A new experimental method for determining local airloads on rotor blades in forward flight

This paper presents a new approach for determining local airloads on helicopter rotor blade sections in forward flight. The method is based on the momentum equation in which all the terms are expressed by means of the velocity field measured by a laser Doppler velocimeter. The relative magnitude of the different terms involved in the momentum and Bernoulli equations is estimated and the results are encouraging.     

Temperature spectra from a turbulent thermal plume by ultrasound scattering

This paper reports the results of a study on temperature inhomogeneities conducted on a thermal plume by using ultrasound scattering as a non-intrusive measurement technique. The plume rises from a metallic disk which can be heated up to 800 °C. The working fluid is air at atmospheric pressure. In the measurement technique, an incoming ultrasound wave is emitted towards the thermal plume. The incident wave is scattered because of non-linear couplings with the flow instabilities present in the measurement region. The scattered wave carries information about those flow instabilities. The technique allows for the retrieving of this information. The shape of the obtained spectrum of temperature fluctuations as a function of wave vector modulus is consistent with previous theoretical analysis. Three qualitatively different regions were identified: first, a production region characterized by a q² law; secondly, a region with behavior as per q⁻³ associated with a buoyancy region and; finally, a dissipation region associated with a q⁻⁷ law. These spectral regions characterize the energy transfers mechanisms among the length scales of flow investigated here. A coefficient of anisotropy γ was defined to analyze anisotropic features of the flow.     

Optimal output feedback stabilization

We show that optimal stabilization of a linear dynamic plant can be implemented on the basis of the solution of linear matrix inequalities even if the plant state cannot be measured. By way of example, we obtain optimal control laws for a double inverted pendulum assuming that only the lower link deflection angle is measured.     

Two-dimensional compressible viscous sink flows

A theoretical investigation of two-dimensional viscous compressible sink flow is presented. An analytic solution in parametric form is obtained for specific values of the ratio of specific heats. For the more general case, a number of asymptotic solutions were also obtained for different flow regimes including hypersonic, transonic, acoustic and low Reynolds number flow.     

Thermal cracking in railroad vehicle wheels subjected to high performance stop braking

An investigation of thermal cracks observed in the wheels of certain electric multiple unit (EMU) locomotives in North American commuter rail service is summarized. The cause is found to be partial reversal of the wheel rim residual hoop stress, which is initially compressive from the manufacturer's quench treatment. The residual stress reversal is caused by thermal stresses during high performance stop braking. Crack propagation and failure mechanisms are summarized. Measures for prevention are discussed.     

Hele-Shaw flows with a free boundary produced by multipoles

An extension of the method of moments proposed by Richardson to Hele-Shaw flows with a free boundary generated by multipoles is considered. The evolution of the circular contour is investigated in relation to the operation of a single multipole of ordern at the zero or at an infinitely remote point. It is shown that a solution exists only up to a certain momentt ^*, when on the boundary of the domainn symmetric cusps directed towards the multipole are formed. For an arbitrary initial domain it is possible to obtain an estimate of the period of existence of a solution.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 5, pp. 121–127, September–October, 1993.     

On a class of constitutive models for highly deforming compressible materials

Summary The physical admissibility of a constitutive model for highly deforming hyperelastic compressible materials, introduced in [1], is examined in the light of the classical Backer-Ericksen, ordered forces and strengthened tension-extension inequalities. A generalization of this material model is also given, and the conditions for its physical adminissibility are discussed.

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Über eine Klasse von konstitutiven Modellen für hoch formveränderliche, kompressible Materialien

Übersicht Die physikalische Zulässigkeit eines konstitutiven Modells für hoch formveränderliche, hyperelastische, kompressible Materialien, die in [1] dargestellt sind, wird anhand der Backer-Ericksen-Ungleichungen, der Ungleichungen der Folge der Spannungsgrößenordnungen und anhand der Ungleichungen des positiven Tangentenmoduls geprüft. Es wird auch eine Verallgemeinerung dieses Materialmodells dargestellt. Die Bedingungen für seine physikalische Zulässigkeit werden erörtert.

     

Friction factors of finite and infinite square arrays of roughened pins

Friction factors of square arrays of roughened pins in smooth channels have been measured for a range of pin pitch to diameter ratios and roughness heights and for different sizes of array. The influence of the smooth channel has been removed in two ways; by extrapolating the results for a fixed pitch-to-diameter ratio to an infinite number of pins and by calculation from the finite array results. The resultant friction factors are compared with each other and with data obtained by testing single pins in smooth circular channels and transforming by various methods to the fully rough situation.