Technical Reports

Aerodynamic Forces on Freight Trains. Volume II. Full-Scale Aerodynamic Validation Tests of Trailer-on-a-Flat Car (Series II).

  • 09
  • Aug
  • 2016
AUTHOR: Federal Railroad Administration
OFFICE: RPD
SUBOFFICE: RPD-30
REPORT NUMBER: FRA/ORD-76-295.II
KEYWORDS: Freight cars, Aerodynamic forces, Flat cars, Trailers, Containers, Aerodynamic drag, Aerodynamic loads, Wind tunnel models, Streamlining
ABSTRACT: Aerodynamic forces were measured on full-scale Trailer-on-a-Flat Car (TOFC) configurations and a reliable data base was established for validation of wind tunnel test programs. The drag, side and lift forces were determined on two trailers mounted on an instrumented flat car, each by means of a specially designed force-balance system. Two TOFC configurations (Configuration 1 with a loaded buffer car leading the instrumented flat car and Configuration 2 with an empty buffer car) were tested under different wind conditions. In addition to the aerodynamic resistance of the trailers, total tractive resistance of the TOFC was measured via instrumented couplers. The results indicate good agreement between the full-scale aerodynamic drag data and the wind tunnel data from the tests at the Calspan Corporation. The wind tunnel tests conducted at the California Institute of Technology exhibited significantly higher drag values than the full-scale measurements, especially at high wind angles. The foregoing conclusions apply to both Configurations 1 and 2. It was found that Configuration 2 experienced consistently larger drag than Configuration 1. Measurement of the total tractive resistance enabled a rough estimation of the rolling resistance of the instrumented flat car. The present tests show that at 50 mph the aerodynamic drag accounts for 50 to 60 percent of total train resistance and the rolling resistance takes the remaining share. At 90 mph, the drag force amounts to approximately 55 to 70 percent of the total resistance.
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