J. F. Milthorpe

On the shearing zone around rotating vanes in plastic liquids: theory and experiment

Abstract The fracture zone (or shearing surface) around a four-bladed vane rotating in a Bingham liquid has a diameter D c which is significantly larger than the vane diameter. In typical plastic liquids D c / D ≈ 1.00–1.05. We have measured D c and the rheology of some automotive greases. We have also photographed the fractural surface in a transparent Bingham liquid and have found it to be approximately cylindrical. Computer simulations of a four-bladed vane rotating in a Bingham liquid have produced a value of D c / D = 1.025 which agrees well with experimental data on two viscoelastic automotive greases. We have not been able to obtain agreement between experiment and theory on the dependence of D c / D on τ y /η p . The experimental and theoretical data presented here support the use of the vane for yield stress measurements if the diameter correction is applied. The present experimental data suggests the vane diameter has little or no effect on D c / D .

Finite element and boundary element methods for extrusion computations

Abstract The present paper reports some new finite element and boundary element results for the expansion of a plane jet of Maxwell fluid. Finite element results for the axisymmetric problem are also presented. The boundary element method represents a new method of solving this problem. The Maxwell stresses are evaluated by integrating along the streamlines; these are then incorporated in the boundary element formulation. The new results are compared with existing finite element solutions of this problem. Although all sets of results predict the same overall behaviour, there is still little agreement on the exact behaviour

The shape of low Reynolds number jets

New experiments and new finite element computations with surface tension of jet shapes at Reynolds numbers up to 100 were made. Good agreement between experiment and computations was obtained.

Active control of swept shock wave/turbulent boundary-layer interactions

We look at active control of the swept shock wave/turbulent boundary-layer interaction using smart flap actuators. The actuators are manufactured by bonding piezoelectric material to an inert substrate to control the bleed/suction rate through a plenum chamber. The cavity provides communication of signals across the shock, allowing rapid thickening of the boundary-layer approaching the shock, which splits into a series of weaker shocks forming a lambda shock foot, reducing wave drag. Active control allows optimum control of the interaction, as it would be capable of positioning the control region around the original shock position and control the rate of mass transfer. The actuators are modelled using classical composite material mechanics theory, namely analysis of a laminate with a uniform cross section. Furthermore a finite element modelling program (ANSYS 5.7) was used to produce improved results

Optimal design of an Australian medium launch vehicle

Conceptual design of a satellite launch vehicle is a multidisciplinary task which must take into account interactions of disciplines such as propulsion, aerodynamics, structures, guidance and orbital mechanics. We discuss the initial modelling of a clean sheet design for a putative Australian medium launch vehicle capable of placing an Ariane-44L equivalent payload into geostationary transfer orbit. While the Ariane-44L vehicle design is a three and a half stage vehicle, the alternative design is for a straight three stage vehicle. The “ideal velocity” or delta-V capability of the AR44L is first derived from published data. The proposed design is then modeled using a spreadsheet. The gross lift-off weight of the vehicle is then minimised while still providing the same delta-V as Ariane. Various differences between the two vehicles are discussed. The initial design of a launch vehicle as presented here is based on a simple stack model optimised automatically using an evolutionary algorithm. The efficiency of the proposed approach and the reasons for using evolutionary algorithms is discussed along with future developments in the areas of multi-objective formulations of the design optimisation problem as well as the vehicle model from the standpoint of a number of system considerations.

Normal shock wave/turbulent boundary-layer interaction control using ‘smart’ piezoelectric actuators

This paper looks at active control of the normal shock wave/turbulent boundary layer interaction (SBLI) using smart flap actuators. The actuators are manufactured by bonding piezoelectric material to an inert substrate to control the bleed/suction rate through a plenum chamber. The cavity allows rapid thickening of the boundary-layer approaching the shock, which splits into a series of weaker shocks forming a lambda shock foot, thus reducing wave drag. Active control allows optimisation of the interaction, as it would be capable of either positioning the control region around the original shock position using a series of unimorph flaps or fixing the shock position by controlling the rate of mass transfer. The level of control achieved by unimorph piezoelectric actuators is not large because of small amounts of deflection possible. It is believed that to provide optimal control a piezoelectric material, which can provide greater strain and hence higher amounts of deflection is needed. However, currently such a piezoelectric material is not commercially available.

Investigation of Unswept Normal Shock Wave/Turbulent-Boundary-Layer Interaction Control

An analytical model for the unswept normal shock wave/turbulent-boundary-layer interaction control using an upstream and downstream unimorph piezoelectric flap actuator has been proposed. The amount of flap deflection controls the bleed/suction rate through a plenum chamber. The cavity allows rapid thickening of the boundary layer approaching a normal shock wave, which splits into a series of weaker shocks forming a lambda shock foot, leading to a reduction in the wave drag. The analysis provides an understanding of the control influences produced in an experimental investigation of an unswept normal shock wave/turbulent-boundary-layer interaction at a Mach number of 1.5. It has also been validated by application to the normal shock wave/boundary-layer interaction control system using mesoflaps for aeroelastic transpiration described in previous transonic/supersonic shock wave/ boundary-layer interaction studies.

Shallow Rectangular Cavities at Low Speeds Including Effects of Yaw

This paper presents a low-speed investigation of flow anddrag characteristics of straight and shallow rectangular cavities including the effects of yaw. All the flow regimes of cavity flow, that is, “open, ”“ transitional,” and “closed” wereinvestigated.Measurementsconsistedofpressuredata(bothmeanand fluctuating)andoil flowvisualization.It was found that with a cavity at zero yaw, the drag, based on the projected frontal area of the cavity, increased from opentoclosed.Theeffectofyawwassuchthattherelativedragofthecavityinallthe flowregimesshowedadecrease with increase in yaw angle. This decrease varied between 20 and 35% at the highest yaw angle (45 deg) tested. Nomenclature CD = drag coefficient based on projected frontal area of cavity Cf = skin friction coefficient Cp = pressure coefficient C � = drag coefficient based on planform area of cavity d = cavity depth, mm f = frequency, Hz l = cavity length, mm m = mode number M = Mach number Re = Reynolds number U = freestream velocity w = width, mm x,y,z = coordinates in the streamwise, vertical, and spanwise directions centered on the cavity axis and measured from the cavity front face � = time lag constant (defined in text) � = boundary layer thickness at the cavity leading edge, mm � = momentum thickness, mm � = ratio of convective speed of vortices to the freestream speed � = density = yaw angle, deg 1 =i nfinity

An Investigation into Supersonic Swept Cavity Flows

*† ‡ An experimental investigation was conducted to determine the flow characteristics of swept cavities in the supersonic flow regime at a freestream Mach number of 2. The investigation described herein focused on obtaining information mainly on the mean flow features although some data on cavity flow pressure oscillations was also obtained. The data consisted of s urface oil flow visualisation, and steady and unsteady pressure measurements. The length to depth ratios of the cavities investigated were 8 and 16, typical of the “open” and “closed” type. The results of the swept cavities, when compared to the datum case s of straight cavities (of the same length to depth ratios), showed some marked and unusual differences. In particular, with the ‘short’ swept cavity (L/D=8), the flow resembled quasi open flow behaviour, distorted by the spanwise cross flow across the cav ity. In the case of the ‘long’ swept cavity (L/D=16), flow features resembling, ‘closed’ ‘transitional’, and ‘open’ seem to exist across the whole span.

Theoretical Analysis of Unswept Normal Shock Wave/ Boundary Layer Interaction Control Using Streamwise Flaps

This paper provides a theoretical model f or normal unswept shock wave/boundary layer interaction ( SBLI ) control using an upstream and downstream flap. The amount of flap deflection controls the bleed/suction rate through a plenum chamber . The cavity allows rapid thickening of the boundary layer approachin g the shock, which splits into a series of weaker shocks forming a lambda shock foot, thus reducing wave drag . Th e analysis assist s in the understanding of the control influences produced in the SBLI . It is applied to the MART system at M 1=1.4 as well as to validate and improve the understanding of unimorph flap control at M 1=1.5 .