Entrained air in bore-driven swash on an impermeable rough slope

Han Jing Dai, Gustaaf Adriaan Kikkert, Bo Tao Chen, Dubravka Pokrajac

Research output: Contribution to journalArticle

3 Citations (Scopus)
4 Downloads (Pure)

Abstract

The aim of the present investigation is to clarify the role and evaluate the importance of air entrainment
in the swash zone by carrying out a set of detailed laboratory experiments. Experiments involved
generating a single, highly repeatable, large-scale, bore-driven swash event on a sand-rough impermeable
beach with slope 1:10. Measurements that yield the characteristics of the entrained air, including the void
fractions, bubble size and bed-parallel bubble velocity, and the hydrodynamics are obtained at five crossshore
locations in the swash zone using an optical probe and a combined PIV/LIF system. The results
show that two distinct bubble clouds enter the swash zone, the first is the result of local entrainment at
the wave tip and the second are the remaining bubbles of the air that is entrained at the second plunge
point of wave breaking before the wave starts climbing the beach. The void fractions are up to 0.20 and
bubble size up to 20mm which are similar to air entrainment after wave breaking in the surf zone and
deep water. Local entrainment of air continues in the swash zone, but void fractions decrease rapidly
with distance up the slope and no air is present after flow reversal. Energy dissipation in the swash zone
attributable to entrained air is at least of order 1% of the total energy dissipation. This is smaller than in
the surf zone or deep water because of the smaller volume of entrained air and the greater total energy
dissipation in the swash zone.
Original languageEnglish
Pages (from-to)26-43
Number of pages18
JournalCoastal Engineering
Volume121
Early online date27 Dec 2016
DOIs
Publication statusPublished - Mar 2017

Fingerprint

Air
Air entrainment
Void fraction
Energy dissipation
Beaches
Water
Sand
Hydrodynamics
Experiments

Keywords

  • bores
  • entrained air
  • experimental measurements
  • hydrodynamics
  • swash zone

Cite this

Entrained air in bore-driven swash on an impermeable rough slope. / Dai, Han Jing; Kikkert, Gustaaf Adriaan; Chen, Bo Tao; Pokrajac, Dubravka.

In: Coastal Engineering, Vol. 121, 03.2017, p. 26-43.

Research output: Contribution to journalArticle

Dai, Han Jing ; Kikkert, Gustaaf Adriaan ; Chen, Bo Tao ; Pokrajac, Dubravka. / Entrained air in bore-driven swash on an impermeable rough slope. In: Coastal Engineering. 2017 ; Vol. 121. pp. 26-43.
@article{4cfab71028e743889e009e7f29df0e2b,
title = "Entrained air in bore-driven swash on an impermeable rough slope",
abstract = "The aim of the present investigation is to clarify the role and evaluate the importance of air entrainmentin the swash zone by carrying out a set of detailed laboratory experiments. Experiments involvedgenerating a single, highly repeatable, large-scale, bore-driven swash event on a sand-rough impermeablebeach with slope 1:10. Measurements that yield the characteristics of the entrained air, including the voidfractions, bubble size and bed-parallel bubble velocity, and the hydrodynamics are obtained at five crossshorelocations in the swash zone using an optical probe and a combined PIV/LIF system. The resultsshow that two distinct bubble clouds enter the swash zone, the first is the result of local entrainment atthe wave tip and the second are the remaining bubbles of the air that is entrained at the second plungepoint of wave breaking before the wave starts climbing the beach. The void fractions are up to 0.20 andbubble size up to 20mm which are similar to air entrainment after wave breaking in the surf zone anddeep water. Local entrainment of air continues in the swash zone, but void fractions decrease rapidlywith distance up the slope and no air is present after flow reversal. Energy dissipation in the swash zoneattributable to entrained air is at least of order 1{\%} of the total energy dissipation. This is smaller than inthe surf zone or deep water because of the smaller volume of entrained air and the greater total energydissipation in the swash zone.",
keywords = "bores, entrained air, experimental measurements, hydrodynamics, swash zone",
author = "Dai, {Han Jing} and Kikkert, {Gustaaf Adriaan} and Chen, {Bo Tao} and Dubravka Pokrajac",
note = "The authors gratefully acknowledge financial support from the Hong Kong Research Grant Commission under grant number 613711 and the TUYF Charitable Trust under grant number TUYF12EG06.",
year = "2017",
month = "3",
doi = "10.1016/j.coastaleng.2016.10.002",
language = "English",
volume = "121",
pages = "26--43",
journal = "Coastal Engineering",
issn = "0378-3839",
publisher = "Elsevier",

}

TY - JOUR

T1 - Entrained air in bore-driven swash on an impermeable rough slope

AU - Dai, Han Jing

AU - Kikkert, Gustaaf Adriaan

AU - Chen, Bo Tao

AU - Pokrajac, Dubravka

N1 - The authors gratefully acknowledge financial support from the Hong Kong Research Grant Commission under grant number 613711 and the TUYF Charitable Trust under grant number TUYF12EG06.

PY - 2017/3

Y1 - 2017/3

N2 - The aim of the present investigation is to clarify the role and evaluate the importance of air entrainmentin the swash zone by carrying out a set of detailed laboratory experiments. Experiments involvedgenerating a single, highly repeatable, large-scale, bore-driven swash event on a sand-rough impermeablebeach with slope 1:10. Measurements that yield the characteristics of the entrained air, including the voidfractions, bubble size and bed-parallel bubble velocity, and the hydrodynamics are obtained at five crossshorelocations in the swash zone using an optical probe and a combined PIV/LIF system. The resultsshow that two distinct bubble clouds enter the swash zone, the first is the result of local entrainment atthe wave tip and the second are the remaining bubbles of the air that is entrained at the second plungepoint of wave breaking before the wave starts climbing the beach. The void fractions are up to 0.20 andbubble size up to 20mm which are similar to air entrainment after wave breaking in the surf zone anddeep water. Local entrainment of air continues in the swash zone, but void fractions decrease rapidlywith distance up the slope and no air is present after flow reversal. Energy dissipation in the swash zoneattributable to entrained air is at least of order 1% of the total energy dissipation. This is smaller than inthe surf zone or deep water because of the smaller volume of entrained air and the greater total energydissipation in the swash zone.

AB - The aim of the present investigation is to clarify the role and evaluate the importance of air entrainmentin the swash zone by carrying out a set of detailed laboratory experiments. Experiments involvedgenerating a single, highly repeatable, large-scale, bore-driven swash event on a sand-rough impermeablebeach with slope 1:10. Measurements that yield the characteristics of the entrained air, including the voidfractions, bubble size and bed-parallel bubble velocity, and the hydrodynamics are obtained at five crossshorelocations in the swash zone using an optical probe and a combined PIV/LIF system. The resultsshow that two distinct bubble clouds enter the swash zone, the first is the result of local entrainment atthe wave tip and the second are the remaining bubbles of the air that is entrained at the second plungepoint of wave breaking before the wave starts climbing the beach. The void fractions are up to 0.20 andbubble size up to 20mm which are similar to air entrainment after wave breaking in the surf zone anddeep water. Local entrainment of air continues in the swash zone, but void fractions decrease rapidlywith distance up the slope and no air is present after flow reversal. Energy dissipation in the swash zoneattributable to entrained air is at least of order 1% of the total energy dissipation. This is smaller than inthe surf zone or deep water because of the smaller volume of entrained air and the greater total energydissipation in the swash zone.

KW - bores

KW - entrained air

KW - experimental measurements

KW - hydrodynamics

KW - swash zone

U2 - 10.1016/j.coastaleng.2016.10.002

DO - 10.1016/j.coastaleng.2016.10.002

M3 - Article

VL - 121

SP - 26

EP - 43

JO - Coastal Engineering

JF - Coastal Engineering

SN - 0378-3839

ER -