Kuo-Huey Chen

Experimental Characterization of the Unsteady Flow Field behind Two Outside Rear-View Mirrors

The unsteady flow field behind two outside rear-view automobile mirrors was examined experimentally in order to compile a comprehensive database for the validation of the ongoing computational investigation effort to predict the aero-acoustic noise to the outside rear-view mirrors. This study is part of a larger scheme to predict the aero-acoustic noise due to various external components on automobiles. To aid with the characterization of this complex flow field, mean and unsteady surface pressure measurements were undertaken in the wake of two mirror models. Velocity measurements with particle image velocimetry were also conducted to develop the mean velocity field of the wake. Two full-scale mirror models with distinctive geometrical features were investigated.

Localized Cooling for Human Comfort

Author(s): Wang, Mingyu; Wolfe, Edward; Ghosh, Debashis; Bozeman, Jeffrey; Chen, Kuo-huey; Han, Taeyoung; Zhang, Hui; Arens, Ed | Abstract: Traditional vehicle air conditioning systems condition the entire cabin to a comfortable range of temperature and humidity regardless of the number of passengers in the vehicle. The A/C system is designed to have enough capacity to provide comfort for transient periods when cooling down a soaked car. Similarly for heating, the entire cabin is typically warmed up to achieve comfort.Localized heating and cooling, on the other hand, focuses on keeping the passenger comfortable by forming a micro climate around the passenger. This is more energy efficient since the system only needs to cool the person instead of the entire cabin space and cabin thermal mass. It also provides accelerated comfort for the passenger during the cooling down periods of soaked cars. Additionally, the system adapts to the number of passengers in the car, so as to not purposely condition areas that are not occupied.The present paper reports on a fundamental study of localized cooling to achieve comfort in a vehicle environment. The individual cooling streams are evaluated by human comfort riders for effectiveness and limitations. Based on the local cooling studies, combination local cooling strategies are then created and evaluated by riders.

Automotive Mirror Wind Noise Simulations and Wind Tunnel Measurements

Numerical simulations using Fluent were conducted to study the wind noise generated by GMT 360 mirror, one of the two mirrors mounted on the top of a specially designed table in the GM aerodynamics Lab (GMAL) wind tunnel. This study is part of an on-going project to develop a transient CFD procedure to accurately predict wind noises generated by the exterior surfaces of a moving vehicle. This paper focuses mainly on the numerical aspects of using large eddy simulation (LES) to predict both the flow and noise for the GMT 360 mirror with inlet speeds of 70 and 90 mph at 0 yaw angle. The design and scope of the wind tunnel test are also described. The mirror-on-the-table test was done with four flow speeds, 30, 50, 70 and 90 mph and three yaw angles, 0, -10 and +10 degrees for each mirror. The data collected during the test are: (1). time averaged static pressure along the centerline of the table, (2). nine surface microphones for noise sources, and (3). six far field microphones, 18 inches above the top surface of the table. The Fluent’s LES approach for wind noise predictions were conducted with reasonably fine mesh, up to 18 millions. Both dynamic and constant coefficients in the Smagorinsky sub-grid scale (SGS) model were used. It reveals that the LES simulations with the dynamic coefficient show improved accuracy than the model with the constant coefficient despite the fact that both models, in general, compare very favorable for the static pressure distribution and the noise spectra for both flow speeds. The transient LES result right above the table surface shows a very complex flow structure which is responsible for the noise generation.

Simulations of flow and noise generated by automobile outside rear-view mirrors

Numerical simulations of the flow and noise generated by two different automotive outside rear-view mirrors are investigated. The mirrors were mounted on the top of a specially designed table for simulations and wind tunnel tests. A decoupled two-stage methodology is applied that requires CFD simulations to collect pressure variations at solid surfaces followed by an acoustic post-processing of the data recorded. For the flow simulations, URANS (Unsteady RANS), DES (Detached Eddy Simulation) and LES (Large Eddy Simulation) turbulence modeling approaches are used. This study is part of an on-going project to develop a transient CFD procedure to accurately predict wind noise generated by the exterior surfaces of a moving ground vehicle. The Curles formulation in low Mach number limit is used to calculate the acoustic pressure generated by the pressure fluctuations at solid walls. Reasonable agreement (within 5 dB) between measurements and predictions has been achieved both for the flow and sound characteristics (with denser mesh quality). It is found that the URANS and DES approaches underestimate surface pressure fluctuations and therefore, result in underestimated sound pressure levels. The LES approach on the other hand (particularly with the dynamic subgrid viscosity model) provides better agreement for the time-averaged surface pressure distributions and for the sound pressure levels.

Energy efficiency impact of localized cooling/heating for electric vehicle

The present paper reports on a study of the HVAC energy usage for an EREV (extended range electric vehicle) implementation of a localized cooling/heating system. Components in the localized system use thermoelectric (TE) devices to target the occupants chest, face, lap and foot areas. A novel contact TE seat was integrated into the system. Human subject comfort rides and a thermal manikin in the tunnel were used to establish equivalent comfort for the baseline and localized system. The tunnel test results indicate that, with the localized system, HVAC energy savings of 37% are achieved for cooling conditions (ambient conditions greater than 10 °C) and 38% for heating conditions (ambient conditions less than 10 °C), respectively based on an annualized ambient and vehicle occupancy weighted method. The driving range extension for an electric vehicle was also estimated based on the HVAC energy saving.

Simulations of High Reynolds Number Air Flow Over the NACA-0012 Airfoil Using the Immersed Boundary Method

Abstract The Immersed-Boundary Method is coupled to an incompressible-flow RANS solver, based on a two-equation turbulence model, to perform unsteady numerical simulations of airflow past the NACA-0012 airfoil for several angles of attack and Reynolds numbers of 5.0x10 5 and 1.8x10 6 . A preliminary study is performed to evaluate the sensitivity of the calculations to the computational mesh and to guide the creation of the computational cells for the unsteady calculations. Qualitative characterizations of the flow in the vicinity of the airfoil are obtained to assess the capability of locally refined grids to capture the thin boundary layers close to the airfoil leading edges as well as the wake flow emanating from the trailing edge. Quantitative analysis of aerodynamic force coefficients and wall pressure distributions are also reported and compared to experimental results and those from body-fitted grid simulations using the same solver to assess the accuracy and limitations of this approach. The Immersed-Boundary simulations compared well to the experimental and body-fitted results up to the occurrence of separation. After that point, neither computational approach provided satisfactory solutions.

Validation of the Immersed Boundary CFD Approach for Complex Aerodynamic Flows

Standard CFD methods require a mesh that fits the boundaries of the computational domain. For a complex geometry the generation of such a grid is time-consuming and often requires modifications to the model geometry. This paper evaluates the Immersed Boundary (IB) approach which does not require a boundary-conforming mesh and thus would speed up the process of the grid generation. In the IB approach the CAD surfaces (in Stereo Lithography –STL- format) are used directly and this eliminates the surface meshing phase and also mitigates the process of the CAD cleanup. A volume mesh, consisting of regular, locally refined, hexahedrals is generated in the computational domain, including inside the body. The cells are then classified as fluid, solid and interface cells using a simple ray-tracing scheme. Interface cells, correspond to regions that are partially fluid and are intersected by the boundary surfaces. In those cells, the Navier-Stokes equations are not solved, and the fluxes are computed using geometrical reconstructions. The solid cells are discarded, whereas in the fluid cells no modifications are necessary. The present IB method consists of two main components: 1) TOMMIE which is a fast and robust mesh generation tool which requires minimum user intervention and, 2) a library of User Defined Functions for the FLUENT CFD code to compute the fluxes in the interface cells. This study evaluates the IB approach, starting from simple geometries (flat plate at 90 degrees, backward facing step) to more complex external aerodynamics of full-scale fully-dressed production vehicles. The vehicles considered in this investigation are a sedan (1997 Grand-Prix) and an SUV (2006 Tahoe). IB results for the flat plate and the backward-step are in very good agreement with measurements. Results for the Grand-Prix and Tahoe are compared to experiments (performed at GM wind tunnel) and typical body-fitted calculations performed using Fluent in terms of surface pressures and drag coefficients. The IB simulations predicted the drag coefficient for the Grand-Prix and the Tahoe within 5% of the body-fitted calculations and are closer to the wind-tunnel measurements.

General Motors LLC Final Project Report: Improving Energy Efficiency by Developing Components for Distributed Cooling and Heating Based on Thermal Comfort Modeling

On November 3, 2009, General Motors (GM) accepted U.S. Department of Energy (DOE) Cooperative Agreement award number DE-EE0000014 from the National Energy Technology Laboratory (NETL). GM was selected to execute a three-year cost shared research and development project on Solid State Energy Conversion for Vehicular Heating, Ventilation & Air Conditioning (HVAC) and for Waste Heat Recovery.

Study of Drag Reduction Devices for a Square Back Vehicle Configuration Using RANS CFD Simulations

The aerodynamic flow around a simplified road vehicle model with and without drag reduction devices is investigated. The simulations are carried out using the unsteady RANS in conjunction with the ν2-f turbulence model. The corresponding experiments are performed in a small wind tunnel which includes pressure and velocity fields measurements. The devices are add-on geometry parts (a box with a cavity and, boat-tail without a cavity) which are attached to the back of the square-back model to improve the pressure recovery and reduce the flow unsteadiness. The results show that the recirculation regions at the base are shortened and weakened and the base pressure is significantly increased by the devices which lead to lower drag coefficients (up to 30% reduction in drag). Also, the results indicate a reduction of the turbulence intensities in the wake as well as a rapid upward deflection of the underbody flow with the devices in place. A suppression or damping of the unsteadiness is the common element of the devices studied. The baseline configuration (square-back) exhibits strong three-dimensional flapping of the wake. The main shedding frequency captured agrees well with the available experimental data. Comparisons with the measurements show that the simulations agree reasonably well with the experiments in terms of drag and the flow structures.Copyright

High Reynolds Number Airfoil Simulations Using the Immersed Boundary Method

The Immersed-Boundary Method is coupled to an incompressible-flow RANS solver, based on a two-equation turbulence model, to perform unsteady numerical simulations of airflow past the NACA-0012 airfoil for several angles of attack and Reynolds numbers of 5.0×105 and 1.8×106. Qualitative characterizations of the flow in the vicinity of the airfoil are obtained to show the need for locally refined grids to capture the thin boundary layers close to the airfoil leading edges. Quantitative analysis of aerodynamic force coefficients and wall pressure distributions are also reported and compared to experimental results and those from body-fitted grid simulations using the same solver to assess the accuracy and limitations of this approach. The Immersed-Boundary simulations compared well to the experimental and body-fitted results up to the occurrence of separation. After that point, neither computational approach provided satisfactory solutions.Copyright