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Plasma actuators are devices that with two electrodesand a dielectric material can ionize the air around itand thus control the airflow. They have considerable potentialfor a multitude of reasons, one of which being that they haveno moving parts, making them easy to produce and hard tobreak. Using this technology on the front of vehicles like truckscould be revolutionary in increasing fuel efficiency and thusreducing emissions. A model of a plasma actuator in COMSOLMultiphysics was used to simulate the effect it has on the airaround it. The focus of the project has been to optimize thedesign of an actuator for increased velocity in the air around it.This has been done with regards to properties of the appliedvoltage, the distance between the electrodes and material ofthe dielectric. Parametric analyses of all the above propertieswas performed. Close-to-optimal values of some of the abovementioned parameters were successfully calculated. However,other parameters, such as the horizontal distance between theelectrodes, were beyond the model’s capability to determine usingthe described method. / Plasmaställdon är anordningar som medtvå elektroder och ett dielektriskt material kan jonisera luftenrunt sig och på detta sätt styra luftflödet. De har betydandepotential av en mängd anledningar, varav en är att de inte har några rörliga delar, vilket gör dem lätta att producera och ochsvåra att förstöra. Användande av denna teknologi på fronterav fordon som lastbilar skulle kunna vara revolutionerande förökad bränsleeffektivitet och därmed minska utsläpp. En modellav ett plasmaställdon i COMSOL Multiphysics användes för attsimulera effekterna den har på luften runt sig. Projektets fokushar varit på att optimera ett ställdons design för ökad hastigheti luften runt den. Detta har gjorts med avseende på egenskaperhos den tillförda spänningen, avståndet mellan elektroderna ochdielektrikumets material. Parametriska analyser för alla dessaegenskaper har genomförts. Nästintill optimala värden för någraav de ovan nämnda parametrarna beräknades med framgång.Andra parametrar, som det horisontella avståndet mellan elektroderna,var bortom modellens förmåga att bestämma vidanvändande av den beskrivna metoden. / Kandidatexjobb i elektroteknik 2021, KTH, Stockholm

A series of experiments were conducted in a F109 turbofan engine to investigate the unsteady wake profiles of an Inlet Guide Vane (IGV) at a typical spacing to the downstream fan at subsonic and transonic relative blade velocities. The sharp trailing-edge vanes were designed to produce a wake profile consistent with modern IGV. Time averaged baseline measurements were first performed with the IGV located upstream of the aerodynamic influence of the fan. Unsteady experiments were performed with an IGV-fan spacing of 0.43 fan chords. High-frequency on-vane pressure measurements showed strong peak-to-peak amplitudes at the blade passing frequency (BPF) of 4.7 psi at the transonic fan speeds. High-frequency total pressure measurements of the IGV wake were taken between the IGV and fan. Results showed that the total pressure loss coefficient of the time averaged IGV wake is reduced by 30% for the subsonic fan, and increased by a factor of 2 for the transonic fan compared to the baseline. Time resolved wake profiles for subsonic fan speeds show constructive and destructive interactions over each blade pass generated by the fan potential flow field. Time resolved wake profiles for the transonic fan speeds show that shock interactions with the IGV surface result in the wake shedding off of the vane at the BPF. Furthermore, the effectiveness of trailing edge blowing (TEB) flow control was investigated. TEB is the method of injecting air aft of the IGV to reduce the low pressure regions (deficits) in the viscous wakes shed by the vanes. Minimizing the IGV wakes reduces the forcing function on the downstream fan blades, thereby reducing high cycle fatigue. The TE span of the vane contains discrete holes at the axial centerline for TEB. Baseline results showed that TEB eliminates the IGV wake, while using only 0.03% of the total engine mass flow per IGV. TEB for the subsonic fan at the close spacing shows complete wake filling using the same mass flow as the baseline. TEB for the transonic fan shows a reduction of 68% in the total pressure loss coefficient, while requiring 2.5 times the mass flow as the baseline. / Ph. D.

A technique to infer circumferential total pressure distortion intensity found in serpentine inlet airflow was established using wall-pressure fluctuation measurements. This sensing technique was experimentally developed for aircraft with serpentine inlets in a symmetric, level flight condition. The turbulence carried by the secondary flow field that creates the non-uniform total pressure distribution at the compressor fan-face was discovered to be an excellent indicator of the distortion intensity. A basic understanding of the secondary flow field allowed for strategic sensor placement to provide a distortion estimate with a limited number of sensors. The microphone-based distortion estimator was validated through its strong correlation with experimentally determined circumferential total pressure distortion parameter intensities (DPCP). This non-intrusive DPCP estimation technique was then used as a DPCP observer in a distortion feedback control system. Lockheed Martin developed the flow control technique used in this control system, which consisted of jet-type vortex generators that injected secondary flow to counter the natural secondary flow inherent to the serpentine inlet. A proportional-integral-derivative (PID) based control system was designed that achieved a requested 66% reduction in DPCP (from a DPCP of 0.023 down to 0.007) in less than 1 second. This control system was also tested for its ability to maintain a DPCP level of 0.007 during a quick ramp-down and ramp-up engine throttling sequence, which served as a measure of system robustness. The control system allowed only a maximum peak DPCP of 0.009 during the engine ramp-up. The successful demonstrations of this automated distortion control system showed great potential for applying this distortion sensing scheme along with Lockheed Martin's flow control technique to military aircraft with serpentine inlets. A final objective of this research was to broaden the non-intrusive sensing capabilities in the serpentine inlet. It was desired to develop a sensing technique that could identify control efforts that optimized the overall inlet aerodynamic performance with regards to both circumferential distortion intensity DPCP and average pressure recovery PR. This research was conducted with a new serpentine inlet developed by Lockheed Martin having a lower length-to-diameter ratio and two flow control inputs. A cost function based on PR and DPCP was developed to predict the optimal flow control efforts at several Mach numbers. Two wall-mounted microphone signals were developed as non-intrusive inlet performance sensors in response to the two flow control inputs. These two microphone signals then replaced the PR and DPCP metrics in the original cost function, and the new non-intrusive-based cost function yielded extremely similar optimal control efforts. / Ph. D.