Anomalous intensification of vortex heat transfer in the case of separated air flow over an inclined groove in a hot isothermal region of a flat plate

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Abstract

Anomalous heat transfer intensification in turbulent separated air flow over a long groove of moderate depth made in a plate inclined at an angle of 45° to the freestream is revealed both experimentally and numerically. The region under investigation includes a rectangle heated to 100°C by saturated water vapor. The Reynolds number varied from 103 to 3×104. Using the gradient heatmetry the twofold increase, as compared with the case of a flat plate, of the heat transfer coefficient on the groove bottom is established at the Reynolds number Re = 3×104. The relative Nusselt number in different regions of the groove is determined both in the physical experiment and in the RANS calculations with the application of multiblock computational technologies and the SST model in the VP2/3 software package. The results are in good agreement in the turbulent flow regime at Re = (5, 10, and 30) ×103.

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About the authors

S. А. Isaev

St. Petersburg State Marine Technical University; St. Petersburg State University of Civil Aviation

Author for correspondence.
Email: isaev3612@yandex.ru
Russian Federation, St. Petersburg; St. Petersburg

S. Z. Sapozhnikov

Peter the Great St. Petersburg Polytechnic University

Email: isaev3612@yandex.ru
Russian Federation, St. Petersburg

D. V. Nikushchenko

St. Petersburg State Marine Technical University

Email: isaev3612@yandex.ru
Russian Federation, St. Petersburg

V. Yu. Mityakov

Peter the Great St. Petersburg Polytechnic University

Email: isaev3612@yandex.ru
Russian Federation, St. Petersburg

V. V. Seroshtanov

Peter the Great St. Petersburg Polytechnic University

Email: isaev3612@yandex.ru
Russian Federation, St. Petersburg

Е. B. Dubko

St. Petersburg State University of Civil Aviation

Email: isaev3612@yandex.ru
Russian Federation, St. Petersburg

References

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2. Fig. 1. Photo of the thermophysical stand (a) and a diagram of the experimental setup with dimensions indicated, mm.

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3. Fig. 2. Calculated analogue of the experimental heat-insulated plate with a heated isothermal section with T = 373 K, in the center of which there is an inclined groove (a), and a multi-block computational grid of four fragments: 1 - external Cartesian grid with a height of 8.8; 2 - adjacent to the heated section wall grid with a height of 0.7; 3 - curvilinear elliptical O-type grid matched to the groove surface; 4 - "patch" on the central zone of the groove (b).

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4. Fig. 3. Comparative analysis of the calculated (1–6) and measured (7–10) relative Nusselt numbers Nu/Nupl (a) and static pressure drops P–Ppl (b) in a characteristic cross-section of the transition from the inlet spherical segment to the cylindrical trench, as well as the profiles of the longitudinal velocity component Q(y) in the coupled coordinate system (s, y, t) at the central point of the characteristic cross-section (c) at different Reynolds numbers. 1 — Re = 103; 2 – 5×103 (1, 2 — laminar regime); 3, 8 – 5×103; 4, 9 – 104; 5, 1 – 3×104; 6, 7 — 6.7×104 [5] (3–10 turbulent regime).

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5. Fig. 4. Comparison of the calculated distributions of the relative friction f/fpl (a, b) and the static pressure difference P–Ppl (c, d) in the longitudinal middle section of the groove (a, c) and the characteristic section of the transition from the inlet spherical segment to the cylindrical trench (b, d) at different Reynolds numbers. 1 — Re = 103; 2 – 5×103 (1, 2 — laminar regime); 3 — 5×103; 4 — 104; 5 — 3×104 (3–5 — turbulent regime).

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6. Fig. 5. Comparison of the calculated distributions of the relative Nusselt numbers Num/Numpl averaged over transverse strips (a–d) along (a, c) and across (b, d) the control section with an inclined groove (a, b) and the section limited by the groove contour (c, d) at different Reynolds numbers, as well as the Nu/Nupl field with the applied air spreading pattern in the vicinity of the groove at Re = 3×104 (d). 1 — Re = 103; 2 – 5×103 (1, 2 – laminar regime); 3 — 5×103; 4 — 104; 5 — 3×104 (3–5 – turbulent regime).

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7. Fig. 6. Dependences on the Re number of the thermal efficiency Numm/Nummpl 1, 2 and the relative frontal resistance Cx/Cxpl 3, 4 of the control section of the plate with a groove – 1, 3 and the section limited by the groove contour – 2, 4.

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