry is obtained significantly different with respect to the experimental results.