David Angland

Measurements of flow around a flap side edge with porous edge treatment

Wind-tunnel experiments were performed to investigate a flap side-edge vortex, which is a contributor to airframe noise. The flowfield investigation showed that the peak turbulent stresses were contained in the shear layer that rolled up to form the flap side-edge vortex. The wake from the main element was also entrained by the side-edge vortex. The near-field pressure fluctuations where the turbulent shear layer impinged on the flap side edge were broadband in nature from a Strouhal number of 10 to 50. Hot-wire measurements on the downstream vortex identified a broadband instability centered around a Strouhal number of 13.2. A porous side-edge treatment was applied to the half-span flap to modify the flap side-edge flowfield. The effect of applying a porous side edge was to reduce the Reynolds stresses contained within the vortex and the shear layer that formed it. The porous material also had the effect of displacing the vortex further away from the flap surface. This led to a reduction in the broadband pressure perturbations measured at the flap side edge. Compared with the accuracy of the measurements of the aerodynamic forces, the aerodynamic impact of the porous flap side edge was almost negligible.

High-Order Hybrid Cell-Centered Method for Computational Aeroacoustics

High-order cell-vertex finite difference schemes applied to multi-block structured grids are used widely in computational aeroacoustics for their low-dispersion and low-dissipation properties. Structured grids for complex geometries may contain discontinuous grid metrics at multi-block interfaces. In this work it is demonstrated that the grid-induced errors from such interfaces can be reduced by applying finite difference schemes in the cell-centered space. Further reduction of these grid-induced errors can be achieved by applying an additional finite volume method, which serves as an interface condition. In this paper, the development of a hybrid cell-centered finite difference and finite volume method is demonstrated. An interpolation scheme is derived from a high-order finite difference scheme to apply the finite volume method at interfaces. The order of accuracy of this hybrid method is demonstrated and the method is used to simulate the flow around a single cylinder, tandem cylinders, and a complex isolated wheel. Comparisons with experimental measurements and numerical predictions show that the hybrid method can provide accurate results at block interfaces and can be applied to high-order simulations of complex geometries.

Active flow separation control by a position-based iterative learning control algorithm with experimental validation

A novel iterative learning control (ILC) algorithm was developed and applied to an active flow control problem. The technique uses pulsed air jets to delay flow separation on a two-element high-lift wing. The ILC algorithm uses position-based pressure measurements to update the actuation. The method was experimentally tested on a wing model in a 0.9 m × 0.6 m low-speed wind tunnel at the University of Southampton. Compressed air and fast switching solenoid valves were used as actuators to excite the flow, and the pressure distribution around the chord of the wing was measured as a feedback control signal for the ILC controller. Experimental results showed that the actuation was able to delay the separation and increase the lift by approximately 10%–15%. By using the ILC algorithm, the controller was able to find the optimum control input and maintain the improvement despite sudden changes of the separation position.

Slat noise feedback control with a dielectric barrier discharge plasma actuator

An experimental investigation into the attenuation of slat tonal noise has been conducted with a dielectric barrier discharge plasma actuator placed along the leading edge of a slat. Tests were performed on a three-element model in an anechoic chamber at a freestream velocity of 25 ms , corresponding to a Reynolds number of 5.5 10 based on the main element chord. Near and far eld acoustic measurements showed the presence of tonal features between geometric angles of attack of 0 and 6 . At a geometric angle of attack of 2 eight tonal features were present in the spectra between 0.9 kHz and 8.5 kHz. Five of these tones were attenuated using both open and closed loop control methods with a 20 dB reduction observed in the dominant tone. A proportional feedback controller was implemented for closed loop control. A parametric study of the controller found a set point value of 0, xed time step of 0.2 s, proportional gain of -60 and a duty cycle range of 10% to 15% to provide the best performance with regards to the attenuation of the tonal features. The performance of the actuator was determined to be highly dependent on both its duty cycle and applied voltage. Any reduction in supplied energy to the actuator was coupled with a reduction in its ability to attenuate the tones. The advantage of using the closed loop proportional controller over its open loop counterpart was expected to be the thermal stability as, unlike in the open loop case, the actuator would not be at constant peak operation.

Wavy leading edge airfoils interacting with anisotropic turbulence

Leading edge noise reductions caused by serrations have been shown to be sensitive to the length scales of vortical disturbances. In order to improve the understanding of wavy leading edge airfoils as a noise reduction technology, this paper examines the effects of anisotropy on turbulence-airfoil interaction noise by means of computational aeroacoutic simulations. A synthetic turbulence method is used to generate fully three-dimensional, divergence-free, homogeneous anisotropic turbulence, which is injected in a linearized Euler equation solver to model the noise generation. Moderate variations in turbulence length scales, which are representative of the anisotropy in aero-engine fan wakes, are tested for a NACA 0012 airfoil with a wavy leading edge. This work focuses on the noise sources in the near-field by examining the distortion of the turbulent structures and velocity spectra in the vicinity of the noise sources, the unsteady pressure and its spectral density on the airfoil surface, the magnitude-squared coherence between velocity and pressure fluctuations on the noise sources, and the correlation between noise sources along the span for various degrees of anisotropy. Numerical results show that small variations in the turbulence length scales can produce significant changes in the spectral content of the noise sources at the peak and root regions. The loudest noise source is always located in the root region for the cases examined and this source is mainly affected by the transverse velocity fluctuations. To reduce the correlation between noise sources in the peak and root regions, the ratio between the chordwise length scale and the amplitude of the serrations, and the ratio between the spanwise length scale and the wavelength of the leading edge should satisfy lx/(2h)<1 and lz/λ≤0.5, respectively.

Numerical simulations of single and tandem wheelsfor aerodynamic loads prediction

The aim of this work is to improve the accuracy and efficiency of unsteady aerodynamic loads prediction of landing gears in flight conditions, as part of the UK ATI ALGAAP (Advanced Landing Gear Aero-loads and Aero-noise Prediction) project. Delayed DetachedEddy Simulations (DDES) with the Spalart-Allmaras turbulence model are performed to obtain the desired prediction improvement, both with the fully-turbulent inflow and with laminar inflow and fixed transition. The reference geometries for the current simulations are generic scaled landing-gear wheels in single and tandem configurations, which have been experimentally tested within the project. An experimental database, consisting of mean and unsteady aerodynamic loads, on-surface pressures and velocity fields from particle image velocimetry, is used for CFD validation. The results show the importance of modelling the transition in order to reproduce the experimental data in the transitional regime and to correctly capture the physical flow features. The proposed high-efficiency DDES simulations improve the accuracy of the results with respect to the standard DDES model both on single and tandem wheels. The discrepancy between simulations and experiments on the total mean drag coefficient of tandem wheels is within 7% at zero angle of attack and up to 15% at higher angles of attack.

The Use of Blowing Flow Control to Reduce Bluff Body Interaction Noise

When an unsteady wake from an upstream body impinges on a downstream body, the resultant interaction noise can be significant. The use of distributed blowing through the surface of a cylinder to reduce this source of noise was investigated experimentally. Two configurations were tested, one with a cylinder upstream of an H-beam (denoted the OH configuration) and the other with an H-beam upstream of the cylinder (denoted the HO configuration). The mean velocities and velocity fluctuations were determined in the flowfield using particle image velocimetry. The application of blowing to theOHconfiguration reduced the streamwise Reynolds stress (u0u0). This resulted in a noise reduction of 9.2 dB at a Strouhal number (St) of 0.2. There was a broadband noise reduction of 3 dB averaged over a Strouhal number range 0:05 < St < 5. The effect of blowing on the HO configuration was to inhibit the strong crossflow Reynolds stress (w0w0) between the H-beam and the cylinder. This resulted in a noise reduction of 15 dB at a Strouhal number of 0.8. There was a broadband noise reduction of 4.6 dB averaged over the frequency range 0:05 < St < 6:3. The effect of blowing produced additional high-frequency noise. This additional noise was minimized with blowing applied through a sintered plate with a very small pore diameter.

The effect of flow circulation on the scattering of landing gear noise

An investigation into the scattering of landing gear noise sources by a lifting wing is presented. A two-dimensional test case is used in the investigation. The noise sources are represented by a monopole, which is located at the approximate position of a landing gear underneath a wing geometry. A linearized Euler equation solver is used to simulate the scattering of the monopole by the wing. The effect of a non-uniform flowfield due to circulation induced by a lifting wing is quantified as the difference in acoustic scattering over uniform and non-uniform base flows. The results show that increasing the angle of attack, or increasing the Mach number, leads to a small increase in the sound pressure level towards the ground. However, the observed increase is relatively small. A boundary element method solver is then used to investigate the same problem, and existing uniform and non-uniform flow boundary element formulations are evaluated to see which more accurately predicts the effect of flow. The results show that the uniform flow boundary element formulation is more accurate in predicting the effect of flow than the non-uniform flow approximation for this particular problem, and that the extra computational effort required for the non-uniform flow approximation does not yield a more accurate result.

Iterative Learning Control for Trailing-Edge Flap Lift Enhancement with Pulsed Blowing

A novel iterative learning control algorithm was developed and applied to an active flow control problem. The technique used pulsed air jets applied to a trailing-edge flap to enhance the lift. The iterative learning control algorithm used position-based pressure measurements to update the actuation. The method was experimentally tested on a two-element high-lift wing in a low-speed wind tunnel. Compressed air and fast switching solenoid valves were used as actuators to excite the flow, and the pressure distribution around the chord of the wing was measured as a feedback control signal for the iterative learning controller. Experimental results showed that the actuation was able to delay the separation and increase the overall lift by ΔCL=0.3 over the angle of attack range and increase CLmax from 2.7 to 3.0 compared to the nonactuated case. By using the iterative learning control algorithms, the controller was able to track the target lift, and by using an optimum control algorithm with an extended refere...

Unsteady force and flow features of single and tandem wheels

Wind-tunnel experiments are presented in this paper for two different models, single wheel and tandem wheels. The tests are performed in the 2.1 m × 1.5 m wind tunnel at the University of Southampton. The aims of the experiment are to gain a better understanding of the flow past simple landing-gear components and to generate a CFD validation database. Since the model is designed to study basic landing-gear components, the wheel geometry is simplified, with no detailed elements in the assembly. The tandem-wheel configuration is formed of two in-line wheels that can be tested at different inter-axis distances and various angles of attack. Mean and unsteady data of aerodynamic loads and on-surface pressures are measured. A vibration test is performed in situ on the model assembly to validate the unsteady-load measurements. Particle Image Velocimetry (PIV) is used to acquire the velocity fields in the wake downstream of the model. The results highlight the low sensitivity of the measured quantities to the three versions of the wheel hub on the single wheel. The mean drag coefficients of the tandem wheels show a low sensitivity to the inter-axis distance, which has stronger effects on the mean lift coefficients and the unsteady aerodynamic loads. The angle of attack determines relevant changes in both mean and unsteady quantities. The pressures on the wheel surface are used for gaining a better understanding of the flow regimes and the effect of tripping the flow. Additionally, the PIV data are used to compare the velocity profiles in the wake and identify the wake vortical structures.