Engineering Prediction Methods Research Articles

Engine Sonic Load Prediction of Blended Wing Body Aircraft

The sonic load of the engine is the input for cabin noise design and acoustic fatigue verification in civil aircraft. Based on the engine static noise database, an engineering prediction method for blended wing body aircraft engine sonic load in flight is developed. In the process of sonic load prediction, the sound source position correction, geometric diffusion, flight effect and airframe scattering effect of engine component noise are considered. The flight effect and air-frame scattering effect of engine component level noise are simulated and analyzed. The overall sound pressure level distribution and sound load spectrum at typical positions of blended wing body aircraft engine are given. The results show that fan inlet noise is the most important component of the engine sonic load on the BWB aircraft surface, and the maximum value of engine sonic load on the upper surface of blended wing body aircraft is 134 dB, which is higher than that of conventional wing crane aircraft.

A new entropy-based metallic material stress relaxation engineering prediction method

The stress relaxation behavior of metallic materials has great influence on its mechanical properties under service conditions especially with high temperatures. This paper proposed a new engineering type of stress relaxation prediction model based on continuous damage mechanics and the second law of thermodynamics. Stress relaxation experiments of nickel-based single crystal DD6 were carried out at different temperatures. The proposed model was verified by experimental data of DD6 and other metallic materials, the results show that the model has good prediction accuracy.

The Effects of Icing on Aircraft Longitudinal Aerodynamic Characteristics

To study the effects of ice accretion on the longitudinal aerodynamic characteristics of an aircraft, a two-part method for predicting longitudinal aerodynamic derivatives of iced aircraft is proposed. For the aircraft with a flight test, a parameter identification system based on maximum likelihood criterion and a longitudinal nonlinear flight dynamics model is established. For the aircraft without a flight test, an engineering prediction method of aerodynamic derivatives based on an individual component CFD calculation and narrow strip theory is established. According to the flight test data of DHC-6 Twin Otter aircraft from NASA, the longitudinal aerodynamic parameters of both clean and artificially iced aircraft are obtained. Additionally, the longitudinal aerodynamic derivatives of the iced aircraft are calculated. Then, the correctness of the prediction method is verified by comparing the calculated results with the identification results. The comparison of these results shows that the prediction method is correct and accurate, and it can be used to calculate the effects of icing on the aircraft longitudinal aerodynamic parameters.

Research on system testability index allocation of substation digital metering system

In the testability engineering of measurement system, if the allocation of testability indicators is not combined with the overall scheme of the system, it will lead to the indicators too high to achieve or too low and thus lack of binding effect. At present, the test scheme for digital metering system can only effectively guarantee the accuracy and reliability of a digital metering device when it runs alone, and can not fully reflect the performance of this device when it runs as part of a complete system. Combining with the digital measurement system of substation, this paper introduces the engineering prediction method into the system, and designs the allocation scheme of testability index and an integrated framework for system-level testability scheme and index allocation. It has reference significance for optimizing the design scheme of testability, reducing the time and cost of testing, and improving the test efficiency.

Large-Eddy Simulations of heated flows in ribbed channels with spanwise rotation

We report on the outcome of a computational study of heat and momentum transport in a heated ribbed straight channel rotated about a spanwise axis. The flow is of both practical and fundamental interest, the latter due to the simultaneous presence in this flow of a number of complicating effects. These include system rotation, mean-flow unsteadiness, large-scale flow separation, and subsequent reattachment; their interactions severely distort the turbulence structure and thus pose this flow as a challenge to engineering prediction methods. In this study, the predictions were obtained using Large-Eddy Simulations with the objectives of assessing the performance of this approach in this flow, and gaining better understanding of the factors that influence the quality of the solutions. Thus, the numerical accuracy of the simulations was determined using Grid Convergence Index (GCI) method, and additionally by comparing results obtained using discretization schemes of different orders of accuracy. The dependence of the computed results on the models for the sub-grid scale correlations in both the momentum and thermal energy equations was checked by performing computations with alternative closure assumptions. These included the Smagorinsky and the dynamic models for momentum, and both linear and non-linear models for the thermal energy fluxes. The computations, which were performed with OpenFOAM, were compared with benchmark experimental data from both heated and isothermal flows. The correspondence between predictions and measurements was generally satisfactory but some important differences remain. It is argued that these are in part due to ambiguities in the way in which temporal and spatial averages are obtained in the computations and in the measurements.

The active-to-passive oxidation transition mechanism and engineering prediction method of C/SiC composites

This paper studied the active-to-passive oxidative mechanism of C/SiC composite under high temperature and oxidative conditions. An analytic model and computational method were established based on the process of gas diffusion in boundary layer and the equilibrium relations in surface chemical reactions. Simultaneously, an engineering equation to predict the oxygen partial pressure of active-to-passive transition was derived under the specific temperature zone. The results indicated that the active-to-passive oxidation transition of C/SiC is closely related to the composition of the material. At certain temperature and oxygen partial pressure conditions, the composite with high carbon content is prone to cause active oxidation which is negative to the oxidation resistance of the material.

Predicting shipboard noise using 3-D acoustic modeling

Predicting and controlling shipboard noise is a daunting task, particularly when the commonly accepted, one-dimensional prediction approaches are used. Numerous powerful acoustic sources are often located in close proximity to sensitive receiver spaces and the ship's structures and systems themselves are not amenable to straightforward abatement techniques. In addition, treatments usually impose adverse space, weight and cost impacts yet the crew and passengers need to be protected. This paper presents an alternative to the common spreadsheet and hand calculation methods of shipboard noise analysis. The paper discusses an SEA based noise prediction method. The primary purpose of this engineering prediction method is to facilitate rapid predictions that preserve the accuracy required for the design of effective treatment of shipboard noise. Two case studies are presented indicating the features and application of the tool.

An Explicit Algebraic Model for Turbulent Heat Transfer in Wall-Bounded Flow With Streamline Curvature

Abstract Fourier’s law, which forms the basis of most engineering prediction methods for the turbulent heat fluxes, is known to fail badly in capturing the effects of streamline curvature on the rate of heat transfer in turbulent shear flows. In this paper, an alternative model, which is both algebraic and explicit in the turbulent heat fluxes and which has been formulated from tensor-representation theory, is presented, and its applicability is extended by incorporating the effects of a wall on the turbulent heat transfer processes in its vicinity. The model’s equations for flows with curvature in the plane of the mean shear are derived and calculations are performed for a heated turbulent boundary layer, which develops over a flat plate before encountering a short region of high convex curvature. The results show that the new model accurately predicts the significant reduction in the wall heat transfer rates wrought by the stabilizing-curvature effects, in sharp contrast to the conventional model predictions, which are shown to seriously underestimate the same effects. Comparisons are also made with results from a complete heat-flux transport model, which involves the solution of differential transport equations for each component of the heat-flux tensor. Downstream of the bend, where the perturbed boundary layer recovers on a flat wall, the comparisons show that the algebraic model yields indistinguishable predictions from those obtained with the differential model in regions where the mean-strain field is in rapid evolution and the turbulence processes are far removed from local equilibrium.

Prediction of vortex shedding from forebodies with chines

An engineering prediction method and associated computer code VTXCHN to predict nose vortex shedding from circular and noncircular forebodies with sharp chines edges in subsonic flow at angles of attack and roll are presented. Axisymmetric bodies are represented by point sources and doublets, and noncircular cross sections are transformed to a circle by either analytical or numerical conformal transformations. The lee side vortex wake is modeled by discrete vortices in crossflow planes along the body; thus the three-dimensional steady flow problem is reduced to a two-dimensional, unsteady, separated flow problem for solution. Comparison of measured and predicted pressure distributions, flow field surveys, and aerodynamic characteristics are presented for noncircular bodies alone and forebodies with sharp chines.

Indoor illuminance: Effect of externally reflected component

The paper presents computer calculations of the effect of the light reflected from the earth on the indoor illuminance, as well as corresponding model measurements. On the basis of these studies an engineering prediction method has been developed to determine the reflected component from the underlying earth surface. It is shown that taking this factor into account makes it possible to reduce the area of windows, in some cases by as much as 40%.

Calculation of Separated Turbulent Flows on Axisymmetric Afterbodies Including Exhaust Plume Effects

A calculative method is presented for turbulent boundary-layer, inviscid flow interactions for axisymmetric configurations of the type used for isolated nozzle afterbody models. The method is applicable to flows with subsonic freestreams, including slightly supercritical flows, and to bodies with high-pressure exhaust plumes or solid plume simulators. Integral boundary-layer and plume entrainment methods are coupled iteratively with a finite-difference inviscid flow method through a boundary-layer plume displacement thickness. Results are presented which indicate that the procedure provides an accurate engineering prediction method for boattail flowfield with moderately underexpanded exhaust flows and for bodies with solid plume simulators.

Viscous Modelling of Wing-Generated Trailing Vortices

SummaryThe trailing vortex wake system generated by a lifting wing of finite span is modelled with a pair of laminar, viscous vortex models of a new type. The embryonic form of this viscous wake model is matched, at several interior collocation points, to the inviscid Betz model of the wake convolution process that transforms the wing trailing-edge vortex sheet into a pair of axisymmetric trailing vortices. In the near-wake and intermediate-wake regions downstream of the wing, the viscous wake model indicates that the trailing vortex characteristics (particularly the peak swirl velocity and the circulation profile) are strongly influenced by details of the wing span load distribution. Using simple eddy viscosity concepts, the viscous wake model achieves good qualitative agreement with test results from a limited selection of published experimental wake investigations. The present laminar theory appears to offer a useful basis for developing an engineering prediction method of aeroplane wake characteristics.