Fluid flow and heat transfer characteristics of separation and reattachment flow over a backward-facing step

Xie, Weilin; Xi, Guannan

doi:10.1016/j.ijrefrig.2016.10.006

Cited by 20 publications

(19 citation statements)

References 24 publications

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“…Fluida yang melewati zona ekspansi secara umum menyebabkan timbulnya vorteks resirkulasi dan titik penyatuan (reattachment point) serta melibatkan perpindahan panas selama proses aliran tersebut. Penelitian terkait aliran berputar pada geometri BFS pada ducting dan komponen mekanikal lain yang telah banyak dilakukan [1], [2], [3], [4], [5], [6] Aliran berputar dapat dilakukan dengan lebih mudah, menarik dan berbiaya rendah dengan menggunakan geometri Backward-facing step (BFS).…”

Section: Pendahuluanunclassified

Analisis CFD pada Geometri Backward-facing Step dengan variasi Bilangan Reynolds

Darmawan

Octavian

2018

JEM

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Sistem tata udara pada bidang perhotelan merupakan salah satu aspek penting untuk menunjang kenyamanan, yang pada daerah pariwisata seperti Bali dengan iklim tropis dilakukan dengan aplikasi pendingin udara (AC). Aliran udara pada hotel bertingkat biasa dibuat terpusat dan dialirkan ke tempat tujuan dengan menggunakan ducting dengan penampang segi empat. Menyesuaikan dengan denah yang ada, seringkali terdapat bagian ducting yang harus dibuat bertingkat pada titik datum yang sama (zona ekspansi). Geometri bertingkat ini dapat menghasilkan kerugian aliran karena pada zona ekspansi tersebut timbul aliran berputar (aliran resirkulasi). Pemahaman terhadap aliran berputar dapat dilakukan dengan lebih mudah, menarik dan berbiaya rendah dengan menggunakan geometri Backward-facing step (BFS). Pada penelitian ini, dilakukan analisis numerik melalui simulasi CFD terhadap aliran resirkulasi pada sebuah geometri backward-facing step, dengan panjang total (L) = 4050 mm, step height (h) = 41 mm, upstream height (H) = 81 mm, rasio ekspansi = 1.5, dan lebar (t) = 20h. Eksperimen dilakukan dengan fluida kerja asap. Untuk mendapatkan hasil yang lebih luas, eksperimen juga dilakukan pada 3 (tiga) variasi bilangan Reynolds: Re = 7.315,79; Re = 21.947,37; dan Re = 29.263,16. Simulasi CFD dilakukan secara 3 dimensi dengan menggunakan model turbulen RNG k-?, mesh jenis triangular dengan jumlah nodal sebanyak 36.806 nodal. Vorteks resirkulasi ditunjukkan melalui zona resirkulasi yang direpresentasikan oleh vektor kecepatan arah-x dan titik penyatuan (reattachment point) yang diukur dari zona resirkulasi. Hasil simulasi CFD menunjukkan bahwa vorteks resirkulasi timbul pada X/h = 29.2 hingga X/h = 35 untuk seluruh bilangan Reynolds uji yang direpresentasikan oleh vektor kecepatan arah-x, dimana Reynolds Re = 7.315,79 menghasilkan titik penyatuan pada X/h > 35 dari zona resirkulasi, lebih jauh dibandingkan dengan yang dicapai oleh bilangan Reynolds yang semakin besar Air conditioning system is an important aspect in tourism industry that has become a priority sector in Bali, Indonesia. It’s tropical climate make the air conditioning system use for cooling system only (AC). The centralized air conditioning system in high rise building uses ducting system with rectangular cross-sectional area which often depends on a given blue print. Some specific area of the blue print may lead to adjustment of the ducting system, e.g. the gradual step of the ducting system. This gradual base of the ducting may cause additional consequences, a recirculation flow at the gradation area (the expansion zone). As already known, the recirculation flow leads to flow losses. This paper discuss an numerical analysis with CFD simulation of a backward-facing step (BFS) geometry. The BFS geometry used in this has total length (L) = 4050 mm, step height (h) = 41 mm, upstream height (H) = 81 mm, expansion ratio = 1.5, and width (t) = 20h. The CFD simulation conducted three dimensionaly with RNG k-? turbulence model, and 36.806 triangular nodes. Recirculation vortices represented by recirculation zone with x-velocity and reattachment point. The result of CFD simulation that is conducted to Reynolds number Re = 7.315,79; Re = 21.947,37; dan Re = 29.263,16 shows that recirculation vortices occur at X/h = 29,2 to X/h = 35 for tested Reynolds number. Reattachment point at Reynolds number of 7.315.79 occur at X/h > 35, which farther than that is achieved at larger Reynolds number.

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Section: Pendahuluanunclassified

Analisis CFD pada Geometri Backward-facing Step dengan variasi Bilangan Reynolds

Darmawan

Octavian

2018

JEM

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“…Authors detect a second Nusselt number (Nu) peak at the middle plane of 3D BFS due to flow instability after Re=1000. Xie and Xi [21] investigate transitional Re numbers for laminar BFS heat transfer with transient CFD and fine mesh. They also show flow instability of transitional flow over Re=1000 and its effects on heat transfer.…”

Section: Introductionmentioning

confidence: 99%

Numerical Forced Convection Heat Transfer of Nanofluids over Back Facing Step and Through Heated Circular Grooves

Abdulkarim¹,

Eleiwi²,

Tahseen³

et al. 2021

MMEP

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Backward facing step arrangement is a classical case for fluid dynamics and heat transfer research. It is well characterized and therefore, used for benchmarking. However, ongoing studies reveal that the geometry also provide advantages in industry, especially in combustion and burners. This work utilizes computational fluid dynamics to investigate a specific laminar back facing step flow heat transfer case. Aluminium oxide nano particles are considered as an additive to water base fluid, forming nanofluid with different volumetric concentrations. Laminar flow passes a back facing step and encounters three circular grooves at bottom surface. All surfaces are adiabatic except the grooves. Constant surface temperature applies to the grooves. According to the simulation results, a separation bubble after back facing step and a reattachment point occur. Grooves alter expected wake due to physical and thermal interference. Investigation parameters are nano-particle concentration and Reynolds number. Reynolds number changes between 10 and 250. Nano particle volume fraction percentage changes between 2 and 6 percent. Sectional heating downstream of the step poses interesting heat flux in the presence of Aluminium oxide nano-particle concentrations. There is a pseudo-linear relationship between parameters and heat transfer. Combined effects of enhanced thermal conductivity and secondary flow structures are seen. As expected, thermal convection increases as flow velocity and nano-particle concentrations increase. Heat flux and accordingly Nusselt number are highly affected from Reynolds number since flow structure changes dramatically. Also, direct proportion is seen between nano-particle concentration and enhanced convection.

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“…Recently, several numerical and experimental studies in the field of BFS flow over various step angles (Bayraktar 2014), control of the reattachment length of a transonic 2D BFS flow (Bolgar et al 2015), simulation of a gently curved BFS (Asgari and Tadjfar 2017), simulation of turbulent flows over a BFS by using a modified partially averaged Navier-Stokes model (Huang et al 2017), heat transfer and fluid flow characteristics of separation and reattachment flow over a BFS (Xie and Xi 2017) and high intensity turbulent flow over a BFS (de la Torre et al 2017) are conducted by scholars. For comparison between the cited works and to identify the novelty of current study, we present a summary of the cited works in Table 1.…”

Section: Introductionmentioning

confidence: 99%

On the Instability of Two Dimensional Backward-Facing Step Flow using Energy Gradient Method

Nowruzi

Nourazar

Ghassemi

2018

JAFM

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In the present paper, the energy gradient method is implemented to study the instability of 2-D laminar backward-facing step (BFS) flow under different Reynolds numbers and expansion ratios. For this purpose, six different Reynolds numbers (50 ≤ Re ≤ 1000) and two various expansion ratios of 1.9423 and 3 are considered. We compared our results of the present study with existing experimental and numerical data and good agreement is achieved. To study of fluid flow instability, we evaluated the distributions of velocity, vorticity and energy gradient function K. The results of our study show that as the expansion ratio decreases the flow becomes more stable. We also found that the origin of instability in the entire flow field is located on the separated shear layer nearby the step edge. In addition, we approved that the inflection point on the profile of velocity corresponds to the maximum of vorticity resulted to the instability.

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Fluid flow and heat transfer characteristics of separation and reattachment flow over a backward-facing step

Cited by 20 publications

References 24 publications

Analisis CFD pada Geometri Backward-facing Step dengan variasi Bilangan Reynolds

Analisis CFD pada Geometri Backward-facing Step dengan variasi Bilangan Reynolds

Numerical Forced Convection Heat Transfer of Nanofluids over Back Facing Step and Through Heated Circular Grooves

On the Instability of Two Dimensional Backward-Facing Step Flow using Energy Gradient Method

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