Cone models of mountain peaks associated with atmospheric vortex streets

Trischka, J. W.

doi:10.1111/j.2153-3490.1980.tb00963.x

Cited by 5 publications

(4 citation statements)

References 15 publications

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“…The peak values in the power spectra are predominantly exerted by the periodic vortex shedding from the hill, in agreement with previous field measurements, laboratory experiments and computational modeling, for example, Trischka, 20 Atkinson, 21 and Schär and Smith 22 . The spectral peak increases with the increasing height as the effect of the hill shadowing becomes smaller.…”

Section: Resultssupporting

confidence: 89%

The effect of parked wind turbines on wind flow and turbulence over a complex terrain

2021

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Wind‐tunnel experiments were performed to study the wind characteristics on a parked wind turbine downwind of three types of hill and over a flat terrain. The focus of the study is on comparing wind characteristics on (a) a wind turbine standing alone and (b) this same type of wind turbine embedded in a wind farm. Particular emphasis is placed on the hill size and shape and the distance between the hill and the wind farm. The hill and wind‐farm models were subjected to an atmospheric boundary layer simulation to create realistic atmospheric conditions. Flow and turbulence were analyzed based on the measured mean flow velocity, Reynolds shear stress, turbulence intensity, and the power spectral density of velocity fluctuations. The experimental results reveal similar trends concerning (a) the wind characteristics obtained on a parked wind turbine embedded in a wind farm downwind of hills of various sizes and shapes and (b) the wind characteristics on this same type of parked wind turbine standing alone in the same position downwind of the same hills. In particular, the discrepancies in the mean flow velocity and turbulence intensity between these test cases are mostly below 5%, thus indicating that a complex terrain clearly has a dominant effect on the wind characteristics, while the effects of parked wind turbines on the wind characteristics are negligible. This important finding indicates that the structural loading of parked wind turbines situated on a complex terrain may be well calculated using the same procedures both for wind turbines standing alone and wind turbines embedded in wind farms if they are both placed at the same distance downwind of the same hills.

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Section: Resultssupporting

confidence: 89%

The effect of parked wind turbines on wind flow and turbulence over a complex terrain

2021

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“…It is interesting to compare the Strouhal number results with measurements made in neutral flow. Neutral measurements of S made by Trischka (1980) at Re = 10 4 are ∼ 0.25 and ∼ 0.23 for cones with the same slope as C1 and C2, respectively. These values are somewhat higher than the values of S 2 c we see in stratified flow although figure 15(b) reveals that for weaker stratification our values for all the obstacles approach those found by Trischka.…”

Section: Measurements In the Wakementioning

confidence: 84%

Experimental studies of strongly stratified flow past three-dimensional orography

et al. 1999

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Stably stratified flows past three-dimensional orography have been investigated using a stratified towing tank. Flows past idealized axisymmetric orography in which the Froude number, Fh=U/Nh (where U is the towing speed, N is the buoyancy frequency and h is the height of the obstacle) is less than unity have been studied. The orography considered consists of two sizes of hemisphere and two cones of different slope. For all the obstacles measurements show that as Fh decreases, the drag coefficient increases, reaching between 2.8 and 5.4 times the value in neutral flow (depending on obstacle shape) for Fh[les ]0.25. Local maxima and minima in the drag also occur. These are due to the finite depth of the tank and can be explained by linear gravity-wave theory. Flow visualization reveals a lee wave train downstream in which the wave amplitude is O(Fhh), the smallest wave amplitude occurring for the steepest cone. Measurements show that for all the obstacles, the dividing-streamline height, zs, is described reasonably well by the formula zs/h=1−Fh. Flow visualization and acoustic Doppler velocimeter measurements in the wake of the obstacles show that vortex shedding occurs when Fh[les ]0.4 and that the period of the vortex shedding is independent of height. Based on velocity measurements in the wake of both sizes of hemisphere (plus two additional smaller hemispheres), it is shown that a blockage-corrected Strouhal number, S2c =fL2/Uc, collapses onto a single curve when plotted against the effective Froude number, Fhc=Uc/Nh. Here, Uc is the blockage-corrected free-stream speed based on mass-flux considerations, f is the vortex shedding frequency and L2 is the obstacle width at a height zs/2. Collapse of the data is also obtained for the two different shapes of cone and for additional measurements made in the wake of triangular and rectangular at plates. Indeed, the values of S2c for all these obstacles are similar and this suggests that despite the fact that the obstacle widths vary with height, a single length scale determines the vortex-street dynamics. Experiments conducted using a splitter plate indicate that the shedding mechanism provides a major contribution to the total drag (∼25%). The addition of an upstream pointing ‘verge region’ to a hemisphere is also shown to increase the drag significantly in strongly stratified flow. Possible mechanisms for this are discussed.

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“…This result may not hold, however, for boundary layers with poor vertical mixing. Increased atmospheric stability may enhance the barrier effectiveness as a vortex street producer (Trischka, 1980). Experiment C yielded positive results in comparison.…”

Section: Discussionmentioning

confidence: 99%

“…Gaster (1969) studied vortex shedding from cones for neutral stratification and found multiple shedding frequencies at various heights. Trischka (1980) studied flow past six volcanic peaks by varying the shapes of smooth aluminium cones in a wind tunnel, attributing differences between observed atmospheric cases and simulated results to stratification in the atmosphere. Pao and Kao (1976), using spheres in a water tank, also discussed the effects of stability on the vortex street.…”

Section: The Vortex Streetmentioning

confidence: 99%

A numerical simulation of an atmospheric vortex street

Ruscher

Deardorff²

1982

Tellus A: Dynamic Meteorology and Oceanography

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A mesoscale mixed-layer model of the planetary boundary layer is applied to the flow past a mountain island during a cold air outbreak over the Kuroshio Current. Utilizing data taken during AMTEX '75, the governing equations are integrated in time to simulate development of a Rarman vortex street downstream of the island of Cheju-do. The use of open lateral boundary conditions and an encroachment scheme which allows some mountain grid points to experience occasional encroachment of mixed-layer fluid as the mixed-layer deepens (and decroachment as the mixed layer thins) is also discussed.Comparing various non-dimensional parameters on vortex-street characteristics, it is shown that the simulated vortex street resembles the observed atmospheric one rather well. Uncertainty in formulating the proper value of the eddy viscosity and the implication this has on Reynolds number comparisons are also discussed. Tellus 34 (1982), 6 0040-2826/82/060555-12%02.50/0 0 1982 Munksgaard, Copenhagen Rev. 110.

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Cone models of mountain peaks associated with atmospheric vortex streets

Cited by 5 publications

References 15 publications

The effect of parked wind turbines on wind flow and turbulence over a complex terrain

The effect of parked wind turbines on wind flow and turbulence over a complex terrain

Experimental studies of strongly stratified flow past three-dimensional orography

A numerical simulation of an atmospheric vortex street

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