Numerical study of impinging jets heat transfer with different nozzle geometries and arrangements for a ground fast cooling simulation device

https://doi.org/10.1016/j.ijheatmasstransfer.2015.12.022Get rights and content

Highlights

  • The model of a ground fast cooling simulation device is introduced.

  • Heat transfer of multiple impinging jets is numerically investigated.

  • The effects of nozzle geometry and arrangement on heat transfer are discussed.

  • 21 different configurations are considered and analyzed.

  • An overall performance evaluation indicator named QU ratio is proposed.

Abstract

In this paper, a comparative study is performed to check the nozzle geometry and arrangement effects on impinging jets heat transfer performance to help the design of a ground fast cooling simulation device which is used for the thermal tests of high speed flight vehicles. Based on the simplified physical model, the impinging jets heat transfer is modeled using the shear-stress transport (SST) k-ω turbulence model. A total of 21 different nozzle configurations including 7 geometries are considered in the numerical simulation. Heat transfer performances concerning heat transfer intensity and heat flux uniformity in different cases are compared with each other. Analysis is given on the corresponding flow fields and surface heat flux distributions. To help the optimization of nozzle geometry and arrangement in designing the device, an indicator named QU ratio is proposed for the overall performance evaluation of the nozzle configurations. The effectiveness of the QU ratio is validated based on the numerical results and it can be used to help determine the best design for certain given conditions of the ground fast cooling device.

Introduction

With the development of technologies, there come the increasing demands for faster planes, rockets, missiles and space crafts etc. The development of such high speed flight vehicles, especially hypersonic flight vehicles [1], [2], [3], imposes harsh requirements on the materials and parts of their bodies. Due to the drastic aerodynamic heating during the flight, the surface temperature of the flight vehicle could exceed 1000 °C. Therefore, it’s very important to use high temperature resistant materials and thermal protection structures on the surfaces of such vehicles to maintain their functions. By exerting high heat fluxes on the test pieces trough radiation heating, many thermal testing facilities, which can be used to simulating aerodynamic heating processes, were built on the ground, and investigations were performed to test materials and structures [4], [5], [6]. Under some circumstances, however, structures and materials on the surface of the flight vehicles may go through certain fast rapid cooling processes after being aerodynamically heated to very high temperatures. The resulting high cooling rates, large temperature gradients and thermal stresses could lead to failure or damage of the relevant components. In consideration of evaluating the structural designs and testing materials before real flight test, ground thermal simulation, especially fast cooling simulation, is badly needed in developing high speed flight vehicles.

Air impingement cooling is characterized by its high cooling capacity in the stagnation zone on the impingement surface. Besides, air is not corrosive and it’s cheap enough to be massively applied without considering recycling. These advantages made this cooling method widely used in many industrial applications such as electrics cooling [7], gas turbine cooling [8] and heat treatment of steel [9]. In order to cool large surfaces, multiple impinging jets should be used instead of a single jet, and such devices with multiple jets have to be carefully designed to obtain the required cooling rate and heat flux uniformity. To the best of the authors’ knowledge, similar devices are rarely reported in literature.

Multiple impinging jets cooling techniques have been the focus of many investigators for long. Different from the single jet situation, interference between adjacent jets and the inevitable crossflow have a great effect on the heat transfer on the target surface. Many investigations aimed to find the influences of different parameters and configuration designs. Xing and Weigand [10] investigated the effects of jet-to-plate spacing on heat transfer for 3 different crossflow schemes. They used a 9 × 9 nozzle array and measured the detailed local heat transfer coefficients in experiments. The influence of jet-to-jet spacing on local heat transfer distribution was experimentally studied by Katti and Prabhu [11]. They have proposed an optimum configuration of 6 × 10 nozzles to minimize the mass flow rate of air per unit area of the cooled surface. Huang et al. [12] measured the heat transfer coefficients on the target surface under an array of 12 × 4 jets and the maximum heat transfer was obtained when the crossflow exited the experimental domain in both flow directions. Ligrani et al. [13], [14], [15] reported a series of experimental investigations of the effects of nozzle hole spacing, temperature ratio, Mach number and Reynolds number on heat transfer. In addition to effects of single factors, the combined effects of the aforementioned parameters were also presented in Ref. [16]. Weigand and Spring [17] reviewed the heat transfer characteristics of multiple impinging air jets and systematically discussed the effects of many influencing factors. Among all the influencing factors, nozzle geometry and arrangement are the most important ones. Comparisons of different nozzle geometries in single jet heat transfer were made by many investigators both numerically and experimentally [18], [19], [20]. In addition to that, a lot of investigations were conducted directly on multiple impinging jets in recent years. Zhao et al. [21] numerically studied the flow and heat transfer characteristics of semi-confined laminar air jets. Circular, rectangular, square and elliptic jets were considered in their study. Elliptic jet holes with the same hydraulic diameter and 5 different aspect ratios were studied by Yan et al. [22] and detailed heat transfer characteristics were measured using transient liquid crystal technique. The aspect ratio and crossflow were found to have significant influence on the impingement locations. Dano et al. [23] reported the experimental results of a 7 × 7 array with confined circular and cusped elliptic jets. Visualization of the flow fields was presented. Chiu et al. [24] not only studied the effects of elliptic jet with different aspect ratios, but also took nozzle arrangement into consideration in their experiments. Performances of circular and cross-shaped circular jets with the same cross section area in a 3 × 3 array were compared in the experiments by Yamane et al. [25] and the influence of the interaction among adjacent impinging jets on heat transfer was discussed. Later, oblique cross-shaped jets were considered in their study [26], which indeed represented a change of the nozzle array arrangement compared to the cross-shaped jets. Caliskan et al. [27] compared the effects of different nozzle geometries on heat transfer and flow field by using a laser Doppler anemometry system and an infrared thermal camera. Elliptic jets were found to offer higher heat fluxes than rectangular jets and a correlation was proposed for the calculation of average Nusselt number on the target surface. By altering the aspect ratios, the effect of nozzle arrangement was simultaneously studied indeed (e.g. nozzles with aspect ratios of 0.5 and 2 in their study can be viewed as nozzles with the same geometry and arranged in different directions).

As can be seen from the above literature survey, heat transfer of multiple impinging jets is complex with various influencing factors. The selection of nozzle geometry and the arrangement of the nozzles will greatly determine the heat transfer on the target surface. If impinging jets are to be adopted in ground fast cooling simulation, detailed comparison and optimization study should be carried out in the designing process according to the requirements. Hence, numerical modeling will be helpful in the design of the device. Turbulence modeling is the major concern when numerical simulation is performed on multiple jets because most of the applied impinging jets lie in the turbulent flow region. Caliskan et al. [27] calculated the heat transfer characteristics of elliptic and rectangular jets with k-ɛ model. A good match was observed between numerical and experimental data. The v2-f model was validated against experimental data by Behnia et al. [28] and this model performed well in accuracy. Xing et al. [29] and Spring et al. [30] conducted combined numerical and experimental investigations. Their works presented a good overall agreement between numerical and experimental results using the SST turbulence model. Chougule [31] reported a CFD study of a 3 × 3 air impingement jets and found that the SST model provided very good prediction of heat transfer and flow at a moderate computational cost. The difference between their experimental data and CFD results was within the range of ±5%. Končar et al. [32] adopted the SST turbulence model to optimize the nozzle diameters of a helium impinging jets cooled divertor in the conceptual fusion power plant. The validation of the calculation against high heat flux experiments proved the feasibility of the SST model. Zuckman and Lior [33] summarized the performance of various turbulent models. The v2-f model and SST model were recommended because of the relatively high accuracy and acceptable solution speed in calculation.

In order to build a desirable and applicable cooling simulation device, suitable heat fluxes should be provided on the test piece surface to obtain the required cooling curves. Ideally, all positions on the surface of large test pieces shall be cooled at exactly the same rate. In practice, uniform cooling is impossible if impinging jets are used and efforts should be dedicated to eliminating the difference between cooling curves of different positions as much as possible. This research is performed to help the design and optimization of the ground fast cooling simulation device. The simplified physical and mathematical models of the device are firstly introduced in Section 2. Subsequently, numerical results of heat transfer with different nozzle geometries and arrangements are shown. A total of 21 configurations are considered in this paper. Comparisons are made on heat performances of different cases based on the magnitude and uniformity of heat flux on the target surface. Some typical flow fields and heat flux distributions are discussed for a further understanding of the nozzle geometry and arrangement effects. Finally, an overall heat transfer performance indicator is proposed to facilitate the evaluation of different nozzle configurations in designing the device.

Section snippets

Physical model

To fulfill the demands of the ground fast cooling simulation tests, a jet plenum is designed accordingly as illustrated in Fig. 1. The compressed air is stored in the air tanks and its pressure is controlled and monitored before entering the plenum. Afterwards, the air expands through the expanding channel of the top plenum. Considering the drastic increase of the cross section area, a distributor is designed and installed at the inlet of the plenum to help evenly distribute the air flow. Steel

Results and discussion

A low air flow rate of Ql = 0.378 m3/s and a high flow rate of Qh = 0.756 m3/s were selected in the numerical simulation to represent the two typical working conditions in the cooling simulation device. Given that the nozzles were of the same cross section area, a low jet velocity of Vl = 29.36 m/s and a high velocity of Vh = 58.72 m/s were set at the velocity inlet in the calculation. The corresponding jet Reynolds number values of the C nozzles are Rej = 15,000 and Rej = 30,000, respectively. Meanwhile, two

Conclusions

A comparative study is performed in this paper to figure out the effects of nozzle geometry and arrangement on impinging jets heat transfer performance in a ground fast cooling simulation device. The multiple impinging jets heat transfer is modeled using the SST k-ω turbulence model. Based on the results of the numerical simulation, the heat transfer performance of different nozzle configurations are obtained and compared with each other. A total of 21 different configurations involving 7 types

Acknowledgements

The study is supported by the Research Project of Chinese Ministry of Education (Nos. 20120201130006, 113055A) and Beijing Institute of Mechanical & Electrical Engineering.

References (35)

  • H.C. Chiu et al.

    Experimental study on the heat transfer under impinging elliptic jet array along a film hole surface using liquid crystal thermograph

    Int. J. Heat Mass Transfer

    (2009)
  • S. Caliskan et al.

    Experimental and numerical investigation of geometry effects on multiple impinging air jets

    Int. J. Heat Mass Transfer

    (2014)
  • M. Behnia et al.

    Numerical study of turbulent heat transfer in confined and unconfined impinging jets

    Int. J. Heat Fluid Flow

    (1999)
  • B. Končar et al.

    Effect of nozzle sizes on jet impingement heat transfer in He-cooled divertor

    Appl. Therm. Eng.

    (2010)
  • P.L. Moses et al.

    NASA hypersonic flight demonstrators—overview, status, and future plans

    Acta Astronaut.

    (2004)
  • S.H. Walker et al.

    The DARPA/AF falcon program: the hypersonic technology vehicle # 2 (HTV-2) flight demonstration phase

    AIAA Paper

    (2008)
  • Y. Moule et al.

    Computational fluid dynamics investigation of a Mach 12 scramjet engine

    J. Propul Power

    (2014)
  • Cited by (42)

    • Convection from multiple air jet impingement - A review

      2023, Applied Thermal Engineering
      Citation Excerpt :

      From the analysis, they found that the SST k-ω model presents a better compromise between computational costs and accuracy. Wen et al. [94] modeled multiple round jets (Re = 35,000) impinging on a flat plate and compared the SST k-ω model with the Standard k-ω model, the Realizable k-ε model, and the v2-f. From the results, they concluded that comparing the prediction with experimental data, the SST k-ω model presents a higher accuracy than the k-ω and k-ε models. Additionally, even if v2-f presents a good accuracy in predicting the average Nussel number, it fails in predicting the stagnation zone.

    View all citing articles on Scopus
    View full text