tài liệu trettel water 2020
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tài liệu trettel water 2020
Chapter 7Water jet trajectory theory17.1 IntroductionPredicting the trajectory and surface water distribution from a tire hose or tire monitor (as see tài liệu trettel water 2020 en in figure 7.1) is difficult a priori. While models exist at present, their accuracy outside the range of their calibration data is questionable. For example, if a model is calibrated for a certain nozzle, it is unlikely that the model would be accurate for a different nozzle, even with an identic tài liệu trettel water 2020 al internal flow system upstream of the nozzle.Given how critical time to extinguishment is to total property and life loss, more accurately predictintài liệu trettel water 2020
g how long it will take for a waterjet to extinguish a fire is essential to more accurately assess risk. The development of an accurate model of the tChapter 7Water jet trajectory theory17.1 IntroductionPredicting the trajectory and surface water distribution from a tire hose or tire monitor (as see tài liệu trettel water 2020 erjets arc used to suppress fire arc varied, from first responders w ho apply hose streams, to deck-mounted fire monitors on boats used to fight fires on the deck or even outside the boat. Fire monitors mounted on towers also are frequently used in fire protection scenarios, e.g.. protection of pulp tài liệu trettel water 2020 wood. There is also recent interest in fully autonomous fire suppression systems, w here prediction of the trajectory from a fire nozzle is essentialtài liệu trettel water 2020
for fast targeting. The model developed in this work would prove useful in accessing and reducing fire risk in all of these scenarios.•An earlier versChapter 7Water jet trajectory theory17.1 IntroductionPredicting the trajectory and surface water distribution from a tire hose or tire monitor (as see tài liệu trettel water 2020 the conference paper as an outline to improve the presentation, correct errors, extend the theory, and improve the validation of the theory. Note that much of the notation has changed since then to he more consistent, be easier to understand, and simplify the results. I am the sole author; Prof. Eze tài liệu trettel water 2020 koye was i IK I tided as an author on the conference paper for his advisory role.163Figure 7.1: Two fire monitors in use by the Portland Fire Departmetài liệu trettel water 2020
nt.Fire monitors can deliver 5000 GPM (~300 L/s) or more through nozzles up to and beyond 3 inches (~7 cm) in diameter, leading to maximum ranges of 2Chapter 7Water jet trajectory theory17.1 IntroductionPredicting the trajectory and surface water distribution from a tire hose or tire monitor (as see tài liệu trettel water 2020 arge waterjets, for example, hose streams and tire monitors. Consider a large water jet launched at a speed Uq and an angle 00 to the horizontal with the center of the nozzle of diameter i/o at a height /to. The nozzle outlet is denoted with 0. so. e.g.. the nozzle outlet diameter is */<>. Sec figur tài liệu trettel water 2020 e 7.2 for an illustration of the problem. This jet gradually breaks up with distance from the nozzle, forming droplets which eventually reach the horitài liệu trettel water 2020
zontal plane. The two quantities of interest are the surface water distribution (i.e.. wetted area) and the maximum range R that the waterjet projectsChapter 7Water jet trajectory theory17.1 IntroductionPredicting the trajectory and surface water distribution from a tire hose or tire monitor (as see tài liệu trettel water 2020 id jet breakup is shown in schematic in figure 2.1. In this frame the X axis is oriented streamwise. This is not the convention for the frame used in the trajectory models. where .V is the distance from the nozzle outlet horizontally. The region of space over w hich liquid water is continuously conn tài liệu trettel water 2020 ected to the nozzle outlet is called the jet core, rhe core flow (dark gray) Starts being depleted of mass (on average) at164Figure 7.2: Basic trajecttài liệu trettel water 2020
ory nomenclature with tiring angle ờ(), tiring height /tn, and maximum range K.the breakup onset location. (Xj). The core ends on average at rhe breakChapter 7Water jet trajectory theory17.1 IntroductionPredicting the trajectory and surface water distribution from a tire hose or tire monitor (as see tài liệu trettel water 2020 uid water exists only as discontinuous slugs and droplets. The lighter gray refers to the region where droplets exist.<*b>Figure 2.1: Jet breakup variables labeled on a schematic liquid jet. Coordinates arc different from figure 7.2. dft is the nozzle outlet diameter. (.Vị) is the average breakup on tài liệu trettel water 2020 set location. ỠỊ is the spray angle, andtài liệu trettel water 2020
s influence the range and trajectory of a waler jet, a review of these factors and what common models consider is needed. In this review. I emphasize Chapter 7Water jet trajectory theory17.1 IntroductionPredicting the trajectory and surface water distribution from a tire hose or tire monitor (as see tài liệu trettel water 2020 shown in figure 1.1.165Figure 7.3: Surface water distribution example: probability density of water reaching distance .V.7.2.1The water jet range anomalyWaterjet range can be estimated by assuming that droplets are emitted directly at the nozzle outlet at the velocity of the jet and that these drop tài liệu trettel water 2020 lets follow a ballistic trajectory with a known drag coefficient. I refer to this as the instantaneous breakup model. This model is known to severelytài liệu trettel water 2020
underpredict the range of the jet. For example. Richards and Weatherhead [RW93. p. 284J report that the instantaneous breakup approach suggests that aChapter 7Water jet trajectory theory17.1 IntroductionPredicting the trajectory and surface water distribution from a tire hose or tire monitor (as see tài liệu trettel water 2020 19.5 m. compared against 50 m found experimentally. I call this discrepancy the range anomaly.Another common approach with large waterjets is to assume that the jet experiences no drag. This is called the dragless approach. This approach over-predicts the range. For example, in the previously mentio tài liệu trettel water 2020 ned case, the dragless range is estimated to be about 68 m.There also arc empirical approaches to estimate range. The most simple empirical approachestài liệu trettel water 2020
are regression equations, which have been used by Lyshevskii |Lys62a] and Theobald [Thc8l|. There also arc computational models which use purely empiChapter 7Water jet trajectory theory17.1 IntroductionPredicting the trajectory and surface water distribution from a tire hose or tire monitor (as see tài liệu trettel water 2020 hich select the droplet diameter distribution by matching range or water distribution data arc similar, e.g.. the model of166Fukui. Nakanishi. and Okamura |FNO80|. These models can lead to unrealistically large droplet diameters, as will be explained. Additionally, the accuracy of empirical models tài liệu trettel water 2020 is questionable aside from the particular system they were calibrated for. This is particularly true given that some of the drag models used are dimentài liệu trettel water 2020
sionally inhomogeneous. Smith et al. |Smi+08, p. 127R] note that empirical models typically require more calibration data than theoretical models for Chapter 7Water jet trajectory theory17.1 IntroductionPredicting the trajectory and surface water distribution from a tire hose or tire monitor (as see tài liệu trettel water 2020 e range anomaly: air entrainment, jet breakup, and large droplets. Each effect exists in reality, but the relative contributions of each effect are not obvious at present.7.2.1.1Effect 1: Reduced drag due to air entrainmentOne hypothesis is that the reduction in apparent drag is due primarily to air tài liệu trettel water 2020 entrainment, as suggested by Murzabaeb and Yarin [MY85], Richards and Weatherhead IRW93, p. 284], and Grose |Gro99. p. 6|. The reasoning is that a hitài liệu trettel water 2020
gher entrainment velocity would reduce the velocity difference between the droplets and the surrounding gas flow (AU) and then decrease the drag (Fd aChapter 7Water jet trajectory theory17.1 IntroductionPredicting the trajectory and surface water distribution from a tire hose or tire monitor (as see tài liệu trettel water 2020 the droplets (or the jet core) and the gas. This momentum coupling is essentially a gas phase momentum source term, much like the source term used to model buoyant plumes that will be discussed in § 7.3.1.5.Air entrainment is not likely as simple as was just discussed. In contrast to the popular sta tài liệu trettel water 2020 tement of the hypothesis, decreasing air entrainment might lead to an increase in range as suggested by Hoyt and Taylor |HT77a|. The logic here is thatài liệu trettel water 2020
t the momentum transfer from the jet to the air results in reduced range. The net effect of air entrainment may either be negligible or non-monotonic,Chapter 7Water jet trajectory theory17.1 IntroductionPredicting the trajectory and surface water distribution from a tire hose or tire monitor (as see tài liệu trettel water 2020 ch air entrainment requires high drag to occur in the first place.167Further, if increased air entrainment explains the range anomaly, then I might expect higher jet turbulence intensity to increase range. This is because as jet turbulence intensity increases, so docs air entrainment IEME80: MESO], tài liệu trettel water 2020 And as air entrainment increases, the relative velocity between the droplets and air decreases, in turn decreasing drag and increasing range. However,tài liệu trettel water 2020
increasing jet turbulence intensity is known to decrease range (RHM52: Oeh58J. This could be despite increased air entrainment helping the jet's rangGọi ngay
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