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No description available.

An experimental parametric sturdy of vane and air-jet vortex generators in a turbulent boundary layer has been carried out. Experiments were carried out in two facilities, one with a free-stream velocity of 20 m/s and a boundary layer thickness (6) of 41.5 mm, and one in a high speed facility at free-stream Mach numbers of between 0.45 and 0.75 and a boundary layer thickness of 20 mm. Cross-stream data were measured at a number of downstream locations using a miniature five-hole pressure probe, such that local cross-stream velocity vectors could be derived. Streamwise vorticity was calculated using the velocity vector data. In the low speed study, vortex generator parameters were as follows: ' Vane vortex generators: thin rectangular vanes with a vane aspect ratio of unity (2h/c = 1), free-stream velocity 20 m/s, incidence (cc = 10', 15', 18', 20'), height-to-boundary- layer- thickness-ratio (h/8 0.554,0.916,1.27,1.639), and strearnwise distance from the vortex generator (x/6 = 3.855,12.048,19.277,26.506). ' Air-jet vortex generators: circular jet nozzles, free-stream velocity = 20 m/s, jet nozzle pitch and skew angles (cc, P= 30', 45', 60'), hole diameter-to-boundary-layer-thickness-ratio (D/5 = 0.098,0.193,0.289), jet-to-free-stream-velocity ratio (VR = 0.7,1.0,1.3,1.6,2.0), and strearnwise distance from the vortex generator (x/8 = 3.855,12.048,19.277,26.506). In the high-speed study, the vortex generator parameters were as follows: Vane vortex generators: thin rectangular vanes with an aspect ratio of unity, incidence ((X 1505 20'), he i ght-to- boundary- I ayer-th i ckne s s-rati o (h/8 = 0.75), strearnwise distance from the vortex generator (x/6 = 8.755 16.25,23.75), and free-stream Mach numbers of 0.45,0.6 and 0.75. Air-jet vortex generators: jet pitch ((x = 30', 45'), jet skew angle (P = 30', 45', 60'), hole diameter-to-boundary-layer-thickness-ratio (D/8 = 0.15,0.3), j et-to- free- strearn-ve loc ity ratio (VR = 1.6), and strearnwise distance from the vortex generator (x/6 = 8.75,16.25,23.75, 31.25), and free-stream Mach numbers of 0.50,0.6 and 0.75. Streamwise vorticity data from the experiment was used to generate prediction techniques that would allow the vorticity profiles, downstream of vane or air-jet vortex generators, to be predicted. Both techniques are based on the approximation of the experimental cross-stream vorticity data to Gaussian distributions of vorticity through the vortex centre. The techniques, which are empirically derived, are simple equations that give the peak vorticity and vortex radius based on the vortex generator parameters. Use of these descriptors allows the assembly of the Gaussian vorticity equation. Both techniques are compared with the experimental data set and were seen to produce peak vorticity results to within 12% and 20% (for the vanes and air-jets respectively), 15% for the radius of the vortex, and 15% and 20% in vortex circulation (for the vanes and air-jets respectively). The two simple prediction techniques allow good prediction of the vortex structure at extremely low computational effort.

An experimental study of active control of fully separated flow over a symmetrical circular-arc airfoil at high angles of attack was performed. The experiments were carried out in a low-speed, open circuit wind tunnel. Angles of attack from 10 to 40 degrees were tested. Low-power input, unsteady excitation was applied to the leading or trailing edge shear layers. The actuation was provided by the periodic oscillation of a 4-percent-chord flap placed on the suction side of the airfoil and facing the sharp edge. Vortex-shedding frequencies were measured and harmonic combinations selected as the applied actuator frequencies. Pressure measurements over the airfoil show that the control increased the normal force coefficient by up to 70%. This supports the idea of vortex capture in the time-averaged sense, enhancing the lift on the airfoil by managing the shear layer roll up. The results indicate the viability of the control of large-scale flow fields by exploiting the natural amplification of disturbances triggered by small-scale actuators. The application of flow control on sharp-edged aircraft wings could lead to improved maneuverability, innovative flight control and weight reduction. These can be achieved by inexpensive, low-power, rugged actuators. / Master of Science

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This thesis deals with flow measuring techniques applied to steady and pulsating gas flows relevant to gas exchange systems for internal combustion engines. Gas flows in such environments are complex, i.e. they are inhomogeneous, three-dimensional, unsteady, non-isothermal and exhibit significant density changes. While a variety of flow metering devices are available and have been devised for such flow conditions, the performance of these flow metersis to a large extent undocumented when a strongly pulsatile motion is superposed on the already complex flow field. Nonetheless, gas flow meters are commonly applied in such environments, e.g. in the measurement of the air flow to the engine or the amount of exhaust gas recirculation. The aim of the present thesis is therefore to understand and assess, and if possible to improve the performance of various flow meters under highly pulsatile conditions as well as demonstrating the use of a new type of flow meter for measurements of the pulsating mass flow upstream and downstream the turbine of a turbocharger. The thesis can be subdivided into three parts. The first one assesses the flow quality of a newly developed flow rig, designed for measurements of steady and pulsating air flow at flow rates and pulse frequencies typically found in the gas exchange system of cars and smaller trucks. Flow rates and pulsation frequencies achieved and measured range up to about 200 g/s and 80 Hz, respectively. The time-resolved mass flux and stagnation temperature under both steady and pulsating conditions were characterized by means of a combined hot/cold-wire probe which is part of a newly developed automated measurement module. This rig and measurement module were used to create a unique data base with well-defined boundary conditions to be used for the validation of numerical simulations, but in particular, to assess the performance of various flow meters. In the second part a novel vortex flow meter that can measure the timedependent flow rate using wavelet analysis has been invented, verified and extensively tested under various industrially relevant conditions. The newly developed technique was used to provide unique turbine maps under pulsatile conditions through time-resolved and simultaneous measurements of mass flow, temperature and pressure upstream and downstream the turbine. Results confirm that the quasi-steady assumption is invalid for the turbine considered as a whole. In the third and last part of the thesis, two basic fundamental questions that arose during the course of hot/cold-wire measurements in the aforementioned high speed flows have been addressed, namely to assess which temperature a cold-wire measures or to which a hot-wire is exposed to in high speed flows as well as whether the hot-wire measures the product of velocity and density or total density. Hot/cold-wire measurements in a nozzle have been performed to test various hypothesis and results show that the recovery temperature as well as the product of velocity and stagnation density are measured. / QC 20120510

This study investigates the effect of chordwisely modulated tip injection on the flow and turbulence characteristics of the tip vortex through experimental measurements downstream of a rectangular half-wing that has an aspect ratio of three. This injection technique involves spanwise jets at the tip that are issued from a series of holes along the chord line normal to the freestream flow direction. The injection mass flow rate from each hole is individually controlled using computer driven solenoid valves and therefore the flow injection geometrical pattern at the tip can be adjusted to any desired waveform shape, with any proper injection velocity. The measurements are performed in a blow-down wind tunnel using Constant Temperature Anemometry and Kiel probe traverses as well as Stereoscopic Particle Image Velocimetry. Current data show consistent trends with v previously observed effects of steady uniform tip injection such as the upward and outward motion of the vortex as well as increased levels of turbulence within the vortex core. The vortex size gets bigger with injection and the total pressure levels get reduced significantly near the vortex core. The injection pattern also seems to affect the size of the wing wake as well as the wake entrainment characteristics of the tip vortex. Depending on the injection waveform pattern and injection momentum coefficient the helicoidal shape of the tip vortex also seems to get affected.

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No description available.