The application of pneumatic metrology to control dimensional accuracy on machined parts is based on the measurement of gas flow resistance through a restricted section formed by a jet orifice placed at a small distance away from a machined surface. The backpressure, which is sensed and indicated by a pressure gauge, is calibrated to measure dimensional variations. It has been found that in some typical industrial applications, the nozzles are subject to fouling, e.g., dirt and oil deposits accumulate on their frontal areas, thus requiring more frequent calibration of the apparatus for reliable service. In this paper, a numerical and experimental analysis of the flow behavior in the region between an injection nozzle and a flat surface is presented. The analysis is based on the steady-state axisymmetric flow of an incompressible fluid. The governing equations, coupled with the appropriate boundary conditions, are solved using the SIMPLER algorithm. Results have shown that for the standard nozzle geometry used in industrial applications, an annular low-pressure separated flow area was found to exist near the frontal surface of the nozzle. The existence of this area is believed to be the cause of the nozzle fouling problem. A study of various alternate nozzle geometries has shown that this low-pressure recirculation area can be eliminated quite readily. Well-designed chamfered, rounded, and reduced frontal area nozzles have all reduced or eliminated the separated recirculation flow area. It has been noted, however, that rounded nozzles may adversely cause a reduction in apparatus sensitivity.

1.
Moller
,
P. S.
,
1963
, “
Radial Flow Without Swirl Between Parallel Discs
,”
Aeronaut. Q.
pp.
163
186
.
2.
Ishizawa
,
S.
,
Watanabe
,
T.
, and
Takahashi
,
K.
,
1987
, “
Unsteady Viscous Flow Between Parallel Disks With a Time-Varying Gap Width and a Central Fluid Source
,”
ASME J. Fluids Eng.
,
109
, pp.
395
402
.
3.
Prakash
,
C.
,
Powle
,
U. S.
, and
Suryanarayana
,
N. V.
,
1985
, “
Analysis of Laminar Flow and Heat Transfer Between a Stationary and a Rotating Disk
,”
AIAA J.
,
23
, pp.
1666
1667
.
4.
Bettahar, A., 1993, “Application des e´coulements radiaux a la me´trologie pneumatique dimensionnelle,” Ph.D. thesis, Universite´ de Valenciennes, France.
5.
Crnojevic
,
C.
,
Roy
,
G.
,
Florent
,
P.
, and
Bettahar
,
A.
,
1997
, “
Influence of Regulator Diameter and Injection Nozzle Geometry on Flow Structure in Pneumatic Dimensional Control Systems
,”
ASME J. Fluids Eng.
,
119
, pp.
609
615
.
6.
Lytle
,
D.
, and
Webb
,
B. W.
,
1994
, “
Air Jet Impingement Heat Transfer at Low Nozzle-Plate Spacings
,”
Int. J. Heat Mass Transfer
,
17
, pp.
1687
1697
.
7.
Behnia
,
M.
,
Parneix
,
S.
,
Shabany
,
Y.
, and
Durbin
,
P. A.
,
1999
, “
Numerical Study of Turbulent Heat Transfer in Confined and Unconfined Impinging Jets
,”
Int. J. Heat Fluid Flow
,
20
, pp.
1
9
.
8.
Wattebot
,
L.
, 1937, “L’amplification pneumatique: Principe, The´orie,” Journal de Me´canique, pp. 70–72.
9.
Fortier
,
M.
, 1950, “Applications industrielles des e´coulements gazeux a la vitesse critique,” Revue chaleur et Industrie, 299, p. 145.
10.
Schlichting, H., 1979, Boundary Layer Theory, McGraw-Hill, New York.
11.
Patankar, S. V., 1980, Numerical Heat Transfer and Fluid Flow, McGraw-Hill, New York.
12.
Roy, G., 1997, “Contribution a` l’e´tude de l’e´coulement radial: Applications en me´trologie industrielle,” Ph.D. thesis, Universite´ Laval, Que´bec, Canada.
13.
McGinn
,
J. H.
,
1956
, “
Observations on the Radial Flow of Water Between Fixed Parallel Plates
,”
Appl. Sci. Res.
,
5
, pp.
255
264
.