Abdullah M. Al-Garni

Experimental Investigation of the Near Wake of a Pick-up Truck

The results of an experimental investigation of the flow over a pickup truck are presented. The main objectives of the study are to gain a better understanding of the flow structure in near wake region, and to obtain a detailed quantitative data set for validation of numerical simulations of this flow. Experiments were conducted at moderate Reynolds numbers (~3×10 5 ) in the open return tunnel at the University of Michigan. Measured quantities include: the mean pressure on the symmetry plane, unsteady pressure in the bed, and Particle Image Velocimetry (PIV) measurements of the flow in the near wake. The unsteady pressure results show that pressure fluctuations in the forward section of the bed are small and increase significantly at the edge of the tailgate. Pressure fluctuation spectra at the edge of the tailgate show a spectral peak at a Strouhal number of 0.07 and large energy content at very low frequency. The velocity field measurements in the symmetry plane show that shear layers form at the top of the cab and the underbody flow region. The cab shear layer evolves more slowly than the underbody flow shear layer and does not interact strongly with the tailgate for the present geometry. Behind the tailgate there is no recirculating flow region in the symmetry plane believed to be due to downwash from streamwise vorticity in the near wake. There are small recirculating regions on the sides of the tailgate symmetry plane extending approximately one tailgate height downstream.

Flow Control for an Airfoil with Leading-Edge Rotation: An Experimental Study

An experimental investigation has been conducted on a two-dimensional NACA 0024 airfoil equipped with a leading-edgerotatingcylinder.Theairfoilwastestedfordifferentvaluesofleading-edgerotationsande apdee ection angles. The effects of the angle of attack ®, the cylinder surface velocity ratio Uc/U, and the e ap dee ection angle ± on lift and drag coefe cients, the size of the separated e ow region, and the stall angle of attack are included. The effect of Uc/U on the boundary-layer growth and turbulence intensity are also shown. Experimental results, for example, showed that the leading-edge rotating cylinder increases the lift coefe cient of a NACA 0024 airfoil from 0.85 at Uc/U = 0 to 1.63 at Uc/U = 4 and delays the stall angle of attack by about 160%. Smoke-wire e ow visualization results were also used to demonstrate the strong effect of the leading-edge rotating cylinder on the size of the recirculation region.

Experimental Investigation of the Flow Around a Generic SUV

The results of an experimental investigation of the flow in the near wake of a generic Sport Utility Vehicle (SUV) model are presented. The main goals of the study are to gain a better understanding of the external aerodynamics of SUVs, and to obtain a comprehensive experimental database that can be used as a benchmark to validate math-based CFD simulations for external aerodynamics. Data obtained in this study include the instantaneous and mean pressures, as well as mean velocities and turbulent quantities at various locations in the near wake. Mean pressure coefficients on the base of the SUV model vary from -0.23 to -0.1. The spectrum of the pressure coefficient fluctuation at the base of the model has a weak peak at a Strouhal number of 0.07. PIV measurements show a complex three-dimensional recirculation region behind the model of length approximately 1.2 times the width of the model. Turbulence properties are also reported, and the largescale turbulent structure in the near wake is investigated using Proper Orthogonal Decomposition (POD) methods. The results suggest that the more energetic modes in the symmetry plane correspond to a vortex shedding process, and the more energetic modes in the center horizontal plane are a lateral flapping motion of the wake and a breathing mode of the mean recirculation region.

Experimental and Numerical Investigation of 65 Degree Delta and 65/40 Degree Double-Delta Wings

In this study, an experimental and numerical investigation was carried out to obtain lift, drag, and pitching moment data on 65 degree delta and 65/40 degree double-delta wings. The experimental tests were conducted at the King Fahd University of Petroleum and Minerals low-speed wind-tunnel facility, whereas the numerical tests were performed using the commercial computational fluid dynamics software FLUENT. Results from both experiments and numerical predictions were compared to other experimental data found in literature as well as to the theory of Polhamus. The results of comparison of surface pressure coefficient distribution and vortex breakdown location show good agreement with experiments. Overall, the comparison of result shows good agreement between different experimental studies as well as good agreement with the computational fluid dynamics predictions and the theoretical calculations.

Failure Forecasting of Aircraft Air-Conditioning/Cooling Pack with Field Data

This paper presents methods for modeling the failure of air-conditioning/cooling packs for a particular type of aircraft with field data. In many regards, field data are highly desirable for more accurate failure prediction by aircraft operators, because the data implicitly account for all actual usage and environmental stresses. It is not always possible to accurately anticipate or simulate these stresses in a laboratory or even in a field test. Field data, in a larger extent, are also important to the manufacturer, because the data identify product deficiencies and areas of improvement. In this study, the failure of the aircraft air-conditioning/cooling pack under a customer-use environment is first modeled at the component level by using the Weibull distribution and its extensions. These include the two-parameter Weibull model, three-parameter Weibull model, mixture model, and phased bi-Weibull model. The number of failures over time is estimated by a renewal process. The failure of the air-conditioning/cooling pack at the system level is then modeled by using the power law process model. The failure trend is tested by the Laplace test. The results give an insight into the reliability and quality of the air-conditioning/cooling pack under actual operating conditions. The models presented here can be used by aircraft operators for assessing system and component failures and customizing the maintenance programs recommended by the manufacturer.

Neural network-based failure rate prediction for De Havilland Dash-8 tires

Abstract An artificial neural network (ANN) model for predicting the failure rate of De Havilland Dash-8 airplane tires utilizing the two-layered feed-forward back-propagation algorithm as a learning rule is developed. The inputs to the neural network are independent variables and the output is the failure rate of the tires. Six years of data are used for model building and validation. Model validation, which reflects the suitability of the model for future prediction is performed by comparing the predictions of the model with that of Weibull regression model. The results show that the failure rate predicted by the ANN is closer in agreement with the actual data than the failure rate predicted by the Weibull model.

Failure-Rate Prediction for De Havilland Dash-8 Tires Employing Neural-Network Technique

An artificial neural-network model for predicting the failure rate of De Havilland Dash-8 airplane tires utilizing the two-layered feedforward back-propagation algorithm as a learning rule is developed. The inputs to the neural network are independent variables, and the output is the failure rate of the tires. Six years of data are used for model building and validation. Model validation, which reflects the suitability of the model for future prediction, is performed by comparing the predictions of the model with that of the Weibull regression model. The results show that the failure rate predicted by the artificial neural network more closely agrees with the actual data than the failure rate predicted by the Weibull model.

PIV Study of the Near Wake of a Pickup Truck

The turbulent flow structure in the near wake of a pickup truck model has been investigated experimentally using Proper Orthogonal Decomposition (POD) analysis of Particle Image Velocimetry (PIV) data. The experiments were conducted in the 2’x2’ wind tunnel at the University of Michigan at Reynolds numbers based on model width of 3x105. A model of a pickup truck with extended cab, 432 mm long by 156 mm wide by 149 mm tall, was used. PIV measurements of the velocity field in several planes of the wake including the symmetry plane were obtained using a large sample size, sufficient to determine the mean flow and the Reynolds stresses in the wake. The mean flow structure in the symmetry plane consists of separated shear layers originating at the edge of the cab and from the underbody flow. For this particular geometry, there is a recirculating flow region behind the cab ending upstream of the tailgate; but there is no mean recirculating flow region behind the tailgate. The mean flow pattern in a horizontal plane behind the tailgate suggests that this is due to trailing streamwise vorticity. POD analysis of the data provides useful information on the unsteady large scale structures in the wake. It is shown that only a few orthogonal modes (~20) contain a large fraction of the fluctuation energy (~60%), as expected. But, more important, the analysis isolates features of the unsteady large scale turbulent structures into different uncorrelated modes. It is shown that the development of vortex shedding in the underbody flow shear layer is described by a few modes, while oscillations of the recirculating region are captured by other modes. This feature of the analysis makes it very useful to the study of the structure and dynamics of complex bluff body wakes.