Showing papers by "Vaughn College of Aeronautics and Technology published in 2001"

Real-time difference imaging analysis of moa galactic bulge observations during 2000

Abstract: We describe observations carried out by the MOA group of the Galactic bulge during 2000 that were designed to detect efficiently gravitational microlensing of faint stars in which the magnification is high and/or of short duration. These events are particularly useful for studies of extrasolar planets and faint stars. Approximately 17 deg2 were monitored at a sampling rate of up to six times per night. The images were analysed in real time using a difference imaging technique. 20 microlensing candidates were detected, of which eight were alerted to the microlensing community whilst in progress. Approximately half of the candidates had high magnifications (≳10), at least one had very high magnification (≳50), and one exhibited a clear parallax effect. The details of these events are reported here, together with details of the on-line difference imaging technique. Some nova-like events were also observed and these are described, together with one asteroid.

Blended wing body airframe mass prediction

Abstract: The blended wing body (BWB) concept is one in which the payload is carried within the inner wing of the aircraft, the local aerofoil sections being deepened to accommodate it. Difficulties, both in design and mass prediction, arise when the payload requires the pressurization of the non-circular cross- sections of the blended wing region. The paper presents a method by which the mass of the BWB airframe may be predicted using an empirically weighted theoretical approach. The ideal wing structure mass is modified by introducing penalties for the secondary structure and, in particular, the payload carrying function. Absolute validation of the method is not possible as no full-size aircraft of this category has been built and flown. Nevertheless, application of the method to several design studies gives reason to believe that it is acceptable for preliminary design purposes.

Control of normal shock wave/turbulent boundary layer interactions using streamwise grooves

Abstract: The effect of streamwise slots on the interaction of a normal shock wave / turbulent boundary layer has been investigated experimentally at a Mach number of 1.3. The surface pressure distribution for the controlled interaction was found to be significantly smeared, featuring a distinct plateau. This was due to a change in shock structure from a typical unseparated normal shock wave boundary layer interaction to a large bifurcated Lambda type shock pattern. Boundary layer velocity measurements downstream of the slots revealed a strong spanwise variation of boundary layer properties whereas the modified shock structure was relatively twodimensional. Oil flow visualisation indicated that in the presence of slots the boundary layer surface flow was highly three dimensional and confirmed that the effect of slots was mainly due to suction and blowing similar to that for passive control with uniform surface ventilation. Three hole probe measurements confirmed that the boundary layer was three dimensional and that the slots introduced vortical motion into the flowfield. Results indicate that when applied to an aerofoil, the control device has the potential to reduce wave drag while incurring only small viscous penalties. The introduction of streamwise vorticity may also be beneficial to delay trailing edge separation and the device is thought to be capable of postponing buffet onset. © 2001 by A N Smith.

U‐99 uninhabited tactical aircraft preliminary structural design

Abstract: Describes preliminary structural design work on a notional uninhabited tactical aircraft (UTA), carried out at Cranfield University. UTAs are seen as an important future element of military fleets. A notional baseline requirement was derived, leading to the evolution of a design solution. The basic requirements for such a UTA are naturally highly classified but, although industry has been hesitant to comment, the baseline requirements and design solution developed herein are believed to be reasonable.

Short‐range, unmanned air vehicle system development at Cranfield

Abstract: In the mid‐1990s Cranfield began work on a programme to develop a short‐range, unmanned air vehicle system for surveillance use. The basic aim of the work was to prove the technologies to provide real time reconnaissance imagery of ground targets to operators having the minimum of skills in air vehicle operations. Cranfield was able to bring a wide range of proven skills to the programme in the areas of airframe and control system design, mathematical modelling and real time simulation plus system integration and flight trials. All of these contributed to the work described here. The programme led to the demonstration of a complete “Observer” system, including the new Cranfield A3 air vehicle, which met the requirements for a robust, simple to operate system for providing the imagery information required without the need to master the complexities of the technologies deployed to provide it.

Assessment of the eN Method as a Transition Prediction Tool for Zero Pressure Gradient Flows with and without Boundary Layer Suction

Abstract: This paper compares theoretical predictions for the onset of transition to turbulence with experimental results observed in a 2-D zero pressure gradient boundary layer (typical unit Reynolds number 2 million) subjected to suction through a perforated strip extending 20cm in the streamwise direction, for suction coefficients in the range 0.001 to 0.01. In the zero suction case experimental observations agreed well with theoretical predictions obtained by using the eN method with a transition criterion of N=9. However, with suction applied this criterion failed to predict transition onset in the post-suction region. The discrepancy is attributed to disturbance effects not accounted for in linear stability theory, made apparent, either directly or indirectly, by the application of boundary layer suction.

Study of the aerodynamics of in-plane motion

Abstract: A computational analysis is performed of the unsteady aerodynamics associated with the blade sections of helicopter rotors in forward flight. The unsteady flow is studied through solutions of the two- dimensional Reynolds averaged Navier-Stokes equations together with a strongly coupled two-equation model of turbulence. Two motions are studied.The first motion is that of an aerofoil subjected to harmonic in-plane oscillations. The influence of advance ratio and reduced frequency is investigated. It is shown that, in the absence of shock waves, the flow is periodic with a reduced frequency equal to that of the forcing motion. However, the flow development lags behind the forcing motion. Furthermore, for constant reduced frequency the phase lag is independent of advance ratio.In addition to harmonic motion, the aerodynamic response to a step change in Mach number is investigated. Using an assumed form of the response of lift coefficient to a step change in Mach number, a lift transfer operator for s...

Experience with the Osher Scheme for Applied Aerodynamics

Abstract: This paper presents some of our experience in using Osher’s approximate Riemenn solver in solving the Navier-Stokes equations for high speed aerodynamic problems. Grid convergence in boundary layers, grid alignment with flow features in multi-dimensional applications and some anomalies in numerical simulations are discussed.

An investigation of Handley Page Jetstream handling during landing

Abstract: Handley Page Jetstream G-NFLC has for many years been used to complement the theoretical teaching material on undergraduate and postgraduate aeronautical engineering courses through a set of airborne laboratories designed to expose students to practical measurements in a realistic environment. It is suspected by some of the Cranfield test pilots that the aeroplane may be prone to pilot involved oscillations in pitch during the flare; the most likely causes are a deterioration in the short period dynamics at aft centre of gravity locations and adverse longitudinal stick force characteristics. To date however, no objective data has been available to support this hypothesis. This study reports upon an experiment designed to quantify these effects by identifying linear models of the short term dynamics from flight-test data, and assessing them against the Gibson dropback and phase rate criteria. As expected, a rearward shift in the centre of gravity causes the airframe short period pitching oscillation (elevator deflection to pitch rate) to become more sluggish, thereby producing a significant reduction in dropback, which can be traced directly to the size of the static margin

Gas Flows Generated by Propellant Burning

Abstract: Exact, analytical, solutions to the set of Euler equations augmented by some rather particular forms of source functions are available, and play a useful role in helping to validate numerical solutions of some complex physical problems. As well as providing support for numerical algorithms, such exact solutions can sometimes also help with an understanding of the physics of a real problem. Here, an investigation of a combustion problem illustrates this fact.

An eddy-viscosity limited algebraic stress model for shock-boundary-layer interaction

Abstract: We present a μ t -limited explicit algebraic stress model for shock-wave-turbulent boundary-layer interactions based on an investigation of various two-equation turbulence models. The results of the κ-ω model, the shear stress transport (SST) model, and a quadratic explicit algebraic stress model are presented and analysed for the Delery channel bump, and the Bachalo and Johnson axisymmetric bump test cases. While the κ-ω model failed to give good predictions, the SST model proved reasonably successful in predicting strong interaction problems. The non-linear quadratic explicit algebraic stress model gave improved results (when compared with the original κ-ω model) for the channel bump test cases, but was not as good as the SST model. Inspired by this investigation, a model formulation is proposed in which Bradshaw's assumption for eddy-viscosity limiting (as used in the SST model) is applied to a quadratic explicit algebraic stress model. The QSST model further improves the SST model for strong shock-boundary-layer interactions