Iraqi Journal of Chemical and Petroleum Engineering 

 Vol.17 No.1 (March 2016) 13- 19 

ISSN: 1997-4884 

 
 
 
 

 

Load Effect on Wall Attachment Fluidics Amplifier Performance 
 

Ali Abdalmohsin AL-Asadi 

University of Baghdad 

 

Abstract 

   An experimental work has been conducted on wall attachment fluidics amplifiers, 

one of them to study the effect of output pressure or load on the amplifier 

performance. The output load has been simulated as a piston connected to the device 

output and the piston can be loaded accordingly. The results shows that the output 

volume flow rate increases as the supply pressure increases under different load and 

the output pressure remains constant as the supply pressure increases under constant 

load. 

    

Key Words: wall attachment, amplifier performance. 
  

Introduction 

   For many years engineers have used 

fluids for transmitting force and energy 

in mechanical systems. For example, 

the flexibility and great power offered 

by hydraulic actuators and motors 

make them attractive for use in many 

control systems, even when the 

systems are essentially electrical or 

electronic. The predominance of 

electronic techniques in computations 

and in control systems may give the 

impression that such systems can 

function only electronically. In fact 

Babbage’s calculating ‘engine’ which 

was perhaps the earliest digital 

computers, with essential conceptual 

features of present day machines, was 

purely mechanical [1], and various 

simple, completely pneumatic control 

systems, such as automatic pressure 

control, have been in commercial use 

for many years. It is only 

comparatively recently, however, that 

techniques have been developed for 

using fluid as a medium for 

computation and for carrying 

significant information in control 

systems. 

   Hydraulic and pneumatic circuits 

which use valves have been developed 

for many automatic processes for 

examples those requiring a controlled 

sequence of events. The conventional 

valves used in such circuits have 

mechanical moving parts and may be 

classed as static device. The term 

arises because forces are developed by 

the static pressure of the fluid, power 

being expended only intermittently 

when the fluid is in motion. 

   A new class of fluid circuit element 

has now been added which may be 

referred to as dynamic. This elements 

called fluidic element, one of them is 

the wall attachment amplifier. In 

dynamic elements the kinetic energy of 

the flowing fluid is all-important and 

in them power is expended 

continuously, (1). An important aspect 

Iraqi Journal of Chemical and 
Petroleum Engineering 

 

University of Baghdad 
College of Engineering 



Load Effect on Wall Attachment Fluidics Amplifier Performance 
 
 

14                                       IJCPE Vol.17 No.1 (March 2016)             -Available online at: www.iasj.net 
 

of such elements is that, they need not 

depend on moving parts for their 

operation, another advantage can be 

claimed for fluidics elements, 

simplicity loading to high reliability to 

operate in extreme conditions of 

temperature, resistance to shock and 

vibration, safe operation in explosive 

atmospheres, freedom from 

interference from radiation, and so on.     

   Additionally, the cost of the elements 

is potentially low. All these feature 

makes them attractive to use in control 

system than the others. 

 

Thee Wall Attachment Principle 

   When a turbulent of fluid emerges 

from a nozzle, as shown in Fig (1-a), it 

continues to move downstream and is 

not deflected in one direction or the 

other. It is found that the turbulent 

motion of the jet entrains particles 

from the surrounding fluid causing it 

spread out as it moves downstream. If 

the entertainment flow on one side of 

the jet is reduced due, say the existence 

of an adjacent wall, the pressure on 

that side of the jet is reduced due to the 

differential entertainment, causing the 

jet to be drawn toward the low-

pressure region. 

   If the wall is positioned correctly, as 

in Fig (1-b), the jet is deflected until it 

touches the wall. Between the jet and 

the wall is low-pressure vortex bubble 

known as the separation bubble or re-

attachment bubble. Stable condition 

occur in the bubble when the amount 

of fluid entertained into the bubble 

from the jet, at the point at which the 

jet attaches to the wall, is equal to the 

amount of fluid reround to the jet by 

the vortex flow inside the bubble. 

   Two important parameters in the 

design of any wall attachment device. 

These are the set back and the wall 

angle. For wall attachment to take 

place the set back should be small; a 

large set back results in the jet 

detaching from the wall at low values 

of flow. The wall angle also affects 

wall attachment since, with very large 

wall angles, attachment may not be 

possible, or may only be achieved with 

difficulty. The effects of wall angle 

and set back are discussed more fully 

in experimental work [1]. 

   If an additional source of fluid can be 

admitted to the separation bubble, by 

the port shown by the broken lines in 

Fig. (1-b), the steady-state operating 

conditions can be controlled. The net 

result of increasing the quantity of 

entertained fluid on the wall side of the 

jet, is that the jet attachment point 

moves further downstream. If the fluid 

flow through the additional port 

becomes sufficiently great, the jet can 

be forced to detach from the wall. This 

is the most commonly used technique 

of controlling the jet in wall 

attachment devices. A good example 

of this method of control is found in 

the wall attachment S-R flip-flop type. 

   The simplest form of wall attachment 

device is the diode, atypical profile 

being shown in Fig(2). When an input 

signal is applied to port 1, the jet 

attachment to the curved wall due to its 

gentle gradient, and the pressure 

recovery at port 2 is approximately 95 

percent of the input pressure. If the 

signal is applied to port 2, most of the 

input fluid escapes through the vent 

opposite of port 2, since the inclination 

of the wall angle to port 1 is too great 

to permit wall attachment. When used 

in this mode the pressure recovery at 

port 1 is approximately 5 percent of the 

pressure applied to port 2[2]. 

 

Literature Review 

   The first projects on fluidics in 

Britain were those started at the 

universities of Birmingham and 

Nottingham and at the college of 

aeronautics at cranfield in 1962, the 

cranfield project used kearffot type hall 

valve in a circuit designed by charnley 

and bidgood (2), while the first work at 



Ali Abdalmohsin AL-Asadi 

 

-Available online at: www.iasj.net                    IJCPE Vol.17 No.1 (March 2016)                                15 
 

Birmingham and Nottingham was 

another turbulent reattachment 

amplifier (3), (4). After that a lot of 

research has been done on fluidics 

logic element. Madellan Mitchell and 

turabull (5), gave experimental results 

for a jet attaching to the piston face of 

hydraulic spool valve at small control 

ports openings and examined the effect 

of cavitation on the bubble formation 

while herman viets (6), working on 

new nozzle development program was 

under taken to produce a time. 

Dependent flow at nozzle exit, the 

oscillatory character of the flow was 

achieved without the use of moving 

parts by incorporating a fluidic feed 

back loop in to the nozzle design. 

 

Description of Apparatus 

 

1- Construction of Wall Attachment  
Device 

   Wall attachment device is often 

small in size but in the present work a 

mid-size one has been designed. The 

device consists of the following parts, 

see Fig. (3): 

i. Device Base 
The device base is design in a way 

allowing to fixed all the parts of 

device on it by using glue and bolts 

as shown in Fig.(4). Where the 

base have (235 mm) length, (165 

mm) width and (5 mm) thickness.  

ii. Power Jet (main jet) 
This is essential part of an 

amplifier have rectangular cross 

section area (8 mm) width and (16 

mm) depth. The supply pressure 

should be generally maintained 

constant and steady. When the 

supply pressure and ambient 

pressure ratio is less than a bout 

(2), the jet is sub-sonic [7]. This is 

usually the situation for most 

bistable amplifiers. 

iii. Control Jets 
One or two control jets are required 

to control the direction of the main 

jet. The control jets generally are 

located at the exit plane of the 

power jet, which have rectangle 

cross sectional area. The width of 

the control jet can be changed from 

(2.5 mm) to (5 mm) and have (1  

mm) depth. 

iv. Splitter 
The splitter is very important part 

of an amplifier. Its function to 

separate the two receiving parts. 

The splitter is generally wedge 

shaped. The end of the wedge can 

be rounding, pointed, and blunt or 

cusp shaped. A sharp splitter (used 

in present work) tends to have a 

higher gain and fast responding but 

it can cause edge tone type 

oscillation as shown in Fig. (5). 

v. Side Walls 
The side walls are also important 

parts of wall attachment amplifier 

type S-R Flip Flop because depend 

the attach of the fluid flow on the 

angle of side wall and setback 

distance. The shape of side walls 

are shown in Fig.(5). 

vi. Receiving ducts 
The size and shape of the receiving 

ducts can influence greatly the 

power output. Where the width of 

receiving ducts (13 mm) and the 

depth (16 mm). 

 

2- Construction of Loading System 
(Pneumatic Piston) 

   The load system consists of a 

pneumatic cylinder have inside 

diameter of (46 mm), outside diameter 

of (50 mm) and length of (125 mm). 

There is a piston inside the cylinder 

connected to a shaft with a diameter of 

(46 mm) as shown in Fig.(6). The shaft 

of piston connected to plate form for 

loading. The cylinder have two holes 

one at the bottom of the cylinder where 

the output of device connection, while 

the second hole near the top of the 

cylinder as shown in Fig.(7). The 

circular which is imposed at the 



Load Effect on Wall Attachment Fluidics Amplifier Performance 
 
 

16                                       IJCPE Vol.17 No.1 (March 2016)             -Available online at: www.iasj.net 
 

bottom of the cylinder to give uniform 

distribution of pressure on the piston 

seal to reduce the leakage between the 

piston and cylinder as shown in 

Fig.(7). 

 

3- Compressor 
   A compressor is used to provide the 

rig with air at pressure in the range [0- 

1000KPa]. A Burdon type pressure 

gauge is used to read the pressure in 

cylindrical of compressor. The volume 

flow rate and pressure that at the rig 

input are regulated by a suitable valve.  

 

4- Valves and Flexible Hose 
   The valves used in this experimental 

work are of type (gate valve). This 

type is used because there ability to 

change the pressure and volume flow 

rate. Flexible hoses are used to join the 

parts of the rig. 
 

Results and discussion 

   The experimental work has been 

done to study the effect of load 

changing on wall attachment fluidics 

amplifier performance. In the work the 

experimental data recorded represent 

the supply pressure, output pressure 

and output volume flow rate, the 

device tested under variable load by 

using pneumatic piston connected to 

output of wall attachment amplifier. 

The relation between the output 

volume flow rate and the supply 

pressure for different load are shown in 

Fig.(8). Where the relation between the 

output pressure and supply pressure for 

different load are shown in Fig.(9). 

From the results it is shown that the 

output volume flow rate (i.e. the input 

volume flow rate), increases gradually 

as the supply pressure increases for 

different constant load, see Fig. (8). In 

the case of output pressure and supply 

pressure, see Fig.(9). In this case it is 

shown that the output pressure 

increases until it reaches a specific 

value, after that the output pressure 

remains constant under different 

constant load, that means the load has 

no effect on the device function, the 

effect is only on the time response of 

the device. 

 

 
Fig. 1, (a) an unbounded turbulent jet entrains fluid particles on all sides (b) a side 

wall causes the jet to deflect towards it 



Ali Abdalmohsin AL-Asadi 

 

-Available online at: www.iasj.net                    IJCPE Vol.17 No.1 (March 2016)                                17 
 

 
Fig. 2, a profile of a wall attachment 

diode 

 

 
Fig. 3, Main parts of wall attachment 

device 

 

 

 
Fig. 4, the base of wall attachment 

device 

 

 

Fig. 5, Wall attachment device control 

unit 



Load Effect on Wall Attachment Fluidics Amplifier Performance 
 
 

18                                       IJCPE Vol.17 No.1 (March 2016)             -Available online at: www.iasj.net 
 

 
Fig. 6, Load system pneumatic piston 

 

 
Fig. 7, Pneumatic piston 

 

 

Fig. 8, The Relation Between supply pressure and Output Volume flow rate 

 



Ali Abdalmohsin AL-Asadi 

 

-Available online at: www.iasj.net                    IJCPE Vol.17 No.1 (March 2016)                                19 
 

 

 

Fig. 9, The Relation Between supply pressure and Output pressure 

References 

1- ARTHER CONWAY, AGuide to 
Fluidics, Macoonaid, London,1971. 

2- MORRIS, N.M.,(Introduction to 
Fluid Logic) Mc Graw – Hill,United 

Kingdom, London, 1973. 

3- CHARNLEY,C.J., and Biggood, 
R.e.(fluid Logic Units and their 

potential for Machine Tool 

Application) September 1964.proc. 

5
th

  Int. machine Tool Design and 

research Conference, University of 

Birmingham pergamon press-

pp.471-498. 

4- FOSTER,K.,JONES,N.S. and 
MITCHEIL, D.G., (Improvements 

to a pure Fluid Sequence Control for 

Machine Tool Application), 

September 1965. Proc.6
th

 Int. 

Machine Tool Design and Research 

Conference, college of Since and 

Technology, Manchester, Pergamon 

press.393-403. 

5- FASTER, K. and JONES, N.S. (A 
Simple Logic Circuit Using Fluid 

Jet Devices), J. vol.5,Pergamon 

press.pp.35-42. 

6- MACLEILLAN.G.D.S, 
MITCHEIL.A.E and 

TURNUBULL.D.E (Flow 

Characteristics Sump. On 

Automatic Control. Inst, Mech. 

Engrs. London. 

7- HERMANN, VIETS (Flip-flop Jet 
Nozzle), Aiaa journal, vol.13 No 10, 

October, 1975, pp.1375-1379. 

8- J.P.Holman (Experimental Methods 
for Engineers), second edition, Mc 

Graw-Hill Kogakuah Ltd, 1971.