Numerical study of leading-edge heat transfer under free-stream turbulence

Lele, Sanjiva K.; Zhang, Xiong

doi:10.2514/6.2001-1016

Cited by 6 publications

(6 citation statements)

References 17 publications

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“…The existence of a threshold in disturbance amplitude is also consistent with earlier observations by Nagib and Hodson (1978) on the formation of vortex pair at the stagnation region of a bluff body subject to the impingement of wakes. Similar flow patterns as those shown in figure 6.3 and 6.4 also emerge in aforementioned experiments (Nagib and Hodson, 1978;Botcher and Wedemeyer, 1989) as well as numerical simulations (Xiong and Lele, 2001;Bae et al, 2003). The quantitative characterization of the flow fields in figure 6.4 in terms of the maximum wall normal disturbance velocity [umoxlj wall vorticity |a;,"| and heat transfer enhancement A/i//i are summarized in Table 6.1.…”

Section: Numerical Resultssupporting

confidence: 52%

“…the streamwise velocity is a linear function of the streamwise coordinate x , and the wall normal velocity IS .ndependent of z. The flow structures induced by free-stream turbulence in a stagnation region are found to be qualitatively similar to those induced bv upstream organized disturbances (Xiong and Lele, 2001). The importance of cal simir'' r^^ uf ^"^ *''"" '^""" ^^^^"^'^ *^^«"eh direct numer- (2003) " ^ stagnation point flow by Bae, Lele, and Sung…”

Section: Introductionmentioning

confidence: 71%

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Stagnation Point Flow and Heat Transfer Under Free-Stream Turbulence

Zhang¹,

Lele²

2004

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Public reporting burden for this collection of information is estinuted to awrage 1 hour per response, including the time for reviewing in maintaining the data needed, and completing and reviewing tWs ooHedion of infbrmatian. SPONSOR/MONITOR'S REPORT NUMBER(S) DISTRIBUTION / AVAILABILITY STATEMENTKppi'oved fcv PMV.1 1 c rclsnsa, distribution unlikiiLoLl SUPPLEMENTARY NOTES 03914. ABSTRACT Stagnation point flow and heat transfer in the presence of free-stream turbulence is investigated through both numerical simulation and theoretical analysis. Large eddy simulations (LES) results for different free-stream turbulent intensity, length scale, and Mach number are reported. The Reynolds stress statistics and budgets are obtained and presented. The numerical results show good agreement with experimental measurements on elevated heat transfer coefficient, and reveals the characteristic vortical flow structures responsible for the observed heat transfer enhancement.The theoretical analysis shows that the vorticity amplification, and hence the heat transfer enhancement, increases with decreasing length scale and reaches a maximum value at about five times the boundary layer thickness. A new correlation for heat transfer enhancement which incorporates turbulence intensity, integral length scale and mean flow Reynolds number is derived and shown to reasonably collapse the recent experimental data. Abstract Stagnation point flow and heat transfer in the presence of free-stream turbulence is investigated through both numerical simulation and theoretical analysis. Large eddy simulations (LES), using fourth order finite difference in curvilinear coordinates and an efficient dual time linearized sub-iteration scheme, are performed to investigate free-stream turbulence impingement upon an elliptical leading edge and the resulting heat transfer enhancement. A new blending procedure is developed through which independent, statistically identical realizations of homogeneous isotropic turbulence are combined to provide realistic representations of free-stream turbulence.Results for diflTerent free-stream turbulent intensity, length scale, and Mach number are reported. Strong anisotropy of the turbulence due to the mean flow strain is observed as the stagnation point is approached. The Reynolds stress statistics and budgets are obtained and presented. These results are expected to provide unique data for turbulence modelling of strain dominated flows. The numerical results show good agreement with the experimental measurements on elevated heat transfer coefficient. It also reveals that small scale, intense vortical flow structures generated at the leading edge by vortex stretching induces significant changes in local thermal boundary layer, causing the observed heat transfer enhancement.In the theoretical study, the distortion of three dimensional unsteady disturbance in an incompressible Hiemenz boundary layer and its effect on the wall heat transfer is analyzed based on linear vortex dynamics. An asymptotic solution for disturbanc...

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Section: Numerical Resultssupporting

confidence: 52%

Section: Introductionmentioning

confidence: 71%

Stagnation Point Flow and Heat Transfer Under Free-Stream Turbulence

Zhang¹,

Lele²

2004

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“…the streamwise velocity is a linear function of the streamwise coordinate x, and the wall normal velocity is independent of x. The flow structures induced by free-stream turbulence in a stagnation region are found to be qualitatively similar to those induced by upstream organized disturbances (Xiong & Lele 2001). The importance of the disturbance length scale has been shown recently through direct numerical simulation of a turbulent stagnation point flow by Bae, Lele & Sung (2003).…”

Section: Introductionmentioning

confidence: 66%

Distortion of upstream disturbances in a Hiemenz boundary layer

Zhang¹,

Lele²

2004

J. Fluid Mech.

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A theoretical analysis of the distortion of unsteady three-dimensional disturbances in a Hiemenz boundary layer and its effect on the heat transfer enhancement is presented. It is shown that the disturbance length scale is a critical parameter in determining the amplification ratio of the incoming vorticity. For large disturbance length scales, the amplification ratio increases when the length scale decreases, and a maximum value occurs at a length scale close to five times the boundary-layer thickness. The unsteadiness of the disturbances is found to reduce the vorticity amplification, but the effect is second order when the frequency is low compared to the mean flow strain rate. The impinging disturbances induce large-amplitude vorticity of opposite sign at the wall whose magnitude controls the heat transfer enhancement. As an application of the present analysis, a new scaling correlation is derived for stagnation-point heat transfer in the presence of free-stream turbulence. The theoretical correlation, expressed in terms of turbulence intensity, integral length scale and mean flow Reynolds number, agrees reasonably well with recent experimental data.

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“…Using numerical simulation of a swept Hiemenz boundary layer, Spalart (1989) found that, out of initial whitenoise disturbances, the most unstable disturbance-mode is the one with the same similarity form as the mean Hiemenz flow, an assumption made in the stability analysis mentioned above. The flow structures induced by free-stream turbulence in a stagnation region were found to be qualitatively similar to those induced by upstream organized disturbances (Xiong & Lele 2001). Bae, Lele & Sung (2000) showed that different length scales generate quite different flow patterns and in turn different heat transfer responses in a plane stagnation-point flow.…”

Section: Introductionmentioning

confidence: 69%

Stagnation-point flow under free-stream turbulence

Zhang

Lele

2007

J. Fluid Mech.

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In this paper, the effects of free-stream turbulence on stagnation-point flow and heat transfer are investigated through large eddy simulation (LES) of homogeneous isotropic turbulence impinging upon an isothermal elliptical leading edge. Turbulent mean flow and Reynolds stress profiles along the stagnation streamline, where the mean flow is strain dominant, and at different downstream locations, where the mean flow gradually becomes shear-dominated, are used to characterize evolution of the free-stream turbulence. The Reynolds stress budgets are also obtained, and the turbulence anisotropy is analysed through the balance between the mean flow strain and the velocity pressure gradient correlation. In the presence of free-stream turbulence, intense quasi-streamwise vortices develop near the leading edge with a typical diameter of the order of the local boundary-layer thickness. These strong vortices cause the thermal fluxes to peak at a location much closer to the wall than that of the Reynolds stresses, resulting a greater sensitivity to free-stream turbulence for the heat transfer than the momentum transfer. The heat transfer enhancement obtained by the present LES agrees quantitatively with available experimental measurements. The present LES results are also used to examine the eddy viscosity and pressure-strain correlations in Reynolds stress turbulence models.

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Numerical study of leading-edge heat transfer under free-stream turbulence

Cited by 6 publications

References 17 publications

Stagnation Point Flow and Heat Transfer Under Free-Stream Turbulence

Stagnation Point Flow and Heat Transfer Under Free-Stream Turbulence

Distortion of upstream disturbances in a Hiemenz boundary layer

Stagnation-point flow under free-stream turbulence

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