bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Theory of Fabric Porosity as Applied to Parachutes in Incompressible Flow
Authors: Payne Peter R. 
Published: July 2016

SummaryMany aspects of parachute behaviour are dominated by the permeability of the canopy cloth. Techniques employing kinematic principles to predict parachute opening behaviour, for example, must first be able to predict the air flow through the canopy material. This paper is concerned with the development of such a predictive capability.The flow of air through cloth of gauze has been studied by many workers; since the 1850’s, in connection with filters; and since the early twenties, in connection with parachutes. Workers in each of these disciplines seemed unaware of the work being done in the other.In the case of parachute cloth permeability we find the foundations being laid down by such eminent workers as Glauert in 1932 and Taylor in 1944. Yet most subsequent writers seem not to be aware of this, and since World War II, there have been many papers “rediscovering” basic principles; often with errors which could have been corrected by reference to the earlier authorities.In this paper we attempt to bring together all the work which has been done in this field, and to rationalize the data by simple mathematical modelling. Individual elements of the model have been proposed before, of course.We then examine the effect of tension on the geometric porosity of fabric, and hence the pressure loss Ap. A theoretical analysis shows that tension is likely to be a major factor. For cloths which have low porosity when unloaded our simple mathematical model shows that, for a given Ap, a stress equal to 50% of ultimate can increase the air volume flow Q by an order of magnitude. In general, the increase in permeability is greatest at the lower values of Ap, indicating that the viscous term is more influenced by tension than the dynamic term. This theoretical result is confirmed by some rather limited experiments carried out by Lashbrook and Marby. But their data also shows that a cloth made from relatively stiff glass fibers can experience areductionin permeability when loaded, due to a “closing up” of the weave. The reasons for this are discussed.
An Alternative Approach to the High Aspect Ratio Wing With Jet Flap by Matched Asymptotic Expansions
Authors: Kida T. , Miyai Y. 
Published: July 2016

SummaryAn alternative method is described for solving the problem of a three-dimensional jet-flapped wing with a high aspect-ratio. This method is similar to the lifting-line theory of Kerney6 or Tokuda7, but differs in that the method of matched asymptotic expansions is applied to an integral equation, derived from the lifting surface theory, rather than a partial differential equation. The advantage of the present method over those used previously is that the necessary outer solutions are obtained directly; it is not necessary to rely upon physical insight or considerable ingenuity. The final results are different from those obtained by the previous authors; it is shown that the present result is correct, by noting some errors in the earlier theories.
The Generalization of a Double Integral Method with Applications to Jets in Unbounded Co-Flows
Authors: Middleton D. 
Published: July 2016

SummaryThe ‘double integral’ method, employed by Squire and Trouncer to calculate the flow of a round turbulent jet in a moving stream, is generalised. Representation of the velocity profile in simple form and use of anarbitraryupper limit of integration in the second application of the momentum integral equation permits the recovery of the well-known similarity solutions for plane and axi-symmetric laminar jets issuing into a quiescent medium. Additionally, an approximation for the decay of centre-line velocity is obtained for the non-similar situation when there is an ambient co-flowing stream. This agrees well with Wygnanski’s perturbation solution for the plane laminar jet. The results of Squire and Trouncer are re-examined in the light of this generalised approach. The work has application to the operation of fluidic sensors.
The Development of High Lift, Single-Component Airfoil Sections
Authors: Kennedy J.L. , Marsden D.J. 
Published: July 2016

SummaryThis paper investigates the possibility of increasing the maximum lift of a single element wing section by the introduction of camber near the trailing edge. The optimum upper surface velocity distribution consists of a constant high velocity “rooftop” over the forward part of the wing section followed by transition and an optimised turbulent boundary layer recovery region to the trailing edge. The height of the rooftop, which essentially determines the maximum lift coefficient, is limited by the amount of recovery attainable without separation of the turbulent boundary layer. An increase in the upper surface velocity at the trailing edge would allow the whole top surface velocity distribution to be raised resulting in a considerable increase in maximum lift. The introduction of camber over the rear part of the wing section should produce the required increase in trailing edge velocity on the upper surface. The practical possibilities of using this technique for increased maximum lift were examined by designing a high lift wing section and testing it in the University of Alberta Low Turbulence Wind Tunnel. The results showed that the new wing section behaved qualitatively as expected. A difference of about 0.5U∞ between upper and lower surface velocities at the trailing edge was achieved, even though the thick boundary layers near the trailing edge tend to reduce the effect of camber. A maximum lift coefficient of 2.64 was measured at a Reynolds number of 1.0 × 106.
Prediction of Viscous Effects in Steady Transonic Flow Past an Aerofoil
Authors: Collyer M.R. , Lock R.C. 
Published: July 2016

SummaryAn account is given of a numerical method for calculating transonic flow past an aerofoil with an allowance for viscous effects, providing that the boundary layer remains fully attached over the aerofoil surface. The method has been developed by combining, in an iterative manner, calculations of the inviscid flow with calculations of the compressible boundary layer and wake. The solution for the inviscid flow is obtained by an iterative scheme, originally established by Garabedian & Korn, which has been modified to give a more realistic representation of shock waves. The boundary-layer development is treated as laminar initially; at a certain transition position a turbulent boundary layer is assumed to develop, and this is determined by the lag-entrainment method of Green et al. Comparisons of the results from the numerical scheme with some experimental measurements are shown for various examples in which shock waves of moderate strength are present. The method predicts, with reasonable accuracy, both the detailed pressure distribution and the variation of drag coefficient with lift coefficient.
Derivation by a Transform Method of Integral Equations of Unsteady Lifting Surface Theory in Subsonic and Supersonic Flow
Authors: Ando Shigenori , Ichikawa Akio 
Published: July 2016

SummaryApplications of “integral transforms of in-plane coordinate variables” in order to formulate unsteady planar lifting surface theories are demonstrated for both sub- and supersonic inviscid flows. It is concise and pithy. Fourier transforms are exclusively used, except for only Laplace transform in the supersonic streamwise direction. It is found that the streamwise Fourier inversion in the subsonic case requires some caution. Concepts based on the theory of distributions seem to be essential, in order to solve the convergence difficulties of integrals. Apart from this caution, the method of integral transforms of in-plane coordinate variables makes it be pure-mathematical to formulate the lifting surface problems, and makes aerodynamicist’s experiences and physical models such as vortices or doublets be useless.
Stability Derivatives of Blunt Slender Cones at High Mach Numbers
Authors: Khalid M. , East R.A. 
Published: July 2016

SummaryThis paper presents a semi-empirical theoretical model for calculating the effect of nose bluntness on the stability derivatives of oscillating slender cones at hypersonic Mach numbers. It is based on a hybrid blast wave analogy/shock-expansion flow model and is used to obtain closed form analytic expressions for the derivatives for oscillating slender cones. Two models based on zero thickness and finite thickness entropy layers are proposed which are seen to be appropriate to the cases of very small and large nose bluntnesses, respectively. The results are compared with new and existing experimental data and with the predictions of previous theoretical methods.
The Effect of Mean Loading on the Fluctuating Loads Induced on Aerofoils by a Turbulent Stream
Authors: Mckeough P.J. , Graham J.M.R. 
Published: July 2016

SummaryThis paper analyses the unsteady lift produced on a thin aerofoil by an arbitrary three-dimensional gust. In particular, it evaluates the effects of α, the angle of incidence of the aerofoil to the mean stream. A thin aerofoil theory which includes the effects of distortion of the turbulence by the mean flow field of the aerofoil is applied to the case of an aerofoil in isotropic turbulence. Some computed results are compared with measurements made on a NACA 0015 aerofoil in grid turbulence in a wind tunnel. It is shown that for isotropic turbulence the effect of mean incidence on the lift spectrum is of order α2, and is significant at low frequencies for the length scale ratios tested.
An Inviscid-Viscous Interaction Method to Predict the Blade-to-Blade Performance of Axial Compressors
Authors: Calvert W.J. , Herbert M.V. 
Published: July 2016

SummaryAn inviscid-viscous interaction method has been developed to predict the blade-to-blade flow in axial compressors. The method is primarily intended for high deflection, transonic (but substantially shock-free) blades where the suction surface boundary layer may be separated near the trailing edge. The inviscid flow is calculated by a time marching method and the viscous flow by integral methods for laminar and turbulent boundary layers. A mixing calculation is then carried out to determine the blade deviation angle and pressure loss coefficient. Predictions have been compared with test results for three high deflection, transonic cascades and there is generally good agreement.
On an Approximation to the Flow Through Axi-Symmetric Contracting Ducts
Authors: Jordinson R. , Rodger J.G. 
Published: July 2016

SummaryA method is given for the calculation of incompressible, inviscid flow through an axi-symmetric contracting duct for which the two dimensional flow with the same meridianal boundaries is known. The method, which is based on Whitehead, Wu and Waters original proposal, assumes that the contraction consists of two separate portions, upstream and downstream respectively. The flow in each portion is calculated and the two portions matched to produce a contraction of given area ratio with preassigned values of the two dimensional ‘overshoot’ and ‘undershoot’ parameters. It is worth emphasizing that in practice it is only necessary to do the calculations once to predict wall velocities for a family of contraction shapes with different area ratios provided they share a common upstream or downstream portion. The results given here show reasonable agreement with the pressure coefficients obtained in experiment for the upstream end of a small scale contraction of area ratio 16:1. There is however a discrepancy between theory and experiment at the downstream end and a qualitative explanation is advanced for this.
The Effects of Swirl on the Performance of Supercritical Convergent-Divergent Nozzles
Authors: Carpenter P.W. 
Published: July 2016

SummaryThe quasi-one-dimensional theory due to Carpenter and Johannesen is applied to supercritical swirling flows in convergent-divergent nozzles. Only flows with uniformly constant stagnation pressure and entropy are considered. Values of exit impulse function and area ratio are given for various types of swirling flow with a range of back-pressure ratios. Thrust coefficients are calculated using these values and specific thrust coefficients plotted against maximum swirl velocity for various cases. In some cases the specific thrust for swirling nozzle flows very slightly exceeds the no-swirl value. The effects of nozzle wall curvature and flight speed on swirling nozzle flows are discussed. The contribution of post-exit thrust to the total thrust is estimated for swirling flow. Finally, the implications are considered of using swirl at the cruise conditions of a typical SST.
Measured Pressure Distributions and Shock Shapes on a Simple Delta Wing
Authors: Squire L.C. 
Published: July 2016

SummaryThis note presents the results of an experimental investigation of the flow over a simple delta wing designed for a Mach number of 3.5. Complete pressure distributions were measured for incidences of 0°, 10° and 20° at Mach numbers of 2.5 and 3.5. A number of schlieren photographs of the shock system around the wing were obtained at the same conditions and surface streamline patterns were studied at M = 3.5. The measurements were made to support numerical calculations which use this wing as a test case.
Forced Convection Near Laminar Separation
Authors: Akinrelere E.A. 
Published: July 2016

SummaryThe singular behaviour of an incompressible boundary layer at separation has been well established by the works of Howarth (1938), Goldstein (1948), Stewartson (1958), Curie (1958) and Terrill (1960). Stewartson (1962) remarked that the existence of the singularity at separation can be regarded as fully established and understood. The skin friction vanishes like where x is the distance to separation, and the stream function close to the wall is described by a series of powers of , with coefficients that are functions of , where y measures distance normal to the wall. At some stages in the expansion of the stream function, terms in log x have to be included. The case of the compressible flow is less satisfactory. Stewartson (1962) was unable to establish singularity at separation and concluded that the general compressible boundary layer cannot have a singularity at separation unless there is no heat transfer from the wall. This has been contradicted by the works of Merkin (1968) and Buckmaster (1970). Curie (1958) also reported that the difficulty encountered in computing the temperature field right down to the point of separation might be due to the singularity there. In this paper, the Goldstein-Stewart son approach is applied to laminar boundary layer flow at low speeds in which density is sensibly constant and the Prandtl number σ is taken as unity. Singularity is established at separation for the temperature field. The heat transfer does not vanish at separation point and is of the form
Some Techniques for Extending the Application of the Discrete Vortex Method of Flow Simulation
Authors: Bromilow I.G. , Clements R.R. 
Published: July 2016

SummarySimulations of vortex sheet dynamics by the discrete vortex method have often shown a growing randomness of the discrete vortices. This paper describes two techniques which attempt to mitigate this tendency whilst preserving the overall structure of the vortex sheet. Clusters of vortices near the points of concentration are amalgamated into a single equivalent vortex and a process of repeated rediscretization of the remaining part of the sheet maintains the integrity of its representation. Use of these techniques allow the flow model to be followed beyond previous expectations, without undue randomisation of the vortex positions. The effects of using these techniques on the overall vortex sheet development are fully investigated in order to validate their use in future investigations.
A Normal Flat Plate Close to a Large Plane Surface
Authors: Everitt K.W. 
Published: July 2016

SummaryThe flow around a normal flat plate close to a large plane surface has been investigated for a range of boundary-layer thickness on the plane surface of 0.72 to 2.53 times the plate height, h. As the gap between the plate and the plane surface is reduced below about 0.55h vortex shedding from the plate is inhibited by the presence of the plane surface. Boundary layer thickness has little effect on the gap at which this occurs, but does affect the strength and frequency of vortex shedding at greater gaps. As the gap between the plate lower edge and the plane surface is decreased towards the critical value of 0.55h, both vortex strength and Strouhal number are more significantly affected when the approaching boundary layer is thin. It is not clear whether this is a result of shear or increased turbulent intensity.
Turbulent Boundary-Layer Development on a Two-Dimensional Aerofoil with Supercritical Flow at low Reynolds Number
Authors: Baker C.J. , Squire L.C. 
Published: July 2016

SummaryDetailed measurements have been made of the boundary-layer development on a small two-dimensional aerofoil with supercritical flow and a weak shock wave, together with similar measurements on the tunnel side wall opposite the aerofoil surface. The Reynolds number of the test is similar to that found in the turbines of jet engines and there is a strong favourable pressure gradient ahead of the interaction of the shock with the boundary layer as often occurs in turbine blade passages. However, whereas the boundary layer on the aerofoil is thin and of the same thickness as that on a turbine blade, the thicker boundary layer on the wall is more typical of that on the hub or casing. The experimental results are compared with results from a wide range of calculation methods. One interesting conclusion from these comparisons is the fact that prediction methods which perform well for the thin boundary layers on the aerofoil do not necessarily perform as well for the thicker boundary layers on the wall.
On the Impingement of Supersonic Jet on a Normal Flat Surface
Authors: Pamadi B.N. 
Published: July 2016

SummaryAn improved method, based on one strip approximation of the method of integral relations which was reported originally by Belov, Ginzburg and Shub, is presented for the calculation of flow parameters in the impingement region of a supersonic, underexpanded jet striking a normal surface located within the first cell. The results are presented for two impingement conditions and found to be in good agreement with the experimental data.
The Unsteady Lift on Bluff Cylindrical Bodies in Unsteady Flow
Authors: Stapountzis H. , Graham J.M.R. 
Published: July 2016

SummaryThe unsteady lift generated on a NACA 0015 aerofoil, a D cylinder (with the flat face down-stream) and an elliptic cylinder was measured when these bodies were exposed to a flow with a two-dimensional sinusoidal upwash at reduced frequencies 0.05 to 0.8. The mean flow Reynolds numbers were in the range 1.2 × 105 to 3 × 105. Unsteady thin aerofoil theory was used in an attempt to predict the unsteady lift on the bluff bodies, as well as the aerofoil section for fequencies in the low range below the vortex shedding frequency. The results were quite accurate for the aerofoil and the D cylinder, but the aerodynamic admittance predicted by this theory for the elliptic cylinder was significantly above that measured experimentally. The movement of the two free separation points was found to play an important role in the characteristic lift behaviour of the elliptic cylinder.
A Laser-Interferometer Method for Determining the Forces on a Freely-Flying Model in a Shock-Tunnel
Authors: Bernstein L. , Stott G.T. 
Published: July 2016

SummaryConventional force-balances, “accelerometer balances” and photographic monitoring of freely-flying models are not suitable for use in the Q.M.C. shock tunnel where the force levels are of order 10N for flow durations of about 1 ms. An interferometric method has therefore been developed for following the trajectory of a weakly-restrained model. The prototype system consists of two simple Michelson interferometers, a single He-Ne laser being employed to provide two measurement and two reference beams so that the motion of two points on the model can be followed. The measurement beams are returned by corner-cube retroreflectors carried on the model which ensures that for each measurement arm the reference and measurement beams recombine at the surface of a photo-detector. As the model moves, interference fringes are produced at the detectors, the cycle dark-light-dark corresponding to a model displacement along the measurement beam of ½λ, about 0.3μm. The frequency-modulated wave-trains produced are recorded using two transient recorders, the data being subsequently played back to a two-channel pen recorder giving a record 500 mm in length corresponding to the test time. The fringe number as a function of time is read manually, and the data analysed by curve fitting to a parabola which yields the accelerations of the measurement points. A knowledge of the inertial characteristics of the model then gives the forces on it. By suitably aligning the beams, lift and pitching moment for a ridge-delta of aspect-ratio 1 were obtained. Two models of the same geometric size but of different inertia were tested. All the data were obtained for model displacements less than 1 mm and pitch rotations less than 0.1°.
An Experimental Investigation of the Wake of an Axisymmetric Body with a Slanted Base
Authors: Xia X.J. , Bearman P.W. 
Published: July 2016

SummaryThe effect of base slant on the base pressure distribution, drag coefficient and vortex shedding characteristics of a model consisting of an axisymmetric main body with an ellipsoidal nose have been investigated for three fineness ratios; 3, 6 and 9. A sudden change in the drag coefficient and separated flow pattern is observed at a critical slant angle (for constant incidence) or at a critical angle of incidence (for a constant base slant angle). The tests confirm that the value of the maximum drag coefficient is extremely sensitive to angle of incidence. Measurements of the frequency of vortex shedding are presented and the structure of the wake is investigated using smoke visualization and hot-wire correlation measurements. The wake is found to be far less stable than that from a two-dimensional bluff body and the vortex structures are sometimes in-phase and sometimes out of phase across the wake. The effect of free-stream turbulence on this family of body shapes is observed to be different to that on three-dimensional blunt-faced bluff bodies. Free-stream turbulence is found to have a minimal effect on base pressure for slant angles giving a recirculating type near wake flow. When longitudinal vortices are present the addition of free-stream turbulence slightly reduces the magnitude of the peak suctions recorded on the base but has little effect on base drag.
Effect of Initial Conditions on Constant Pressure Mixing Between Two Turbulent Streams
Authors: Kangovi Sachidananda 
Published: July 2016

SummaryA study of the process of mixing and wake development has varied applications in wide ranging fields like jet ejectors, wake signatures, base pressure control, combustors, flow over cut-outs, jet noise and jet interactions. In real flows the wake is usually divided into two zones namely, the near field and the far field. The near field is usually controlled by initial conditions which involve two back-to-back boundary layers separating from the trailing edge of a solid surface. In the far field the flow becomes fully developed and assumes self similarity. The properties of fully developed far field have been well established but little is known about the near field. This paper describes the application of an integral analysis to study the effects of initial conditions like velocity ratio, initial boundary layer thickness, compressibility and temperature ratio on the development of near field of the turbulent mixing layer between two compressible, non-isoenergetic streams at constant pressure. Results include velocity and temperature profiles and the location of jet boundary line in the mixing layer. These results show the gradual approach of the mixing layer to self-preservation.