Progress Report Notes:
The progress reports are formatted so that the milestones and major tasks have their status listed immediately below the heading. For any one report, only the tasks that actually received effort during the reporting period will have material in their corresponding sections. Tasks that have not been worked on to the current date will be listed at 0% complete. Tasks that have been completed will be listed at 100% complete. The milestones, major tasks, dates and planned completion status are taken from the project-planning summary.
NOMENCLATURE
Angles and frequencies
Connecting rod axis to cylinder axis
,()Crank angle (individual cylinders), referred to reference-cylinder axis
()Angular displacement of belt drive connected to motor (crankshaft)
() Crankshaft (motor) angular frequency
Lengths
Center of crankpin to center of piston pin (length of connecting rod)
Belt drive displacement
Center of crankshaft to center of crankpin
()Radius of belt drive at engine (motor) end
,Rod lengths to rod cg
Distance of piston pin from cylinder end (exit slot end)
Masses
Equivalent mass at joint of crankpin with connecting rod
Equivalent mass of connecting rod at crank pin end
Mass of crankpin
Equivalent mass of crankpin at connecting rod end
Equivalent mass of crankpin at crankshaft end
Mass of connecting rod
Idealized mass at piston end (including connecting rod) i.e, reciprocating mass
Equivalent mass of connecting rod at
piston end
Mass of piston, piston rings etc
Motor/input parameters
Viscous damping in motor
Current through armature
Polar moment of inertia of armature
Amplifier voltage gain
() Motor voltage (torque) constant
Armature inductance
Armature resistance
Coulomb friction toque in motor
() Armature (input) voltage
Torques and moments
Torque correction due to the angular
acceleration of the connecting rod
Crankshaft inertia torque
Load (total engine) torque
Load (total engine) torque referred to motor shaft
Torque on crankshaft due to air pressure
Torque due to inertia of the reciprocating part
Inertias
Mass moment of inertia (actual) of connecting rod
Mass moment of inertia of idealized connecting rod
Mass moment of inertia (general)
Mass moment of crank shaft
Load mass moment of inertia
Miscellaneous
Load divider constant
() Piston (exit slot) area
Center of gravity
()Force (moment) - general
Acceleration due to gravity
Pressure at jet exit
Universal gas constant
Temperature inside piston cavity
Density of air in/out cavity
Jet momentum coefficient
Jet exit velocity
Width of jet exit
Freestream velocity
Reference or characteristic length
Piston inertial force
1. Development of Compact Reconfigurable SJA’s for Distributed Control:
Planned Status: Start April 15th, 2003 – 100% Complete
Actual Status: 80%
Notes Regarding Milestone:
1.1 Development of Modified Experimental Setups
Planned Status: Start April 15th, 2003 – 100% Complete
Actual Status: 100% Complete
Notes Regarding Tasks:
1.1.1Design Modifications to Wind-Tunnel Setups
For the pitching moment about the model the single-SJA wing developed was mounted on the free-to-pitch setup shown in Figure 1. This figure is repeated here from an earlier report.The free-to-pitch setup is being expanded to also include free-to-plunge capabilities. Design is almost complete. Fabrication is anticipated to start in two weeks.
1.1.2Fabricate and Assemble Parts for Modified Setups
For the pitching moment tests the trailing edge of the wing was restricted from moving with a thin strut, which was equipped with a Futek in-line force sensor. This allowed us to perform a range of experiments, in which, for a variety of angles of attack and actuation operation parameters (particularly frequency), we measured the wing pitching moment directly from the load sensor and not by integrating the wing surface pressures. The freestream velocity of the experiment was 20 m/s. Data were obtained at angles from 17 degrees to 25 degrees. The frequency was tested to a maximum of 100 Hz. The aerodynamic moment was extracted from the measured forces after removal of loads due to the wing mass. The moments are measured about x/c = 0.36. Figure 2 shows the plots of the pitching moment as a function of angle of attack and actuation frequency. These data were also reported in our previous report. New data that were obtained at man more frequencies are included in Section 3.1. The results of the test show that the SJA produces a significant change in aerodynamic moment as the frequency is increased.
1.2 Control Wing with Single SJA, Form Guidelines for Distributed Actuation
Planned Status: Start June 18th, 2003 – 100% Complete
Actual Status: 70% Complete
Notes Regarding Tasks:
1.2.1 Wind-Tunnel Testing of Modified Setups with Single Actuator
1.2.2 Data Reduction and Analysis for Wing/Flow/Control Characterization
Based on the data gathered in the Phase I effort, we have begun to form guidelines for SJA control and have made progress in the controlled system identification: SJA-control and system identification progress report. Tasks accomplished in this area to date are:
- Further developed mathematical models for representing the aerodynamic behavior using Radial Basis Function Networks.
- We have also finalized the hardware for the testing of the closed –loop, free-to-pitch controller in the wind tunnel. This is quite an elaborate setup that interfaces DSpace and the control algorithm with the wing and wind-tunnel hardware. Closed-loop pitch control tests are anticipated to start in two weeks.
1.3 Design, Development and Installation of Reconfigurable and Distributable SJA
Planned Status: Start April 15th, 2003 – 80% Complete
Actual Status: 50% Complete
Notes Regarding Tasks: Because of the inability of the original SJA design to provide control authority at low angles of attack (for < 12°), we have made it a priority to develop an SJA actuator that will fill this void. As discussed in the kick-off meeting presentation, we have decided to focus our initial efforts on designing and developing a “synthetic Gurney flap”: an actuator that can simulate a Gurney flap and provide the necessary authority at low angles of attack. New tasks and sections dealing with the synthetic Gurney flap (SGF) have been added as necessary to document the plans and effort associated with this new development.
1.3.1 Design New SJA Suitable for Distributive Control
In this section, we study the behavior of the SJA by simulation of its nonlinear model under the condition of motor rotation at a constant angular velocity first, and then under a step voltage input. Thus, we mainly focus on the behavior of the following four equations:
(1)
(2)
(3)
(4)
where , and , , ,
, , , , , , , , , (5)
Fig.3 shows the jet exit velocity curves at constant motor frequency , 70 and 40 Hz. These curves show that the jet exit velocity changes periodically with time, and also changes as the motor rotation speed changes, i.e., and changes. Furthermore, a simulation of the jet exit velocity surface is generated for a range of () values. Fig.4 simulates the jet exit velocity for from 100Hz to 140Hz around a nominal value of 120Hz in a 3-D plot. Notice the surface is periodic along the t axis. The 3-D plots in Figs.5-7 are for ranges of 60~120, 0~60, and 0~200 Hz. It shows that the velocity increases as increases, but the period decreases. Fig.8 shows the motor rotation frequency with oscillations when a constant step voltage input v is applied
Fig.3. Jet exit velocity curves for three different
Fig.4. Jet exit velocity surface for of100 ~ 140 Hz
Fig.5. Jet exit velocity surface for of60 ~ 120 Hz
Fig.6. Jet exit velocity surface for of0 ~ 60 Hz
Fig.7. Jet exit velocity surface for of0 ~ 200 Hz
Fig 8. Motor rotation frequency at a constant
The above graphs provide information on the performance of the jet exit velocity for various motor angular velocities. These studies are useful for the design of a controller that will command a certain jet exit velocity time history.
The nonlinear model of a high-power, compact synthetic jet actuator used in open loop flow separation control has been derived. We developed the state space nonlinear model from the voltage input to the jet exit velocity. Simulations of the jet exit velocity at various motor rotation frequencies were performed to demonstrate the results. Furthermore, a simulation was carried out of the motor rotation velocity/frequency response for a step voltage input. Current research is focused on validating the model via open loop experiments and subsequently using the model in closed-loop control and the development of robust controllers.For the dynamic model, we will do further simulations together with the controller development.
1.3.2 Fabricate New SJA with Dynamically Reconfigurable Slot Geometry
1.3.3 Fabricate Distributable SJA (with Dynamically Reconfigurable Slot Geometry)
Task Notes: To this point, we have not fabricated an SJA with an integrated reconfigurable slot (see discussion of reconfigurable slot, section 1.3.5). We have concentrated our efforts more on the development of the synthetic Gurney flap. The integration of the new SJA’s and SGF’s require a more compact actuator.
1.3.4Design and Evaluation of Synthetic Gurney Flap Controller
Although it has been demonstrated that control of flow separation can be used for pitch control at high angles of attack, this mechanism is neither available nor viable at low angles of attack, where aerodynamic efficiency would be marred by large-scale flow separation. At low incidence, the most receptive and effective location for modification to generate pitching moment is the trailing edge. Obvious modifications are the flap. Moments are generated through flap deflection by movement of the rear stagnation point yielding increased vertical momentum transfer. Other trailing edge modifications are pneumatic; either a virtual jet flap, where a high velocity jet is issued from the trailing edge or a blown flap, where the jet is directed over the flap. Super-circulation may also be achieved by using blowing in concert with a Coanda type trailing edge. All these methods are effective but may require significant quantities of air for operation.
The Gurney flap has been shown to be a highly effective, small-scale (typically 0.75 – 1.5% of the chord) modification that can achieve significant lift and pitching moment generation. A typical Gurney flap installation is shown in Fig. 9. The flap functions by essentially increasing the downward deflection of the trailing edge flow, facilitated through the formation of a series of counter-rotating vortices, similar to those of a von Karman vortex street. A consequent effect is an apparent violation of the trailing edge Kutta condition. Experimental data show that finite loading is carried to the trailing edge. For hinge-less flow control the basic tenet of the Gurney flap is attractive, but its implementation would require moving parts. Consequently, we have suggested the implementation of a “Synthetic” Gurney flap, where the flap is pseudo-formed using a jet developed by a SJA or continuous pneumatic supply.
Experimental Details
For initial proof of concept testing, a continuous air supply was implemented using an external high pressure source. A wing was manufactured from foam and balsa to accommodate the continuous jet or SJA. The wing was then covered with heat sink to ensure a smooth surface. A NACA 0015 profile was used. The wing was equipped with end plates to mimic two-dimensional flow. Figure 2 shows the wing and blowing slot details. The width of the slot was 1mm, giving a slot exit area of 0.0002m2. The slot was located 15mm from the wing’s trailing edge. As implemented, the flap is a jet flap, with a large jet inclination (90 deg) angle.
Geometric details of the model are a chord of 0.71m and a span of 0.235m. The tests were carried out in TexasA&MUniversity’s 3’ by 4’ closed-loop wind tunnel. A freestream velocity of 15m/s was used yielding a Reynolds number of 0.7x106. Tunnel turbulence intensity has been measured at less then 0.5%, assuming isotropic turbulence. Data acquisition was facilitated using a 3-component Pyramidal balance. Balance output voltages were read using a 16-bit A/D board. A dedicated software acquisition code has been written for this facility and was used for acquisition and processing. Prior to use for these experiments, the Pyramidal balance was re-calibrated. Subsequent balance verification through application of pure and combined loads suggests accuracies better then 0.6% for lift, drag and pitching moment. Figures 10 and 11 shows the wing installed in the wind tunnel (nearest end plate omitted for clarity).
To achieve blowing, shop air was used as the pneumatic source. Slot exit jet momentum coefficients were measured using a British Standard (Part 1042) orifice plate. The orifice facilitated the measurement of the mass flow rate, which in conjunction with continuity allowed determination of the jet slot exit velocity. The measurement technique was verified using a TSI calibrator which allows accurate measurement of an air jet exhausting from its settling chamber. Air to the calibrator was supplied through the orifice plate. Slot exit velocities were measured and compared with predictions using the orifice. Agreement was generally within 1.5%.
Force Balance Results
In all data, the effects of the jet reaction on lift and pitching moment coefficient have been removed through tare runs; consequently, pure aerodynamic loading is shown. Results are summarized in Figs. 12 and 13. The effects of the jet momentum coefficient, Cmu on the measured lift are shown in figure 12. Also included is a plot showing the lift augmentation ratio. This ratio is defined as (ClCmu≠0- ClCmu=0)/Cmu for the present jet configuration. The ratio clearly shows how the effectiveness of the jet relates to the supplied momentum. A coefficient greater then 1 indicates that augmentation is greater then if the jet had been used purely for its reactive lift. Also included in the data are results for a 0.75% of chord Gurney flap, which was positioned at the same location as the jet. This is a typical size for a Gurney flap, and provides a reference for the lift and moment alteration provided through blowing. The data in figure 12 show that the jet flap shifts the angle of attack for zero lift to negative values, as does a conventional flap. A momentum coefficient of 0.0068 is seen to provide similar lift augmentation to the gurney flap. The magnitudes of the recorded lift also suggest that the end plates were not large enough to ensure 2D flow. Notice that all lift curves appear to have a non-linear increase around 4 deg, as seen on low aspect ratio wings. However, this does not affect the comparative nature of the data presentation. The effectiveness of the blowing may be gauged by examining the lift augmentation ratio (ClCmu≠0- ClCmu=0)/Cmu) shown in the top of the multi-part figure (Fig. 12). As may be seen, the jet greatly augments the lift compared to the momentum added to the flow. Greatest augmentation is seen for the lower Cmu’s; increasing the jets momentum reduces the relative benefit if not the magnitude of the augmentation. The augmentation ratios are of similar magnitude to those calculated by Lockwood and Vogler (1958).
In the present application, the primary significance of the jet is in its impact on the pitching moment, so as to be suitable for hinge-less control. The negative shift of the pitching moment curve, typical of a trailing edge flap, is clearly seen, see Fig. 13. As noted for lift, the zero pitching moment caused by Cmu = 0.0068 is comparable to that generated by a 0.75% chord Gurney flap. The magnitudes of the moment generated, although towards the low end of what a conventional trailing edge flap may generate, are sufficient for pitch control at low angles of attack. Additionally, the required jet momentum coefficients are not excessively large, and are achievable using a SJA (as will be tested in the next phase). Pitch control would be achieved by locating a jet slot on the upper and lower surface, allowing control of the vehicles incidence. Also shown in figure 13 are the dependencies of the zero lift increments of Cm and Cl on the jet momentum coefficient. As may be seen, the greatest augmentation occurs at the lowest Cmu’s, with the increment appearing to monotonically approach a bound for increasing Cmu. Analytic expressions due to Spence (1958) suggest a dependency proportional to Cmu1/2 for Cl.
FlowVisualization
To gain an insight into the similarities/differences of the trailing edge flow physics between the Gurney and Jet flap, flow visualization using Titanium Dioxide was used. A thin plate was attached parallel to the side plates. Visualization of the skin friction lines on the stream-wise plate would then give an indication as to the fluid behavior. Please note that due to the effects of gravity on the fluid medium, the results are purely qualitative and no inferences should be made as to precise locations or trajectories of flow features. Figure 14 presents acquired images for the 0.75% Gurney flap and Jet flap (Cmu = 0.01) at a freestream velocity of 15m/s. The results indicate that despite similar aerodynamic effects, the flow physics present are somewhat dissimilar. The jet flap shows evidence of significant turning of the flow around the trailing edge such that the jet exit becomes functionally the rear separation point. The jet is seen to expand rapidly and deflect streamwise; initially due to pressure gradients across the jet and later due to entrainment and absorption of the free stream axial momentum (Jordinson 1956). The Gurney flap appears to shed a fairly thick wake extending from the separation bubble formed behind the flap. The visualized wake may correspond to the von Karman vortex street identified by Jeffrey (2000). The significant turning of the flow seen with the jet flap is not observed. A line indicating the approximate trajectory of the shear layer shed from the flap extremity is also observed. Comparison of the skin friction patterns also suggests that while the jet flap draws the lower surface boundary layer away from the surface, the Gurney causes deceleration and recompression. It may thus be tentatively inferred that the Gurney augments lift by violating the Kutta condition while the jet flap increases flow turning and hence effective camber near the trailing edge.