Upstream wind tunnel model mounting: The forgotten method for road vehicle aerodynamics

Abstract

A new method for supporting ground vehicle wind tunnel models is proposed. The technique employs a centrally mounted sting connecting the front face of the vehicle, adjacent to the floor, to a fixed point further upstream. Experiments were conducted on a 1/24th-scale model, representative of a Heavy Goods Vehicle, at a width-based Reynolds number of 2.3 × 105, with detailed comparisons made to more established support methodologies. Changes to mean drag coefficients, base pressures and wake velocities are all evaluated and assessed from both time-independent and time-dependent perspectives, with a particular focus within the wake region. Results show subtle changes in drag coefficient, together with discrete modifications to the flow-field, dependent on the method adopted. Subtle differences in base pressures and wake formation are also identified, with mounting the model upstream found to demonstrate retention of many of the beneficial effects of other techniques without suffering their deficiencies. Overall, these results identify the upstream mounting methodology as a viable alternative to currently available and more well-established techniques used to facilitate wind tunnel aerodynamic interrogation.

On the drag reduction of road vehicles with trailing edge-integrated lobed mixers

“…Figure 29(a) presents the streamwise velocity spectra ( E u ) within the side shear layer. For the baseline, these signals capture the characteristic bubble pumping frequency, with a subtle broad peak observed at St W ≈ 0.105, in good agreement to Duell and George 60 (St W ≈ 0.069), Khalighi et al 13 (St W ≈ 0.098), Volpe et al 74 (St W ≈ 0.11), McArthur et al 75 (St W ≈ 0.08), Pavia et al 67 (St W ≈ 0.094) and Rejniak and Gatto 51 (St W ≈ 0.107). With BTT α = 15°, Figure 29(a) shows the pumping peak to be fully suppressed, accompanied by a reduction in magnitudes for St W > 0.2, with the former also observed for BTT α = 20°.…”

“…The use of the upstream sting was found to produce little flow interference at the base, having also a weak influence on the overall wake dynamics. 51 Additionally, the front support setup showed little impact on the underbody exiting flow, retaining the effects of moving ground use observed with the top strut typically used for such applications. Based on these results, 51 the upstream sting support was favoured for the current study.…”

“…51 Additionally, the front support setup showed little impact on the underbody exiting flow, retaining the effects of moving ground use observed with the top strut typically used for such applications. Based on these results, 51 the upstream sting support was favoured for the current study.…”

“…The baseline used (Figure 1) is a simplified 1/24 th -scale model (width, W = 110 mm) representative of a HGV. This model is based on the one used by Rejniak and Gatto, [49][50][51] but incorporates a more streamlined tractor profile to minimise frontal flow separation. Constructed from Perspex, the baseline consists of two primary components: a tractor and trailer bottom section, and a trailer.…”

“…The sting is located close to the ground (0.01 W), below the front stagnation position of the model, to minimise its overall impact. This technique has been previously studied 51 alongside more typical mounting from the sides or top on a similar model, showing improved base flow-field characteristics. The use of the upstream sting was found to produce little flow interference at the base, having also a weak influence on the overall wake dynamics.…”